Recovery of Value Fission Platinoids from Spent Nuclear Fuel PART I: GENERAL CONSIDERATIONS and BASIC CHEMISTRY

Recovery of Value Fission Platinoids from Spent Nuclear Fuel PART I: GENERAL CONSIDERATIONS AND BASIC CHEMISTRY

By Zdenek Kolarik Retired from ForschungszentrumKarlsruhe, POB 3640,76021 Karlsruhe, Germany Present address: Kolberger Str. 9,76139 Karlsruhe, Germany and Edouard V. Renard A. A. Bochvar All-Russian Institute of Inorganic Materials, 123060 Moscow, Russia

Radioactive high-level liquid wastes originating,from reprocessing spent nuclear fuel can be a valuable source ofplatinum metals. The recovery of.fission palladium and rhodium is ofparticular interest and is being investigated worldwide. The radioactivity oj'jiwion platinoids is reduced to a non-hazardous level after decontamination from other fission products by a factor of 10"'. The intrinsic radioactivity offission palladium is weak and can be tolerated in many applications, while that offission rhodium decays to an acceptable level only after storing for about 30 years. With emphasis on recent achievements, this papeK which covers periodical, report and patent literature, reviews the behaviour offission platinoids in basic separation operations. Aqueous methods, such as solvent extraction, ion exchange, electrolysis, precipitation and redox reactions, are dealt with as well as pyrochemical methods, such as molten saltdmetal extraction and solid phase reactions. A second part, to be published in a later issue, considers separation processes.

The management of fission-produced platinum when it was recognised that fission platinoids iso- metals (platinoids), namely ruthenium (Ru), rho&- lated from radioactive high-level liquid wastes um (Rh) and palladium (Pd), has been developing (HLL.Ws) were potentially useful products. As a as a topic of research throughout the history of considerable volume of HLLW is produced world- nuclear chemistry. Efforts directed at separating wide each year during reprocessing spent nudear platinoid radionuclides from irradiated nuclear fuel by the Purex process, the amount of platinoids materials date back to the Manhattan Project in the recovered from the HLLW could contribute 1940s. Since the early 1960s intensive research has towards platinum metals obtained from natural been undertaken in various fields of nuclear chem- sources (1). Recovering Pd and Rh is of most inter- istry, with most attention initially being given to est, with less need to recover Ru because of its two problems: lower commercial value, and because fission Ru First, the behaviour of radioruthenium in the contains a large proportion of the radioisotope Purex (plutonium uranium extraction) process for 106Ru. reprocessing spent nudear fuel. Radioruthenium Recovery of the fission platinoids from HLLW tended to be difficult to separate from uranium is now considered technically feasible and deserv- and plutonium. ing research effort (1). The level of radioactivity of Second, the behaviour of the platinoids during fission products in the recovered platinoids is the waste vitrification process when they form sep- acceptable to safety regulations after decontami- arate phases that cause deterioration in the stability nating by a factor of 10". Intrinsic radioactivity is of the glasses. then the only remaining source of radiation in the A third field of research work developed later platinoid products.

Phtinnm Metah Rm, 2003,47,(2), 7447 74 Fission Pd contains stable isotopes with mass- nuclear fuel and with waste management, but only es of 104 (17 wt.O/o), 105 (29 wt.O/o), 106 (21 *.%), as far as is necessary to understand the nature of 108 (12 wt.?/~)and 110 (4 *.YO), and only one the problem. The review will concentrate on Pd radioactive isotope, namely '07Pd (17 =Yo) with a and Rh, with less emphasis on Ru. half-life of 6.5 x lo6 years. This long half-life may only be a minor problem because '07Pd is a soft p Paths of the Platinoids in the Purex emitter (maximum energy 0.035 MeV) and the Process and Waste Management radiation intensity at the surface of fission palladi- At present, and for the Foreseeable future, the um is only 520 Bq cm-' (2). hydrometallurgical, solvent extraction-based Purex A more serious problem could be the radioac- process wiU be the one predominantly used for the tivity of fission Rh isotopes, "'Rh and 'OmRh, with industrial reprocessing of spent nuclear fuel. The half-lives of 2.9 and 0.57 years, respectively. These wastes resulting &om this process are, and will be, are present in trace mass fractions (fission Rh con- the main source of fission platinoids. However, it sists of almost 100% of the stable isotope '"Rh). is unfortunate that the platiaoid inventory mostly Their radioactivity is reduced to an acceptablelevel splits into waste fractions which differ substantial- after a suitable, and indeed long storage time Q 30 ly in their chemical nature. Thus, in the very first years). There are applications for fission rhodium chemical step of the process - dissolving the fuel where its radioactivity does not conilict with safe- - up to a third of the fission platinoids can remain ty regulations, for instance as components of in an undissolved solid residue where they are construction materials for nuclear reactors. components of a quinary Mo-Tc-Rh-Ru-Pd alloy. It has been suggested that stable isotopes of Pd This solid may be difficult to convert into an aque- and Rh could be exclusively obtained if fission Ru ous solution by any practical route - so it is not the was the only platinoid that was separated. The iso- best source for a hydrometallurgical isolation of tope '"Ru (half-life 368 days) p-decays through the platinoids, but recovering them by a pyro- the daughter isotope '%h (half-life 30 seconds) chemical process is quite feasible. It is, however, and yields stable '"Pd, while stable '"Rh is formed possible to isolate the platinoids by a hydrometal- from '03Ru (half-life 40 days) (3). However, this lurgical procedure from the solution obtained on would leave large and unexploited amounts of Pd dissolving the fuel (dissolver solution), but this is and Rh in the radioactive waste. not advantageous as, at first, large amounts of At present the selective recovery of Pd, Rh and U(VIand PuOpresent in the dissolver solution also Ru from HLLWs is the primary object of could interfere with platinoid separation. Second, research activities on fission platinoids. Less atten- the separation could requite the addition of chem- tion is being given to investigating group icals into the dissolver solution which would separation of the platinoids, a process aimed at interfere with the subsequent operations of the avoiding difficulties in the HLLW vitrification. Purex process. The problem of satisfactory separation of The main ftaction of the fission platinoids is ) radioruthenium from uranium and plutonium in not extracted withU(VI and P.0 in the first the Purex process seems to be largely solved. cycle of the Purex process, and remains in the The recovery of fission platinoids has been aqueous raffinate which is released from the extensively studied in the last decades, for example process as the HLLW stream. Problems may arise in Japan (JNC and JAERI) and in the USA. when the extractant, tributyl phosphate, is degrad- (PNNL). Early work has been reviewed, for ed by radiation and nitric acid. Degradation instance (1,4-7), but there are no surveys of recent products, among them dibutyl phosphate, can, for achievements. This review aims to give up-to-date example, form insoluble Pd compounds, which, information on the most recently published results together with other solids, form the ill-famed inter- of separation research. Part I also deals with plati- face cruds. This interferes with the process and can noid behaviour during the reprocessing of spent cause Pd loss to a material that is difficult to treat.

