Slow-release ferrous effects on synchronous stabilization of lead, cadmium, and arsenic in soil

Zero-valent iron (ZVI)-based materials is considered promising for the synchronous stabilization of soils contaminated with multi-heavy metals (e.g., Pb(II), Cd(II), and As(V)), particularly due to its continuous slow-release ferrous. However, little is known about the effect of slow-released Fe(II) on the stabilization of Pb, Cd, and As in the contaminated soil. In this study, ZVI(Fe⁰) and ball-milled ZVI(B-Fe⁰), with different ability of slow-releasing Fe(II), were used to investigate the effect of slow-released Fe(II) on the simultaneous stabilization of Pb, Cd, and As in soil. The B-Fe⁰, with stronger ability to sustainably release Fe(II), possessed higher stabilization efficiency of Pb, Cd, and As in soil compared to the Fe⁰. After 56 days of B-Fe⁰ treatment, the stabilization efficiency of NaHCO₃-extractable As and DTPA-extractable Pb and Cd reached 72.52%, 43.63%, and 34.71%, respectively. The speciation change analysis demonstrated that soil Pb, Cd, and As were transformed into more stable states with the treatment time. The superior stabilization performance could be attributed to the slow-release of ferrous, which not only increased the content of iron oxide in the soil, but also promoted the conversion of amorphous iron (hydro)oxides (e.g., ferrihydrite) into crystalline magnetite. Consequently, Pb, Cd, and As were effectively stabilized by being incorporated into the structure of the secondary Fe mineral. This study provided valuable guidance for the application of ZVI-based materials in the stabilization remediation of multi-heavy metals contaminated soils.