Zinc Sorption During Bio-oxidation and Precipitation of Manganese Modifies the Layer Stacking of Biogenic Birnessite

The formation and structural evolution of fungal mediate biogenic birnessite are dynamic processes. Although the associations of Zn with the pre-formed biogenic Mn oxides are relatively well understood, the reactivity of the intermediate precipitate at the initial stage of Mn bio-oxidation appears to differ from the final precipitate. In the present work, Zn sorption during precipitation of biogenic Mn oxides was investigated contrasting Zn sorption to pre-formed biogenic Mn oxides, using the Mn-oxidizing fungus Paraconiothyrium sp. WL-2. A substantially higher Zn uptake was found during precipitation of biogenic Mn oxides compared to Zn sorption to pre-formed biogenic Mn oxides. The presence of Zn during Mn oxidation resulted in a biogenic Mn oxide with reduced ordering in the c-axis. The precipitate was identified by X-ray diffraction (XRD) as a layer-type Mn oxide with structural properties similar to hexagonal birnessite. Extended X-ray absorption fine structure (EXAFS) spectroscopy showed that Zn forms triple-corner-sharing tetrahedral coordination ((TCS)-T-IV-Zn) complexes on the surface of birnessite, which may inhibited layer stacking of birnessite in the final products. This study emphasizes the importance of the intermediate precipitates on Zn sorption, and provides insight regarding the dynamic interaction between Zn and Mn oxide in the process of microbiological oxidation. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the supplemental file.