A critical review on chemical analysis of heavy metal complexes in water/wastewater and the mechanism of treatment methods

Efficient mitigation of toxic and recalcitrant heavy metal complexes (HMCs) from water and wastewater is critical to guarantee the environmental health and safety, but still faces many challenges. Although a number of techniques have been developed to deal with HMCs laden water/wastewater, there is still a lack of comprehensive and insightful understanding of the relevant mechanisms. One of the main reasons is the complicated heavy metal speciation in water/wastewater, which masks the speciation distribution and coordination circumstance of heavy metals. In this review, prevalent methods for HMC elimination (e.g., physical separation and chemical decomplexation) are briefly presented and evaluated. Especially, the characterization methods of HMCs, which afford to provide valuable information on the speciation distribution of heavy metals, are underlined and discussed. Furthermore, typical cases are provided to elucidate the essential role of species transformation in the decomplexation of HMCs and the implications for enhanced mitigation of HMCs are also discussed. Finally, the current challenges and perspectives for future study in this field are proposed.