This research seeks to build the fundamental understanding of micelle formation and mobility in supercritical CO2 necessary to develop an innovative phase-transfer extraction system for selectively removing metals (actinides) from contaminated surfaces. We will extract metal ions into supercritical CO2 (scCO2) using CO2 soluble extractants. The surfactants consist of perfluoroether and perfluoroalkyl backbones with phosphate head groups. Experimentation will focus on two main issues: understanding the solubilization mechanism of metals into supercritical CO2 with regards to micelle formation, and studying the interactions between the extractants and surfaces. Surface interactions will include both those with the matrix surface and the surface of the actinide contaminants. Supercritical CO2 has many advantages both for extraction from surfaces and minimization of the environmental impact of separation activities. The gas-like properties of high diffusivity and low surface tens ion will enable penetration of the surfactants and micelles deep into surface pores, inaccessible by aqueous based systems, to aid in the complete decontamination of complex heterogeneous surfaces. The ability to readily control solubility by changing the pressure allows for facile separation of the surfactant and bound metal from the CO2 solvent, allowing concentration of the waste and recycle of the carbon dioxide. The CO2 solvent is an environmentally benign, inexpensive, radiologically and oxidatively stable extraction medium. Secondary waste streams are minimized since no toxic solvents are used. Most importantly worker contact with radioactive material is minimized compared to techniques such as sandblasting which can expose the worker to surface contamination.
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