Fouling Behavior of Multivalent Cations to Cation Exchange Membranes in Reverse Electrodialysis

Abstract

Reverse electrodialysis (RED) represents an energy conversion technology from the salinity difference of concentrated salt solutions (e.g., sea water) and diluted salt solutions (e.g., river water). The RED stack is comprised of an alternating arrangement of cation- and anion-exchange membranes between two electrodes that selectively transfer anions and cations. However, the sea water used for the RED may contain the divalent cations (i.e., Ca2+ and Mg2+). Thus, electrostatic characteristics of divalent cations may lead to membrane surface fouling. The membrane fouling cause increase electrical resistance and the increase of maintenance cost, and a significant decrease in operating performance. In this study, the influence of membrane fouling in RED by divalent cations such as Ca2+ and Mg2+ was investigated experimentally, and equilibrium tests, open circuit voltage, stack resistance, and power density were measured at different operation conditions. Commercially available cation exchange membranes were used. As a result, the divalent ions behaved a reversible foulant to cation exchange membranes caused an increase in resistance. Calcium ion exchanged cation exchange membranes showed higher resistance than magnesium ion exchanged ones. It is also concluded that the number of hydration attached to cations greatly influenced resistance. Acknowledgements This work was supported by the New and Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, and Republic of Korea (No. 20143030071240).