BACKGROUND Although most reported biogenic Mn oxides are hexagonal birnessites, other types of biogenic Mn oxides also commonly occur in the environment. However, sorption characteristics and underlying mechanisms of the adsorption of heavy-metal ions on these biogenic Mn oxides are still rarely addressed. In this study, the sorption mechanisms of Cu(II) on a low valence biogenic Mn oxide, poorly crystallized bixbyite-like Mn2O3 (α-Mn2O3), were investigated. RESULTS The maximum adsorption capacity of Cu(II) onto this biogenic Mn oxide at pH 6.00 was 796 mmol/kg (0.45 mol Cu mol(-1) Mn). The complex structure of adsorbed Cu(II) was constrained using Cu extended X-ray absorption fine structure (EXAFS) analysis, combined with structural parameters of the biogenic Mn oxide with alternately arranged regular and distorted MnO6 octahedra obtained through multiple-FEFF fitting of Mn EXAFS data. The sorbed Cu(II) was found to coordinate with the biogenic Mn oxide particle edges as inner-sphere complexes. At a relatively low Cu(2+) loading (233 mmol/kg, pH 6.00), Cu(II) adsorbed onto the biogenic Mn oxide with two types of coordinated complexes, i.e., (1) coordinated with one regular/distorted MnO6 octahedron as a monodentate-mononuclear complex and (2) with two adjacent MnO6 octahedra as a bidentate-binuclear complex. While, at a relatively high Cu(2+) loading (787 mmol/kg, pH 6.00), only one type of coordinated complex was constrained, the adsorbed Cu(II) coordinated with one regular/distorted MnO6 octahedron as a monodentate-mononuclear complex. CONCLUSIONS This research extends further insight into the bacterial Mn(II) oxidation in the environment and serves as a good reference for understanding the interactions between metal ions and biogenic low valence Mn oxides, which are still poorly explored either theoretically or practically.

中文翻译：

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从土壤中分离的 Bacillus CUA 产生的生物方铁锰矿类 Mn2O3 对 Cu(2+) 的吸收机制。


背景虽然大多数报道的生物源氧化锰是六方水钠锰矿，但其他类型的生物源氧化锰也常见于环境中。然而，这些生物锰氧化物上重金属离子吸附的吸附特性和潜在机制仍然很少得到解决。在本研究中，研究了 Cu(II) 在低价生物成因 Mn 氧化物（结晶不良的方铁锰矿状 Mn2O3 (α-Mn2O3)）上的吸附机制。结果在pH 6.00时，Cu(II)在该生物源氧化锰上的最大吸附容量为796 mmol/kg (0.45 mol Cu mol(-1) Mn)。利用Cu扩展X射线吸收精细结构（EXAFS）分析，结合通过Mn的多重FEFF拟合获得的具有交替排列的规则和扭曲MnO6八面体的生物Mn氧化物的结构参数，约束了吸附的Cu（II）的复杂结构EXAFS 数据。发现吸附的 Cu(II) 与生物氧化锰颗粒边缘协调形成内球复合物。在相对较低的 Cu(2+) 负载量（233 mmol/kg，pH 6.00）下，Cu(II) 吸附到具有两种类型的配位络合物的生物氧化锰上，即（1）与一个规则/扭曲的 MnO6 八面体配位作为单齿单核配合物和（2）与两个相邻的 MnO6 八面体作为双齿双核配合物。而在相对较高的 Cu(2+) 负载量（787 mmol/kg，pH 6.00）下，仅限制一种类型的配位络合物，即吸附的 Cu(II) 与一个规则/扭曲的 MnO6 八面体配位为单齿单核复杂的。 结论这项研究进一步深入了解了环境中细菌Mn(II)氧化，并为理解金属离子与生物低价Mn氧化物之间的相互作用提供了良好的参考，而这种相互作用在理论上或实践上仍缺乏探索。