Synergistic removal of organics from semi-coke wastewater by persulfate and cyanide tailings

Abstract

In this study, the persulfate and cyanide tailings (PS-CTs) were used for the synergistic treatment of semi-coke wastewater to achieve advanced oxidation and in-situ coagulation removal of organics in semi-coke wastewater. The effects of persulfate concentration, reaction temperature, cyanide tailing concentration and initial pH on chemical oxygen demand (COD) removal efficiency were investigated, and the synergistic mechanism in the treatment process was further explored. The results showed that the removal efficiency of COD in semi-coke wastewater was 94.49 % under the conditions of persulfate concentration 0.025 mol/L, reaction temperature 60 °C, cyanide tailings concentration 5 g/L, the initial pH value of 3. The results of the mechanistic analysis showed that in PS-CTs system, pyrite was oxidized by persulfate. The dissolved Fe2+ activated the persulfate to produce SO4− and OH and generated Fe3+ in situ. The hydrolysis of Fe3+ produced a series of complex ions and amorphous iron hydroxides, which could remove some organics by adsorption and sweeping netting. The organics in semi-coke wastewater were effectively removed by the combined effect of oxidation and coagulation. In addition, the PS-CTs system also achieved the oxidative de-cyanidation of cyanide tailings simultaneously, and the total cyanide concentration of treated cyanide tailings was 8.21 mg/kg, and the leaching cyanide concentration was 0.12 mg/L, which was in line with the emission standards. This process implemented the concept of “treating waste with waste”, and provided theoretical support for the treatment of semi-coke wastewater and other organic wastewater.