Preferential sorption of Co2+ ions over Ni2+ ions was achieved using biogenic Mn oxides produced by the Mn-oxidizing fungus Paraconiothyrium sp. WL-2 strain with a maximum selectivity coefficient (αCo) of 18. The selective sorption was based on different sorption mechanism for Co2+ and Ni2+ and unique properties of biogenic Mn oxides. The octahedral Co2+ ions occupy vacancies of central metal sites and edge sites in the octahedral Mn oxide unit structures of biogenic Mn oxides, where they are immobilized by oxidation to CoOOH by Mn(III). In contrast, Ni2+ ions are sorbed primarily on layer edges at circumneutral pHs without oxidation. Selective sorption of Co2+ over Ni2+ on the biogenic Mn oxides results from more vacant sites, higher Mn(III) contents, and larger specific surface areas compared to synthetic Mn oxides.
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