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Over the past 30 years, various methods have been developed for enhancing contaminant removal by zerovalent iron (ZVI), thus accumulating a large amount of quantitative data including the reactivity ( k obs ) and electron efficiency (EE). However, comparisons and relationships of the data are still lacking, which hinders the selection and development of ZVI enhancement methods for practical applications. In this review, a large number of k obs and EE results are systematically summarized and classified into three types based on enhancement mechanisms: regulating iron (hydr)oxide films of ZVI (RIF), accelerating ZVI corrosion (AZC), and coupling of iron reactive species with ZVI (CIRs). Then, the comparisons of k obs and EE by ZVI along with their enhancement multiples (referred to as R k and R EE ) were conducted within the context of RIF, AZC, and CIRs. This review identified that in cases where ZVI exhibited low reactivity toward pollutants, it often possessed a high electron efficiency for pollutant reduction and vice versa. Moreover, there existed correlations between lg k obs (lg R k ) and lgEE (lg R EE ) by ZVI with enhancement methods. These relationships suggest that when both the k obs ( R k ) and EE ( R EE ) parameters are known, the other parameter can be predicted to some extent. Finally, this review discussed the effects of the solution chemistry and iron-related compounds on the k obs ( R k ) and EE ( R EE ) by ZVI with enhancement methods in detail and outlined their potential research needs in future studies.
Li et al. (Wed,) studied this question.