Platinwm Me& b.,2003,47, (2) 75 Ruthenium, present as a nitrosyl complex, is behavioui of platinoids during the denitration can also mainly contained in the HLZW. However, the be very diverse, ranging from hydrolysis in the fraction accompanying uranium and plutonium solution (at pH < 1). through precipitation as may be so large that the hal products are conta- hydroxides (at pH 1-2) to reduction to metals (at minated with "'%I at a %her level than allowed pH > 2). Many other fission products also precip- by exisang specifications. Extensive studies have itate during the denitration, and recovery of the been undertaken to solve this problem, ranging platinoids fiom the complex solid formed would from basic chemistry of fission Ru to flowsheet not be feasible. studies. (Removing Ru as the tetroxide from the During vitrification the platinoids form sepa- dissolver solution has even been considered). rate solid phases in the borosilicate glass melts. If Nowadays this problem seems to have been allowed to accumulate, these solids can influence resolved by adjusting the flowsheet of the first the performance of the melter. Once incorporated Purex cycle. in a glass, the platinoids are practically inaccessible In the HLLW the platinoids are predominantly to chemical recovery. contained as true solutes. The HLLW stream con- Acid Purex waste solutions from defence pro- tains nitric acid at a concentration sufficient to grammes at the Hanford site, U.S.A., were suppress hydrolysis of the elements, and the plati- neutralised with the inevitable formation of solids, noids can participate, for example, in solvent for long-term storage in tanks. The supernatant extraction or ion exchange equilibria. The HLLW @H is 11-12) is buffered by carbonate ions - one is thus a suitable source for hydrometallurgical of its components. The platinoids remain in the separation of the fission platinoids. However, the supematant. This treatment has not been applied HLLW is not allowed to remain in the same state to HLLW fiom civil programmes; thus, akaline it was in when released from the Purex process. solutions are not a typical waste form. For intermediate storage, the HLLW is concen- Nevertheless, for completeness, the behaviour of trated by a factor of 5 to 25 by evaporation; this platinoids during the recovery from such solutions can result in the formation of solids and further is discussed here. loss of Pd. For example, Pd can precipitate as phosphate simultaneously with other fission prod- Behaviour of Platinoids in ucts (phosphoric acid is formed by decomposition Separation Systems of small amounts of butyl phosphates contained in Properties in Aqueous Solutions the HLLW). The solution chemistry of Pd and Rh has been It must be emphasised that any solids present in extensively studied in chloride solutions. The the HLLW concentrate could cause severe dif- chemistry of Pd and Rh, especially of Rh, in nitrate ficulties in any hydrometallurgical partitioning solution is much less - in fact inadequately - process. They would seriously impede the separa- known. tion of platinoids as happens for actinides. It In nitrate solutions Pd is stable in the divalent would be very advantageous to partition the state. This is also the case in 12 M nitric acid, HLLW before it is concentrated by evaporation, where indirect evidence indicates the absence of preferably immediately after its release from the Pdo. It has been shown that the crystals Purex process. obtained by evaporation of the nitrate solutions are Before vitrification of the HLZW concentrate, only of the Pd(II) compound Pd(NO3)2.H20, and the nittic acid is decomposed (denitration) by a not of the Pdocompound Pd(No3)~(0H)2(8). suitable reductant, usdy formic acid. The reac- Rhodium in nitrate solutions is only stable in the tion proceeds at the boapoint of the reaction trivalent state. Under suitable conditions it can be mixture and the resulting acidity or even alkalinity kept in the less stable tetravalent state. is controlled over a wide "ge (2 M HNO3 to pH An important feature of the redox chemistry of - 9) by the amount of formic acid added. The platinoid ions is their ease of reduction to metals,

Pkdnwn Me& Reu., 2003,47, (2) 76 chemically or electrolytically. This can be utilised rides to HLLW is unacceptable. The tendency to separate them and is selective with respect to towards slow reaction kinetics in complex-forming the non-plathum metals. Strong oxidants, such as reactions is a common feature of the platinoids permanganate, oxidise Ru to the tetroxide which is and can limit the throughput in continuous gaseous and thus easily removed from solutions. process operations. This removal is highly selective with regard to metals present in the HLLW. Solvent Extraction PdO does not hydrolyse strongly. Both Pdo Solvent extraction, in conventionalliquid-liquid and particularly Rhw are complexed by nitrite form, is the most practicable method used today for ions. A fraction of Rho(9) and probably also of partitioning. Its basic chemistry is well known as is PdO exists as nitrite complexes in the HLLW, its use in applied chemistry and in large-scale nitrous acid formation from nitric acid is induced engineering works. Important experience has also by the strong radiation. Ruthdurn enters the been gained from its use in large-scale nuclear Purex process, passes through and leaves as vari- separations and &om decades of indusd operation ous complexes of the nitrosy1 ion, ph~O]~+,of the Purex process. The advantages of solvent which forms when the nuclear fuel is dissolved in extraction operations are: nitric acid. The coordination chemistry of the hgh throughput [RUNOl3+ion is very complicated as it can form a ease of continuous operation, and series of nitrato, nitrito and nitro complexes in ability to keep contact time short between the diverse, and often very slow, reactions. The com- extractants and the hlghly radioactive aqueous plexed [RUNO]’+ion seems to be the typical form phase. of Ru in the HLLW, where its nitrate complexes It is desirable but not imperative that inexpen- have analogous compositions to those in pure sive and commercially available extractants are nitric acid solutions (10, 11). used. Paraftinic diluents are preferred in nuclear Both Pd(ll) and Rhoform soluble complex- separation processes currently in operation. es in the alkaline solutions obtained on Extraction chromatography (reversed phase neuaalising the acidic hexwastes to pH 11-12. chromatography) is a less useful procedure in sol- Most fission and corrosion products precipitate as vent extraction, especially for large-scale separ- hydroxides or basic salts, but caesium and tech- ation processes. It has all the disadvantages of ion netium remain in the Supernatant together with exchange (see below) and loss of extractant from the major part of the Pd and Rh. It is difficult to the column is an additional operational hindrance. specify the nature of the soluble complexes In this review, the term ‘distribution ratio’ has because the Supernatant contains large amounts of its usual meaning, that is, the ratio of the total con- complexing anions, such as - 0.5 M nitrate, - 2 M centration of the extracted metal in a particular nitrite, - 1 M carbonate and - 0.3 M sulfate. The valence state in the organic phase to the corre- form of Rhoin the solution may possibly be the spondtng total concentration in the aqueous phase. anionic complex ~(NO)~(C03)~(H~O)2]-(see (12) and references therein). Solvating Estractants All platinoids exhibit a strong afhnity to soft- The extraction of platinoids in a nitrate form is donor complexants, that is, those which bond clearly preferred, as no- ing extra needs to be complexed ions via a nitrogen or sulfur donor added to the HLLW. Extraction in a nitrite form atom. This can help in attaining the required selec- would also be advantageous, but the concentration tivity - if such complexants are considered in the of nitrous acid present in the HLLW is not hlgh choice of extracting, stripping or eluting agents. enough to form extractable complexes. Ad- ing However, the strong tendency of platinoids to larger amounts of nitrous acid or its precursors to form chloride complexes cannot be made use of HLLW is quite acceptable, as they can be easily because ad- ing hydrochloric acid or metal chlo- destroyed in the HLLW when no longer required.

