Removal of copper cyanide by precipitate flotation with ammonium salts

Cyanidation is the most commonly used method for leaching and recovering Au and Ag from ores. In the process, some copper species may dissolve and react with cyanide to form cyanide-copper complexes in a cyanide solution. Waste cyanide solutions must be treated to reduce their cyanide concentrations before they may be safely discharged into tailing storage facilities. In this preliminary work, precipitate flotation techniques were used to remove cyanide-copper complexes from synthetic solutions similar to those found in gold cyanidation plants. Cetyltrimethylammonium bromide (CTAB) and octadecyltrimethylammonium bromide (OTAB) were both employed as precipitants and frothers. Multiple parameters, including reaction time, bubbling time, pH, and surfactant dosage, were investigated. The results show that it is possible to remove up to 84.51% of the cyanide and 81.62% of the copper with a 7.60% water loss when adding 3.75 mg/mg Cu CTAB at a pH of 6. While further decreasing the pH may increase removal efficiencies, the contribution of hydrogen cyanide (HCN) volatilization and stripping will also be greatly increased. Tests performed with an industrial solution corroborated the results obtained using synthetic solutions. This study reveals that precipitation flotation can be used in the gold mining industry as a treatment for cyanidation solutions with high cyanide concentrations discharged into tailings facilities. (C) 2019 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.