Evaluation of the Parameters Effective in the Removal of Cyanide Ions of the Wastewater of Agh-Darreh Gold Processing by Hydrogen Peroxide Method

In the Agh-Darreh gold mine in Iran, the gold is extracted using the cyanidation process. The mine's output wastewater includes ۸۰-ppm free cyanide ion, which is very dangerous environmentally, so the cyanide concentration should be lowered to the allowable limit. Therefore, in this research, the hydrogen peroxide was used to remove the free cyanide ion. In this method, the oxidation changes the cyanide ion into cyanate ion, which is ۱۰۰۰ times less toxic. For this purpose, a test plan was used to model and optimize the parameters effective in the cyanide removal, including time, hydrogen peroxide concentration, pH, and copper (II) sulfate concentration. The results indicated that the increases in the hydrogen peroxide and copper (II) sulfate concentrations had the highest effect in removing the free cyanide ion, respectively. Increasing the pH to ۹.۵ had a positive effect on removing cyanide ion, while the pHs more than ۹.۵ had an adverse effect. Finally, the optimum condition was obtained with a period of ۲۵ minutes, the hydrogen peroxide concentration of ۱.۶ gr/L, pH of ۹.۱۴, and copper (II) sulfate concentration of ۴۶.۹۷ mg/L resulting in the removal of free cyanide ion by almost ۹۴%