Influence of linear flow velocity and ion concentration on limiting current density during electrodialysis

The effects of linear flow velocity and ion concentration on limiting current density (LCD), an important parameter in the design and operation of electrodialysis (ED) devices, was examined. As the applied voltage increased, reduction rate of the conductivity increased. However, it did not increase beyond a certain limit because of the effect of concentration polarization. The maximum applied potential of synthetic wastewater, prepared with NaCl (2,000 mg/L), was 15.4 V and the LCD was estimated to be 77.9 mA/cm(2). When the linear flow velocity of the diluate was increased by 1, 2, and 6 cm/s, LCD increased in direct proportion to the increase in electrical conductivity. The relationships between LCD, linear velocity, and ion concentration were established and parameters a and b were experimentally estimated. In contrast, as a result of changing the linear flow velocity of the concentrate by the same levels, there was no significant difference in the rate of reduction in conductivity. LCD measurements using synthetic wastewater containing various ions, including copper and nickel, and plating wastewater showed that the LCD was slightly higher because the ionic charge was higher than NaCl under the same conductivity conditions. Overall, LCD showed a tendency to be proportional to electrical conductivity.