Selective transport of zinc through activated composite membranes containing di(2-ethylhexyl)dithiophosphoric acid as a carrier

The transport phenomena of transition metal cations through supported activ ated composite membrane (ACM) containing di-(2-ethylhexyl) dithiophosphoric acid (DTPA) as a carrier have been studied. The polyamide top layer of the ACM immobilizes DTPA by trapping it in the polymer net during the interfac ial polymerization process. The comparison of ACM with the corresponding su pported liquid membrane (SLM) shows far higher stability of the former. Thu s, the results of a comparative study of SLM and ACM under identical condit ions show that no metal ions transport through SLM is observed after 1 day working experiment, while ACM demonstrate sufficiently stable transport pro perties within several weeks of their use. A membrane-based process for zin c recovery from hydrometallurgical effluents has been developed. Zinc selec tively diffuses from the feed solution through the ACM into the receiver so lution containing 2.2 M hydrochloric acid, due to the facilitated transport with DTPA acting as carrier in the membrane. The selectivity of DTPA based ACM towards different metal ions is presented and discussed. At pH 2 in th e feed phase, the membrane provides a selective transport of zinc ionic spe cies to the stripping compartment of the membrane cell, while other metal i ons (Al, Ca, Mg, Mn and Ni) with sufficiently high stability of the DTPA-co mplexes remain in the feed compartment. Such a selectivity is based on the differences of the dynamic behaviour of the metal ions transport. (C) 1999 Elsevier Science Ltd. All rights reserved.