Evaluation of the electrodialysis process for the treatment of metal finishing wastewater

Metal finishing wastewater containing ions of Zn, Ni, Cu, Fe and Al, as well as of Na and CN in alkaline pH was treated by electrodialysis. The treatment was conducted in a laboratory cell and in a pilot plant unity. The experiments were carried out using Nafion and Selemion membranes. Results showed most of the metallic ions to have an anionic nature, due to the formation of coordination complexes. Each metallic ion showed a different rate of extraction from the treated solution, depending on the galvanostatic or potentiostatic operation mode. Zn, Ni and Cu have shown higher extraction under galvanostatic control. For Al, higher extraction was observed when the experiment was conducted in a potentiostatic mode. Fe ions exhibited an unexpected behavior, not being removed in the same way as the other ions. The best extraction results were obtained within 2-3 h of treatment.