Determination of the limiting current density in electrodialysis desalination as an empirical function of linear velocity

Electrodialysis is known to be a useful membrane process for water desalination. The limiting current density (LCD) in the electrodialysis process is an important parameter which determines the electrical resistance and the current utilization. Usually, LCD depends on membrane and solution properties as well as on the electrodialysis stack construction and various operational parameters such as the flow velocity of the diluate solution. Therefore, a reliable determination of LCD is required for designing an efficient electrodialysis plant. In this study, LCD was measured in an electrodialysis flow cell system of given geometry and spacer configuration as a function of the linear velocity. The coefficients a and b of an equation describing LCD as a function of the linear flow velocity of the diluate solution, i_lim=aCu^b, were determined from a plot of the measured LCD over the electrolyte concentration versus the linear velocity on a double logarithmic scale. It was found that the coefficient b was related to the hydrodynamic conditions, while the coefficient a was affected by the cell geometry, electrolyte concentration and the membrane properties.