PhfimmMu& Rev., 2003,47, (2) 77 Palladium Extraction - The extractability of 0.014 M HNo3, the distribution ratio of PdQI) PdOnitrate by tribuglpbosphnte PP)is low. As a reaches a maximum of - 90 at 0.5 M HN03. €unction of nitric acid concentration the distribution Useful distribution ratios are attainable at I 4 M ratio of Pdoattains its highest value of - 1.3 with HNo3, and PdQI) is extracted selectively over neat TBP and the value of 0.23 with 30% TBP in and Tho(19). decane, both have sharp fnaxima at O.a.7M HN03 The above pridne-based exfractants seem to be (13). applicable only in halogenated diluents, where the Tdkv@bo&ine oxides (alkyl= butyl, isoamyl or extraction efficiency shghtly decreases in the order: octyl) in benzene diluent extract PdQI) nitrate 1,2-dichloroethane > dichloromethane > 1,Z- from 0.2-4 M HN03 more effectively than TBP. dichlorobenzene > chloroform. The extraction However, the extraction is suppressed by nitric efficiency is markedly lower in a toluene diluent. acid and could be of importance only at < 1 M As might be expected, similar but pure OWPW donon HNo3 (14). in l&dichloroethane extract PdO nitrate very Bfinctional tdosbhorrl extmctants, such as &yl- weakly. These are l,~-~beny~bo~binyI-3-ox~en- @beny~-N,N-&isobu~hadamyhetby~bo~bineoxides tane, 1,5-bis-[(2-dipbeny~bo~biny~pbeno~]-3-oxa- (alkyl = octyl, 2-ethylhexyl or 2,4,4-trimethyl- pentane, l,j-bis-[(Z-~beny~bo~bi~hetbygpbenoyJ-3- pentyl), do not show any noteworthy ability to oxapentane and l,S-dipbeny~bo~binyl-3,6,9-trioxa- extract Pd(II) (15). undecane (1 9). Dizlkvl subids extract Pdo nitrate more The extraction of PdQI) nitrate by a?akvlsn&des effectively than other oxygen donor extractants. A is very effective. For example, 0.25 M &b@~lsu&th distribution ratio of 16.5 is attained in extracting in benzene extracts PdO with distribution ratios Pdm by a 0.05 M solution of doc&/ su&xide in of several hundreds from 2 1 M mas. It is not Solvesso 100 from simulated HLLW containmg too serious a drawback that the distribution equi- 3.1 M nitric acid (16). Di(2-etbylbegg sivfoxide librium is attained slowly after a phase contact of appears to extract Pd(II) nitrate less effectively. A 8-10 hours. Sufficiently high (even if non-equilib- 0.05 M solution in toluene - a diluent with similar rium) distribution ratios (> 10) can be attained properties to Solvesso 100 - gives a distribution after - 5 minutes if the extractant concentration is ratio of 3.55 in extracting Pdo from 3.0 M hlgh enough, for instance 0.67 M (20). Even a very HNOS while a 0.2 M solution in Solvesso 100 dilute solution of &b@glsuyide (0.002 M) in chlo- gives a distribution ratio of 10.0 (17). roform extracts initially 0.001 M Pd(Il) from 2 M Results of counter-current experiments indicate HNOj with a distribution ratio of 6.1 (21). that N,N‘ -dimethyl-N,N -dibugl-2-tn- Dibexylsu&, at a concentration of 10 vol.% in & in a branched alkane is also able to extract dodecane, gives distribution ratios for Pdo,after Pdm nitrate. A non-uniform distribution ratio of a 30 minute phase contact, of 1000-5000 at 0.14 Pd(II), namely 3.5 or 11, has been observed in M HNOs. The separation factor from Pb@) and extraction by a 0.51 M solution of the extractant Moois extremely high at - lo6 (22). Finally, a from simulated HLLW at 3.5 M nitric acid (18). distribution ratio of 13.7 is attained after a 45 Pdm nitrate is also effectively extracted by less minute phase contact of simulated HLLW con- common mixed nitmmdoxwen donor firi&ne-based taining 3.1 M HNO3 with 0.0005 M d~qlSUfOXide exfnactants, such as 2,6-6-in Solvesso 100 (16). pyridine, 2,6-bis(4-dipbeny~bosphiny/-2-oxabuty~- Two possible ways of accelerating the extrac- pyrihne, 2,6-bis[2-(dipbe~~hozpbinygpbeno~methy-tion rate of PdQI) chloride have been described, pyridine and 2,6-bis[2-(diphey~bo~b~nylmethy/)-and should also be invesagated in nitrate media. pbenoymetby&dne. The extracting power of the One of them uses j’uorinated a-pmetrical su&des as compounds shghtly increases in the given order. In extractants, such as j-(chlom~~ommetbyg-3,3)4)4,5)- extraction by a 0.002 M solution of the second of 6,6,6-octafluomhexyl Z-bydmyetLyl su@ or 6-(cbhw- the above extractants in 1,Zdichloroethane from ~$i’uommethy~-3,3,4,4~5~5,6,6,7,8,8,8-doakcaj’uomo~I-

