On the Interfacial Layer in Desalting Side of Anion Exchange Membrane in Hydrogen Carbonates Electrodialysis

Abstract

The author studied on phenomena ocurred in the interfacial layer in desalting side of anion excha nge membrane in sodium and potassium hydrogen carbonates electrodialysis. The Schlieren.Diagonal method, previously reported, was employed for observation of the interfacial layer. The decomposition of hydrogen carbonate ion (carbonate decomposition) similar to the water decomposi.tion, HCO3-.HCO32-, has been suggested to occur by the auther, Differences of the state of the interfacial layer between in the water decomposition and in the carbonate decomposition were studied in this paper. The following results were obtained:(1) There was a state of the interfacial layer obviously distinguishable fromones at both normal and water decomposition conditions at the condition between them. At the condition, the carbonate decomposition seemed to occur(Fig.2and 5).(2)When the carbonate decomposition occurred, oncentration distribution in the interfacial layer became linear, where small but quick changes were observed (Fig.2and 5).(3)States of the interfaciaUayer of an anion exchange membrane ih hydrogen carbonates solutions apPeared similar to that of a cation exchange membrane in sodium chloride solution in the foration process of the interfacial layer and in the befavior at the water decomposition. It seemed to be owing to the difference in the transport numbers of solute ions in each solutions (Fig 2, 3a d.5).(4)For a membrane without treat ment for giving low permeability to divalent anions(M-1), abreak point in current, voltage relation was observed at the beginning of the water decomposition.For aembrane with this treatment(M-), however, two break points corresponding to both the carbonate and the water idecemposition were observed(Fig.1and 4).(5) Analytical data of transfered quantity of total carbonates seemed also to proveoccurrence of the carbonate decomposition at conditions mentioned above(Table 1).