Details
| Original language | English |
|---|---|
| Pages (from-to) | 258-276 |
| Number of pages | 19 |
| Journal | Geochimica et cosmochimica acta |
| Volume | 144 |
| Publication status | Published - 1 Nov 2014 |
Abstract
Ferric oxyhydroxides play an important role in controlling the bioavailability of oxyanions such as arsenate and phosphate in soil. Despite this, little is known about the properties and reactivity of Fe(III)-organic matter phases derived from adsorption (reaction of organic matter (OM) to post-synthesis Fe oxide) versus coprecipitation (formation of Fe oxides in presence of OM). Coprecipitates and adsorption complexes were synthesized at pH 4 using two natural organic matter (NOM) types extracted from forest floor layers (Oi and Oa horizon) of a Haplic Podzol. Iron(III) coprecipitates were formed at initial molar metal-to-carbon (M/C) ratios of 1.0 and 0.1 and an aluminum (Al)-to-Fe(III) ratio of 0.2. Sample properties were studied by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), N2 gas adsorption, dynamic light scattering, and electrophoretic mobility measurements. Arsenic [As(V)] adsorption to Fe-OM phases was studied in batch experiments (168h, pH 4, 100μM As). The organic carbon (OC) contents of the coprecipitates (82-339mgg-1) were higher than those of adsorption complexes (31 and 36mgg-1), leading to pronounced variations in specific surface area (9-300m2g-1), average pore radii (1-9nm), and total pore volumes (11-374mm3g-1) but being independent of the NOM type or the presence of Al. The occlusion of Fe solids by OM (XPS surface concentrations: 60-82atom% C) caused comparable pHPZC (1.5-2) of adsorption complexes and coprecipitates. The synthesis conditions resulted in different Fe-OM association modes: Fe oxide particles in 'M/C 0.1' coprecipitates covered to a larger extent the outermost aggregate surfaces, for some 'M/C 1.0' coprecipitates OM effectively enveloped the Fe oxides, while OM in the adsorption complexes primarily covered the outer aggregate surfaces. Despite of their larger OC contents, adsorption of As(V) was fastest to coprecipitates formed at low Fe availability (M/C 0.1) and facilitated by desorption of weakly bonded OC and disaggregation. In contrast, 'M/C 1.0' coprecipitates showed a comparable rate of As uptake as the adsorption complexes. While small mesopores (2-10nm) promoted the fast As uptake particularly to 'M/C 0.1' coprecipitates, the presence of micropores (<2nm) appeared to impair As desorption. This study shows that the environmental reactivity of poorly crystalline Fe(III) oxides in terrestrial and aquatic systems can largely vary depending on the formation conditions. Carbon-rich Fe phases precipitated at low M/C ratios may play a more important role in oxyanion immobilization and Fe and C cycling than phases formed at higher M/C ratios or respective adsorption complexes.
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Geochemistry and Petrology
Sustainable Development Goals
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In: Geochimica et cosmochimica acta, Vol. 144, 01.11.2014, p. 258-276.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Properties and reactivity of Fe-organic matter associations formed by coprecipitation versus adsorption: Clues from arsenate batch adsorption
AU - Mikutta, Robert
AU - Lorenz, Dennis
AU - Guggenberger, Georg
AU - Haumaier, Ludwig
AU - Freund, Anja
N1 - Funding information: We are grateful to the German Research Foundation (DFG project MI 1377/3-1 ) for financial support, Hilal Alemdar and Roger-Michael Klatt for laboratory assistance, and the editor and reviewers for their helpful comments on the manuscript.
