Evaluation of the Zn2+ transport properties through a cation-exchange membrane by chronopotentiometry.

In this work the effect of zinc concentration, pH, and boric acid concentration on the zinc transport properties through an IONICS 67-HMR-412 cation-exchange membrane was evaluated. The limiting current density and the transport numbers were determined by means of chronopotentiometry. A model between the limiting current density and the bulk zinc concentration was established, assuming a potential relationship between the zinc transport number through the membrane and the bulk zinc concentration together with the Levich equation for the DBL thickness. A decrease in the initial pH value of the solutions causes considerable modifications both in the plateau region and in the overlimiting current density region of the current-membrane potential curves. The results show that the presence of boric acid produces the precipitation of zinc metaborate on the anodic layer of the cation-exchange membrane.