Geologic repositories are accepted as the best long-term disposal and storage solution for high-level nuclear waste. Due to the long half-lives of several actinides (242Pu (t1/2 = 3.5 x 105 years), these materials remain present in the environment for many years and pose threats to human and environmental health. Therefore, it is necessary to understand how these materials move and behave so they may be safely stored out to 1 million years, as required by law. In this research project, the interaction between europium and aluminum (hydr)oxide mineral phases was studied through a series of batch-sorption experiments in order to analyze sorption trends and predict sorption behavior. These experiments were designed to test the partitioning of the europium between the aqueous and solid phases over the pH range 3 to 10 and as a function of mineral concentration, europium concentration, and ionic strength. Europium, which has an oxidation state of +III, was studied as an analog to the +III oxidation state of plutonium, which can exist at four different oxidation states (+III, +IV, +V, +IV). Aluminum (hydr)oxides contain key surface termination sites found in the clay materials which will be used to backfill nuclear waste storage repositories. The four minerals chosen—corundum (α-Al2O3), γ-alumina (γ-Al2O3), gibbsite (Al(OH)3), and bayerite (α-Al(OH)3)— have distinct structures and acidities based on ratios of oxygen and aluminum at the surface. Current debate in the scientific community centers around how minerals with similar chemical compositions, but different surface terminations and surface acidities, have an influence sorption behavior. Results show that at low europium concentrations, sorption behavior is similar in the presence of corundum, γ-alumina, and gibbsite with slight preference to bayerite. At higher europium concentrations, all minerals follow the same sorption pattern, which is shifted to a higher pH value.

Europium sorption to aluminum (hydr)oxide minerals

253rd National Meeting (2017)

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