Electrolytic Production of Thallium Metal and Its Oxide from TI(I) and TI(M) Nitrates
,I ,I I 1'1 Ii, I,1I
IndianJournalofChemicalTechnology Vol.2,September1995, pp. 266-270
Electrolytic production of thallium metal and its oxide from TI(I) and TI(m) nitrates
1MMKenawy,MA H Hafez, AA EI-Khouly& YCharibGoudah ChemistryDepartment,FacultyofScience,MansouraUniversity,Mansoura,Egypt ~eceived28October1994;accepted10M~y 1995
The cathodic and anodic deposition of thallium as a pure metal or its oxide from different baths containing TI(I) or TI(ITI)nitrates with some suitable additives has be,en investigated. The quantity and quality of the metal and its oxide have been found to be dependent on the type of the bath used. The effect of different parameters such as pH (1-12), current density (0.01-4.0 A dm-Z), tem• perature (20-60°C), electrode type (platinum and graphite), metal and additives concentration on the cathodic and anodic efficiencies and on the quality of deposit has been studied. The interfering ef• fect of some cations and anions has also been studied. Spectrophotometric, polarographic, AAS and X-ray diffraction techniques revealed the purity of separated deposit to be 99.9%. A suitable me• chanism for the formation of the element and its oxide is suggested. An analytical application for preconcentration and separation of th~um from its natural ores and alloys using the proposed elec• trolytic method has been found to be satisfactory and successful.
Thallium and its salts are extremely toxic, hazar• of AR grade poduct in bidistilled water. The dous, skin contact ingestion and inhaiation are all Tl(III) content was determined by titration with dangerous, also have great effect on plants, ani• standard NazEDTA solution using xylenol orange mals and humanI. Its compounds are used for de• indicator9, whereas TI(I) was analysed gravimetri• stroying vermin, ling worm and ant. The thalli• callylO as TI I . Ail other chemicals used were of um(II) and OH free radical induce damage to AR quality and used without further purification. DNA and trypsin as complex in individual bio• A double wall electrolytic cell with two com• mols2• Since TIBr and TII are transparent to long partments separated by a porous diaphragm and wavelength, there are possibilities for their use in connected to an ultrathermostate ( ± 0.05°C), was photosensitive diode and infrared detector. used II. The catholyte was provided with a plati• Few electrochemical methods were found in li• num sheet electrode or cylindrical graphite el~c• terature about thallium and Tlz03 production. trode, whereas the anode was a platinum wire, Cathodic deposition of thallium was studied by and vice- versa during anodic deposition. The elec• Fouda3 from aqueous baths containing some addi• tric current was supplied from a constant current tives such as Cl-, F- and SOr- at current density supply. The galvanostatic measurements were car•
of 0.4 A dm - Z and pH = 9. Toney et al.4 deposit• ried out with a constant current device and a digi• ed thallium on Ag and Au as a monolayer. Under tal multimeter (PM-2517X). Ail the electrode pot• controlled potential thallium was deposited on entials were measured with reference to SCE at polycrystalline Ag and Au substrate5-? The co• 25 ±0.05°C. deposition under controlled potential of Pb and The metal deposit or its oxide was dissolved in Tl (1:2) on polycrystalline Ag was also investigat• 5 mL hot nitric acid and made up to 25 mL by ed8• bidistilled water and was analysed spectropho• In the present investigation, efforts have been tometrically, after quantitative oxidation to TI(ill) made to determine the optimum conditions for by Brz-water1Z, using semi-xylenol orange in acet• production of highly pure TI and TlzO 3 by eIec• ate buffer (pH =4, 1=0.1 (KNO 3 at A. =520 trodeposition, and to develop a simple and rapid nm)13. electrolytic preconcentration and separation of TI The average current-voltage curves were re• fromits natural ores and miilerals. corded by polarograph model E-506 (Metrohm Herisau Switzerland) in acetate bufferl4, pH = 4. Experimental Procedure Perkin-Elmer model 2380 AAS was used with A standard solution of Tl(I) and TI(ill) nitrate Pye Unicam hollow cathode lamp for thallium es• w~ prepared by dissolving the required amounts timation, A= 276.8 nm.
