Unraveling the Mechanisms of Fe Oxidation and Mn Reduction on Mn Indicators of Reduction in Soil (IRIS) Films
Date
2023-04-25
Journal Title
Journal ISSN
Volume Title
Publisher
Environmental Science and Technology
Abstract
Indicators of reduction in soil (IRIS) devices are low-cost soil redox sensors coated with Fe or Mn oxides, which can be reductively dissolved from the device under suitable redox conditions. Removal of the metal oxide coating from the surface, leaving behind the white film, can be quantified and used as an indicator of reducing conditions in soils. Manganese IRIS, coated with birnessite, can also oxidize Fe(II), resulting in a color change from brown to orange that complicates the interpretation of coating removal. Here, we studied field-deployed Mn IRIS films where Fe oxidation was present to unravel the mechanisms of Mn oxidation of Fe(II) and the resulting minerals on the IRIS film surface. We observed reductions in the Mn average oxidation state when Fe precipitation was evident. Fe precipitation was primarily ferrihydrite (30–90%), but lepidocrocite and goethite were also detected, notably when the Mn average oxidation state decreased. The decrease in the average oxidation state of Mn was due to the adsorption of Mn(II) to the oxidized Fe and the precipitation of rhodochrosite (MnCO3) on the film. The results were variable on small spatial scales (<1 mm), highlighting the suitability of IRIS in studying heterogeneous redox reactions in soil. Mn IRIS also provides a tool to bridge lab and field studies of the interactions between Mn oxides and reduced constituents.
Description
This document is the Accepted Manuscript version of a Published Work that appeared in final form in Environmental Science and Technology, copyright © 2023 American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.est.3c00161. This article will be embargoed until 04/25/2024.
Keywords
birnessite, ferrihydrite, lepidocrocite, goethite, synchrotron X-ray absorption spectroscopy, rhodochrosite
Citation
Limmer, Matt A., Franklin A. Linam, Abby E. Evans, and Angelia L. Seyfferth. “Unraveling the Mechanisms of Fe Oxidation and Mn Reduction on Mn Indicators of Reduction in Soil (IRIS) Films.” Environmental Science & Technology 57, no. 16 (April 25, 2023): 6530–39. https://doi.org/10.1021/acs.est.3c00161.