Smelting-slag sites in ecologically fragile regions pose persistent risks of heavy-metal release. This study developed a multiwaste-induced reducing reactive layer composed of steel slag, flue-gas-desulfurization gypsum, chicken manure, and crop straw to achieve synchronous mineralization of cationic (Cd, Cu, Zn, Pb) and anionic (As) metals. Packed-column tests and field demonstration at two smelting-slag sites in Guangxi and Yunnan, China, systematically evaluated the effects of reactive-layer composition, organic-layer thickness, and soil-cover depth on leaching toxicity and microbial dynamics. The optimized configuration (0.5: 0.5: 3: 6 for steel slag, flue-gas-desulfurization FGD gypsum, straw, and chicken manure; 2 cm organic layer; 30 cm soil cover) rapidly inhibited leaching, with As, Cd, Cu, and Zn reduced by 89%–99% within 12 months in columns. In the field demonstration, As, Pb, and Zn decreased by 99.8%, 99.4%, and 86.5%, respectively, with As stabilized at around 0.05 mg L−1 (Class I surface water quality standard in China) and metal speciation shifting toward reducible and residual fractions. Microbial analysis revealed the enrichment of anaerobic functional groups (e.g., Proteobacteria), which facilitated sulfide mineralization and long-term stabilization. These findings highlight the multiwaste-induced reducing reactive layer as a low-cost, site-adaptive, and sustainable strategy for in situ remediation of smelting-slag sites, providing a practical engineering solution and a mechanistic foundation for heavy metal source control.
Su et al. (Fri,) studied this question.
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