Effects of Phosphate, Red Mud, and Biochar on As, Cd, and Cu Immobilization and Enzymatic Activity in a Co-Contaminated Soil

Arsenic (As), cadmium (Cd), and copper (Cu) are the primary inorganic pollutants commonly found in contaminated soils. The simultaneous stabilization of three elements is a preferred approach for mixture-contaminated soils which has received extensive research attention. However, few studies have focused on immobilization efficiency single amendment elements. In this study, phosphate, red mud, biochar were used to remediate As (237.8 mg kg−1), Cd (28.72 Cu (366.5 kg−1) co-contaminated soil using 180-day incubation study. BCR (European Community Bureau Reference) extraction method, NH4H2PO4–extractable As, diethylenetriamine penta-acetic acid (DTPA)–extractable analyzed at different time intervals. results indicated that application mud significantly reduced DTPA–Cd concentrations during incubation, while decrease NH4H2PO4–As was much less than Cu. After 180 days treatments decreased by 2.15~7.89% 3.01~9.63%, respectively. Unlike biochar, phosphate concentration Cu, but failed lower As. method confirmed addition increased reducible fraction due surface complexes with Fe oxide. Canonical correspondence analysis (CCA) demonstrated pH available Cd, factors driving changes enzymatic activity. Soil showed positive correlation urease catalase activities, negative observed between soil-available enzyme activities. This study revealed it difficult simultaneously reduce bioavailabilities one amendment. Further modifying these amendments or applying combined will be conducted, order develop an efficient immobilizing