Comparison of Leaching Agents for Evaluating the Stabilization Efficiency of Heavy Metals in Stabilized Soils

The performance of commonly used single-extraction methods for evaluating the stabilization efficiency of heavy metals in stabilized soils was compared.Agricultural soil near an abandoned metal mine was treated with a limestone-steel slag mixture and oak-derived biochar.After stabilization, the leaching behavior of As, Pb, Zn, Cu, Cd, and Ni was evaluated using five single-extraction methods: 0.1 N HCl, 1 N HCl, Mehlich-3, CaCl 2 , and TCLP.The results showed that soils stabilized with the limestone-steel slag mixture exhibited consistent reductions in extractable concentrations of all tested metals when assessed using 0.1 N and 1 N HCl.In contrast, Mehlich-3, CaCl 2 , and TCLP revealed stabilization effects only for specific metals.Arsenic stabilization was effectively detected only by inorganic acid extractions, whereas Zn and Cd also showed measurable stabilization under CaCl 2 extraction.For biochar-treated soils, stabilization effects were observed primarily when extracted with 0.1 N HCl, while CaCl 2 extraction indicated stabilization only for Zn.Other extraction methods failed to detect meaningful stabilization for most metals.The results suggest that, under the conditions of this study, the stabilization effectiveness of the oak-derived biochar used in this experiment may be limited compared to that of the alkaline limestone-steel slag mixture.Overall, the results demonstrate that the evaluation of stabilization efficiency is highly dependent on the choice of leaching agent, as different extractants target distinct metal fractions in soil.This study indicates the necessity of selecting appropriate extraction methods based on the stabilizing agent and target metals when assessing post-treatment stabilization performance.