Silver sulfide leaching with thiosulfate in the presence of additives Part II: Ferric complexes and the application to silver sulfide ore

Ferric complex alternatives to the cupric–ammonia catalyzed thiosulfate system including ferric–EDTA, ferric–oxalate and ferric–citrate were studied with a silver sulfide rotating disk. Of these complexes, ferric–EDTA and ferric–oxalate were the most promising alternatives. All ferric complexes tested were unreactive towards thiosulfate, but are reduced by sulfides present in the ore. When leaching a silver sulfide ore, the most effective lixiviants were ferric–EDTA and the cupric–ammonia thiosulfate systems. None of the thiosulfate alternatives were able to recover as much silver as cyanide leaching, likely due to the presence of other silver minerals which may not be amenable to thiosulfate leaching. Although less silver was recovered, less than 1% of mercury in the ore was leached by thiosulfate complexes compared to 50% mercury recovery by cyanide.