Silver sulfide leaching with thiosulfate in the presence of additives Part I: Copper–ammonia leaching

Thiosulfate is a promising alternative for the hydrometallurgical treatment of silver sulfide ores. In this study, the copper–ammonia catalyzed thiosulfate leaching of a silver sulfide rotating disk is investigated. The leaching of silver sulfide by a copper–ammonia thiosulfate solution occurs either by the substitution of cupric or cuprous for silver. The cupric reaction is favored due to a thermodynamic barrier to the cuprous reaction. At 1mM copper, there is evidence of partial chemical control for copper–ammonia leaching with a maximum silver dissolution rate achieved when cupric is stabilized in solution with ammonia and for solutions with high thiosulfate availability. The addition of ethylenediaminetetraacetic acid decreased the leaching rate of the silver sulfide disk due to decreased cupric reactivity, although this comes with the benefit of increased cupric stability. •Copper–ammonia catalyzed thiosulfate leaching of silver sulfide is by substitution of cupric or cuprous for silver.•The cupric reaction is favored over cuprous reaction due to a thermodynamic barrier, even though Cu2S and Ag2S have similar structures.•Copper–ammonia leaching with low copper concentrations (1mM) leaches silver most rapidly for stable cupric–ammonia complexes with high thiosulfate availability.