2, University of South Carolina, Columbia, South Carolina, United States
3, CEA, Bagnols-sur-Ceze, , France
Hierarchical materials containing multiscale porosity are promising candidates for improving the performance of radioactive waste containment matrices. Understanding the effect of multiscale porous structures and chemistry on diffusion, extraction kinetics, and capacity for radioactive species is important in designing advanced waste form materials. In this work, we will present a 3D microstructural-dependent diffusion model for investigating the effect of porous structures, and thermodynamic and kinetic properties on uptake kinetics during ion exchange. To demonstrate the model’s capability we simulated Sr2+ uptake kinetics in porous Na-LTA zeolites. The thermodynamic and kinetic properties of the ion exchange system were assessed from experimental data. The effect of zeolite particle size, chemical potential and heterogeneous diffusivity on the spatial and temporal evolution of Sr2+ and Na+, and Sr2+ uptake kinetics in a spherical zeolite particle and an aggregation of zeolite particles were simulated and compared with experimental results. It is found that the uptake is kinetically limited by two diffusion phenomena in agreement with experimental observations. Predicted microstructure dependent uptake kinetics is also consistent with experimental data. The model can also be extended to study the effect of bonding phase in the beads of Na- zeolite, and the anisotropic thermodynamic and kinetic properties in salt-inclusion compounds on ion exchange kinetics.
This work was supported as part of the Center for Hierarchical Waste Form Materials, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award No. DE-SC0016574.