An investigation of operating conditions on anodic oxidation of synthetic sulfide-containing wastewaters at the surface of a platinum electrode using cyclic voltammetry

Abstract

In this paper, cyclic voltammetry (CV) was used to study the effects of operating parameters (i.e., sulfide concentration, sodium chloride concentration as supporting electrolyte, temperature, mixing speed, and potential scan rate) on the anodic oxidation of synthetic sulfide-containing wastewaters at the surface of a platinum electrode. The results revealed that anodic oxidation could be used to eliminate sulfide from wastewaters in a wide concentration range, and the oxidation current was an ascending function of the sulfide concentration. The supporting electrolyte concentration had a negligible effect, as the sulfide dissociated in the aqueous media and brought electrical conductivity to the solution. The optimum concentration of electrolyte was found to be 0.05 mol/L. Increasing temperature improved the kinetics of the oxidation reactions and enhanced the electrical conductivity of the solution, which resulted in increasing the anodic oxidation rate. However, at higher temperatures, undesired side reactions were activated which resulted in lowering the power efficiency of the desired anodic oxidation reactions. The optimum operating temperature was found to be 40 – 60 °C. The mixing speed had a periodic effect on the sulfide oxidation. It decreased the diffusion resistance and also the residence time of sulfide at the electrode surface. These phenomena affected the anodic oxidation oppositely and hence, a middle value around 200 rpm was found to be the optimum. By increasing the potential scan rate, the time of performing the reactions in each cycle increased and the overall oxidation progress improved. It was found that mass transfer resistance was a limiting step in the overall reaction. Based on the findings, anodic oxidation has the potential for treating sulfide-containing wastewaters and in the future may be a competitor for conventional treatment processes.