The study of mercury sorption products in model systems using appropriate in situ molecular-scale probes can provide detailed information on the modes of sorption at mineral/water interfaces. Such studies are essential for assessing the influence of sorption processes on the transport of Hg in contaminated natural systems. Macroscopic uptake of Hg(II) on goethite (α-FeOOH), γ-alumina (γ-Al2O3), and bayerite (β-Al(OH)3) as a function of pH has been combined with Hg L III-edge EXAFS spectroscopy, FTIR spectroscopy, and bond valence analysis of possible sorption products to provide this type of information. Macroscopic uptake measurements show that Hg(II) sorbs strongly to fine-grained powders of synthetic goethite (Hg sorption density Γ=0.39-0.42 μmol/m2) and bayerite (Γ=0.39-0.44 μmol/m2), while sorbing more weakly to γ-alumina (Γ=0.04-0.13 μmol/m 2). EXAFS spectroscopy on the sorption samples shows that the dominant mode of Hg sorption on these phases is as monodentate and bidentate inner-sphere complexes. The mode of Hg(II) sorption to goethite was similar over the pH range 4.3-7.4, as were those of Hg(II) sorption to bayerite over the pH range 5.1-7.9. Conversion of the γ-Al2O3 sorbent to a bayerite-like phase in addition to the apparent reduction of Hg(II) to Hg(I), possibly by photoreduction during EXAFS data collection, resulted in enhanced Hg uptake from pH 5.2-7.8 and changes in the modes of sorption that correlate with the formation of the bayerite-like phase. Bond valence calculations are consistent with the sorption modes proposed from EXAFS analysis. EXAFS analysis of Hg(II) sorption products on a natural Fe oxyhydroxide precipitate and Al/Si-bearing flocculent material showed sorption products and modes of surface attachment similar to those for the model substrates, indicating that the model substrates are useful surrogates for the natural sediments. © 2003 Elsevier Inc. All rights reserved.
CITATION STYLE
Kim, C. S., Rytuba, J. J., & Brown, G. E. (2004). EXAFS study of mercury(II) sorption to Fe- and Al-(hydr)oxides: I. Effects of pH. Journal of Colloid and Interface Science, 271(1), 1–15. https://doi.org/10.1016/S0021-9797(03)00330-8
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