Molecular insights into the simultaneous removal mechanisms of As(Ⅴ) and Cd(II) in iron tailings slag-biochar composites.

Arsenic and cadmium contamination frequently coexist in the real environment. However, it remains a challenge for their simultaneous removal due to their distinct physicochemical properties at low cost. To this end, a cost-effective magnetic biochar adsorbent (ITBNa800) was prepared using biomass waste and iron tailings slag. This composite adsorbent exhibits excellent performance in the simultaneous removal of aqueous As(V) and Cd(II) even at high concentrations with removal efficiencies of up to 99.98% and 96.04%, respectively. Electrostatic action, precipitation, and complexation were adsorption mechanisms. As(V) and Cd(II) were synergistic and competitive adsorption. As(V) removal was mainly due to physical and chemical adsorption, and 42.40%-58.59% of As(V) had been converted to As(III). Cd(II) removal was mainly due to chemical adsorption. Iron oxide and aluminum oxide in ITBNa800 were the keys to As(V), As(III), and Cd(II) adsorption. DFT calculations revealed iron oxide complex As(V), As(III), and Cd(II) molecular clusters through bidentate binuclear, bidentate binuclear, and monodentate binuclear pathways, respectively. Aluminum oxide complex Cd(II) molecular cluster through a bidentate mononuclear pathway. We hope the ITBNa800 adsorbent and its involved mechanism could offer inspiration in the simultaneous treatment of As and Cd pollution.