Phosphorus-modified biochar cross-linked Mg–Al layered double-hydroxide composite for immobilizing uranium in mining contaminated soil

The decommissioning of uranium mill tailings (UMTs) is usually accompanied by uranium (U) contamination in soil, which poses a serious threat to human health and ecological safety. In this study, a novel phosphorus-modified bamboo biochar (PBC) cross-linked Mg–Al layered double-hydroxide (LDH) composite (“PBC@LDH”) was successfully prepared by phosphate pre-impregnation and a hydrothermal method with Mg–Al LDH. Physicochemical analysis revealed that phosphorus-containing functional groups and Mg–Al LDH were grafted onto the pristine biochar (BC) matrix. Laboratory-scale incubation and column leaching experiments were performed on the prepared BC, PBC, and PBC@LDH. The results showed that, at a dosage of 10%, the PBC@LDH composite had a commendable ability to immobilize U in soil. After 40 days of incubation with the stabilizer, the more mobile U was converted into immobilized species. Furthermore, during a column leaching experiment with simulated acid rain, the cumulative loss and leaching efficiency of U were remarkably reduced by PBC@LDH treatment compared with the control, reaching 53% and 54%, respectively. Surface complexation, co-precipitation, and reduction described the adsorption and immobilization mechanisms. In conclusion, this research demonstrates that the PBC@LDH composite offers a potentially effective amendment for the remediation of U contaminated soil.