Synthesis and characterization of a novel magnetic calcium-rich nanocomposite and its remediation behaviour for As(III) and Pb(II) co-contamination in aqueous systems.

Herein, a novel magnetic calcium-rich biochar (MCRB), prepared by loading Fe3O4 nanoparticles (Fe3O4 NPs) on crab shell-derived biochar, was studied for remediation of arsenic and lead co-contamination. Characteristics of the MCRB demonstrated that Fe3O4 NPs adhered on the biochar matrix uniformly. Batch experiments on the effects of pH, contact time and initial concentrations revealed that for both metals, removal by the MCRB was pH-dependent with an optimal pH of 6, and that the MCRB had a strong ability for removing arsenic and lead with maximum removal capacities of 15.8 and 62.4 mg g-1, respectively. The mechanisms of the simultaneous removal of arsenic and lead involved both competitive and synergistic effects. The As(III) addition enhanced Pb(II) removal by 5.4-18.8%, while the presence of Pb(II) suppressed As(III) removal by 5.8-17.8%. Competitive complexation of the two metals with biochar was responsible for the suppression, while the enhancement was due mainly to the formation of the Pb(II)-As(III)-FeO ternary surface complex with As(III) as the bridging molecule. These new insights can further our understanding of the application of MCRB as a potential material for use in the treatment of arsenic and lead co-contamination.