Date of Award

5-2017

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Plant and Environmental Science

Committee Member

Dr. Brian A. Powell, Committee Chair

Committee Member

Dr. Timothy A. DeVol

Committee Member

Dr. Lawrence Murdoch

Committee Member

Dr. Daniel I. Kaplan

Abstract

Savannah River Site (SRS) is historically contaminated with 137Cs. Understanding the subsurface mobility and behavior of cesium is imperative to risk assessments of the historical contamination. This study focuses on the geochemical factors influencing cesium sorption to SRS soils including clay composition, pH and the impact of competing cations. SRS soil contains both 1:1 and 2:1 phyllosilicate minerals, which have been found to control cesium sorption in soil systems. Kaolinite (1:1) is in relative abundance compared to the 2:1 fraction allowing the study of the influence 2:1 clays have on sorption. The 2:1 clays have been found to contain high affinity cesium sorption sites that can influence the sorption of cesium over time. Batch sorption and desorption experiments were conducted with variable ionic strength, pH and competing ion composition. Freundlich isotherm models were fit to the batch sorption data showing the impact of competing ions in the system. However, a non-equilibrium and time dependent reversibility behavior observed in the data informed the need for a focused kinetic experiment. The kinetic limitations of cesium sorption and the potential for decreased reversibility over time due to an observed aging process was then examined. A multi-site kinetic sorption model has been proposed based on these kinetic data, which describes the sorption as being controlled by the 1:1 and 2:1 clay fraction with emphasis on a high affinity 2:1 sorption site. Linear sorption behavior was observed in isotherm plots of the kinetic data at the lowest cesium concentrations while non-linear equations were required to describe the higher concentration isotherms. This is in support of the presence of a high affinity, low concentration sorption site which becomes saturated due to high cesium/site ratios realized in the higher aqueous cesium samples. A series of column transport experiments at low cesium concentrations showed minimal advective or diffusive transport of cesium confirming the non-linear sorption behavior observed in the batch experiments. These columns also showed the importance of the cesium/site ratio on the distribution of cesium between the proposed sorption sites.

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