Modeling of the equilibria of yttrium(III) and europium(III) solvent extraction from nitric acid with PC-88A

The equilibria of yttrium(III) and europium(III) (RE) extraction with PC-88A dissolved in Shellsol D70 from nitric acid solutions were studied under nonideal conditions in order to develop a chemically-based model enabling the engineering prediction of the equilibrium distribution ratios. The distribution of the extractant between the nitrate solution and the diluent was also examined. As a result, it was found that (i) the majority of PC-88A is dimerized in the organic phase, (ii) the cation exchange extraction is predominant in the low-acidity region, and (iii) solvation extraction becomes appreciable in the high-acidity region. By using a model that considers these two extraction equilibria together with the complexation of the RE with NO3-, the nonideality of the PC-88A dinner, and the competing extraction of HNO3, the extraction equilibrium constants and the coefficient for the effective concentration of the extractant were determined by the nonlinear least-squares method. The proposed model can reproduce the experimental data with good accuracy for single-metel systems over wide feed concentration ranges of RE up to 0.1 kmol(.)m(-3). nitric acid (0.05 to 3kmol(.)m(-3)), and the extractant (0.25 to 1 kmol(.)m(-3)). Its applicability to the prediction of the extraction front a binary metal system was also confirmed.