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Moreover, the metal deposit and its oxide were Effect of different baths- The baths were ar• subjected to X-ray diffraction measurements using ranged according to the current efficiency (ca• a method described earlier!5 (PW 1846· Philips'. thodic or anodic). The maximum current efficien• PW generator, 2 (J range 10-90°, with CuKa, cy (percentage) was found to be 48% in case of A= 1.542 A and Cu filter). Analysis gave purity of TI+ nitrate using MeOH bath and 98.1% for TP+ TI metal 99.99% on the cathode. The metal has a nitrate from thiosulphate bath. The stoichiometry hexagonal close packed crystal with 2 (J, 32.00, of- Tl + and TP + complexes was confirmed by 32S and 68.2°. The process of crushing, grinding conductometric titration of both Tl + and TIH ni• (100 mesh), decomposition by different fusion trates solutions. mixtures and dissolution of various ores samples Effect of pH-The effect of pH on cathodic and were carried out as described in literature 16. For anodic current efficiency of some selected baths each sample "'"0.5 g was dissolved in aqua regia. was studied at pH values varied from 1 to 12 un• In order to remove the interferences of other der certain specific conditions. It has been ob• cations, selective precipitation of thallium as TII served that the best efficiency was obtained in the followed by dissolution was carried out. Thallium pH range of 6-8. This range was decreased to a (ill) ion (formed by the action of aqua regia), was value of 4 during deposition of metal from TI+ reduced by 1 g sodium sulphite, adjusting the pH using thiourea (TU) bath. No deposition occurred to 4 and filtering any precipitate formed. To the below pH of 2 for most baths. This may be due' clear solution 0.5 g of Na2EDTA and 5 mL of to the attack of the deposit by hydrogen ions re~ 1M KCN were added and heated to about 80°C suIting in its dissolution (Fig. 1). On the other in fuming cupboard. Finally, 0.3 g KI was added hand, at higher pH values a decrease in current to the hot solution with constant stirring until the efficiency was observed, which may be due to: (i) formation of yellow precipitate. After 1 h TI(I) hydroxide formation!7, (il) non-adherent nature of iodide was separated and dissolved in aqua regia deposit and (ill)higher polarization at higher pH. and subjected to the electrolysis using thiosul• Cathodic efficiency (CE %)-Fig. 2 reveals a phate bath. gradual increase in CE % (except TV bath) with Results and Discussion increasing current density during d6position of The effect of different parameters which play metal from TIH or TI+ on a Pt-electrode until a an important role in the deposition process was maximum value was found to be 95-99% (accord• extensively studied in order to determine the opti• ing to bath type) at 0.4 A dm-2 in case of TP+ mum conditions necessary for the electrolytic pro• and 55-79% at 0.2 A dm-2 for TI+. Such incre• duction of the metal and its oxide. ment may be attributed to the increase of positive
.i>T\from TI (III) ii) Tl2I>3 otG'lOdt! iii) ntrom TI (I) (0) glycerol 100 1OO~(b) DMA (e) EDA (d) MeOH
.~ ,... u .C 'u• :.:•
c)DMF 6128I)f10I1261)4 24 02 0) MeOH 2 pH b)TUd)Amm. Ill. 10lff 20 I
Fig. I-Effect of pH on current efficienty at constant temperature, 25°C'for thallium and T1203 deposition from different . types of baths [current density=U.4 ACIro-l, time=lO min' on platfuum electrode] 268 INDIAN J. CHEM. TECHNOL., SEPTEMBER 1995
From Tl (III) From TI ( I) 11203 on Cl1fOCl. QJ Tu a)MeOH 1) glycerol b) sfljQt (pH :6) b)Tu at(pH:4) 2) DMA e clAY c)DMF 3) EDA d18,:' dlPH 4) M.OH e )Amm. solution from Ti (//l) f) Amm. solution
0IJ -.!::l r::u~ 1.52.0.2.51.51.1.0 0I0.5 ., 0 O. 5 •••.. uIu 60 C~ ,.., 40 II!
