Recent advances on decomplexation mechanisms of heavy metal complexes in persulfate-based advanced oxidation processes

In some industrial wastewater, heavy metals combine with organic complexing agents to form heavy metal complexes (HMCs). These HMCs can be difficult to decompose and remove through conventional techniques due to their higher stability than free heavy metal ions. In recent years, persulfate based advanced oxidation processes (PS-based AOPs) have been recognized as a viable technique for HMCs degradation. Nevertheless, a comprehensive and in-depth understanding of the relevant HMCs decomplexation mechanisms in PS-based AOPs is still lacking. This review delineates the current progress of HMCs decomplexation in PS-based AOPs. We discuss the distinctions between the two widely used oxidant types in PS-based AOPs techniques. Moreover, we summarize and highlight the decomplexation mechanisms based on electron and energy transfer, and degradation pathways of HMCs. We also emphasize the effects of environmental water constituents, namely pH, inorganic ions, and natural organic matter (NOM), on HMCs decomplexation. Ultimately, we identify the existing challenges and perspectives that will steer the direction of advancing PS-based AOPs to remove HMCs.