Extraction and recovery of ions in the cyanide-free brass electrodeposition effluent

In recent years, researchers have developed new industrial processes to make them less harmful to the environment and to the human health. The brass electroplating industry (copper and zinc), in general, uses cyanide as a complexing agent in its processes, although this compound is toxic. Therefore, complexing agents alternative to cyanide have been assessed, such as EDTA, sorbitol and glycerol. Among them, EDTA stands out for being already used in several industrial applications. Although the authors have observed that EDTA is able to generate uniform brass deposits with brightness, the treatment of the effluent generated in this process has not been studied yet.

Traditionally, the effluents from electrodeposition industries are treated by chemical precipitation. However, this method requires the addition of chemicals and generates a sludge that is disposed in waste landfills. Therefore, it is necessary to evaluate alternative methods for treating the effluent from this process. Among the alternative methods for treating it, the use of electrodialysis has shown to be promising, since this technique allows the extraction and the recovery of ions into the electrolytic bath. To guarantee the viability of electrodialysis, it is important to evaluate the transport properties of the ions that pass through the membranes, to reduce the electrical resistance and, consequently, the energy consumption. Therefore, this study aims at treating, by electrodialysis, the effluent generated in the cyanide-free brass electrodeposition using EDTA as a complexing agent. The electrodialysis has been tested under two electric current modes: one lower and the other greater than the limiting current density of the membrane system.

In addition, chronopotentiometry has been used for evaluating transport properties of copper-EDTA and zinc-EDTA complexes that pass through the membranes during electrodialysis. In this stage of the study, the influence of the proportion of copper/zinc metals, the pH of the solution and the concentration of EDTA on the transport properties of the membrane system has been evaluated, such as the limiting current density, the electrical resistance and the energy required to change the mechanisms of ions transport. After the extraction of the ionic species by electrodialysis, the recovery of ions into the electrodeposition bath has been also evaluated. Therefore, studies on cyclic voltammetry and electrodeposition have been performed using the electrolytic bath with the recovered ions, for verifying the quality of the brass electrodeposits.