Removal of Cl(−I) from acidic industrial wastewater through oxidation: a review on methods and mechanisms

Abstract

An abundance of acidic wastewater containing high concentrations of Cl(−I) is produced annually in industries. The traditional precipitation, ion exchange and physical separation methods for Cl(−I) removal possess the major limitation of low efficiency, making it necessary to develop new approaches with high efficiency. Recently, the technology of advanced oxidation process (AOPs) and ligand-to-metal charge transfer process (LMCT) has attracted considerable attention for the oxidation removal of Cl(−I), where the various intermediate active species with extremely high oxidability exhibit the ability to oxidize Cl(−I). In this article, the efficiency, mechanisms, advantages, limitations, developmental trends and potential improvements of the electrolysis, UV-induced and strong-oxidant-dominated oxidation approaches for Cl(−I) removal are reviewed in detail. The oxidation approaches exhibit the common advantage of high efficiency. However, the potential secondary pollution of Cl₂ gas and the high requirement for wastewater quality limit the actual application. Before the electrolysis and UV-induced oxidation methods can be applied, the energy consumption must be further reduced. Additionally, the slow release and stability of the Na₂S₂O₈, NaBiO₃ and PbO₂ agents should be further studied in the strong-oxidant-dominated oxidation approaches. This study provides the effective removal of Cl(−I) from acidic industrial wastewater with the theoretical foundation and technical support.