Mechanism Study\non the Immobilization of Cu<sup>2+</sup>/Pb<sup>2+</sup> in Aqueous\nPhase by Mineral Co-Milling-Modified\nBiochar

A large number of studies have shown that the modification\nof biochar\ncan greatly improve its adsorption capacity. This study adopts a one-step\nball milling technology without solvent medium, using sawdust biochar\n(600 °C) and attapulgite/diatomaceous earth to prepare MABC10%/MDBC10%\n(mass ratio: 10% attapulgite/diatomite +90% biochar coabrasive). Characterization\nexperiments show that attapulgite/diatomite was successfully loaded\non biochar and has more C/O functional groups and wider adsorption\npore sizes. Adsorption kinetics and isotherm experiments show that\nthe adsorption process of MABC10% and MDBC10% on Cu<sup>2+</sup>/Pb<sup>2+</sup> was mainly multilayer chemical adsorption. The adsorption\ncapacities of MABC10% and MDBC10% for Cu<sup>2+</sup> were 40.85 and\n65.20 mg·L<sup>–1</sup>, respectively. The adsorption\namounts of Pb<sup>2+</sup> were 82.63 and 71.32 mg·L<sup>–1</sup>, respectively. The particle diffusion model shows that the adsorption\nprocess was controlled by both the surface adsorption rate limitation\nand boundary layer diffusion. The higher acidity in the solution will\ncause part of the negative charges on the surface of attapulgite/diatomite\nto be neutralized, thereby hindering its adsorption of Cu<sup>2+</sup>/Pb<sup>2+</sup>. The presence of coexisting ions did not significantly\naffect the adsorption performance. Mechanistic studies have shown\nthat pore diffusion, active sites provided by C/O functional groups,\nelectrostatic interactions, and cation exchange are the main mechanisms\nof MABC10% adsorption of Cu<sup>2+</sup>/Pb<sup>2+</sup>. In summary,\nMABC10% has a significant adsorption synergistic effect compared to\nMBC. It was an economical and effective adsorbent, and the higher\nthe pH value of the wastewater, the more significant the adsorption\neffect.