The ion-exchange and extraction equilibria of Cu2+ and Zn2+ from aqueous sulfate solutions at pH = 1.9 in bi- and triphase systems (Resin-Organic solution of extractant-Aqueous solution) involving solid resins (either iminodiacetic (IDA) or (aminomethyl)phosphonic (AMP)) and an organic solution of extractant in heptane (either LIX 860, phosphoric acid bis(2-ethylhexyl) ester (DEHPA), or dithiophosphoric acid bis(2-ethylhexyl) ester (DEHDTPA)) have been studied at 22 °C. The values of the equilibrium separation factor α for Zn2+-Cu2+ exchange and the degree of Cu2+ extraction, E, in triphase R-Org-Aq systems depend on the relative selectivity of the resin over the extractant (or vice versa) toward the ion couple under study. The ion-exchange interaction in the triphase system proceeds via three interfaces representing three possible routes for the mass transfer. Each interface can be characterized by the corresponding ion-exchange reaction and related α value. A comparison of the extraction behavior of DEHPA and DEHDTPA toward Cu2+-Zn2+ mixtures in the bi- and triphase systems of different types has shown that the presence of the resin significantly facilitates the solvent extraction of the ionic species that are not extracted in the liquid-liquid systems. The maximum extraction degree of the "nonextractable" metal ion is observed in a resin-organic solution of extractant biphase systems (aqua-impregnated resin (AIR) systems), which can be attributed to the changes of both hydration of metal ions and pH in the resin phase. Taking into account these characteristics, one-stage extractive purification of Cu2+ from a Cu2+-Zn2+ mixture in a DEHPA-IDA resin AIR system has resulted in the rise of the product (CuSO4) purity from 98.1 to 99.8%. Purification of Zn2+ from a Cu2+-Zn2+ mixture in an AIR system involving DEHDTPA and AMP resin has allowed the purity of ZnSO4 to be increased from 52.5 to 99.3%. The results of this study are the first successful demonstration of the applicability of the AIR concept to enhance the selectivity of metal ion separation.
|Publication status||Published - 3 Sept 1997|