Study on the Thiophosphinic Extractants. I. The Basic Properties of the Extractants and the Phase Behavior in Their Saponified Systems*

Commercial extractants Cyanex 302 and Cyanex 301 have been purified, and their sodium salts prepared. The basic physic-chemical parameters, such as solubility and pKa values in water of the acids, cmc of the salts, have been reported. The phase behaviors during saponification of purified extractants by NaOH have been measured. The system of monothiophosphinic extractant is similar to that of purified Cyanex 272 except when the middle phase of the former appears at lower neutralization fraction and the volume of the third phase is bigger. But there is no third phase formed in dithiophosphinic acid extractant system and it always maintains the equilibrium of bottom phase microemulsion with the excessive oil phase (Winsor type I). The pseudo-ternary phase diagrams of unpurified Cyanex 302 (or Cyanex 301)-n-C6H14-NaOH (2.4 mol/L) are compared with Cyanex 272 system. There are some differences in all of 3L, 2L, L and D regions. The pseudo-ternary phase diagrams of purified sodium salt NaA-n-C5H11OH-kerosene (80%, w/w)-H2O system for different extractants have also been drawn. The mono-phase microemulsion (w/o) area increases with the increasing of sulfur atom in extractants, indicating that the replacement of oxygen atom by sulfur makes sodium salt more hydrophilic.