Copper Elimination in Cyanidation Effluents

"Cyanidation is the most used method to recover gold and silver from their ores. In this process, other metals besides gold and silver may sometimes dissolve and interfere with the efficiency of extraction. Copper is one of those metals, reaching concentrations as high as 1000 mg/L in some cyanidation plants, making difficult the extraction and purification processes, and increasing the operating costs.This preliminary work was intended to study the feasibility of using amines to form a precipitate and to eliminate copper from a synthetic solution containing high copper and cyanide concentrations, as is the case of some cyanidation effluents. The solid formed is removed from the solution using conventional filtration techniques. Seven amines were evaluated at different pH values and amine additions. Up to 90% of copper present may be removed at the natural pH of the effluent (alkaline). The remaining copper would permit to recycle the solution back to the cyanidation process. IntroductionCopper is generally considered the most problematic metal in gold leaching due to the rapid formation of copper cyanide complexes when some readily-soluble minerals are processed (e.g., azurite, malaquite, cuprite, chalcocite and bornite). The copper solubilization as cuprous cyanide complexes leads to a significant economic penalty in terms of excessive cyanide consumption and high cost for cyanide elimination. When activated carbon is used to recover gold and silver, the copper-cyanide complexes decrease the efficiency of the process because of the competition of the cuprocyanides with the aurocyanide for the adsorptive sites on the activated carbon (Rees and Deventer, 1999).Several techniques have been developed to attempt to overcome the problems caused by the copper presence in cyanidation solutions, notably: acidification-volatilization-regeneration (AVR), ion exchange-electrolysis or solvent extraction-electrowinning (Lu et al., 2002). In this work the use of some amines is proposed to remove the copper-cyanide complexes by precipitation of a copper-cyanide-amine solid. The process was evaluated for different amine additions and pH values, using copper-cyanide synthetic solutions of composition similar to that presented by some cyanidation plants with high copper."