The transport of AI(III), Fe(III), Ti(IV), and Na(I) ions through charged polysulfonated membrane under Donnan dialysis conditions has been studied as a function of HCl concentration at room temperature. In this process. the membrane is separated by. two electrolyte solutions: one side (donor phase) is initially, red mud aqueous solution containing Al(III), Fe(III), Ti(IV). and Na(I) ions and the other side is HCl solution at different concentrations with no external potential field applied. The transport of metal ions through membranes was correlated with the flux data, as well as with estimated diffusion coefficients. It was observed that the transport of metals is influenced by, the HCl concentration and the flux of ions increased with H+ ion concentration in the receiver phase. (C) 2001 Elsevier Science.