SOME ASPECTS OF THE AQUEOUS CHEMISTRY
OF ZIRCONIUM AND RUTHENIUM IN RELATION
TO NUCLEAR FUEL REPROCESSING
A thesis submitted for the degree of
DOCTOR OF PHILOSOPHY
in the Faculty of Engineering of the
University of London
by
M. AMIN ANJUM, BSc (Hops), MSc (Punjab), MSc (London), DIC, ARIC
Department of Chemical Engineering and Chemical Technology, Imperial College of Science and Technology, London, S. W. 7. April 1972 ABSTRACT
The ion-exchange behaviour of ruthenium IV, nitrosyl ruthenium III and zirconium IV has been investigated with a view to the utilization of anion-exchange resins for the separation of ruthenium and zirconium from plutonium solutions in nuclear fuel reprocessing.
Both cation and anion-exchangers have been used for the removal of ruthenium IV. Increases in nitric acid concentration decreased the extent of removal by the cation-exchanger as did increases in ruthenium concentration at lower acidities. Studies of the anion-exchange behaviour -3 in nitric acid concentration range of 0.1 to 7.5 mol dm -3 showed that maximum adsorption occurs at 3.5 and 5 mol dm acid for ruthenium IV and nitrosyl ruthenium III respectively. From solutions of comparable strength nitrosyl ruthenium was adsorbed to a greater extent. When the nitrate ion concentration was kept constant a decrease in hydrogen ion concentration resulted in higher removal by the anion- exchanger. The results are discussed in terms of the species of ruthenium and the properties of the resin involved. The adsorbed ruthenium was found to be difficult -3 to remove. Thus 7.5 mol dm acid removed about 30% -3 of adsorbed ruthenium while 0.6 mol dm acid removed only about 10%. 3
The characterization of the species of ruthenium has not been completed. Although electrophoresis and ion-exchange data pointed to the presence of different complexes under different conditions, studies involving spectrophotometry failed to detect any such changes.
The ion-exchange behaviour of zirconium was investigated -3 in the nitric acid range of 0.01 to 9 mol dm . At low acidities (e.g. 0.01 mol dm-3) both cation and anion exchange removed similar amounts. Increases in acidity decreased adsorption by the cation exchange. In the case of the anion-exchanger maximum adsorption was found 3 to occur at 0.1 and 7.5 mol dm acid. These maxima are explained in terms of the formation of polymers at lower acidities and of anionic complexes at higher acidities. The adsorbed zirconium was readily eluted with nitric -3 -3 acid stronger than 5 mol dm but removal by 0.6 mol dm acid was found to be difficult (i.e. <15%). A simple exponential equation C = J0.2241E- developed in this s work can predict the f' action of zirconium C/Co remaining on the resin after a contact time t (in minutes) of the -3 resin with the acid (>5 mol dm ).
On the basis of results obtained a flow sheet for the removal of ruthenium and zirconium by an anion-exchange process has been developed. 4.
ACKNOWLEDGEMENTS
The author wishes to express his gratitude to Dr. P. G. Clay for his help and encouragement in the completion of this work.
Thanks are also due to Professor G. R. Hall under whose guidance the earlier part of this work was completed.
Many healthy discussions on the ion-exchange work with
Dr. M. Streat are also acknowledged. Last but not the least, help given by Professor G. N. Walton in the preparation of this thesis is gratefully acknowledged.
Thanks are also due to my friends and specially to P for making some very difficult times in London seem pleasant.
Financial support from the British Council, made available in the form of a Colombo Plan Scholarship sponsored by the Atomic
Energy Commission, Pakistan, is gratefully acknowledged. 5.
CONTENTS
Page
Abstract 2
Acknowledgements 4
Chapter 1 GENERAL INTRODUCTION 11
1.1 Nuclear Fuel Reprocessing 12
1 1.1.1 Present Day Processing Techniques 13
1.1. 2 Fission Products in Solvent Extraction 14
1.2 Ion Exchange Resin and Nuclear Fuel Reprocessing 17
1.3 Present Work : Aims and Objects 18
Chapter 2 RUTHENIUM 22
2.1 General Chemistry 23
2.1.1 The Valency States of Ruthenium 23
2.1.1.1 The Oxidation-Reduction Potentials 34 of Different Valency States
2.1.1.2 Ion-Exchange Behaviour of Non- Nitrosyl-Ruthenium Compounds 36
2.1.2 Nitrosyl-Ruthenium Compounds 38
2.1.3 Behaviour of Ruthenium in Nuclear Fuel Reprocessing 43
2.1.3.1 Solvent Extraction of Nitrosyl- Ruthenium Compounds 45
2.1.3.2 Ion-Exchange Behaviour of Nitrosyl-Ruthenium 49
2.1.3.3 Waste Disposal of Ruthenium in Nuclear Fuel Reprocessing 51
2.2 Experimental 54
2.2.1 Materials Used 54
2.2,2 Preparations 56 6.
Page
2.2.2.1 Ruthenium Tetroxide 56
2.2.2.2 Ruthenium IV 56
2.2.2.3 Preparation of Nitrosyl-Ruthenium Nitrates 58
2.2.3 Estimations 59
2.2.3.1 Ruthenium 59
2.2.3.2 Determination of the Valency of Ruthenium 66
2.2.3.3 Estimation of Copper and Chromium 67
2.2.3.4 Capacity and the Swollen Volume of Resin 68
2.2.4 Spectrophotometry 72
2.2.4.1 Instrument Used ' 72
2.2.4.2 Scan of the Spectra 73
2.2.4.3 Representation of the Data 76
2.2.5 Electrophoresis 77
2.2.6 Ion-Exchange : Adsorption and Elution 79
2.2.7 Paper Chromatography 79
2.3 Results 81
Z. 3.1 Properties of the Resins 81
2.3.1.1 Ultraviolet Absorption Spectra of Resin Washings 82
2.3.2 Ruthenium Tetroxide 86
2.3.3 Ruthenium IV Studies 89
Z. 3.3.1 Characterization of Ruthenium IVSolutions 89
2.3.3.1.1 UV Spectrum of Ruthenium IV 91
2.3.3.1.2 Reduction of Ruthenium IV 91
2.3.3.1.3 Presence of Chloride Ion in Ruthenium IV Solutions 94
2.3.3.1.4 Solutions of Ruthenium IV in Nitric Acid 94 7.
pag e
2.3.3.2 Effect of Addition of Nitrate Ion to Ruthenium IV Solutions 95
Z. 3.3. Z. 1 Ultraviolet Spectra of Solutions 95
2.3.3.2.2 Polymerization of Ruthenium IV : Spectrophotometric Evidence 98
2.3.3.2.3 Infra-Red Spectrum 101
2.3.3.3 Electrophoresis
2.3.3.4 Ion-Exchange Studies 105
2.3.3.4. I Adsorption of Ruthenium IV by Zeokarb-225 105
.v/ 2.3.3.4.2 Use of Ion-Exchange for the Deter-
mination of Charge 109
2.3.3.4.2.1 Cady' s Method 109
2.3.3.4.2.2 Application of the Method to Ions
of Known Charges 112
2.3.3.4.2.3 Application of the Method to
Ruthenium Species 112
2.3.3.4.3 Adsorption of Ruthenium IV by Ionac XAX- 1284: Effect of Shaking Time 118
2.3.3.4.3.1 Adsorption of Ruthenium IV by Ionac XAX- 1284: Effect of Ruthenium and Nitric Acid Concentration 120
2.3.3.4.4 Elution of Adsorbed Ruthenium by Nitric Acid 124
2.3.3.5 Solvent Extraction, Thin Layer and Paper Chromatography 127
2.3.3.6 Effect of Heat and Irradiation 129
2.3.4 Nitrosyl Ruthenium Nitrates 131
2.3.4.1 Anion-Exchange Behaviour of
Nitrosyl Ruthenium Nitrates 135
2.3.4. 1.1 Adsorption 135
2.3.4.1.2 Elution 137 8
2.3.4.2 Paper Chromatography of Nitrosyl Ruthenium Nitrates 139
2.4 Discussion 147 2.4.1 Ruthenium Tetroxide 148 2.4.2 Preparation of Ruthenium IV 150 2.4.3 Ruthenium IV in Nitrate Ion Media 152 2.4.3.1 Ion Exchange Behaviour 153 2.4.3.1.1 Adsorption 153 2.4.3.1.2 Elution of Ruthenium IV from Ionac XAX-1284 157 2.4.3.7 Some Further Properties of the Nitrates of Ruthenium IV 161 2.4.4 Nitrosyl-Ruthenium Nitrates 162 2.4.4.1 Anion-Exchange of the Nitrosyl- Ruthenium Nitrates 163 2.4.4.1.1 Adsorption 163 2.4.4.1.2 Elution of Adsorbed Ruthenium 165 2.4.4.2 Paper Chromatography of the Nitrosyl Nitrates of Ruthenium 166
Chapter 3 ZIRCONIUM 167 3.1 General Chemistry 168 3.1.1 The Oxidation States 168 9.
Page
3. I. 2 Aqueous Solutions of Zirconium IV 169
3. I. 3 Complex Formation 171
3. I.4 Ion-Exchange Studies of Zirconium IV 173
3. I. 5 Behaviour of Zirconium in Nuclear Fuel Solutions 175
3. I. 5. I Solvent Extraction of Zirconium 175
3. 2 Experimental 179
3. 2. I Materials and Apparatus 179
3. 2. 2 Resin Preparations 180
3. 2. 2. 1 Resin Capacities 181
3. 2. 3 Preparation of Solutions 181
3. 2. 4 Estimation of Zirconium 181
3. 2. 4. I Gravimetric 181
3. 2. 4. 2 Colourimetric Method 182
3. 2. 4. 3 Estimation of Zr-95 185
3. 2. 5 Adsorption of Zirconium by the Resin 188
3. 2. 5. 1 Equilibrium Experiments 188
3. 2. 5. 2 Column Experiments 188
3. 2. 6 Washing of the Loaded Resin 190
3. 2. 7 Elution of Zirconium 190
3. 3 Results 192
3. 3. I Adsorption from Nitric Acid 192
3. 3. 2 Effect of Change of Nitrate Ion Concentration at Constant H4 Ion Concentration 192
3. 3. 3 Effect of the Aqueous Phase Concent- ration of Zirconium on Adsorption 194
3. 3.4 Effect of Resin Cross-linking on the Adsorption of Zirconium 198 10 Page 3.3.5 Reproducibility of the Results on Adsorption from Dilute Acid Solutions 199 3.3.6 Column Loading 199 3.3.7 Adsorption of Zirconium by a Cation-Exchange Resin 202 3.3.8 Elution of Adsorbed Zirconium 205
3.4 Discussion 209 3.4.1 Adsorption of Zirconium from Nitric Acid 209 3.4.2 Effect of Change of Nitrate Ion Concentration on Adsorption 214 3.4.3 Effect of Aqueous Phase Concentration of Zirconium on Adsorption 216 3.4.4 Effect of Resin Cross-linking on Adsorption 218 3.4.5 Elution of Adsorbed Zirconium 219
Chapter 4 CONCLUSIONS 223 4.1 Ruthenium 224 4.2 Zirconium 228 4.3 Flow Sheet 229
References 231
Appendices 247 Appendix 1 Spectrum of Nd3 248 Appendix 2 Spectrum of Benzene in Cyclohexane 249 Appendix 3 Spectrum of Nitric Acid 250
Appendix 4 cyalues of Ru IV in Hc104 251 Appendix 5 Sample Calculations of Charge 253 Appendix 6 Values for RuNO-Nitrates 255 Appendix 7 Adsorption of RuNO-Nitrates by Ionac XAX-1284 256 11.
CHAPTER - 1
GENERAL INTRODUCTION 12.
1.1. NUCLEAR FUEL REPROCESSING
In the last two decades the use of atomic energy for power
production has steadily increased. All present day reactors are based on uranium (both natural as well as slightly enriched) as fuel.
However the energy that is available in the world's known reserves of
uranium - 235 is less than that available in known fossil fuel reserves.
The full utilization of atomic power will therefore ultimately depend
on the development of plutonium breeder reactors (Baker et. al. , 1958).
The reprocessing requirements which are of not much economic
significance in thermal reactor fuels will become much more
important. The costs of fast breeder reactor operation are
sensitive to the out-of-reactor fuel inventory and there is consequently
a strong economic incentive for reprocessing short-cool fuel. The
burn up will be high in fast breeder reactors and there will be an
economic necessity for the reprocessing of short cooled spent fuels
to reduce the out-of-reactor fuel inventory costs. A comparison
based on 10,000 MW(e) for thermal and fast reactors makes the
point more clear (Steunenberg et. al. , 1970).
Fast Breeder Reactor Thermal Reactor
Core Blanket
Daily Processing Rate
Uranium (kg) 156 262 1061
Plutonium (kg) 45 11 8
Fission Products (kg) 22 4 30
Burn Up MWd/te 100,000 14,200 30,000
Specific Power kW/kg 150 N6 12 13.
However the need for fission product decontamination will be less
stringent.than in the case of thermal reactors. This is due to two
reasons. Firstly the fission product impurities have very low capture
cross sections for fast neutrons. Secondly, there is bound to be a
build up of radioactive isotopes of uranium and plutonium in extensively
recycled fast reactor fuels. This would necessitate the use of, at
least, semi-remote fuel fabrication in any case. This tolerance
for low decontamination factors (DF's) could be exploited to an
advantage by having a closed, on-site fuel reprocessing facility for
the removal of at least the most valuable constituent i. e. plutonium.
1.1.1. PRESENT DAY REPROCESSING TECHNIQUES
Present day commercial plants for the reprocessing of nuclear
fuels are based on solvent extraction. The extractants used have
been hexone (Lawroski et. al., 1958 and Flagg, Chapter VI, 1966),
and tri-n-butylphosphate, TBP, (Caller, 1955; Flanary, 1955; and
Flagg, Chapter V). In the most widely used TBP process the fuel
is dissolved in nitric acid. TBP diluted with an inert solvent is used
as extractant. Plutonium in the +4 state is extracted along with the
uranium, leaving behind most of the fission products. The plutonium is
partitioned from uranium by contacting the organic phase with a ferrous sulphamate aqueous strip solution. Plutonium is reduced
to the non-extractable trivalent state and returns to the aqueous phase.
Further purification of plutonium is carried out by repeating the
extraction (in the +4 state) and strip cycles. Overall fission product
7 8 decontamination factors of 10 - 10 are obtainable. 14.
A number of other methods are in development stage. All these methods aim at quick and efficient removal of plutonium and lowered damage to the extracting media. These include (a) use of amines as solvents (Baker, 1958 and Winchester et. al. , 1958);
(b) Fluoride volatility processes (Barghusen et. al. , 1970; Strickland et. al. , 1970; and Stevenson et. al. , 1970); (c) electrorefining of molten salts of the fuel (Feder, 1956; Mota, 1956, and Harmon et. al. , 1970); (d) ion exchange resins (discussed in section 1. 2).
1.1.2. FISSION PRODUCTS IN SOLVENT EXTRACTION
The nuclear fuels are cooled for more than 90 days before they are reprocessed. At this stage the significant fission products are Zr-95 (and the daughter product Nb-95) and Ru-106 and Ru-103.
It is the behaviour of these elements which makes the handling and reprocessing difficult.
Zr, Nb and Ru are all extracted by TBP to some extent.
Zr becomes more troublesome in the presence of the degradation products of TBP and the dilutent. (Nb is believed to behave similarly to Zr and has not been studied separately to any large extent).
TBP decomposes under the action of ionizing radiation and nitric acid to give dib.utyl phosphoric acid (HDBP) and monobutyl phosphoric acid (H2MBP). The concentration of these degradation products is -3 -6 -3 about the same as that of Zr and Nb (10 to 10 mol dm ).
(Brown & Fletcher, 1958). Another decomposition product is n-butylnitrate, n-C4H9NO3. The zirconium present reacts as follows (Moffat et. al. , 1961). 15.
TBP +Radiation. or HNO ----> HDBP -V C H NO 3 4 9 3
Zr(NO3)4 +HDBP --> Zr(NO3)3 DBP (Soluble)+ HNO3
Zr(NO3)3 DEP +HDBP-> Zr(NO3)2 (DBP)2 (ppt.) 71-HNO3
The relative complexing efficiency of the various ions present in the
process is as below (Naylor, 1967 pp. 120-42)
_ 4+ > Pu4+ 2+ 3+ 5+ > U 0 > (RuNO) > Nb Z 2+ UO ions, because of their large concentration (U : Zr = : 1)
shield the HDBP from zirconium to some extent but the overall effect
of the presence of HDBP is the retention of Zr in the organic layer.
The behaviour of H MBP is similar to that of HDBP though its- 2 complexes are less extractable and it is formed to a lesser extent
(a factor of about 10 less).
Another factor of significance in the retention of zirconium is diluent degradation (Orth, 1965). The nature of diluent degradation
products and their complexing action is still not very well established.
Nitroparaffins and carbonyl compounds are said to be responsible for zirconium complexing. It has been recently reported that carbonyl
compounds rather than the nitroparaffins are responsible for Zr
retention. (Stieglitz, 1971). The production of these carbonyl -6 -3 -3 compounds is low (10 mol dm at a dose of 40 Whdm ) compared
with the production of monofunctional degradation products like
nitroparaffins. (These are formed at a rate that `is higher by a
factor of 1000). Stable operation in Purex process is dependent on
the balance between the rate of production of TBP and diluent degradation
products and their subsequent removal in the solvent recovery system. 16.
Zr causes trouble in two other ways. In doses exceeding
10 7 rads good phase separation is masked by Zr. (Tsujino et. al. ,
1966). Secondly Zr is not only extracted as its complexes with degradation products but it also follows the uranium solvent extraction product by adsorption on finely divided particulate material that is present. Thus, it has been reported that approximately two thirds of Zr-Nb Y activity is due to such adsorption (Bruce, 1957). This solid may contain uranium, phosphate, iron, manganese etc. The higher retention of Zr in Dounreay processing (as compared to that observed at Windscale, Duncan 1965, Wallace, 1965) was thus attributed to the presence of Mo and Fe. (The dose received by
TBP in the Dounreay experiment was 10 times that received at
Windscale).
Ruthenium is the major 13 contaminant of nuclear fuels.
Both Ru- 103 and Ru-106 are formed (in the approximate ratio of
Ru-103 : Ru-106 = 7. 5:1, (Hardwick, 1953)). In a fuel solution containing 200-300 g uranium dm-3 (from 3000 MWd/te burn up) -4 -3 the expected concentration is 1 to 2 x 10 mol dm for natural or -3 -3 near natural uranium and 10 mol dm for enriched fuels (Brown and Fletcher, 1957). ,The DF in the first TBP cycles varies widely, 5 sometimes being as low as 10 and at other times as high as 10 3 (Fletcher & Scargill, 1965), but usually it is about 10 .
The ruthenium decontamination factors are less affected by
HDBP or H MBP though ruthenium does form TBP-soluble complexes. 2 Ruthenium nitrate complexes extracted by TBP are easily washed out by sodium carbonate. The complexes with HDBP and H MBP need 2 longer washing but are eventually removed. Ruthenium complexes with 17. diluent degradation products are, however, strongly bonded and are
very difficult to remove (Kennedy et. al. 1965). Some evidence has recently been published as to the presence of dimeric species of ruthenium that are retained in the solvent stream (Joon, 1971).
1.2. ION-EXCHANGE RESINS AND NUCLEAR FUEL REPROCESSING
Ion-exchange has emerged as an important chemical engineering unit operation and ion exchangers have been used in a variety of operations e.g. purification of water, separation of rare earths, separation of metals from ores, and sugar refining, etc.
Ion-exchange resins are also used in the separation of uranium and thorium from ore pulps and clear solutions . (An excellent review on such uses has been published by Korkish (1970) ). Again ion-exchange was one of the first methods tried for the separation of plutonium from uranium and fission products in the Manhattan
Project in 1942-44. (Boyd & Schubert, 1970). Two cycles of cation-exchange and one of anion-exchange were used but the 7 decontamination factors were below the required value (10 ).
Remote control apparatus have been used for the separation of fission products by ion exchange resins (Morgan et. al. , 1957).
The use of ion exchange resins in the purification and concentration of plutonium and other valuable actinide elements has been demonstrated. (Hardy, 1958). Wheelwright (1969) has reported the versatility of an ion-exchange facility installed adjacent to a conventional large-scale chemical plant. This facility has been used to separate kilogram quantities of Am, Cm, Pm, Sr, Pu, Np, Cs, Te,
Rh and Pd. Plutonium from purex plants has been concentrated and 18.
further decontaminated (from fission products and uranium) by the
use of cation (Bruce, 1958) and cation-anion exchange (Prevolt, et. al.,
1958) columns.
A pilot plant based on purely ion exchange resins for the
separation of plutonium from uranium and fission products has been
built in Canada. (Flagg, 1961, p. 323). Other pilot plant scale
purification and concentrations of plutonium have been reported.
(Euraec.-1639, 1966; Bonnevie-Svendsen, 1966; Kraak, 1967 and
Ferguson, 1968). The use of anion-exchange resins in Purex solvent
clean up has been reported recently (Schulz, 1971). The solvent is passed through a bed of strong base anion exchanger. The degradation products and the fission products are retained by the resin. Elution of loaded resin with a few bed volumes of 3 M HNO 3 0. 05MHF and 4M NaOH removes all the sorbed yellow colour and 95 95 106 106 Zr - Nb activity but only 55-65% of the Ru - Rh activity.
The primary advantage of the method is that it eliminates the large volumes of waste.
1.3 PRESENT WORK: AIMS AND OBJECTS
From the preceding discussion two things are apparent.
First, that the use of ion-exchange resins in the nuclear fuel industry is not new. Ion-exchange resins, in one way or the other, have, to some extent, been always used. Secondly, two of the most important and troublesome (in terms of their yield, half-life and radiations) fission products are zirconium and ruthenium. For this reason, zirconium and ruthenium were selected for the present studies. 19.
The use of anion exchange resins for plutonium purification has
been widely demonstrated but the valuable experience and mass of
experimental data available on solvent extraction put any other
contender of reprocessing in a difficult position. However, the high
concentration of products, low waste volumes and the compactness
of the as sociated equipment make ion-exchange an attractive technique
• for consideration for future reprocessing. It is claimed (James, 1967)
that in the purification of plutonium from a one-cycle Purex process,
a single cycle of anion exchange can replace three solvent extraction
cycles as well as the evaporation-concentration problem of the
product. The radiation and thermal stability of anion exchallge
resins have been shown to be satisfactory (Natarajan, 1963;
Coady, 1968; and Hall, 1969) and practicable engineering techniques
for handling ion-exchange proces sing have been proposed (Cloete and
Streat, 1963; Hall et. al., 1964). These developments gave a
stimulus for the examination of ion exchange resins as adsorption
media for plutonium and fis sion products. Natarajan (1963) and
Coady (1968) have shown that weak-base resins are the most
'radiation-resistant. Therefore the resin selected for these studies
was a 'weak-base resin based on vinyl pyridine, Ionac XAX-J284. The
general structure of this resin is as follows
--CH--CH--CH--CH--CH-- ()A 2 , 2 20.
In fuel solutions, ruthenium almost exclusively occurs as
nitrosyl nitrates and nitrosyl nitrites. Only a small fraction (<1%)
occurs as ruthenium IV complexes. The nature of nitrosyl complexes
of ruthenium has been well characterized through the works of
Fletcher and his associates (1955-68). After some preliminary work by Anderson et. al. (1955)the nitrates of ruthenium IV have been little studied. These were of minor significance in nuclear
fuel reprocessing. Martin and Gillies (1957) reported that ferrous
sulphamate used for the reduction of plutonium also removed the
NO group from nitrosyl ruthenium complexes. In solvent extraction
this would not cause any problems because of two reasons: (a) the simple nitrates are inextractable by TBP (b) there will always be some NO
present to complex the ruthenium present. In an ion exchange process the reason (a) may or may not apply and the behaviour of these non- nitrosyl complexes may become important especially if they are
produced while in contact with the anion exchange resin. Again the study of nitrate complexes of ruthenium IV was of academic interest.
On the basis of this, two types of studies are reported in this thesis:
1. Study of the complexing of ruthenium IV by nitrate ions.
A number of techniques including spectrophotometry (UV and IR), electrophoresis, paper chromatography and ion exchange method of charge determination were tried. The information obtained is presented in a subsequent section and the nitrate complexing discussed.
2. Study of the anion exchange behaviour. Here both the ruthenium IV nitrates and nitrosyl ruthenium nitrato complexes were studied. Their adsorption and elution behaviour were studied. Paper chromatography 21. was used to determine the percentages of different nitrato complexes adsorbed by the resin.
The work on zirconium was mostly confined to its adsorption and elution from the anion exchange resin. (Some of the earlier work on zirconium was submitted as an M. Sc. report to the London
University). The adsorption under variable conditions of acid and nitrate concentration was studied and related to the complexes reported to be present in such solutions. The desorption of adsorbed zirconium was studied in detail and included the effect of different nitric acid concentrations and different flow rates. 2 2 .
CHAPTER - 2
RUTHENIUM 23.
2. 1 GENERAL CHEMISTRY
Ruthenium shows highly complex and little understood behaviour as a transition element. Its structure corresponds to the arrangement 7 1 4d 5s and it can exist in nine valency states (from 0 to 8). In its properties ruthenium resembles osmium far more than it does iron.
It also shows behaviour analogous to that of iridium and rhodium in the trivalent state. Given below is a brief description of its behaviour in its different valency states, specially the valency states of 2(nitrosyl complexes), 3, 4 and 8.
2.1.1. THE VALENCY STATES OF RUTHENIUM
Ruthenium (0) and Ruthenium (1).
Zerovalent ruthenium is represented by carbonyl and phosphine compounds (Griffith, 1967). However, some olefine complexes e.
C H Ru°C H (Muller et. al. 1966) and nitrosyl carbonyls, e. g. 8 10 8 10 [RuCl(NO) (CO) (PPh3)3] (Laing et. al. 1970) have also been reported.
The compounds containing ruthenium (I) include the carbonyl halides, Ru(CO)Br, Ru(CO)I (Anderson, 1947), nitrosyl halides
(Ru(NO)Br2, Ru(NO)Ia (Irving, 1966) and some simple halides which are present in solution only (Griffith, 1967 p. 145).
Ruthenium (II)
Apart from numerous nitrosyl complexes, ruthenium II is present in a number of phosphine, arsine and stibine compounds
(Griffith, 1967, p. 128). It can be prepared by the reduction of compounds of higher valency state: thus hydrogen (Brito et. al. 1966), titanium III (Cady, 1957), and hypophosphorous acid (Dwyer et. al. 1946) have all been used. 24.
The existence of this valency state in simple compounds is still in doubt. According to Cotton and Wilkinson (1968, p. 992) no simple compounds are known. Griffith (p.142-3) doubted the formation of simple unhydrated RuC12 (if at all formed the main species could be
RuC12(H20)4) but reported black crystalline RuB12 and the blue solution of RuI . Ru0 and RuS do not exist. Cady (1957) found 2 that both air and perchlorate ion would oxidize simple ruthenium II compounds.
Complexes of ruthenium II are numerous and fairly stable. In all its complexes it shows hexacovalency except in a carbonyl compound,
Ru(CO)2C12 where it is four covalent (Sidgwick, 1950). In the ruthenium (II) chloro-aquo system, ERu(H20) 6"324- has been obtained by the electrolytic reduduction of mono and dichloro aquo ruthenium III species (Griffith, p. 160) and the ionic species i. e. [Ru(H20)61 24-and
[RuCl(H20)5 ] have been separated, (Buckly, 1967). The cyanides are all of the ferrocyanide type M4 [Ru(CN)61 . Despite hexacovalency, the amine compounds have only 2, 4 or 5 NH groups. [Ru(NH3)5 (H2Ort- 3 2+ Elu(NH3)4 (H20)2j etc. react with nitrogen to give nitrogen monomer compounds (Elson, 1970).
There are many nitrosyl complexes of ruthenium II. In these, there is usually one nitrosyl group (exceptions like [Ru(NO)2 (PPh3)21 have been reported (Grundy, 1970)). The RuNO group occurs in many
complexes involving other ligands but only the nitro and the nitrate complexes are of interest in nuclear technology. These will be discussed in section (2.1.2). A scheme of complexes other than these is given below (Johnson et. al. 1964). 25.
[13.u(N0)(NH3)4C11 Cl2 Ru(N0)(NH3)2(NO2)2(OH) Ru(N0)(NO3)(SO4)(H20)3
HC1 or 210° NH 3 I Vu(N0)(NH:3)4(01-),C12 Na2t.tZu(N0)(NO2)4(OH HNOI".Ru(NOXN03)3(H20)H20
NH NaNO 2 11420X 3
NH [Ru(NO) 0131 Ru(NO) C13. 3H10 Ru(NOXN0 4 3)(0X)(H20)2
iNtei
Ru(NOXdir)C13 dip Kz&i..{ N Kpc Kz5zu(No( py-d0)92, cis & trans Nal , e n
u.(NOXter)C11C py r C
[RA( NOX N H3)2(e CH) ]l z z.ti(NoX eit(a-35112 Ru(NCXpirX ON) C 1 K[R41\0(pAc141
C1 pyr HC1 pyr
(N ()2 (en)Oa% 1P4NO(en)2Cill2 R.,(NOApyr)2C12 l Cl R..(NOXpir)z(C/-1) Cl2
pyr: pyridine en: ethylenediarnmin.e dip: dipyridyl ter: terpyridyl OX: oxalate 26.
Ruthenium (III) and Ruthenium (3. 5)
Ruthenium III is the most common state of ruthenium.
The anhydrous trichloride (Griffith, p. 136) and the tribromide
(Canterford et. al. , 1968) have been prepared by the direct union of elements in presence of carbon monoxide. Using an appropriate reducing agent, the higher valency states are easily reduced to this state. Thus KI in hydrochloric acid (Crowell et. al. , 1928), 2+ 2+ 34- Hg 2 , Sn. , Ti (Cady, 1957, p. 31) all reduced Ru04 to ruthenium III. 96% alcohol reduces ruthenium IV to ruthenium III
(Starik et. al. , 1957). Electrolytic reduction was used by Wehner et. al. (1950) but later work (Cady, 1957) showed that the product was a polymer and not a simple compound.
The most extensively studied compounds of ruthenium III are the chlorocomplexes. Gmelin (1970) reported nine monomeric 2+ Jr, complexes i. e. RuCl , RuC12 (both cis and trans), RuC13 (both cis 2- 3 - and trans), RuCT (both cis and trans). RuCl and RuCl 4 5 6 'Griffith (1967, p. 137) has summarized the reactions of the trichloride
as follows:
•
'2..u(bipy)3]3÷
C1 5.tu(NO)X5 ]2 [R uC12(SnC13) 2]2 SnC1 2 LL diA1H4 RuHC Xd ipbo s) 2 '•'• RaC4dilhos)2 [Ru(bipy) 3-12+ HX
H 2 R c i(PFt. 3 c 2 RuCl3(PFh3) bipy NOS [RuNO(OH)(NO2)4] 3 2+ en, Zn > 113,u( en) 3,
C H LuC 1 ( C H )-1 C 7 H8 RuCl 6 6 1T-C6H6)21tur 3 7 8 n < Al -Ala. E 3 [Ru(NH5)5H2013+
RuC1 Cl- Ru(NH3) 2+ [Ru(NH3) 5 4 NH3 [Ruci61- [RuCl5H20-12- 2 HX OX HC1 Ru(NH 3)6,3 +
Heat [Itu(NH3)5X1 X2 - 02 [RIC 16]3 2 2- 16 + [RuOX [Ru302(NH3) 14 28.
