Selective cloud point extraction of uranium from thorium and lanthanides using Cyanex 301 as extractant

A cloud point extraction (CPE) process using TX-114 as nonionic surfactant and bis(2,4,4-trimethylpentyl)dithiophosphinate (Cyanex 301) as extractant was successfully applied to extract UO22+ selectively and quantitatively in the presence of Th4+ and lanthanide ions. The thermodynamic parameters of the interaction between the related metal ions and the micelles were obtained by isothermal titration calorimetry (ITC), and the binding constant followed the order of UO22+ > Th4+ > La3+, consistent with the result of extraction selectivity. In the absence of NaCl, the stability constants beta(1) and beta(2) of the UO22+-Cyanex 301 complex in the micellar system were determined via UV-vis spectroscopic titration to be 6.3 x 10(3) and 2.0 x 10(5), respectively. In the presence of 0.10 mol L-1 NaCl, the stability constants beta(1) and beta(2) were measured to be 5.9 x 10(3) and 1.0 x 10(7), separately. It is believed that the combination of UO22+ and Cyanex 301 leads to the formation of a neutral complex, which enters the micelles and results in a high extraction efficiency.