Effect of biofilm coatings at metal-oxide/water interfaces II: Competitive sorption between Pb(II) and Zn(II) at Shewanella oneidensis/metal-oxide/water interfaces

TitleEffect of biofilm coatings at metal-oxide/water interfaces II: Competitive sorption between Pb(II) and Zn(II) at Shewanella oneidensis/metal-oxide/water interfaces
Publication TypeJournal Article
Year of Publication2016
AuthorsWang, Y, Gélabert, A, Michel, FM, Choi, Y, Eng, PJ, Spormann, AM, Jr, GEBrown
JournalGeochimica et Cosmochimica ActaGeochimica et Cosmochimica Acta
Volume188
Pagination393-406
Date Published09/2016
ISBN Number0016-7037
KeywordsAlumina, Biofilm, Competitive sorption, Hematite, LP-XSW-FY, Metal partitioning, Metal-oxide surface, Pb, Shewanella oneidensis, X-ray standing wave, Zn
Abstract

Competitive sorption of Pb(II) and Zn(II) on Shewanella oneidensis MR-1 biofilm-coated single-crystal α-Al2O3 (1 −1 0 2) and α-Fe2O3 (0 0 0 1) surfaces was investigated using long-period X-ray standing wave-florescence yield (LP-XSW-FY) spectroscopy. In situ partitioning of aqueous Pb(II) and Zn(II) between the biofilms and underlying metal-oxide substrates was probed following exposure of these complex interfaces to equi-molar Pb and Zn solutions (0.01 M NaNO3 as background electrolyte, pH = 6.0, and 3-h equilibration time). At higher Pb and Zn concentrations (⩾10−5 M), more than 99% of these ions partitioned into the biofilms at S. oneidensis/α-Al2O3 (1 −1 0 2)/water interfaces, which is consistent with the partitioning behavior of both Pb(II) or Zn(II) in single-metal-ion experiments. Thus, no apparent competitive effects were found in this system at these relatively high metal-ion concentrations. However, at lower equi-molar concentrations (⩽10−6 M), Pb(II) and Zn(II) partitioning in the same system changed significantly compared to the single-metal-ion systems. The presence of Zn(II) decreased Pb(II) partitioning onto α-Al2O3 (1 −1 0 2) substantially (∼52% to ∼13% at 10−7 M, and ∼23% to ∼5% at 10−6 M), whereas the presence of Pb(II) caused more Zn(II) to partition onto α-Al2O3 (1 −1 0 2) surfaces (∼15% to ∼28% at 10−7 M, and ∼1% to ∼7% at 10−6 M). The higher observed partitioning of Zn(II) (∼28%) at the α-Al2O3 (1 −1 0 2) surfaces compared to Pb(II) (∼13%) in the mixed-metal-ion systems at the lowest concentration (10−7 M) suggests that Zn(II) is slightly favored over Pb(II) for sorption sites on α-Al2O3 (1 −1 0 2) surfaces under our experimental conditions. Competitive sorption of Pb(II) and Zn(II) at S. oneidensis/α-Fe2O3 (0 0 0 1)/water interfaces at equi-molar metal-ion concentrations of ⩽10−6 M showed that the presence of Pb(II) ions decreased Zn(II) partitioning onto α-Fe2O3 (0 0 0 1) significantly (∼45% to <1% at 10−7 M, and ∼41% to 3% at 10−6 M), whereas adding Zn(II) caused only small changes in Pb(II) partitioning (∼59% to ∼47% at 10−7 M, and ∼26% to ∼23% at 10−6 M), suggesting that Pb(II) strongly outcompetes Zn(II) for sorption sites on S. oneidensis-coated α-Fe2O3 (0 0 0 1) surfaces. Our study implies that caution should be taken when applying results obtained from partitioning studies of single-metal-ion systems to mixed-metal-ion systems at complex biofilm/mineral interfaces.

DOI10.1016/j.gca.2016.04.054