A novel electrolytic-manganese-residues-and-serpentine-based composite (S-EMR) for enhanced Cd(II) and Pb(II) adsorption in aquatic environment

Electrolytic manganese residue (EMR) is the waste slag generated from the electrolysis manganese industry. As a promising exploitable adsorbent, EMR has become a hot research topic. However, EMR’s low adsorption capacity has limited its applications as an efficient adsorbent. In this study, the EMR was mixed with serpentine and calcined (at 800 °C for 2 h) to prepare a composite adsorbent (S-EMR) with its specific surface area of 11.998 m²·g⁻¹ (increased compared to the original EMR) and improved adsorption capacities for Cd²⁺ (98.05 mg·g⁻¹) and Pb²⁺ (565.81 mg·g⁻¹). Kinetic studies have shown that the pseudo-first-order kinetics (PSO) model could best describe the adsorption kinetics of S-EMR for Cd²⁺/Pb²⁺, implying that the chemisorption process is the rate-limiting step. The effects of different interfering ions on S-EMR’s adsorption for Cd²⁺/Pb²⁺ may be due to the difference in their electronegativity. Results of response surface methodology tests showed that pH had the highest influence on adsorption, and the removal efficiency of S-EMR reached 99.92% for Cd(II) and 94.00% for Pb(II). X-ray photoelectron spectroscopy (XPS) analyses revealed that chemical precipitation was the predominant mechanism for Cd²⁺/Pb²⁺ removal, and the adsorption mechanisms were associated with ion exchange and electrostatic attraction. The results showed that S-EMR could be used as an effective adsorbent for the removal of Cd(II)/Pb(II) from water bodies, rendering dual benefits of pollution control and resource recovery.