Detailed properties of the chlorocomplexes have been studied. Thus separation of cis and trans forms (Darig et. al. 1967), dipole moments
(Mercer et. al. 1965), and lability of the chloride ligand (Anderson et. al. 1968) have been reported.
Fletcher et. al. (1965) showed that nitric acid reacted with
Rua-1-in the following manner.
3 + + 4Ru -1- 4H -I- NO Ru(NO)3++ 3Ru4+-i- 21-120 3 Ruthenium III chloride in aqueous solution can activate molecular hydrogen to bring about the reduction of RuIV or Fe(III). (Harrod, 1961 and Halpen et. al. 1966). The sulphate complexes (Lagarer, 1968)
EDTA complexes (Scherzer, 1968) and variety of other amino and other complexes (Griffith, 1967, Gmelin, 1970) have been reported but are not of any direct concern with the present work.
The valency state of 3.5 has been reported by Cady (1957) and
Fletcher (1965). Cady suggested that it could arise from a dimer containing one atom in the 4 state and the other in the 3 state.
Fletcher suggested that a binuclear form of ruthenium II was oxidized to ruthenium 3.5 as follows:
4+ [Ru(OH)2Rui Ru + Air RuIV 2 Ginzburg et. al. (1966) showed that RuIV in H2SO4 on evaporation o at 100-120 produced Ru3. 5.
Ruthenium IV
Compounds of this valency state are few but are very stable.
Methods of preparation are discussed in Section 2.2.2.2. Of the simple compounds, the chloride is known only in the hydrated state, 29.
RuC14 5H20, and in the related hydroxochloride Ru(OH)C13, (Cotton &
Wilkinson, p. 102). Canterford (1968) reported the presence of
Ru C1 in the vapour phase in the reaction between chlorine and 4 ruthenium. The tetrafluoride is also known. Another simple and
a very stable compound is the dioxide, RuO2. It has dioxide
bridging in its structure (Fletcher et. al. 1968).
0 0 Ru 0V
Its hydrate was formulated by the above workers as RuO2-tx yH2O
where x has values up to 0.12 and y is often 1 or 1.3. Chemisorbed
oxygen is responsible for the excess oxygen. The ionic radius, 4+ 0.6 A° is lower than 0. 65A° for Ru and shows that the average
oxidation state is greater than +4.
In aqueous solutions, the monomeric ruthenium exists as a
doubly charged cation over a wide range of hydrogen ion concentration
(pH 7 to 6 rnol dm-3). Shukla (1962) proposed the presence of
[Ru (H20)614+ but it was only a speculation' and no proof was given.
Two points of view exist as to the nature of this cation. According to
the first (Wehner, et. al. 1952 and Paramonova, 1960), it is present 2+ as Ru(OH) and results from the stepwise complexing of RuIV with
OH ions. According to the other view (Gortsema, 1961, Atwood, 1962
and Votovenko, 1969), it is a ruthenyl ion and exists as Ru02+
Electrons from oxygen are assumed to be transferred to the unfilled
4d orbitals of ruthenium thus forming a molecular bonding orbital.
No direct proof has been put forward for any of these views. KMnO 4
oxidation of RuIV failed to solve this difference. (Koltunov et. al. 1968).
However, Vdovenko et. al. (1969) studied the first stability constants 30. of sulphate complexes and found that these values agreed closely to the values obtained for vanadium and titanium for which "yl" ions are known. They found that in the formation of these "yl" ions the water molecules in the inner coordination sphere were replaced by the sulphate ions and the metal oxygen bond was not broken. As a result, the values of the stability constants of quadrivalent metals (e. g. Ru, log !)= 2.74) were close to the stability constants of the sulphate complexes of bivalent metals (e. g. Ni, log r: 2. 76). In view of the foregoing discussion, it is more likely that ruthenium exists as ruthenyl ion.
A characteristic feature of ruthenium IV is its extensive poly- merization in aqueous solutions. Cady (1957) attributed the "inertness to chemical attack" shown by RuIV to the presence of polymers.
Polymers with molecular weights of 1000 within the limits of +1000 or -500 were reported by him. The polymer is built up by the addition of RuO2xH2O or Ru(OH)4xH2O units to monomeric RuIV (Gortsema,
1960). The polymeric forms were shown to depolymerize on adsorption by a cation-exchange resin (Atwood et. al. 1961). Another phenomenon of importance in the aqueous solutions is the excessive hydrolysis observed at increasing pH. Colloidal particles are also o formed at higher pH. Large particles of radius 34. lA were observed at a pH of 6.8 and )2 = 0.10 (Kepak et. al. 1970).
Of the complexes of ruthenium IV the arnnaines are few and uncertain. Complex halides are well known. The chloro complexes have been well studied. Conversely complexing by sulphate, oxalate, nitrate and perchlorate is weak (decreasing in this order). (Fletcher et. al. 1954). Polynuclear structures have been proposed for chlorocomplexes (Fletcher et. al. 1962 and 1966). 31.
Thus
HTH
0 Binuclear Ru Ru 0 HOH or HOH 84-
•/// Ru-0 —Ru 0 HOH
Complexes containing elementary'nitrogen e.g. [Ru(NH ) N ] X 3 5 a 2 have also been reported (Allen, 1966).
Ruthenium (V), (VI) and (VII)
The pentavalent state is an extremely unfavourable state
(Cotton & Wilkinson, p. 1004) and apart from the pentafluoride, RuF5 and its complexes, [RuF6Yno well established compounds have been reported (Griffith, p. 128). RuF5 exists as tetrarn.eric units of
Ru4 F (Figgis et. al. 1964). and Ru409 have been claimed 20 Ru205 (Griffith, p. 153) but not established. However, Ba3Ru2Mg 09 has been studied and well characterized. (Callaghan, 1966).
Starting from the highest valency (i. e. 8) state of ruthenium, the hexavalent state is the first that forms a fluoride. However, it does not form any simple chlorides or oxychlorides (Canterford, 1968).
This state is best known in the ruthenales, M2RuO4, which are unstable in acids (Connick, 1954) and disproportionate to-1-4 and-I-8 states. 32.
2 Ru(VI) —> Ru(IV) Ru(VIII) 4 Chlorocornplexes like [Ru20 C110] etc. are also known
(Woodhead & Fletcher, 1962).
The heptavalency is confined to the perruthenates (Griffith, 1967 and Cotton & Wilkinson, 1968 p. 1005), M(Ru04) which correspond to the permanganates. These may be formed by alkaline fusion of the metal or its salts under the condition that alkali is deficient (excess alkali forms ruthenates). They are stable when dry but decompose in solution to give ruthenates, Ru0 2and oxygen.
Ruthenium VIII
The only established compound of octavalent ruthenium is the tetroxide, Ru04. All ruthenium salts can be oxidized to Ru04 by using an appropriate oxidizing agent. It exists in two forms. The first, prism shaped yellow crystals, sublimes at 270. The second, a brown substance, is obtained by heating the dry crystals at 80-85° -3 (Avtokratova, 1969, p. 144). It is soluble in water (0.13 mol dm at 250, Connick, 1952), and much more so in CC14 (Kd = 58, Martin,
1954). It is slightly extracted by TBP but is insoluble in diethyl ether because it is reduced at the interphase (Nikolaskii, 1957). In aqueous solution it dissociates as:
Ru0 H2O H 2Ru0 5 14-1- HRu0 4 and
H Ru 0 OH- HRu 0 + 2 5 4
Martin (1954) reported dissociation constant values of 6.8+0.3 x 10-12 -15 and 5.7— 0.8 x 10 for the acid and basic dissociations respectively. 33.
Ru0 has a symmetrical tetrahedral structure (Dodd, 1961 and 4
Ortner, 1961) Its general reactions canbe summarized as follows
(Griffith, p.148).
z Ru(NOXN CS) 5 KC 1-1C1 HC1 HCI V 4- rap Cq [RuC16]2- RuCt' al.[ Ru(NC)C151 3 > ru(NO) (CEIX NH3) 3 4]
34.
2.1. 1.1 THE OXIDATION-REDUCTION POTENTIALS OF DIFFERENT
VALENCY STATES OF RUTHENIUM
Ruthenium systems do not behave ideally and the measurement of
oxidation-reduction potentials is very difficult 'and in some cases of
qualitative nature only. This is due to a number of factors. Some
times (as in RuIII - RuIV) the system is irreversible and the actual
species reacting are not known for certain. In potentiometric
titration there is a drift over long periods of time showing slow reactions
or slow equilibration of the products or even the slow equilibration
of the electrodes. (Cady, 1957). As examples of reactions proceeding
in one direction only, we can quote the following:
RuIII 4Ru0 RuIV 4 2+ Ru04+Fe > RuIII 2+ RuIV +Fe > No reaction
Although the potentials are at best semiquantitative they give an
indication of the behaviour of any particular system. Thus, although
the information obtained on the couple RVII RuIII is not definitive the 3+ results show that the couple is sufficiently negative to enable Ti
to reduce RuIII quantitatively to RuII. A summary of the potential
diagrams obtained by different workers is given on the following page. .THE OXIDATION - REDUCTION POTENTIALS OF DIFFERENT VALENCY STATES OF RUTHENIUM
Acid Ru _Run RuII RuIII RuIII RuIV RuIV RuVI RuVI—RuVII Referenc
-0.45 2+ 0.3 2- -1.3 - 1.75 2- -1.25 HC1 Ru Ru Rucl5 Rucl5OH2 Ru0 Ru0 Latimer -1.5 "I 4 (1952)
HC1 RuII -O. 084* 0.05 RuIII -0.96± 0.002 RuIV Backhous 0.82 i-0.002 et. al. RuIII RuV HBr (1949)
0.15 *0.05 -1.3 -1.33 HTFA RuII RuIII Ru(3. 5) RuIV Ru(4.2) RuVIII -1.1 -1.07 Cady (19 -0. 1 0.991-0.07 -1.33 HC 104 RuII RuIII RuIV -1. Ru(4.38) RuVIII
No acid -0.35 -O. 59 Silve'rm.a -3 RuIV RuVI RuVII 1. °° RuVIE Imol dm (1954) KOH -0.57
0.1 RuIII -0.65 (Fblarcgraphically) RuIV Niedrach 1M HC10 RuII 4 -0.85 (Potentiom.etrically) (1951) 36.
2.1. 1. 2. Ion-Exchange Behaviour of Non-Nitrosyl Ruthenium Compounds
The information available on the behaviour of non-nitrosyl ruthenium
towards ion exchange resins is scanty and confusing. The types of
species present in a solution are dependent on the conditions of
preparation. Unfortunately no standard technique has been used for
the preparation of the solutions and so it is not easy to compare the
published data in a meaningful way. Thus Ichikawa et. al. (1961)
prepared the ruthenium solutions by dissolving metallic ruthenium in aqua regia, evaporating to dryness and then dissolving the residue in nitric acid. It was believed by them that in this way they obtained chlorocomplexes. No proof was, however, given for the absence of nitrosyl complexes which could be produced in the presence of boiling nitric acid. Bunney et. al. (1959) prepared RuIV by reducing Ru04 with ethyl alcohol. Miki et. al. (1970) prepared a mixture of RuIII and
RuIV by dissolving commercial "ruthenium trichioride" in hydrochloric acid. The above account shows that due to different types of solutions used, the comparison of results summarized below is of a qualitative nature only.
In hydrochloric acid, Bunney (1959) found maximum adsorption -3 onto Dowex-2 at 2 mol dm HC1 (Kd values of 7, 380 and 20 being -3 achieved at 0.1, 2 and 13 mol dm HC1). Complexes of ruthenium III are not quantitatively adsorbed by Dowex-1. Furthermore, these complexes are said to be partially reduced on the resin (Avtakratova,
1969). However, when the chlorides are boiled with nitric acid, a quantitative adsorption is achieved. Chloride form of Permutit ES
(a strongly basic anion exchanger) adsorbed the ruthenium chloride
-3 which could be eluted with large excess of 2 mol dm HC1 but if the 37.
OH form of the resin was used, quantitative elution was not possible even with hot concentrated 1-IC1. Conversion of polymeric ruthenium to monomeric form on a low cross-linked (2-4%) resin, Dowex 50W-x2 was reported by Atwood et. al. (1961). Berman et. al. (1958) used ammonium chlororuthenate and studied the adsorption on Amberlite
IRA-400. They found a steady decrease in the adsorption in going from aqueous (log Kd 2. 2) to 8 mol dm -3 HC1 (log Kd 0. 65). Their attempts to separate Ru from Rh. were unsuccessful because the adsorbed ruthenium could not be eluted. They found that ruthenium III complexes were adsorbed only to a small extent. Miki et. al. (1970) separated -3 0.1 mol dm solution of evaporated residue of hydrochloric acid solution of ruthenium (III & IV) and nitrosyl ruthenium (III) on a cation exchanger Dowex 50 x-4 (in H' form). The nitrosyl ruthenium species were eluted with 0.1 mol perchloric acid and the ruthenium specie's with
-3 3 mol dm hydrochloric acid containing 50 vol. % alcohol. (Kepak et. al.
(1967 & 1968) separated ruthenium and nitrosyl ruthenium by adsorption on ferrous hydroxide.)
In sulphuric acid, adsorption of ruthenium IV on Dowex-2 showed a minimum at 1 mol dm-3 sulphuric acid and then rose again at higher acidities. (Bunney, 1959). Sorokin et. al. (1970) reported a maximum
-3 at 1 mol dm sulphuric acid on a cation exchanger Ku-2. They found -3 that 83% of ruthenium could be adsorbed at 1 mol dm acid. However, they did not find any minima. (Cf. Bunney et. al. 1959) On increasing the acidity of adsorption on anion exchangers AV-17 and AN-1. It is, however, not clear how they prepared their solutions.
38.
Similar curves of adsorption vs acidity in case of nitric acid were reported by Bunney and Ichikawa. Both show a decrease in Kd -3 in going from 0.1 to 15 mol dm. nitric acid. An interesting feature of the Bunney curves is that the Kd value for uranium and ruthenium -3 is almost the same (7-8) at 7.5 mol dm nitric acid. This will be commented on in a subsequent section on the use of ion exchange resins in nuclear fuel reprocessing.
2.1.2. NITROSYL-RUTHENIUM COMPOUNDS
Ruthenium forms more (well over one hundred) nitrosyl complexes than any other element. NO has a single electron in an antibonding
orbital (Cotton & Wilkinson, 1968, p. 748). It can lose this electron
+ to give a nitrosonium ion, NO which then donates to the central atom with metal-nitrogen back bonding. It is also possible that the electron in the antibonding orbital should remain on the NO which would then donate ME-N-0 as in [Fe(NO)(CN)5 without back bonding. These 3 complexes would have one unpaired electron and not many of them have been observed. The third possibility of an electron being transferred from the metal to NO to give NO is discounted by Cotton and Wilkinson (p. 749). (It was only in compounds like [Fe Br(N0)(das)d where das o-phenylenebisdimethylarsinc, that Felthan (1966) showed the presence of NO). + Most nitrosyl complexes can then be envisaged as involving NO and in which an electron has been transferred to the central atom, reducing its oxidation state by I. The complexes presumably also involve the donation of a lone-pair of electrons from the nitrogen to the central atom with concurrent back bonding from filled orbitals on
39. •
the metal to the (now) empty -TV antibonding molecular orbital of the + NO . This can be represented by
M NO —,..>.M .4- NO + 2- M N 0 M = N =
The M-N-O group is linear. MaXek (1966, pp. 80-82) argued that
there is a delocalization of electron density along the M-N-O bond and there
fore it is not very accurate to talk in terms of integral numbers about the
charge on the NO group or even the oxidation state of the central atom + He thought that the true configuration of the central atom lies between NO
and NO . The degree of back donation determines which extreme would 5 be operative. Thus, for example, d and NO° is reached only in a doubly
protonated pr(CN)5(NO)T1- formed as an intermediate in the reduction of pr(CN)5(NO)]3"-. In the case of ruthenium, the nitrosyl complexes are diamagnetic
and their properties are best explained on the basis of dative 1 -bonding
between the (NO) group and the central ruthenium atom. The bond
formed is extremely stable. The formal oxidation state of ruthenium
is considered to be 2. This lower valency state of ruthenium is
stabilized by the presence of a good acceptor like (NO). (Fletcher,
1955, Zryagintser, 1958 and Griffith, 1966). The bond N-O in NO+ is
stronger than the N-0 bond in NO°. This is shown from the 1R measure- 1 + ments which show a stretching frequency of 2150-2400 cm in NO salts
as compared to 1840 cm-1 in NO. In a compound like Nat £Ru(NO)(OH)
(NO2)4 1, the Ru-N distance in the metal-nitro grouping is 2.079 t 0. 003A
while the distance in the metal-nitrosyl grouping is 1.78 ± 0. 003A°
(Griffith, 1966). The shorterdistance in the latter case shows bonding. 40.
The nitrosyl ruthenium, RuNO, complexes very strongly with chlor- ide, cyanide and nitrite ions and moderately so with nitrate ions
(Fletcher, 1954). Of these only the nitrite and the nitrate ions are present in nitric acid solutions of irradiated nuclear fuels. Depending upon the concentrations of nitrate and nitrite ion, RuNO forms complexes of the following type (Duncan, 1966).
(3-x) ÷ [Ru(N0)(NO3)x (H20)5_x x = Oto4 and
[Ru(No)(NQ _x_ y (H2 _x-y1 z )x (No3)y (oH)3 O)5
x+ y = Oto4
These complexes can be prepared in the laboratory as described by
Fletcher et. al. (1955, 1965). The nitro complexes are relatively more stable than their nitrate counterparts.
The nitrate complexes although less stable than the nitro complexes are more troublesome as they can be extracted into the organic phase in the solvent extraction plants. In these, the nitrate ions are located in the inner coordination sphere of the complexes, the dissociation of which is very slight. Transfer of the nitrate ion into the outer sphere of these complexes takes place mainly as a result of slow hydrolysis. Thus (Jenkin, 1956)
Ru(N0)(NO3)3(1420)2i+1-120---> Fu(N0)(NO3)2(OH)(F120)21 HNO3 I_
Or iltu(N0)(NO3)3(OH)(H20)1—> ..Z..u(N0)(NO3)2(OH)(1120)d HNO3 41. and similarly
[Ru(N0)(NO3)2(OH)(H20)2] 4- Hz 07:-tu(N0)(NO3)(OH)2(H20)zi 4-HNO3 etc.
Hydrolysis studies give an insight into the nature of these complexes and their behaviour. Individual species can be identified (Nikolaskii, et. al. 1970) and separated (Raaphorst, 1963). The hydrolysis of the nitro complexes can be seen from the scheme below (Pichkov et. al. 1966).
The Ru-NO bond is stable and it is difficult to break this bond by normal chemical substitution or oxidation-reduction methods. Ozone and permanganate ion oxidize it to Ru0 (Feber, 1958) but ions like 4 persulphate, dichromate, ceric and bismuthate are ineffective.
Hydrazine also reduces this group (Jenkin, E, 1960). Reaction is faster in nitrate media than in the chloride media. The reaction taking place is: (Jenkin, E. , 1960) NH NH + RuNO 2 2 RuIV ÷ NH + H2O 4 4 , 6H e CI nitrate RuIII chloro complex RuIV nitrate complex
Ferrous sulphamate reduces the nitrasyl group fairly rapidly
(Martin et. al. , 1957) when the final product is a non-nitroso ruthenium IV hydroxynitrate e.g.
Ru(N0)(NO3)x (OH)3_3(--> Ru(NO3)x (OH)4_3( ( oH)1-
[....u(N (N 02 )4 H2o)]
0 [Ru( No) vo2)3 (H.2 0 )21 [Ru(N ax Noz)(ori)(1-1203 1.Ru(N 0) (N 02,)3(OH )212 -
[1,1(NOXN02)2(H20)3] ER4N o) (N o2)2 ( ) ( H2 o)2p-[Ru(N (No2)2 ( )2 (H2o)I#. ERLNO)(NO2)2(OH)3]
, z [Ru (N o) (NO2) (H20)4 2 (N 9 (NO2) (OH) (H2O)31 liku (iv o) (No2 ) (oH )2(1-T2o )21 NNovozxcH)3020]---_-Ftio(NO2)(cr14 -
[Ru (No) ozoc(H20)5r,-- [Ru(Nc)(oH)(HzO)412 --, [Ru(N0)(CE-1)z(1-12,0)3]-.7-_-. [Ru(NO(CH)3(1-120)21 [F.k.t(N 0 (0 .11)4'FT2 r(NO(01-1)5:
2.1.2.1 Scheme of Hydrolysis of Nitro Complexes of Nitrosyl Ruthenium (Pichkov et. al. 1966) 43.
2.1.3. BEHAVIOUR OF RUTHENIUM IN NUCLEAR FUEL
REPROCESSING.
It was stated earlier that ruthenium is the major contaminant in irradiated nuclear fuels. In most process solutions ruthenium is 4 -3 -3 present to the extent of 10 to 10 mol dm (Naylor, 1967).
In the absence of nitrite ion, the ruthenium would have existed as ruthenium IV (Harmon, 1957), but under the conditions present in a dissolver (where there is a lot of nitrous acid present) it is practically all present as the stable nitrosyl complexes. Ruthenium IV is less than 1% (Brown, 1960) This ruthenium IV may be present as paramagnetic compotinds of valency 4 or as brown diamagnetic compounds, having the tentative formula (RuORu) VI. These compounds although present to a negligible extent in process solutions can appear under certain oxidizing conditions. Brown et. al. (1958) reported that -3 (RuORu) VI nitrate was formed in 3 mol dm nitric acid by a photochemical reaction and that in acid concentrations higher than -3 9 mol dm , a ruthenium IV complex and a violet nitrate complex were successively formed.
The nitrocomplexes exist to the extent of 40-70% and the rest are mostly nitrate complexes, although some of the complexes were found to behave differently from both these two types (Naylor, 1967).
Only the nitrate complexes are extracted into the organic phase and the behaviour of the synthetic solutions of nitroso nitrates in this respect is very nearly the same as the behaviour of ruthenium in fuel solutions
(Zyaginster et. al. 1958). This supports the assumption that extractable radiorutheniu.m is present as nitroso nitrates.
There now seems to be some agreement on the more detailed 44.
structure of the nitrosyl nitrate species present in fuel solutions.
It is now believed (Scargill et. al. 1965, Wallace, 1961) that there are five species present. These are the mono, the two isomers of di-, and the tri- and tetra-nitrate complexes. Most workers have failed to isolate uncomplexed (Van Ooyen et. al. , 1964) nitrosylruthenium and - the doubly charged ion Etu NO(NO3)512 (Campbell, 1970). The tetra and the trinitrate complexes are the most extractable complexes. -3 They constitute about 60-70% in 10 mol dm nitric acid (Van Ooyen, 1964)
The two dinitrate complexes are the cis and tran forms. The higher nitrate complexes hydrolyse to lower nitrate complexes. Thus in an o aqueous solution, it requires only 90 seconds at 25 C for 25% of the trinitrate tomplex to hydrolyse to the dinitrato (Fontaine, et. al. , 1965).
Properties of these nitrosyl complexes have been extensively studied and made use of in separating the nitro and nitrate complexes.
Miki et. al. (1970) used cation exchange resin for the separatinn of nitrosyl ruthenium (III) from ruthenium (III & IV). Wain et. al. (1960), used paper chromatography to separate the nitro and the nitrato complexes
They used methylisopropylketone (MIPK) and dibutycellosolve (DBC) as eluting agents. The proportion of dinitro complex in fuel solution was the difference between the amount of ruthenium eluted by MIPK to an RF, value of >0. 9 and that eluted by DBC with an RF value of 70.15. But this technique was shown to be sensitive to the presence of uranium and to the precise experimental conditions. Scargill et. al. (1963) modified this method and used DBC only as the eluting agent. They found a slightly labile nitro species eluting with RF *70.18. This could lead to wrong calculations if both DIPK and DBC were being used. However, it was found that the ratio of the dinitro complexes eluted with RF>0. 18 45. to the nitrate complexes eluted with the same R and under similar E conditions was constant at 1:5. Thus if the fraction of nitrate complexes was f then that of the dinitro complexes would be 0. 2f. f could be determined from a pure nitrate mixture. Now, if we had a mixture of both nitro and nitrate complexes, such that the fraction of nitrato was x (and hence that of the nitro complexes 1-x) and that if the fraction of this mixture eluted with R ) 0. 18 be F then F
F = xf 0.21 (1-x)
f having been already determined for 100% nitrato complexels.
Then x = F - 0.2f & 1-x = f-F 0. 8f 0. 8f and hence the percentage of nitro and nitrato complexes could be determined.
This method is claimed to be much more accurate and less sensitive to the presence of uranium.
2. 1. 3. 1. Solvent Extraction of Nitrosylruthenium Complexes
The most extractable complexes of ruthenium are the nitroso- nitrates and to a smaller extent the nitroso nitrites. A number of solvents have been tried for their extraction. Nikolaskii et. al. (1957) studied their distribution in diethylether and TBP/Kerosene. They found that ruthenium extraction increased with increase in nitric acid concentration (with solvents of diethyl ether type). Distribution co- efficients of 0.03, 0.08, 0.24 and 0.36 were obtained for aqueous phase nitric acid concentration of 1, 2, 4 and 6 mole dm-3. Compounds extractable with ether gradually transformed into non-extractable compounds on standing in solutions of low acidity. Mason et. al. (1962) used trilaurylamine in toluene and found that the tetra and penta 46. nitrato complexes were extracted in the acid forms rather than anionic forms. For freshly prepared solutions the nitro complexes were found to be much more extractable than the nitrato complexes at low acidities. With tri-n-octylamine, Shevchenko et. al. (1962) found a decrease in the extraction of nitrosyl ruthenium with increase in nitric acid concentration g. DR of 0.40, 0. 17, 0. 07, 0.04, O. 02 -3 and 0.1 were obtained for 1, 2, 3, 4, 5 and 6 mol dm nitric acid).
The extracted compound was believed to be Ru NO(NO3)3 with two molecules of TOA. HNO3. Scargill et. al. (1965) studied the extraction of nitrosyl nitrato complexes by dibutyl cellosolve (1,2 di-n-butoxy ethane) and butex. With dibutyl cellosolve, maximum extraction took place at 7 mol dm-3 HNO3, while the extraction fell rapidly in case of butex on increasing the acidity.
The methods used for the commercial reprocessing of nuclear fuels are mostly based on TBP (Purex process) and hexone (redox process). In both these solvents the behaviour of ruthenium is very unpredictable. A number of techniques like the use of acid deficient systems (to minimize extraction) or feed treatment (oxidation of ruthenium to Ru0 ) have been suggested for better decontamination. 4 Organic masking agents (e. g. Oxalic acid, tartronic acid, ED TA, thiourea etc.) has also been used to decrease the extraction of ruthenium
TBP (Joon, 1967). Another way of improving the decontamination is the conversion of the more extractable nitrato complexes to the less extractable nitro complexes. Thus, for a 90% conversion Scargill et. al.
(1965, A) obtained a 10 fold improvement in DFRu with 20-30% TBP.
With butex, however, they found no improvement for 30% conversion because of the high extractability of the dinitro complex. Oxidation 47,
of ruthenium to volatile Ru.04 has been used to improve the DF.
Harmon, 1957).
The extraction of the nitroso nitrates by TBP proceeds through one
or two fast solvation reactions to give a disolvated product. According
to Joon (1970), the TBP molecules are most probably bonded via hydrogen
bridges to the inner sphere coordinated aquo groups. The most extractable
species are the tri- and the tetranitrato complexes with the latter being
extracted more strongly than the former (Fletcher et. al. 1965A;
Scargill, 1964). The two complexes of next highest extractability are the
two isomers of dinitrato complex. The mononitrato complex RuNO(NO3)
(OH)2(H20)2 is not extracted (Niolaskii et. al. 1958). A number of factors like acid concentration, temperature, time of contact, and
concentration of free TBP, affect the extraction of these complexes.
Some other factors like the variation in activity coefficients of species in aqueous and organic phase, the change in dissociation of nitric acid etc. etc. also add to the complexity of the results (Greenfield et. al. ,
1964).
An increase in the acidity of the aqueous phase decreases the extraction of ruthenium (Brown et. al. , 1957; Nikolaskii et. al. , 1958; -3 Nikolaev et. al., 1962). This decrease continues till about 12 mol dm
acid and then levels off (Greenfield, 1964). Nikolaev et. al. (1962) and
El-Guebeily et. al. (1964) obtained maximum extraction at about 0.5 -3 mol dm nitric acid. The decrease in D at higher acidities is related Ru to the decrease in concentration of free TBP. An increase in TBP concentration increases the D (distribution coefficient of ruthenium) Ru
(Brown, 1957 and El-Guebeily, 1964), DRu has a negative temperature coefficient. Shevchenko et. al. (1961) reported a 5 fold decrease in D Ru 48. in going from 10 to 80°C. The temperature gradient was approximately constant. This may be attributed to the exothermic character of the process (El Guebeily, 1964), and the increase in hydrolysis of the higher nitrato complexes to lower nitrato complexes (El-Guebeily, 1964 and Shevchenko, 1961) i. e. the equilibrium shifts to the right in the following:
[RUNO(NO3) 3(H2 0) 2] ERU(N0)(NO3) 2( OF1)(H20)21"
[RUNO(NO3)( OF1)2.(H20)
The extraction of ruthenium is shown to be independent of ruthenium concentration (El-Guebeily, 1964).
The part played by the TBP degradation products (DBP and MBP) has been described earlier. In spite of all these studies, the behaviour of ruthenium is still very complex and the prediction of DF (decontamin- ation factor) difficult. Fletcher et. al. (1966) attribute the low DF to the presence of complexes of following type in successive cycles (plus the complexes due to MBP and DBP)
Position 6 being occupied by TBP or H2O in TBP phase. NO 49.
2.1.3.2. Ion Exchange Behaviour of Nitrosyl-Ruthenium
The general use of ion exchange resins in fuel reprocessing was discussed in the previous chapter. Ion exchange resins (both cationic and anionic) have been used for the separation as well as the characterization of the species present in the nitric acid solutions of nitrosyl nitrates. Miki et. al. (1970) used cation exchanger Dowex 50,
X-4 for the separation of nitrosyl ruthenium III from Ruthenium (III & IV) from hydrochloric acid media. Minami et. al. (1958) earlier on had developed a general scheme for the separation of fission products for chlo ide media. Guillon et. al. (1963) suggested the use of an anion exchange resin for the separation of anionic chloro complexes (obtained by dissolving irradiated fuel in hydrochloric acid) from other fission products. They found that if the solution was originally in nitric acid, the conversion to chlorocomplexes was rather difficult. Minami et. al.
(1958) found that fission product ruthenium showed the presence of 3 cationic, neutral and anionic species. Thus from a 4 mol dm nitric acid, 54% was adsorbed by a cation exchanger and 20% by an anion exchanger; the rest passed through unadsorbed. Knoch et. al. (1965) used ion exchange paper (paper treated with a liquid anion exchanger tri-n-octylamine) for the separation of fission products. Prohaska
(1958) reported that ruthenium could be removed from uranium streams in the Purex process by heating the stream with thiourea and then passing it through an ion exchange column. As much as 90% removal was reported. The adsorbed ruthenium was stripped with 6 mol dm-3 nitric acid. The capacity of the resin was shown to remain high after stripping.
