Reactivity of structural iron in natural nontronite and synthetic Fe-phyllosilicate
EMSL Project ID
48563
Abstract
Our research goal is to develop a mechanistic model of the clay structural iron (Fe) reactivity and further characterize essential redox properties of Fe-rich phyllosilicates. Our experimental approach includes using the redox-active elements – arsenic (As), chromium (Cr), antimony (Sb) and selenium (Se) to quantify the direction and kinetics of electron transfer from clay structural Fe(II) and Fe(III). Our investigation of the redox behavior of the natural Fe-rich smectite clay – nontronite NAu-1 concluded that this substrate is redox active, but only when some structural Fe(III) is reduced to Fe(II). Nontronite NAu-1 contains chemical impurities; therefore to exclude potential influence of these impurities on the redox behavior, we synthesized pure Fe phyllosilicate substrate. The Fe phyllosilicate was characterized with X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Small Angle X-ray Scattering (SAXS), and Fourier Transformed Infrared (FTIR) spectroscopy. These analyses showed that the synthetic phyllosilicate has similar to the NAu-1 morphology and mineral structure. To complete the characterization of this synthetic substrate, and to decide whether it can be used as a chemical analog for the natural nontronite clay in the reactivity studies, we propose to use Mössbauer spectroscopy at EMSL. We will quantify the Fe(II) and Fe(III) content in the structure, determine coordination chemistry (4- or 6-fold coordination) around iron atoms, and detect potential iron oxide impurities which may have precipitated during the phyllosilicate synthesis. Mössbauer spectroscopy is a specialized technique, and is not readily available at the standard analytical and characterization laboratories. Also, interpretation of the spectra is complicated, and EMSL has the world-class expertise in modeling the Mössbauer data. Access to the EMSL User Facilities would therefore greatly benefit this project. This project focuses on the fundamental understanding of the redox chemistry at the clay mineral surfaces. This improved fundamental understanding of the clay structural Fe(II)/Fe(III) redox couple behavior will enable the development of better biogeochemical cycling and transport models, and inform the best strategies for the remediation of environmental systems contaminated with organic and inorganic pollutants.
Project Details
Project type
Limited Scope
Start Date
2014-09-02
End Date
2014-11-02
Status
Closed
Released Data Link
Team
Principal Investigator
Related Publications
Ilgen A.G., Dunphy D.R., Kruichak J.N., Kukkadapu R.K., Cerrato C.M., Argo J.M., and Washington R.E. Controls on the reactivity of clay structural Fe(II)/Fe(III) redox couple. Abstract. 249th ACS National Meeting, Denver, CO, March 22-26, 2015
Ilgen AG, RK Kukkadapu, DR Dunphy, K Artyushkova, JM Cerrato, JN Kruichak, M Janish, CJ Sun, JM Argo, and RE Washington. 2017. "Synthesis and characterization of redox-active ferric nontronites." Chemical Geology 470:1-12. doi:10.1016/j.chemgeo.2017.07.010
Ilgen AG, RK Kukkadapu, RE Washington, and K Leung. X-ray absorption, Mössbauer, diffuse reflectance spectroscopies and density functional theory calculations of Fe(II)/Fe(III) redox couple in ferric nontronites. Abstract. 255th ACS National Meeting, New Orleans, LA, March 2018