Remediation of As(III) and Cd(II) co-contamination and its mechanism in aqueous systems by a novel calcium-based magnetic biochar

<p dir="ltr">A novel calcium-based magnetic biochar (Ca-MBC), made by pyrolyzing the mixture of rice straw, iron oxide (Fe₃O₄) and calcium carbonate (CaCO₃), was developed in this study for remediation of co-pollution of arsenic and cadmium. Characteristics of the material showed that Fe₃O₄ and CaCO₃ were adhered on the surface of biochar. The experiments on the effects of pH, adsorption kinetics and isotherm revealed that the Ca-MBC had a great ability to adsorb arsenic and cadmium within 0.5 h for cadmium and 12 h for arsenic with a maximum adsorption capacity of 6.34 and 10.07 mg g⁻¹, respectively, and that the adsorption of both metals was pH-dependent from 2 to 12 with an optimal pH of pH 5. The mechanism of co-adsorption of Cd(II) and As(III) included both competitive and synergistic effects. The presence of As(III) enhanced Cd(II) adsorption by 3–16% while Cd(II) addition suppressed As(III) adsorption by 15-33%. The synergistic effects on As(III) and Cd(II) adsorption had resulted from the electrostatic interaction and the formation of type B ternary surface complexes. These new insights provide valuable information for the application of Ca-MBC as a potential adsorbent in treatment of water contaminated with As(III) and Cd(II).</p>