Contribution of Raman Spectroscopy to the Comprehension of Limiting Phenomena Occurring with a Vinylpyridinium Anion Exchange Membrane during the Electrolysis of Cr(VI) Solutions

Limiting phenomena occur during the recovery of chromic acid solutions by electrodialysis using a poly(4-vinylpyridinium) anion exchange membrane (AEM). An increase of the cell electrical resistance appears as the current is applied. As for other AEMs, the inner acid concentration is very high compared to that of the equilibrating solution. Raman spectroscopy shows the presence of polychromate ions. Moreover, a competition takes place between the dichromate ions and the poly(4-vinylpyridinium) exchange sites toward protons. The deprotonation of the sites and the very low mobility of the polychromate counterions explain the increase of the electrical resistance.