Recovery of heavy metal complexes from wastewaters: A critical review of mechanisms and technologies

Heavy metal complexes (HMCs) pose significant ecological challenges while also holding attractive economic value. This review comprehensively summarizes advanced techniques for recovering HMCs from wastewater, including reductive recovery, oxidative decomplexation-recovery, and non-redox separation. Physical and chemical separation approaches utilize specific properties of metal complexes for efficient segregation. Specifically, we explore oxidative decomposition techniques, emphasizing the underlying mechanisms and practical application for selective and non-selective decomplexation techniques. The crucial role of cathodic potential on the efficiency and selectivity of electrochemical reduction processes is also examined. In addition, a comprehensive cost assessment, including energy consumption, associated with these recovering processes is investigated, and opinions on the inadequacy of current studies are provided. Overall, this review uniquely integrates findings on selective physical separation, oxidation, and reduction processes as well as the cost assessments for these techniques, providing a novel and comprehensive perspective on heavy metal recovery. It aims to bridge existing gaps in literature and advance the development of effective recovery methodologies for HMCs.