NEW APPROACH IN THE MODELING OF THE EXTRACTION EQUILIBRIUM OF ZINC WITH BIS-(2-ETHYLHEXYL) PHOSPHORIC-ACID

The extraction equilibrium of the possible test system for reactive ex traction zinc sulphate/bis-(2-ethylhexyl)-phosphoric acid (D2EHPA)/n-h eptane was studied at 25 degrees C. The results from slope analysis, c omputer modelling and quantitative FT-IR spectroscopy have been compar ed. The computer program SXLSQA was used for modelling the equilibrium taking into account the non-ideality of both phases, based on the Fit ter approach for the aqueous phase and the regular solution theory of Hildebrand/Scott for calculating organic phase activity coefficients. The three methods employed provide the same result. that the dominatin g zinc complex in the organic phase is ZnR(2)(RH), Some analytical imp rovements have been carried out, such as purification of D2EHPA, a pur ity determination method for D2EHPA, an analytical method for the dete rmination of D2EHPA concentration in aqueous solutions. FT-IR has also been used to illustrate the role of water in the formation of the org anic metal complexes. While in the extraction of nickel an appreciable amount of water is co-extracted, the extraction of zinc does not show the same behaviour.