PMnxm Metab Rev., 2003,47, (2) 78 2-bydmxyetbyl su@ie. Extraction of initially 0.005 M 6,9,12'-tri3biahpaa2cane (0.0005 M) gives a value of Pd(II) by a 0.005 M solution of one of these 1.1. The macrocydic extractants 1-o@i-2,5,8-trid&- extractants in toluene from 3 M HC1 reaches an gchnonane (0.002 M) and 1-octyl-3,7,11,15-~~atbh- equilibrium after 2&30 minutes, compared with gchbexadecane (0.001) M give values of 1.08 and the 1 to 3 hours needed with simple dialkyl sulfides 5.8, respectively. In extraction from a real dissolver (23). The other way is to add alkylammonium salts solution (a solution obtained from irradiated as phase transfer catalysts. These can shorten the nuclear fuel in contrast to a simulated solution pre- approach to an equilibrium from > 30 minutes to pared from non-radioactive chemicals and labelled 512minutes. At a concentration of 0.0017 M they with radioactive tracers) 6,9,12-h3biab~taa2cane accelerate the extraction of Pdoby 0.1 M dhyl proved to be very selective for Pdo(21). sn@& in kerosene from 2 M HCl, with accelerating Examples of some less common efficiency increasing in chloride order: dqhmo- snfinr &nor extractan& are &yknebic(O-bu$xantb&) ninm < Akqnat 336 < biisoodyhmoninm (24). or &yknebic(O-isobn&/.xantbat~ with alkylene being Dieseljkel is perhaps the cheapest source of J& methylene to butylene. These are able to extract &a% exfractant - with some of the sulfides still not Pd(Q nitrate at a low concentration (0.0025 M) in being fully identified. The diesel fuel contains, dichloroethane, but again the distribution equilib- besides sulfides and strong reductants, organic rium is only slowly established in 1 hour and there nitrogen and oxygen compounds which can also are some solubility problems (27). A nitmen &nor extract Pdo nitrate. The N and 0 compounds extractant, namely a-benpin &e (as dilute as can be removed by contacting the fuel with a 0.0001 M in Solvesso 100) extracts Pdonitrate HNO3/&CrZO7solution followed by washes with from 2 M HNO3 with a distribution ratio of 1.7 NaOH and solutions or, alternatively, by a (16). wash with 57% H2SO4. After this either the sulfides can be separated by extraction into 86% Rhodium Extraction - The extractability of sulfuric acid or the treated fuel can be used as an RhQII) nitrate by&h lextrits is even weaker intrinsically ready-to-use solvent, that is, a solution than that of Pd(II). Thus, undiluted TBP yields, at of sulfide compounds in a mixed paraffin, aromat- 1-15 M HNos, distribution ratios of 0.1-0.01 (28), ic and naphthene diluent (25). This solvent but these ratios were found after a phase contact extracts Pdofrom 2-3 M HNos with a distribu- time of 2 minutes and are possibly non-equilibrium tion ratio of 10-100, and with a hgh selectivity values. over actinides(III-VI), RuONO, Cso, Sro, Diisoamyl methylphosphonate in diethylbenzene Ce(IIIJ and ZrO(26). extracts Rhonitrate from < 5 M nitric acid under Triisobn~&bo$bine sn@& is even more effective harsh conditions, that is, at a high concentration than di-n-alkyl sulfides. A solution as dilute as of the extractant (50"h) and of saltinput agents (1.6 O.OOO1 M in Solvesso 100 extracts Pd(Il) with dis- M N(No$,+ 1 M Nw03) (29). tribution ratios of 0.64, 0.96, 1.40 and 1.60 at 0.1, Triocty/pho$hine oxide in xylene, unfortunately 1.0,3.0 and 6.0 M HNo3, respectively. A distribu- studied at a phase contact time of 2 minutes, extracts tion equilibrium is attained after 45 minutes (16). Rh(III) nitrate very weakly (28), to a similar extent J%rai& chain and maomclit tbioetbeq exhibit a as &yl~b~~-N~-d~o~&~a~~~lmetby&~$bine very hgh extraction efficiency for Pdo. This is As(alkyl= octyl, 2-ethylhexyl or 2,4,4trimethyl- illustrated by data on Pdo extraction from ini- pentyl) (15). tially 2 M HNos + 0.001 M Pd(N03)~by O.OOO5- It is unfortunate that Rho nitrate is not 0.002 M extractants in chloroform. The bidentate extracted by &kyi sn&ah, which are so effective extractants: 6,9-ditbiatetra&cane, 6,lO-ditbiqenta- for Pdo. After a phase contact time of 30 min- &mne, 9,13-&thnmsane and 6,ll-dithiabexa&cane utes, a 10 vol.% solution of dhql sn&& in (all 0.001 M) give distribution ratios of 7.1,39,29.3 dodecane yields distribution ratios for Rhoas and 42, respectively. The tridentate extractant low as 0.001-0.002 (22).

Phnirwm Mchh h.,2003,47, (2) 79 Ruthenium Extraction - Nitrosylruthenium(LIl) As the anion of this mineral acid does not partici- is well extracted by 7BP, especially in the form of pate in the formation of the extracted complex, the trinitrate RuNo(No&, but nitric acid suppresses Cyanex 302 should also be able to extract Pd(II) the extraction. For example, when the trinitrate is from nitric acid solutions. extracted by 30% TBP in dodecane the distribution To study the extraction chromatography (men- ratio decreases from 63 at 0.1 M HNo3 to 0.9 at 4 tioned earlier) of Pd(II), bis(2,4,4-tri'met~lp~~~- M HNO3. This happens after a phase contact time &tbic@bospbinic acid was encapsulated into capsules of 30 seconds; after longer contact times (2 5 of Ca alginate gel. The uptake of Pd(II) from 0.13 minutes) the distribution ratio decreases due to M HN03is so slow that a distribution equilibrium conversion of the triniaate to less extractable nitrate is only attained after 3 days, but it is selective with complexes (30). With 0-dichlorobenzene as diluent, regard to Ru(III)NO and Rh(I1I). In spite of the the extractabilityof the whole Ru(III)NO from 1-8 slow uptake rate, column operation was shown to M HNOS increases in order: TBP < triodylpbospbine be possible (37). oxide < &-@-tob+N,N-&ht$a&am yhetbylpbospbine Also usable as an extractant for Pd(II) is 2- oxide < &to~~b~~etby~e~bospbine&ox& (31). byd~~-5-noyiben~c@b~one(LlX65N). A 0.01 M solution of it in a 9:l ratio in heptane:chloroform ,\cidic llstractants extracts Pd(II) from 1 M HCl at a distribution ratio Palladium Extraction -An extractant as common of - 40. Unfortunately, the extraction rate is slow, and generally efficient as &(2-etby&eg&bo@botic acid requiring a contact time as long as 25 hours to extracts Pa@) very weakly. This is clearly shown by attain distribution equilibrium. Ad- Aliquat 336 data obtained in a chloride system (32). A chloroform as a phase transfer catalyst shortens the equilibra- solution of a less common gpen hnw extractant, 5- tion time, but to no better than 4 hours (38). Since metbyi-2,3-bexane&one&oxhe, extracts Pd(II) at pH chloride ions do not participate in the formation of 0.5-1.5 (33). This compound is limited to the the extracted complex, it can be expected that laboratory scale. D65Nwill also extract PdQI) from solutions of A surprising ability to extract Pd(II) is exhibited nitric acid. Still to be found are the extraction rate by a nrrjed nitmedoym donor edactant, NJV- in the absence of chloride ions and the chemical bis[a -(1 -psenr/--met5I-5-byd~~~-~ra~ob~hen+- stability of UX65N. den+l,3-di.min.propmpane, the en01 form of a Schiff base. In toluene diluent it extracts > 50% Pd(IT) Rhodium Extraction - RhQII) is extractable by from 1 M nitric acid even at an initial concentra- dinoylnqbbtbahnesu&nic acid in kerosene, but only at tion as low as 0.0004M. The distribution low concentrations of nitric acid (0.1-1.0 M). The equilibrium is attained in < 20 minutes (34). Rh3+ion is incorporated into an inverted micelle of Pdois also rather effectively extracted from a the extractant, and a distribution equilibrium is nitrate solution by a snhr donor &actant, bis(2,4,4- reached in < 15 minutes. At 2 M HNOl and 0.2 M tri'metby~n4~&tbi~bospbinicacid (Cyanex 30 1). The extractant the Rh(I1I) distribution ratio is low (39). distribution of Pdowas measured only down to pH 0.8 where, at a phase contact time of 30 min- Ruthenium Extraction - Nitrosylruthenium is utes, a phase volume ratio 0rganic:aqueous of 0.5 extracted by a 0.2 M solution of bs(2,4,4-tri.metby/- and 0.2 M extractant in kerosene, the extracted penty()ditbiopbo.phinic acid in kerosene with low percentage of PdO is practically 100% (35). It is efficiency. The distribution ratio decreases from 4 quite possible that Pd@) may also be extracted at pH 4.0 to 0.2 at pH 1.1 (35). well at nitric acid concentrations typical of HLLW. Difficulties can arise due to limited stability of the Basic Estractants extractant toward oxidation. Palladium Extraction - AS with solvating Bis(2,4,4-trimetby~en~~monotbiophorphacid extractants, it is desirable to extract platinoids in a (Cyanex 302) can extract Pd(II) from 1 M HCl(36). nitrate or nitrite form. &nes extract Pd(II) nitrate

