Purification of metal plating rinse waters with chelating ion exchangers

A wide range of chelating ion exchangers was tested for their abilities to remove Zn, Ni, Cu and Cd from solutions simulating waste effluents from the metal-plating industry. The task was to reduce metal discharges to the environment so that metal-plating shops could keep up with the modern, more stringent regulations of waste effluents. The resins were tested by batch and mini-column experiments. Decontamination factors (DFs) as high as 700 and capacities up to 3.3 meq/mL were measured at the 5% breakthrough (BT) point in mini-column tests. Complexing agents, especially cyanide, considerably reduced the performance of the resins with only a few exceptions. Ammonium seemed to improve the ion-exchange performance of some chelating resins and capacities higher than the theoretical values, given by the manufacturer, were measured. Comparative experiments between chelating, strong acid and weak acid ion-exchange resins showed that the advantage of chelating exchangers over strong and weak acid exchangers is a very low metal BT level, even as low as 2 μg/L, which is very important, especially in the end-of-pipe polishing.