Nano Zero-Valent Iron and Its Modifications for the Remediation of Heavy Metal-Contaminated Soils from Zinc–Lead Mine Areas in China

Nano zero-valent iron (nZVI) and its modified forms are promising for remediation of heavy metal-contaminated soils, but bare nZVI aggregates and oxidizes readily. In this study, carboxymethyl cellulose (CMC), polyvinylpyrrolidone (PVP), and sodium dodecyl sulfate (SDS) were used to prepare modified nZVI. The modifiers increased electrostatic repulsion and steric hindrance, inhibited aggregation, and maintained reactivity. The modified particles were smaller (5–15 nm vs. ~50 nm for nZVI) and more dispersible. In three heavy metal-contaminated soils from Zn–Pb mine areas in China, modified nZVI showed improved mobility and retention; column effluent Fe reached 595.5 mg/L for P-nZVI in S1 and 639.6 mg/L for C-nZVI in S3, although mobility varied with soil properties. After stabilization, TCLP leaching of Zn, Cr, Pb, and Cu decreased significantly. Zn leaching was reduced by up to 95.0% (P-nZVI, S3) and 93.49% (C-nZVI, S2); Cr leaching was reduced by up to 98.6% (S-nZVI, S3) and 97.0% (P-nZVI, S3); Pb and Cu reached below detection limits under optimized treatments (C-nZVI or P-nZVI at 1.0 g/L Fe) in selected soils. The K value, defined as (F1 + F2)/(F3 + F4 + F5), decreased by up to 16.25% for Zn, 11.88% for Cr, 13.63% for Cu, and 10.04% for Pb. Because K represents the ratio of labile to stable fractions, its decrease indicates a shift from labile to stable fractions, enhanced immobilization, and reduced bioavailability. Overall, PVP-modified nZVI performed best for Zn and Cr, whereas CMC-modified nZVI was most suitable for Pb and Cu.