Another use of ion exchange resins has been the characterization of the anionic and cationic species. Kraak (1959) used anion 50. exchanger Dowex-1 and cation exchanger Dowex-50, and found four types of species. The one that eluted first from the cation exchanger was attributed to the anionic complexes. The other three were regarded as di- mono- and non-nitrato complexes. (Their order of elution was di, mono and non-nitrato). Fletcher et. al. (1960) reported that the magnitude of adsorption of ruthenium complexes by Zeokarb-225 was in the order Group A> Group B > Group C > Group D. (The groups A,
B, C and D correspond to the mono, di, tri and tetra and penta nitrato complexes respectively). Wallace (1961) found that there were four species. Three of these could be adsorbed by a cation exchanger. -3 Of these three one could be removed with 0.5 mol dm nitric acid and -3 the other with 2 rnol dm while the third could not be removed even 3 -3 with 6 mol dm nitric acid or 0.3 rnol drn La(C104)3 These three species were c onsidered to be [RuNO(NO3)2(1-120)31-4- [Ru(NO)(NO3)
(1-120)4 and polynuclear 0)1 3+ The unadsorbed species EuNO(H2 5.1 were, of course, neutral or anionic. Van Raaphorst et. al. (1963) similarly separated three species with NO3/Ru ratios of 1.96±0.05,
0. 99 ± 0. 05 and<0. 01 respectively.
Anion exchange resins also remove ruthenium from nitric acid solutions. Fletcher et. al. (1960) attributed this partly due to physical adsorption and partly to the presence of anionic species. All the above authors reported the presence of anionic species. Wallace (1961) thought that both [RuNO(NO3)0 2- and [RuNO(NO3)4(H20)1 complexes were present. But these species were not separated. Later work by
Fletcher et. al. (1965) showed that penta nitrato complexes were less significant. Campbell (1970) confirmed the presence of a singly charged anionic species RuNO(NO3)4 (F120) in 6 mol dm-3 nitric acid. [ 51,
2.1.3.3. Waste Disposal of Ruthenium in Nuclear Fuel Reprocessing
More than 95% of ruthenium favours the aqueous phase while the
rest is extracted into the organic phase along with the desired products
(uranium and plutonium). Both these fractions present problems. That
following the product stream must be removed otherwise there will be
build up of ruthenium in the solvent at each extraction. (Harmon, 1957A).
Use of ozone and/or permanganate ion removes most of ruthenium as
Ru0 from the feed solution. However, this treatment leads to the 4
production of RuO and radiocolloids. Ruthenium following the aqueous 2
raffinate has to be removed to make the waste liquid safe for disposal.
A brief description of the different techniques used is given below.
One simple method of partial removal was studied by Belloni
et. al. (1959). The ruthenium is adsorbed on various surfaces. At, a
pH of 3, the adsorption order was found to be, glass KAg (Pt PVC was, glass < PVC cationic, neutral and anionic), the cationic species could be adsorbed by cotton. The process of adsorption was shown to be a cation exchange by Berry (1960). He found that the amount adsorbed decreased in the presence of competing cations or by ligands that formed complex anions 2+ with ruthenium. The species RuNO NO2 was assumed to be the major adsorbing species (determined from the number of occupied sites). Sachse et. al. (1962) reported the partial removal of ruthenium by adsorption on Redgendorf clay. The presence of neutral and anionic species makes it impossible to adsorb the ruthenium quantitatively on the cation exchange clay. Ruthenium can be volatilized as Ru0 by 4 heating nitric acid solutions. The volatilization increases with increase 52. -3 in acidity up to 8 mol dm acid when a plateau is reached (Wilson, 1957). Nikolaev et. al. (1959) distilled micro quantities of ruthenium from nitric acid in presence of persulphate and silver ions. Oxidants like 2- Cr0 Cr 0 13r0 and Mn0 were less effective and needed 4 ' 2 ' 3 4 removal of nitric acid for quantitative results. May et. al. (1958) found that small quantities of chloride ion catalysed the oxidation of ruthenium from nitric acid solutions. Increase in acidity increased -3 volatilization up to 11.9 mol dm nitric acid. The volatilized ruthenium has to be contained. Edwards (1959) found that silica gel beds could be efficiently used for adsorption of ruthenium produced 3 in the off gases of radioactive waste calciners. A DF of 10 was reported and the efficiency of the bed was shown to be constant even after the adsorption of 40g ruthenium per cubic foot of the gel. Rhodes (1959) reported the design of an absorber of ruthenium from an air-nitric acid-water phase. DF's of 100-1000 were obtained and no breakthrough was found even after the adsorption of 58g of ruthenium per cubic foot of silica gel. The bed was regenerated by washing with water. Gresky (1956) reported the use of para-periodic acid for the oxidation of ruthenium to the tetroxide. The ruthenium was adsorbed as ruthenium dioxide on solid organic materials. Another technique used for the removal of ruthenium has been to coprecipitate it with some other element and remove it by adsorption. Studies at the Mound Laboratory (1956) showed that ruthenium could be coprecipitated with ferro ferrocyanide which is specific for ruthenium. Activated carbon was used for adeorptfon. Gardner et. al. (1960) reported the removal of various ruthenium species by floc precipitation. It was shown that nitro complexes were the cause for the low ruthenium decontamination factors obtained in various effluent 53. treatments. Thus 61 ppm aluminium plus 5.6 ppm ferric at pH 10 removed 100, 97.3 and 58. 5% respectively of ruthenium IV nitrate, nitrato and nitro complexes after 5 minutes of stirring at 20°C. Another method is to coprecipitate ruthenium with Mn02. Mn(NO3)2 is added and the pH raised to 11.5. 17.5% ruthenium is removed with each precipitation(Morgan,1961). It is adsorbed on metal (8g iron 2g aluminium (40 mesh each) ). A decontamination factor of 200 was obtained by Kuhlmann (1970) by a simple procedure. The effluent at a pH of 1-3 was percolated onto activated iron (Fe heated under an atmosphere of hydrogen at 900°C) at >70°C. Afterwards the pH was raised to 8-10 and the effluent treated with zeolites. Kepak (1970) showed that hydrated Fe2O3 containing 0. 1-5% Ag 2O had high sorption capacity for ruthenium. A 4% aqueous suspension of the above was used in aqueous solution containing -5 -3 10 mol dm. ruthenium. The distribution coefficients obtained 5 3+ 4 3+ were 1.2x10 for RuNO and 4.2 x 10 for Ru in comparison with 8. 4x10 3 and 4. 8x103 obtained on Fe(OH) only and 3. 9x104 and 3 2. 8x104 respectively with Ag 2O only. 54. 2.2 EXPERIMENTAL 2.2.1. MATERIALS USED All chemicals used were of analytical reagent grade. The ion exchange resins used in this study were Zeokarb-225 (Permutit Co.) and Ionac XAX-1284 (Ionac Chemical Corporation, USA). The resins were washed successively with the following to remove any soluble impurities. i. Deionized water ii. Alcohol or Methanol iii. Acetone iv. Deionized water. The starting material for ruthenium was 'Ruthenium Trichloride' (Halewood Chemicals, England). The true nature of this commercial product has been a subject of much controversy. According to Sidgwick (1950, p. 1466) this water soluble, hygroscopic, substance is a trihydrate (i. e. RuC13 3H20). The compound RuCl3 (prepared from the elements in the presence of-carbon monoxide) is insoluble in water. Pantani (1962) studied the spectra of this so called ruthenium trichloride and showed that the spectra in different hydrochloric acid concentrations corresponded to the spectra of ruthenium IV complexes. It was, there- fore, of interest to know the nature of the material used in the present work. Spectra of the ruthenium trichloride solutions were recorded (Figure -1). Curves A & B correspond to acid concentrations of 1 and 5 -3 mol dm respectively. The spectra obtained here agree with the spectra reported by Wehner et. al. (1952) for ruthenium IV chloride. Thus it is believed that the ruthenium is quadrivalent in this so called 0. 8 0.6 0.4 cd 0.2 0 ZOO 300 400 500 600 ;' (nm) Figure 1 UV Spectrum of Ruthenium Trichloride in HC1 mg/1) -3 5 mot dm.-3 HC1; 1mo1 dm HC1. 56. trichloride. Woodhead. and Fletcher (1962) quoted a ruthenium oxidation number of 3. 96 - 3.98 in a number of samples. The other ruthenium compound used was ruthenium -106 obtained from Radiochemical Centre, Amersham, as nitrosyl nitrates. It was used as such in the study of nitrato complexes but was converted to Ru IV in other studies. 2. 2. 2. PREPARATIONS 2. 2. 2. 1. Ruthenium Tetroxide Ruthenium tetroxide was the intermediate in the preparation of ruthenium IV from the "ruthenium trichloride". Chloride ion was first removed by repeated fuming with sulphuric acid. The solution was then cooled and a 5% solution of KMnO added. The yellow 4 fumes of ruthenium tetroxide evolved were collected in two traps cooled in liquid nitrogen. In those cases where ruthenium -106 was also present in the distillation flask, a third trap of carbon tetra- chloride was also used. Ruthenium tetroxide condensed as a solid. In most cases, the tetroxide was immediately dissolved in perchloric acid and reduced to ruthenium IV, However, the tetroxide has been found to be stable for several weeks at low temperatures. (Silverman et. al. 1954). 2. 2. 2. 2. Ruthenium IV A number of different methods for the reduction of ruthenium tetroxide to ruthenium IV have been used. Wehner et. al. (1950) used an electrolytic reduction technique for the preparation of ruthenium III and IV. Niedrach et. al. (1951) used excess of hydrogen peroxide for the reduction of ruthenium tetroxide. Yafee et. al. (1950) used a 200 per cent 57. excess of H202. All the above reductions were carried out in per chloric acid. Nikolaskii et. al. (1957) reduced a solution of tetroxide in nitric acid with 5% hydrogen peroxide. Cady (1957), in addition to the electrolytic reduction also tried the electrolytic and chemical oxidation of RuIII as well as the chemical reduction of Ru0 with 4 mercurous ion. However, he did not study any of these reactions in detail. The method selected in the present studies was based on the reduction of tetroxide with an excess of hydrogen peroxide. In most -3 of the cases the reduction was carried out in 1.0 mol dm perchloric -3 acid, although in a few cases the reduction was carried out in 2 mol dm nitric acid. The solution of Ru0 was first cooled in ice and hydrogen 4 3 peroxide was introduced at a rate of 0.5 cm per minute with constant shaking. During this time the reaction vessel was kept immersed in a mixture of ice and water. According to Cady (p. 57, 1957), the variables that affect the properties of ruthenium IV are rate of mixing and concentration of reagents, reducing agent employed, and the temperature of the solution during reaction. In all our preparations, all of these things were kept constant as far as possible. After the addition of excess of hydrogen peroxide, the solution was boiled for 10-15 minutes and then immediately cooled. The above solution of ruthenium IV was characterized, as described in the results, by measuring its spectrum and also by deter- mining the amount of iodine liberated on its reduction to ruthenium III. The presence of ruthenium III and ruthenium II was not checked. According to Cady (1957) air oxidizes RuII to Rulil and RuIII is unstable in perchloric acid at room temperatures. It is rapidly oxidized to RuIV by perchloric acid. As the presence of chloride ions in Ru IV solutions 58. could not be established it is reasonable to assume that there was no formation of ruthenium III in these preparations. The presence of chloride ion was checked by the method of Niedrach et. al. (1951) except that ruthenium IV was oxidized with silver peroxide and not with persulphate. The solution was then tested with silver nitrate. Each solution prepared in the above way was scanned spectro- photometrically and the valency state determined by the potassium iodide method. Any particular preparation was used for not more than three months. After each preparation, the solution was centrifuged and found to be free of any precipitate (of Ru02.H20). In some cases, solid samples of the nitrate were prepared. In these cases it was preferred to reduce the Ru0 in nitric acid. 4 Samples were compared with those where HNO had been introduced 3 after reduction and found to behave similarly. Excess of acid was vacuum distilled. Distillation was carried out below room temperature. -5 After the removal of the acid, the solid mass was evacuated at 10 m.m of mercury for 2 hours. These solids were used for 1R spectra. They were shown to be free from RuO 2by dissolving in dilute acid and centrifuging - the absence of a black ppt. confirming that RuO 2was not present. 2.2.2.3. Preparation of Nitrosyl Ruthenium Nitrates A stock solution of nitrosyl ruthenium nitrate complexes was prepared by the method of Fletcher et. al. (1955). Ruthenium trichloride (prepared by the action was dissolved in water and a mixture of NO-NO2 -3 oft-J8mol dm. nitric acid on copper) bubbled through the solution. The solution was then boiled, cooled and centrifuged, mixed with concentrated hydrochloric acid and evaporated nearly to dryness. It 59. was then dissolved in water and centrifuged again (to remove any RuO2, if present). A plum coloured solution was obtained. To this solution, after boiling, sodium hydroxide was added until a pH of more than 11 was achieved. The nitrosyl hydroxide was then precipi- tated, at a pH of 6. 4 obtained by the addition of dilute perchloric acid. The precipitate was separated by centrifugation. It was then washed with portions of acetone-water (9:1) mixture until the washings were free of any chloride ion. The precipitate was redissolved in sodium hydroxide boiled, and reprecipitated at a pH of 6. 4. It was again washed with acetone-water mixture and then finally dried at 80°C. -3 The above solid was dissolved in 8 mol dm nitric acid and refluxed for more than an hour (Fletcher, 1960). It was then cooled and stored. At this stage the tracer, obtained as nitrosyl nitrato complex was added. This stock solution was then used to prepare further solutions of lower and higher acid concentrations. All these solutions were aged for at least a week before use. 2.2.3. ESTIMATIONS 2.2.3.1. Ruthenium In some of the earlier work on the spectra of ruthenium and in the charge determinations, chemical methods were used to determine the concentration of ruthenium. In the later work on the adsorption of ruthenium on ion-exchange resins, radioactive ruthenium was used. The methods applied are discussed below. Most of the spectrophotometric methods for the determination of ruthenium required standardization. As the exact formula of the "ruthenium trichloride" was not known (as discussed in the previous section) and as this substance was hygroscopic, solutions of ruthenium 60. had to be standardized gravimetrically. A simple method of Taimni et. al. (1954) was used for this purpose. The procedure was as following: A portion of ruthenium chloride in dilute hydrochloric acid was taken and made slightly alkaline with ammonium hydroxide. Excess of -3 sodium sulphide (2 mol dm ) was then added. This was followed by 3 -3 50-60 cm of 8 mol dm acetic acid and 5-10g of ammonium acetate. The acetic acid decomposes the thiosalt to give an easily filterable sulphide precipitate. The mixture was boiled for 4-5 minutes, cooled and boiled again. It was cooled and the precipitate filtered through a weighed sintered crucible.of porosity 4. The pressure during filtration was kept as low as possible. The precipitate was washed successively with water, alcohol and ether. It was sucked dry at the filter pump and then dried in a vacuum desiccator to constant weight as Ru2S32H2O. The reproducibility was very good. Six samples analyeed in the above way gave values within 1-2% of each other. A number of methods are available for the spectrophotometric determination of ruthenium (e.g. Banks (1957), Manning (1962), Oka (1963), Belew (1961, etc.) The first two methods involve the distillation of Ru0 into a suitable complexing agent (1, 10- phenanthroline 4 and 2-nitroso-l-naphthol respectively) but were avoided because of the distillation of very low quantities of ruthenium was not expected to be very accurate. The method of Potts (1970) was simple but could only be used in hydrochloric acid or otherwise involved the distillation of Ru04 into HC1. The methods of Oka and Belew were simple and were tried. The method of Oka (1963) involved heating of a ruthenium sample -3 in HC1 at 70°C with 0.5 mol dm ammonium thiocyanate. Unfortunately 61. this method was sensitive to the original volume of the sample as well as the amount of the thiocyanate added. It was expected that in later stages larger volumes of dilute ruthenium solutions would be involved. So the other method i. e. Belew (1961) was preferred, and was used in the rest of these studies. This method was applied as follows. A sample of the ruthenium was taken in a separating funnel 3 containing about 5 cm of aluminium nitrate reagent (prepared by dissoll.i 3 ving 452 g. of aluminium nitrate and 12.6 cm of concentrated nitric acid in a litre of water). 30-40 mg. of silver peroxide were added along 3 with 7cm of carbon tetrachloride. The mixture was shaken for 2 minutes and the organic layer taken in another separating funnel con- 3 taining 10 cm of.l mol dm-3 sodium thiocyanate. The aqueous layer 3 of the first separating funnel was re-extracted twice with 5cm portions of carbon tetrachloride. (In the original paper, only two extractions were recommended but three extractions gave better reproducibility). These two extractions were combined with the first and this second flask shaken for 2 minutes , whereupon the blue colour of the thiocyanate complex appeared. The aqueous coloured complex was taken and centrifuged to remove any carbon tetrachloride or silver peroxide particles. The colour was allowed to develop for one hour before reading at 590 .nrri. This method is independent of the thiocyanate concentration in -3 the range of 0.2 to 2.0 mol dm . The colour is stable for at least 24 hours. The method worked fairly well in perchloric, hydrochloric and nitric acids. A calibration curve„ was prepared from a solution standardized gravimetrically. (Figure -2). 5 samples containing 62. ai 0.32 0.28 0.24 0 0.20 59 t a 0.16 bance r Abso 0.12 0.08 0.04 0.0 20 40 60 80 100 120 140 iig Ru Figure -2. Estimation of Ruthenium as a Thiocyanate Complex 63. 100 pg of ruthenium each were analysed. The results obtained are shown in the table below. The reproducibility and accuracy of the method is obvious. No. Ruthenium Error Present Found Per cent 1 100 jig 101.0 +1 2 100 " 100.0 NIL 3 100 " 99. 8 -0.2 4 100 " 100.0 NIL 5 100 " 101.4 +1.4 106 106 Ru Rh COUNTING Ru-106 is a pure beta emitter. It decays to the short lived Rh-106, which gives both betas and gammas. The decay scheme is as follows (Lederer et. al. , 1967) 106 106 106 Ru 367d Rh 30S Pd > 44 -13 45 > 46 / el max = O. 039Mev 4 betas of energy: p, = 3.53, ft= 3.1, P3= 2.4 8z 94 2.° More than 70% is p i. p4 is 2-3%, rest is No Y's a and 133 19 Vs have been reported. Some of these being O. 512Mev(21%), 0.662 (11% doublet) 1.05(1.5% doublet), 1.13 (0.5% doublet) etc. The radiochemical purity of the isotope was checked by Y-spectro- metry. A germenium crystal, coupled with 4000 multi channel analyser 64. (Intertechnique) was used for the Y-spectra. A plot of such a spectrum is shown in Figure-3. In the present work two types of samples were encountered: (a) liquid samples (b) solid samples (in the form of resin and paper 3 chromatography strips). The liquid samples (lcm in each case) were 3 taken in small stoppered glass tubes (capacityr4 2cm ) and then counted in a well type sodium iodide crystal. The well type crystal has the obvious advantage of better geometry over an ordinary crystal, since the crystal-dectetor surrounds the sample on two sides. The linearity of the response of the counter was checked over a wide range of counting rates. Thus when solutions of varying activity but of the same volume were counted, a linear relation was found between the con- centration of the solution and the count range of 500 cps to 7000 cps. Resin samples were also counted in similar glass tubes. To the 3 sample 0.50 cm of water were added before counting. Addition of water made the resin settle at the bottom of the tube. The same (within± 2%) amount of resin was used in all the samples, and the error due to different self absorption was eliminated by having the resin settled at the bottom in each case. In the case of paper chromatography, the small paper strips were folded (four times) and mounted on aluminium planchets and then counted under an end-window type Geiger counter. These strips were numbered in advance and then folded in the same direction so as to keep the self-absorption constant. Cl) 0 0 1.13 Mev Channel Number - Rh106 Figure -3 Y-Spectrum of Ru106 66. 2.2.3.2. Determination of the Valency of Ruthenium Following Wehner et. al. (1950) and Cady (1957), potassium iodide was used to determine the oxidation number of the prepared ruthenium IV. Potassium iodide was used by the above workers as well as by Crowell et. al. (1928) for this purpose. The iodide ion acts as a reducing agent in acid solution and the equivalent amount of iodine liberated can be titrated against standard sodium thiosulphate solution. 3 In the actual procedure 2 cm of ruthenium solution along with 3 -3 3 40 cm of 1 mol dm perchloric acid and 10 cm of 10% sodium chloride were taken in a two necked flask. Oxygen-free nitrogen was passed through the flask for 5 minutes to remove any oxygen present in 3 the system. 10 cm of 10% potassium iodide were then added and the flask immediately stoppered. The contents were left under a slight pressure of nitrogen and were fully wrapped in black paper (to exclude light) for one hour. (The time of reaction was determined by trial). The liberated iodine was titrated against standard sodium thiosulphate. During the titration, nitrogen was continuously passed over the mixture. Acid solutions of iodide are readily oxidized by the oxygen of the air (Vogel, 1966, p.343). 4 I -I- 0 -t- 2I 2-1-2H 0 2 2 and the reaction is catalysed by strong light. Thus the exclusion of air and light is important and this was achieved by passing the nitrogen and wrapping the reaction vessel with black paper. Blanks were run along with the reaction and corrections made to the amount of iodine liberated. The loss of iodine by volatilization was avoided by the presence of a slight excess of potassium iodide which reduces the vapour pressure of iodine by complexing it as I3 67. 2. 2.3.3. Estimation of Copper and Chromium Both copper and chromium were used for the standardization of the method for charge determination. So accurate estimation of these elements was essential. The following methods were used. Copper was determined by the method of Vogel (1966, p. 358). A sample solution was taken and the mineral acid removed by the addition of a little sodium carbonate. A slight turbidity that was produced by the addition of sodium carbonate was removed with a few drops of acetic acid. To this solution, a 10% solution of potassium iodide was added. The liberated iodine was titrated against standard sodium thiosulphate. The reactions taking place are: 4- 2 Cut 4- 41 \ 2 CuI + I 2 or 2+ 2 Cu + 51 -^1°` 2 CuI 1 3 252032 + I ---s S 406 24. 31 3 Chromium: two methods were used for the determination of chromium. In the first (Vogel, 1966, p.311), the chromic salt was converted to the dichromate by boiling with excess ammonium persulphate in presence of a little silver nitrate. Excess of the persulphate was removed by boiling the solution. Thus - 0 (AgNO ) 2 2Cr31- 4.. 35208 .4- 7H 3 Cr 0 - 6HSO + 8H+ 2 2 7 4 2 Boiling 2S 0 2H 0 Oz 4- 4HS0-4 2 2 To the dichromate thus produced, a known excess volume of standard ferrous salt solution was added. The amount of ferrous used for the dichromate salt produced was determined by titrating the excess ferrous against standard potassium permanganate. 68. The above method, however, was not very efficient for those solutions where the concentration of chromium was very small. For these the Unican Atomic Absorption Spectrophotometer, SP-90, was used. The standard absorption wave length recommended (Unlearn, SP-90, Instruction Manual), was 357.9 nm but practically 358. 9 nm was found to be the absorption maximum with our spectrometer and this wave length was used. A calibration curve, as shown in Figure 4 was constructed and the measurements of the concentration of chromium in dilute solutions were made from this. The instrument was operated for emission as the cathode lamp needed for absorption was not available. 2.2.3.4. Capacity and the Swollen Volume of Resin A. Capacity The capacity of cation exchange resin (Zeokarb-225) was determined in both sodium and hydrogen forms. In the case of sodium form, the resin was converted to the hydrogen form. Oven-dried (100°C) resin was taken in a stoppered weighing bottle and accurately weighed. If it was in the sodium form it was converted to the hydrogen form by passing dilute HC1 through a small column containing the resin. Excess of acid was removed by successively washing with methylalcohol. Complete removal of the hydrochloric acid was checked with methyl red (HI. ion detection) or by silver nitrate (chloride ion detection). This resin, as prepared above, was taken in a titration flask and 3 50 cm of water added. To this 0.5 - 1.0 g. of sodium chloride was added and the sample stirred for half an hour. It was then titrated against standard sodium hydroxide. After each addition of sodium hydroxide the resin sample was left stirring for a few minutes. Phenolphthalein was used as an indicator. Appearance of a persistent (10-15 minutes) pink 69. 70 ) rn 60 9n. 358. ( 50 n io s is Em t 40 - rcen Pe 30 — 20 _ 10 4 4 1 1 10 20 30 40 ppm Chromium Figure -4 Estimation of Chromium by Flame-photometry. 70. colour was taken as an end point. The capacity of the resin was then calculated from the number of moles of sodium hydroxide used for a known weight of the resin. The determination of the capacity of weak-base resins is not as simple as the capacity determination of cation exchange resins. In general principle the method of Fisher et. al. (1955) was used. Oven-drie o (at 50 C) (Ionac-XAX) resin in nitrate ion form was weighed and taken in a glass column with a sintered disc of porosity I. 7% hydrochloric acid was passed through the column at a slow flow rate. A large excess of acid was passed to ensure complete conversion of the resin from nitrate to the chloride form. Interstitial acid present was removed by washing the resin with methanol. Absence of chloride ions (no precipitate with silver nitrate) in the washings was taken to indicate the complete removal of acid. . The first washings gave a white precipitate with silver nitrate but after a few washings this precipitate was not formed, instead a white turbidity appeared. This turbidity persisted even after long washing. Probably some of the hydrochloride groups attached to the nitrogen group of the pyridine ring were being washed off. So in determining the capacity of these resins that point was taken at which there was no precipitate formed and the turbidity produced by one wash was the same as produced by the next wash. The resin was freed from unadsorbed acid in another way. After equilibrating the sample with 7 per cent hydrochloric acid, it was washed -2 -3 with 10 mol dm hydrochloric acid. The washed sample was taken in a small tube with a sintered disc bottom. This tube was placed in a centrifuge tube and centrifuged for half an hour at 400G. The resin was then taken in a column. 71. After this point both the samples (prepared either by washing with methanol or by centrifugation) were eluted with 4 per cent sodium sulphate solution. The chloride content of the eluate was determined by Volhard's method. In the case of methanol washed sample, this was a measure of the capacity of resin. However, in the case of other sample, a correction was applied for the amount of acid present in the heads even after centrifugation. This correction was determined by soaking a sample of the resin in water and then centrifuging it under similar conditions and for the same time. The increase in weight of the sample was taken as the weight of water sticking to the resin. The same amount of acid was thus assumed to be sticking to the resin and the amount of chloride ion equivalent to this acid was subtracted from the final reading. These treatments gave concordant results. B. Swollen Volume of the Resin A sample of resin (Zeokarb-225, 4, 8 & 20% crosslinked) under investigation was taken and allowed to swell in water for 24 hours. It was then taken between the folas of blotting paper and rubbed until it coul flow easily over the paper. A sample was then weighed and taken in a density bottle. To this cyclohexane was added and the bottle and contents weighed again. Weight (and thereby volume) of the cyclo- hexane displaced by the resin was thus determined in the usual way. The resin sample was then dried in an oven at 100°C for 16 hours and weighed. This was the weight of resin whose swollen volume was equal to the volume of the displaced cyclohexane. Volume per unit weight then was determined. 72. 2.2.4. SPE C TROPHOT OMETRY In the present work spectra of ruthenium solutions were frequently measured as test of the purity and stability of ruthenium IV samples was the absorption spectrum. Spectra of ruthenium VIII solution were also measured in the lower UV region because these spectra have not been previously reported. 2.2.4.1. Instrument Used A Unicam SP-700A, double beam recording spectrophotometer was used. In this instrument the principle of differential spectroscopy is applied. In this technique the difference in absorption (at the same wave length) of two samples is measured. The two samples differ in their content of the component to be investigated. In the SP-700A, a beam of monochromatic light is divided into parts and passed at 25 c/s alternately through the reference and the sample cell and then allowed to fall on a single radiation detector. The signal produced is amplified and then fed to two output channels (R & S) by an electronic switch called a distributor, which switches synchronously with the alteration of the beams through the cells. The signals in R and S are rectified and then passed to the recorder which records the ratio S/R (equal to the transmittance of the sample cell with respect to reference cell). When the reference solutions contain highly absorbing substances, available energy levels at the band width used are drastically reduced. Slits have to be opened wide and the energy on the detector increased. This instrument has five resolution control settings. Neighbouring positions give rise to levels of detector energy differing by a factor 10 or slit widths differing by a factor of about 1.7. The highest 73. numbered position corresponds to the highest energy or the smallest slit width. A combination of these two can be used to measure spectra even in the presence of highly absorbing standards. Calibration of the Instrument: A linear Eder' s Law plot of absorbance versus concentration of the absorber is generally taken to be indicative of linearity of the response of the detecting system of the photometer. However, this is not always true (e.g. Cannon et. al. , 1953). Apart from the detector inefficiency, a number of other sources of error have been encountered and reported (Goldring et. al. 1953). It was, therefore, necessary to calibrate the instrument against some solutions whose spectra were well known. Spectra of aqueous solution of neodymium nitrate and of benzene in cyclohexane were measured and compared with published results (Appendices 1 and 2). For day to day check a dydemium filter No. 700871 was used. It was found that the accuracy and wavelength resolution of the instrument was excellent. Fused silica cells supplied by Thermal Syndicate Ltd. were used because of their better transmittance characteristics. 2.2.4.2. Scan of the Spectra In the present work we were interested in nitrate ion media. 