Adsorption of Pb, Cu and Cd from Water on Coal Fly Ash-Red Mud Modified Composite Material: Characterization and Mechanism

Abstract

The rational utilization of solid waste has always been a worldwide concern. In this study, coal fly ash (CFA) and red mud (RM) were used in combination to synthesize efficient heavy metal adsorbents. A new way of resource recycling was provided with the collaborative reuse of CFA and RM. To obtain the modified composite materials, CFA and RM were mixed and melted in three ratios. After modification, these materials were then utilized to adsorb Pb, Cu, and Cd in water in both single and ternary systems. The physicochemical properties of CFA, RM, and three modified composite materials were measured by X-ray diffraction analysis, energy dispersive X-ray spectroscopy, scanning electron microscope, Fourier transform infrared spectroscopy, vibrating sample magnetometer, surface area analyzer, and porosity analyzer. In the single and ternary systems, the effects of the modified composite material dosage, solution pH, initial concentration of heavy metals, and adsorption time were discussed, and the results were better fitted with the Langmuir isotherm and the pseudo-second-order kinetic. It was discovered that the modified composite materials had a greater specific surface area (63.83 m2/g) than CFA and RM alone, as well as superior adsorption capacity and magnetic characteristics. The adsorption capacities of C1R4 for Pb, Cu, and Cd were 149.81 mg/g, 135.96 mg/g, and 127.82 mg/g in the single system, while those of Cu and Cd decreased slightly in the ternary system, and the preferential adsorption order of the modified composite materials for heavy metal ions was Pb > Cu > Cd. Among the three modified composite materials, C1R4 had the best adsorption capacity.