COUPLED TRANSPORT OF ZN(II) THROUGH A SUPPORTED LIQUID MEMBRANE CONTAINING BIS(2,4,4-TRIMETHYLPENTYL) PHOSPHINIC ACID IN KEROSENE .2. EXPERIMENTAL EVALUATION OF MODEL-EQUATIONS FOR RATE-PROCESS UNDER DIFFERENT LIMITING CONDITIONS

Abstract

The kinetics of the permeation of Zn(II) from its aqueous solution through a solid supported liquid membrane containing bis(2,4,4-trimethyl pentyl) phosphinic acid (cyanex 272) solution in kerosene has been studied under different experimental conditions. The metal ion flux across the membrane is found to be dependent upon the concentrations of Zn(II) and H+ in the feed solution and carrier in the membrane phase. The rate-limiting conditions have been precisely delineated and the model parameters have been determined under such conditions, It has been observed that at high carrier concentration and at high pH value, the Zn(lI) flux can be described by the diffusion of ZnL(2)(HL) and ZnL(2)(HL)(2) species. At low carrier concentration and possibly at low pH[, the rare-limiting step is the interfacial reaction for the formation of ZnL(2) and ZnL(2)(HL). The overall Aux is first order with respect to Zn(II) concentration up to 4.0 mol m(-3) and 0.75 order with respect to dimeric carrier concentration.