Mineralogy and geochemistry of manganese: A review of publications

The relatively low hydrolyzing capacity of Mn(II) leads to the formation of oxides rather than hydroxides of this element in soils. The formation of vernadite, birnessite, todorokite, and lithiophorite was recently proved in soils. Vernadite with an Fe admixture and Mn-containing iron minerals, i.e., ferroxyhyte, ferrihydrite, and magnetite, were also found. Fe-vernadite and Mn-ferroxyhyte are the most abundant in soils. Manganese oxidogenesis is the most intensely pronounced in the soils of steppe and forest-steppe zones, in which the assemblage of Mn-containing minerals is wider than in taiga soils. Carbonates are able to inhibit the development of Mn oxidogenesis. The bulk of Mn compounds are confined to the silt rather than to the clay fraction, since manganese oxides are negatively charged in the pH interval typical of the bulk of soils. Manganese oxides are able to retain heavy metals, i.e., Co, Ni, Zn, and others. The active participation of Mn oxides in Cr(III) oxidation raises its mobility and toxicity. Manganese oxides may favor humus formation by taking part in phenol oxidation.