Enhanced natural degradation of cyanide tailings: Integrated application of solar drying system and UV irradiation.

Cyanide tailings are the bulk solid waste generated by the production processes of gold mines. Since the highly toxicity of cyanide affects its disposal and comprehensive utilization, a decyanation treatment is needed. However, wide-ranging industrial uses of the current decyanation methods are restricted due to the treatment effects and costs. Based on the natural degradation method, the cyanide treatment effect was enhanced by raising the treatment temperature, increasing the ultraviolet (UV) irradiation and turning the pile periodically. Using the Arrhenius equation, the activation energies of the cyanide hydrolysis reactions were calculated as 52.22 kJ/mol and 34.59 kJ/mol for heating alone and for heating combined with UV irradiation, respectively. At 60 ℃, the cyanide tailings reached the discharge standard (leachate, total cyanide (CNt)< 5 mg/L) after 8 h of treatment. Moreover, after adding UV irradiation (with an intensity of 120 μW/cm) and a hydrogen peroxide spray (spraying intensity, 2 mL/kg) to the above conditions and shortening the treatment time to 7 h, the cyanide tailings reached the standard for use in building materials (leachate, CN <0.5 mg/L). Based on these results, UV irradiation, ventilation, spraying and pile-turning were integrated into the solar drying room to form an enhanced natural degradation system, which was applied in the semi-industrial scale treatment of the cyanide tailings. The results showed that the cyanide tailings consistently met the standards for discharge and use in building materials, successfully verified the conditions and effects of the laboratory treatment, and reduced the treatment cost by more than 50 %.