5 NO has a band of low intensity (molar absorption coefficient = 7 x 10 ) 3 at about 300 nm (Beaven, 1961) and NO a much broader and somewhat more intense one with a maximum at 355 nm. They both "cut off" at around 240 nm. However, as stated earlier, the double beam spectrophotometer could be used for measuring nitrate solutions -3 up to 250 nm. The concentration limit was 0.4 mol dm . In 74. appendix 3 , two spectra are shown. In A, the spectra of pure -3 -3 0.1 mol dm nitric acid against water and in B, spectra of 0.4 mol dm -3 nitric acid against 0.3 mol dm are shown. It is seen that the instrument could be used up to 250 nm even in the presence of low concentrations (0.4M) of nitrate ion. This advantage of being able to record the spectra in the pros ence of nitrate ion had, however, to be used with extreme caution. If the strong absorbance of the standard is ignored on the assumption that this will be cancelled out instrumentally, quite misleading results can be obtained. Thus consider, for example, the spectrum shown in -3 Figure-5. This is a spectrum of ruthenium-nitrate in 1 mol dm nitric acid. There are two well-defined peaks at 260 and 323 nrn. But in actual fact these two peaks have arisen from the strong absorption of nitrate ion in this wave length region. If we look at the spectra of nitric acid (Appendix 3), we find a minimum in absorption at 260 nm. At this wave length the absorbance is not too high for the recorder to go off scale. Thus there is still some light passing through the sample cell. Now the sample cell contains ruthenium which also absorbs at this wave length. So the recorder rises to record the absorbance of ruthenium. It thus shows a maximum at a point corresponding to the minimum of the nitrate ion. As v.e go to higher wave lengths, the absorbance of nitrate ion increases, the light passing through the sample cell is drastically reduced and thus the pen records a lower value of absorbance. Similarly we get another peak at 323 nm because the maximum of nitrate ions is around 300 rim and at 323 the absorbance is getting low. Thus, two peaks, which do not exist in reality are recorded. To avoid this, it is always advisable to bance Absor (nm) -3 Figure-5 Erroneous Spectrum of Ruthenium Nitrate in 1 mol dm HNO 3 76. scan two blank solutions such that the sample cell contains a slightly known excess of the absorbing constituent and see if the difference can be accurately measured. If it can be measured reliably, then the instrument can be used up to that concentration of the component in the reference cell. Spectra of solutions were taken in hydrochloric, nitric and perchloric acid media. Only nitric acid absorbs in the UV region. Its absorption and the problems associated with it have been discussed in the preceding section. It was shown that the SP700 spectrophotometer -3 could be used up to a concentration limit of 0.4 mol dm nitric acid. So in all cases where the spectrum of a compound was taken in nitric -3 acid, the acid concentration was always below 0.4 mol dm . In the case of other two acids, spectra could be taken up to even 200 nm wave length. Spectra were taken as follows. Blank solutions were prepared which contained all the constituents of the sample except the component under study. The multipot of the instrument was set in such a way that a 100% transmission line was obtained on scanning the blank solution in both reference and the sample cell. Absorbance was then recorded for the blank. Sample was then taken in the sample cell and recorded. Blank reading if more than 0.5 per cent of the total scale (usually 0.0-1.1 absorbance) was subtracted before any calculations were made. Z. 2.4.3. Representation of Data The spectra are shown graphically. Against the wave length (in nanometers) are plotted either the absorbance or molar 2 -1 absorption coefficient. This latter term E , is measured in m mol and 77. is equal to: (McGlashan, 1967) Absorbance lc where 1 = length of the cell in meters c = concentration in moles per cubic meter. This in essence is the same as the term used in the older literature except that it involves the Si units of measurements. Thus the length of the light path is in meters instead of previous centimeters and the concentration is in moles per cubic meter rather than in moles per litre. Values obtained with term in use will thus be 5 higher by a factor of 10 than quoted in the literature. 2. 2. 5. ELECTROPHORESIS In the beginning a simple arrangement was used to study the electrophore of ruthenium solutions. Two carbon electrodes were dipped in the electrolyte taken in two shallow glass vessels. The electrodes were connected to the power supply leads through platinum wires. A power unit type 1182B (Isotope Development Ltd. Aldermaston) was used as source of power. It had a voltage range of 0 to 500 and a current range of 0 to 150 mA. The paper with the spot was spread over a glass plate. The ends of the paper strip (Whalman No. 1) were dipped in the electrolyte. Before putting the paper on the glass plate it was wet- ted with the electrolyte and the excess electrolyte removed by pressing between the folds of blotting paper. A drop of the solution under investigation was then applied in the middle of the paper. This arrangement though very simple and apparently reasonable for working in electrophoresis gave rise to some problems which could 78. not be overcome. First was the heat generated by the passage of the current. This in some cases resulted in the charring of the paper. Another difficulty was the change in the distribution of the field around the spot, which affected the movement of the spot as a drop in field decreased the movement. Also in case of concentrated electrolytes, the current increased and the voltage dropped to very low values. In some cases, even the hydrodynamic flow of the electrolyte moved the spot. So the use of this apparatus was abandoned. A more sophisticated commercial equipment, a 10 kilowatt electrophoresis unit supplied by Miles Hivolt Ltd., England, was then used by the courtesy of the Biochemistry Department. This had a voltage range of up to 10 kv and a current range of up to 500 mA. Paper is under air pressure from both sides. Cold water is circulated at 3 a rate of about 8,000 cm per minute through the bottom and the top plates touching the paper. This keeps the temperature of the paper low even during the passage of high current, thus avoiding evaporation of the spot. Movement of the spot by the flow of electrolyte is stopped by (a) placing the drop in the middle of the paper and (b) by not dipping the paper directly into the electrode compartments. Instead separate papers are dipped in the electrolyte and the paper containing the spot touches these papers. These papers thus form a sort of wick. Electrolytic products in the electrode compartments are kept away by means of a little partition in the compartments which keep the paper wick and the electrode separated from each other. Despite all these advantages, this equipment, unfortunately, could not be used with radioactive solutions, because the laboratory where it was placed was not licensed for the use of long-lived hard beta or gamma emitters. Thus only inactive solutions were studied. This necessitated the use 79. of concentrated solfttions. The disadvantage of using high concentration solutions will be discussed subsequently. 2.2.6. ION EXCHANGE ADSORPTIONS & ELUTIONS Adsorption was studied by the batch method. A small weighed 3 quantity (usually 0. 2g) was equilibrated with 20 cm of the solution containing appropriate amounts of ruthenium, acid and nitrate ion. The weight ratio of the solid and aqueous phase was always about 1:100. This high ratio ensures that there is no appreciable volume change and the overall concentration decrease is not too high to change the nature 3 of the species present. The mixtures were taken in 50 cm stoppered conical flask and shaken mechanically for a predetermined time to reach equilibrium. The elution of adsorbed ruthenium was, however, studied in small columns. These columns were prepared by introducing sintered discs (of porosity 1) at the bottom of a small glass column (1 cm o.d). The results of adsorption are expressed as moles of ruthenium adsorbed per kilogram of resin. The results of elution have, however, been expressed in terms of the percentage of the activity eluted. In the adsorption studies variation in nitrate or hydrogen ion concentration at a constant concentration of one or the other, was achieved by adding perchloric acid or sodium nitrate, as the case may be. 2.2.7. PAPER CHROMATOGRAPHY Gelman model No. 51325-1 apparatus was used for paper chromatography. Whattman No. 1 strips (N, 2.5 cm wide and 13 cm long) were cut and marked every 0.5 cm. These strips were then 80. left in an atmosphere of the vapours of 3 methyl isopropyl ketone for about 2-3 hours. When applying the drop, the paper strips were not taken out of the box, but instead the cover plate lifted a little and the drop immediately applied. More of the eluting solvent was then poured in the box and the solvent allowed to run up. When the solvent front reached mark no. 18, the strip was taken out and immediately dried under an infra red lamp. The strips were then cut and counted as described earlier. 81. 2.3. RESULTS 2.3.1. PROPERTIES OF THE RESINS In the present studies ion-exchange resins were not only used for studying the adsorption and elution behaviour of ruthenium and zirconium but they were also used to characterize the type of complexes present in the solution under investigation. A study of the properties of these resins was, therefore, essential. Exchange capacity and the swelling weight are two of the most important properties. In the studies in which the charges of complex ions are measured by the method of Grinberg et. al. (1961), the volume of fully swollen resin per gram of dry resin is also required. The exchange capacity is a measure of the available exchange sites on the resin. This is commonly expressed as milli-equivalents per gram of dry resin (meq/g). The number of actual sites exchanged in a given reaction can, however, be different from the actual exchange capacity. The number of exchangeable sites is influenced by several factors e.g. the solution concentration, the exchange kinetics, temperature and even the pH of the medium. This latter factor important particularly in the case of weak base resins where a certain pH value must be attained before all the exchange sited can be fully ionized. The swelling of resins in different solvents is common. The present studies refer to swelling in aqueous solutions only. The volume 3 of fully swollen resin has been expressed in m per kg of resin and is the volume occupied by one kilogram of swollen resin measured in cubic metres. The swelling weight is defined as the number of grams of water absorbed per gram of dry resin. Some workers have also 82. used the term "Specific Swelling Weight" and have expressed it in terms of number of grams of water absorbed by that amount of the resin whose exchange capacity is one miliequivalent. The numerical values for some of the characteristic properties of the resins (i. e. Ionac - XAX and Zeokarb - 225) are given in Tables 1 and 2. 2.3.1.1. Ultraviolet Absorption Spectra of Resin Washings In some experiments on the determination of charge of ruthenium species, the absorption spectra of a solution of RuIV treated with the cation exchanger Zeokarb - 225 (8% crosslinked) showed an absorption peak at 228 nm. This peak could not be related to any of the expected ruthenium species. It was suspected that something was being washed out from the resin itself. This led to the following study. 3 A sample of Zeokarb - 225 was shaken with 0.10 mol dm perchloric acid. This perchloric acid on scanning also showed an absorption peak at 228 nm. The above solution when tested with a solution of barium chloride gave a white preciptate. This showed that probably some sulphate ions were present. When the precipitate was filtered and the solution scanned again, the absorption peak still persisted. Another fresh batch of Zeokarb - 225 (8%) was taken in a -3 column and dilute perchloric acid ( <0.1 mol dm ) was passed through the column continuously for 10 hours. It was then divided -3 into two parts. One part was shaken with 1.0 mol dm perchloric acid. This solution when scanned showed some absorbance at 228 nm.. The second part of the sample was used for capacity 83. TABLE 1. Properties of the Anion Exchange Resin Ionac - XAX Property Resin XAX-I283 XAX-I284 XAX-1285 Weak Base Capacity (rneq/g) 5.3 4.5 4.3 Percentage cross-linking (D.V.B. content, To) 5 10 15 Swelling Weight (gH2O/g resin) 1. 50 0.72 0.52 Specific Swelling Weight (gH20/meq resin) 0.283 0.160 0. 121 Particle size (standard screen, U.S.) -20-t50 -40+-70 -40+70 Radius in cm 0.045-0.015 0.021-0.01 0.021-0.01 pK values* 5.4 5. 6 5. 0 * Ref. Coady, (1969) 84. TABLE 2 Properties of the Cation Exchange Zeokarb-225 Property Percentage Cross-linking 20 8 4 Mesh size 14-52 14-52 14-52 Capacities (meq/g) (a) Nat Form 4.605 (b) 1-1+ Form 4.95 5.13 5.232 Swollen Volume (cm3/g) 1.28 2.75 Swelling Weight (g1-120/g resin) 0.582 2.092 Specific Swelling Weight • 0.113 0.399 85. determination. Only a very small change in capacity (1. 7%) was observed. The aqueous solutions of the following were scanned to see if any of these had an absorption peak at 228 nm. (I) Sulphuric acid -3 (2) Sodium Sulphate in 0: 10 mol dm perchloric acid (3) Ammonium persulphate (4) Benzene sulphonic acid (5) Toluene sulphonic acid (6) Sodium metabisulphate. It was found that none of the above solutions had an absorption peak at 228 nm. In fact all solutions (except I & 2) have their absorption peaks at wave lengths greater than 240 nm. Sodium sulphate shows some absorbance in the region of 200-250 nm. Two samples of the same resin but of different batch were put through three cycles of adsorption and elution and shaken with -3 1 mol dm perchloric acid. The resulting liquid gave no precipitate with barium chloride but showed strong absorption at 228-30 nm. From the above results it appears that perchloric acid elutes material from the resin which has absorption maximum at 228 nm, and that allowance for this must be made in any future work involving spectrophotometry of resin treated solutions. Secondly as the material does not correspond to any of the above substances which could have been the degradation products of the resin, it can be safely assumed that the perchloric acid is not breaking up either the functional groups or the matrix of the resin. 86. 2.3.2. RUTHENIUM TETROXIDE Ruthenium tetroxide was an intermediate compound in our preparations of ruthenium IV from commercial "ruthenium trichloride", and the following observations were made on it. In water the tetroxide gave a yellow coloured solution with absorption maxima at 308-12 and 385 nm. In about 12 hours the tetroxide was partially reduced to black ruthenium dioxide (RuO2.H20) which could be separated by centrifugation. The formation of this black precipitate was sometimes preceded by the formation of a dirty-green coloured solution. The tetroxide was more stable in perchloric acid (compared to its solution in water, nitric and hydrochloric acids). The spectrum in -3 1. 0 mol dm perchloric acid is shown in Figure 6. The peaks were stable for 15-20 hours and then started decreasing in intensity until after about 95 hours the peaks disappeared and a black precipitate was formed. -4 -3 -3 The spectrum of a 1.5 x 10 mol dm solution of Ru04 in 0.3 mol dm nitric acid is shown in Figure 7. Comparing Figures 6 and 7 the spectra • are similar at the start but the solutions are less stable in nitric acid and marked change takes place in the peak at 310 nm even in one hour. In about twenty hours, the peak at 385 levelled off and the solution acquired a black colour. In hydrochloric acid, the tetroxide is immediately reduced with the formation of chloro complexes (and not Ru02° 0 as in the case H2 of nitric and perchloric acids). In dilute acid the reduction and complex- ing is slow. In IM acid, a peak at 310 nm was detected but this started decreasing in less than 15 minutes with the production of a peak at 226 nm. In stronger acid (6M) the reduction was almost immediate. • 1 I I 200 300 400 500 (nm) CO Figure -6 UV Spectrum of Ru04 in 1M HC1O4 0.50 0 I I 1 i 200 300 400 500 600 A (nal) Figure -7 UV Spectrum of Ru04 in 0.3 mol dm-3 HNO3 : Effect of Aging -3 (Ru04 = 1:5 x 10-4 mol dm ) 89. The changes that take place on ageing are essentially the changes in the degree of complexing (Figure 8). Solution B was 10 times stronger than Solution A. This concentration difference was necessary because the absorption in the region 300-600 nm was comparatively smaller than the absorption in the region 200-300 nm. As seen from Figure 8, absorption maxima are observed at 233 and 450 nm in a solution 15 minutes old. On aging the solution for 24 hours, the first absorption maximum vanishes altogether while the second shifts to a higher wave length (i. e. 485 nm). 2.3.3. RUTHENIUM IV STUDIES 2.3.3.1. Characterization of Ruthenium IV solutions The method of preparation of ruthenium IV (both with and without a Ru-106 tracer) has been described in the experimental section (Section 2.2.2.2). Hydrogen peroxide was the only reducing agent used in all the preparations for ruthenium and the conditions of the reaction were kept constant in all the preparations. Ruthenium IV -3 solutions in 1.0 mol dm perchloric acid were used up to a time limit of 3 months. While preparing a solution, the rate of mixing of the reagents, and the temperature of the solution were kept constant. Previous workers (e. g. Cady (1957), Wehner (1950) ) reported ruthenium solutions of intermediate valency states of (3. 5), (4. 2) and (4. 2), (4. 5) respectively. Solutions prepared by the reduction of ruthenium tetroxide with hydrogen peroxide had therefore to be characterized before using them. As stated above, similar solutions were obtained by keeping the reaction conditions the same each time. Absorbance 0.0 0.70 200 Figure -8 UV Spectrum ofRu0 (Solution Bwas 10times strongerthan Solution A) 300 4 A(nm.) in6moldm. 400 -3 HC1:Effect ofAging 500 • 600 91. However, in some preparations different values were obtained and these preparations were discarded. Again, within a set of experiments, the same sample was used. In the following, the properties of a typical sample of ruthenium IV are given. In all other samples used, the values were within ± 50/0 of these values . • 2.3.3.1.1. u. V. Spectrum of Ruthenium IV The ultraviolet absorption spectrum of a ruthenium IV sample -3 in 1.0 mol dm . perchloric acid is shown in Figure 9. Also shown is the spectrum obtained by Wehner et. al (1950). Our values are slightly lower than those of Wehner in the region 250-350 nrn. Values of molar absorption coefficient are given in Appendix 4. 2.3.3.1.2. Reduction of Ruthenium IV Previous \vorkerp,(Cro\vell et. al. (1928) and Wehner et. al. (1950) ) established that iodide ion in perchloric acid reduced ruthenium IV to ruthenium III. This reduction of ruthenium IV to ruthenium III was us ed as a further test (i. e .. in addition to U V spectrum measurements) to establish the complete reduction of Ru0 to RuIV in our samples~ The 4 procedure was as follows: 3 0.5 - 2.0 cm -3 of ruthenium solution (containing,....; 3 x 10- 3 mol dm -3 ruthenium) were taken in 40-50 cm of O. 80 mol dm -3 perchlori acid. 0.5 g of sodium chloride and 0.5 - O. 6 g of potassium iodide \vere then added. Nitrogen gas \vas passed over the n1.ixture while the reaction was allowed to proceed for 15-20 minutes. The liberated iodine was titrated against 0.01 mol dm -3 sodinrn thiosulphate. The re ac tion Molar Absorption Coefficient x Figure -9 UV Spectrum ofRutheniumIV in1MHC10 Present Work ; (nm) ------• Wehner et.al.(1950) 4 s 93. with thiosulphate was also carried in an atmosphere of nitrogen. Amounts of ruthenium taken and iodine liberated (calculated from sodium thiosulphate titration) are given below: Ru(IV) + I > Ru( III) -I. i 12 I +25 0 -> 3 4. S 40 3 2 3 6 Ruthenium Taken Iodine Liberated (Micromoles) (Micromoles) B/A A 27.46 13.26 0.482 13.73 6.65 0.484 13.73 6.72 0.490 MEAN = 0.485 According to reaction (I), 0.50 moles of iodine would be liberated per mole of ruthenium IV reduced to ruthenium III. The small difference of 3% from theoretical values actually varied in the range of ± 3% in different preparations. In most cases the values were less (by r•-,3%) than the theoretical values. Reactions involving iodine are quite sensitive to the presence of oxygen. Two sources of error (Vogel, p. 343) are: (a) loss of iodine due to its volatility, and (b) production of iodine from acid solutions of the iodide by autoxidation. + 41 -I-- 0 + 4H ----> 21 4- 2H 0 2 2 2 These errors can be minimized by the methods discussed in a previous section (2.2.3.2). However, it is reasonable to allow for a 3% experimental error. 94. 2.3.3.1 3. Presence of Chloride Ion in Ruthenium IV Solutions Most of the stock solutions of ruthenium IV were stored in 1.0 mol dm-3 perchloric acid. Occasional checks of the presence of chloride ions were made to make sure that the perchlorate ion was not reduced to the chloride ion. The presence of chloride ion was tested as follows: An aliquote of ruthenium IV solution was taken and shaken with silver peroxide. This oxidized the ruthenium to the tetroxide which was removed by heating the solution. To the rest of the solution, a solution of silver nitrate was added. Absence of a white precipitate or turbidity showed the absence of chloride ion. Neidrach et. al. (1951), used a similar method for chloride ion detection. He used persulphate ion (in presence of silver ion) to oxidize ruthenium in order to avoid interference from ruthenium IV which forms stable complexes with chloride ions. 2.3.3.1.4. Solutions of Ruthenium IV in Nitric Acid In some cases ruthenium tetroxide was dissolved in dilute nitric acid and then reduced to ruthenium IV. The absence of nitrosyl complexes was assured in each case by measuring the molar absorption coefficient . The molar absorption coefficient of ruthenium IV is much higher than that of the nitrosyl ruthenium and hence the presence of the latter would decrease its overall value. But if the values obtained are consistent with the values for ruthenium IV then the absence of nitrosyl ruthenium is almost certain. These solutions were prepared..to see if there was any difference between these and the solutions which were prepared by the addition of nitric acid to the perchloric acid solutions of ruthenium IV. It was 95. found that all the solutions showed similar behaviour. 2.3.3.2. Effect of the Addition of Nitrate Ion to Ruthenium IV Solutions The change in the nature and the behaviour of quadrivalent ruthenium present in non complexing perchloric acid was studied as a function of nitrate ion. A number of techniques were tried to establish if any complex formation took place. The techniques used and the results obtained are given in the following pages. 2.3.3.2.1. Ultra Violet Spectra of Solutions After making allowance for the absorption of the nitrate ion itself, the ultra violet spectra of solutions containing varying amounts of ruthenium IV and nitrate ion were recorded with a view to finding any changes. The spectra of solutions of ruthenium IV remained unchanged with the addition of nitrate ions (Figure 10). In the case of higher nitrate ion concentration it was not possible to study the spectrum below 330 nm. The effect of nitrate ion at different acidities was the -3 same. The effect of ageing on solutions of low (0.05 mol dm ) and -3 high (3 mol dm ) nitrate ion concentration is shown in Figure 11. Spectra were in fact unchanged even after 10-15 days. The above results (Figures 10 & 11) refer to solutions prepared from ruthenium IV in perchloric acid by the addition of nitric acid or sodium nitrate (as required for the composition of the sample). The spectra of those solutions which were obtained by dissolving vacuum dried nitrate solutions of ruthenium IV were more or less the same as obtained in the above solutions except that slightly higher values of Absorbance 0.5 0.0 Figure -10 300 Constant Hydrogen Concentration of1.0moldm UV SpectrumofRuIV-Nitrate:Effect ofNitrateIonConcentrationat Nitrate IonConcentration (moldm 400 0.01; --- 0.10; 0.25 (nm) 500 -3 ) : -3 (Ru= 600 9. 68 x10 -5 moldm 3 700 ) 0.5 -5 0.4 Ruthenium = 9,68x10 mol dm. EH+] = 1.0 mol dm-3 0.3 ,o 0. 2_, o tn .-6•• • di ...• .... •• ...... 00 300 400 500 600 700 (nrn.) Figure -11 UV Spectrum of RuIV-Nitrate : Effect of Aging of the Solution NO3 Time After Preparation 0. 05M 4 Hours 0,05M 604 Hours 3M 4 Hours 3M 120 Hours 98. I absorbance were obtained at 480-90 nm (the absorption maximum). The spectrum of one such solution is shown in Figure 12. The effect of acidity on the molar absorption coefficient was also studied. In the first type of solution (involving no vacuum drying) the effect of acidity in the region 250-300 nrn is shown in Figure 13, and that at 480 - 90 nm in the following table. -4 Ru = 4. 5 x 10 mol dm-3 A = 485 nm Acidity E x 10-5 1) 1MHNO 728 3 3MHNO 756. 6 3 6MHNO 776 3 The effect of acidity in case of solutions of vacuum dried samples is clear from Figure 12. Here too, the effect was more marked below 350 nm. This increase was much less marked in those solutions where the acidity was changed immediately before scanning. One reason for this could be that very strong perchloric acid "drives off" some nitrate ions from the complex. But practically this would have only a small contribution as the total concentration of the ruthenium (and hence the nitrate ion associated with it) is small. 2. 3. 3. 2.2. Polymerization of Ruthenium IV: Spectrophotornetric Evidenc The changes in spectra of nitrate solutions were followed only up -3 to a fortnight. The spectra in perchloric acid (1. 0 mol dm ) were, however, followed for longer periods of time. The over all effect of storage for long periods was that higher values of molar absorption coefficient were observed. Thus the following values were recorded. • 4 3 CO 0 250 300 350 400 450 500 550 600 2i(wm) Figure -12 Absorption Spectrum of RuIV-nitrate = Effect of Perchloric Acid Acid, mol dm-3 :----- = 0.1; = 1.0; = 5.0; ...... 9 0 Abs orbance Figure -13UVSpectrumofRuIV-Nitrate :EffectofI--I Nitrate IonConcentration of0.1moldm Acid Concentration (mol dm. 0.1 ; --- 3.0; -3 (nrn.) ) : ..—..._..— 5.0; -3 . (Ru=2.2665x10 I. Ion ConcentrationatConstant -4 7.5 moldm -3 ) 101. Age of RuIV solution E x 10-5 ( = 485) max (m2 mol-1) Fresh 728 6 months 780 18 months 794 The solutions were centrifuged before scanning. There were no oxide particles present in any case. 2. 3. 3. 2. 3. Infra-Red Spectrum -3 A nitric acid (7. 5 mol dm ) solution of ruthenium IV was vacuum dried. The solid obtained is highly hygroscopic. The KBr pallet ( 1% by weight) was therefore prepared in a dry-box. The infra red spectrum of this solid, as a 250 mg KBr disc was recorded (Figure 14). The various peaks will be discussed later; the most prominent being -1 _1 at: 3420 cm 1, 1870 cm , 1625 cm , 1385 cm andand a double peak -I at 1080 and 1020 cm-1. Some weak peaks are at 2425 cm , 2170 cm , 1265 and 460 cm-l . 2.3.3.3. Electrophoresis The ultra violet spectra of ruthenium IV solutions did not show any noticeable changes on changing the nitrate ion concentration. There was some evidence from older literature of some complexing of the ruthenium IV by the nitrate ion though it was thought to be weak. It was thought, that if nitrate complexing did take place a whole series of complexes with different charges would be present. The presence of these different charged ions could be shown by their movement under the influence of an electric field. This led to the use of electrophoresis on the nitric • 100_ 80 ion t 60 rp Abso t 40 Percen 20 1 '200 1)00 1000 1400 1800 2200 2600 3000 3400 3800 Wave Number (Cm 1) Figure -14 1R Spectrum of RuIV Nitrate 103. acid solutions of ruthenium IV. As discussed in Section 2.2, the arrangements available in our own laboratories were not very efficient. On the other hand, though a much more reliable and efficient equipment was available in the Biochemistry Department, it could not be used with radio-active solutions as the laboratories were not licensed for this type of radio-activity. Therefore inactive solutions of relatively higher ruthenium concentration were used and the movement of the spot examined visually. The spots were too dim to be photographed. How- ever, a graphic representation of the same is shown on the following page. The high concentration regions show where the concentration of the actual spot seemed maximum. The rest of the colouration 3 2 -3 was tailing of the spot. 0.02 cm of a 1.01 x 10 mol dm ruthenium solution were applied as a spot. The electrolyte was a 0.1 mol dm-3 nitric acid. Four samples, with nitric acid concentrations of 0.5, 2.0, 4. 9 -3 and 9.0 mol dm were used. These have been marked I, 2, 3 and 4 respectively. As is clear from the figure, both samples 1 and 2 moved through the same maximum distance under the influence of 1000 and 1500 volts. In the first case (voltage = 1000), both showed only one concen- tration maximum. However in the second case (voltage = 1500), sample 2 showed two concentration maxima. (It must be pointed out that although in the diagram all concentration maxima seem to have the same intensity it was not the case in actual practice. As the total amount of ruthenium in each spot was the same, the more a spot moved, the less intense it became. Similarly if the spot divided into two parts, its intensity decreased accordingly). It was thus possible to show that 1011 . Anode Cathode 2 3 4 5 6 7 Electrophoresis of RuIV-Nitrate 1 : Original position of the spot 2 : Sample 1 v = 1000 time = 30 min. 3 : Sample 2 v = 1000 time = 30 min. 4 : Sample 1 v = 1500 time = 30 min. 5 : Sample 2 v = 1500 time = 30 min. 6 : Sample 3 v = 1000 time = 30 min. 7 : Sample 4 v = 1000 time = 30 min. v = voltage applied 105. in sample 2 at least two of the complexes showed different movement. The spreading of the spot can either be due to tailing or due to the presence of complexes of intermediate charges. Wet paper also resulted in a diffused spot. Under the same voltage of 1000 volts, the movement of sample 3 was very small but definitely towards the cathode. With sample 4 the movement was mostly negligible. In one run a movement towards the anode was observed (with sample 4) but the movement was small and in other experiments no movement was observed. Thus in general the movement of the spot decreased with increase in the nitric acid concentration of the spot. 2.3.3.4. Ion-Exchange Studies Both cation and anion exchanger were used to study the adsorption and elution characteristics of ruthenium IV nitrate and to examine if any charged complexes were formed. Electrophoresis studies reported in the preceding section showed qualitatively that complexes of varying charges were present. Cation exchanger, Zeokarb - 225 was used to determine the charge of the cationic complexes. Information on the charge of ions is of interest in connection with the study of the behaviour of ruthenium in nuclear fuel reprocessing using anion-exchange resins. 2.3.3.4.1. Adsorption of Ruthenium IV by Zeokarb-225 The adsorption of ruthenium on a cation exchanger is not of much direct interest as far as the study of the removal of fission product ruthenium by an anion-exchanger is concerned. However, use of a cation exchanger for the determination of charge of speCies at various 106. nitric acid concentrations was intended. Along with this the comparative behaviour of the cation exchanger was also of interest. This led to the following study of the behaviour of ruthenium on Zeokarb - 225 under similar conditions as the study with the anion-exchange resin Ionac XAX 1284. The adsorption is influenced both by the nitric acid and the ruthenium concentration. At low acidity, when the cationic complexes dominate there is obviously more adsorption. Lower ruthenium concentration also helps in greater removal of ruthenium by the resin (Table 3). The effect of acidity is given in Table 4. Keeping in mind the results of Table 3 (i. e. higher adsorption at lower concentration) a -3 qualitative correlation is seen. In going from 7.0 to 0.30 mol dm nitric acid the adsorption increased by a factor of more than 20. The effect of changing both acidity and nitrate ion concentration is given in Table 5. It is clear that lower concentrations of both nitrate and hydrogen ion give higher adosprtion. When the nitrate ion concen- tration was kept constant and that of the hydrogen ion concentration r changed, the adsorption showed a decrease with increase in LH j. + -3 Thus at a H ion concentration of 0. I mol dm , the adsorption -2 -1 -3 -1 was 1.068 x 10 mol kg while it fell to 2.057 x 10 mol kg at + . -3 H ion concentration of 7.0 mol dm . At the same hydrogen ion con- -3 -2 -1 centration of 0.10 mol dm , the adsorption was 1.068 x 10 mol kg -3 -2 -1 -3 at 7.0 mol dm nitrate and 1.148 x 10 mol kg at 6.0 mol dm nitrate On the other hand, when the nitrate ion concentration was kept constant -3 at a low value of 0.1 mol dm , the adsorption increased with decrease in -2 -1 H ion concentration. Thus an adsorption of 1.425 x 10 mol kg was -2 -1 obtained in 6. 