The present status of the raw material base in the gold industry requires specific ways to recover gold and silver from ores. Most gold is closely associated with sulfides which require flotation followed by pressure or bacterial oxidation. The next stages of processing usually require using expensive operations for the preparation of leaching._x000D_
A lot of researchers want to find a new alternative solvent for the extraction of precious metals from these products. According to the authors, one of the best ways is to use sulfur-based solvents (thiosulfate, sulfite, and their various mixtures)._x000D_
Thermodynamics of gold and silver thiosulfate dilution are calculated for conditions: the concentration of Au - 200 mg/L, oxygen - 3.2 mg/L, thiosulfate - 79 mg/L, OH- - 170 mg/L. the general result is the possibility of process remains under standard conditions._x000D_
(rAu = = 0.035 V, G298 = - 29.18 kJ/g-atom )._x000D_
Silver with thiosulfate forms two strong complexes: [AgS203]- and [Ag(S203)2]3-._x000D_
G0 = -1027 kJ/mol. The complex [AgS203]- is less stable: G0 = 486 kJ/mol._x000D_
It should be noted that despite the high stability of gold complexes, the sodium thiosulfate may decompose to sulfite and elemental sulfur during the process, especially when heating. Gold is slightly soluble in the sodium sulfite solution, however it forms the strong complex [Au(SO3)2]3-._x000D_
Depending on the concentration of free S2O32-ions, silver with sodium sulfite forms three complexes: [AgSO3]-, [Ag(SO3)2]3- and [Ag(SO3)3]5-._x000D_
The dissolution speed of gold in sodium sulfite solution may be in the same range as it is during cyanidation. In this case, a practical application of sulfite process can be also used, especially for the products containing free elemental sulfur._x000D_
In conclusion, sulfite-thiosulfate gold lixiviants can be used for concentrates after pressure oxidation of the cakes._x000D_
CITATION:Gudkov, A, Zhuchkov, I and Mineev, G, 2010. Thermodynamics of non-cyanide gold solvents, in Proceedings XXV International Mineral Processing Congress (IMPC) 2010, pp 319-324 (The Australasian Institute of Mining and Metallurgy: Melbourne).