Treatment of wastewaters from cyanide-free plating process by electrodialysis

Cyanidric compounds are used in certain stages of electroplating processes. However, the toxicity of the cyanide stimulates the development of alternative raw materials. Therefore, the utilization of cyanide-free compounds requires the consolidation of treatment methodologies for this novel type of wastewater generated. One of the alternatives that is currently available consists of the replacement of the cyanide by 1-hydroxyethane 1,1-diphosphonic acid (HEDP). In this study it was employed an HEDP based electrolyte, which was used to produce solutions that simulate the rinse waters of copper strike baths. The application of electrodialysis (ED) in a closed system was evaluated by considering the recovery of the copper, the HEDP and the water. The trials were carried out in an ED cell which contains five compartments. The results showed the extraction of up to 99.7% of the copper and up to 94.4% of the HEDP from the working solution. By varying the pH values, along with the construction of speciation diagrams, it was achieved a separation of the Cu(II)-HEDP complexes. While the characteristics of the treated solutions enabled their reutilization in the rinse tanks, the concentrated solutions can be reused in the electrolyte in order to replace ions lost by drag-out.