Solubility Thermodynamics of CyMe 4 -BTBP in Various Diluents Mixed with TBP.

The two organic ligands 6,6'-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenzo[1,2,4]triazin-3-yl)[2,2']bipyridine (CyMe 4 -BTBP) and tri-butyl phosphate (TBP) have previously been investigated in different diluents for use within recycling of used nuclear fuel through solvent extraction. The thermodynamic parameters, KS , ΔCp , ΔH0 and ΔS0 , of the CyMe 4 -BTBP solubility in three diluents (cyclohexanone, octanol and phenyl trifluoromethyl sulfone) mixed with TBP have been studied at 288, 298 and 308 K, both as pristine solutions and pre-equilibrated with 4 mol · L -1 nitric acid. In addition, the amount of acid in the organic phase and density change after pre-equilibration have been measured. The solubility of CyMe 4 -BTBP increases with an increased temperature in all systems, especially after acid pre-equilibration. This increased CyMe 4 -BTBP solubility after pre-equilibration could be explained by acid dissolution into the solvent. Comparing the ΔH0 and ΔS0 calculated using ΔCp with the same parameters derived from a linear fit indicates temperature independence of all three thermodynamic systems. The change in enthalpy is positive in all solutions.