Precipitate gold from gold thiosulfate1/20/2024 Dissolution rates of gold and silver in thiosulfate are comparable to those for thiourea and faster than cyanide. It is also used as fertilizer and from an environmental standpoint, has a definite advantage over cyanide. Ammoniacal Thiosulfate LeachingĪmmonium thiosulfate has been used in photography for many decades. However, acid pre-leaching of soluble copper was required in order to reduce thiourea consumption to acceptable levels. Thiourea leaching from an oxidized gold-copper ore with 90-95% gold extraction was also reported (McInnes et al., 1989). This option, however, is likely to be limited because of acid consuming gangue and neutralization costs preceding cyanidation (Dorr and Bosqui, 1950). It has been concluded that cyanide consumption can be reduced by ammonia addition however, copper dissolution increases and gold recovery decreases as the ammonia to cyanide ratio increases.Īnother option is the removal of oxidized copper minerals by acid leaching, and gold recovery by subsequent cyanidation. Treatment options for such ores have recently been reviewed and the chemistry of leaching with CN-/NH3 and CN-/CO3²- mixtures have also been discussed in detail (Muir et al. These types of ores are not readily amenable to flotation concentration and are highly soluble in ammonia and alkaline cyanide solutions as well as acidic lixiviants (Hedley and Tabachnik, 1968, Shantz and Reich, 1978). Major processing difficulties arise with oxidized or transition type ores where copper sulfides are partially or wholly oxidized. Gold remaining in copper tailings can be recovered by conventional cyanidation. This association often allows a high grade copper-gold concentrate to be produced which is usually shipped to a smelter. Unlike gold associated with pyrite and arsenopyrite in refractory ores, the gold particles in many chalcopyrite ores are often discrete, allowing a significant portion of gold to be liberated by fine grinding (Gasparrini, 1983). Gold is commonly associated with chalcopyrite association with tetrahedrite, tennantite, as well as bornite and chalcocite also occurs. Thiosulfate leaching of manganiferrous (Zipperian et al., 1988, Kerley, 1981), carbonaceous (Hemmati et al., 1989), and low grade ores (Langhans et al., 1992), and high grade copper concentrates (Changling et al., 1992) were also reported recently. Gold dissolution was strongly affected by temperature, copper and thiosulfate concentrations, and oxygen partial pressures or on the degree of copper oxidation. Studies on the ammonium thiosulfate extraction of gold and silver from sulfide concentrates and various (ammoniacal) pressure leach residues (Berezowsky and Sefton, 1979), and dissolution of pure gold under pressure oxidation conditions in ammonium thiosulfate solutions (Tozawa et al., 1981), have shown that the chemistry of these systems is quite complex. The leaching chemistry of this process was recently investigated in great detail (Flett et al. It was also recognized that unreacted silver sulfide could be leached when copper sulfate was added to thiosulfate solutions (Russell, 1885). In the Patera process, which was used for silver recovery for many years (Lidell 1945), silver was extracted from silver chloride by sodium thiosulfate leaching of chloridizing-roasted ores and concentrates. Thiosulfate leaching of gold and silver has been known since 1858. Oxidized copper minerals, as well as chalcocite and bornite, dissolve in cyanide solutions, and in many cases, recovery of gold from fouled solutions becomes very difficult, if not impossible. pyrrhotite, stibnite, etc.) present major challenges in processing these ore-types. The treatment of refractory ores and presence of cyanicides (e.g. In addition to environmental considerations, several factors have influenced the search for alternative lixiviants for gold.Ī major drawback of the cyanidation process lies in its inherently slow kinetics. However, considerable interest has been expressed in non-cyanide lixiviants since the early 1980’s. It is cost-effective and achieves excellent extractions from a wide range of ores. Cyanide has been used in the mining industry for gold and silver recovery for almost a century.
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