Applications of electrodialysis for acid pickling wastewater treatment

In acid pickling before electroplating, the effective acid concentration de teriorates while the dissolved metal concentration increases continuously. By introducing electrodialysis (ED) between this operation and the followin g rinsing baths, these disadvantages are largely rectified. Recovered acid is continuously returned to the pickling bath and the amount of waste is dr astically reduced. Depleted solution is reused in rinsing baths. Moreover, ED can avoid metallic impurity build-up in the acid pickling bath. First ma nipulations conducted on our laboratory equipment failed. So, ion-exchange membranes (IEMs) were characterized by conductivity measurements and polari zation curves. Afterwards, a new selection of IEMs was performed. Faradic y ields were calculated for various commercial anion- and cation-exchange mem branes (AEMs and CEMs) in a Hittorf cell and ED conditions were refined. Th e relation between the hydrodynamics of ED and the limiting current density was checked by new measurements based on a tracer method successfully appl ied to electrochemical cells by our laboratory. (C) 2000 Elsevier Science S .A. All rights reserved.