TY - JOUR
T1 - Emerging investigator series
T2 - Interdependency of green rust transformation and the partitioning and binding mode of arsenic
AU - Van Genuchten, C.M.
AU - Behrends, T.
AU - Dideriksen, K.
N1 - Funding Information:
We acknowledge funding provided by the Dutch Organization for Scientific Research in a Veni Grant to CMvG (Project No. 14400). Synchrotron experiments were performed partly at the DUBBLE beam line at the ESRF, Grenoble, France, with assistance from Dipanjan Banerjee. We also thank Ryan Davis for technical support during synchrotron data collection at SSRL. Use of SSRL, SLAC National Accelerator Laboratory, was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Contract No. DE-AC02-76SF00515.
Funding Information:
We acknowledge funding provided by the Dutch Organization for Scientic Research in a Veni Grant to CMvG (Project No. 14400). Synchrotron experiments were performed partly at the DUBBLE beam line at the ESRF, Grenoble, France, with assistance from Dipanjan Banerjee. We also thank Ryan Davis for technical support during synchrotron data collection at SSRL. Use of SSRL, SLAC National Accelerator Laboratory, was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Contract No. DE-AC02-76SF00515.
Publisher Copyright:
© The Royal Society of Chemistry 2019.
PY - 2019/9
Y1 - 2019/9
N2 - We investigated the impact of aging-induced structural modifications of carbonate green rust (GR), a mixed valent Fe(ii,iii) (hydr)oxide with a high oxyanion sorption affinity, on the partitioning and binding mode of arsenic (As). Suspensions of carbonate GR were produced in the presence of As(v) or As(iii) (i.e. co-precipitated with As(iii) or As(v)) and aged in anoxic and oxic conditions for up to a year. We tracked aqueous As over time and characterized the solid phase by X-ray absorption spectroscopy (XAS). In experiments with initial As(v) (4500 μg L-1, As/Fe = 2 mol%), the fresh GR suspension sorbed >99% of the initial As, resulting in approximately 14 ± 8 μg L-1 residual dissolved As. Anoxic aging of the As(v)-laden GR for a month increased aqueous As to >60 μg L-1, which was coupled to an increase in GR structural order revealed by Fe K-edge XAS. Further anoxic aging up to a year transformed As(v)-laden GR into magnetite and decreased significantly the aqueous As to <2 μg L-1. The As binding mode was also modified during GR transformation to magnetite from sorption to GR particle edges to As substitution for tetrahedral Fe in the magnetite structure. These GR structural modifications altered the ratio of As partitioning to the solid (μg As/mg Fe) and liquid (μg As per L) phase from 2.0 to 0.4 to 14 L mg-1 for the fresh, month, and year aged suspensions, respectively. Similar trends in GR transformation and As partitioning during anoxic aging were observed for As(iii)-laden suspensions, but occurred on more rapid timescales: As(iii)-laden GR transformed to magnetite after a day of anoxic aging. In oxic aging experiments, rapid GR oxidation by dissolved oxygen to Fe(iii) precipitates required only an hour for both As(v) and As(iii) experiments, with lepidocrocite favored in As(v) experiments and hydrous ferric oxide favored in As(iii) experiments. Aqueous As during GR oxidation decreased to <10 μg L-1 for both As(v) and As(iii) series. Knowledge of this interdependence between GR aging products and oxyanion fate improves biogeochemical models of contaminant and nutrient dynamics during Fe cycling and can be used to design more effective arsenic remediation strategies that rely on arsenic sorption to GR.
AB - We investigated the impact of aging-induced structural modifications of carbonate green rust (GR), a mixed valent Fe(ii,iii) (hydr)oxide with a high oxyanion sorption affinity, on the partitioning and binding mode of arsenic (As). Suspensions of carbonate GR were produced in the presence of As(v) or As(iii) (i.e. co-precipitated with As(iii) or As(v)) and aged in anoxic and oxic conditions for up to a year. We tracked aqueous As over time and characterized the solid phase by X-ray absorption spectroscopy (XAS). In experiments with initial As(v) (4500 μg L-1, As/Fe = 2 mol%), the fresh GR suspension sorbed >99% of the initial As, resulting in approximately 14 ± 8 μg L-1 residual dissolved As. Anoxic aging of the As(v)-laden GR for a month increased aqueous As to >60 μg L-1, which was coupled to an increase in GR structural order revealed by Fe K-edge XAS. Further anoxic aging up to a year transformed As(v)-laden GR into magnetite and decreased significantly the aqueous As to <2 μg L-1. The As binding mode was also modified during GR transformation to magnetite from sorption to GR particle edges to As substitution for tetrahedral Fe in the magnetite structure. These GR structural modifications altered the ratio of As partitioning to the solid (μg As/mg Fe) and liquid (μg As per L) phase from 2.0 to 0.4 to 14 L mg-1 for the fresh, month, and year aged suspensions, respectively. Similar trends in GR transformation and As partitioning during anoxic aging were observed for As(iii)-laden suspensions, but occurred on more rapid timescales: As(iii)-laden GR transformed to magnetite after a day of anoxic aging. In oxic aging experiments, rapid GR oxidation by dissolved oxygen to Fe(iii) precipitates required only an hour for both As(v) and As(iii) experiments, with lepidocrocite favored in As(v) experiments and hydrous ferric oxide favored in As(iii) experiments. Aqueous As during GR oxidation decreased to <10 μg L-1 for both As(v) and As(iii) series. Knowledge of this interdependence between GR aging products and oxyanion fate improves biogeochemical models of contaminant and nutrient dynamics during Fe cycling and can be used to design more effective arsenic remediation strategies that rely on arsenic sorption to GR.
UR - http://www.scopus.com/inward/record.url?scp=85072352923&partnerID=8YFLogxK
U2 - 10.1039/c9em00267g
DO - 10.1039/c9em00267g
M3 - Article
C2 - 31353376
AN - SCOPUS:85072352923
VL - 21
SP - 1459
EP - 1476
JO - Environmental Sciences: Processes and Impacts
JF - Environmental Sciences: Processes and Impacts
SN - 2050-7887
IS - 9
ER -