PY - 2014/11/1
Y1 - 2014/11/1
N2 - Ferric oxyhydroxides play an important role in controlling the bioavailability of oxyanions such as arsenate and phosphate in soil. Despite this, little is known about the properties and reactivity of Fe(III)-organic matter phases derived from adsorption (reaction of organic matter (OM) to post-synthesis Fe oxide) versus coprecipitation (formation of Fe oxides in presence of OM). Coprecipitates and adsorption complexes were synthesized at pH 4 using two natural organic matter (NOM) types extracted from forest floor layers (Oi and Oa horizon) of a Haplic Podzol. Iron(III) coprecipitates were formed at initial molar metal-to-carbon (M/C) ratios of 1.0 and 0.1 and an aluminum (Al)-to-Fe(III) ratio of 0.2. Sample properties were studied by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), N2 gas adsorption, dynamic light scattering, and electrophoretic mobility measurements. Arsenic [As(V)] adsorption to Fe-OM phases was studied in batch experiments (168h, pH 4, 100μM As). The organic carbon (OC) contents of the coprecipitates (82-339mgg-1) were higher than those of adsorption complexes (31 and 36mgg-1), leading to pronounced variations in specific surface area (9-300m2g-1), average pore radii (1-9nm), and total pore volumes (11-374mm3g-1) but being independent of the NOM type or the presence of Al. The occlusion of Fe solids by OM (XPS surface concentrations: 60-82atom% C) caused comparable pHPZC (1.5-2) of adsorption complexes and coprecipitates. The synthesis conditions resulted in different Fe-OM association modes: Fe oxide particles in 'M/C 0.1' coprecipitates covered to a larger extent the outermost aggregate surfaces, for some 'M/C 1.0' coprecipitates OM effectively enveloped the Fe oxides, while OM in the adsorption complexes primarily covered the outer aggregate surfaces. Despite of their larger OC contents, adsorption of As(V) was fastest to coprecipitates formed at low Fe availability (M/C 0.1) and facilitated by desorption of weakly bonded OC and disaggregation. In contrast, 'M/C 1.0' coprecipitates showed a comparable rate of As uptake as the adsorption complexes. While small mesopores (2-10nm) promoted the fast As uptake particularly to 'M/C 0.1' coprecipitates, the presence of micropores (<2nm) appeared to impair As desorption. This study shows that the environmental reactivity of poorly crystalline Fe(III) oxides in terrestrial and aquatic systems can largely vary depending on the formation conditions. Carbon-rich Fe phases precipitated at low M/C ratios may play a more important role in oxyanion immobilization and Fe and C cycling than phases formed at higher M/C ratios or respective adsorption complexes.
AB - Ferric oxyhydroxides play an important role in controlling the bioavailability of oxyanions such as arsenate and phosphate in soil. Despite this, little is known about the properties and reactivity of Fe(III)-organic matter phases derived from adsorption (reaction of organic matter (OM) to post-synthesis Fe oxide) versus coprecipitation (formation of Fe oxides in presence of OM). Coprecipitates and adsorption complexes were synthesized at pH 4 using two natural organic matter (NOM) types extracted from forest floor layers (Oi and Oa horizon) of a Haplic Podzol. Iron(III) coprecipitates were formed at initial molar metal-to-carbon (M/C) ratios of 1.0 and 0.1 and an aluminum (Al)-to-Fe(III) ratio of 0.2. Sample properties were studied by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), N2 gas adsorption, dynamic light scattering, and electrophoretic mobility measurements. Arsenic [As(V)] adsorption to Fe-OM phases was studied in batch experiments (168h, pH 4, 100μM As). The organic carbon (OC) contents of the coprecipitates (82-339mgg-1) were higher than those of adsorption complexes (31 and 36mgg-1), leading to pronounced variations in specific surface area (9-300m2g-1), average pore radii (1-9nm), and total pore volumes (11-374mm3g-1) but being independent of the NOM type or the presence of Al. The occlusion of Fe solids by OM (XPS surface concentrations: 60-82atom% C) caused comparable pHPZC (1.5-2) of adsorption complexes and coprecipitates. The synthesis conditions resulted in different Fe-OM association modes: Fe oxide particles in 'M/C 0.1' coprecipitates covered to a larger extent the outermost aggregate surfaces, for some 'M/C 1.0' coprecipitates OM effectively enveloped the Fe oxides, while OM in the adsorption complexes primarily covered the outer aggregate surfaces. Despite of their larger OC contents, adsorption of As(V) was fastest to coprecipitates formed at low Fe availability (M/C 0.1) and facilitated by desorption of weakly bonded OC and disaggregation. In contrast, 'M/C 1.0' coprecipitates showed a comparable rate of As uptake as the adsorption complexes. While small mesopores (2-10nm) promoted the fast As uptake particularly to 'M/C 0.1' coprecipitates, the presence of micropores (<2nm) appeared to impair As desorption. This study shows that the environmental reactivity of poorly crystalline Fe(III) oxides in terrestrial and aquatic systems can largely vary depending on the formation conditions. Carbon-rich Fe phases precipitated at low M/C ratios may play a more important role in oxyanion immobilization and Fe and C cycling than phases formed at higher M/C ratios or respective adsorption complexes.
UR - http://www.scopus.com/inward/record.url?scp=84908381672&partnerID=8YFLogxK
U2 - 10.1016/j.gca.2014.08.026
DO - 10.1016/j.gca.2014.08.026
M3 - Article
AN - SCOPUS:84908381672
VL - 144
SP - 258
EP - 276
JO - Geochimica et cosmochimica acta
JF - Geochimica et cosmochimica acta
SN - 0016-7037
ER -