Potential Drop & Ionic Flux in Desalting Electrodialysis Units

In this paper, the differential equations governing the ionic flux, current intensity and potential drop for an electrodialysis (ED) unit are derived in terms of ionic concentration, ionic diffusion coefficient in both water and membranes, ionic electric transfer numbers and membrane properties. These equations are solved to obtain the unit potential difference together with the ionic flux of counter and co-ions through the membranes. The power required for the unit is obtained by multiplying the potential drop by the integral of the current intensity along the flow passage. The minimum power required is calculated and compared with an approximate analysis for the ED unit at different working conditions. The ratio between minimum power and approximate power ranges from 62-46 percent at Cfof2000 ppm to 26-19 percent at Cfof 10000 ppm by using compartment thickness of 0.5-1 mm, respectively.