0 mol dm-3 H+ ion while a value of 5.683 x 10 mol kg 107. Table 3 Adsorption of Ru by Zeokarb-225 : Effect of Solution Concentration EH1 E\1037.1 3 lu] 3 Amount Adscirbed (mol dm-3 ) (mol dm ) (mol dm ) (mol Kg ) 4 -2 0.50 0.30 7.023x10 5.5886x10 4 2 0.50 0.30 4.689x10 5.7586x10 -4 -3 7.0 7.0 4.04x10 2.057x10 -4 -3 7.0 7.0 2.02x10 3.783x10 Table 4 Adsorption of Ru IV by Zeokarb-225 : Effect of Nitric Acid Concentration Ulu] [ HNO3J Amount Adsorbed (mol dm ) mol dm-3 mol Kg -4 -3 4.04x10 7.0 2.057x10 -4 -3 4.04x10 6.0 5.35x10 4 -3 8.08x10 3.54 8.55x10 -4 -2 7x10 0.30 5.315x10 108. Table 5 Adsorption of Ru by Zeokarb - 225: Effect of Change of Both Nitrate and Hydrogen ion Concentration -4 -3 Ruthenium Concentration = 4.04 x 10 mol dm 4- ENO Ruthenium Adsorbed [E1 1-3 3 ] -3 mol dm mol din mol kg-1 -2 0.1 7.0 1.068 x 10 -2 0.1 7.0 1.051 x 10 -3 1.0 7.0 6.686 x 10 -3 3.0 7.0 6.156 x 10 -3 7.0 7.0 2.057 x 10 -2 0.1 6.0 1.148x 10 -3 0.12 6.02 9.600 x 10 -2 6.0 0.10 1.425 x 10 -2 0.50 0.10 5.683 x 10 2 * 1.0 0.10 5.573 x 10 -4 -3 * Solution Concentration .7- 7.023 x 10 mol dm 109 + -3 was obtained at an H concentration of 0.5 mol dm . 2.3.3.4.2 Use of Ion-Exchange Resin for the Determination of Charge Charges of ionic species in solution have been measured by means of ion-exchange resins (e.g. Cady, 1958; Paramonova, 1960 and Grinberg, 1961. The last two methods could not be used because of the difficulty in separating the ruthenium species into cationic, anionic and neutral fractions (as needed in Paramonova method) and also due to the errors involved in measuring distribution coefficients at very low liquid phase concentrations (as in the Grinberg method). These low concentrations are necessary to keep the activity coefficient change to a minimum. The method of Cady and Connick (1958) though not devoid of all flaws looked more promising and was tried. 2.3.3.4.2.1 Cady's Method (1958) In this method, concentrations instead of activities are used for the general ion-exchange reaction: n+ + n+ + M + nH M + nH (1) Quantities with bars indicate the resin phase concentrations. From equation (1), the equilibrium quotient becomes: (Mn+) (H+)n Q (2) (Mn+) (H+)n 110 To solve this equation, results of two equilibrations are needed. The conditions for these two results are so chosen that mole fraction of ruthenium and hydrogen in the resin phase are kept nearly the same in two experiments. n+ The fraction of M in resin phase is much smaller than + that of H . Equation (2) then becomes: (H+) n1 (Mn+) (H+)n2 (3) (H+) (mn+)2 (H+)n2 where 1 and 2 refer to two experiments performed at + different H ion concentration of the solution phase. The quantities in equation 3 can either be determined or calculated e.g. n+ 1. M in g atoms = measured -3 2. H + in mol dm = capacity (equivalents/kg) - n(Mn+) 3. M in g atoms/kg = Amount of Ru taken - Amount left in solution x 1000 weight of resin 4. (e) final in mol dm-3 = (H+) initial + n(Mn+) W V where V is volume of solution in contact with W g of resin. These values are substituted in equation (3) and the value of n is found by successive approximation (see appendix 5). In the above approach the effects of activity coefficients are minimized but not eliminated. Change in the degree of hydrolysis in both phases is expected not to change the value of n. Consider'the reaction: n+ M + (n - x)H+ + xH (n x)-1- + 2O > M (OH) x nH 111 (M(OH)x(n - x)+) (H+)n = (mn+) (H+) (n x) (H20)x As long as (H+) is constant the form of equation does not change and n is still the charge of species M. Other important things that must remain unchanged are the degree of complexing and the degree of polymerization. The concentrations of hydrogen ion, and ruthenium were kept the same in all experiments and the concentration of nitrate ion was only changed in the two sets of experiments. However, as the concentrations in the resin phase can be different from the aqueous phase, some more work is needed before it can be assured that both these factors remained constant in our determinations. The results should therefore, be taken with this effect in mind'. Charge/Atom The above method gives the charge per species. Charge per atom can also be determined by making use of the fixed ion exchange capacity of the resin. If we adsorb ruthenium cations (x atoms) on say, Zeokarb-225 + which contains some H ions as well and then elute both ruthenium and hydrogen with y moles of a divalent cation M2+ then charge per atom of ruthenium would be: 2y + z x where z is the moles of hydrogen. This method is not sensitive to hydrolysis but is 112 sensitive to changes in polymerization and degree of complexing. 2.3.3.4.2.2 Application of the Method to Ions of Known Charge The above methods (of charge/species and charge/ atom) were applied to ions of copper and chromium. The results are shown in tables 6 - 8. 2.3.3.4.2.3 Application of Method to Ruthenium Species It was not possible to separate the individual ruthenium species present and the method consequently had to be applied to solutions containing presumably more than one type of specie. The results are shown in tables 9 - 11. 113 Table 6 Charge per Chromium/Copper Atom in Chromic and Cu2ric Salts Solution Concentration Charge/Atom -3 moles dm Initial Final Cr Cu Cr Cu Cr Cu -4 -5 1 5.854 x 10 NIL 5.028 x 10 8.166 x 10_ 3.051 1.965 -4 -5 2 5.854 x 10 NIL 4.842 x 10 8.20 x 10_ 3.054 1.964 1 Weight of cupric form resin = 1.3413 g 2 Weight of cupric form resin = 1.4362 g Table 7: Charge Per Chromic Ion n+ Expt. No. Total Cr n+ Initial H+ Volume of Resin taken Capacity of Cr Cr 11+ Cr x g atoms (H.+) solution Resin g • atoms g atoms V initial nj 3 V per litre per 1000g for mol dm Cm3 g meq (H )final -5 2 3 Cr-1-1 7.76x10 0.495 25.0 2.2472 11.573 2.029x10 3.4292x10 3.082x10 -5 -5 z -3 Cr-1-2 7.76x10 0.949 50.0 2.8209 14.527 10.004x10 2.537x10 1.431x10 n = 2.9 Table 8: Charge Per Cupric Ion ,n+ n+ Resin taken Capacity of Cu n+ Cu .r14- Cu W Expt. No. Total Cu Initial H Volume - n g atoms (H )initial V W Resin taken g atoms g• atoms for %. V 11.) mol dm-3 Cm3 grams meq per litre per 1000 gm (H )final -4 -3 -5 2.067 7.9x10 0.1086 2.17906x10 -Cu-1-1 5.94x10 0.48 20.0 0.4013 1.86 -5 Cu-1-2 6.24x10 0.95 30.0 0.3205 1.651 1.45x10-3 0.05897 6.3x10-4 -4 -3 -5 0.1192 1.94236x10 , Cu-2-1 5.767x10 0.48 20.0 0.3259 1.678 9.4x10 2.10 -3 -4 Cu-2-2 5.767x10-5 0.95 30.0 0.3608 1.858 1.38x10 0.04509 5.4228x10 -5 -4 -3 0.48 20.0 0.4013 2.067 8.9x10 0.09885 1.98342x10 Cu-3-1 5.767x10 1.96 Cu-3-2 5.767x10-5 0.95 30.0 0.3205 1.651 1.45x10-3 0.04421 7.2x10-4 MEAN = 1.973 • • Table 9: Charge per Ruthenium Ion -3 Nitrate Ion Concentration = 0. 10 mol dm + Expt. No. Total Ru n+ Initial H Volume of Resin taken Capacity of (Ru 1.1. at (Ru 11, (Ru nbt. g. atoms W the Resin equilibrium gm atoms (14 )initial solution VT (R.u.n r 3 V g meqs. g atoms per 1000 g mol dm 3 Cm per litre -5 5 2 4 Ru-1-1 1. 4046x10 1. 0 20. 0 0. 2481 1. 278 1. 0989x10 5. 573x10 6. 913x10 3.0 -5 6 2 4 Ru-1-2 1.4046x10 0. 50 30. 0 0. 2464 1. 269 1. 373x10 5. 683x10 4. 668x10 -5 5 2 -4 Ru-2-1 1.4046x10 1. 0 20. 0 O. 2472 1. 273 1. 0439x10 5. 597x10 6.918x10 2 -5 -5 z 4 Ru-2-2 1.4046x10 0.50 30. 0 O. 2494 1. 284 1.359x10 5. 615x10 4. 668x10 MEAN = 2. 9 Table 10: Charge per Ruthenium Ion -3 Nitrate Ion Concentration = 0.30 mol dm Expt. No. Total Ru n't Initial H1L Volume of Resin taken Capacity of (Ru at (Ru n+. (Ru. n solution the Resin equilibrium g atoms g atoms (H ) initial _3 V g meqs g atoms per 1000 mol dm-3 Cm-3 Cm per litre a S -5 5 Ru-3-1 1.4046x10 1.0 20.0 0.2431 1.252 Z. 3008x10 2 4 5.5886x10 6.793x10 1.3 -5 -6 4 Ru-3-2 1.4046x10 0.50 30.0 0.2391 1.231 9.24x10 5.7586x10 4.5896x10 -5 -5 2 4 Ru-4-1 1.4046x10 1.0 20.0 0.2450 1.262 2.747x10 5.5039x10 6. 748x10 1.37 -5 -2 -4 Ru-4-2 1.4046x10-5 0.50 30.0 0.2570 1.323 1.0302x10 5.3451x10 4.579x10 Mean n = 1.365 118 Table 11 Charge Per Atom of Ruthenium Amount of Resin Capacity Ruthenium rH ] Charge per Resin taken (for hydrogen) Adsorbed Eluted Atom g moles moles moles 3 5 0.5388 2.7748x10 3.9553x10 -3 2.668x10 2.70 3 5 3 0.4962 2.5554x10 3.9557x10 2.45x10 2.66 Mean = 2.68 2.3.3.4.3. Adsorption of Ruthenium IV by Ionac XAX-1284: Effect of Shaking Time 3 3 20 cm samples were shaken in 50 cm pyrex glass bottles by means of a mechanical shaker. Each flask was shaken for a definite time and the amount of ruthenium adsorbed was determined from the change in the concentration of the solution in contact with the resin. The results are given in Table 12. A minimum shaking time of two hours was needed to reach -3 equilibrium in 7.0 mol dm nitric acid and at ruthenium concentration -4 -3 of 4.04 x 10 mol dm. . With other concentrations of acid and ruthenium the time to reach equilibrium was more or less the same. No samples were shaken for less than four hours and in some cases duplicate samples were shaken for up to 24 hours. 119 Table 12 Adsorption of Ruthenium IV by Ionac XAX-1284: Effect of Shaking Time -3 Nitric Acid Concentration = 7.0 mol dm -3 -3 Ruthenium Concentration = 4.04 x 10 mol dm 3 Volume of Solution = 20.0 cm Amount of Shaking Time Ruthenium Resin (Hours) (g) Remaining in Adsorbed by solution Resin (mol dm- 3) (mol/ kg) -4 -4 0.5018 0.50 4.035x10 2.265x10 -4 0.5005 1.0 3.875x104 7.319x10 4 0.5012 2.0 3.461x10 2.321x103 -4 -3 0.5012 4.0 3.461x10 2.321x10 -4 0.5012 8.0 3.442x10 2.397x103 0.5020 24.0 3.452x104 2.354x103 -4 0.5013 30.0 3.412x10 2.515x103 -4 -3 0.5014 52.0 3.452x10 2.357x10 120 3.3.4.3.1. Adsorption of Ruthenium by Ionac XAX-1284: Effect of Ruthenium. and Nitric Acid Concentration The adsorption of ruthenium as a function of nitric acid and ruthenium concentration was studied. The effect of ruthenium con- -3 centration was studied at an acid concentration of 7.5 mol dm . On -4 -3 the other hand, a ruthenium concentration of 4.04 x 10 mol dm. was selected for studying the variation of adsorption with change in acidity. The effect of concentration of ruthenium is shown in Figure 15. It -4 -3 is seen that after a concentration of,""3.0 x 10 mol dm is reached, the effect of concentration is negligible. There is a very sharp increase in adsorption on changing the concentration of dilute -4 -3 ruthenium solutions (Ru <3.0x10 mol dm ). In most of the results quoted, the ruthenium concentration was in the region of -4 -3 3-5x10 mol dm . The variations of adsorption as the nitric acid concentration was changed is given in Table 13. A maximum is obtained at about 3. 5 mol -3 dm nitric acid. At lower acid concentrations adsorption is small and gradually increases to this maximum. Further increase in the -3 acid concentration beyond 3.5 mol dm decreases the adsorption. -3 The change in adsorption beyond 7.0 mol dm nitric acid seems to level off i. e. further increase in acidity does not change the adsorption. The adsorption of ruthenium as reported above gave rise to two possibilities. Firstly that anionic species were formed and taken up by the anion exchanger. Secondly that no real ion exchange took place but rather some sort of physical adsorption was involved. To test these two hypotheses the following experiments were carried out. 2.5 — O X 2.0 — bA O 1. 5 — Zi o.) 1.0 z O 0.5 (14 0 1 2 3 4 5 6 7 -3 4 Solution Phase Concentration (mol dm x10 ) Figure -15 -3 Adsorption of RuIV by Ionac XAX-1284 : Effect of Ru Concentration in 7.5 mol drn HNO 3 122 Table 13 Adsorption of Ruthenium IV by Ion.ac XAX-1284: Effect of Nitric Acid Concentration -4 -3 Ruthenium Concentration in Solution = 4.04x10 mol dm Nitric Acid Ruthenium/Kg Resin (mol dm-3) (moles) -3 0.60 2.64 x 10 2 2.00 1.42x 10 -2 3.54 1.81 x 10 -3 6.0 9.36 x 10 -3 7.0 2.374 x 10 -3 7.5 2.50 x 10 Polystyrene beads (8% DVB) were pretreated in the same way as the resin and then equilibrated with a ruthenium solution of the following concentration. -4 -3 Ruthenium = 4.04 x 10 mol dm -3 Nitric Acid = 3.5 mol dm 3 Volume of solution taken = 20 cm Ig of polystyrene beads failed to remove any ruthenium from this solution on shaking for 24 hours, suggesting that physical adsorption was not responsible for the removal of ruthenium by ionac XAX-1284. 123 The above experiment was repeated several times and the adsorption found in no case supported the belief that true ion exchange was taking place. However, the possibility of adsorption due to complex formation with the function groups of the resin cannot be ruled out at this stage. This will be discussed later. If ionic species are involved their formation would be expected to depend upon the nitrate and the hydrogen ion concentration of the solution. In a simple system the higher nitrate ion concentration should give higher concentration of anionic species. Hydrogen ion concentration should have a less marked effect at moderate concentrations (very low acid concentrations would hydrolyse the ruthenium present to a very high degree). At very low nitrate ion concentration (Table 13), the adsorption was small. To see whether the hydrogen ion concentration would make any significant change, adsorption from solutions of varying concentrations was studied. In most of these experiments the ruthenium concentration -4 -3 was 4.04 x 10 mol dm . The results obtained are shown in Table 14 It is seen that at low acid and high nitrate concentrations, the adsorption of ruthenium is very high. On the other hand if the acidity is increased, the adsorption is low. Thus as shown in Figure 16, there is a rapid decrease in adsorption as hydrogen ion concentration is increased. High acidity and low nitrate ion concentration does not improve the adsorption at all. Thus at a H • NO3 ratio of ' -2 0. 1 : 6. 0, the adsorption was 1.5 x 10 moles/kg of resin but on reversing the ratio i. e. 6. 0 : 0. 1, the adsorption decreased by a 124 Table 14 Adsorption of Ruthenium IV by Ionac XAX-1284: Effect of Nitrate and Hydrogen Ion Concentration -4 -3 Ruthenium Concentration = 4.043 x 10 mol dm -3 Volume of Solution Taken = 20.0 cm No. [H1 1\TIO. - ] Ruthenium Adsorbed 3 1 (moles kg ) (mol dm-3) (mol dm- ) -2 1. 0. 10 6. 0 1.500 x 10 -2 2. 0.12 6.02 1.478 x 10 -2 3. 0.10 7.0 1.197 x 10 -3 4. 1.0 7.0 9.487 x 10 -3 5. 3.0 7.0 7.220 x 10 6. 3.5 0.10 Nil -4 7. 6.0 0.10 7.743 x 10 -4 factor of f•-*' 20 (i. e. to 7.74 x 10 moles). This adsorption of -4 7.74 x 10 moles/kg actually corresponded to an adsorption of only 4. 8%. The effect of acidity is apparently that of protonation of the anions formed. 2.3.3.4.4. Elution of Adsorbed Ruthenium by Nitric Acid Having studied the adsorption of ruthenium by Ionac XAX-1284 under different conditions it was of interest to find out how much of the adsorbed ruthenium would come out on washing with nitric acid. Two -3 acid concentrations of interest were 7.5 and 0.60 rnol dm because 125 1.20—! (sic, O 741 1. 0 0 (1) 0 0.80 N 0.60 1:4 0.40 0.20 0 1 1 1 1 1 0 1 2 3 4 5 6 7 [In mol dm-3 Figure -16 Adsorption of RuIV by Ionac XAX-1284 : Effect of H ion Concentration at a Constant [NO 1= 3 -3 7.0 mol dm 126 these were the concentrations expected to be used in the actual fuel cycle for the adsorption and elution of plutonium. The following procedure was adopted. 106 Two solutions of Ru(IV) were aged for about a week in -3 106 7.50 mol dm nitric acid. (For the preparation of Ru(IV) see experimental section). Weighed quantities of Ionac XAX-1284 were then added and the solution shaken for 24 hours. After this time, the resin was taken in two small columns, and immediately washed with small portions of cooled ( (,)5°C) de-ionized water, until the washings 3 were free of any radio activity. (This was tested by counting c lcm of washings in a well-type sodium iodide scintillation crystal. When activity of the washings dropped to the background level, the washings 3 were taken to be free of activity). About 50 cm of water were sufficient to wash out any unexchanged activity. The resin samples were then taken on a filter paper and freed from the adhering water. They were then taken in counting tubes, 3 0.5 cm of water added, and the samples were then counted in the well scintillation crystal. This was taken as the activity of ruthenium present on the resin. One of the resin samples was then eluted with -3 -3 0. 60 mol dm nitric acid and the other with 7.50 mol dm nitric acid. 3 A slow flow rate of 0.25 - 0.30 cm /minute was maintained. 10. 0 cm3 3 samples of the eluate were collected. 1.0 cm of these samples was counted and the total activity present in the sample counted. After 3 passing 100 cm of the eluting solution, the resin was again taken on a 3 filterpaper and then counted in a tube along with 0.50 cm of water. The difference of the two resin countings was taken as the amount of activity removed by washing with a particular concentration of nitric acid. 127 The results of the elutions are shown `in Figure 17. (Duplicate results were taken and average values have been quoted). It is seen that -3 7.5 mol dm nitric acid removed about 23 per cent of the activity -3 while 0. 60 mol dm removed only about 5 per cent of the activity. It shows that most of the ruthenium that goes to the resin, tends to stick -3 to it. From the shape of the curves, it appears that 0. 6 mol dm nitric acid could not remove the total activity because the curve is -3 levelling off. There is less levelling off in case of the 7.5 mol dm nitric acid. However, even here the complete removal of activity 3 from 0.200 g of resin would require at least 500 cm of acid on the basis of the most optimistic extrapolations. This, in process terms, would be an enormous volume. 2. 3. 3. 5. Solvent Extraction, Thin Layer and Paper Chromatography As reported in the previous sections, the cation exchange resin showed quantitatively the presence of cationic complexes of ruthenium in the nitric acid media. The uptake of ruthenium from nitrate solutions by an anion exchanger showed the presence of anionic complexes. Having established the presence of these complexes, it was of interest to know their solvent extraction and chromatographic behaviour which could then be compared with the behaviour of the more established nitrosyl nitrates. The nitrosyl nitrates can be separated from each other by paper and thin layer chromatography. Both diluted (with n-hexane) and undiluted tri-n-butyl phosphate was used for the extraction of ruthenium nitrates from solutions in nitric acid and also from the solid obtained by vacuum drying. In no case did the ruthenium pass into the organic layer. 128 24 20 d e ov 16 Rem ity iv t 12 Ac e tag n 8 Perce 4 20 40 60 80 100 120 3 Volume of Acid Passed, Cm Figure -17 Elution of Adsorbed Ru by Nitric Acid -3 -3 0 7. 5 mol dm HNO -; 7: 0. 6 mol dm HNO 3 3 3 -1 Flow Rate = 0.25 - 0.30 Cm min 129 Similarly carbon tetrachloride also failed to extract any ruthenium nitrate. The following solvents were tried in attempts to separate the nitrates of ruthenium on a thin layer of alumina and silica. I. Isobutyl methyl ketone 2. Ethyl methyl ketone 3. Digol (Diethylene glycol) 4. Xylene 5. 1:1 mixture of ethyl methyl ketone and digol. It was observed that the spot did not move in.any case except with solvents 2 and 5 where a small movement was noted. An R value F of 0.1 - 0.2 can be quoted. However, all attempts to improve the movement or the separation of the spot into more than one parts failed. The overall movement was so small that no detection of any separation was possible. In the paper chromatography of nitrosyl nitrates of ruthenium methylisopropyl ketone has been widely used. The same solvent was used for the nitrates of ruthenium IV. The spots stayed at the starting line in all cases in accord with the previous work of Fletcher et. al. (1955, 1960, 1965). 2. 3. 3. 6. Effect of Heating and Irradation The presence of nitrate complexes of ruthenium IV in any significant quantities in a dissolver solution is ruled out by the presence of quantities of nitrous acid in the system. Even if these complexes are formed in small quantities in the dissolver solution and in the subsequent reducing treatments (e.g. the use of ferrous 130 sulpharn.ate), they will be subjected to irradiation from the fission products as well as from uranium and plutonium and also to heat if higher temperatures are used for the extraction. It was therefore interesting to see their behaviour under these two conditions i. e. heat and irradiation. -3 Ruthenium IV solutions, both in nitric acid (7. 5 mol dm ) -3 and perchloric acid (1. 0 mol dm ) were boiled. Both acids oxidize ruthenium IV to ruthenium VIII. Boiling for less than an hour in perchloric acid oxidized the ruthenium but it took more than two 4 hours to completely oxidize a solution containing 5.4x10 moles of -3 ruthenium and 7.5 mol dm nitric acid. -3 The effect of irradiation of a ruthenium IV sample in 7.5 mol dm -4 -3 nitric acid was very interesting. 25cm3 of a 8.08x10 mol dm -3 ruthenium IV in 7.5 mol dm nitric acid were irradiated in the Co-60 irradiation facility for 184 hours to a total dose of about 4 6x10 kJ/kg. The colour of the solution which was reddish-brown in the beginning turned yellowish (like that of the nitrosyl nitrates). A strong smell of oxides of nitrogen was also found, however, no attempt was made to analyse the gases evolved. The absorption spectra of the irradiated solution was measured and compared with that of ruthenium IV and ruthenium nitrosyl nitrate. In the following table, values of molar absorption coefficient of the three are given. After irradiation, the solution was left for two weeks before scanning. 131 Table 15 Comparison of Molar Absorption Coefficient of Unirradiated and Irradiated Solutions 2 -1 Solution Molar Absorption Coefficient (m mol ) 350 nm 400 nm 450 nm 485 nm 500 nm 8 7 7 7 7 RuIV 1.205x10 7.04x10 6.77x10 7.28x10 7.04x10 7 6 6 6 RuIV Irradiated 2.13x10 9.9x10 8.66x10 9.33x10 6 8.53x10 Solution cin 7. 5 mol drn nitric acid) 7 6 6 6 6 Ru-nitrosyl 1.57x10 9.33x10 8.50x10 9.20x10 8.33x10 nitrate The results suggest that solutions of RuIV in nitric acid, on irradiation form the nitrosylnitrate of ruthenium. The small difference in the values of E may be due to the presence of minute quantities of ruthenium IV. 2.3.4. NITROSYL RUTHENIUM NITRATES The preparation of these nitrates has been discussed in the experimental (Section 2.2.2. 3). A solution of nitrosyl ruthenium -3 nitrate was aged in 7.5 mol dm nitric acid for a fortnight. The -3 solution was diluted to 0.3 mol dm nitric acid and immediately -4 -3 scanned. (A ruthenium concentration of 3. Ox10 mol dm was used for the wave length region 270-300 nm and a higher 'concentration of 132 -3 -3 1.2 x 10 mol dm for the region 300-650 nm). The spectrum is shown in Figure 18. The values of molar absorption coefficient are given in Appendix 6. These values agreed very well. with the published data available in the region 330 - 600 nm. -3 A portion of the nitrosyl nitrate solution in 7.5 mol dm nitric acid was vacuum dried as in the case of simple nitrates. An IR spectrum of this solid was obtained using the KBr disc technique. It exhiluted about 25 well defined absorption bands as listed below. The spectrum is shown in Figure 19. -1 IR Bands of Nitrosyl Ruthenium Nitrate (cm ) 3625 (W), C3460 (S), 2760 (W), 2425 (m-s) 2090 (W). 1885 (V.S), 1765 (m), 1695 (m-.$) 1675 (m-s), 1625 (sh), 1532 (W), C1380 (V.S) 1325 (sh), 1300 (W), 1120 (V.W), 1090 (V. W) 1048 (V. W), 985 (V.W), 840 (m-s), 825 (m) 798 (W), 572 (W), 533(V. W), 465 (W), 390 (V. W) where s = strong, m = medium, W = Weak, V = Very, sh = shoulder. These bands will be discussed later. Having established the identity of the nitrosyl nitrates, two sets of experiments were performed. In the first, the adsorption and elution of ruthenium on an anion exchange resin was studied. In the second, paper chromatography of both aged and resin treated solutions was studied. An account of these studies is given in the following pages. • • 3.0 r-i 0 O 2. 0 C.) • .-4 U 0 U ta.4 0 rn 0 1 . 0 Cd 0 300 400 500 600 (nrn) Figure -18 UV Spectrum of Nitrosyl Ruthenium Nitrate in 7.5 M HNO 3 -3 (Solution diluted to 0.3 mol dm acid and scanned immediately) • 100 80 n io t 60 -- orp Abs t n 40 ce r Pe 20 I I I I I I i 200 600 1000 1400 1800 2200 2600 3000 3400 3800 4000 Wave Number (Cm-1) Figure -19 1R Spectrum of Nitrosyl Ruthenium Nitrates 135 2.3.4.1. Anion Exchange Behaviour of Nitrosyl-Ruthenium Nitrates 2.3.4.1.1. Adsorption All solutions used were aged for at least 2 weeks before use. 106 106 3 Ru - Rh was used as a tracer. 11.0 cm samples were prepared and aged along with the tracer in appropriate nitric acid concentration. 3 1.0 cm of each sample were taken and counted in a well type crystal 3 scintillation counter. The remaining 10.0 cm of solution were equilibrated with an accurately weighed quantity of resin (Ionac XAX-1284). 3 After the equilibration, 1.0 cm samples were again counted under similar conditions. The decrease in activity of the solution was taken as the amount adsorbed by the resin. The results of adsorption are shown in Figure 20. It is seen that as the concentration of nitric acid is increased, there is an increase -3 in the amount adsorbed, until a maximum is reached at about 5 mol dm. nitric acid. Further increase in the acidity causes a drop in the amount adsorbed. The rise in adsorption is more sharp than the fall in adsorption. It was of interest to see whether the adsorbed ruthenium was being taken up by an anion exchange process or if it was some sort of physical adsorption on the resin and the glass walls of the flask. The possibility of adsorption of some sort of colloidal ruthenium would be much higher in the case of low acid solutions. Two acid concentrations, namely, -3 3 0.5 and 1.0 mol dm were chosen. 10 cm samples of nitrosyl ruthenium -5 nitrate (Ru. = 1.35x10 moles) were equilibrated with polystyrene beads (8% DVB and -1452 mesh size). It was found that even after 54 hours of shaking, the activity of the solution was unaltered. 0.2045 g and 0.2052 g of resin were used for the two samples respectively (same as 136 0 2.0 4.0 6 . 0 8.0 1 0 .0 -3 Nitric Acid, mol dm Figure -20 Adsorption of RuNO-Nitrate by Ionac XAX-1284: Effect of Nitric Acid Concentration 137 the amount of resin in other samples). It was experimentally determined that in these adsorption studies an equilibrium was reached with the resins in about 2-3 hours. In most of the experiments, the samples were shaken overnight and a much longer time of equilibration was thus given. 2.3.4.1.2. Elution of Adsorbed Nitrosyl Ruthenium Nitrates A resin sample was equilibrated with a nitrosyl ruthenium -5 nitrate solution in 7.50 mol dm. nitric acid. The resin was left in the ruthenium solution for 3 days after shaking for 24 hours. The resin sample was then taken in a small column and washed with cold o water (r45 C) till the washings, when counted, showed the absence of any activity. Rest of the procedure was the same as described for the elution of simple nitrates (Section 2. 3. 3.4.4). -3 The resin was then eluted with 7.50 mol dm nitric acid at 3 3 a flow rate of 0.3-0.4 cm per minute. 100 cm of solution were thus passed. Samples were collected and counted. Afterwards the resin was also counted. A total of 18.3 % of activity was removed by this washing. The results are shown in Figure 21. About 81% of 3 the removable activity was removed by the first 40 cm of nitric acid. 3 After that the curve starts levelling off. Thus the first 40 cm removed about 15% of total activity and the next 60 cm3 removed only 3. 3% activity. From the levelling off of the curve it is obvious that it is not -3 possible to remove whole of the adsorbed ruthenium with 7.5 mol dm nitric acid. The above resin was then taken in a small column, and washed witl -3 0. 6 mol dm nitric acid. Trial runs had shown that the elution was Percent Activity Removed 10 15 25 20 30 5 Figure-21 (Hollow pointsrefer totheelutionofthosesamples Elution ofAdsorbedNitrosylRuthenium Nitrates where Ru wasallowedtoage ontheresin) 0) 0=Elutionwith 7.5M HNO J A 40 Volume ofAcidPassed;Cm Elution with0.60M HNO 60 80 100 3 3 3 120 138 139 3 very slow, so a slower flow rate of r-1 0. 1 cm per minute was used. These results are also shown in Figure 21. A very small amount is -3 removed with 0. 6 mol dm nitric acid. In the above sample, the adsorbed ruthenium was left on the resin for quite a long time before washing. It was of interest to see the behaviour of adsorbed ruthenium which had not been allowed to age on the resin. Two samples of ruthenium were aged as usual -3 (in 7.5 mol dm nitric acid) and contacted with the resin for a short time of half an hour. These were immediately washed with cold water. One sample was then eluted with 7.5 and the other with ' -3 3 0. 6 mol dm nitric acid. The flow rate used was 0.3 cm /min. in both cases. The results are shown in Figure 21 (curves III & IV). It is seen that comparatively greater proportions of ruthenium could be removed by immediate washing and that aging on the column resulted in higher levels of more permanently fixed ruthenium. The flow rate is quite important. Slower flow rates (1. e. larger time of contact) would remove more of ruthenium. In one experiment 46. 5% 3 of adsorbed ruthenium activity was removed with 100 cm of -3 3 7.5 mol dm nitric acid at a flow rate of 0. I cm /minute. However • in no case was it possible to remove all the activity from the resin. 2.3.4.2. Paper Chromatography of Nitrosyl Ruthenium Nitrates Methyl isopropyl ketone was used as an eluting agent. The ketone was equilibrated with nitric acid before using. RF, values were determined. Solutions were aged and then paper chromatograms were run. In those cases where anion exchange resin was used for adsorption studies, shorter times of equilibration (1- hour) were given. Resin was shaken with the sample for half an hour, and immediately an aliquote of the sample solution was taken on the paper strip. Short contact was necessary because otherwise the solution species reached their equilibrium again. Half an hour is reasonably short time to prevent ruthenium species to reach equilibrium. The complexes present are divided into 4 groups depending upon the RF, value. Figure 22 shows the percentages of these four groups of complexes with respect to different nitric acid concentrations. Group A predominates in low acid concentrations and decreases rapidly as the concentration of acid is increased. Groups B and C increase up -3 to the acid concentration of 4 mol dm and then remain almost constant. This is only roughly true because at higher acid concentrations, i. e. > 6 mol dm-3, there is a decrease in the percentage of B and C as well. Group D, which is the highest nitrato complex or a group of complexes, however shows a gradual increase with the increase in acid concentration. Figures 23-26 show the curves obtained in the paper 3 chromatography of solutions in 0.5, 1.0, 3.0 and 7.5 mol drn nitric acid respectively. Figures 24-26 also show the effect of the resin, on the proportion of different species present in solution. It is seen that generally the amount of species with high RF value (>0.5) decreased on contact with the resin while that of the species with lower R Fvalues, increased. These results are summarized in Table 16. 100 80 60 C 40 1111) 20 0 1 . 0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 Nitric Acid (mol dm-3) Figure -22 Relative Amounts of Different RuNO -Nitrate Complexes in HNO3 A = Rf value 0. 12; B = Rf value 0.12-0.50; C = R f value 0.5-0. 9; D= R value 0. 9-1. 0 f 44 36 28 r1 20 $.1 X4 Scale 0 0.25 0.50 0.75 1•.00 R f Value Figure -23 Chromatogram of RuNO-Nitrate Complexes at Equilibrium in 0. 5M HNO3 40 36 — 30 r i I 26 '1. 12 i I i 0 0.25 0.50 0.75 1.00 R Value f Figure -24 Chromatogram of RuNO-Nitrate Complexes at Equilibrium in 1M HNO3 Effect of Removal by Anion-Exchanger Ionac XAX-1284 0 = Before Treatment with Resin; (....:: = After Treatment with Resin 26 24 20 16 ium hen t 0 Ru t 12 n Perce 8 4 at Oa, c)- -1 0 0.25 0.50 0.75 1.00 R Value f Figure -25 Chromatogram of RuNO-Nitrate Complexes at Equilibrium in 3M HNO3 : Effect of Removal by Anion-Exchanger Ionac XAX-1284. 0 = Before Treatment with Resin; :''. = After Treatment with Resin Per cent Ruthenium 42 44 30 34 38 — Figure -26 0 I Chromatogram ofRuNO-Nitrate ComplexesatEquilibrium in7.5M HNO Effect ofRemoval byAnion-Exchanger Ionac XAX-1284. 