Study on mechanism of gold leaching by thiourea in the presence of sodium sulphite

Abstract

The linear potential sweep voltammetry and electrochemical methods were used to study the mechanism and kinetics of gold dissolution in thiourea solution in the absence and presence of sodium sulphite. The results show that in the absence of sodium sulfite the dissolution rate of gold in thiourea solution is relatively slow and it increases with the increase of the concentration of thiourea and decreases with pH. Thiourea is easily oxidized to formamidine disulphide, which reduces the leaching efficiency and increases reagent consumption. In the presence of sodium sulphite, the effective concentration of thiourea is increased and the dissolution rate of gold in thiourea solution is greatly increased. The activation energy required for gold dissolution in thiourea solution with sodium sulphite is 20.9 kJ·mol⁻¹ in the absence of sodium sulphite. It is evident that sodium sulphite has a significant effect on the electrochemical reaction kinetics of gold in thiourea solution.

Keywords

gold leaching / thiourea / sodium sulphite / mechanism

References

[1] MacArthur J S, Forrest R W, Forrest W. Processing for obtaining gold and silver from ores[P]. US Patent, 403, 1889. 202.

[2] LanghansJ W, LeiK P V, CarnahanT G. Copper-catalyzed thiosulfate leaching of low grade gold ores[J]. Hydrometallurgy, 1992, 29: 191-191

[3] ZipperianD, RaghavanS, WilsonJ P. Gold and silver extraction by ammonium thiosulfate leaching from a rhyolite ore[J]. Hydrometallurgy, 1988, 19: 361-361

[4] JiangTao, XuShi, ChenJin. Techology and mechanism of catalytic leaching gold with thiosulphate at ambient temperature[J]. J CSIMM, 1991, 22(Suppl.): 96-104

[5] GroenewaldT. The dissolution of gold in acidic solution thiourea[J]. Hydrometallurgy, 1976, 1: 277-277

[6] SchulzeR G. New aspects in thiourea leaching of precious metals[J]. Journal of Metalls, 1984, 36(6): 62-62

[7] LI J, Miller J D. Thiourea decomposition by ferric sulfate oxidation in gold-leaching system[A]. Presentation at the SME Annual Meeting[C]. Denver, Colorado, 1997.

[8] Gabra G. A kinetics study of leaching of gold from pyrite concentrate using acidified thiourea[A]. Kudrk V, Corrigan D A, Liang W W. Precious Metals: Mining, Extractive and Processing[C]. 1984. 145–172.

[9] XiaoGuan-qiang. A study of reactivity of gold leaching by thiourea[J]. Gold, 1988, 6: 4-4

[10] PutnamG L. Chlorine as a solvent in gold Hydrometallury[J]. Engng Min J, 1944, 145(3): 70-70

[11] DadgarA. Refactory concentrate gold loading: Cyanide vs. bromine[J]. Journal of metals, 1989, 41(12): 37-37

[12] QiP H, HiskeyJ B. Electrochemical behavior of gold in iodine solution[J]. Hydrometallurgy, 1993, 33: 161-161

[13] Barbosa-Filho O, Monhemius A J. Leaching of gold in thiocyanate solutions-Part 1: Chemistry and thermodynamics[J]. Trans Inst Min Metall(Sect. C: Mineral Process Extr Metall), 1994, 103.

[14] FangZ H, MuhammedM. Leaching of precious metals from complex sulphide ores on the chemistry of gold lixiviation by thiourea[J]. Mineral Processing and Extractive Metallurgy Review, 1992, 11: 39-60

[15] SunCi-xiResearch method of corrosion electrochemistry (in Chinese) [M], 1988, Beijing, Chemical Industry Press: 13-13