Details
| Original language | English |
|---|---|
| Pages (from-to) | 218-236 |
| Number of pages | 19 |
| Journal | Geochimica et cosmochimica acta |
| Volume | 391 |
| Early online date | 28 Dec 2024 |
| Publication status | Published - 15 Feb 2025 |
Abstract
Antimony (Sb) is a metalloid extensively used in industrial products with a high potential for accumulation in organic-rich soils. Under oxic conditions, dissolved Sb occurs in its pentavalent oxidation state, Sb(V), but little is known about sorptive interactions between Sb(V) and natural organic matter (OM). Therefore, we conducted batch experiments with Sb(V) and particulate OM (POM) of peat as a model sorbent for particulate soil OM. We varied reaction time (1–21 d), concentrations of Sb(V) (1–218 µM) and POM (1–5 g L−1), pH (1.5–10.5), as well as type (NaCl and CaCl2) and concentration of the background electrolyte (no salt, 0.01 and 0.1 M). Additionally, we explored the molecular mechanism of Sb(V) binding to POM at pH ≤ 4 using X-ray absorption spectroscopy. Based on this information, we modelled Sb(V) sorption data with the Stockholm Humic Model (SHM). Sorption of Sb(V) to POM did not cause Sb reduction and decreased from 109 mmol kg−1 at pH 3 to 72.4 mmol kg−1 at pH 5 (1 g L−1 POM, 0.01 M NaCl). Although sorption maxima were found at pH 1.8–2.8, up to ∼ 10 % of total Sb(V) was still removed from solution at pH 6. An increase in POM concentration, ionic strength, and the presence of Ca2+ promoted Sb(V) sorption. The high Sb(V) sorption capacity of POM was associated with a low binding affinity. Sorption kinetics of Sb(V) were slow and generally showed bi-phasic patterns. Apparent half-life times of the fast and slow sorption process at pH 4 and 5 were on average 12.7 and 117 h, respectively. The slowly sorbing Sb(V) was ascribed to diffusion of Sb(V) into net-negatively charged POM particles. X-ray absorption spectroscopy analyses showed 6.3 ± 0.4 O atoms at 1.98 ± 0.01 Å (mean ± SD), followed by 2.1 ± 0.4 C atoms at 2.82 ± 0.05 Å, implying pentavalent Sb in octahedral coordination and bidentate complexation by polycarboxylic, hydroxy-carboxylic, and/or polyol ligands in 5- or 6-membered ring structures. The SHM accurately described Sb(V) sorption edges and sorption isotherm data collected at pH 3–5. SHM calculations implied that Sb(V) sorption to POM may be quantitatively relevant even at pH > 7 and impairs the precipitation of Ca-antimonates at acidic pH. We also predicted competition effects showing that Al, Pb, and MoO42− can cause substantial desorption of Sb(V) when present in excess over Sb(V). Model predictions also indicated that Sb(V) complexation by POM in organic soils becomes negligible in presence of > 1 wt% metal oxides. Overall, our results show that although POM has an enormous potential for Sb(V) sequestration over a broad pH range, competing ions and mineral sorbents may strongly decrease Sb(V) binding by POM. This implies that Sb(V) binding to POM is only relevant in oxic metal-poor soil environments such as ombrotrophic peats, organic surface layers, and OM-rich microenvironments of mineral soils.
Keywords
- Antimonate, Soil organic matter, Sorptive interactions, Stockholm Humic Model, X-ray absorption spectroscopy
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Geochemistry and Petrology
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In: Geochimica et cosmochimica acta, Vol. 391, 15.02.2025, p. 218-236.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Antimony(V) reaction with particulate natural organic matter
T2 - Sorption behavior, binding mechanism, and environmental implications
AU - Mikutta, Christian
AU - Christl, Iso
AU - Hockmann, Kerstin
AU - Niegisch, Max
AU - Schnee, Laura S.
