Sorption of Co(II), Ni(II), and Zn(II) on Biogenic Manganese Oxides Produced by a Mn-Oxidizing Fungus, Strain KR21-2

Abstract

The characteristics of Co(II), Ni(II), and Zn(II) sorption on freshly produced biogenic Mn oxides by a Mn-oxidizing fungus, strain KR21-2, were investigated. The biogenic Mn oxides showed about 10-fold higher efficiencies for sorbing the metal ions than a synthetic Mn oxide (γ-MnO₂) on the basis of unit weight and unit surface area. The order of sorption efficiency on the biogenic Mn oxides was Co(II) > Zn(II) > Ni(II), while that on the synthetic Mn oxide was Zn(II) > Co(II) > Ni(II). These sorption selectivities were confirmed by both sorption isotherms and competitive sorption experiments. Two-step extraction, using 10 mM CuSO₄ solution for exchangeable sorbed ions and 10–20 mM hydroxylamine hydrochloride for ions bound to reducible Mn oxide phase, showed higher irreversibility of Co(II) and Ni(II) sorption on the biogenic Mn oxides while Zn(II) sorption was mostly reversible (Cu(II)-exchangeable). Sorptions of Co(II), Ni(II), and Zn(II) on the synthetic Mn oxide were, however, found to be mostly reversible. Higher irreversibility of Co(II) and Ni(II) sorption on the biogenic Mn oxides may partly explain higher accumulation of these metal ions in Mn oxide phases in natural environments. The results obtained in this study raise the possibility to applying the biogenic Mn oxide formation to treatment of water contaminated with toxic metal ions.

Keywords:

• Sorption
• Metal ions
• Biogenic manganese oxide
• Mn-oxidizing fungus

Acknowledgments

The authors are grateful to Dr. G. Yuan, Landcare Research, New Zealand, and an anonymous reviewer for their valuable help in revising the manuscript, and to Mrs. Anne Austin, Landcare Research for improving the English. This work was partly supported by a Grant-in-Aid for Young Scientists (B) (16710052) from the Ministry of Education, Culture, Sports, Science and Technology of Japan