A Novel and Holistic Approach for Remediating Zn-, Pb-, and Cd-contaminated Soils Using Potassium Bisulfate and Ammonium Bisulfate as Leaching Agents

Abstract

Green, efficient, and cost-effective soil leaching technologies have emerged as an innovative strategy for remediating heavy metal-contaminated soils. In this study, we proposed NH₄HSO₄ and KHSO₄ as novel eluents for removing heavy metals from contaminated soils and investigated the effects of various factors, including leaching temperature, liquid to solid ratio (L/S), time, and molar concentration ratio, on their efficacy. We also examined the mineral contents and structural properties of the contaminated soil before and after leaching using the novel eluents via scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction spectroscopy, and Fourier transform infrared spectroscopy. The results indicated that the leaching rates of Zn, Pb, and Cd using NH₄HSO₄ and KHSO₄ (25 °C, 360 min, L/S = 20, and 0.075 mol/L) were 86.17%, 45.97%, and 79.92% and 89.12%, 46.185%, and 84.32%, respectively. Furthermore, these eluents improved the quality of the treated soil by slightly increasing its N and K contents without altering its structure. The leaching rates of Zn in the exchangeable and acid-soluble, reducible, and oxidizable forms by KHSO₄ were best fitted by the Avrami–Erofeev equation, diffusion via the product layer, and the new shrinking core model, respectively. The heavy metal proportion in the oxidizable and residual fraction increased after leaching. Based on these findings, NH₄HSO₄ and KHSO₄ show promise as effective agents for the rapid, efficient, cost effective, and sustainable remediation of heavy metal-polluted soils.