Fabrication of Thermally Activated Lead-Zinc Tailings/Sodium Alginate Composites for High-Efficiency Adsorption of Cu2+/Cd2+

Wastewater containing Cu 2+ and Cd 2+ poses a huge threat to the surrounding environment and human safety. To treat such wastewater, this study developed a novel composite adsorbent (LZT 850 @SA) from thermally activated LZT and sodium alginate (SA). LZT was thermally activated at 850°C (LZT 850 ). The composite LZT 850 @SA was synthesized by mixing LZT 850 powder with SA solution under optimized conditions (20°C, 4 g/L SA, 90 min). Adsorption performance for Cu 2+ /Cd 2+ was evaluated under varying pH, contact time, temperature, and concentration. Kinetics, isotherms, selectivity, and regeneration were systematically studied. Activation at 850°C enhanced LZT crystallinity and created pores (SSA: 5.46 m 2 /g). SA compositing formed unique fibrous architectures and amorphous-crystalline interfaces, significantly increasing SSA to 16.31 m 2 /g (BET). XRD confirmed the dominant phases (CaCO 3 , CaO, MgO) in LZT 850 and phase transition upon SA compositing. SEM/HRTEM revealed SA's transformation of the granular LZT 850 surface into a highly porous, roughened morphology with uniform particle distribution. At pH 6, LZT 850 @SA exhibited exceptional adsorption capacities of 223.47 mg/g (Cu 2+ ) and 227.99 mg/g (Cd 2+ ), reaching equilibrium within 120 min. Adsorption followed pseudo-second-order kinetics and Langmuir isotherm models, indicating chemisorption-dominated monolayer adsorption. Mechanisms involved chemical coordination (C=O, O-C=O, O-H, iron oxides), ion exchange, coordination and electrostatic interactions. The composite demonstrated excellent selectivity and retained 81.9% (Cu 2+ ) and 85.52% (Cd 2+ ) adsorption capacity after 5 regeneration cycles. This provides a new strategy for the composite of solid waste and biopolymers, and at the same time offers technical insights for the treatment of heavy metal-polluted wastewater.