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 to be feasible. The waste salt consists mainly of NaCl, with ~ 1.31 wt% of organic impurities. A TiO2 nanotube electrode was employed for the photoelectrocatalytic treatment of brine with NaCl concentration of 270 g L−1 prepared from waste salt. After preliminary treatment, the total organic carbon content (TOC) of the waste salt brine was reduced to 50 mg L−1, with a removal ratio of 85%. It is able to meet the standard of refined brine in the chlor-alkali industry (TOC < 20 mg L−1) with further treatment. A study on the photoelectrocatalytic mechanism reveals that the main oxidative species 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.