High-efficiency and low-carbon remediation of zinc contaminated sludge by magnesium oxysulfate cement

Electroplating sludge is classified as a hazardous waste due to its extremely high leachability of potentially toxic elements. This study concerns the use of magnesium oxysulfate cement (MOSC) for the stabilisation/solidification (S/S) of Zn-rich electroplating sludge. According to X-ray diffraction and thermogravimetric analyses, Zn was mainly immobilised through both chemical interaction and physical encapsulation in the MOSC hydrates of 5Mg(OH)(2)center dot MgSO4 center dot 7H(2)O (5-1-7) phase. The crystal size analysis, elemental mapping, and extended X-ray absorption fine structure (EXAFS) analysis proved that the Zn2+ was also incorporated in the structure of 5-1-7 phase. Unlike Portland cement system, hydration kinetics, setting time, and compressive strength of the MOSC system were only negligibly modified by the presence of Zn, indicating its superior compatibility. Subsequent S/S experiments demonstrated that the MOSC binder exhibited an excellent performance on immobilisation efficiency of Zn (up to 99.9%), as well as satisfying the requirements of setting time and mechanical strength of sludge S/S products. Therefore, MOSC could be an effective and sustainable binder for the treatment of the Zn-rich industrial wastes.

Automated summary

This study investigates the use of magnesium oxysulfate cement (MOSC) for stabilizing/solidifying Zn-rich electroplating sludge, showing that Zn was immobilized through chemical interaction and physical encapsulation in the MOSC hydrates. The MOSC system demonstrated superior compatibility compared to Portland cement system, with excellent immobilization efficiency and meeting the requirements for setting time and mechanical strength of sludge S/S products, indicating its effectiveness for treating Zn-rich industrial wastes.