Equilibrium analysis of solvent extraction of yttrium (III) and europium (III) from hydrochloric acid with P507

For the accurate prediction of equilibrium distribution ratios of rare earth metals during solvent extraction under non-ideal conditions, the extraction equilibria of yttrium (III) and europium (III) from the hydrochloric acid solutions with P507 in Shellsol D70 were studied. A chemically-based model was established and the extraction equilibrium constants were determined by the nonlinear least squares method. The proposed model involves the cation exchange reaction and the solvation extraction in the low and high acidity regions, respectively. In the model, the nonideality of the aqueous phase and was corrected by considering the complexation of the metals with Cl− and by replacing [ ] with its effective concentration, respectively. This model was verified by fair agreement between the calculated metal distribution ratios and those experimentally obtained in the single metal systems. The feed concentrations for the systems are in wide ranges of the metal (up to 0.1 mol/L), hydrochloric acid (0.07-3.00 mol/L) and the extractant (0.25-1.00 mol/L). The model enables the engineering prediction of the equilibrium distribution ratios with good accuracy in a binary metal system.