Scale Formation by Electrode Reactions in Capacitive Deionization and its Effects on Desalination Performance

The effects of scale formation of hardness material caused by electrode reactions on the desalination performance of the membrane capacitive deionization (MCDI) were investigated. During the repeated adsorption and desorption process for the influent containing Ca2+ ion, changes in effluent concentration and cell potential with respect to the number of adsorption were analyzed. It was found that OH- generation at the cathode was initiated at about 0.8 V or more of cell potential. In addition, the scale of Ca(OH)(2) was formed on the surface of cathode carbon electrode by combining adsorbed Ca2+ ions and OH- ions generated from electrode reaction. As the scale was forming, the electrical resistance of carbon electrode was increasing, which resulted in the decrease of the adsorption amount. In the case of the operation at 1.5 V cell potential, the adsorption was reduced to 58% of the initial adsorption amount due to the scale formation.