Simultaneous removal of Cr, Cu, Zn, and Cd by nano zero-valent iron modified sludge biochar in high salinity wastewater.

[Display omitted] • Cr, Cu, Zn and Cd could be removed simultaneously by nZVI@SBC. • NO 3 – and HA promote the removal of Cr, Cu, Zn and Cd. • Cr and Cu were reduced by nZVI and then removed through co-precipitation. • The removal of Cd and Zn were driven by alkali precipitation and complexation. Cr, Cu, Zn, and Cd commonly coexisted in the electroplating wastewater with high salinity and organics, while their removal was often investigated individually. In this study, the simultaneous removal of Cr, Cu, Zn, and Cd was investigated by nano zero-valent iron modified sludge biochar (nZVI@SBC). The results showed that nZVI@SBC could significantly improve the removal efficiency of the four heavy metals (HMs) in high salinity wastewater. NO 3 – (N-NO 3 –) and humic acid (HA) could promote the removal of Cr, Cu, Zn, and Cd, and PO 4 3- (P-PO 4 3-) could enhance the removal of Cd. EPR analysis demonstrated the generation of 1O 2 in different water matrices. The 1O 2 intensity increased in the presence of NO 3 – and HA, which indicated the acceleration of the nZVI corrosion and the promoted electron transfer in the system. To further understand the reaction mechanism, the variation of nZVI@SBC structures and compositions during the treatment process were characterized by SEM-EDS, XRD, BET, and XPS. Cr and Cu were removed through adsorption and co-precipitation after reduction by nZVI, while Cd and Zn were removed by alkali precipitation and complexation. This work improves the understanding of simultaneous removal of HMs by nZVI@SBC and provides a cost-effective approach for the electroplating wastewater treatment. [ABSTRACT FROM AUTHOR]