Effects of inorganic ions on the transfer of weak organic acids and their salts in electrodialysis process

Abstract

Electrodialysis has been considered to be a competitive technology in the treatment and reclamation of organic saline wastewater. As a kind of typical compounds in industrial wastewater, the mass transfer property of organic electrolyte were important to the operation of the treatment process and product quality. The benzoic acid/sodium benzoate and citric acid/sodium citrate in the electrodialysis process and diffusion process were investigated in this paper. The effects of cations (Na+, K+, Mg2+, Ca2+) and anions (Cl- and SO42-) were discussed. The mass transfer of organic acids and their salts through the ion exchange membrane has two forms: electromigration and diffusion, both of which were affected by the degree of ionization, molecular size and molecular structure. The contribution of electromigration was found to be predominant over that of diffusion as a current is applied. The influence of inorganic ions mainly includes dehydration of organic matter and water content of the membrane. These opposite effects play different roles in the mass transfer of organic acids and their salts through the ion exchange membrane with and without current. It was also shown that the existence of organic acids and their salts had little effect on the mass transfer properties of inorganic salts.