Journal
CHEMOSPHERE
Volume 262, Issue -, Pages -Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.chemosphere.2020.128082
Keywords
Photochemical oxidation; Mn(III) intermediates; Transformation mechanism; Disproportionation
Categories
Funding
- National Key Research and Development Program of China [2018YFD0800304, 2017YFD0801000]
- National Natural Science Foundation of China [41571228, 41877025, 41877528]
- Fundamental Research Funds for the Central Universities [2662018JC055, 2662017JC025]
- US Department of Energy, Office of Basic Energy Sciences, Division of Chemical, Biological and Geological Sciences [DE-FG02-86ER13622]
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This study reveals the important role of Mn(III) intermediates in the formation of natural Mn oxide minerals. The rate of oxidation of Mn2+ to Mn(IV) oxide minerals decreases with increasing initial Mn2+ concentration, while the increase in NO3- concentration, pH, and temperature promotes Mn2+ photochemical oxidation. Additionally, at low ligand concentrations, the photochemical formation rate of Mn(IV) oxide minerals increases with increasing ligand concentrations.
As important natural oxidants and adsorbents, manganese (Mn) oxide minerals affect the speciation, bioavailability and fate of pollutants and nutrient elements. It was found that birnessite-type Mn(IV) oxide minerals can be formed in the presence of NO3- and solar irradiation. However, the photochemical formation and transformation processes from Mn2+ to Mn(IV) oxide minerals remain unclear. In this work, the Mn(IV) oxide minerals were confirmed to be photochemically formed mainly due to the disproportionation of Mn(III) intermediates generated from the oxidation of Mn2+ in the presence of NO3- under UV light irradiation. The oxidation rate of Mn2+ to Mn(IV) oxide minerals decreased with increasing initial Mn2+ concentration due to the lower disproportionation rate. The increase in NO3- concentration, pH and temperature promoted Mn2+ photochemical oxidation. The photochemical formation rate of Mn(IV) oxide minerals increased with increasing ligand concentrations at low ligand concentrations. Ligands affected the formation of Mn(IV) oxide minerals by promoting the formation and reducing the reactivity of Mn(III) intermediates. Overall, this work reveals the important role of Mn(III) intermediates in the formation of natural Mn oxide minerals. (C) 2020 Elsevier Ltd. All rights reserved.
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