Reclamation of acid with electrodialysis process: Influence of selective ion-exchange membranes

Abstract

Electrodialysis (ED) could concentrate salt solutions, but the leakage of H+ ions across the anion-exchange membrane (AEM) obstructed their application in waste acid recovery. Selective electrodialysis (SED) with acid blocking AEM and monovalent selective cation-exchange membrane (CEM) has the ability of reclaiming acid with high concentration efficiently. This study investigated the individual effect of the two selective ion-exchange membranes by comparing the acid reclamation performance of configurations with standard AEM and CEM (A-C), acid blocking AEM and standard CEM (SA-C) and acid blocking AEM and monovalent selective CEM (SA-SC) for etching solution treatment after diffusion dialysis. Substituting acid blocking AEMs for the standard ones could significantly increase the recovered acid concentration. An acid concentration plateau was reached quickly, but Cu2+ ions transfer through the CEMs continuously due to the low H+/Cu2+ ratio in the dilute of SA-C configuration. The monovalent selective CEM obstructed the migration of Cu2+ through the CEM and broke the balance of H+ migration into and out of the dilute through CEM and selective AEM individually. The configuration of SA-SC has the highest current efficiency and the configuration of A-C has the lowest. The utilization of selective membranes increased the purity of the recovered acid, and decreased the specific energy consumption simultaneously. The acid concentration could be further improved by higher current or enlarged dilute volume in SA-SC configuration. During the ED process, H+ concentration difference between the concentrate and the dilute plays a crucial role on the current efficiency for acid recovery.