Abstract
Conspectus: Redox reactions of Fe- and Mn-oxides play important roles in the fate and transformation of many contaminants in natural environments. Due to experimental and analytical challenges associated with complex environments, there has been a limited understanding of the reaction kinetics and mechanisms in actual environmental systems, and most of the studies so far have only focused on simple model systems. To bridge the gap between simple model systems and complex environmental systems, it is necessary to increase the complexity of model systems and examine both the involved interaction mechanisms and how the interactions affected contaminant transformation. In this Account, we primarily focused on (1) the oxidative reactivity of Mn- and Fe-oxides and (2) the reductive reactivity of Fe(II)/iron oxides in complex model systems toward contaminant degradation. The effects of common metal ions such as Mn2+, Ca2+, Ni2+, Cr3+ and Cu2+, ligands such as small anionic ligands and natural organic matter (NOM), and second metal oxides such as Al, Si and Ti oxides on the redox reactivity of the systems are briefly summarized.
Highlights
Iron and manganese are the first and third most abundant transition metals in the earth’s crust (Martin, 2005)
We focus on assessing recent developments and current understanding in the redox reactions of Fe- and Mn-oxides in complex systems, which will provide a bridge to connect the findings from simple model systems with those from natural environmental systems
Using the obtained P values, the authors revealed that higher concentrations of model natural organic matter (NOM) (Aldrich humic acid, alginate, or pyromellitic acid) in the ternary systems (MnO2 + goethite + NOM) had larger P values, indicating that the NOM promoted the oxidative reactivity of MnO2 in the ternary mixtures
Summary
Iron and manganese are the first and third most abundant transition metals in the earth’s crust (Martin, 2005). 2008; Zhang and Weber, 2013) and the global geochemical cycles of many elements, such as O, N, P and S (Borch et al, 2010; Sunda, 2010) These reactions have been widely accepted as surface reactions, and the change in the oxide surface properties would significantly influence the overall reactivity (Anderson and Benjamin, 1990b; Meng and Letterman, 1993; Taujale et al, 2016; Huang et al, 2019a; Huang et al, 2019b). Natural organic matter (NOM) is a complex mixture of organic materials that vary from one source to another It is ubiquitous in natural environments and has a large impact on the fate and transformation of contaminants (Davis, 1984; Redman et al, 2002). We focus on assessing recent developments and current understanding in the redox reactions of Fe- and Mn-oxides in complex systems, which will provide a bridge to connect the findings from simple model systems with those from natural environmental systems
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