Removal of Cu2+ from AMD by goethite modified biochar combined with sodium alginate: characterization, performance and mechanisms†

Efficient and environmentally friendly removal of Cu²⁺ from wastewater has been the focus of recent research. However, the acid mine drainage (AMD) produced during the mining process, characterized by low pH and high concentrations of toxic heavy metals, poses a significant challenge for Cu²⁺ removal. Therefore, in this study, corn stalks were selected as raw materials, and a goethite-modified biochar material (GMB) was prepared using the hydrolysis co-precipitation method at different temperatures and raw material ratios. Additionally, sodium alginate was used as a chelating agent to construct a composite material (SGB). The adsorption process, removal efficiency, and adsorption mechanism of Cu²⁺ in acidic mine wastewater by GMB and SGB were investigated through batch adsorption experiments and characterization. Results showed that GMB adsorption followed the second-order kinetic and Langmuir models, with a maximum capacity of 51.23 mg g⁻¹ at 25 °C, indicating single-layer homogeneous chemisorption. The Thomas model accurately described SGB's dynamic adsorption, with a high correlation (R² = 0.94) and a maximum capacity of 117.68 mg g⁻¹. Both materials performed well under acidic conditions (pH 2.0–5.5) and in the presence of competing ions (Na⁺, Ca²⁺, Cl⁻, NO₃⁻, SO₄²⁻). The characterization results indicated that the adsorption mechanism of GMB for Cu²⁺ primarily involved physical adsorption, electrostatic interactions, surface complexation, and co-precipitation. Additionally, after five adsorption–desorption cycles, GMB maintained a capacity of 29.55 mg g⁻¹, while SGB improved Cu²⁺ removal from 72.71% to 94.27% compared to GMB alone. In conclusion, GMB and SGB demonstrated significant potential for Cu²⁺ remediation in acid mine drainage.