Adsorption properties and mechanisms of Cd by co-pyrolysis composite material derived from peanut biochar and tailing waste

Cadmium (Cd) contamination in aquatic systems is a widespread environmental issue. In this study, a solid waste iron tailings and biochar hybrid (Fe-TWBC) was successfully synthesized derived from co-pyrolysis of peanut shell and tailing waste (Fe-TW). Characterization analyses showed that the metal oxides from solid waste iron tailings successfully loaded onto the biochar surface, with more functional groups in Fe-TWBC. The Fe-TWBC had a maximum capacity of 95.06 mg·g^-1 on Cd²⁺ adsorption, which was 1.40 times to pristine BC (70.46 mg·g^-1) and 2.53 times to Fe-TW (37.51 mg·g^-1). The adsorption behavior followed the pseudo-second-order kinetics and Freundlich models. DFT calculations revealed that the O-top of Fe-O group was the most chemically reactive site for Cd²⁺ adsorption with the high adsorption energy values of - 4.05 eV, short O-Cd bond lengths (2.133 Å), low electrostatic potentials in small blue regions near the O atom of Fe-O group, low energy gap (0.22 eV) and large electrophilic Fukui index (f^- = 0.18). Overall, these findings suggest that Fe-TWBC is effective in removing Cd²⁺ from aqueous solution and promotes the utilization of biowaste and solid waste iron tailing waste for cleaner production.