Solubility of tris(2-methylbutyl) phosphate in supercritical carbon dioxide and its application for the recovery of uranium from U-Zr and U-Th aqueous solutions

The employment of supercritical fluid extraction (SFE) within the nuclear industry may reduce the environmental burden by reduction in solvent waste generation. In this perspective, a SFE based method was developed for selective extraction of uranium from U-Zr and U-Th solutions using tris-(2-methylbutyl) phosphate (T2MBP) as a ligand in supercritical carbon dioxide (SCCO2). Prior to SFE studies, the utilisation of T2MBP in SCCO2 was examined by carrying out solubility measurements using dynamic flow technique at (313−333) K and (10−20) MPa. T2MBP has sufficient solubility in SCCO2 and ranges from 2.55 × 10-2 mol·mol-1 to 8.95 × 10-2 mol·mol-1. The solubility increases with pressure and decreases with temperature, resulting in retrograde solubility behaviour. The experimental solubility data was successfully correlated using different density based semi-empirical equations. Based on the solubility data, selective recovery of uranium from U-Zr and U-Th solutions was demonstrated using SCCO2+T2MBP. [Display omitted] •First report on solubility of tris(2-methylbutyl) phosphate (T2MBP) in SCCO2.•Correlation of T2MBP solubility with density based empirical/semi-empirical models.•Development of method for selective extraction of uranium from U-Zr feed solution.•Demonstration of U-Th separation using SCCO2 containing T2MBP.