Pkdnum Me& Rev., 2003,47, (2) 80 complexes only moderately. For example, when 0.33 be noted that &put 336 in benzene extracts M &kj&m&e (TOA)is used as extractantin benzene, Rhowith moderate efficiency in an undefined, the distribution ratio reaches a maximum value of possibly sulfate form at pH 0.3-9.5 (44). 1.6 at - 1.2 M HNO3 (40). TriAykamine and fnhbdeykminein benzene give a similar result, indeed, Ion Exchange and Sorption seeming to be shghtly less effective than TOA (41), Ion exchange has been applied to radiochemical while &oqhmine, oghineand hakykamine extract processes to treat highly radioactive solutions. PdOmarkedly less efficiently that TOA (40). When However, it is less useful than solvent extraction the organic phase is 10 vol.% TOA in dodecane because it is discontinuous and has a limited througl- modified with 5 vol.?h dodecanol, the distribution put, even when a quasi-continuous operation mode is ratio of PdQI) decreases monotonously with possible. The contact time between the exchanger increasing acid concentration from - 15 at 0.1 M and the radioactive solution is rather long, and OF- HN03 to - 0.6 at 3 M HNO3 and - 0.2 at 6 M ational difficulties, such as plugging the column, HNo, (22). cannot be completely eliminated. On the other hand, At < 1.5 M HNo, the extraction by TOA in one advantage is that platinoids can be sorbed &om benzene is supported by nitrite ions which exhibit strongly acidic solutions. The distribution coeffi- a visible effect at a concentration as low as 0.005 cient, K4 used here is defined as: M (W- Kd = Nu,=.V/", .rn QWammonium bases are powerful extractants for PdQI) nitrate complexes. As with TOA, NM,= and N,, are the metal amounts in a particu- the distribution ratio reaches its maximum value at lar valence state in the ion exchanger and solution, a rather low concentration of nitric acid. However, respectively, V is the volume (in ml) of the solu- at an appropriate extractant concentration the dis- tion and m is the mass (ii g> of the ion exchanger. tribution ratio could be high enough to extract Pdm at nitric acid concentrations typical of Anion I kchangers HLLW. Palladium(I1) - can be sorbed from solutions As an example, 0.042 M solutions of tnoql- containing several moles of nitric acid per litre. A metL$ammonium and teirao@kammonizm ni&& in comparison of data from (45)with previously pub- benzene yield for Pdm, maximum distribution lished data (see references therein) shows that at 6 ratios of - 20 and - 4.5, respectively, at 0.5 M M HNO, the strongest affinity to PdO is exhib- HNO,. With the former extractant the ratio is still ited by a tertiary/quatemary type exchanger: - 1.3 for 3 M HN03(42). 4-~~-&met~lben~m~~k)pbe~I(AR-OI). The exchange rate, however, is so slow that no distrib- Rhodium Extraction -Rho nitrate complexes ution equilibrium is attained even after 20 hours of appear to be very weakly extractable by Ambediite contact at 60°C. Common commercial anion LA-1 and triisooctylamine in xylene from 1-14 M exchangers from the U.S.A., such as tertiary HNO,. Distribution ratios of < 0.01 have been Amberbte ZRA-93ZU and quaternary Amberbte found, unfortunately after a short phase contact time IRA-900,A~berlitc IRN-78, Dotvex 1x8400 and of 2 minutes (28). With 10 vol.% TOAin dodecane Dotvex 2x8400 sorb Pd(II) from 6 M HN03 modified with 5 voL% dodecanol and at a 30 minute much less efficiently, but a distribution equilibrium phase contact time, the distribution ratio of Rho is attained after 1 hour at 6OOC. When Pd(II) is decreases monotxmously from - 0.06 at 0.1 M HNO3 sorbed on Dotvex 1x8 and hMfemTR-78 from to - 0.001 at 6 M HNO, (22). 0.1 M HNO,, an equilibrium is attained after 0.5-1 RhQII) is efficiently extractable as a nitrite hours both at 20 and 60°C. However, the distrib- complex by tn'o&mine. Unfortunately, with 0.5 M ution coefficient at 60°C is Wer by a factor of extractant in qlene, appreciable distribution ratios 1.2-1.5. The dependence of the distribution coef- of Rhoare attained only at pH > 2 (43).It must ficient of PdO on the nitric acid concentration is

