A study of iron(III) transport through an immobilised liquid membrane using the phosphine oxide Cyanex 923 as carrier has been carried out using batch experiments. A model is reported describing the transport mechanism which consists of (i) a diffusion process through a feed aqueous diffusion layer, (ii) a fast interfacial chemical reaction and (iii) a diffusion of HFeCl4. 2L through the membrane. The mathematical equations describing the rate of transport are derived which correlate the membrane permeability coefficient to diffusional and equilibrium parameters as well as the chemical composition of the system, such as carrier concentration in the membrane phase and hydrochloric acid in the feed phase. The experimental data are explained with the derived equations and the diffusion resistances to mass transfer are evaluated. The influence on the transport of stirring speed in the feed phase and the nature of the diluent have also been discussed.