PRELIMINARY INVESTIGATIONS OF EUROPIUM INTERACTIONS WITH SEPIOLITE AND CRYPTOMELANE AS AN ANALOG FOR PLUTONIUM REMEDIATION TECHNOLOGY

Immobilization of highly radioactive waste materials such as plutonium (Pu) has been under investigation for many years. Significant quantities of Pu have contaminated the environment as a result of nuclear weapon production and testing. It is important to gain knowledge in fate and transport of plutonium, and identify risks in migration strategies. This calls for an assessment of new remediation technologies. Pu has been shown to strongly sorb to clays and zeolites and one of the most promising methods of radionuclide retention is adsorption by minerals. Two minerals, sepiolite and cryptomelane, are proposed as being particularly promising as they often have high sorption capacities.

This project uses europium as an analog for Pu in the environment, to investigate the interactions between europium and sepiolite and cryptomelane. This study primarily investigates Eu interactions with sepiolite and cryptomelane using transmission electron microscopy. The sepiolite used for this study was obtained from Two Crows, Nevada and had been previously partially characterized. BET surface areas and pore volumes were determined for unmodified sepiolite and preliminary exchanges of Eu sepiolite. A relative increase in BET surface area of approximately 20%, with a related 8% increase in pore volume was observed post reaction. Transmission electron microscopy indicates that spherical round nanoparticles (~3 to 10 nm) of europium oxide glass form in the reaction and these show some textural relationship to sepiolite fibers, suggesting a possible catalytic precipitation.

The cryptomelane used for this study was synthesized using the sol-gel reaction between KMnO₄ and fumaric acid. Reaction of cryptomelane with europium nitrate solutions indicates that a sponge-like europium oxide glass precipitates catalytically on the surface. Both sepiolite and cryptomelane induce catalytic precipitation of Eu and thus as an analog show some promise as a geotechnology to sequester Pu in the environment. Specific sorption mechanisms and the exact causes for precipitation are topics for ongoing work.