Plrftirrrm Me,+& Rm,2003,47, (2) 81 nonmonotonous; the maximum dismbution coef- and 3 M HN03, respectively (45). Similarly, plati- ficients at 2-2.5 M HNO3 and 20°C are - 35 with noids are weakly sorbed on Russian cation Dotvwr 1x8 and - 95 with hMteM-78. exchangers. In 3.0 M HNO3 the sulfonic acid resin Thiourea is effective in the elution of PdO (45). Ku-2X8 gives Kd values for Pd(II), Rh(II1) and The strongly basic resin AV-17X8 from Russia, Ru(1II)NO of 9, 0.5 and 5, respectively, and the comparable with, for example, Do- 7x8, gives phosphoric acid resin KRF-2Ot-60 gives the & val- dismbution coefficients for Pd(II) of 64, 56 and ues 9, < 5 and 3, respectively (46). 200 at acidities of 0.5, 3.0 and 8.0 M HNo3, Four Russian aminocarboxylic resins (trade respectively. Similarly, a strongly basic pyridinium names WZZ, ANKB-2, ANKB-35 and h43-5U) sorb anion exchanger (VF-1Ap) gives, for the same Pd(I1) effectively from 3 M HNo3, yiddmg Kd acidities, Kd values of 64, 77 and 35, respectively. values of 850, 350, 150 and 160, respectively. A stronger affinity to Pd(II) is exhibited by a weak Ru(1II)NO is moderately sorbed, with Kd being ly basic anion exchanger (AN-lM), which yields 51,45,43 and 55, respectively, for the resins. The Kd = 475,350 and 120, respectively, and, esped- WZZ, ANKB-35 and MS-50 resins sorb Rh(II1); ly, by a strongly basic phosphonium anion Kd is 230,24 and 5, respectively (46). exchanger (UFO) which yields Kd = 900,500 and Semiquantitative data on the chelating amide 200, respectively (46). oxime exchanger CS-346 show that Pd(I1) is Rhodium(II1) - is generally less efficiently sorbed sorbed well from 0.5-6 M HNo3, while Ru in an by anion exchangers than Pdo. In sorption on unspecified chemical state is sorbed rather weakly Doatex 1x8 and hberlte M-78 from 0.5 M and Rh(II1) is sorbed very weakly (22). mo,,a dismbution equilibrium is attained after 1 The affinity of inorganic sorbents for Pd(II), hour both at 20 and 60°C, but the distribution again in sorption from 3 M HNO,, decreases as: coefficients are hgher at 6OOC. As a function of cn hexagyanofm.tsi&cagei (FS-15, Kd = 100) > Ni the nitric acid concentration, the dismbution coef- hexqanojinate/sikca gei (FS-14, Kd = 74) > Cd ficient reaches maximum values of - 13 with (GsM, Kd = 36) > &dft?#.f Tio$zdz(121 to 25:1, Doatex 1x8 and - 8 with AmbnJite LNR-78 at 20°C Kd = 9). The weak sorption of Rh(II1) is charac- and 2-3 M HNo3 (45). The Russian quaternary tensed by Kd = 10 on FS-14 and FS-15 and Kd < ammonium (AV-l7X8), weak basic ammonium 5 on GSM and TiO2:Zd2. Ru(1II)NO is sorbed (AN14), pyridinium (VI-lAp)and phosphonium very weakly on FS-14 (Kd - 4), FS-15 (Kd - 2) and PFO)resins sorb RhPlI) from 3 M HN03with a Ti02:ZKh (Kd - 0.5) (46). distribution coefficient of < 5 (46). Nitrosyiruthenium(II1) - is sorbed by the qua- Otlier Sorbcnts ternary ammonium (AV-I7X8), pyridinium Pd(I1) is strongly sorbed from 0.5 M nitric acid (vp-1Ap)and phosphonium PFO)resins from 3 solutions on active carbon. As break-through curves M HNos with dismbution coefficients as low as indicate, Tc(VII) is sorbed with a comparable effi- 1.3, 6 and 11, respectively (46). ciency, and Rh(II1) is weakly sorbed. Various The strongly basic resin hMteIRA401 complex forms of Ru(1II)NO appear to exhibit sorbs both Pd(II) and RhQII) efficiently enough different affinities for adbe carbon, so the observed from aged alkaline supernatant solutions, obtained sorption of Ru(I1I)NO ranges from as weak as that by the alkalisation of Purex process wastes (12). of RhPI) to stronger than that of Pd(II) (47,48). Pd is also sorbed from alkaline Purex wastes on Cation Exchangers active carbon more strongly than Rh (49). Using cation exchangers is hardly applicable to the uptake of platinoids from strongly acidic solu- Precipitation tions. The adsorption of Rh(II1) on Dotvwc5OWat Precipitation is a discontinuous process and is 2OoC is strongly suppressed by nitric acid, the dis- possibly difficult to perform on a large scale, es@y tribution coefficients being - 55,9 and 1 at 0.5, 1 in treating amorphous precipitates like hydroxides.

Phittntn Met& h.,2003,47, (2) 82 The liquid/solid phase separation is much less equipment, the potentially clean separation of complete than, for example, in ion exchange, and is deposited metal from the solution and the limited still much less clean than the liquid/liquid phase production of secondary wastes. separation in solvent extraction. A considerable amount of the liquid phase may be occluded by Electrochemical Reduction the precipitate, and this makes it difficult to wash Pd(I1) is deposited from a simulated HLLW out solutes that are required to remain in the onto a Pt cathode at a potential of -0.2 to 0.1 V supernatant. These disadvantages can be (vs. SCE) and a current density of 8-70 mA cm-’ compensated by the high selectivity of some (53). The deposition rate on a tantalum electrode precipitation reactions. at -0.1 V (vs. SCE) and 40°C decreases in the order of Pd > Rh > Ru (the onpal source does Precipitation of Platinoid Compounds not specify the initial chemical form), and the Pd(I1) is precipitated as Pd1.1C2.1WI4.1N2Oin the deposition rate also decreases when the concentra- partial denitration of the HLLW by sucrose at tion of nimc acid is increased from 0.5 to 5 M. reflux temperature (50). Some precipitation meth- Uranium(Vl), even at concentrations as 2 0.001 M, ods require chloride ions to be added to the strongly decelerates the deposition of Pd (54). The HLLW, but nowadays this is considered unaccept- effect of Uomight be a hindrance if Pd is to be able. The methods are mentioned here only deposited directly from a dissolver solution. because they have been suggested as a way of sep- Accordmg to present knowledge, Pd appem to be arating platinoids from the HLLW. Thus, Cs2PdCL the only fission platinoid deposited at a rate suit- can be precipitated, if the Pd(II) in the HLLW is able for a separation process. oxidised to PdOeither electrochemically or by At 100 ppm levels, Pd(I1) and Ru(1II)NO NaClO, and a source of chloride ions is added (51). mutually influence their deposition rates from 3 M Hardly applicable to HLLW is precipitation of HNo3. The deposition of Pd(II) is slightly slowed salts of the type Cs@Cl~SnC13),1 where M is a by the presence of Ru(III)NO, while the presence platinoid (52). The addition of HCl and SnC12 up of Pd(II) markedly accelerates the deposition of to concentrations as high as > 2 M and - 0.1 M, RuoNO(55). respectively, is required. Pd(II), Rh(II1) and Ru(1II)NO are precipitated with efficiencies of Chemical Reduction and Photoreduction 97 to 100%. Pd(I1) is reduced to metal by u.rm&c md, and A Rh(II1) fraction of 9696% is precipitated the precipitation yield from simulated HLLW as hydroxide from simulated radioactive waste decreases with increasing nitric acid concentration. containing 20 wt% acetate at pH 8-12. More than The reported concentration of ascorbic acid need- 90% Pbo remains in the supernatant solution. ed to precipitate > 99% Pd is 0.03-0.06 M at 0.54 Rh(III) can be separated from Moo,particular- M HNO3 (56) or 0.04 M at 2 M HNO, (57). The ly at pH 12, where 87% Moois not precipitated precipitation is selective with respect to Rh(II1) (22). and Ru(IV) (56, 57) and also Moo, Fe(III), Precipitation of platinoids in metal form is dealt Nd(lII), Sr(II) and Cso (57). The precipitation of with below as a redox reaction. Pd(II) as metal is practically complete after 20 minutes (57), but Pd redissolves as the solid/liquid Electrochemical and Chemical Redox Reactions system ages. Redissolving starts after 14 hours and Although in many systems electrolytic deposi- is complete after 18 hours; it is ascribed to oxidation is a discontinuous and time consuming tion of ascorbic acid by HNO3 mediated by the operation, it is still a prospective method for iso- Pd(II)/Pd(O) and Fe(Il)/Fe(III) couples (57). lating platinoids - mainly due to the easy and The precipitation of Pd(I1) from simulated selective reduction of Pd(II) to metal. Also advan- HLLW is effective even in the presence of 0.5 M tageous are: ease of scale-up and simplicity of the oxalic acid. At 0.25 M ascorbic acid and 0.4-2 M

