Photoelectrocatalytic Treatment and Resource Utilization of Industrial Waste Salt for Chlor-Alkali Electrolysis

Abstract Pesticides, fine chemicals and many other chemical industries usually produce a large amount of waste solid salt which is detrimental to the environment when treated by burning and rigid landfill. In contrast to traditional disposal strategies, resource utilization of waste salt is beneficial for both the environment and economy. However, the current technique for the resource utilization of waste salt, such as nanofiltration, is high-cost and hard to popularize. In this study, the photoelectrocatalytic treatment of waste salt obtained from the glyphosate industry and its utilization as a raw material for chlor-alkali electrolysis are proved feasible. The waste salt consists mainly of NaCl, with ~1.31 wt% of organic impurities. By virtue of photoelectrocatalytic treatment with a TiO2 nanotube electrode, the percentage of the total organic carbon (PTOC) of the waste salt, which was prepared into the brine, can be reduced to 5*10⁻4, with a removal ratio of 85%, and it is able to meet the standard of refined brine in the chlor-alkali industry (PTOC<2*10⁻4) after further treatment. A study on the photoelectrocatalytic mechanism reveals that the main oxidative substances contributing to the degradation are holes (h⁺) and chlorine active substances other than Cl· under the condition of high Cl⁻ concentration. The organic impurities in the waste salt are poisonous to both the electrode and membrane in the process of chlor-alkali electrolysis, leading to an increase in the voltage. With photoelectrocatalytic treatment, most of the organic impurities can be removed so that the waste salt can be utilized as a raw material for chlor-alkali electrolysis.