Date of Award

12-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Environmental Engineering and Science

Advisor

Brian A. Powell

Committee Member

O. Thompson Mefford

Committee Member

Fred J. Molz

Committee Member

Lindsay Shuller-Nickles

Abstract

Colloid-facilitated transport of the actinides has been observed previously in the field on the kilometer scale. The objective of this work is to investigate the mechanisms of colloid-facilitated transport with controlled settings and conditions. The experimental work in this dissertation investigates transport of a ternary complex with iron oxide colloids, organic ligands and actinides in the presence of quartz or a natural sandy soil as well as simplified systems building up to the ternary complexes. The first three papers investigate the following: (1) unsaturated transport of iron oxide colloids in a natural sandy soil lysimeter with and without natural organic matter, (2) sorption and reduction of plutonium on iron oxide colloids through batch sorption and ATR FT-IR experiments, and (3) the reversibility of sorption in ternary systems with variable ligands and salts, a natural sandy soil and plutonium. The fourth and final paper brings together the concepts investigated in the first three papers to demonstrate colloid-facilitated transport of the actinides on iron oxide colloids and fulvic acid through quartz or natural sandy soil in laboratory scale column experiments. The ATR FT-IR experiments observed surface-mediated reduction in real time and measured peaks for Pu(VI) and Pu(V) sorbed to hematite for the first time at ~916 and 836 cm-1, respectively. Batch experiments with Pu showed that sorption is strong at near-neutral pH and desorption is minimal even in the presence of different ligands. However, the lability of sorbed Pu complexes may be changing with time. This body of work has shown that colloidal transport of iron oxides and associated contaminants is minimal under unsaturated conditions and in the presence of natural, clay-sized soil coatings. While organic ligands significantly increased transport of iron oxide colloids and associated contaminants in the saturated quartz sand systems, the increase in transport was not significant in the presence of natural soils with clay-sized coatings. The following complexes are listed in order of mobility in quartz: fulvic acid - actinide > iron oxide colloid - fulvic acid - actinide > dissolved actinide > precipitated actinide ~ iron oxide colloid - actinide.

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