A three-stage chemical cleaning of ion-exchange membranes used in the treatment by electrodialysis of wastewaters generated in brass electroplating industries

After long-term electrodialysis, cleaning the membranes is crucial to extend their lifetime. In this work, we evaluate the effects of a three-stage chemical cleaning on electrochemical and structural properties of anion- and cation-exchange membranes. Membranes used in the electrodialytic treatment of a synthetic effluent from the cyanide-free brass electrodeposition were cleaned using 0.1, 0.5 and 1.0 mol·L−1 NaOH solutions. The electrochemical behavior of the membranes was evaluated after each cleaning step by chronopotentiometry. Additionally, changes in the membrane structure and composition were analyzed by FTIR-ATR and SEM/EDS. While the membranes undergo a decline in some electrochemical features after the electrodialysis process, the cleaning with 0.1 mol·L−1 NaOH showed to be the most effective in recovering the properties characteristic of the virgin membranes: the limiting current density increased by 84% after the cleaning, whereas the ohmic and overlimiting resistances decreased by 47% and 55%, respectively. In contrast, the 0.5 and 1.0 mol·L−1 NaOH solutions degraded the membranes and reduced their fraction of conductive area, especially for the anion-exchange one. This favored fouling/scaling occurrence, as noticed by a prominent increase in the potential drop of the anion-exchange membrane. FTIR-ATR and SEM/EDS analyses confirmed fouling/scaling, as well as degradation of the ion-exchange membranes. •The NaOH solution in 0.1 mol·L−1 is the most suitable to clean the membranes.•Solutions in 0.5 and 1.0 mol·L−1 degraded their functional groups and the polymer.•The degradation of the membranes favored the occurrence of overlimiting phenomena.•The degradation reduced the fraction of conductive area of both membranes.•The features of the anion-exchange membrane were strongly affected by the cleaning.