20 (e, 0
'0.2 0.4
3.0 3.5 4.0 0.5 1·0 1.5 2.0 25 3.0 3.5 Current Density,A dm-2
Fig. 2- Effect of current density on current efficiency at pH = 8 and constant temperature = 25°C for thallium and Tl203 from nitrate different baths on a platinum electrodes
charge on the metal ion. Above these current bath used) were found below 0.1 A dm-2• At cur• densities, a continuous decrease in CE % was ob• rent density> 0.4 A dm-2, a non-adherent ran• served and then tend to flatten out with rising domly oriented deposit was obtained. The most current density. suitable CD ranges from 0.2-0.4 A dm-2• The use of graphite electrode led to the decrease in AE % A minimum value of 7.5-4.9% for TP and by 8oio (at 0.4 A dm-2, DMA and EDA). This 13.5-7.5% for Tl3+ \\'as obtained at a current may be attributed to higher. value of oxygen over• density of 4 A dm - 2. This is due to the competi• voltage on Pt than graphite 18. On using glycerol tion of hydrogen evolution with metal deposition bath a large decrease of •••53% (at 0.4 A dm-2) at cathode. At current density < 0.02 A dm - 2 a was observed, which may be due to the blocking very thin film of metal was obtained from most of active centres on the graphite electrode by gly• baths which may be attributed to the low rate of cerol. cathodic reduction. On the other hand, at current Effect of metal ion (Tl +, Tl3+) concentration• density > 0.5 A dm - 2 a randomly oriented, large The effect of thallium ion concentration in the crystals deposit was found. The use of graphite catholyte on CE % was studied in the range from electrode lead to the increase in CE % by .",more 0.1-200 mgIL, at constant ligand concentration. It than Pt-electrode, this may be attributed to the was found that the CE % increased sharply at higher value of hydrogen overvoltage on graphite first on increasing the thallium ion concentration than on Pt-electrode18• in the concentration r.ange 0.5-25 mgIL, then Anodic efficiency (AE %)-The percentage reached a maximum value of 100 and 90% for anodic efficiency as a function of current density TU and MeOH on U8ing TI +. In case of TP + us• for Tlz03 dep08ition on Pt-electrode from TI + ing S20~- and alizarin yellow (AY), the maximum using different baths was determined. As expected value of CE % (100%) was obtained at •••25 from anodic polarization curve, the current effi• mglL of TP +. Also the anodic current efficiency ciency curves fall sharply at first and then tend to was reached 100% at mefal ion concentration flatten out with rising current density (Fig. 2). •••25 mglL for glycerol and methanol baths. At This is due to the competition of oxygen evolu• lower value of thallium ion concentration < 0.5 tion With Tl203 deposition. The maximum values mglL, no cathodic and anodic depositions were of AE % range from 92-99% (accordin~ to the occurred from any used bath.
I '! I KENAWY el aL: ELECfROLYTIC PRODUCTION OF lHAWUM METAL 269
Table I-Analytical results of thallium separation from different samples S20~- bath, current density = 0.4 A dm -2, pH = 6, T= 25°C and duration time = 60 min. n= 6 Sample Sample, name and occurrence Tl found S, TI (standard), 00. % % ~ method, % 1 (a) Synthetical sample: TII0%, Cu 50%, Zn 10%, Al1O%, Ni 10%, Fe 10% 9.90 1.01 10 2 TII0%, Zn 50%, Ag 10%, Cd 10%, Pb 10%, Se 8%, Te 2% 9.90 0.92 10 3 TII0%, In 10%, Pb 45%, CO 5%, Ni 15%, Cr 15% 9.95 0.95 10 4 TII0%, In 30%, Al40%, Ga 10%, Fe 10% 10.10 0.5 10 5 TI 5%, Cd 90%, Cu 5% 4.95 0.40 5 6 Tll °(0, Fe 30%, As 10%, Se 10%, Te 10%, Cd 30%, Zn 9"k 1.02 0.35 1.0
(b) (Ore sample & alloy)* 1 Crookes, Te mineral 18.10 1.10 18.20 2 Hutchinsonite mineral 20.35 1.20 20.50 3 Marcasite mineral 0.9 1.10 0.85 4 Lorandite mineral 30.20 1.30 30.40 6 Urbaite mineral 25.62 0.95 25.80 7 Cassiterite ore 9.10 0.85 9.10 8 Aluminium alloy 0.05 0.40 0.05 Dubay, Dopbal factory. *Average of three weighed samples (0.5-1 g)/100 mL S, is the relative standard derivation n is the number of repetition of experiment
