Characteristics of heavy metal separation and determination of limiting current density in a pilot-scale electrodialysis process for plating wastewater treatment.

Recent development in industry has led to increased water usage, while intensifying water shortage. Electrodialysis has been proposed as a technique for minimizing the generation of secondary environmental pollution problems and effectively treating harmful substances such as heavy metals in industrial wastewater. As electrodialysis is affected by several factors, it is crucial to provide necessary information about the operating elements. This study investigates the effect of linear flow velocity on the removal of heavy metals in an electrodialysis pilot plant. The results of the experiment showed that increasing the linear flow velocity from 0.6 to 5.1 cm/min increased the voltage from 17.3 to 40 V. In addition, the limiting current density (LCD) showed a linear relationship with the linear flow velocity, increasing from 1.4 to 5.9 A/m2 as the linear flow velocity increased proportionally in the same voltage range. The empirical correlation coefficients a and b for the mass transfer coefficient K, which can be expressed as a nonlinear function of the linear flow velocity, were estimated to be 1.8519 and 0.7016, respectively. In the batch operation, the ion-separation rate in the electrodialysis process was estimated with the shift order kinetics of the first-order and zero-order constants via regression analysis of experimental data. The ion separation rate in the diluate and the ion concentration rate in the concentrate decrease as the experiment number increase. This may be due to the reverse diffusion of ions transferring to the diluate owing to the high concentration of ions in the concentrate. Therefore, ion concentration in the concentrate has to be maintained at an appropriate level. Copper ions are deposited on the cathode electrode surface, although not uniformly.