Natural Mn oxides, in particular those of microbially-mediated origin, are among the strongest of scavengers for metal ions in natural waters and are powerful oxidants for organic material. Although relatively low in absolute abundance, biogenic Mn oxides are ubiquitous in the environment and occur as high surface area grain coatings or as fine suspended particulate matter. This mode of occurrence facilitates interaction with surrounding reactants. As a consequence, biogenic Mn oxides are profoundly important to the global biogeochemical cycling of contaminants, trace nutrients, and carbon. In recent years, much progress has been made in understanding the physical end electronic structures of these remarkable materials and their mechanisms of formation. Their reactivity generally derives from a highly defected, nano-scale layered structure, often occurring as unstacked sheets. This motif, produced by bacteria and fungi in oceans and freshwater sedimentary environments, is responsible for contaminant sequestration in terrestrial systems and is linked to enhanced Mn concentrations in the marine photic zone. Mn(III) is an important intermediate in the oxidation Mn(II) to Mn(IV), and recent studies have implicated reactive oxygen species as being important participants in this reaction. This talk will review these studies and provide specific examples of biogenic Mn oxide occurrence and reactivity in sedimentary and marine environments.

Biogenic Mn oxides: Occurrence, structure, reactivity, and formation mechanisms

247th National Meeting (2014)

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