For nearly three decades, zero-valent iron (ZVI) has been used in wastewater treatment and groundwater and soil remediation. ZVI can degrade contaminants by reactions of adsorption, redox, and co-precipitation. It can also react with oxidants like hydrogen peroxide, persulfate, and ozone to produce highly reactive radicals that can rapidly remove and even mineralize organic contaminants. However, the application of ZVI is also limited by factors such as the narrow pH range and surface passivation. The addition of chelating agents such as nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), or citrate to the ZVI-based processes has been identified to greatly increase the iron stability and improve the efficiency of contaminant degradation. From the perspective of commonly used organic and inorganic chelating agents in ZVI applications, the review addresses the current status of ligand-enhanced ZVI degradation of organic contaminants, illustrates the possible reaction mechanism, and provides perspectives for further research.

Zero-valent iron/peroxymonosulfate (Fe⁰/PMS) has been considered as a promising approach for wastewater treatment. Anions and cations are widely present in wastewater and have significant effects on the performance of the Fe⁰/PMS system for wastewater treatment. Thus, in the present study, tartrazine was selected as the target model; SO₄²⁻, NO₃⁻, HCO₃⁻, and Cl⁻ were selected as representative anions and Ca²⁺, Cu²⁺, Mg²⁺, and Mn²⁺ were chosen as representative cations. The effect of these anions and cations on tartrazine removal and major radicals in the Fe⁰/PMS were systematically investigated. The presence of a certain concentration of SO₄²⁻ and Cl⁻ had positive, NO₃⁻ had negative, and HCO₃⁻ had negligible effects on tartrazine removal in the Fe⁰/PMS system. SO₄²⁻ and HCO₃⁻ had a small effect on the contribution proportion of reduction, SO₄^•− and ^•OH; a certain concentration of Cl⁻ could enhance the contribution proportion of ^•OH; and NO₃⁻ would decrease the contribution proportion of SO₄^•− and ^•OH. A certain concentration of each of Ca²⁺, Cu²⁺, Mg²⁺, and Mn²⁺ could enhance the tartrazine removal in the Fe⁰/PMS system. Ca²⁺, Cu²⁺, and Mg²⁺ had no effect of the contribution of reduction, SO₄^•− and ^•OH, while a certain concentration of Mn²⁺ could enhance the contribution proportion of SO₄^•−. These results can provide some references for the Fe⁰/PMS system to treat actual wastewater containing anions and cations.