Effect of complexing agent (ligand) concentra• (ii) change of electrode surface and pH during tion- It has been found that the maximum effi• deposition which change metal over voltage. ciency of thallium metal and thallium oxide depo• sition occurred at certain concentration range of Analytical Application for Separation of ligand. For thallium (1lI)nitrate ten milligrams per Thallium litre of 111 and sodium thiosulphate were neces• A simple method for quantitative separation of sary. For the anodic deposition of thallium (1lI) thallium as a pure metal is based on masking all oxide from TI+, 20 mgIL of DMA and 50 mgIL interfering ions, which may be present with it in of glycerol were found to give maximum efficien• synthetic' alloys or natural ores by the strongest cy. complex-forming agents such as Na2EDTA and! Effect of temperature and time- Increasing the or CN- according to the cations present. Follow• bath temperature from 30 to 60°C favoured the ing this method thallium (I) was precipitated as deposition of metal or its oxide and led to the rise TIT (Ksp = 6.8 x 10-8) which was dissolved in in the recovery percentage (R%) from 60 to 80% aqua-regia. The resulting solution was subjected for TI+ (111 bath); 80-90-%for TP+ (SzO~- bath) to electrolysis conditions in order to obtain a and 57-72% for Tlz03 (glycerol bath). This was pure metal. attributed to the acceleranon of deposition, ionic It was found experimentally, using the proposed migration and fast evolution of Hz or Oz gases method that it was possible to separate TI from a adsorbed on the electrode surface. large number of samples containing; PbH, Cu2+, Also the effect of deposition time. was studied As3+, Fe3+,,, Se4+ Te6+ Sb3+ , Cd2+,,, Ag+ Zn2+ in the range 2-40 min. (Pt. electrode CD = 0.4 A In3+,Al3+,Ga3+, Nj2+,Co2+ and Cr3+. dm - z and T = 25°C). At time < 5 min a very thin The analytical results of deterniination of TP + film of cathodic or anodic deposit was obtained. in a series of synthetic samples and naturally oc• Increasiilg the deposition time led to a sharp in• curring ores containing thallium with another me• crease in recovery, R%, till ~ 10 min, then a tals are shown in Table 1. These results (average gradual rise of recovery, R%, was observed. This of two determinations for three different weighed may be due to: (i) decrease of metal ions concen• samples) are in good agreement with the value tration which causes a lower rate of deposition; obtained by the standard classical method 19. The I ,I
270 INDIAN 1.CHEM. TECHNOL., SEPTEMBER 1995 relative standard deviation as calculated by the 7 Toney M F, Gordon J G, Samant M G, Boryes G L, Mel• range method19, was found to be 0.35-1.30% roy 0 R, Yee P & Sorensen L B, Phy Rev B Condens Matter, 46(16) (1992) 9362. (AAS method). From the analytical result, it is 8 Bharathi S, Yengaraman V & Rao G P, Appl SUIt Sc~ clear that the preconcentration by electrodeposi• 47(3) (1991) 293. tion for thallium in ore alloys and synthetical 9 West T S, Complexometry with EDTA and related rea• samples are simple, reliable and can be applied gents, 3rd (BrogliaPress, London, UK),1969, 49. with good reproducibility. 10 Bassett J, Denney R C, Jeffery G H & Mendham J, Vog• el's text book of quantitative inorganic analysis, 4th ed Longman Sc.& Tech, London), Ed., 1986,482. 11 Kenawy I M M, Hafez M A H & Abd Elwanees S, Bull Acknowledgements Sco Chim France, 128(1991) 677. The authors would like to express their sincere 12 Goto H, Kakita Y & Ichinose N, Sci Rep Ritu, Japan, 20 gratitude to Mr M S EI-Din the Chief of Geolo• (2-3)(1968) 70. gia! Museum, Mansoura University for providing 13 Hafez M A H, Abdallah A M A & Wahdan T M A, Ana• us with all of the ores under investigation. lyst, 111(1986)663. 14 Milner G W C, The principles and application of polaro• graphy and other electroanalytical process, 5th ed (Long• mans, Green & Co. Ltd., London), 1966,261. References 15 Cullity B D, Element of X-ray diffraction, 2nd ed (Addis• 1 Kemper F H & Bertram, Met their compd environ merian on & WesleyPub., California), 1978, 140, 517. emest(VCH Pub., WeinheimGermany), 1991, 1227. 16 Richard R, Sample pretreatment and separation (Wiley & 2 Josimovic L R, Ruvarac I A, Jandovic I A & Javanovic S Sons,New York), 1987,60. V,J Serb Chem Soc, 56(5)(1991) 271. 17 Durent P J & Durrent B, Introduction to advanced inoT'• 3 Fouda A S, Indian J Techno~ 25 (1987) 498. gonic chemistry, 2nd ed' (Longman spp. Ltd, London), 4 Toney M F, Gorden J G & Melroy 0 R, Proc Spie Int 1970,595. Sac Opt, (1991) 1551. 18 Maron S H & Lando J B, Fundamentals of physical 5 TongY & Futak T E, Electrochim Acta, 36 (1991) 1873. chemistry (MacmillanPub, London), 1974,609. 6 Koos 0 A & Richnond G L, J Phys Chern, 96(6) (1992) 19 Miller J C & Miller J N, Statistics for analytical chemistry, 3770. 1st ed. (Ellis Horwood Ltd, New York), 1986,43,53.
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