Transport of Iron and Cobalt Complex Ions through Liquid Membrane Mediated by Methyltrioctylammonium Ion with the Aid of Redox Reaction

Abstract

A new type of carrier-mediated metal transport through liquid membrane is presented. The system involves redox reactions rather than acid-base reactions which have often been utilized in metal transport systems, Iron ion was selectively transported and concentrated through the membrane via a chloride complex by use of a lipophilic quaternary ammonium ion, rnethyltrioctylammonium (MTOA. Q'). as a carrier. The two aqueous solutions of different redox potentials were separated by a polymer-supported liquid membrane in which MTOA .chloride (Q+ .CI-) was dissolved as the carrier. Iron(l1l) ion in hydrochloric acid media formed a FeCIT type complex which was readily extracted to the organic membrane phase as an ion-pair complex Q + . F e C k . On contact with a reducing agent on the other side of the membrane. iron(1ll) was reduced to iron(I1) and liberated into aqueous solution; the chloride complexes of iron( 11) are too hydrophilic to stay in the membrane phase. On the other hand. cobalt ion was transported via nitrilotriacetic acid (NTA) complex by MTOA carrier in a similar manner to the iron transport. The nature of the transport reactions was studied under various operational conditions (redox agents, carrier and ligand concentration, pH, coexisting metals, etc.). The extension of these transport reactions to a water-in-oil-in-water type emulsion system as well as to a photcassisted transport system was studied.