Experimental and modelling study of ruthenium extraction with tri-n-butylphosphate in the purex process

- Extraction of ruthenium from nitric acid media by TBP/TPH was studied at lab-scale.
- A thermodynamic model based on Mikulin equation and Sergievskii-Dannus model was developed.
- Good agreement between experimental and calculated distribution ratios was obtained.
- Mathematical model was tested successfully during a counter-current PUREX hot test performed in mixer-settlers.
- The model is not yet able to simulate the retention of ruthenium in the irradiated organic solvent.

Ruthenium extraction by tri-n-butylphosphate (TBP) from nitric acid was studied and modelled in the conditions of the PUREX process. Experimental distribution ratios obtained for water, nitric acid and ruthenium were described with a physicochemical model based on the application of the mass action law on each extraction equilibrium and by taking into account deviations from thermodynamic ideal behaviour both in aqueous and organic phase using Mikulin and Sergievskii-Dannus equations. The best agreement between experimental and calculated ruthenium extraction isotherms was obtained by considering the formation of two complexes TBP2RuNO(NO3)3(H2O)2̅ and TBP3RuNO(NO3)3(H2O)2̅ in organic phase. This model was implemented in the CEA-AREVA PAREX process simulation code and used to simulate ruthenium behaviour in a counter-current PUREX hot test performed in mixer-settlers.

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