Aqueous hybrid liquid membrane process for metal separation - Part I. A model for transport kinetics and its experimental verification

A novel liquid membrane (LM) system, denoted as an aqueous hybrid liquid membrane (AHLM), was developed for the separation of solutes. It utilizes an aqueous solution of a polyelectrolyte las a carrier), flowing between ion-exchange membranes (IEMs). The membranes, which separate the carrier solution from feed and strip solutions, enable the transport of solutes and water, but block the transfer of the carrier to the feed or to the ship. Blocking the carrier is achieved through the membranes' ion exchange properties or through their retention abilities, due to pore size. A theoretical model was developed for the simulation of AHLM transport kinetics. Model predictions of transport rates and concentration profiles are based on independent experimental measurements of (a) individual mass-transfer coefficients of the solutes in all liquid boundary layers and (b) facilitating parameters of the ion-exchange membranes, denoted as IEM potential, and of aqueous LMs, denoted as LM facilitation potential (LMF potential). Experiments were designed to test the validity of the theoretical model simulation. Removal of Cd, Cu and Zn from simulated wet-process phosphoric acid (WPA) feed solution was investigated. Water-soluble polyvinylsulfonic acid (PVSA) or its sodium salt were used as the LM, separated from the feed and strip streams by Neosepta cation-exchange membranes. Experimental results are in satisfactory agreement with the theoretical model calculations. Module optimization characteristics are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.