This document is a summary of the R&D activities associated with the Engineered Barrier Systems Work Package. Multiple facets of Engineered Barrier Systems (EBS) research were examined in the course of FY19 activities. This report is focused on delivering an update on the status and progress of modelling tools and experimental methods, both of which are essential to understanding and predicting long-term repository performance as part of the safety case. Specifically, the work described herein aims to improve understanding of EBS component evolution and interactions. Ultimately, the EBS Work Package is working towards producing process models for distinct processes that can either be incorporated into performance assessment (PA), or provide critical information for implementing better constraints on barrier performance. The main objective of this work is that the models being developed and refined will either be implemented directly into the Geologic Disposal Safety Assessment (GDSA) platform, or can otherwise be indirectly linked to the performance assessment by providing improved bounding conditions. In either the case, the expectation is that validated modelling tools will be developed that provide critical input to the safety case.

Component (thermodynamics)

Bounding overwatch

10.2172/1598757

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High‐affinity amide‐lanthanide adsorption to gram‐positive soil bacteria

Environmental Microbiology Reports (2023)

Elliot Chang Laura N. Lammers Céline Pallud

Abstract The gram‐positive soil bacterium, Arthrobacter nicotianae , uses multiple organic acid functional groups to adsorb lanthanides onto its cell surface. At relevant soil pH conditions of 4.0–6.0, many of these functional groups are de‐protonated and available for cation sorption and metal immobilization. However, among the plethora of naturally occurring site types, A. nicotianae is shown to possess high‐affinity amide and phosphate sites that disproportionately affect lanthanide adsorption to the cell wall. We quantify neodymium (Nd)‐selective site types, reporting an amide‐Nd stability constant of log 10 K = 6.41 ± 0.23 that is comparable to sorption via phosphate‐based moieties. These sites are two to three orders of magnitude more selective for Nd than the adsorption of divalent metals to ubiquitous carboxyl‐based moieties. This implies the importance of lanthanide biosorption in the context of metal transport in subsurface systems despite trace concentrations of lanthanides found in the natural environment.

Amide

10.1111/1758-2229.13162

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Direct Exchange Mechanism for Interlayer Ions in Non-Swelling Clays

Environmental Science & Technology (2016)

Luis Ruiz Pestana Kedarnath Kolluri Teresa Head‐Gordon Laura N. Lammers

The mobility of radiocesium in the environment is largely mediated by cation exchange in micaceous clays, in particular Illite—a non-swelling clay mineral that naturally contains interlayer K+ and has high affinity for Cs+. Although exchange of interlayer K+ for Cs+ is nearly thermodynamically nonselective, recent experiments show that direct, anhydrous Cs+-K+ exchange is kinetically viable and leads to the formation of phase-separated interlayers through a mechanism that remains unclear. Here, using classical atomistic simulations and density functional theory calculations, we identify a molecular-scale positive feedback mechanism in which exchange of the larger Cs+ for the smaller K+ significantly lowers the migration barrier of neighboring K+, allowing exchange to propagate rapidly once initiated at the clay edge. Barrier lowering upon slight increase in layer spacing (∼0.7 Å) during Cs+ exchange is an example of "chemical-mechanical coupling" that likely explains the observed sharp exchange fronts leading to interstratification. Interestingly, we find that these features are thermodynamically favored even in the absence of a heterogeneous layer charge distribution.

Anhydrous

Illite

Charge exchange

10.1021/acs.est.6b04747

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Citations (41)

Surface complexation model of rare earth element adsorption onto bacterial surfaces with lanthanide binding tags

Applied Geochemistry (2019)

Elliot Chang Aaron Brewer Dan Park Yongqin Jiao Laura N. Lammers

Rare-earth element

10.1016/j.apgeochem.2019.104478

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