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Aqua-Impregnated Resins. 1. Mass Transfer Active Interfaces in Bi- and Triphase Systems Involving Solid Polymer and Two Immiscible Liquid Phases

1997; American Chemical Society; Volume: 13; Issue: 18 Linguagem: Inglês

10.1021/la970261v

1520-5827

Dmitri Muraviev, Maria Oleinikova, Manuel Valiente,

Crystallization and Solubility Studies

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.