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EEWR Brown Bag Seminar with Myriam Agnel, Visiting Student Research Collaborator

Speaker: Myriam Agnel, Visiting Student Research Collaborator
Series: EEWR Brown Bag Seminars
Location: Engineering Quad E225
Date/Time: Friday, April 12, 2019, 12:00:00 p.m. - 01:00:00 p.m.

Abstract:

Ion exchange in Fougèrite: influence of  crystal size and structural defects

Myriam AgnelFougèrite is a Fe(II)/Fe(III) layered double hydroxide found in hydromorphic soils. Its layers are positively charged because of the occurrence of mixed FeII/III valence states. The charge is compensated by exchangeable anions located in the interlayer space. Consequently, fougèrite, where present, participate to the biogeochemical cycling of anions, including nutrients or pollutants, in the environment. This mineral is also studied in material sciences for its redox properties and its possible applications to soil decontamination. In this study, we carried out a detailed analysis of some of green rust (synthetic fougèrite) ion exchange properties, with the aim to contribute to a better understanding and prediction of the biogeochemical cycle of anionic compounds in soils.

We investigated the Cl-/SO42- exchange mechanism on two kinds of green rust having similar layer structures, but having particle size distributions either in the nanometer or in the micrometer size range. Those samples also contained various degrees of staking faults. Samples were characterized by a combination of chemical and physical methods, including synchrotron high-energy X-ray scattering and synchrotron in situ and time-resolved X-ray diffraction in order to understand the link between exchange and modifications of the structure. Total anion exchange capacity and CI/SO42- selectivity coefficients (Kex) were obtained from modelling of aqueous chemistry data and microprobe analyses. Those data allowed us to build a chemical model to predict green rust behavior toward CI/SO42- exchange. We are working on molecular dynamic simulations to figure out exchange mechanisms at the atomic scale.