Removal of nitrate by electrodialysis

A nitrate-specific anion-exchange membrane was prepared from chloromethylated polysulphone by partially aminating it with a secondary amine followed by a tertary amine for completion. The presence of amine groups are required for anion transport. When the nitrate-chloride ratio was equal, nitrate flux was larger than chloride flux by a factor of 1.6 in alkaline medium and 2 in acidic medium. In alkaline medium, the nitrate transport is more than one in all ratios. Selectivity in the transport of anions through ion-exchange membranes under applied electric field, though a desirable area, is not yet achieved satisfactorily. The ions which are all charged take part in migrating across the membrane equally according to the functional group of the membrane. It appears some mechanism is needed to retard one particular ion and accelerate other ion during transport process to bring out selectivity. Perhaps the introduction of polyfunctional groups in the membrane may help in the selectivity. An attempt has been made by Eyal and Kedam to introduce tertiary amino and quarternary ammonium groups. A similar procedure was adopted in this investigation. The transport ratios of nitrate to chloride in different proportions of the mixture in an electrodialysis cell is described in this investigation at three different pH values.