A new approach to the determination of thermodynamic equilibrium constants in ion-exchange and solvent extraction processes
is described. A plot of the logarithm of the distributing species activity in the aqueous phase as a function of its concentration
in the non-aqueous phase has an inflection point. The ordinate of the inflection point gives directly the logarithm of the
thermodynamic equilibrium constant of the reaction considered. This was made possible by finding that the ratio between n
power of the free extractant molecule (or free site) activity and the activity of the distributing species-extractant complex
is unity as this point.
A simple graphical method for determination of thermodynamic equilibrium constants, developed for ion-exchange and solvent
extraction processes, was successfully applied to a liquid exchangersystem. Close values of the thermodynamic equilibrium
constants for the system uranyl chloride—hydrochloric acid—di-2-ethylhyxyl phosphoric acid—toluene (K=7.8±0.8) were obtained
when the ionic strength of the aqueous phase was varied and the concentration of di-2-ethylhexyl phosphoric acid in the organic
phase was kept constant, and vice versa.