Synergistic Stabilization and Ecological Restoration in Multi-Metal Contaminated Soil: The Efficacy of Fe/Mn (Hydr)oxide-Phosphate Composites (FMPs) for Cd, Pb, Cu, Zn

Soil heavy metal pollution, especially multi-metal contamination, is a serious environmental challenge. Stabilization has become a practical method to reduce pollution while maintaining soil ecological functions. In this study, functional materials (FMPs) composed of Fe/Mn (hydro)oxides and phosphate minerals were prepared by optimizing the molar ratio of Fe(II), Fe(III), Mn(II), and PO ₄ ³⁻ . Contaminated topsoil from a mining area was used to simulate real-world conditions. After 60 days of FMPs application at 5 wt.%, DTPA-extractable Cd, Pb, Cu, and Zn levels were reduced by 70.10%, 99.82%, 68.30% and 75.05%, respectively, meeting stabilization standards (HJ 1282–2023). Notably, FMPs promoted the conversion of Cd, Pb, Cu, and Zn from labile (F1/F2) to stable (F3/F4) fractions. Additionally, FMPs significantly increased soil pH, EC, TP, AP, and NH ₄ ⁺ -N, while enhancing S_ACP, S_CL, and S_CAT activities, but lowered Eh, NO ₃ ⁻ -N, AK, and S_UE activity. Microbial community analysis showed that FMPs changed soil microbial communities, decreasing bacterial diversity and richness (p < 0.05), but increasing fungal diversity and richness (p < 0.05). Molecular ecological networks indicated stronger bacterial connections and simpler fungal networks, with low-abundance taxa playing crucial ecological roles. These results underscore the effectiveness and environmental sustainability of FMPs for remediation of multi-metal contaminated soils.