In-Depth Study on the Effects of Impurity Ions in Saline Wastewater Electrolysis

Concentration followed by electrolysis is one of the most promising ways for saline wastewater treatment, since it could produce H-2, Cl-2,Cl- and an alkaline solution with deacidification potential. However, due to the diversity and difference of wastewater, knowledge on the suitable salt concentration for wastewater electrolysis and the effects of mixed ions are still lacking. In this work, electrolysis experiments of mixed saline water were conducted. The salt concentration for stable dechlorination was explored, with in-depth discussions on the effects of typical ions such as K+, Ca2+, Mg2+, and SO42-. Results showed that K+ had a positive effect on the H-2/Cl-2 production of saline wastewater through accelerating the mass transfer efficiency in the electrolyte. However, the existence of Ca2+ and Mg2+ had negative effects on the electrolysis performance by forming precipitates, which would adhere to the membrane, reduce the membrane permeability, occupy the active sites on the cathode surface, and also increase the transport resistance of the electrons in the electrolyte. Compared to Mg2+, the damaging effect of Ca2+ on the membrane was even worse. Additionally, the existence of SO42- reduced the current density of the salt solution by affecting the anodic reaction while having less of an effect on the membrane. Overall, Ca2+ & LE; 0.01 mol/L, Mg2+ & LE; 0.1 mol/L and SO42- & LE; 0.01 mol/L were allowable to ensure the continuous and stable dechlorination electrolysis of saline wastewater.

Automated summary

Concentration followed by electrolysis is a promising method for treating saline wastewater, producing H-2, Cl-2, Cl- and an alkaline solution. However, knowledge on suitable salt concentration and effects of mixed ions remains lacking. In this study, electrolysis experiments were conducted on mixed saline water, exploring stable dechlorination salt concentrations and discussing the effects of K+, Ca2+, Mg2+, and SO42-. Results showed K+ had a positive effect on H-2/Cl-2 production, while Ca2+ and Mg2+ had negative effects due to precipitate formation, and SO42- reduced current density. Ca2+ ≤ 0.01 mol/L, Mg2+ ≤ 0.1 mol/L, and SO42- ≤ 0.01 mol/L were found to ensure continuous and stable dechlorination electrolysis of saline wastewater.