Electrochemical oxidation degradation of xanthate and its mechanism: Effects of carbon chain length and electrolyte type

There are a lot of residual flotation reagents such as xanthate remaining in the mineral processing wastewater, which must be deeply removed for recycling or discharge. However, there are few studies using electrochemical oxidation to remove xanthate. This article employs the electrochemical oxidation method to treat simulated xanthate-containing wastewater, which investigates the mechanisms involved in removing four xanthate homologues under different electrolyte conditions. Results show that under 1 g/L of Na2SO4, current density of 40 mA/cm2, initial pH of 7.0, and initial concentration of xanthates 1 mM, four alkyl xanthates can be completely removed within 60 min. The COD removal and TOC removal can reach 71.42%–88.61% and 54.23%–81.50%, respectively. By contrast, NaCl electrolyte is more favorable for xanthate degradation. The generated SO42− concentration can reach 145.4 mg/L at 60min, resulting in the sulfur mineralization ratio (ηs) of 75.72%. Regardless of the electrolyte type, as the carbon chain length increases, the xanthate degradation rate accelerates, accompanied by higher COD and TOC removal. The results of UV–vis spectra and LC–MS indicate that intermediate substances such as xanthate peroxides and alcohols are first formed in the process, ultimately leading to the complete mineralization of small molecule substances such as SO42−, CO2, and H2O. The fate of S and Cl elements confirms it. EPR and probe fluorescence spectroscopy results indicate that in Na2SO4 electrolyte, the main active substances are ·OH and a small amount of SO4∙–. Additionally, the production of ·OH increases as the electrolysis time is prolonged. In NaCl electrolyte, ·OH undergoes a series of reactions with Cl− to convert into Cl∙ and active chlorine, which constitute the primary reactive oxygen species.