Kinetic and equilibrium studies on the adsorption of Zn2+ from aqueous solution by water-quenched blast furnace slag (WBFS)

In this work, adsorption removal of Zn²⁺ from aqueous solution by water-quenched blast furnace slag (WBFS) was investigated. The physicochemical properties of the slag were characterized by ICP, SEM and XRD. Batch experiments were carried out to test the mechanism, kinetics and thermodynamics of adsorption process of Zn²⁺ on WBFS. The results showed that the experimental data yielded excellent fit with Langmiur model. The RL values were found between 0 and 1 for all concentrations, indicating a favorable adsorption of Zn²⁺ on the WBFS. The enthalpy change (ΔH) and entropy change (ΔS) were 52.45 kJ·mol^-1 and 167.52 J·mol^-1·K^-1, respectively. The results showed that the adsorption of Zn²⁺ onto WBFS was feasible, endothermic and the system disorder increased with duration. The negative ΔG values were obtained only at temperatures higher than 318 K for Zn²⁺ adsorption. This indicated that the values of ΔG decreased with increasing temperature. The adsorption process was found to follow pseudo-second-order kinetic model and chemical adsorption was the main adsorption process. The contents of metal element in the eluate of WBFS were low, indicating WBFS an ideal choice for removing Zn²⁺ from aqueous solution.