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

Abstract

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 (CyMe4-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, Δ Cp, Δ H0 and Δ S0, of the CyMe4-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 CyMe4-BTBP increases with an increased temperature in all systems, especially after acid pre-equilibration. This increased CyMe4-BTBP solubility after pre-equilibration could be explained by acid dissolution into the solvent. Comparing the Δ H0 and Δ S0 calculated using Δ Cp 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.