Selective Sorption of Co²⁺ over Ni²⁺ Using Biogenic Manganese Oxides

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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 (α_Co) 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.