Removal of Cr(vi) in wastewater by Fe-Mn oxide loaded sludge biochar

Sludge biochar loaded with Fe-Mn oxides (FMBC) was prepared and employed to remove Cr(vi) from wastewater. The influences of solution pH, co-existing ion, contact time, adsorption temperature and Cd(vi) concentrations on removing Cr(vi) by FMBC were investigated. The Cr(vi) adsorption on FMBC had strong pH dependence. Additionally, Na⁺, Mg²⁺, Ca²⁺, SiO₃^2-, NO₃^- and Cl^- ions exhibited no influence on Cr(vi) removal efficiency for FMBC, whereas there were inhibition effects of Pb²⁺, Cu²⁺, Ni²⁺, CO₃^2-, SO₄^2-, and PO₄^3- on removing Cr(vi). The Cr(vi) adsorption from solution for FMBC was well described by models of pseudo-second-order and Langmuir, and the largest Cr(vi) removal capacity of FMBC reached 172.3 mg g^-1. FMBC had good capacity for treating electroplating wastewater and mineral dissolving wastewater containing Cr(vi). After five regenerations, the 50 and 5 mg L^-1 Cr(vi) removing efficiency of FMBC was 82.34% and 97.68%, respectively. The Cr(vi) removal for FMBC involved adsorption-reduction and re-adsorption of Cr(iii) generated by reduction. These results indicated that FMBC has good prospects for remediating Cr(vi)-containing wastewater.