0 = Before Treatment with Resin; 0.25 I R f Value 0.50 I (1 = After Treatment with Resin...... • 0.75 I 1.00 1 3: tit -IN. 1-1 146 Table 16 Percentages of Different Nitrosyl- ruthenium-nitrates in Nitric Acid (From Methyl Isopropyl Ketone Elution) BEFORE EQUILIBRATION WITH THE RESIN R A F value > 0.12 0.12-0.50 0.50-0.90 0.90-1.00 HNO 3 -3 mol dm 0.50 83.04 7.03 7.31 2.61 1.0 71.60 9.50 12.50 6.30 3.0 47.75 19.99 22.91 9.48 7.50 13.49 17.90 23.86 44.70 AFTER EQUILIBRATION WITH THE RESIN 1.0 73.23 10.72 11.47 4.58 3.0 51.78 29.54 14.00 4.70 7.50 19.40 23.67 23.86 32.88 147 2. 4. DISCUSSION The type of species most likely to be present in fuel solutions has been discussed previously (Section 2. 1). The present work was intended as a study for the use of an ion-exchange plant for the separation of ruthenium (and zirconium) from the fuel solutions. number of factors would influence the behaviour of ruthenium in such a plant. It is considered that the most important factors would be: (a) whether ruthenium is present as positive ions, negative ions or neutral molecules. The negative ions would be readily taken up by an anion-exchanger while the positive ions would tend to stay in the aqueous phase. Neutral molecules may also be taken up by simple physical adsorption. (b) A second important factor will be the charge of the ions. The higher the charge, the greater will be its adsorption. The anion- exchanger would normally show a higher selectivity for divalent ions over monovalent ions. (c) A third factor is the size of the ion or the molecule. Ruthenium may polymerize to form polymer aggregates containing more than one ruthenium atom, It may also complex with NO, NO3 and H2O. Larger • molecules will find it difficult to expand the resin matrix sufficient to allow penetration and may thus fail to adsorb. In solution the cations are generally affected by the presence of other anions and only slightly so by the other cations. Similarly anions are affected mostly by cations and not by anions. A lot is known about the species of nitrosyl ruthenium (Fletcher et. al. 1955 to 1965) but little if any work has been published on the behaviour of ruthenium IV. One reason for this has been the negligible amount of this valency state 148 present in fuel solutions. The present work was aimed at elucidating the following aspects of ruthenium IV behaviour: (a) Whether it would be present as cations or anions or both (plus of course the neutral molecules) (b) What will be the charge of these cations and anions, and (c) The extent of polymerization. Conversely as a lot of information was available on the species of nitrosyl ruthenium, its anion-exchange behaviour only was studied. Some investigation of the behaviour of ruthenium tetroxide was justifiable as it happened to be an intermediate in our preparations of ruthenium IV. The preparation of ruthenium IV has been considered in detail because of the extreme importance of the characterization of the starting material in ruthenium chemistry. 2.4.1. RUTHENIUM TETROXIDE The absorption spectrum in perchloric acid (Figure 6) was in reasonable agreement with. those reported in literature (Wehner et. al. 1950; Silverman et. al. 1950; and Connick et. al. 1952). In nitric acid (Figure 7) the tetroxide is stable only for a short time. Thus although in perchloric acid, the absorption peaks at 310 and 385 nm remained unchanged for 15-20 hours, they showed a decrease in intensity in about an hour in the case of nitric acid. After 20 hours the first absorption maximum at 310 nm remained (with decreased intensity) but that at 385 disappeared. The colour of the solution changed from yellow to brownish black and black particles could even be seen floating on the surface. The brownish colour could be due to the formation of some ruthenium IV while the black particles are that of the hydrated dioxide. 149 The reason for thinking that the reduction leads more to the formation of ruthenium IV and less to nitrosyl ruthenium (RuNO III) is apparent from Figure 7. It is seen that the absorption in the region 400-600 nm increased. Comparing with Figures 9 and 18 it is seen that in this region the absorption of nitrosyl ruthenium is less than that of Ru0 and that of ruthenium IV is higher than both. In 4 other words the production of nitrosylruthenium would have led to lower absorption values in this region. The nitrite ions produced by the reduction of nitric acid are unlikely to produce much RuNO because for this to happen a larger (double that of Ru) concentration of these ions would be needed (Martin and Giles, 1957). The tetroxide is not stable in hydrochloric acid. Except in case, of very dilute acid the characteristic peaks were absent within a few minutes of the preparation of the solution. In strong acid (6M) (Figure 8), a transitory absorption maximum at 233 nm was stable only for about 15 minutes. The absorption maximum observed at 450 nm changed to 487 nm on aging and can be explained in terms of 4+ chloro complexes based on IV and Ru respectively Ru202 (Woodhead and Fletcher, 1962). The absorption maximum at 233 nm is due to some intermediate although no attempt was made to identify this. Up to 24 hours no production of ruthenium III (e.g. [RuCl5H20]2-) was observed. (Its absence was shown by the absence of characteristic absorption maximum). The above brief study of ruthenium tetroxide thus showed: (a) Presence of pure Ru0 in HC1O in our preparations. 4 4 (b) Ru0 is stable in HNO for about an hour and then decomposes 4 3 to lower valency states with nitrosyl ruthenium (if at all 150 present) forming only some minor fraction (c) In HCI it decomposed to complexes previously reported but showed no sign of the formation of RuIII in 24 hours. 2. 4. 2. PREPARATION OF RUTHENIUM IV As we wanted to study the behaviour of ruthenium IV it was necessary to demonstrate clearly that our starting solutions contained ruthenium in this valency state only. Hydrogen peroxide was used as a reductant both in perchloric and nitric acid. Formation of ruthenium IV under these circumstances has been reported in literature (Anderson, • et. al. 1954; Fletcher et. al. 1954; Nikolaskii et. al. 1957; Martin et. al. 1957; and Avtokratova, 1969). The intermediate valency states ranging from 3. 5 to 4. 5 reported by Wehner (1950) and Cady (1957) were shown to be absent. The following properties of the solutions supported this belief. The spectrum (Figure 9) agreed reasonably with that reported by Wehner (1950). The small difference can be attributed to higher polymerization in case of Wehner's solutions as shown by Cady (1957). The spectrum was identical with those reported (Wehner, 1950; Brito, 1966) in the region above 400 nm thus showing the absence of valency state 4.2 and 3. 5 (which has a peak at 340-50 nm) (Cady, 1957). The reaction with potassium iodide further showed that inter- mediate and lower valency states were absent. If ruthenium III was present it would react with the perchlorate ion to give chloride ion. Thus + - 8 Ru 8H -41- C10 —> 8 Ru4.4-• + Cl 4H 2O 4 151 But in our preparation, the chloride ion was shown to be absent. The absence of any chloride ion also ensured the absence of any subsequent formation of chlorocomplexes. The nitric acid used was boiled and freed from any oxides of nitrogen. The above study thus showed that our starting solutions contained ruthenium only in the +4 valency state. • 152 2.4.3 Ruthenium IV in Nitrate Ion Media In nitric acid solutions of irradiated nuclear fuels ruthenium is mainly present as nitrosyl complexes (Brown, 1960). Ruthenium IV, however, can be produced under conditions where the nitrosyl group, NO, is removed. These conditions are introduced in order to achieve higher decontamination from ruthenium and also to promote the reduction of Pu IV. Thus Martin et. al. (1957) and Jenkin (1960) showed that ruthenium IV is produced on treatment of such solutions with either ferrous sulphamate or hydrazine. It was suggested that hydrazine brought about the following reaction (Jenkin, 1960). + Ru NO 4e + 6H Ru IV + NH4 + H20 3 Ru III RU IV Nitrato complexes The ruthenium III was not stable and further reacted with nitric acid to give 25% Ru NO and 75% Ru IV (Fletcher et. al. 1965). 3+ + 3+ 4+ 4 Ru + 4 H + N5'3 Ru NO + 3 Ru + 2 H2O This makes the study of the behaviour of ruthenium IV in nitrate ion media important in considering the use of ion-exchange for the removal of ruthenium from solutions containing plutonium. 153 2.4.3.1 Ion-Exchange Behaviour 2.4.3.1.1 Adsorption Both cation-exchanger Zeokarb-225 and anion-exchanger Ionac XAX-1284 were employed in studies of the adsorption of ruthenium IV from nitric acid solutions. At lower acidities the uptake by Zeokarb-225 was much higher than that by the Ionac XAX-1284 (a difference by a factor of about 15)(Tables 3, 4, 13 and 14). The removal by Zeokarb-225 is due to ion-exchange as well as to physical adsorption while that due to anion-exchanger is more probably an effect of physical adsorption. At low acidities when the concentration of ruthenium is increased, the removal by Zeokarb_225 is decreased (Table 3). Increase in ruthenium concentration is known to lead to higher degrees of polymerization and it is probable that the larger polymer aggregates so produced become incapable of penetrating the resin bead and thus cannot be adsorbed. Similar effects were observed in the case of zirconium (section 3.4) where it was found that more zirconium could be adsorbed either by keeping zirconium concentration low or by using cation-exchanger of lower crosslinking. Low cross-linked resin can allow the penetration of comparatively larger polymeric molecules. The effect of ruthenium concentration on removal by an anion-exchanger was studied at 7.5 mol dm-3 nitric acid. Increase in Ru concentration 154 -4 leads to higher removal up to a concentration of 2 x 10 -3 mol dm and then the removal remains constant over a wide range. Increase in nitric acid concentration at fixed ruthenium concentration decreased adsorption by the cation-exchange. Thus the value of Kd decreased from about -3 -3 100 at 0.3 mol dm to about 6 at 7 mol dm (Table 4). On the other hand the adsorption by the anion-exchanger increased with an increase in nitric acid till it reached -3 a maximum at 3.5 mol dm acid and then decreased again. The curve of adsorption against nitric acid concentration is similar to many such curves reported for other transition metals (Bunney et. al. 1959; Marinsky, 1969 p. 326). Adsorption by the anion-exchanger at low acidities is presumably of physical nature only because ruthenium has a great tendency to form polymers and even colloids at low acidities. At higher acidities, however, some other factors must also be involved. Thus although the adsorption by the anion-exchanger was maximum at -3 3.5 mol dm nitric acid, 10% crosslinked polystyrene beads failed to remove any ruthenium. This showed that the adsorption was more than a surface phenomenon and some sort of anionic species ( the nature of which will be discussed later) may be involved. The decrease in -3 adsorption beyond 3.5 mol dm acid is probably a combined 155 effect of the following factors. (a) The concentration of acid in the resin phase is higher than that in the solution phase (Chu et. al. 1959). This leads to a decrease in the ionization,of the exchange sites i.e. equilibrium shifts to the left. This decreases + -1. -1"-/-NH NO3 < > -.„NII + NO3 the number of available exchange sites. (b) Anionic species like H(NO3 )2 may be produced which would compete for the exchange sites. Marcus et. al. (1964) postulated the formation of this species in media of low dielectric constant. The dielectric constant of the resin phase is low and this species could thus be produced in this phase. By virtue of its formation in situ and low size it will have easy access to the exchange sites again decreasing their availability. In contrast to the behaviour of ruthenium in high -3 acid (>3.5 mol dm ) solutions where the removal decreases by increase in acidity, the removal from solutions of low acidity but of comparable nitrate strength increases with decrease in acidity. Thus when the nitrate ion -3 is kept constant at 7 mol dm , the removal decreased + with increase in H ion concentration (Figure 16). 156 In other words adsorption from salt solutions of comparable nitrate strength was higher than from acid solutions. A similar effect was observed in the adsorption of zirconium (section 3.4) and lanthanides (Marcus et. al. 1959) from nitrate media. This effect is discussed in detail in section 3.4. Briefly in salt solutions the contribution from factor (b) above is decreased. In addition to this, the formation of the ions of the following type (which is an extended case of ion-pair formation) (Glasstone, 1960, p. 969) takes place. + — [M - NO 3 - M ] and NO3 - M - NO3 Because of the high nitrate concentration the cation M is surrounded very closely by the nitrate ions and is taken up as an anion. 157 2.4.3.1.2 Elution of Ruthenium IV from Ionae XAX-1284 -3 7.5 and 0.6 mol dm nitric acid were used for desorption of ruthenium IV from the anion-exchanger. (The ruthenium was previously adsorbed from 7.5 mol dm-3 -3 acid.) Although 7.5 mol dm acid removed appreciably -3 more ruthenium than 0.6 mol dm acid, complete removal was difficult. Thus 100 cm3 of 7.5 mol dm-3 acid removed 3 23% of activity from 0.2 g resin while 0.6 mol dm removed only about 5% (Figure 17). The reason for this behaviour is not fully understood although the behaviour of desorption of nitrosyl ruthenium is similar (section 2.4.4). The following factors may be involved in this peculiar behaviour. (i) Mc Niven (1953) suggested that ruthenium might be present as a reduced form in the resin phase. (ii) As the resin was treated with water for the removal of interstitial ruthenium, increased hydrolysis may lead to (a) big polymeric aggregates which cannot penetrate outwards from inside the resin and (b) some hydrated oxide Ru02.xH2O which is insoluble and stays in the resin. (iii) Another possibility is the reaction of ruthenium with the pyridine ring present in the resin structure. Work of Saldadze et. al. (1969), however, shows that 158 the coordination properties of substituted 2-vinylpyridine (as Ionac XAX-1284) resins for transition metal ions are not only reduced by the change in the basicity of pyridine nucleus but also by the steric difficulties for the formation of these complexes. Furthermore in presence of acid, + the salt form of pyridine nitrogen NH does not form any coordination compounds as the N-H link is stronger than the N-metal link. However some contribution from such a process during treatment with water may be possible. Our observations have shown that ruthenium IV in nitrate solutions undergoes adsorption on both anionic and cationic resins but not on polystyrene beads. Further- more with increasing nitrate ion concentration there was a decrease in adsorption by the cation-exchanger whereas there was an increase in adsorption by the anion- exchanger. The most obvious explanation of these results is that both positively and negatively charged ruthenium species are formed under appropriate conditions of nitrate concentration and that the adsorptions are at least in part due to true ion-exchange. However this interpretation must be qualified as a result of the following points. (a) It is not possible to elute all the adsorbed ruthenium from the anion-exchanger i.e. the following reaction is not truely reversible. Resin-Nitrate + Ruthenium IV Resin-Ruthenium + Nitrate 159 This suggests that some of the processes taking place are not ion-exchange. However, the behaviour of nitrosyl ruthenium (where the nitrate complexes are certain) is also similar. (b) The interconversion of ruthenium IV to nitrosyl ruthenium on the resin may be a possibility although under comparable nitrate concentrations this was not observed in solution phase. (c) The presence of positively charged species was shown by electrophoresis. The movement of the spot (towards cathode) was dependent on the concentration of nitric acid: lower the acidity, higher the movement (section 2.3.3.3). (d) Work based on Cady's method of charge determination showed that positive cations were present. However, as the extent and changes in polymerization under the conditions of the experiment are not very certain, the results must be taken with caution. (e) The UV spectrophotometry did not show any changes in the spectra on changing the media from perchlorate to nitrate ion. The only changes observed were in the region 250 - 300 nm where a small increase in absorption was observed with increase in nitrate ion concentration (Figure 13). 160 (f) The infra-red spectrum (Figure 14) showed that most of the nitrate ion was present as ionic nitrate -1 and only a small absorption at 1265 cm showed the presence of a bound nitrate. In view of the above although the behaviour of ruthenium IV towards cation and anion exchange is well established the causes for the behaviour are less certain. Although ion-exchange and electrophoresis pointed to the possibility of complexing the spectrophotometric work did not support this idea of complexing of simple ruthenium IV. According to Fletcher (1958), ruthenium mostly exists as ERu - 0 - Ruri- The charge per atom found (Table 11) also supports this. It also explains the low _magnetic moments of ruthenium IV. The value expected for two unpaired 4d electrons in d2sp3 bonding is about 2.9 B.M while the value found was 0.9 B.M (Fletcher, 1958). The low value suggests the presence of more paired electrons than given by the 2 3 d sp . It has been suggested that the ruthenium occurs as a unit of two atoms with oxygen bridging and involves 3 3 d sp arrangement. In view of the tendency of ruthenium to form polymers, the presence of such a species over a wide range of acidities would not be surprising. As to whether this species would undergo complexing needs more experimental data to decide conclusively. 161 2.4. 3.7. Some Further Properties of the Nitrates of Ruthenium IV The solvent extraction and the effect of irradiation and temperature onthese nitrates was studied (Sections 2. 3. 3. 5 and 2. 3. 3. 6) with a view to understanding their process behaviour. The solvent extraction behaviour for a wide variety of solvents was as expected. None of the solvents extracted any nitrates. Previous workers (Nikolaskii, 1957; Fletcher et. al. 1955, 1960, 1965) have reported a similar behaviour. Methyl isopropyl ketone which has been widely used for the chromatographic separation of nitrosyl nitrate did not affect a spot of these nitrates in paper chromatography. Heating of ruthenium IV nitrates both in nitric and perchloric acid, oxidized them to ruthenium VIII. Use of nitric acid in the removal of ruthenium by heating and purging with air was discussed in Section 2.1.3.3. The effect of irradiation was interesting. The colour of the solution changed and the U. V. spectrum showed a marked change. The values of molar absorption coefficient decreased greatly and approached the values for nitrosyl nitrates. The colour of the solution also resembled that of the nitrosyl nitrates. The overall effect seems to be the conversion of the ruthenium IV - nitrate to the nitrosyl nitrate (or may be even nitrosyl nitrito - nitrate). The exact mechanism was not studied. Irradiation of nitric acid gives a number of products of which nitrite is most important (Kazanjian et. al. 1970). The production of gaseous NO is small from direct irradiation but it can be produced from the nitrous acid (Cotton & Wilkinson p. 349) produced during radiolysis 3HNO = HNO + H2O + ZNO 2 3 Hydrogen and the nitrite ion produced presurnablyreduce ruthenium IV to lower valency states which are stabilized by immediate complexing with the NO. I62 Ru IV i- N'O -) RullI -1- NO; Z III 0+ NO N02--~ Ru NO N0 Rll -I- + + 3 (oxygen is also produced by the radiolysis of HN0 with a G value 3 of r.../ 0.7). RutheniuIU III reacts \vith nitric acid to give ruthenium IV and nitrosyl • ru thenium. + RullI + H + NO; --7 RuNO III ... RuIV .+ H 2 0 This shows that any ruthenium IV nitrates produced in the proces s strealU will be liable to attack by both heat and irradiation. 2.4.4. NITROSYL RUTHENIUlvi NIT.RATES The nitrates of nitrosyl ruthenium were prepared by the method published by Fletcher and his co-\vorkers. As a further standardization of these solutions the U. V. spectrum was recorded, (Figure 18). The agreement of the molar adsorption coefficient values with those reported in literature (Fletcher et. al. 1960) showed that the samples prepared were the nitrato complexes. The infra red spectrum was recorded {for comparison \vith that of the ruthenium IV nitrates} also showed • the presence of complexes (Figure 19). The m.ajor peaks of the in:l'Ta red spectrunl can be assigned as follo\vs (Gatehouse et. al. 1957; Fletchel 1958; Scargill et. al. 1961; Cotton and Wilkinson, 1968 p.995; McAlister, 1967). -1 3460 em due to abs orbed water -1 1885, 1695 and 1675 cm due to N-O stretching -1 due to O-N0 1532 em 2 -1 1380 CITI. due to NO; ,NO~ 1 due to ON0 1300 crn- 2 163 ° -1 1048 cm due to ONO, NO3 985 cm-1 due to RuNO -1 840 cm due to NO 3 825 cm-1 due to NO2,NO3 ' - 1 798 cm due to ONO 2 572 due to RuNO (Ru-N stretching) 533 due to Ru-OH Thus the spectrum shows the presence of nitrosylruthenium, bound and ionic nitrates. As a whole series of complexes (cationic, neutral and anionic) will be present, the presence of the above groups are readily explained. 2.4.4.1. Anion-Exchange of the Nitrosyl Ruthenium Nitrates 2.4.4. I. 1. Adsorption The adsorption of a mixture of nitrosyl nitrates from nitric acid is shown in Figure 20. The experiment with polystyrene beads showed that the adsorption was not due to removal by surface adsorption but due to ionrexchange. However, there is one drawback in taking the ion-exchange of ruthenium as showing a true equilibrium reaction i.e. Ru(1\10)(NO3):- qR-NO3 (R) Ru(N0)(NO3)x q NO 3 The reason for this is that adsorbed ruthenium does not come out as easily as it goes into the resin phase. Some authors (Nikolaskii et. al. 1966) preferred the use of "apparent equilibrium" or "maximum adsorption" in describing the amount taken by the resin. Some of the reasons leading to the above irreversibility will be discussed a little later. 164 . Data available in literature (Kraak, 1959; Fletcher, 1960; Wallace, 1961) relates to adsorption on strong base anion-exchange resins. -3 Fletcher et. al. (1960) found an adsorption maximum at about 3 mol dm nitric acid on Deacidite FF. In our case with the weak base resin, -3 Ionac XAX-1284, the maximum adsorption occurred at 5 mol dm acid. The initial increase in adsorption is obviously due to the formation of higher nitrato complexes. The percentage of these anionic complexes (Group D) increases (Fig. 22) as the concentration of nitric acid is to increased. The cause of decrease in adsorption on going/still higher acid concentrations is more or less similar to the one discussed in Section 2.4.3. 6. 1. The mechanism of adsorption was not investigated in detail. Nikolaskii et. al. (19,66) showed that in dilute acid solutions the part played by diffusion processes (i. e. (a) diffusion of the ions in the outer solution and (b) the diffusion of the ions inside the resin grain) was small. The limiting process was thought to be the chemical reaction. However, in present studies with higher nitric acid concentrations of -3 1-10 mol dm (compared with pH of 1-11 used by the above authors) it cannot be agreed that diffusion processes did not play any part. The results of the elution studies showed that longer the resin was left loaded with ruthenium, the more difficult it became to elute it. This could be either due to the diffusion of the ions into the inner parts of the resin or some chemical reaction. Hydrolysis reactions (as envisaged by the above authors) are less likely due to the high acid and low water content of the resin. Some further nitration of the ruthenium species in the resin phase cannot be ruled out. Thus it seems more likely that in acid solutions the process is ion-exchange coupled with some chemical reactions which are probably the further 165 nitration of the species. As discussed earlier, the coordination properties of the resin under consideration were quite poor. 2.4. 4. 1. 2. Elution of Adsorbed Ruthenium The results are shown in Figure 21. In no case was it possible to remove all the ruthenium with nitric acid. The aged samples behaved differently from the fresh samples. As discussed above, both diffusion and the chemical reaction seem to play their part. As the removal is comparatively rapid initially and then falls off it seems probable that the ions that have penetrated far into the bead are difficult to remove. Another possible cause is that there exist two types of anionic species. One of these is removed by washing with HNO while the other is 3 difficult to remove. The decrease in the percentage of removable ruthenium on aging the ruthenium loaded resin, shows that this second form is produced more on the resin itself. If the monovalent and divalent anions are considered then it is probably the second species that is formed on the resin. In aqueous solution both monovalent and divalent (with the first as predominant) exist. In the resin phase and on aging, the monovalent species takes up another nitrate ion and forms the divalent ion. Thus 2- [Ru (NO)(NO3)41 + NO3 ---> Erk,u(NO)NO3)5] The increas e in. the size of the species inside the resin phase also adds to the difficulty of the removal simply because of the physical hindrances involved. Thus the difficulty experienced in the desorption of adsorbed ruthenium can be attributed partly due to the diffusion of the species inside the resin grain and partly due to further complexing inside the 166 'bead. The part, if any, played by complexing of ruthenium with nitrogen of the resin cannot be ruled out. Some further work is needed before the mechanism of adsorption and desorption can fully be understood. Similar difficulties of the removal of adsorbed ruthenium have been reported by others (Kraak, 1959; Schulz, 1971). 2.4.4.2. Paper Chromatography of the Nitrosyl Ruthenium Nitrates The assignment of groups (i. e. A, B, C and D) has been based on the R value (Figure 22). The changes noticed in the percentages F of various groups as the concentration of nitric acid is raised agree with those reported in literature (Fletcher et. al. , 1960; Wain et. al. 1960). The ion-exchange resin removed mostly the complexes of group D and some of group C (Figures 24-26 and Table 16). Group D contains the tetra and the penta nitrato complexes while the group C contains trinitrato complexes. Adsorption of a trinitrato complex may be by physical adsorption or its further nitration to the higher nitrato •, complexes in the resin phase. After treatment with the resin, the per- centage of groups C and D decreases while that of groups A and B increases. As the anion-exchanger does not adsorb groups A and B, their relative amount in the liquid phase increases. 167 CHAPTER - 3 ZIRCONIUM 168 3.1. GENERAL CHEMISTRY Natural zirconium is a mixture of five stable isotopes: Zr-90 (51.46%), Zr-91 (11.23%), Zr-92 (17.11%), Zr-94 (17.40%) and Zr-96 (2. 8%). Unstable, radioactive, isotopes of mass numbers 86, 87, 88, 89, 93 and 95 have been prepared. Its chemical behaviour is very similar to that of hafnium. Under the influence of the lanthanide contraction, the atomic radii (Hf = 1. 44A° and Zr = 1.45A°) and the ionic radii (Hf4+ 0. 75A & Zr-= 0. 74A) are virtually identical (Cotton & Wilkinson, 1968, p. 913) and hence the similarity in properties. 3.1.1 THE OXIDATION STATES The oxidation states of zirconium are +2, +3 and+4 and at least one compound of zerovalent zirconium, (Zr(dipyr)3) has been reported (Cotton and Wilkinson, p. 919). Oxidation states lower than 4 are unimportant but anhydrous ZrCl and ZrC1 2have been prepared by the 3 reduction of ZrC1 by Zr metal (Swaroop et. al. 1964) and ZrI by 4 3 the reduction of ZrI with aluminium (Watt et. al. 1961). These 4 compounds are unstable and have strong reducing properties in aqueous solutions. Zr(IV) on the other hand is an extremely stable state and has weaker oxidising powers than Ti(IV) and Ce(IV) (Blumenthal, 1968). Simple compounds of zirconium IV are few in number and include the halides and oxides. The halides show sublimation on heating (Elinson, 1969). The white crystalline refractory oxide, ZrO is known. 2 According to Cotton and Wilkinson (1968, p. 916) no true hydroxide, Zr(OH) exists, the precipitate obtained from aqueous zirconium salts 4 on addition of alkali being Zr0 0. On long standing, meta zirconic 22 169 -18 acid ZrO(OH) (dissociation constant = 1 x 10 , Elinson, 1969) is 2 formed. Zirconates may be obtained by heating oxides, hydroxides, nitrates, etc., of zirconium with similar compounds of other metals at 1000-2500°. 3.1.2. AQUEOUS SOLUTIONS OF ZIRCONIUM IV Zirconium compounds in aqueous solutions are characterised by their high degree of hydrolysis and a tendency to form various complex ions and polynuclear compounds. Depending on the composition of the solution, its age and the method of preparation, zirconium ions may be present as oxo, hydroxo and aquo ions. There has been some 2+ controversy as to the existence of the zirconyl ion, Zr0 . It was contended to be present in the zirconyl chloride (Chauvenet, 1920) and sulphate (Nabivanates, 1961). However, most of the earlier and recent workers (Britton, 1925; Clearfield, 1956; Muha, 1960; Singh, 1961; Khaitonov, 1968; and Beden, 1970) disagree with the pres'ence of any Zr = 0 bond. The controversial "zirconyl chloride" is shown to contain cyclic-4-n.uclear cation with diol bridges (Emeleus & Anderson, 1960; Woodhead & Fletcher, 1966). There is no evidence for Zr = 0 group in nitrate and oxalate compounds and the infra red bands at -1 850-900 cm close to the region characteristic of M = 0 groups are attributed to the Zr-O-Zr groups (Cotton & Wilkinson, p. 917). Simple halides and nitrates are hydrolysed in aqueous solutions -2 -3 and give acidic solutions (e. g. 5 x 10 mol dm zirconium chloride has a pH of 1, (Elinson, 1969) At acidities greater than 2 mol dm -3 unhydrolysed species exist (Connick & Reas, 1951; Larsen et. al. 1954 and Yogodin, 1970). The following table shows the effect of pH on the nature of species present in absence of cornplexing agents ri o pH Assumed principal forms of Zr in solution (Starik, 1960) 3+ ZT Zr(OH) (monomers) 3+ 2+ 0-1.0 Zr , Zr(OH) , Zr(OH) , (monomers) 3 f 1. 0-1. 5 Zr(OH) , Zr(OH)4 (Monomers) 1. 5-4. 0 Zr(OH)4 (monomer), [Zr(01-I):-x I polymers n and pseudo colloids 4. 0-12. 0 [Zr(OH)41 true colloids >12 Zirconates. Solovkin et. al. (1966) showed that in case of small quantities -3 of zirconium, H+ ion concentration as high as 4 mol dm was needed for complete supression of hydrolysis. A phenomenon accompanying the hydrolysis of zirconium in low acidity solutions is the polymerization. Trirners and tetramers have been shown to be present in dilute zirconium solutions (Zr concentration -4 -3 -3 of about 10 mol dm and acid concentrations of 1-2 mol dm ), (Connick & Reas, 1949; Zielen, 1954). Ultra centrifugation, dialysis and cryoscopy have been used for the determination of the degree of polymerization and structures like (Roy, 1968) : [ Zr n have been suggested. The polymerization decreases with an increase in the acidity. Thus for a zirconium nitrate solution (0. 1 - 0.25 viol dm 3) the polymeriaation factors of 20, 9. I, 7. 7 and 7.7 were reported for -3 acid concentrations of 0, 0.04, 0.7 and 1.0 mol dm respectively (Komarov, 1968). Elinson (1969, p. 24)15.as related the mechanism of polymer 171 formation to olation. In olated compounds, the metal atoms are linked through bridging OH groups. The process of formation of rolt compounds from hydroxo compounds is called olation and the conversion of 'ol' groups to bridging groups (with the loss of a proton) is known as oxolation. (Nation is often accompanied by oxolation or anion penetration or by both. Hydrolytic polymerization leads to the formation of colloids. Ayres (1947) reported that 0.'1 mol dm-3 zirconium nitrate in water did not show any ionic character and was fully colloidal. Partial colloidal nature of zirconium in HC1 and HNO have been reported by others as 3 well (Starik, 1957A; Solovkin, 1962). Zr can form pseudocolloids by adsorption on particles of contaminants present in solution (Starik, 1960A; Kyrs et. al. 1966). 