A novel phosphate rock-magnetic biochar for Pb 2 + and Cd 2 + removal in wastewater: Characterization, performance and mechanisms

The purification of industrial wastewater contaminated by lead (Pb) and cadmium (Cd) has become a global hot research topic at present. In this study, a novel phosphate rock–magnetic biochar (PR–MCLB) was prepared from phosphate rock (PR) and cow litter, and its removal efficiency and adsorption mechanisms for Pb2+ and Cd2+ in aqueous solution were explored. PR–MCLB maximum theoretical adsorption capacities (Qe,cal) of 451.24 and 120.87 mg g−1 at 25 °C for Pb2+ and Cd2+, respectively, which were approximately 1.5–42.4 and 1.1–21.0 times higher than the Qe,cal of phosphorus–modified or cow litter–derived biochar, respectively, as mentioned in previous studies. Acid conditions (pH 3.5–5.5) and coexisting cations (Ca2+, Zn2+, Mg2+ (10–200 mg L−−1)) have almost no adverse effect on the performance of PR–MCLB. Mechanistic analysis showed that phosphate and carbonate on PR–MCLB played a crucial role in immobilization, with 54.03% of Pb2+ and 39.12% of Cd2+ being immobilized through mineral precipitate formation. A total of 21.24% of Pb2+ and 32.22% of Cd2+ were deposited on the PR–MCLB surface by ion exchange. This is followed by the cation-π interactions and surface complexation, contributing 9.11% and 11.10% for Pb2+ and 7.36% and 18.71% for Cd2+, respectively. These results indicated that PR–MCLB, as a efficient and environmentally friendly material, exhibits immense potential for application in the remediation of wastewater contaminated with Pb2+ and Cd2+.