Preferential Elimination of Ba²⁺ through Irreversible Biogenic Manganese Oxide Sequestration

• Main Authors: Yukinori Tani, Satomi Kakinuma, Jianing Chang, Kazuya Tanaka, Naoyuki Miyata
• Format: Article
• Language: English
• Published: MDPI AG 2021-01-01
• Series: Minerals
• Subjects: biogenic manganese oxide; Mn(II) oxidizing fungi; sequestration of barium(II) ion; Acrenonium strictum; birnessite
• Online Access: https://www.mdpi.com/2075-163X/11/1/53
• ISSN: 2075-163X

Biogenic manganese oxides (BMOs) formed in a culture of the Mn(II)-oxidizing fungus <i>Acremonium strictum</i> strain KR21-2 are known to retain enzymatic Mn(II) oxidation activity. Consequently, these are increasingly attracting attention as a substrate for eliminating toxic elements from contaminated wastewaters. In this study, we examined the Ba²⁺ sequestration potential of enzymatically active BMOs with and without exogenous Mn²⁺. The BMOs readily oxidized exogenous Mn²⁺ to produce another BMO phase, and subsequently sequestered Ba²⁺ at a pH of 7.0, with irreversible Ba²⁺ sequestration as the dominant pathway. Extended X-ray absorption fine structure spectroscopy and X-ray diffraction analyses demonstrated alteration from turbostratic to tightly stacked birnessite through possible Ba²⁺ incorporation into the interlayer. The irreversible sequestration of Sr²⁺, Ca²⁺, and Mg²⁺ was insignificant, and the turbostratic birnessite structure was preserved. Results from competitive sequestration experiments revealed that the BMOs favored Ba²⁺ over Sr²⁺, Ca²⁺, and Mg²⁺. These results explain the preferential accumulation of Ba²⁺in natural Mn oxide phases produced by microbes under circumneutral environmental conditions. These findings highlight the potential for applying enzymatically active BMOs for eliminating Ba²⁺ from contaminated wastewaters.