Thiourea solution

Crystals of [Tc(tu)6]Cl3 or [TcCl(tu)5]Cl2 are often employed for the synthesis of technetium(III) complexes. However, since the direct reduction of pertechnetate with excess thiourea in a hydrochloric acid solution yields [Tc(tu)6]3+ in high yield [37], direct use of the aqueous solution of the thiourea complex would be preferable for the synthesis of the technetium(III) complex without isolation of the crystals of the thiourea complex. In fact, technetium could be extracted from the aqueous solution of the Tc-thiourea complex with acetylacetone-benzene solution in two steps [38]. More than 95% extraction of technetium was attained using the following procedure [39] First a pertechnetate solution was added to a 0.5 M thiourea solution in 1 M hydrochloric acid. The solution turned red-orange as the Tc(III)-thiourea complex formed. Next, a benzene solution containing a suitable concentration of acetylacetone was added. After the mixture was shaken for a sufficient time (preliminary extraction), the pH of the aqueous phase was adjusted to 4.3 and the aqueous solution was shaken with a freshly prepared acetylacetonebenzene solution (main extraction). The extraction behavior of the technetium complex is shown in Fig. 6. The chemical species extracted into the organic phase seemed to differ from tris(acetylacetonato)technetium(III). Kinetic analysis of the two step extraction mechanism showed that the formation of 4,6-dimethylpyrimidine-... 

The development of more benign alternatives to cyanide for gold-leaching (see Section 9.17.3.1) such as thiourea, thiocyanate, or thiosulfate, which form stable complexes in water has prompted research to identify suitable solvent extractants from these media. Cyanex 301, 302, 272, Ionquest 801, LIX 26, MEHPA, DEHPA, Alamine 300 (Table 5) have been evaluated as extractants for gold or silver from acidic thiourea solutions.347 Whilst the efficacy of Cyanex 301 and 302 was unaffected by the presence of thiourea in the aqueous feed, the loading of the other extractants is severely depressed. Formation of solvated complexes of gold and of an inner-sphere complex of silver has been proposed.347... 

Urbanski, T. S. Fornari, P. Abbruzzese, C. Gold electrowinning from aqueous-alcoholic thiourea solutions. Hydrometallurgy 2000, 55, 137-152. 

Orgul, S. Atalay, U. Reaction chemistry of gold leaching in thiourea solution for a Turkish gold ore. Hydrometallurgy 2002, 67, 71-77. 

Gonen, N. Leaching of finely disseminated gold ore with cyanide and thiourea solutions. Hydrometallurgy 2003,69,169-176. 

Dzul Erosa, M. S. Mendoza, R. N. Medina, T. I. S. Lavine, G. L. Avila-Rodriguez, M. Recovery of Ag and Au from Aqueous Thiourea solutions by liquid-liquid extraction. International Solvent Extraction Conference, Cape Town, South Africa, Mar. 17-21, 2002, 902-907. 

Porous silicon is under extensive study, largely due to its luminescence properties. For electroluminescence, however, some form of contact has to be made with the Si, and this necessitates deposition of another phase inside the pores of the Si in order to contact as much as possible of the internal area of the high-surface-area Si. With this in mind, CdS has been deposited inside the pores of porous silicon via a two-stage method [73]. Cd(OH)2 was deposited from an ammoniacal bath at pH 8, followed by conversion of the Cd(OH)2 to CdS by treatment with thioac-etamide at pH 8. This was repeated several times until the pores were essentially filled with CdS. The reason that this two-stage process was needed is that either the Si was unstable at the temperatures and pH values needed to deposit CdS from a thiourea solution, or CdS was formed in solution rather than on the Si surface using thioacetamide. 

There have been a few reports on epitaxial deposition of PbS on various singlecrystal substrates. PbS (n-type) was epitaxially deposited on (111) Ge (5.4% mismatch) from a Pb(N03)2/KOH/thiourea solution at room temperature with (111) orientation [34] (although another study using apparently the same conditions found the deposit to be p-type and polycrystalline with some (100) preferred orientation [35]). From a similar solution (with addition of some ethanol), PbS was deposited on single-crystal CdS (ca. 6.6% mismatch) with varying degrees of epitaxy [36]. On the (0001) faces of CdS, the growth was (111) [(111) cubic corre-... 

Tetrakis[thiourea]tellurium Dithiocyanate6 3.0 g (7.6 mmol) of bis[thiourea]tellurium dithiocyanate are dissolved in 75 ml of 10% aqueous thiourea solution at 40°. The solution is filtered, the filtrate is kept at 20° overnight, and the deposited crystals are collected yield 3.4 g (72%). 

It is also soluble in acid solutions containing thiourea, which stabilizes Cu1 as a complex acid thiourea solutions are also used to dissolve copper deposits in boilers. 

Van Deventer, J.S.J., Reuter, M.A., Lorenzen, L. Hoff, P.J. (1990). Galvanic interactions during the leaching of gold in cyanide and thiourea solutions. Minerals Engineering, 3(6), 589-597. 

When the dissolution and recovery are done using acidic thiourea solutions, the cathodic reaction is the reduction of gold-thiourea complex (34)... 

C. M. Juarez, A. J. B. Dutra, An investigation on gold electrowinniig from acidic thiourea solutions in Aqueous Electrotechnologies Progress in Theory and Practice, (Ed. D. B. Dreisinger), TMS, Orlando, 1997, pp. 231-245. 

Note. Small amounts of copper in the sample should be masked with 1-2 ml of 5% thiourea solution before addition of the a-furildioxime. 

The ion-by-ion process has been analysed from in situ QCM measurements for the deposition of CdS from ammonia-thiourea solutions, using the measurement of initial growth rates over a wide range of experimental conditions [34]. A general mechanism has been derived for the deposition of a binary compound MX ... 

This atom-by-atom growth mechanism fits experimental results very well for CdS deposition from QCM investigations in ammonia-thiourea solutions, as shown in figure 13. The rate constants take into account the equilibrium composition of the bath with respect to the concentration of the various cadmium complexes with hydroxide ions and ammonia (see section 3). 

With the temperature increase in the range 298-333K, there is observed the increase in Au(III) ions sorption compared to that of Pd(II) ions. The sodium nitrate(III) and thiourea solutions were used as eluents. Sodium nitrate(III) (2 M, pH 4.7) desorbs 75% of Pd(II) practically not washing out Au(III) from the ion exchanger, whereas thiourea (0.5 M, [H ] 0.1 M) enables almost quantitative recovery of gold(III) containing trace amounts of palladium (II) ions. 

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