,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. "'H!'II! "I I , I' "'''1'1'1' "I' r I" "lrl'""1 '''II "1"1'" I 1 '1'1'1' """ KENAWY et at.: ELECTROLYTIC PRODUcnON OF THALliUM METAL 267 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.