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The speciation of hexavalent U and tetravalent Pu will be examined in the TBPdodecane- nitric acid systems. This topic is chosen based on data needs for separation modeling identified by the AFCI. Emphasis will be placed on studying the influence of nitrate and acetohydroxamic acid on U and Pu speciation as well as conditions where a third phase forms in the organic phase. The organic phase will be 30 % TBP in dodecane. Equal volumes of aqueous and organic phase will be used. The speciation of the actinides in the aqueous and organic phase will be determined by a number of different spectroscopic and radiochemical techniques. Additionally the actinide distribution between the phases as a function of conditions will be determined. The project data will be incorporated into models to evaluate separations under a variety of conditions.
Work in this quarter focused on 3rd phase formation studies with the uranyl system. which happens with the organic phase spontaneously splits into a light and a heavy phase. This phenomenon occurs when the uranium and nitric acid concentrations exceed a certain threshold. Current theories include that the third phase forms gradually in small reverse micelles when uranyl and nitric acid reach a certain limiting organic concentration (LOC) that makes it thermodynamically favorable to separate and form a different structure. This is analogous to the critical micelle concentration (cmc) in surfactant micelle formation. The third phase formation is quite dependent on temperature. There has been some work indicating that the UV-visible spectrum changes at certain wavelengths as the system approaches third phase, indicating a variation in the uranyl electronic structure as this third phase begins to form.
Nitric acid; Plutonium; Radioactive wastes – Purification; Separation (Technology); Speciation (Chemistry); Tributyl phosphate; Uranium
Nitric acid; Radioactive wastes--Purification; Tributyl phosphate
Analytical Chemistry | Chemical Engineering | Chemistry | Oil, Gas, and Energy | Physical Chemistry
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Fundamental Chemistry of U and Pu in the TBP-Dodecane-Nitric Acid System: Quarterly Report.
Available at: https://digitalscholarship.unlv.edu/hrc_trp_separations/88