Evaluation of two ion-exchange membranes for the transport of tin in the presence of hydrochloric acid

The transport properties of two ion-exchange membranes in the presence of tin, as Sn(II) and Sn(IV), were investigated by chronopotentiometry and current–voltage curves. Since tin forms positively or negatively charged complex species in solution, the effect of the counterions on the transport phenomena through both cation- and anion-exchange membranes was evaluated. The speciation diagrams of Sn(II) and Sn(IV) as a function of the chloride concentration and pH were calculated for all the tin and HCl concentrations in order to explain the values of parameters like the limiting current (Ilim), the resistance of the ohmic region (R1st) and the resistance of the overlimiting region (R3rd). In the case of the anion-exchange membrane (AEM), the chloride ions were the species responsible for current transfer through the membrane in the cases of both Sn(II) and Sn(IV). The formation of a Sn(IV) precipitate at low HCl concentration was reflected by a diffusion relaxation behaviour characteristic of the bipolar membranes. Protons are the main counterions capable of crossing the cation exchange membrane (CEM) for both tin oxidation sates. The contribution of Sn(II) to the water splitting phenomenon was evident for every HCl concentration by the increase of the membrane potential in the chronopotentiometric curves and by the appearance of a Sn(OH)2 precipitate located at the anodic side of the CEM.