Effect of calcium and carbonate concentrations on cationic membrane fouling during electrodialysis

Abstract

Fouling, which is the accumulation of undesired solid materials at the phase interfaces of permselective membranes, is one of the major problems in electrodialysis. The aim of the present work was to investigate the effect on the fouling of cation-exchange membranes of the composition in calcium and carbonate of a model solution to be treated by electrodialysis. No fouling was observed at 400 and 800 mg/L of CaCl(2) in the absence of carbonate, while at only 400 mg/L CaCl(2) with carbonate, a deposit was observed. This difference could be explained by the buffering capacity of the carbonate, which affects the treatment duration with and without sodium carbonate. Since the duration was longer with carbonate, more calcium ions were able to migrate across the CMX-S membrane, which explained the higher deposit on its surface. Furthermore, whether there was carbonate in the solution treated by electrodialysis or not, the deposit on the surface of the cationic membrane was calcium hydroxide. However, this fouling formed during conventional ED was easily cleaned by an acid procedure.

Effect of calcium and carbonate concentrations on anionic membrane fouling during electrodialysis

“…For membranes used with solutions containing sodium carbonate, the increase in the thickness of the membranes was also in accordance with these previous results; a visual deposit was observed at 800 and 1600 mg/L of CaCl 2 on the AEM membrane and a significant increase from 0.74 to 10.27 mg/g dry membrane in calcium concentration was reported in the membranes. Furthermore, in comparison with our previous work [7] on the cationic membranes used during these experiments, the deposit thickness values for the anionic membranes was lower than those previously reported for the CMX-S membrane: 0.014 vs 0.052 mm after 4 ED treatments of solution containing sodium carbonate and 1600 mg/L CaCl 2 . The fouling of the CEM membrane was 3 times higher, while it is well known that anionic membrane are more susceptible to fouling than cationic membrane.…”

“…The membrane electrical conductivity was measured with specially designed cell (conductivity clip) from the Laboratoire des Matériaux Echangeurs d'Ions (Créteil, France) as previously described by Bazinet and Araya-Farias [7]. The membrane electrical conductivity κ (mS/cm) was calculated as follows [8,9]:…”

“…It was proposed that due to the basic pH on the side of the membrane in contact with the NaCl solution, the calcium would precipitate while the calcium migrated through the CEM was blocked by the AEM where it formed another fouling. On the side of the CEM membrane in contact with the NaCl solution, the precipitate was identified recently as calcium hydroxide [7].…”

Electrodialysis of calcium and carbonate high concentration solutions and impact on composition in cations of membrane fouling

“…The monovalent ions had migrated first during the ED treatment and then the divalent cation. Furthermore due to the basic pH on the side of the membrane in contact with the NaCl solution, the calcium would precipitate to form calcium hydroxide [18].…”

Removal of inorganic trace contaminants by electrodialysis in a remote Australian community

“…The fouling of ion-exchange membranes is the main problem of electromembrane technologies. High levels of calcium and magnesium hardness and the formation of divalent and trivalent ion hydroxides [20] can lead to membrane fouling. The build-up of a scalant layer on the ion-exchange membranes leads to an increase in cell resistance, which in turn reduces the effectiveness of the ED process and leads to a decrease in membrane integrity [21].…”