Abstract
Arsenic (As) contamination of drinking water is a threat to global health. Manganese(III/IV) (Mn) oxides control As in groundwater by oxidizing more mobile AsIII to less mobile AsV. Both As species sorb to the Mn oxide. The rates and mechanisms of this process are the subject of extensive research; however, as a group, study results are inconclusive and often contradictory. Here, the existing body of literature describing AsIII oxidation by Mn oxides is examined, and several potential reasons for inconsistent kinetic data are discussed. The oxidation of AsIII by Mn(III/IV) oxides is generally biphasic, with reported first order rate constants ranging seven orders of magnitude. Reanalysis of existing datasets from batch reactions of AsIII with δ-MnO2 reveal that the first order rate constants reported for As depletion are time-dependent, and are not well described by pure kinetic rate models. This finding emphasizes the importance of mechanistic modeling that accounts for differences in reactivity between MnIII and MnIV, and the sorption and desorption of AsIII, AsV, and MnII. A thorough understanding of the reaction is crucial to predicting As fate in groundwater and removing As via water treatment with Mn oxides, thus ensuring worldwide access to safe drinking water.
Highlights
Drinking water contamination by inorganic contaminants, such as carcinogenic arsenic (As), is a major threat to global health [1]
Studies on AsIII oxidation by Mn oxides cite the potential of Mn oxides to remove As from drinking water and predict subsurface As mobility
This can only happen if the knowledge generated by these studies is carefully parsed to elucidate mechanisms, applied to in situ remediation methods or ex situ engineered systems
Summary
Drinking water contamination by inorganic contaminants, such as carcinogenic arsenic (As), is a major threat to global health [1]. The ability to predict the fate of contaminants in groundwater is crucial for ensuring continued access to safe drinking water To achieve this goal, it is necessary to develop a thorough understanding of the interaction of trace minerals phases with common groundwater contaminants. Mn oxides exhibit high sorption capacities, with specific surface areas (SSAs) up to the order of 100 m2 /g [10,11] These traits allow Mn oxides to have an impact on the biogeochemical cycling of many environmental contaminants, including organic contaminants [4], selenium (Se) [12,13,14], chromium (Cr) [15,16], uranium (U) [17,18], and arsenic. A thorough understanding of AsIII oxidation by Mn oxides presents a critical opportunity for reducing the impact of As on human health, by predicting and controlling As in drinking and irrigation water
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