科研之友
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摘要
The pentavalent oxyanions antimonate (Sb(V)) and arsenate (As(V)) are toxic metalloids in environmental systems. In this study, we compare their sorption and surface speciation on 2-line ferrihydrite (Fh), delta-MnO2 and Na-montmorillonite (Mont) at pH5.5. The Sb(V) and As(V) sorption affinity and the highest measured surface excess (mmol:g) show that mineral reactivity towards Sb(V) or As(V) sorption increases in the order of Mont < delta-MnO2 < Fh. In addition, Sb(V) showed greater uptake relative to As(V) by both Fh and delta-MnO2. Using differential pair distribution d-PDF) analysis of high-energy X-ray scattering data, we found that the larger SbO6 octahedron (RSb-O = 1.95 angstrom) can bind in both single edge-(E-1) and double corner-sharing (C-2) geometries to Fh and delta-MnO2, whereas the smaller AsO4 tetrahedron (RAs-O = 1.69 angstrom) binds only in the C-2 geometry. Thus, a greater number of surface sites support Sb(V) adsorption relative to As(V) adsorption on Fh and delta-MnO2. Conversely, Mont supports only C-2 adsorption geometries, which is consistent with the similar uptake behaviors of Sb(V) and As(V) on this mineral. Finally, we indexed atomic pairs from adsorbed Sb(V) and As(V) at R > 6 angstrom in the d-PDFs. The analysis of the intermediate-ranged surface structure of our samples substantiated our interpretations of oxyanion adsorption geometries and provided information regarding changes in the underlying mineral surface upon ion adsorption. Our results show that the differences between Sb(V) and As(V) interactions with reactive soil minerals, including their sorption geometries, are linked to their distinct first-shell coordination environments.
- 出版日期2016-7-1
