Comparative study of auxiliary oxidants in cyanidation of silver sulfide

• Conventional cyanide leaching of synthetic acanthite is inefficient.
• The addition of H2O2 and CaO2 increase silver recovery from synthetic acanthite.
• LeachWELL™ has superior performance than peroxides for synthetic acanthite.
• Lead nitrate is an efficient and powerful additive in acanthite cyanide leaching.

Lower extraction of silver than gold in conventional cyanidation process has been commonly observed in practice. Acanthite (Ag2S) is one of the typical silver minerals with low solubility in aqueous cyanide medium, which contributes to low overall silver extraction. The performance of different auxiliary oxidants, including hydrogen peroxide (H2O2), calcium peroxide (CaO2), and LeachWELL™, in cyanidation of synthetic silver sulfide has been investigated with the purpose of increasing the rate and extent of silver extraction. The addition of H2O2 does not only promote cyanidation of silver sulfide, but also increases the consumption of cyanide and hydroxide. Comparatively, the addition of CaO2 exhibits less impact on silver extraction under the experimental conditions. LeachWELL™ has a better performance than H2O2 and CaO2 in terms of increasing silver extraction and reducing cyanide and alkaline consumptions. The slurry pH exhibits insignificant effect on the performance of LeachWELL™ during leaching of silver sulfide. Similar performance of LeachWELL™ and lead nitrate on cyanidation of silver sulfide indicates that Pb(NO3)2 acts as the main active component in cyanidation process. Leaching of natural lead-bearing acanthite sample without auxiliary oxidant results in higher silver extraction compared to leaching of synthetic Ag2S. Addition of H2O2 or CaO2 during leaching of lead-bearing acanthite can promote silver extraction while the addition of LeachWELL™ exhibits little effect.