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September 8–11, 2025
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NextGen MURR Working Group established in Missouri
The University of Missouri’s Board of Curators has created the NextGen MURR Working Group to serve as a strategic advisory body for the development of the NextGen MURR (University of Missouri Research Reactor).
M. H. Lletzke, R. W. Stoughton, Marjorie P. Lietzke
Nuclear Science and Engineering | Volume 16 | Number 1 | May 1963 | Pages 25-30
Technical Paper | doi.org/10.13182/NSE63-A26475
Articles are hosted by Taylor and Francis Online.
A generalized least squares technique has been used to calculate equilibrium constants and their variation with medium in solvent extraction equilibria by minimizing the difference between observed and calculated distribution ratios. The model involved a Debye-Hückel term for low and a linear term for high ionic concentration corrections (i.e., activity coefficient changes) in the aqueous phase, consistent with current semitheoretical treatments. In the organic phase either no correction or a linear term in volume % TBP was found adequate to about 20 vol. % TBP. The method involved the evaluation of the assumed parameters in the least squares sense while iteratively correcting for ionic strength changes with varying (calculated) ionic concentrations. Due to imprecision of the data and to convergence difficulties encountered in nonlinear procedures, it was not feasible to evaluate as many parameters as desired, and hence the model had to be oversimplified in some cases. Nevertheless, the method has been successfully applied to the extraction of uranyl nitrate and nitric acid by TBP dissolved in an inert diluent. It is suggested that with sufficiently precise and consistent data the method is capable of evaluating all the equilibrium parameters involved in relatively complex extraction systems. A series of computer programs has been written in an attempt to calculate distribution ratios in relatively complex solvent extraction systems. The general procedure involved setting up equilibrium expressions and determining the parameters by a generalized least squares technique. The present paper describes calculations on the distribution of UO2(NO3)2 and HNO3 between an aqueous phase and an organic phase consisting of tributyl phosphate (TBP) dissolved in an inert diluent (Amsco 125-90W).1 Since it was desired to keep the model simple and since convergence difficulties were encountered when the model was made more realistically elaborate, the assumed equilibria do not necessarily involve all species which may have been shown to exist in some of the solutions in question (e.g., UO2NO3+ and UO2(NO3)2).
