Reactivity of iron-bearing phyllosilicates with uranium and chromium through redox transitions zones
EMSL Project ID
44687
Abstract
Iron-bearing phyllosilicate minerals are widely distributed and often account for about half of the iron in soils and sediments. They play an important role in environmental processes such as contaminant migration at DOE sites. These minerals help establish the physical/hydrogeological conditions of redox transition zones because of their small size and limited hydraulic conductivity, and disproportionately buffer the redox conditions through the transition zone because they provide a large solid-phase reservoir of Fe(III)/Fe(II). The iron redox cycling of clay minerals can be mediated by iron reducing prokaryotes and sulfate-reducing bacteria. Multiple phyllosilicates have been used for microbial reduction studies. The extent and rate of Fe(III) bioreduction depends on a number of experimental conditions. Reduction of structural Fe(III) to Fe(II) in phyllosilicates tends to change a number of clay mineral properties. Biological reduction of iron-bearing phyllosilicates leads to a variety of Fe(II) species associated with phyllosilicates, and they have been shown to reduce Cr(VI), Tc(VII) and U(VI). However, changes in their reactivity as these reduced phyllosilicates become reoxidized are currently unknown. Our preliminary study suggests that redox cycling of nontronite NAu-2, an iron-rich smectite, could produce irreversible structural changes. Multiple Fe(III) sites exist in pristine NAu-2, and upon reduction, Fe(III) from a certain structural site is preferentially reduced with resulting Fe(II) distributed between structure and interlayer/surface. However, MOssbauer spectroscopy measurements of bioreduced samples, as well as those treated to exchange interlayer/adsorbed Fe(II) over a variable temperature range are needed to definitely differentiate these species. The presence of two sets of sextets in 4.5 K spectra for the bioreduced NAu-2 suggests the presence of two domains of Fe in the nontronite structure: Fe(II) and Fe(III), which implies that electron transfer takes place from clay edges to the interior of the structure. However, the detailed mechanisms of electron transfer are still poorly known. The research proposed here is to further determine Fe speciation as a result of multiple cycles of Fe redox and subsequent reactivity towards U and Cr reduction. Specifically, we hypothesize 1) Biological reduction of phyllosilicate-Fe(III) followed by reoxidation of phyllosilicate-Fe(II) will irreversibly alter the Fe speciation within the clay mineral structure; 2) Kinetic reactivities of phyllosilicate-Fe(II) towards reduction of U(VI) and Cr(VI) and phyllosilicates-Fe(III) towards U(IV) and Cr(III) are controlled by the distribution of Fe(II) and Fe(III) within each phyllosilicate mineral; The research consists of four tasks: 1) Preparation of bioreduced and reoxidized clay minerals; 2) Examination of inter-valence electron transfer; 3) Mineralogical characterization of as a function of multiple redox cycles; 4) Reactivity of phyllosilicates with Cr and U. Three clay minerals with a range of Fe content will be used that are commonly present at DOE sites. Multiple cycles of reduction and reoxidation will be carried out and Fe speciation as a function of these cycles will be studied by Mossbauer spectroscopy, electron microscopy and X-ray diffraction. The bioreduced and reoxidized clay minerals will be reacted with Cr and U to understand their reactivity related to the distribution of Fe(II) and Fe(III) within each clay mineral.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2011-10-01
End Date
2014-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Bishop M.E., H. Dong, P. Glasser, B.R. Briggs, M. Pentrak, J.W. Stucki, and M.I. Boyanov, et al. 2019. "Reactivity of Redox Cycled Fe-bearing Subsurface Sediments Towards Hexavalent Chromium Reduction." Geochimica et Cosmochimica Acta 252. PNNL-SA-141702. doi:10.1016/j.gca.2019.02.039
Bishop ME, P Glasser, H Dong, BW Arey, and L Kovarik. 2014. "Reduction And Immobilization Of Hexavalent Chromium By Microbially Reduced Fe-bearing Clay Minerals." Geochimica et Cosmochimica Acta 133:186-203. doi:10.1016/j.gca.2014.02.040
Yangjian Cheng, Hailiang Dong, Zhibin Ke, Libor Kovarik, Tingting Zhang, Li Zhang. 2022. "Resource recovery: Adsorption and biomineralization of cerium by Bacillus licheniformis." Journal of Hazardous Materials 426:127844. https://doi.org/10.1016/j.jhazmat.2021.127844
Yang J, RK Kukkadapu, H Dong, ES Shelobolina, J Zhang, and J Kim. 2012. "Effects of Redox Cycling of Iron in Nontronite on Reduction of Technetium." Chemical Geology 291:206-216. doi:10.1016/j.chemgeo.2011.10.013
Zhao L, H Dong, RK Kukkadapu, A Agrawal, D Liu, J Zhang, and RE Edelmann. 2013. "Biological Oxidation of Fe(II) in Reduced Nontronite Coupled with Nitrate Reduction by Pseudogulbenkiania sp. Strain 2002." Geochimica et Cosmochimica Acta 119:231-247. doi:10.1016/j.gca.2013.05.033