Abstract
BackgroundAlthough 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.ResultsThe 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 Cu2+ 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 Cu2+ 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.ConclusionsThis 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12932-015-0020-6) contains supplementary material, which is available to authorized users.
Highlights
Most reported biogenic Mn oxides are hexagonal birnessites, other types of biogenic Mn oxides commonly occur in the environment
Though the biogenic Mn oxide (Bixbyite) in this study differs in structure with birnessite, the Cu-Mn distance (3.37 Å and 3.44 Å) in the two sorption samples should be unlikely in incorporation mode
There is a little difference in the coordination mode between the low and high Cu2+ loading samples, probably because there are still some adsorption sites in the low Cu2+ loading sample (233 mmol/kg), resulting in the shift of some sorbed Cu2+ in the monodentate mononuclear (MM) complex to the bidentate binuclear (BB) complex, a more stable geometric structure
Summary
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. At a relatively low Cu2+ 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. At a relatively high Cu2+ 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
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