3.1.3. COMPLEX FORMATION Due to its high charge, small radius and low ionization potential, Zr(IV) is a typical complex former. The tendency of inorganic ligands to form complexes with zirconium lies in the order: 0I-1>f>- PO3- > SO2- ,,- NO Cl C10 (Elinson, 1969, p.28). 4 3 . 4 Complex formation in solutions of mineral acids has been reported. Among the best known complexes of Zr(IV) are the halogen anions, [ZrX6 They hydrolyse less than the corresponding ZrX4, indicating the stability of the complex anion EZrX The 6 following table gives the stability constants of the complexes of zirconium with the three mineral acid ligands. 172 Acid Stability Constants References 4 Pa P 3 /6 HC1 1.2 0.29 0.1 Ryabchikov, 1964 and Parasilova, 1970 HNO 2.2 1.3 0.55 0.15 Solovkin, 1958 3 H SO 466 3.48 3.92 Solovkin, 1962 2 4 x 103 x 105 The sulphate complexes have the highest stability constants of the three. Contrary to its behaviour in HCI and zirconium for HNO3' neutral and anionic complexes even at very low sulphate ion concentrations -3 At sulphuric acid concentrations greater than 0.75 mol dm (Solovkin, 1962) only neutral and anionic species exist. In nitric acid, although complex formation is weaker than in sulphuric acid, both anionic and cationic complexes have been reported. -3 In 0.3 to 2 mol dm acid, only neutral and positively charged species predominate. At higher acid concentrations, species like Zr(NO3)5 and Zr(NO3)62 also exist (Starik, 1957A; El-Guebeily, 1965). At low acidities, the nitrate complexes are usually present as nitrato-hydroxo aqu ions. The species present in zirconium nitrate solutions can be as follows (Emelius & Anderson, 1960). '73 rOdnZy(OH) p ar. 8 + [Zr4(OH)8(H 0)1 6] 2 -I- 4+ 3t. 2-4- [Zr(H20)8 Jj4 ---:_ -- [Zr(OH)(H20)1—[Zr(OH)2(Hal --1-Zr(OH)3(H20);]__. lr 4 + [Zr(OH)NO3(I-120)3j2 pr(OH)21\103(H20)y] 1r .1- \IP [zr(NO3),(H20):-1-'-i- pr(OH)(NO3)2(H2 -t r(OH2)(NO3)2(H20)z Nit 2- [Zr(OH)2(NO3)41 Increasing Increasing 3.1.4. ION EXCHANGE STUDIES OF ZIRCONIUM As discussed earlier, zirconium forms both cationic and anionic complexes in solution. The ion exchange behaviour of these complexes can be a great help in studying their nature. Larsen et. al. (1954), using a cation exchanger, Amberlite IR-120, showed that at -3 4+ 1-2 mol dm hydrogen ion, zirconium existed as unhydrolysed, Zr species in the aqueous phase. Strelow et. al. (1965) studied the adsorption and elution behaviour of Zr and a number of other elements using cation exchanger Bio-Rad Ag 50W-X8. The behaviour of the anionic complexes formed by zirconium in mineral acid was also reported (Bunney, et. al. 1959). Thes results confirm the presence of negatively charged complexes in these '74 media. The nature of complexes in solution can be changed by changing the nature of the complexing agents present. Adsorptions from mixed acid e.g. H2SO4-HF (Danielson, 1968), HNO3 and organic acids (Dobrushina et. al. 1970), have been studied. Some organic acids e.g. formic acid (Qureshi, 1968) and malonic acid (Khopkar, 1969) also form anionic complexes and can be used for the separation of zirconium (by an anion exchanger) from other elements. The separation of zirconium from non radio-active elements is of interest to the analytical chemist while the separation from fission products concerns the chemist working with the nuclear fuel reprocessing. Most of the work cited above (along with that of Korkisch, 1969 and Kazantsev, 1970) relates to the separations from inactive elements. Methods, based on ion exchange have been developed fc the iDaration of Zr-95 and Nb-.95 from different complexing media; e. g. from 1-1F (Leaf, 1959; Archundia, 1968); from HC1-HF (Hardy, 1964); from HC1 (Nachod, 1956) and nitric acid (El-Guebeily, 1965). , Zr and Nb have been removed from solution by adsorption on various surfaces like silica gel (Nikolaskii B.P. et. al., 1960) quartz and filter papers (Stasik, 1960), polymeric adsorbents like Fluoroplast-4 • (Starik et. al. 1962) and fluorinated glass (Starik et. al. 1962). Zr-95 can be separated from Sc-46 and Fe-59 by using anion exchangers e.g. De-Acedite FF. (Arden, 1965), Minami et. al. (1958) and Abrao et. al. (1965) used both cation and anion exchange columns for the separation of a whole series of fission products. In the first studies, Zr was adsorbed by the cation exchanger as a chloride complex while in the second it separated as an anionic oxalate complex. 175 3.1.5. BEHAVIOUR OF ZIRCONIUM IN NUCLEAR FUEL SOLUTIONS As discussed earlier, Zr forms a series of nitrato complexes -3 -3 in nitric acid. At the concentration level of 10 mol dm found in -3 dissolver solution mol dm HNO ), fission product zirconium is 3 most likely to be present as non-polymeric nitrato complexes (Duncan et. al. 1966). The nitrate concentration after dissolution is -3 about 4-6 mol dm and it is probable that the species present are the tetravalent species. Some anionic complexes like Zr(NO3)5 and Zr(NO ) will also be present. At low acid concentration, however, 3 6 hydrolytic polymers would prevail. The overall chemistry is fairly straightforward and the species behave as would be expected. However, about 10% of zirconium shows abnormal extraction behaviour. This has been largely attributed to the complexes of zirconium with TBP and diluent degradation products and to a form of zirconium which shows colloidal behaviour (Naylor, 2- 1967, pp. 101-19). The equilibrium between the higher, Zr(NO3)6 and the lower, Zr(OH)(NO3)3 species is attained fairly rapidly (Duncan et. al. 1966). 3.1.5.1. SOLVENT EXTRACTION OF ZIRCONIUM A number of solvents have been tried for the extraction of fission product Zr-95 from nitric acid and mixed acid media. Extraction by tri-n-octylamine is small and extracts only the unhydrolysed species with any readiness (Shevchenko et. al. 1962). Zirconium oxalate complexes (from a mixture of nitric acid and oxalic acid) are extractable by amines in chloroform (only the dispersed amine phase extracts Zr-95 and not the chloroform phase). (Vdovenko, et. al. 176 1960). Even p-dicresyl phosphate - chloroform (Patapova, 1962) and di-n-octyl sulphoxide - carbon tetrachloride (Kulesza, 1970) have been used for the separation of Zr-95. But all these methods have been only used in the separation of Zr-95 from other fission products and not from fissile materials present in the nuclear fuel solutions. The chief extractant used (at the present time) for nuclear fuel reprocessing is tri-n-butyl phosphate (TBP). One way of removing the hydrolysed and colloidal species (which cause trouble in the solvent extraction streams) is by passing the feed solution over solids like silica gel (when more than 90% of Zr and Nb is adsorbed). Another way (Feber, 1958) is by the precipitation in situ of Mn0 which 2 then adsorbs Zr and Nb. When contacted with the organic phase Zr is extracted mostly as a tetranitrate, with 2 molecules of TBP i. e. Zr(NO3)4 2TBP (Korovin et. al. 1967). The following mechanisms of extraction of zirconium have been proposed (Sinegribova et. al. 1966; Korovin et. al. 1967A). 2+ Zr0 -4- 2H + 4NO- + 2TBP Zr(NO ) .2TBP +. H2O 3 3 4 4+ Zr -1- 4NO --1- nTBP Zr(NO )4 ,nTBP 3 3 + ZrO 2 + 2H + 4NO ÷ 2TBP H ZrO(NO ) .2TBP 3 2 3 4 2+ Zr0 + 2NO m(HNO3.TBP) ZrO(NO )2'm(HNO3. TBP) 3 3 The extractable compound is formed at the interface of phases (Yogodin 2- et. al. 1969). The extraction of Zr(NO ) as an ion pair acid has been 3 6 also suggested by Greenfield et. al. (1964). From media where fluoride ions are present, the species extracted was shown to contain one fluoride and three nitrate ions (Hinckok et. al. 1959). Where the concentration of fluoride ion is higher than that of Zr, ions like Ca24 '77 are added to remove the excess fluoride. Extraction of zirconium depends upon the temperature, the acid concentration, uranium concentration and also on the type of species. The species - discussed above show the following behaviour: (Naylor, 1967, pp. 101-19). Type of Probable Extractability into Complexing Agent Complex TBP From -3 -3 0. Olmol dm 3mol dm HNO HNO 3 3 A TBP Zr(NO)4 2TBP Medium High B HDBP or H2DBP Zr(NO3)2 2DBP Low High C Degradation Z r(Hydroxamic High High products of acid) the diluent D Organophilic Colloidal High Carrier in Silica - adsorbed (entrained) Aqueous Zr Phase For the Zr(NO ) 2TBP complex higher concentrations of acid are 3 4 more favourable. The increase in the distribution coefficient D Zr has been attributed to the decrease in concentration of water (with increase in acidity) which results in the shift of the equilibria to the right (Bxown, Fletcher et. al. , 1958). [Zr0(1-120)n NO3] NO3 [ZrO(H20)n-I. (NO3)2] 4-1-120 or 2i (Hz o)m(No3)21 _i_ 2NO [Zr(H2 (NO t11i-2 0 p 3 0)m-2i4. 2 Increasing temperature also increases D : the minimum value being Zr at 25-30°C (Shevchenko et. al. 1961). Presence of uranyl nitrate leads to a considerable reduction in D . This is due to displacement of Zr 178 zirconium as well as a reduction in the activity coefficient in the organic phase (Adamskii et. al. 1961). • 179 3.2. EXPERIMENTAL 3.2.1. MATERIALS AND APPARATUS 3.2.1.1. Materials All materials used were of AR grade and were used without further purification. Sodium nitrate, perchloric acid, hydrochloric acid and nitric acid were all supplied by Hopkin and Williams. Alizarin Red S was a product of BDH. Zirconium nitrate of 99. 99% purity with a 200 ppm hafnium content, was supplied by. Halewood Chemicals Ltd. No attempt was made to separate hafnium from zirconium. Zr-95 isotope, was purchased from Amersham. Most of the work described was carried out with a weak base resin, Ionac XAX, which was a gift from the Ionac Chemical Corporation, USA. The resin that was mainly used was 10% crosslinked Ionac XAX-1284 with a mesh size of 40-70. In some experiments 5% and 15% crosslinked resins, represented as Ionac XAX-1283 and Ionac XAX-1285, respectively were also used. Some of the properties of these resins are given in Table I. Zeocarb-225, a cation exchange resin of the Permutit Company was also used in some of the low acid and aqueous solution studies. Resins of 2%, 4-5%, 8% and 20% DVB content were used. 3.2.1.2. Apparatus Ordinary pyrex glass apparatus was used. In the column experiments, small columns of 1 cm inner dia, and 6-10 cm length were used. 50 ml ground glass necked conical flasks were used for Z8 0 equilibration experiments and were shaken in a shaker at a moderate speed. All colourirnetric estimations of zirconium were made using SP.500 Unicam spectrophotometer. Both lcm and 4cm silica cells were used. A germanium crystal detector, supplied by the Nuclear Enterprises Ltd. , coupled with a 4000 Channel analyser DIDAC 4000 made by "Intertechnique", France, was used for...the estimation of Zr-95. 3.2.2. RESIN PREPARATION Before use in actual experiment or the determination of capacity etc. the resins were put to a purification process as described in section 2.3. I. In the regeneration of the resin, the washing with acetone and methanol were however omitted. The complete removal of chloride on regeneration was checked with silver nitrate and occasional capacity checks. After equilibration with nitric acid, the resin was dried in an oven at 50-60°C and weighed quantities of this resin were used as such. No attempt was made to remove the nitric acid adsorbed by the beads. This was to avoid any hydrolysis of the bound nitrate ions. The very small amount of nitric acid left in the resin pores, which is converted to a more concentrated form on drying (Coady, 1968, p. 42) does not result in any appreciable error in weighing or in the normality of the bulk solution in equilibration experiments. 181 3.2.2.1. Resin Capacities The weak and strong base capacities of the Ionac resins were determined by the Fisher-Kunin (1954) method, using the Juracka and Stamburg (1962) modification. A brief description of this method is given in Section 2.2.3.4.The values obtained have been quoted previously (Table 1). 3. 2. 3. PREPARATION OF SOLUTIONS Sodium nitrate was used with nitric acid in making solutions of constant nitrate ion concentration and variable hydrogen ion concentration, while perchloric acid replaced sodium nitrate for solutions of constant hydrogen ion concentration. Stock solutions of zirconium were prepared in 7. 5M nitric acid and standardized for zirconium content. Solutions in this high acidity were stable for several months. For adsorption experiments, aliquots of this stock solution were diluted as required. 3. Z. 4. ESTIMATION OF ZIRCONIUM 3. 2. 4. 1. Gravimetric The concentrated stock solution was standardized by this method as the colourimetric method needs a calibration curve and the commercial product supplied as 'Zirconium Nitrate' was not totally soluble. 5 ml. of the stock solution were taken and the zirconium was precipitated with 1:1 ammonium hydroxide (Freund et. al. , 1953). The precipitate was filtered through Whatman filter paper no. 41 and ignited in a pre-weighed and cleaned silica crucible. Heating was continued for 4 hours. (It was found 182 that further heating did not produce any change in the weight of the oxide formed). The residue was weighed as Zr02. Three samples were estimated in this way and they agreed with each other to within 1-2%. The average value was taken as the concentration of the stock solution. 3.2.4.2. Colourimetric Method The gravimetric method was lengthy and could not be used for very small amounts of zirconium. So, after standardising the stock solution, the latter was then used for developing a calibration curve based on the colour reaction of zirconium with alizarine red S. This dye has the formula 0 OH 4+ (Sodium alizarine sulphonate) and reacts with Zr0 and Zr ions. (Mayer et. al., 1952). The colour reaction proceeds in presence of fair amounts of acid, in absence of which the hydrolysed form of zirconium fails to react. The acidity should not be too high as this would suppress the ionization of the dye. pH of 1 to 1.8 was thought to be adequate by Parissakis et. al. (1963). The reaction of the dye was shown to be as below by them„ 0H OH 0 flN . 0 3 At ow pH Inc eased pH 183 The possible structure for Zr alizarine complex is: \ o •ZY 0 0 The method used was as follows. A sample of zirconium containing 50-250 kig of zirconium (Sandell, 1950) was taken in a 100 cm3 flask. Hydrochloric acid was added so that the final concentration of the acid after the addition 3 -3 of 10 cm of aqueous dye solution was about 1.5 mol dm (Mayer et. al. , 3 1952). Then 10 cm of 0. 15% W/V solution of the dye were added. Colour development was allowed to proceed at room temperature for 3 one hour. After this period, the volume was made up to 100 cm and the colour intensity read against a reagent blank at 510 nm. In the literature, the use of other wave lengths has also been recommended e.g. Green (1948) ; 520, Mayer (1952), 520 nm, Sandell (1950), 525. Manning (1954) 530 nm. Hoshkins et. al. (1960) however, suggested 510 rim for improved linearity in the case of trace amounts of zirconium. It was experimentally found that the linearity of the curve was best at 510 nm and all the estimations were made at this wavelength. Higher amounts of nitric acid tend to bleach the colour and as it was expected that samples containing nitric acid to the extent of -3 7-8 mol dm would be involved, the effect of nitric acid was studied in detail. Figure 27 shows the effect of nitric acid on the determination of zirconium. It is seen that between 1-2.5 mol dm-3 the method works reliably and consequently in all estimations where nitric acid • , 100 80 d un fo 60 r di 40 20_ 1 1 1 0 1 2 3 4 5 6 - 3 mol dm HNO3 Figure -27 Effect of HNO on the Estimation of Zr. 3 185 was involved the acidity was adjusted to lie in this range. Solutions of zirconium standardized by the gravimetric method were used for the calibration curve (Fig. 28). For very dilute solutions 4cm silica cells were used, while for others lcm cells were quite adequate. The estimation was found to be reproducible within 3.2.4.3. Estimation of Zr-95 Zr-95 is always contaminated with its daughter Nb-95, and it is very difficult to remove Nb-95 to significantly low levels. The methods of Connick et. al. (1949) and Huffman et. al. (1951) did not give satisfactory results. Use was therefore made of a lithium-drifter germanium detector and Figure 29 shows the separation of three peaks (2 due to Zr-95 and one due to Nb-95). The first zirconium peak is at 0.724 Mev and the other at 0.756. With the multi-channel analyser the two peaks (each 49% of total Zr) were separated from each other by about 36 channels. The Nb-95 peak at 0.765 Mev was 45 channels away from the first peak and only 9 channels away from the second peak. Therefore the peak occurring at 0.724 was counted in all standards and sample thus avoiding any counts contributed by the Nb-95 present. Marsh et. al. (1968) have used a similar method for testing the separation of Zr-95 and Nb-95. Six p.1 samples of radioactive solution were taken on aluminium planchets, dried, and then counted. This was taken as a measure of the initial activity. Other samples were calculated similarly. 186 m 10 n 5 t a bance Absor 0 0.50 1.0 1.5 3 mg Zr/100 Cm Figure -28 Calibration Curve for the Estimation of Zr. • 0. 765Mev Nb-95 0 U 0. 756Me O. 7241Vlev Zr-9 Zr-95 650 700 750 800 850 Channel Number Figure -29 y Spectrum of Zr95 - Nb95 188 3.2.5. ADSORPTION OF ZIRCONIUM BY THE RESIN 3.2.5.1. Equilibrium Experiments In these experiments 25 ml of zirconium solution containing the appropriate amount of acid was equilibrated with about 0.5 gm of accurately weighed oven-dried resin. The ratio of the solution volume to that of the resin was thus high 01:100). This minimized the changes in solution concentrations produced by losses in solvent volume due to resin swelling. The flasks were shaken in a shaker for two hours. The speed of the shaker was adjusted so as to keep the resin constantly mixed 0.p. with the solution (rather than settled on the bottom of the flask). It was separately determined that the adsorption reached equilibrium in about an hour. The two hours time was selected to be sure that equilibration was complete even in the case of low acidity solutions where there is possibility of the existence of bigger species that diffuse slowly. The effect of shaking time is shown in Figure 30. It was tried that the same concentration be used in those experi- ments where a comparison was to be made. But as shown in the results section, the concentration was not a determining factor for Kd in adsorption from ttrong acid solutions. 3.2.5.2. Column Experiments Most of the work quoted in here was accomplished using the batch equilibration method. Only a few experiments were done in which the same solution was circulated repeatedly through a small bed of resin in a small column. s 5- 4 3 2 0 I 1 2 3 Shaking Time, Hourg Figure -30 Adsorption of Zirconium by Ionac XAX-1284 : Effect of Shaking 19 0 • 3.2. 6. WASHING OF THE LOADED RESIN The adsorption of zirconium was always small, so the amount of adsorbed zirconium could not be determined by noting the difference in bulk concentration. Therefore the adsorbed zirconium had to be eluted. This necessitated preliminary washing of the resin to remove the zirconium solution sticking to the beads. The equilibrated resin was transferred to a small column and washed with small portions of water repeatedly. 50-60 ml of water was sufficient to remove the sticking zirconium. It was feared that washing with water could lead to the removal of some exchanged zirconium. But it was proved not to be the case. Samples washed with methanol gave the same results. Lister (1951) also found that washing of the zirconium form of resin was feasible without any fear of the elution of zirconium. 3. 2. 7. ELUTION OF ZIRCONIUM The elution experiments were carried out not only to determine the amount of zirconium adsorbed but also to study the behaviour of adsorbed zirconium in relation to its removal under conditions where adsorbed plutonium would be removed. An equation, giving a relation between the time of flow and fraction of zirconium removed by 7. 5M nitric acid was derived and is discussed later. The elutions were carried out by putting the resin in a small column and passing the eluting agent at a slow flow rate of >I ml/min. I-IC1 was preferred in those experiments where the aim was only to know the amount adsorbed. This was because the method of estimation worked better with HC1 (of concentration 1M). The other alternative 191 was nitric acid of concentration 4M which is not good for colour development of the zirconium-alizarine complex. Earlier, Kraus (1956) had suggested the use of dilute hydrochloric acid for the removal of zirconium. Tailing was avoided by using slow flow rates and large volumes of the eluting agent. It was found that 100 ml of IM hydro- chloric acid would remove all the adsorbed zirconium under our conditions. As a check to the completeness of removal of zirconium from the resin, a material balance study was carried out. Theoretically the amount of zirconium taken initially should be equal to the sum of the amount adsorbed by the resin and the amount remaining in solution. This was studied by determining the amount of zirconium both in solution as well as in the resin. This is shown in the following table. The reliability of the results is evident. TABLE 17 -3 Material Balance Study in 7.5 mol dm HNO 3 No. Zr Zr Zr Total Zr Difference Taken (resin) in solution (mg) To (mg) (mg) (mg) 1 2.700 0.0275 2.650 2.6775 - 0.83 2 3.4 0.15 3.24 3.39 -0.3 3 4.40 0.100 4.20 4.30 - 2.20 4 9. 50 0.055 9.40 9. 455 - 0.50 5 2.00 0.019 1.95 1.969 - 1.50 6 15.00 0.055 14.95 15.055 t0.3 192 3.3. RESULTS For most of the work reported in this section 10% cross- linked anion exchanger Ionac XAX-1284 was used. However, in some cases anion exchanger of different cross-linking and also a cation exchanger Zeokarb-225 were also used. Unless otherwise stated, the results refer to the resin Ionac XAX-1284. 3.3.1. ADSORPTION.FROM NITRIC ACID The adsorption of zirconium from nitric acid solution is shown in Figure 31. Adsorption increases with an increase in acidity and -3 a first maximum is reached at 0.1 mol dm nitric acid. As the concentration of acid in the aqueous phase is increased still further -3 the adsorption decreases sharply reaching a plateau at 3-4 mol dm -3 acid. Going from 4 mol dm-3 acid to 7 mol dm a slight increase in adsorption is again apparent. Further increase in acidity decreases the adsorption though the decrease is much smaller as compared to the one observed after the first maximum and the overall -3 changes in adsorption between 3 to 9 mol dm acid are small. 3.3.2. EFFECT OF CHANGE OF NITRATE ION CONCENTRATION AT CONSTANT HYDROGEN ION CONCENTRATION. Previously (Anjum, 1968) the effect of changing hydrogen ion -3 concentration at constant nitrate ion concentration of 7 mol dm was reported. It was shown that on increasing the acidity from 0.5 to 7 mol dm-3 an exponential curve was obtained. The adsorption decreased -3 -1 -3 t -4 from 2.735 x 10 mol kg at 0.5 mol dm H to 8.68 x 10 mol .k g -1 • 2.6 2. 2 — 1.8 1. 0 — 0. 6 _ O. 2 i i I I 1 i '1 1 1 1 2 3 4 5 6 7 8 9 HNO mol dm-3 3 Figure -31 Adsorption of Zirconium by Ion.ac XAX-1284: Effect of HNO3 Concentration '31 1.94 -3 -4 -1 -3 at 1.5 mol dm and subsequently to 3.47 x 10 mol kg at 7 mol dm The situation with the change of nitrate ion concentration at constant hydrogen ion 'concentration is the reverse of the above. The results are shown in Figure 32. Four acid concentrations around the first maximum adsorption point were selected. As the adsorption changed -3 very little in the region 3-9 mol dm the acid concentrations selected were confined to the lower acidity region. An increase in the nitrate ion always increased the adsorption. The position of these curves with respect to each other is best understood with reference to Figure 31. Attempts to study the effect of nitrate ion in absence of any acid were unsuccessful because the zirconium present precipitated as the hydroxide on shaking in presence of sodium nitrate. 3.3.3. EFFECT OF THE AQUEOUS PHASE CONCENTRATION OF ZIRCONIUM ON ADSORPTION -3 Three acid concentrations of 0.5, 4.0 and 7.5 mol dm were selected. Increase in the concentration of zirconium present at equilibrium normally results in an increase of the adsorption -3 (Figure 33). In the case of 7.5 mol dm acid, there is almost a linear relation between the amounts of zirconium in the aqueous and -3 the resin phase. In case of 4 mol dm acid, the situation is the -3 same up to about the aqueous phase concentration of 9 x 10 -3 mol dm . Above this concentration, the curve starts dropping off and tends -3 to level off. A few experiments with 6 mol dm acid showed that -3 the curve was almost identical with that obtained for 7.5 mol dm acid. 2 1 2 3 4 5 6 7 -3 Nitrate Ion Concentration, mole dm Figure -32 Adsorption of Zirconium by Ionac XAX-1284: Effect of Nitrate Ion Concentration at Constant Ion Concentration • 0 8 12. 16 20 3 Solution Concentration, mol dm-3x 10 Figure -33 Adsorption of Zr by Ionac XAX-1284 : Effect of Solution Concentration 197 -3 In the case of 0.5 mol dm acid the effect of zirconium concentration in the aqueous phase is more marked. The adsorption shows a sharp increase in going from very dilute sdution to about -3 -3 3 x 10 mol dm zirconium. .Beyond this aqueous phase con- , • centration, the adsorption is changed very little on increasing the concentration. The reproducibility of results is not very high (see section 3. 3. 5) and has a strong relation to the age and history of the solution. Solutions used in the above three curves were freshly prepared. The effect of the age of solution in case of low acidity solutions is very prominent. Low acidity and high zirconium concentration favours polymer formation. The effect of storage of zirconium in low acid solution is apparent from the following table (Table 18). The amount adsorbed from a month old solution is much smaller than that from a fresh solution. The difference decreases as we come close to the plateau region of -3 the curve for 0.5 mol dm acid (Figure 33). TABLE 18 Adsorption of Zirconium by Ionac XAX-1284 : Effect of the Age and Concentration of the Solution -3 Nitric Acid Concentration = 0.5 mol drn Aqueous Concentration Adsorption by the Resin from Fresh Solution 1 Month Old Solution -3 3 -1 3 mol dm x 10 mol kg x 10 mol kg x10'3 0.85 4.40 0.74 1.59 5.80 1.39 2.20 6.33 1.955 5.26 7.26 5. 38 8.76 7.5 6. 45 198 3.3.4. EFFECT OF RESIN CROSSLINKING ON THE ADSORPTION OF ZIRCONIUM The adsorption of zirconium from aqueous and dilute nitric acid solutions is markedly affected by the crosslinking (i. e. the DVB content) of the resin. Three resins, namely Ionac XAX-1283, XAX-1284 and XAX-1285 (all anion exchangers) with nominal DVB content of 5, 10 and 15% respectively were examined. The results of adsorption from solutions of different acidity are given below. (Table 19). It is apparent that resins of low crosslinking show higher absorption, especially at low acidities. Solutions of the same age were used in these studies. TABLE 19 Adsorption of Zirconium by Ionac : Effect of Resin Cr os slinking Amount Adsorbed by the Resin Ionac XAX-1283 Ionac XAX-1284 Ionac XAX-1285 Acid Concentration (5% DVB) (10% DVB) (15% DVB) -3 3 -l 3 -l 3 -l 3 mol dm x 10 mol kg x 10 rnol kg x 10 mol kg x 10 0.00 0.1756 0.120 NIL 0.05 0.92 0.52 NIL 0.10 2.45 2.35 1.146 0.5 3.332 1.54 0.97 4.0 0.660 0.549 7.5M 1.400 0.748 0.436 199 3.3.5. REPRODUCIBILITY OF THE RESULTS ON ADSORPTION FROM DILUTE ACID SOLUTIONS As stated earlier, solutions of zirconium in presence of small amounts of acid are not very stable. As soon as the acidity is lowered, hydrolysis coupled with polymerization sets in. The extent to which this will go will depend upon the age, the amount of acid and other conditions of storage. It was, therefore, of interest to check the reproducibility of these results. Results shown in Figure 32 were repeated after a few months. Solutions were prepared under similar conditions. The shape of the curves (Figure 34) is the same but the points show quite a wide spread. Even the original points (shown as hollow points compared to the repeated points which are shown solid) show a spread. The reproducibility was found to be much better in case of strong acid solutions. 3.3. 6. COLUMN LOADING All the results quoted above were obtained by using a batch equilibration technique. Use of column for adsorption when small amounts of resin are involved is not very convenient and is time consuming. The equilibrium is reached slowly. To show that similar results were obtained by both the techniques, a column was 3 prepared with 2 grams of dry weight resin. 200 cm of a solution 2 -3 -3 containing 1.1 x 10 mol dm zirconium in 7. 5 mol dm nitric 3 acid were circulated at a flow rate of 1.5 cm per minute. It was found (Figure 35) that the equilibrium was reached in about 80 hours. Beyond this the amount adsorbed remained the same. Comparing Figures 33 and 35 it is seen that the total amount adsorbed is very nearly the same in both cases. 4— '2 °"" X + A 1. OM H kr' 1 2 3 4 5 6 7 -3 Nitrate Ion Concentration, mol dm Figure -34 Adsorption of Zirconium by Ionac XAX-1284 :Reproducibility of Results (Solid Points Represent Results Repeated after 3 Months) 200 0 50 100 150 Time of Flow, Hours Figure -35 Adsorption of Zirconium by a Column of Resin 2 02 3.3.7. ADSORPTION OF ZIRCONIUM BY A CATION EXCHANGE RESIN From the anion exchange behaviour of zirconium it was apparent that in neutral and dilute acid solutions only cationic and polymeric species would be present. The adsorption by the anion exchanger was low and decreased with the increase of nitric acid. This could not have been so if true anionic complexes were being formed. It was, therefore, thought that cation exchange behaviour be studied. Zeokarb-225 was selected for this purpose. Again, the results from anion exchangers of different crosslinking suggested that species of big molecular size existed. If this was so one would expect greater adsorption by resin of low crosslinking. Furthermore, if apart from the true cationic species, colloids and polymeric neutral molecules were involved in some sort of physical adsorption, the results should be similar whatever the nature of the resin. For the same resin, the adsorption should be greater for the resin of smaller particle size. The following studies were carried out. 3 -3 -3 25 cm of a solution containing 1.84 x10 mol dm and appropriate acidity were equilibrated with 0. 5g of the resin. The amounts adsorbed are shown in Table 20. Results obtained with the anion exchanger, lonac, are also given for comparison. 203 TABLE 20 Adsorption of Zirconium by Zeokarb-225 and Ionac: Effect of Cross linking 3 Zeokarb-225, (mol kg -1x10) Ionac (mol kg l x10 ) Nitric Acid 2% 4-5% 8% 20% 5% 10% 15% mol dm DVB DVB DVB DVB DVB DVB DVB 0.00 80.75 2.395 0.186, NIL 0.1756 0.120 NIL (3 -97r 0.05 90.50 2.805 0.472 NIL 0.920 0.52 NIL * Results with 100-200 mesh resin. Other results were with 14-52 mesh resin. Four things are clear from the above table: (a) Adsorption is much higher in the case of low crosslinked resin. (b) Adsorption onto higher crosslinked resins is similar in both types of resins. • (c) Smaller particle size removes more zirconium. (d) Adsorption increases in going from pure aqueous solutions to -3 dilute (0.05 mol dm ) acid solutions. 3 In the case of higher nitric acid ( >1 mol dm ) concentrations, one would expect lesser adsorption by the cation exchanger. Effect of the variation of nitric acid on the adsorption of zirconium by Zeokarb-225 (8%) was therefore studied. 0. 