Date of Award

5-2017

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Environmental Engineering and Earth Science

Committee Member

Dr. Brian A. Powell, Committee Chair

Committee Member

Dr. Mark Schlautman

Committee Member

Dr. Lindsay Shuller-Nickles

Abstract

Diffusion rates of 237Np(V), 3H, and 22Na through Na-montmorillonite were studied under variable dry bulk density and temperature. Distribution coefficients were extrapolated for conservative tracers. Two sampling methods were implemented, and effects of each sampling method were compared. The first focused on an exchange of the lower concentration reservoir frequently while the second kept the lower concentration reservoir consistent. In both sampling methods, tritium diffusion coefficients decreased with an increase in dry bulk density and increased with an increase in temperature. Sodium diffusion rates followed the same trends as tritium with the exception of sorption phenomena. Modeling the accumulated activity breakthrough in the effluent revealed small amounts of sorption for sodium diffusion. Neptunium diffusion rates from effluent analysis were also generally shown to decrease with an increase in dry bulk density at all temperatures. Because 237Np(V) adsorbs onto the montmorillonite surface, little breakthrough was observed in the effluent with the exception of the lower dry bulk densities of 1.15 and 1.30 g·cm-3. Effluent data was modeled and effective diffusion coefficients and Kd values were extracted. An increase in neptunium sorption was observed at an increase in elevated temperature. Likewise, an increase in diffusion rates with an increase in temperature was also seen. Concentration profile analysis was performed qualitatively. It was determined that presently published analytical solutions to the diffusion equation cannot encompass all conditions in this study. Further analysis using a commercial modeling software such as COMSOL is required to extrapolate diffusion and distribution coefficients for sorbing species. The trends in the concentration profiles showed a decrease in the transport of neptunium with an increase in dry bulk density and temperature. No firm conclusions about sorption can currently be drawn without proper modeling of the concentration profiles. Future work should focus on further optimization of sampling method two as well as experimental setup, including a lower ionic strength to stop corrosion production. Although concentration profile analysis proved inconclusive, effluent analysis from the lower dry bulk densities is promising in predicting diffusion and sorption trends.

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