Optimization of cyanide detoxification in gold mine tailings using sodium percarbonate

Abstract

Wastewater containing cyanide, produced during gold extraction operations, poses a significant environmental threat and requires detoxification procedures that comply with rigorous regulatory standards, including those set by the International Cyanide Management Code (ICMI). Sodium percarbonate was evaluated as an oxidizing agent for the treatment of hydrometallurgical tailings contaminated with cyanide, which is formed at the Altyntau Kokshetau enterprise in Kazakhstan. The operating conditions were optimized using the response surface methodology based on the central composite design (CCD). In experiments carried out at room temperature, pH, oxidizer dose and reaction time were identified as the main factors. The composition of the waste and the transformation of cyanide were monitored using ICP-OES, FTIR spectroscopy, and spectrophotometric quantification of residual cyanide. Treatment with sodium percarbonate reduced the cyanide concentration to below the ICMI limit of 0.2 mg/L and obeyed the biphasic pseudo-first-order kinetics. Of the parameters investigated, pH exhibited the most pronounced influence; it further modulates radical stability and governs the equilibrium between HCN and CN^-. The aggregate findings demonstrate that sodium percarbonate constitutes a scalable, environmentally benign alternative to conventional methods for cyanide detoxification in gold-mining effluents.