@article{f17a1771f1934d48bd15783b47bd5a81,
title = "Influence of clay mineral weathering on green rust formation at iron-reducing conditions",
abstract = "Green rusts (GR) are important drivers for trace metal and nutrient cycling in suboxic environments. We investigated whether green rusts would incorporate aluminum (Al) or other elements from naturally-formed clay minerals containing easily-weatherable clay minerals (e.g. mica, interlayered clays). We isolated the clay minerals from a Matapeake silt loam soil by removal of silt and sand, organic matter, and reducible oxides to study mechanisms of interaction between Fe(II) and soil-sourced clay minerals. We conducted batch Fe(II) sorption experiments at multiple near-neutral pHs (6.5–7.5) and reaction times (2 h–365 days). Mineral transformations were characterized by selective extractions, X-ray diffraction (XRD), and Fe X-ray absorption spectroscopy (XAS) analyzed by shell-fitting and linear combination fitting (LCF) with natural and synthetic standards. Clay mineral fraction contained a mixture of quartz, kaolinite, interlayered vermiculite, mica, and chlorite with significant structural Fe (2.6% wt). Uptake of Fe(II) increased with pH and kinetics were rapid until 5 days, followed by slow continuous Fe(II) uptake. Citrate-bicarbonate desorption kinetics from Fe(II) sorbed clay released more Al and silicon (Si) compared with unreacted soil clay fraction whereas magnesium (Mg) and potassium (K) were unaffected. Citrate-bicarbonate extracted Fe contained more Fe(II) than an ideal GR with an Fe(II)/Fe(III) molar ratio of 5.50. Analysis of the Fe EXAFS by both LCF and shell fitting was best modeled as a combination of Fe(III)-clay reduction to Fe(II) and precipitation of GR and Fe(II)-Al LDH. After 7 days of Fe(II) sorption, LCF identified 55.2% total Fe in clay, 33.4% GR(Cl) and 11.4% Fe(II)-Al LDH. These results provide novel evidence of Fe(II)-Al LDHs precipitating on naturally-formed soil clay minerals as a minor phase to GR. The geochemical implications are that GRs formed in soils and sediments should be considered to have Al and Si as well as Mg substitutions affecting their structure and reactivity.",
keywords = "Aluminosilicate, Aluminum, EXAFS, Fougerite, Kinetics, Selective extraction, Shell-fitting",
author = "Betts, {Aaron R.} and Siebecker, {Matthew G.} and Elzinga, {Evert J.} and Luxton, {Todd P.} and Scheckel, {Kirk G.} and Sparks, {Donald L.}",
note = "Funding Information: Funding for this research was provided by the National Institute for Food and Agriculture Project NC 1187. We acknowledge the facilities utilized at the Advanced Material Characterization Lab (AMCL) at the University of Delaware (UD) for hosting instrumentation used in this paper. We acknowledge contributions to the data collected by Chin Chen Kuo for ICP-MS measurements at AMCL, and Anna Evers for lab assistance with laboratory extractions at UD. MRCAT operations are supported by the Department of Energy (DOE) and the MRCAT member institutions. This research used resources of the APS, a DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Although EPA contributed to this article, the research presented was not performed by or funded by EPA and was not subject to EPA's quality system requirements. Consequently, the views, interpretations, and conclusions expressed in this article are solely those of the authors and do not necessarily reflect or represent EPA's views or policies. Funding Information: Funding for this research was provided by the National Institute for Food and Agriculture Project NC 1187. We acknowledge the facilities utilized at the Advanced Material Characterization Lab (AMCL) at the University of Delaware (UD) for hosting instrumentation used in this paper. We acknowledge contributions to the data collected by Chin Chen Kuo for ICP-MS measurements at AMCL, and Anna Evers for lab assistance with laboratory extractions at UD. MRCAT operations are supported by the Department of Energy (DOE) and the MRCAT member institutions. This research used resources of the APS, a DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Although EPA contributed to this article, the research presented was not performed by or funded by EPA and was not subject to EPA's quality system requirements. Consequently, the views, interpretations, and conclusions expressed in this article are solely those of the authors and do not necessarily reflect or represent EPA's views or policies. Publisher Copyright: {\textcopyright} 2023",
year = "2023",
month = jun,
day = "1",
doi = "10.1016/j.gca.2023.04.001",
language = "English (US)",
volume = "350",
pages = "46--56",
journal = "Geochimica et Cosmochimica Acta",
issn = "0016-7037",
publisher = "Elsevier Limited",
}