Mechanism of ultrasound-enhanced alkaline selective leaching of zinc from steel waste: experimental and DFT simulation analysis

Abstract

The efficient and selective recovery of Zn from hazardous solid waste steel zinc slag (SZS) has always been a complex problem. In this study, ultrasound-enhanced alkaline leaching (UAL) technology was used to improve the leaching effect of Zn in SZS and achieve a high degree of separation of Zn from impurity ions such as Pb and Fe. Density functional theory (DFT) simulation was used to deeply analyze the adsorption energy, charge density difference, and density of states of the ZnO–NaOH, PbO–NaOH, and Fe₂O₃–NaOH adsorption systems, and it was found that the interaction between ZnO and NaOH was the strongest. Using ultrasound-enhanced NaOH leaching of SZS under optimal conditions, the leaching rates of Zn, Pb, and Fe were 99.36%, 3.08%, and 0.09%, respectively. The experimental results are consistent with the DFT calculation results. In addition, ultrasound can effectively destroy the mineral structure through the cavitation effect and mechanical effect, significantly reducing the Zn activation energy of 9.97 kJ mol⁻¹, which is the main reason for improving the Zn leaching rate under the ultrasonic system. The Zn leaching rate increased by 12% under the UAL system, the reagent consumption decreased by 25%, and the leaching time was shortened by 50%. The selective leaching mechanism of Zn from SZS under the UAL system was revealed by combining DFT simulation, leaching experiments, and characterization analysis. The results of this study confirmed that the UAL technology can selectively recover Zn from SZS with high efficiency and low cost, providing a new strategy for the resource utilization of zinc-containing hazardous wastes.