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DOE OSTI · 1532325

A structural coarse-grained model for clays using simple iterative Boltzmann inversion

Schaettle, Karl·Ruiz Pestana, Luis·Head-Gordon, Teresa·Lammers, Laura Nielsen
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Abstract

Cesium-137 is a crucial byproduct of nuclear energy generation and is environmentally threatening due to its long half-life and affinity for naturally occurring micaceous clays. Current experimental observations of illite and phlogopite mica indicate that Cs+ is capable of exchanging with K+ bound in the anhydrous interlayers of layered silicates, forming sharp exchange fronts, leading to interstratification of Cs- and K-illite. We introduce here a coarse-grained (CG) model of the anhydrous illite interlayer developed using iterative Boltzmann inversion that qualitatively and quantitatively reproduces features of a previously proposed feedback mechanism of ion exchange. The CG model represents a 70-fold speedup over all-atom models of clay systems and predicts interlayer expansion for K-illite near ion exchange fronts. Contrary to the longstanding theory that ion exchange in a neighboring layer increases the binding of K in lattice counterion sites leading to interstratification, we find that the presence of neighboring exchanged layers leads to short-range structural relaxations that increase basal spacing and decrease cohesion of the neighboring K-illite layers. We also provide evidence that the formation of alternating Cs- and K-illite interlayers (i.e., ordered interstratification) is both thermodynamically and mechanically favorable compared to exchange in adjacent interlayers.

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Schaettle, Karl, Ruiz Pestana, Luis, Head-Gordon, Teresa, Lammers, Laura Nielsen. 2018-02-20. A structural coarse-grained model for clays using simple iterative Boltzmann inversion. https://doi.org/10.1063/1.5011817

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