Electrochemical activation of periodate with graphite electrodes for degradation of high concentrations of thiocyanogen (SCN−) in mineral processing tail liquid

Abstract

Cyanide has been widely used in gold extraction due to its cost-effectiveness, high selectivity and recovery. Regrettably, its wide application also leads to the presence of a large amount of thiocyanogen (SCN⁻) in the tail liquid of mineral processing plants, which affects the quality of the effluent water, and thus poses a threat to the ecological environment and human health. This paper investigates the degradation of high concentration of SCN⁻ in water using electrochemical oxidation/periodate (E-GP/PI) system. A degradation rate of 90.25 % of SCN⁻ was achieved by optimising various operating parameters. The effects of organic matter and typical heavy metal ion concentrations on the degradation of SCN⁻ were investigated, and it was found that Cu²⁺ was able to promote the degradation of SCN⁻ through the formation of stable complexes with SCN⁻, which enhanced the degradation rate to 96.48 %. However, the presence of Octadecyltrimethylammonium bromide (OTAB) and butylxanthin hindered the degradation process, where 500 mg/L of OTAB reduced the degradation rate of SCN⁻ to 80.88 %, while 100 mg/L of butylxanthin reduced the degradation rate to 78.66 %. On this basis, experiments were carried out using real wastewater samples and SCN⁻ degradation efficiencies of about 90 % were obtained. Afterwards, through electron paramagnetic resonance analysis, free radical burst, ion chromatograph and other research techniques, IO₃ and O₂^– were obtained as the main drivers of SCN⁻ degradation and SCN⁻ degradation pathways were elucidated. Finally, the E-GP/PI system was shown to be effective in reducing the ecotoxicity of SCN⁻ by increasing the 24-h LC₅₀ from 12.5 % to 48.5 % in a toxicity test with daphnia. This study provides a new idea for the green and efficient treatment of SCN⁻ rich beneficiation tail liquid.