TY - JOUR
T1 - Antimonate and arsenate speciation on reactive soil minerals studied by differential pair distribution function analysis
AU - van Genuchten, Case M.
AU - Peña, Jasquelin
N1 - Funding Information:
We gratefully acknowledge the following researchers for their technical assistance and/or advice along the various stages of this work: Kevin Beyer, Karena Chapman, Alejandro Fernandez-Martinez, Francesco Marafatto, Thierry Adatte and Ian Bourg. We acknowledge support from the Sandoz Family Foundation and BCV Foundation . Use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357 .
Publisher Copyright:
© 2016 Elsevier B.V.
PY - 2016/7/1
Y1 - 2016/7/1
N2 - 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), δ-MnO2 and Na-montmorillonite (Mont) at pH 5.5. 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 < δ-MnO2 < Fh. In addition, Sb(V) showed greater uptake relative to As(V) by both Fh and δ-MnO2. Using differential pair distribution function (d-PDF) analysis of high-energy X-ray scattering data, we found that the larger SbO6 octahedron (RSb-O = 1.95 Å) can bind in both single edge-(1E) and double corner-sharing (2C) geometries to Fh and δ-MnO2, whereas the smaller AsO4 tetrahedron (RAs-O = 1.69 Å) binds only in the 2C geometry. Thus, a greater number of surface sites support Sb(V) adsorption relative to As(V) adsorption on Fh and δ-MnO2. Conversely, Mont supports only 2C 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 Å 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.
AB - 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), δ-MnO2 and Na-montmorillonite (Mont) at pH 5.5. 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 < δ-MnO2 < Fh. In addition, Sb(V) showed greater uptake relative to As(V) by both Fh and δ-MnO2. Using differential pair distribution function (d-PDF) analysis of high-energy X-ray scattering data, we found that the larger SbO6 octahedron (RSb-O = 1.95 Å) can bind in both single edge-(1E) and double corner-sharing (2C) geometries to Fh and δ-MnO2, whereas the smaller AsO4 tetrahedron (RAs-O = 1.69 Å) binds only in the 2C geometry. Thus, a greater number of surface sites support Sb(V) adsorption relative to As(V) adsorption on Fh and δ-MnO2. Conversely, Mont supports only 2C 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 Å 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.
KW - Antimony
KW - Arsenic
KW - Differential pair distribution function
KW - Oxyanion biogeochemistry
KW - Soil minerals
UR - http://www.scopus.com/inward/record.url?scp=84960856771&partnerID=8YFLogxK
U2 - 10.1016/j.chemgeo.2016.03.001
DO - 10.1016/j.chemgeo.2016.03.001
M3 - Article
AN - SCOPUS:84960856771
SN - 0009-2541
VL - 429
SP - 1
EP - 9
JO - Chemical Geology
JF - Chemical Geology
ER -