N1 - Publisher Copyright: © 2024 The Authors
PY - 2025/2/15
Y1 - 2025/2/15
N2 - Antimony (Sb) is a metalloid extensively used in industrial products with a high potential for accumulation in organic-rich soils. Under oxic conditions, dissolved Sb occurs in its pentavalent oxidation state, Sb(V), but little is known about sorptive interactions between Sb(V) and natural organic matter (OM). Therefore, we conducted batch experiments with Sb(V) and particulate OM (POM) of peat as a model sorbent for particulate soil OM. We varied reaction time (1–21 d), concentrations of Sb(V) (1–218 µM) and POM (1–5 g L−1), pH (1.5–10.5), as well as type (NaCl and CaCl2) and concentration of the background electrolyte (no salt, 0.01 and 0.1 M). Additionally, we explored the molecular mechanism of Sb(V) binding to POM at pH ≤ 4 using X-ray absorption spectroscopy. Based on this information, we modelled Sb(V) sorption data with the Stockholm Humic Model (SHM). Sorption of Sb(V) to POM did not cause Sb reduction and decreased from 109 mmol kg−1 at pH 3 to 72.4 mmol kg−1 at pH 5 (1 g L−1 POM, 0.01 M NaCl). Although sorption maxima were found at pH 1.8–2.8, up to ∼ 10 % of total Sb(V) was still removed from solution at pH 6. An increase in POM concentration, ionic strength, and the presence of Ca2+ promoted Sb(V) sorption. The high Sb(V) sorption capacity of POM was associated with a low binding affinity. Sorption kinetics of Sb(V) were slow and generally showed bi-phasic patterns. Apparent half-life times of the fast and slow sorption process at pH 4 and 5 were on average 12.7 and 117 h, respectively. The slowly sorbing Sb(V) was ascribed to diffusion of Sb(V) into net-negatively charged POM particles. X-ray absorption spectroscopy analyses showed 6.3 ± 0.4 O atoms at 1.98 ± 0.01 Å (mean ± SD), followed by 2.1 ± 0.4 C atoms at 2.82 ± 0.05 Å, implying pentavalent Sb in octahedral coordination and bidentate complexation by polycarboxylic, hydroxy-carboxylic, and/or polyol ligands in 5- or 6-membered ring structures. The SHM accurately described Sb(V) sorption edges and sorption isotherm data collected at pH 3–5. SHM calculations implied that Sb(V) sorption to POM may be quantitatively relevant even at pH > 7 and impairs the precipitation of Ca-antimonates at acidic pH. We also predicted competition effects showing that Al, Pb, and MoO42− can cause substantial desorption of Sb(V) when present in excess over Sb(V). Model predictions also indicated that Sb(V) complexation by POM in organic soils becomes negligible in presence of > 1 wt% metal oxides. Overall, our results show that although POM has an enormous potential for Sb(V) sequestration over a broad pH range, competing ions and mineral sorbents may strongly decrease Sb(V) binding by POM. This implies that Sb(V) binding to POM is only relevant in oxic metal-poor soil environments such as ombrotrophic peats, organic surface layers, and OM-rich microenvironments of mineral soils.
AB - Antimony (Sb) is a metalloid extensively used in industrial products with a high potential for accumulation in organic-rich soils. Under oxic conditions, dissolved Sb occurs in its pentavalent oxidation state, Sb(V), but little is known about sorptive interactions between Sb(V) and natural organic matter (OM). Therefore, we conducted batch experiments with Sb(V) and particulate OM (POM) of peat as a model sorbent for particulate soil OM. We varied reaction time (1–21 d), concentrations of Sb(V) (1–218 µM) and POM (1–5 g L−1), pH (1.5–10.5), as well as type (NaCl and CaCl2) and concentration of the background electrolyte (no salt, 0.01 and 0.1 M). Additionally, we explored the molecular mechanism of Sb(V) binding to POM at pH ≤ 4 using X-ray absorption spectroscopy. Based on this information, we modelled Sb(V) sorption data with the Stockholm Humic Model (SHM). Sorption of Sb(V) to POM did not cause Sb reduction and decreased from 109 mmol kg−1 at pH 3 to 72.4 mmol kg−1 at pH 5 (1 g L−1 POM, 0.01 M NaCl). Although sorption maxima were found at pH 1.8–2.8, up to ∼ 10 % of total Sb(V) was still removed from solution at pH 6. An increase in POM concentration, ionic strength, and the presence of Ca2+ promoted Sb(V) sorption. The high Sb(V) sorption capacity of POM was associated with a low binding affinity. Sorption kinetics of Sb(V) were slow and generally showed bi-phasic patterns. Apparent half-life times of the fast and slow sorption process at pH 4 and 5 were on average 12.7 and 117 h, respectively. The slowly sorbing Sb(V) was ascribed to diffusion of Sb(V) into net-negatively charged POM particles. X-ray absorption spectroscopy analyses showed 6.3 ± 0.4 O atoms at 1.98 ± 0.01 Å (mean ± SD), followed by 2.1 ± 0.4 C atoms at 2.82 ± 0.05 Å, implying pentavalent Sb in octahedral coordination and bidentate complexation by polycarboxylic, hydroxy-carboxylic, and/or polyol ligands in 5- or 6-membered ring structures. The SHM accurately described Sb(V) sorption edges and sorption isotherm data collected at pH 3–5. SHM calculations implied that Sb(V) sorption to POM may be quantitatively relevant even at pH > 7 and impairs the precipitation of Ca-antimonates at acidic pH. We also predicted competition effects showing that Al, Pb, and MoO42− can cause substantial desorption of Sb(V) when present in excess over Sb(V). Model predictions also indicated that Sb(V) complexation by POM in organic soils becomes negligible in presence of > 1 wt% metal oxides. Overall, our results show that although POM has an enormous potential for Sb(V) sequestration over a broad pH range, competing ions and mineral sorbents may strongly decrease Sb(V) binding by POM. This implies that Sb(V) binding to POM is only relevant in oxic metal-poor soil environments such as ombrotrophic peats, organic surface layers, and OM-rich microenvironments of mineral soils.
KW - Antimonate
KW - Soil organic matter
KW - Sorptive interactions
KW - Stockholm Humic Model
KW - X-ray absorption spectroscopy
UR - http://www.scopus.com/inward/record.url?scp=85215865373&partnerID=8YFLogxK
U2 - 10.1016/j.gca.2024.12.030
DO - 10.1016/j.gca.2024.12.030
M3 - Article
AN - SCOPUS:85215865373
VL - 391
SP - 218
EP - 236
JO - Geochimica et cosmochimica acta
JF - Geochimica et cosmochimica acta
SN - 0016-7037
ER -