Recovery and Concentration of Metal Ions. IV. Uphill Transport of Zn(II) in a Multimembrane Hybrid System

Abstract

A study has been made on the uphill transport of zinc cations across a multimembrane hybrid system (MHS) composed of two ion-exchange membranes (IEM) separated by a bulk liquid membrane (BLM). The fluxes of the Zn(II)/H countertransport were investigated as dependent on the composition and structure of ion-exchange polymer membranes (i), the solvent of a liquid membrane (ii), the feed and strip membrane area ratio (iii), and the pH of the feed solution (iv). The IEMs of various ionogenic groups (sulfonic acid, carboxylic acid, quaternized amine) and of various structure (clustered, gelatinous, porous) were examined in the MHS containing the BLM with di(2-ethylhexyl)phosphoric acid as a carrier of Zn(II) cations. It has been found that the Zn(II) fluxes are dependent on the properties of both the BLM and polymer membranes, i.e., on the BLM solvent viscosity (i), the nature and concentration of the IEM ion-exchange sites (ii), and the IEM thickness (iii). The best results were obtained when using hexane as the BLM solvent and the Nafion-117 membrane (perfluorinated polymer, sulfonic acid groups) as the cation-exchange membrane (CEM). The influence of the area ratio (feed-to-strip interface) has been checked for A f/A g equal to 3:1, 1:1, and 1:3. It was found that the asymmetry of the system leads mainly to some changes in the accumulation of transported species in a liquid membrane phase.