A mathematical model for equilibrium distribution of Uranium(VI), Plutonium(IV) and Nitric Acid in purex solvent extraction processes

A total of 351 data points for distribution of uranium(VI), plutonium(IV) and nitric acid between aqueous nitric acid solutions containing these components and organic solutions of 20 volume percent tri-n-butyl phosphate (TBP) in a normal paraffin hydrocarbon diluent were collected from the available literature and systematically screened to prune erroneous data.

The seven parameters for nitric acid distribution in a mathematical model for equilibrium distribution of uranium(VI), plutonium(IV) and nitric acid between aqueous nitric acid solution of the components and organic solution of TBP in an aliphatic diluent were re-evaluated using the minimum variance location procedure. With the new parameter values, the prediction for nitric acid distribution coefficients was improved.

A nonlinear simultaneous regression procedure was then used to re-estimate all 21 parameters, except those for TBP concentration effects, in the mathematical model. The coefficients of determination for plutonium and nitric acid were improved, but there was little change in the coefficients for uranium. The use of the nonlinear simultaneous regression procedure to construct an empirical model for equilibrium distribution of uranium(VI), plutonium(IV) and nitric acid was demonstrated.