Gold and Silver Cyanidation from a Residue Produced by Leaching Dead-Roasted Copper White Metal

Abstract

The present work discusses the gold and silver recovery by cyanidation from a solid leach residue produced by a new alternative of processing copper matte or white metal. The leach residue contains mainly hematite, cupric ferrite, insolubles and precious metals. By cyanide leaching this residue, over 95% of gold can be extracted with solutions containing 0.06 g/L of KCN at 45°C in 24 hours, while silver extraction was less than 2.5% for the same conditions. Significant amounts of silver (45%) can be extracted only under a strong KCN concentration of 1.2 g/L.Cyanidation temperature affects the gold and silver dissolution. An increase in temperature increases the gold dissolution, while the opposite effect was found for silver. The low silver dissolution appears to be the result of the roasting step of the copper white metal. Although no direct evidence of a silver-iron ferrite or silver-copper double oxide was found in the residue, results indicate that metallic silver dissolves in the ferrite both by intergranular diffusion and Fick's diffusion, with a diffusion coefficient of 5 × 10-4 sq.cm2/s at 800°C.