Recent advances of nano zero-valent iron (nZVI) on the remediation of heavy metals polluted environment: Modified methods, mechanisms, influencing factors and application challenges

Remediation of heavy metal-contaminated water and soil has become a significant challenge. Nano zero-valent iron (nZVI) exhibits great potential in environmental remediation due to its excellent removal properties for heavy metals. This review provides a comprehensive overview of advances in nZVI, modified nZVI, and related composites for heavy metal remediation in soil and water. First, this paper summarizes different preparation routes for nZVI and several recent modification methods, such as surface coating, sulfidation, and oxyanion modification. Meanwhile, removal capacities of heavy metals by some modified nZVI are listed and compared. Second, the general interaction mechanisms of heavy metal cations or anions and nZVI are recapitulated as adsorption, reduction, oxidation, and co-precipitation. Third, the factors influencing heavy-metal removal in the environment, including pH, oxidation-reduction potential (ORP), and natural organic matter (NOM) are systematically discussed. Finally, perspectives on the challenges of nZVI practical utilization at contaminated sites are highlighted and proposed for further development.