Mechanism Study on the Immobilization of Cu²⁺/Pb²⁺ in Aqueous Phase by Mineral Co-Milling-Modified Biochar

A large number of studies have shown that the modification of biochar can greatly improve its adsorption capacity. This study adopts a one-step ball milling technology without solvent medium, using sawdust biochar (600 °C) and attapulgite/diatomaceous earth to prepare MABC10%/MDBC10% (mass ratio: 10% attapulgite/diatomite +90% biochar coabrasive). Characterization experiments show that attapulgite/diatomite was successfully loaded on biochar and has more C/O functional groups and wider adsorption pore sizes. Adsorption kinetics and isotherm experiments show that the adsorption process of MABC10% and MDBC10% on Cu²⁺/Pb²⁺ was mainly multilayer chemical adsorption. The adsorption capacities of MABC10% and MDBC10% for Cu²⁺ were 40.85 and 65.20 mg·L^-1, respectively. The adsorption amounts of Pb²⁺ were 82.63 and 71.32 mg·L^-1, respectively. The particle diffusion model shows that the adsorption process was controlled by both the surface adsorption rate limitation and boundary layer diffusion. The higher acidity in the solution will cause part of the negative charges on the surface of attapulgite/diatomite to be neutralized, thereby hindering its adsorption of Cu²⁺/Pb²⁺. The presence of coexisting ions did not significantly affect the adsorption performance. Mechanistic studies have shown that pore diffusion, active sites provided by C/O functional groups, electrostatic interactions, and cation exchange are the main mechanisms of MABC10% adsorption of Cu²⁺/Pb²⁺. In summary, MABC10% has a significant adsorption synergistic effect compared to MBC. It was an economical and effective adsorbent, and the higher the pH value of the wastewater, the more significant the adsorption effect.