5g resin was equilibrated -3 -3 with 25cm3 of solution containing 2.321 x 10 mol dm zirconium. The adsorption decreases as the acidity is increased. (Figure 36). -3 This decrease is less sharp beyond 4 mol dm acid. 12 -, 10 i i r 1 r I 0 1 2 3 4 5 6 HNO3 , mol dm-3 Figure -36 Adsorption of Zirconium by Zeokarb -225 : Effect of Nitric Acid 2 05 3.3.8. ELUTION OF ADSORBED ZIRCONIUM In the previous sections, the results of the adsorption of zirconium under different conditions are reported. Having established that when contacted with an anion exchanger zirconium present in -3 7.5 mol dm nitric acid would tend to be adsorbed, it was of interest to see what would be the behaviour of this zirconium with respect to removal. If an anion exchanger is to be used for the removal of fission product zirconium one would naturally be interested in the subsequent elution of the adsorbed zirconium. Nitric acid of different strength was tried as an eluting agent. First of all Ionac XAX-1284 -3 was partially loaded with zirconium from 7.5 mol dm nitric acid, washed with cold water and then taken in a small glass column 3 and 100 cm of acid of appropriate strength were passed at a flow rate of 3 0.4 cm /minute. The amounts elated were expressed as the percentage of the total amount adsorbed. It is seen (Figure 37) that nitric acid -3 of strength more than 6 mol dm can remove almost all the adsorbed -3 zirconium, while 0.5 mol dm acid would remove only ") 12% of it under similar conditions. In a nuclear fuel reprocessing cycle (or in the final clean up of -3 plutonium), if 7.5 m.ol dm acid is used for adsorption, the same acid could be used as a back wash reagent for the removal of adsorbed zirconium. For this reason, the removal of adsorbed zirconium with -3 7.5 mol dm acid was studied in some detail. Effect of rate of flow in a narrow range was studied. The amount of resin taken was lg. The inner diameter of the column Was lcm.The exponential elution curve obtained (Figure 38) can be expressed in terms of an exponential equation which could predict the elution behaviour with a reasonable • • 100 90 80 70 60 50 d te 40 Elu Zr 30 t n rce 20 --\ Pe 10 0 I i II I I r 1 i 1 1 2 3 4 5 6 7 8 9 -3 HNO3) mol dm Figure -37 Elution of Adsorbed Zr by HNO3 (Flow Rate = 0.4 cm3/min. , 100 cm3 acid passed) Percent Zr on Hu Resin Figure -38 0 20 0= 1.2But 14C1Eluant 0 z0.4; 40 Elution ofAdsorbedZirconiumwithHNO Flow Rates,cm Time ofContact,Minutes. 60 = 0.8 80 ; ; 3 /minute o = 1.2 100 120 3 297 140 208 accuracy. This equation will be discussed subsequently. It is seen that the elution is independent of flow rate in the range of 3 3 0.4 crn /minute to 1.2 cm /minute. Results obtained by using a radioactive Zr are also shown in the figure and agree with those obtained using chemical methods. Hydrochloric acid is a better eluting agent. As shown in the above figure, the elution is easier. However, the possibility of the use of hydrochloric acid in any fuel reprocessing cycle is remote because of the corrosive nature of the acid. In the present work, hydrochloric was widely used for the elution of adsorbed zirconium for studies on adsorption. The method of estimation worked better in a hydrochloric acid media. • 209 3.4. DISCUSSION 3.4.1. ADSORPTION OF ZIRCONIUM FROM NITRIC ACID These results are shown in Figure 1. The curve can be divided into three parts: (a) <0.1 mol dm-3 acid, (b) 0.1 to -3 -3 3 mol dm acid and (c)> 3 mol dm acid. Adsorption by an anion-exchanger would ordinarily be attributed to the presence of anionic complexes. The presence of such anionic complexes of zirconium in high concentration of nitric acid has been widely demonstrated and has been previously discussed. (section 3. 1). However, the presence of anionic complexes in low acidities would be highly improbable. We shall examine the three regions of the curve separately.. -3 As we go from aqueous solutions to solutions 0.1 mol dm in nitric acid, the adsorption increases but this increase in adsorption is not due to higher percentages of anionic complexes. The possibility of any true ion exchange is ruled out as shown by the work of Schubert et. al. (1950). Schubert et. al. (1949) had earlier shown that in aqueous solutions about 70% of zirconium was colloidal. These colloidal particles of zirconium can be present as the hydroxide and may be positively charged or may even become negatively charged by combination with nitrate or hydroxyl ions (Starik et. al. , 1957, A). The colloidal tendencies of group IV and V elements are well known. So one factor causing the adsorption of zirconium in this region is the presence of colloidal zirconium. The bulk electrolyte acts as a coagulating agent and the resin functions 210. as an adsorbant because of its high surface area. Moreover, the resin because of its high concentration of ionic charge, can also act as a coagulating agent. It was experimentally observed that when -3 an aqueous solution of zirconium containing 7 mol dm sodium nitrate was shaken with the resin, coagulated particles could be seen and separated by centrifugation. Adsorption of molecular forms of zirconium on fluorinated -3 glass surfaces has been observed from 0.1 mol dm nitric acid (Starik et. al. , 1962, A). Similarly polymeric adsorbents were shown to adsorb zirconium from even higher acid concentrations -3 (0. 5 to 1.0 mol dm ). The size of the molecule will be very important in this type of adsorption. In the region under consideration -3 (i.e..<-• 0.1 mol dm acid), great hydrolysis and polymerization of zirconium is to be expected. The number of zirconium atoms per polymer molecule in this acid range would vary from 3 to 5 (Roy, 1968). For resins with 10% DVB the pore size is about 4-6 A° in 2-f- dia while the molecule CO = Zr - O - Zr = 01 has a dia of 8-10 A° (Lister et. al., 1952). Thus it can be expected that most of these species would be excluded purely on the basis of the size of the molecule. On the basis of the above discussion it is reasonable to assume that at low acid concentrations most of zirconium exists either as colloidal particles or as polymerized hydrolytic products. It is the colloidal and the neutral molecules that adsorb onto the anion exchange resin. The positively charged and the highly polymerized species are not taken up by the resin. As the acid concentration is 211 increased, the size of the polymeric molecules decreases and the species come within the size range where they can penetrate into the resin and be adsorbed. Now if colloidal and the neutral molecules were responsible for absorption one would expect similar results no matter whether the resin used is anionic or cationic in nature. This in fact was proved experimentally (Table 3). As shown in this table the uptake of zirconium by 10% crosslinked anionic and cationic resins is similar. Furthermore, in the case of cation exchanger 8% Zeokarb-225 it is seen that the adsorption increased markedly (15-20 times) on decreasing the mesh size of the resin. Smaller particles furnish more surface for the adsorption of the colloidal and neutral particles. Another notable thing in this table is that the absorption increases as the crosslinking is decreased. This is as expected from adsorption of polymeric species. Again with both cationic and anionic resins, the amount adsorbed increases -3 in going from pure aqueous solutions to 0.05 mol dm acid solutions. The amounts adsorbed by the two resins (of 5% crosslinking) are different. There is more adsorption by the cationic resin than by the anionic. -3 Next we come to the acid region extending from 0.1 to 3 mol dm. . -3 There is a sharp decrease in adsorption up to 2 mol dm acid and then the adsorption curve starts levelling off. Paramonova et. al. (1956) observed similar behaviour of adsorption by an anion exchanger PE-9 when they found that the adsorption decreased from 80% at -3 -3 0.1 mol dm to 15% at 1 mol dm acid. The strong nucleoriailic nature of the OH groups makes the anion penetration of the following type (leading to the formation 212 of anionic complexes) 11+ ADMIMMI. (11-1).4- OH OH / NHO \NO za 3 ••••• =Ely less probable at low acidities. However as the acidity increases the possibility of such reactions increases. Solvokin et. al. (1962) reported the formation of anionic complexes at acid concentrations -3 greater than 0.5 mol dm . The anionic species formed would contain OH groups besides the NO groups (Marcus, 1966), i. e. 3 reactions of the following type take place pr(OH)x(H2 n NO- 0Lx (4-344± 3 pr(OH)x(NO3)n (H 0) _344-x-r9+ 2 6 Some of these complexes would be expected to form inside the resin • phase as the acid concentration inside the resin phase is much higher than in the aqueous phase (Chu et. al., 1959). -3 In this acid region, the adsorption below 0.5 rnol dm is -3 thus due to reasons similar to those of the acid region <0.1 mol dm . The decrease in adsorption is due to decrease in the number of zirconium atoms IDer colloidal or neutral aggregate which are adsorbed. -3 Beyond 0.5 mol dm anionic complexes are also adsorbed but the decrease in the aggregate size is also more pronounced. The curve 2 -3 beyond 2 mol dm levels off as only the monomeric anionic complexes are adsorbed. The presence of anionic species is also evident from the fact that the adsorption by the cation exchanger (Figure 36) also shows a decrease in this region. In the acid range of 3-9 mol dm -3 the adsorption shows only a slight variation. The adsorption increases by about 15% in going -3 from 3 to 7. 5 mol dm acid. Beyond this the adsorption starts decreasing (though the decrease is quite small). In this acid range -3 -3 and the zirconium concentration of the order of 10 mol dm zirconium is present as non-polymeric nitrate complexes. Most of zirconium present will be as Zr(NO ) but a rapid equilibrium would 3 4 2- exist between this and the higher Zr(NO ) or Zr(OH) (NO ) and 3 6 2 3 4 lower Zr(NO3)3(OH) complexes (Solovkin, 1957; Duncan & Naylor, 1966). Here the adsorption is mostly pure ion exchange between the anionic complexes in the solution and the exchangeable nitrate on the resin. Both Bunney et. al. (1959) and Kolthoff et. al. (1962) -3 report an adsorption maximum at 8 mol dm nitric acid. Our -3 maximum is at about 7.5 mol dm acid which is reasonably close. Nitrate ion concentration reaches a maximum in nitric acid at about -3 8 mol dm (Harned et. al., 1950). This behaviour is therefore to be expected when nitrate ions are involved in complex formation. -3 The decrease in adsorption observed in going beyond 8 mol dm acid is partly due to this decrease in available nitrate ions (for complexing) and partly due to the protonation of anionic complexes. (This protonation effect has been discussed in detail in section 2. 4. 3. 6. 1). . The cation exchange (using Zeokarb-225) is shown in Figure 36. The curve is similar to the one reported by Lister (1952). At an -3 acid concentration of about 2 mol dm zirconium mostly exists as 4 4- Zr ions. As the concentration of acid is increased complexes 2 + like Zr(NO3)3 41, Zr(NO ) etc. would be formed. It has been 3 2 reported that for the cation exchanger KU-2, the affinity of the ions for the resin decreases in the order Zr4÷ > Zr(014)3÷>Zr(OH)2÷ 2 >Zr(OH)3+ (Bodashkova et. al., 1970). Similarly one would 41- 3-F,„ expect the affinity to decrease like Zr >Zr(NO ) "Zr(NO )2+. 3 32 and so on. Along with these cations, more and more anions would be formed which will also decrease the adsorption. The decrease in adsorption is therefore possibly due to the formation of anions (which do not adsorb) and cations of lower charge (which have smaller affinity for the resin). 3.4.2. EFFECT OF CHANGE OF NITRATE ION CONCENTRATION ON ADSORPTION If the hydrogen ion concentration is kept constant and only the nitrate ion concentration is changed (by the addition of sodium nitrate) the adsorption of zirconium by the anion exchanger is found to increase with increasing nitrate ion concentration (Figure 32). The position of these curves with respect to each other is best understood with reference to Figure 31. The effect is least marked in the case of -3 hydrogen ion concentration of 0.05 mol dm . Here one could not expect any anionic complexes even at nitrate concentrations of 1-7 -3 mol dm . The other curves show a sharper increase in adsorption 2 15 -3 which starts levelling off at nitrate concentrations of f 6 mol dm . In all cases, the adsorption is higher from solutions containing sodium nitrate than from acid solutions of comparable nitrate ion concentration. This phenomenon of higher adsorption from salt solutions than from acid solutions has been observed in other systems as well. Thus -3 the distribution coefficient for Am(III) in 8 mol dm lithium nitrate was found to be 220 compared with a value of less than I for 8 mol dm 3 nitric acid (Marcus, 1966). The resin phase differs from the aqueous phase in that the effective dielectric constant of 30 is much lower than that of water. This value further decreases to a limiting value of about 2 when the adjacent charge sites are about 5A° apart. (It may -1 be noted that a resin with exchange capacity of 5 mol kg each charge site has an available volume of 300 A°, corresponding to a charge separation of about 7A° (Goldring, 1966)). This low dielectric constant helps in the formation of ion-pairs and acid associations. Thus in an aqueous phase concentration of 12m in HC1 it was found that the concentration inside the resin was 24 m (Chu et. al. , 1959). Similar higher concentrations of nitric acid would be expected in the resin. In nitric acid ion-pair (11. --- NO ) formation as well as the formation 3 of ionic species, H(NO ) has been observed at higher acid concentrations. 3 2 (Marcus et. al. , 1964). The dimerization of the acid increases in solvents of low dielectric constant. The process of ion pair formation may even involve triple ions [H - NO3 - H & [NO3 H - N0 1 1 3 (Glas stone, 1960). In the case of nitric acid, therefore, ion pairs, triple ions and anionic species would be formed. Nitrate ions would preferentially combine with the hydrogen ions in all these processes. Conversely 216 in the case of sodium nitrate solutions, there is no possibility of any anionic species. Ion-pair formation will of course be there but the zirconium ions will easily compete with the sodium ions for the nitrate ion. The ion-pairs formed at the resin sites HNO 3 N I 3 *'Y. CH cH2 3 would thus leave a smaller number of available exchange sites and thus decrease adsorption. The anionic species, H(NO ) will also 3 2 compete with the anionic complexes but will have a better chance because of smaller size and because they can be formed on site. However, in the case of sodium nitrate solutions these factors will be absent. Again, there will be some chances for the formation of triple ions of the type _ NO - M and NO - M - NO 3 3 31 I II where M may be Zr(NO3)3 Combination II though not an anionic complex could still be adsorbed at an exchange site. This explains why there is more adsorption from sodium nitrate solution (of comparable nitrate concentration) than from HNO3. 3.4.3. EFFECT OF AQUEOUS PHASE CONCENTRATION OF ZIRCONIUM ON ADSORPTION -3 This is shown in figure 33. The curve representing 7.5 mol dm acid is almost a straight line. As discussed earlier at this acid 2 TI concentration one would expect only the anionic complexes to be adsorbed by the resin. In that case, the increase in. adsorption is fairly simple to understand. As the concentration of zirconium increases, so does the concentration of anionic complexes. In other words the equilibrium shifts towards the right in the following type of reaction. 4+ )3+ HNO3 2 - Zr + HNO --> Zr(NO -- Zr(NO ) 3 3 3 6 -3 The firat part of the curve for 4 mol dm acid is again linear and the above discussion applies to this as well. Beyond the Zr concentration -3 of 9 x 103 mol dm the curve is no longer linear. The amount of anionic complexes formed decreases as the available nitrate concentration is insufficient. The third curve in Figure 33 shows a more marked effect of -3 zirconium concentration. Here (0. 5 mol dm acid) the adsorption increases sharply with the increase in aqueous phase concentration and then becomes constant. As discussed earlier, here the adsorption is not due to anion exchange. At this acidity considerable hydrolysis and polymerization takes place. As the concentration of solution is increased the size of the polymer molecules also -3 increases. Thus at 1 mol dm. perchloric acid the number of zirconium atoms per polymer molecule were found to be 2.6 and 1Q 4 -2 -3 at zirconium concentrations of 10 and 10 mol dm respectively (Larsen, 1951). As the concentration of zirconium is increased, the size of the molecule increases and so more of zirconium is -3 -3 adsorbed. But after a certain concentration (>4 x10 mol dm ) 2 18 the size of the molecules becomes too large to be adsorbed. A state of equilibrium (between the larger and smaller molecules) seems to be reached. This fact is also born out by the results shown in Table 18. Freshly prepared solutions show more adsorption than the aged solutions. The difference between the adsorptions from fresh and aged solutions (of the same zirconium concentration) decreases as the concentration of zirconium is increased. Now both ageing and higher concentration lead to increased polymerization. After a certain concentration (or time) the size of the molecule becomes almost constant. Thus the changing degree of zirconium polymerization with zirconium concentration appears to control the adsorption from -3 0.5 mol dm nitric acid. The reproducibility of results in solutions of low acid concentration is not very high (Figure 34). This is presumably a reflection of the fact that the size of the molecule would vary according to the age, the concentration and even the method of preparation of the solution. 3.4.4. EFFECT OF RESIN CROSSLINKING ON ADSORPTION The results (Table 19) show that the resins with lower cross- linking adsorb more zirconium. The small difference in their capacities (Table 1) and the additional fact that in no case was the whole capacity utilized, do not explain this behaviour. The only possible explanation is based on the size of the molecule. When an ion is too large to fit into the pores without considerable expenditure of energy to expand the resin matrix, it is discriminated against by the resin. Resins of lower crosslinking can accommodate polymer molecules of higher 219 molecular weight and thus in a given solution the lower crosslinked resin will be available to a greater proportion of the zirconium species with a consequent increase in adsorption. This effect of higher adsorption by low-crosslinked resins is more marked in the case of solutions of low acid concentration. Nov it is well known that the electrolyte penetration in a low crosslinked resin is much greater than in the resin with high crosslinking. The conditions inside a low crosslinked resin are thus much closer to those in the aqueous phase. Consequently the highly hydrated molecules that would normally prefer the aqueous phase would more freely enter the resin phase and be adsorbed (Diamond et. al. , 1966). 3.4.5. ELUTION OF ADSORBED ZIRCONIUM The effectiveness of elution of adsorbed zirconium with different nitric acid concentrations is shown in Figure 37. The effect of flow -3 rate with 7.5 mol dm nitric acid is shown in Figure 38. It is seen that the elution is independent of flow rate (at least over the flow rate range studied). All the points lie on a smooth exponential curve. Elution with hydrochloric acid shows a bitnilar curve but is more efficient. An equation of the type F a e could be derived for this curve. Here F would be the fraction of the zirconium remaining on the resin and can be found from C/ where Co C = Amount of zirconium left at time t C = Original amount of zirconium present at time zero o K = a constant. In other words 220 -K J C = e C 0 In C = - K ft— Z 0 or log C = -2.303 Krt- C o K can thus be calculated by plotting log C against the square root C o of the time of contact (time for which the elution was carried out). The value of K was found to be 0.224 from Figure 39. The column size has been ignored in this discussion. The volume of the eluant involved in the elution is very large compared with the volume of the column and consequently the movement of the exchange band through the column is not very important. (Hart et. al., 1958). The equation should thus be independent of the column size. -0224rt The equation C = e works reasonably well in predicting C o the elution of adsorbed zirconium. The following table shows a comparison of results obtained experimentally and those calculated from the equation. TABLE 21 Comparison of Experimental and Calculated Results Time of Contact Percentage of Zirconium Remaining on the Resin with Acid Experimental Calculated 4 73.0 63.9 9 56.0 51.1 25 35.0 32.6 36 27.0 26.1 49 20.0 20.8 64 14.0 16.7 91 10.3 13.2 100 8.0 10.6 121 6.5 8.5 221 -0.00 -0. 20 -0.40- -0.60— log C/ Co -1. 00- -1.2 _ -1.4 -1.6 — -1.7 0 2 4 6 8 10 12 t Figure -39 Plot of log C VsJ t Co 3 Flow Rates, Cm /nun 0 0.4 ; 4Zt = 0.8 ; = 1.2 222 Two things should be noted about the above equation and the results calculated from it. Firstly, the straight line showing the plot of log C VsJ has been drawn such that instead of meeting the Co zero value of log C at zero time it meets it at time of I minute. In C o other words, even after the passage of acid for one minute, the resin still has the whole of zirconium load. This is not very surprising. As small amounts of resin were used and the column length was small, one would expect a great deal of channelling in the column. This would result in some of the liquid passing without eluting any zirconium. Again, the elution reaction is not an instantaneous reaction. Thus it would take about a minute or so before the elution starts. Secondly, the values predicted by the equation are always lower than the actual values. This is probably because the zirconium from inside the head takes more time to elute than from the outer parts of the bead. This effect is more marked in the case of ruthenium and has been discussed previously. a 223 CHAPTER 4 CONCLUSIONS ' 224 The aim of the present work was the study of ion- E :change behaviour of (a) ruthenium IV, (b) nitrosyl ruthenium III, (c) zirconium IV and (d) to use the above results in assessing the possibility of the use of anion- exchange resins in nuclear fuel reprocessing. A number of conclusions in this respect can be drawn from the work reported in this thesis. 4.1 RUTHENIUM Both cation and anion-exchange resins removed ruthenium IV from nitric acid solutions. Removal by the cation-exchanger is high at low acidities. At low acidities, decreases in ruthenium concentration also result in higher removals - a fact that is consistent with polymer formation at low acidities (Tables 3 and 4). Increasing the acid concentration decreased the removal by the cation exchanger. On the other hand removal by the weak-base anion-exchanger increased with increases -3 in nitric acid concentration reaching a maximum at 3.5 mol dm . -3 At 7.5 mol dm acid, increasing the concentration of ruthenium IV increased the adsorption up to a concentration -4 -3 of 3 x 10 mol dm beyond which the adsorption remained constant. (Table 13 and Figure 15). In all these solutions, the absence of nitrosylruthenium in the aqueous phase was ensured by molar absorption coefficient measurements. However, the possible formation of nitosylruthenium 225 in the resin phase can not be ruled out. The anion-exchange behaviour of the nitrosylnitrates of ruthenium was comparable to that of ruthenium IV. Adsorption increased with increase in nitric acid and -3 reached a maximum at 5 mol dm . For comparable solution concentrations the adsorption of nitrosylnitrate was higher than that of ruthenium IV (cf. Table 13, Figure 20). Paper chromatography showed that mostly the anionic and neutral species of nitrosyl ruthenium were removed by the anion-exchanger. The complete elution of either form of adsorbed ruthenium has been found to be impossible both with -3 dilute (0.6 mol dm-3) as well as strong (7.5 mol dm ) nitric acid. Ruthenium IV was more resistant to elution than the nitrosylruthenium. The elution behaviour is complicated by the ageing of ruthenium on the resin. It has been shown that up to 50% of nitrosylruthenium -3 nitrates can be removed by 7.5 mol dm acid if the adsorbed ruthenium is not allowed to age on the: resin. 3 More generally only about 30% can be removed by 7.5 mol dm acid. The characterization of ruthenium IV species is incomplete and further data are required. Indications of complex formation shown by ion-exchange and electrophoresis are not supported by spectrophotometry. 226 4.2 ZIRCONIUM From the foregoing studies a better understanding of the behaviour of zirconium has been reached. Indications of colloid formation and polymerization at low acidities have been found. The decrease in adsorption by a cation- exchanger on increasing the crosslinking of the latter suggests the adsorption of polymers of various sizes. Similarly the increase in adsorption on decreasing the particle size (thus increasing the surface area per unit weight) of the resin suggests the presence of colloids. Zirconium forms anionic complexes in nitric acid which are taken up by the anion-exchanger. However, only a small fraction of the Zirconium present is removed: the amount depending upon the liquid phase concentrations of zirconium and nitric acid. In the acid range >2 mol dm-3 maximum adsorption takes place at 7.5 mol dm-3 acid (Figure 31). The effect of zirconium concentration at -3 acidities >2 mol dm is such that the distribution coefficient (0.4) remains constant over a wide range. However, at lower acidities where the removal is by physical adsorption only, the curve obtained is of a different nature (Figure 33). Here again, as in the case of ruthenium, increase in nitrate ion concentration at a fixed hydrogen ion concentration resulted in increased removal by the anion-exchanger (Figure 32). 227 The behaviour of adsorbed zirconium is simpler than that of adsorbed ruthenium. All of it can be removed by washing with nitric acid ( 5 mol dm-3)(Figure 37). In batch equilibration it takes about an hour for the zirconium to reach adsorption equilibrium in 7.5 mol dm-3 nitric acid. The elution by the same acid is, however, a slower process. It takes about 100 minutes to remove about 90% of zirconium (Figure 38). On the other hand 0.6 mol dm-3 acid would remove only 10 - 15% in the same time. All the above factors would be advantageous in the use of anion-exchange resins in nuclear fuel reprocessing. After the first adsorption cycle, introduction of a strong acid scrub section would remove most of the adsorbed zirconium. In the elution step, zirconium would have a small tendency to follow the strip stream thus giving an additional separation. Any zirconium left on the resin could be easily removed by a strong acid wash in the resin reconditioning step. The behaviour of zirconium in its removal from the resin can be calculated from the elution equation (section 3.4.5). 228 4.3 FLOW SHEET In order to illustrate the results of present studies on ruthenium and zirconium a flow sheet is produced here. A number of simplifications have, however, been made because of the lack of published and experimental data. Thus the behaviour of ruthenium and zirconium were studied separately and they are considered here together without taking into account any interaction between them. Similarly the effect of the adsorptions of uranium and plutonium have not been taken into account. All indications are that both uranium and plutonium because of their high concentrations and high distribution coefficients will suppress the adsorption of ruthenium and zirconium on weakly basic resins. A resin to solution volume ratio of 1:100 has been used in the calculations. The concentrations of ruthenium and zirconium are those published for the Windscale plant (Naylor, 1967). A high acid flow sheet is envisaged because the removal of uranium and plutonium is maximum in strong acid solutions and elution of adsorbed plutonium can be easily achieved with dilute acid. After adsorption from 7.5 mol dm-3 nitric acid, the resin is scrubbed with the same acid to remove adsorbed zirconium From the results reported, it is found that about 229 10% of ruthenium will be adsorbed.. Thus starting with 2 - 7 x 10-2 moles of ruthenium in 100 dm3, in one cycle, 1.37 - 4.25 x 10-4 moles will follow the plutonium stream and 0.96 - 3.3 x 10-4 moles will remain on the resin while the rest will follow the waste product stream. An overall decontamination factor of about 1600 will be achieved. 3 100 dm of solution would contain about 10-2 to -1 -4 -3 -3 10 moles of zirconium (i.e. 10 to 10 mol dm ). The distribution coefficient in this range is 0.4. Taking a resin to solution ratio of 1;100 about 0.4% of zirconium will be adsorbed in the adsorption step. Most of this adsorbed zirconium will be subsequently removed in the scrub section. The flow sheet calculated is given on the next page. • • FLOW SHEET FOR THE REMOVAL OF Zr and Ru BY AN ANION-EXCHANGER 3 Eeed, 100drn Wash -2 Elution Resin Recorrlitioning ~:~Ru=2-7x10 moles Msorption -3 ~:, Zr= 1 0-2 _1 O-lmoles 7 .Smol ern 0.6mol dn-3 From -3 + Pu,U etc. 7. Smol elm HN0 HN0 3 3 HN0 3 lKg Resin IKg Resin , 1Kg Resin -4 lKg Resin 4 Counter current Ru= 2-7xI0- moles Ru=1.1- 3.8x10 mole Ru=0.96-3.3xI0-4 Resin Resin Contractor Zr= 4xlO-4_4x10-Smoles ,Resin Zr = Trace ,. moles Transfe> ' Trans:fet T + Pu, 11 etc. 7' +Pu Zr = Trace > Other ELements = Trace -2 Ru=1.98-6.93xlO mdes Ru= O. 9-1. 2x1 O_4 moleJ. \VProduct -3 -4 Zr= mos t of it Zr=9.6xI0 -9.6x~Jes ,II Ru= 1.37 -4.2Sxl O-SmoJes Resin Recirculatio +U' etC. or to Waste + U etc. Zr = Trace Dispos al when the + Pu Adsorbed Activity Becomes Too High ~:~ These results are based on separate studies for ruthenium and Zirconium. The concentrations of Zr and Ru are those generally present in dissolver solutions.' The calculations are based on results quoted in Figures 20, 21, 31, 33, 37 and 38. lkg resin is assumed to be equilibrated with appropriate solution~- 231 REFERENCES op 232 REFERENCES Abrao, A. and Nastasi, M. J. (1965) Brazilian Report IEA--101• Allen, A.D. and Senoff, C. 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Stewart (1952) t\> -t=. to 50 .... 1 I r- 200 220 240 260 280 300 A (nrn) Appendix -2 UV Spectrum of Benzene in Cyclohexane Present Work; Field et. al. (1961) 0.8 0. 6 bance r 0.40 o Abs 0.20 0.0 I i i I 250 270 290 310 330 350 Anna) Appendix -3 UV Spectrum of Nitric Acid -3 -3 -3 0.4 mol dm. against 0.3 mol dm ; -- 0.1 mol dm against water 251 APPENDIX 4 Molar Absorption Coefficient Values for Ruthenium IV in -3 1 mol dm Perchioric Acid -8 Wave Length Molar Absorption Coefficient x 10 (nm) (m2 mol- I) 210 4.598 214 4.470 218 4.279 222 4.151 226 4.010 230 3.832 234 3.589 242 3.065 250 2.707 258 2.464 266 2.335 274 2.261 282 2.183 290 to 306 2.139 310 2.098 318 1.98Q 326 1.794 330 1.675 340 1.421 350 1.205 370 0.880 252 Contd. . . -8 Wave Length Molar Absorption Coefficient x 10 (nm) (m2 mol-1) 390 0.728 420 0.626 430 0.629 `440 0.650 450 0.677 470 0.704 475 0.724 480 0.728 485 0.711 490 0.707 500 0.704 520 0.616 550 0.420 580 0.288 600 0.230 650 0.129 vt 700 0.102 253 APPENDIX 5 Sample Calculations of the Charge of Complex Calculation of the charge of the complex based on the values of Table 9 are shown below to make the technique of calculation more explicit. The equation for charge determination as shown in the text is (Runi-)1(Hy 1 = (Run+)2(H+)2 (Run+)1 ( 7 )7 (Run4)2(1-11. )2 where n is the charge of the species and bars indicate the resin phase. Substituting values from Table 9 (5.573x10 2) (1.0+6.913x10-4n)n = (5.683x10-2)(0.50+4.668x10 4te (1.0989x10-5) (5.15-5.573x10-2n)n (1.373x10-6)(5.15-5.683x10-2n)n on rearranging -2 -5 4 5.683x10 x1.0989x10 t (1.0+6.913x10 n) x (5. 15-5. 683x10 2n)n 5.573x10-2x1.373x10-6 (0.5044.668x10-441 (5.15-5.573x10-2n) n L. H. S. 7: 62.4505 = 8.1616 7.6517 R.H.S. = (1000+0.693n)n x (51.5-0.5683n)n (500+0.4668n)1' (51.5-0.5573n)n Different successive values are then assigned to n, till R.H.S. becomes equal to L.H.S. When n = 2 R.H.S. = 3.9888 When n. = 3 R.H.S. = 7.965 When n = 4 R. H. S. = 16.12 254 So the value lies between 3 and 4 and closer to 3 than to 4. So When n = 3.1 R. H. S. =. 8.549 and when n = 3.033 R. H. S. = 8.1638 which is very nearly the same as the L.H.S. So the equation is satisfied when n = 3.033 Hence the value calculated for n will be 3.033. 255 APPENDIX 6 Molar Absorption Coefficient Values for Nitrosyl Ruthenium -3 Nitrates in 7.5 mol dm Nitric Acid (The solution was diluted to 0.3 mol dm-3 nitric acid and immediately scanned) -6 Wave Length Molar Absorption Coefficient x 10 (nrn) (m2mo1-1) 270 313.3 280 173.3 290 100.0 300 49.83 310 31.25 316 24.17 . 320 20.83 326 18.75 330 18.17 350 17.5 380 11.67 400 9.33 430 8.33 450 8.50 485 9.25 500 8.33 550 4.83 600 1.67 630 0.75 650 0.42 :)256 APPENDIX 7 Adsorption of Nitrosyl Ruthenium Nitrate by Ionac XAX-1284 : Effect of Nitric Acid 3 Volume of Solution per Sample = 10.0 cm -5 Amount of Ruthenium per Sample = 1.35 x 10 moles Equilibration Time = 10 Hours. Amount of Ruthenium Adsorbed Nitric Acid Amount of Resin Per Sample Per kg Resin Taken -3 6 3 mol dm g moles x 10 moles x 10 0.30 0.1986 0.756 3.806 0.50 0.1999 0.919 4.597 1.0 0.1990 1.0768 5.411 3.0 0.2004 1.598 7.974 5.0 0.2017 2.009 9.960 7.50 0.2004 1.805 9.006 10.0 0.2008 1.660 8.266 t.