Electrodialysis of hydriodic acid in the presence of iodine

Electrodialysis of hydriodic acid was studied in the presence of iodine and in the HI molality range of 8–12 mol/kg using commercial ion exchange membranes, CMH and APS. Owing to the high transport numbers of counter ions and low water permeation of the membranes, the increase of HI molality was possible by electrodialysis in spite of the high HI molality of the test solution. Interesting phenomena with respect to the anion exchange membrane, APS, were observed in the electrodialysis. Firstly, the membrane strongly suppressed the H2O permeation. Secondly, apparently, neutral iodine molecules were transported through the membrane even against the concentration gradient. The transportation occurred toward the reverse direction of the anion permeation. These phenomena were discussed in terms of an iodine adsorption and a charge transfer interaction between iodine and the polymer matrix.