Structural factors of biogenic birnessite produced by fungus Paraconiothyrium sp. WL-2 strain affecting sorption of Co ²⁺

The surface reactivity of biogenic birnessite is attributed to its structure. However, structural control of heavy metal adsorption on biogenic birnessite is not well understood. Here a poorly-crystalline birnessite was produced by the fungus Paraconiothyrium sp. WL-2 strain under ambient pH and temperature conditions. The structure was characterized by X-ray absorption spectroscopy and X-ray diffraction. Sorption behaviors of Co ²⁺ were compared with Zn ²⁺. The primary product of the Mn bio-oxidation is hexagonal birnessite with a turbostratic structure. XAFS analysis demonstrated that the biogenic birnessite consists of octahedral sheets with Mn(IV) as the central metal and some vacant sites. Mn(III) atoms are coordinated to some of the vacant sites in the interlayer. The adsorption of Co ²⁺ by the biogenic birnessite is higher than Zn ²⁺. The excess adsorption of Co ²⁺ than Zn ²⁺ is nearly the same as the excess release of Mn from the biogenic birnessite. These results strongly suggested that the interlayer Mn(III) can oxidize the adsorbed Co ²⁺ to Co ³⁺, resulting in excess adsorption of Co ²⁺ compared to Zn ²⁺ by biogenic birnessite.