The Adsorption Characteristics of Phosphorus-Modified Corn Stover Biochar on Lead and Cadmium

In order to achieve the purpose of efficiently removing lead and cadmium as the main heavy metals from wastewater, this paper explores the adsorption properties of cadmium ions and lead ions on biochar under different modified conditions prepared from corn stalks as raw materials and potassium phosphate as surface modifiers. Before preparing biochar (BC), the mass ratios of 1:1 and 1:2 (corn stalks to potassium phosphate) were used for pre-modification, and the oxygen-restricted pyrolysis processes of 350 °C, 550 °C and 750 °C were used for treatment. The study discussed the individual and composite adsorption effects of biochar on Pb2+ and Cd2+ under different conditions. The experimental results show that phosphorus modification has changed the physical and chemical properties of the original biochar. Among them, the biochar (2PBC550) with an impregnation ratio of 1:2 and a pyrolysis temperature of 550 °C (2PBC550) exhibits excellent adsorption properties. When the pH of the simulated wastewater is 5 and the amount of adsorbent is 30 mg·L−1, the maximum adsorption capacity of Pb2+ and Cd2+ is 145.48 mg·g−1 and 14.533 mg·g−1, respectively, which are 6.46 times and 3.67 times of the original biochar. The Pb2+ and Cd2+ adsorption data of 2PBC550 fit well with the quasi-secondary dynamics and Langmuir isothermal models, indicating that the adsorption process is controlled by single-layer chemical adsorption. In the composite metal system of Pb2+ and Cd2+, 2PBC550 exhibits a stronger affinity for Pb2+ than Cd2+. Through the analysis of characterization methods such as SEM, FTIR, XRD and XPS, it is proved that the adsorption of Pb2+ and Cd2+ by 2PBC550 is due to precipitation, complexation and π electron interaction. Therefore, 2PBC550 shows great application potential in the repair of wastewater containing Pb2+ or Cd2+.