Phtinnm Metab Rev., 2003,47, (2) 83 HN03the precipitated hction of Pd is 9%99%; counter-current contact of two immiscible molten this decreases to - 10Y0 at 4 M HN03 (58). Both phases is much less easy than in solvent extraction. Pd(I1) and Rh(II1) are reduced to metallic form A further disadvantage is in partitioning the in the denitration of HLLW by refluxing with HLLW, namely the need to convert an acidic formic acid, when the nitric acid concentration is nitrate solution to an oxide or chloride solid. It is a reduced from an initial 3.5 M HN03to pH 2 (59). common feature that platinoids are not mutually The platinoid metals are obtained in a mixture with separated in pyrochemical procedures and a mix- other solids, mainly hydroxide precipitates. ture of two or all three fission platinoids is the The photon&ctioon of the platinoids to metals is resulting product. Thus, further separation is need- possible in the presence of TiOz powder as photo- ed and is conveniently achieved in a hydromet- catalyst. With a 2 kW xenon lamp as a hght source allurgical procedure after dissolving the product in and in 3 M HNo3 containing 20% ethanol, 100Y0 nitric acid. Pd and - 90% Rh are reduced after 60 minutes. The reduction of the initial Ru(II1) is slower at - L\traction b\ Moltcn \lctA ,~ndSalt\ 60 and - 80% after 60 and 90 minutes, respective- Pd and Rh are extractable into some molten ly; the reduction of initial Ru(III)NO is quite metals from a LiC1:KCl (5050 mol?h) melt. Both inefficient (%3% after 60-90 minutes) (60). are quantitatively extracted (- 100Yo) into Zn at 8OO0C, into Cd at 500 and 65OoC, and into Pb and ( )iidatiun of liuthenium Bi at 600 and 800"C, respectively. A 70 to - 100% Ru(1II)NO can be electrooxidised in synthetic fraction of Ru is extracted at 600 and 800°C into HLLW to RUo4 at 3OoC, 2 2 V (vs. SCE), 2 12 mA Zn, while Cd, Pb and Bi extract - 5 to - 40% of cm-' and at air flow 0.4-1 1 m-'. Ru04 gas is Ru at 5W00"C (62). formed at a Pt anode, and transferred with the air One variation of the molten salt/metal extrac- stream into an absorbing solution containing, for tion involves melting a particular salt/metal example, HC1 and ethanol (53). During the oxida- system. After cooling a metal button containing tion to RUo4 by bubblulg ozone, more than 98% the platinoids and a glass phase containing other Ru can be recovered from a solution that is fission products are formed. To achieve this, glass obtained by dissolving a Pb phase button (see (borosilicate type, developed for the vitrification of below) in boiling 3 M nitric acid (61). It should be radioactive wastes), a metal oxide scavenger and a mentioned that large-scale operation would proba- reductant are added to fission product oxides, and bly be fundamentally disturbed by the easy the mixture is melted at llOO°C. A comparative reduction of RuO4 to the almost insoluble solid study (63) has shown that SbZO3, Bi2O3and PbO RuOZ,which deposits on the walls of reaction ves- scavengers can be reduced to metals by graphite, sels and pipe connections. charcoal, flour, corn starch, sugar and silicon, but SnO and CuO are reduced only by graphite. A Pyrochemistry 30-100% fraction of Pd or Rh and a 20-100% The advantages of this method are due to the fraction of Ru are found in the metal button. Both nature of the materials handled, namely molten the yield to the button and the quality of the glass inorgaoic salts, metals and/or alloys, or solids. phase are dependent on the nature of the scav- These display hgher radiation stability than aque- enger and the reductant. The quality of the glass ous solutions or organic compounds in phase is best when the scavenger is PbO and poor- hydrometallurgical processes. Since the process est when the reductant is charcoal. streams have smaller volume than in hydrometa- In a slmpler form of the method the scavenger lurgy, the operations can be performed in compact is added as a metal, and no reductant is needed. equipment. The discontinuous nature of many of Thus, platinoids are extracted into molten Pb after the operations and the difficulty in achieving con- it is added in metallic form (61, 64). Platinoid tinuous operations are disadvantages. The recovery is 85-100% in melang Pb mth NaZB40,

Platinnm Me& Rm,2003,47, (2) 84 or BzO3 both in an argon atmosphere and under known to exttact Pd efficiently from nitric acid bubbling air, and independent of temperature at solutions and can be used for extraction from 75&1100”C. Using Na2B407as the glass-forming HLLW. The chemistry of Pd in nitrate-based sol- material allows somewhat lugher recoveries than vent extraction systems is known. Searchmg for

achieved with B203 (64). new extractants and more detailed investigation of High selectivity for Ru over Pd has been the basic chemistry of Pd may be useful but observed in systems where molten magnesium and unnecessary. uranium:chromium eutectic (weight ratio 19:l) [4] Rh is generally less extractable by known form two separate phases. At 900-950°C Pd and extractants than Pd, and knowledge of its basic Ru distribute themselves in favour of the magne- chemistry in nitrate solutions is insufficient. sium and eutectic phases, respectively, giving a Further investigations are needed, aimed at separation factor of lo6.A similar picture has been improving the efficiency and selectivity of Rh sol- found at 750-85OoC in a system with magnesium vent extraction. and uranium:iron eutectic (weight ratio 8911) [5] Conditions for the satisfactory electrolytic phases. There is no separation in the molten alu- deposition of Pd from nitrate solutions are largely minium:bismuth system at 700-9OO0C, where known, and the method can be adapted to recov- both the Pd and Ru much prefer the aluminium er Pd from HLLW. The deposition of Rh is slow phase (3). for practical application and further investigations are necessary. Rcactions Involving Solids [6] F’yrometallurgical treatment appears to be the A super-lugh-temperature reduction of the only feasible option to separate the platinoids from platinoids in a calcined radioactive waste proceeds the dissolver residue. The treatment can convert under an Ar atmosphere at 1800°C. As the origi- the residue to a form that is soluble in dilute nitric nal source can be understood, the platinoids are acid. However, with the present state of knowl- reduced without ad- a reductant. They sepa- edge, the platinoids are not mutually separated and rate, together with Mo as a metal phase, from the are contaminated by some fission products. rest of the solid which mainly consists of lan- Subsequent hydrometallurgical separation is need- thanide oxides (65). Elsewhere, platinoids have ed after dissolving the product of the pyrochemical been reported to be reduced at 2 1600°C in the procedure in a mineral acid. The possibility of presence of AlN, BN, TiN or Si& as reductants combining the obtained solution with the HLLW (66). A metal phase and an oxide phase are instead of treating it separately should be checked. formed, the former containing the bulk of plati- Separation processes will be looked at in Part II noids and the Mo. of this paper, to be published later.

