Study on the adsorption properties of Cr(<scp>vi</scp>), Cu(<scp>ii</scp>) and Cd(<scp>ii</scp>) in acid mine wastewater by coal gangue loaded nano-FeS

This study prepared a novel composite material, coal gangue loaded nano-FeS (nFeS-CG), to remove Cr(vi), Cu(ii) and Cd(ii) from Acid Mine Wastewater (AMD). The system evaluated the synchronous removal effect of nFeS-CG on Cr(vi), Cu(ii), and Cd(ii) in AMD. The effects of nFeS-CG dosage, initial pH, reaction time and initial concentration on the adsorption of Cr(vi), Cu(ii) and Cd(ii) in AMD were investigated. The adsorption mechanism of nFeS-CG for Cr(vi), Cu(ii) and Cd(ii) in AMD was studied by adsorption isotherms, adsorption kinetics and adsorption thermodynamics models, combined with SEM, XRD, FTIR and XPS. The optimum conditions for the adsorption of Cr(vi), Cu(ii) and Cd(ii) in AMD by nFeS-CG were dosage of 7 g L^-1 and reaction time of 155 min. The best removal rates were 94.08%, 84.08% and 71.36%, respectively. The adsorption of Cr(vi), Cu(ii), and Cd(ii) by nFeS-CG conformed to the Langmuir model and the pseudo-second-order kinetic model, indicating that the adsorption process was monolayer adsorption and was dominated by chemical adsorption. The thermodynamic results showed that the adsorption process was an endothermic process, and the temperature rise was beneficial to the adsorption. The characterization results and mechanism analysis showed that the removal mechanism of Cr(vi), Cu(ii) and Cd(ii) by nFeS-CG was mainly electrostatic adsorption, redox and precipitation. Co-existing ions, leaching toxicity and recycling experiments proved nFeS-CG's strong practical application potential as a low-cost adsorbent for simultaneous removal of multiple heavy metals in AMD. This study provides technical reference for coal gangue utilization and AMD remediation.