A novel phosphate rock-magnetic biochar for Pb[formula omitted] and Cd[formula omitted] removal in wastewater: Characterization, performance and mechanisms

Abstract

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+.