Conclusions References [l] Fission platinoids (I‘d, Rh and Ru) are distrib- “Feasibility of Separation and Utilization of Ruthenium, Rhodium and Palladium from Hgh- uted between two fractions of wastes that result Level Wastes”, IAEA Technical Report Series, No. from reprocessing spent nuclear fuel, namely 308, LAEA,Vienna, 1989 radioactive high-level liquid waste (HLL.W) and B. N. Zaitsev, V. A. Korolev, V. P. Pop& Yu. 2. the undissolved fuel residue. Prokopchuk and M. N. Chubarov, RadofiiMa, 1988, 30, (3), 411; Sou. Radocbem., 1988,30, (3), 387 [2] The platinoids of main interest (I‘d and Rh) F. J. Smith and H. F. McDuffie, S@. SCi Techno/., are preferably recovered from the HLLW by a 1981, 16, (9), 1071 hydrometallurgical process. Solvent extraction and R J. Newman and F. J. Smith, Phtinum Me& Rex, electrolytic deposition are the preferred methods, 1970, 14, (3), 88 H. Koch and A. Schober, Iso@etpi&, 1976,12, (2). while precipitation and ion exchange or extraction 49 chromatography are less favoured. R Thompson, Report AERE-R-11966, U.K. At. [3] Numerous extractants (mainly S donors) are Energy Res. Establ., Harwell Lab., 1986

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Phfinnm Metuh Rcv., 2003,47, (2) 86 54 K. Koizumi, M. Ozawa and T. Kawata, J. Nucl. Sci 63 G. A. Jensen, A. M. Platt, G. B. Mellinger and W. J. Tecbnol., 1993,30, (ll), 1195 Bjorklund, Nucl Techno/., 1984, 65, 305 55 M. Ozawa, Y. Tanaka, C. Oohara and H. Tanuma, 64 K. Naito, T. Matsui, H. Nakahlra, M. Kitagawa and Proc. Int Conf. Future Nud. Systems: Challenge H. Okada,J. Nucl. M&., 1991,184,30 Towards 2nd Nucl. Era Advanced Fuel Cycles (Global 65 M. Horie, Trans. ENS/ANS-Foratom Conf, (ENC '97), 5-10 Oct., 1997, Yokohama, Japan, p. 1232 '90), 2%28 Sept, 1990, Lyon, France. Verlag 56 S. H. Lee, C. H. Jug, J. S. Shon and H. Chung, S$J. Rhejnland, Koln, Germany, 1990, Vol. IV,p. 2281 Sd. Techol, 2000,35, (3), 411 66 M. Uno, Y. Kadotani, H. Kinoshita and C. Miyake, 57 E.-H. Kim, J.-H. Yo0 and C.-S. Choi, Wochim. J. Nucl Sd. Tecbnol., 1996,33, (12), 973 A&, 1998,80, 53 58 E.-H.K~~,D.-Y.C~U~~,W.-H.K~~,Y.-J.S~I~,E.H.The Authors Lee and J.-H. Yo0,J. NWCL Sci. Tccbno, 1997.34, (3), 283 Zdenek Kolarik retired from the Forshungszentrum Karlsruhe in 59 Wu Chuanchu, Liu Yuanfang and Jiang Lingen, J. 1998. He was a member of the research staff in the Institute of Nncl Wochem. (Chin.), 1986, 8, (3), 147 Hot Chemistry and then in the Institute of Nuclear Waste. His 60 T. Nishi, N. Uetake, F. Kawamura and H. Yusa, particular interest was separation chemistry, especially solvent extraction. He participated in work aimed to refine reprocessing of Truns. Am. Nucl Soc., 1987,55,242 spent nuclear fuel by the Purex process and adapting the process 61 M. Myochin, K. Kawase, Y. Wada, Y. Kishimoto, M. to fast breeder fuel. He also participated in developing a process to Ayabe, M. Hatta and K Arita, Proc. Int Conf. Nud. separate actinides from radioactive high-level liquid wastes. Waste Management Environ. Remed., 5-11 Sept, 1993, Prague, Czech Rep., ASME, New York, Edouard Renard is a group leader at the A. A. Bochvar All-Russian U.S.A., 1993, Vol. 1, p. 663 Institute of Inorganic Materials, Moscow. He works in separation chemistry, particularly with solvent extraction. His research work 62 H. Moriyama, K. Kinoshita, T. Seshimo, Y. Asaoka, has been directed to further the development of the Purex process K. Moritani and Y. Ito, Proc. 3rd Int Cod. Nud. for reprocessing fast breeder fuel and recently to the development Fuel Reprocessing Waste Managanent (RECOD of a process for the recovery of fission platinoids from radioactive '91), 14-18 Apt, 1991, Sendai, Japan,Vol. II, p. 639 high-level liquid wastes.

Ruthenium Complexes Aimed at Chagas' Disease The parasite Typmosoma me causes Chagas' dis- Now, in a further attempt to produce complexes ease, a major health problem in Latin America. The that combine the antitrypanosomal activities of both disease is transmitted by insects, blood transfusion the metal and ligand, researchers at the Universidade and maternal infection to the foetus. The poorest de So Paulo, Brazil, Universidad de la Rephblica, environments suffer most. Debilitating illness leads Uruguay, and Univexsidad Naciod de La Plata and to later death. Transmission is attacked by vector Instituto IFLP, Argentina, have synthesised new insect control and blood screening. Drug treatment Ru(II) complexes (2). The complexes have general (usually Nifuttimoxm and benznidazole) is used for formula, pu'C12(DMSO)&] (DMSO = dimethylsd- acute, early, indeterminate and congenital cases. As foxide; L = 5-nitro-2-furaldehyde semicarbazone T. mi@ antigens can stimulate autoimmunity, immu- (Ll), N4-n-butyl-5-nitro-2-furaldehydesemicarba- nisation is not possible. zone (L2) and 3-(5-nitiofuryl)amIeine semicarba- Nifurtimoxm is inefficient at treating the chronic zone (L3)). The complexes have been characterised stage of the disease and has undesirable side effects. and crystal and molecular smctures of the L1 and L2 To counter this, semicarbazones derived from 5- complexes determined. The Ru atom in both crystals nitrofurfural have been synthesised and show activity is in a similar octahedral environment, equatorially against T. [email protected] compounds generate nitro anion coordinated to the semicarbazone molecule, acting as radicals, which may be the cause of their activity. a bidentate ligand though the N and 0 atoms. Work Earlier work has shown metal complexes of some to evaluate the activity of these Ru complexes on the antiuypanosomal drugs (imidazole and thiazole proliferation of in vitm T. Cm@ cultures is underway. derivatives) are more active against T. me than the free hgands. As there are similarities between metal References drugs &playing anti-0~ and trypanod& activity, 1 C. S. Allardyce and P. J. Dyson, Plblinwn Metals h., 2001,45, (2), 62 ruthenium complexes with antiuypanosomal hgands 2 L. Otero, P. Noblia, D. Gambino, H. Cerecetto, M. have been synthesised. However, ruthenium semicar- ~~~a~~,J. A. and 0.E. pito, rnoq. ck,,,. bazones have received less attention for this use (1). Ah,2003,344,85

PIotinwm Me& Rm, 2003,47, (2) 87