Sorption of Co²⁺ ions on the biogenic Mn oxide produced by a Mn-oxidizing fungus, Paraconiothyrium sp. WL-2

A Paraconiothyrium sp. WL-2 of Mn-oxidizing fungus is highly tolerant to Mn²⁺ ions, and capable of oxidizing more than 380 mg dm^-3 of Mn²⁺ ions, leading to the formation of a large amount of insoluble Mn(III, IV) oxides. The biogenic Mn oxides were characterized by X-ray diffraction, FT-Infrared spectroscopy, elemental analysis, measurement of specific surface area, scanning electron microscopy, and measurement of zeta potential, in comparison with the synthetic Mn oxides. It was found that the biogenic Mn oxide is poorly crystalized birnessite, with higher porosity and much more weakly bounded Mn(II) on the surface than the synthetic Mn oxide. Cobalt(II) ions were sorbed and incorporated as Co(III) into the structure of the biogenic Mn oxide. Sorption efficiency in the biogenic Mn oxide was 5.6 times as high as that in the synthetic ones. Relation of the relased Mn ²⁺ ions to the immobilized Co suggested that Mn(IV) is preferentially used as oxidants over Mn(III) in the biogenic Mn oxide, and emphasized that the existence of Mn(III) in the biogenic Mn oxide activates the geochemical cycles of Mn and the other involved elements in environments.