Abstract
Growing environmental concerns have led to the development of cleaner processes, such as the substitution of cyanide in electroplating industries and changes in the treatment of wastewaters. Hence, we evaluated the treatment of cyanide-free wastewater from the brass electroplating industry with EDTA as a complexing agent by electrodialysis, aimed at recovering water and concentrated solutions for reuse. The electrodialysis tests were performed in underlimiting and overlimiting conditions. The results suggested that intense water dissociation occurred at the cathodic side of the commercial anion-exchange membrane (HDX) during the overlimiting test. Consequently, the pH reduction at this membrane may have led to the reaction of protons with complexes of EDTA-metals and insoluble species. This allowed the migration of free Cu2+ and Zn2+ to the cation-exchange membrane as a result of the intense electric field and electroconvection. These overlimiting phenomena accounted for the improvement of the percent extraction and percent concentration, since in the electrodialysis stack employed herein, the concentrate compartments of cationic and anionic species were connected to the same reservoir. Chronopotentiometric studies showed that electroconvective vortices minimized fouling/scaling at both membranes. The electrodialysis in the overlimiting condition seemed to be more advantageous due to water dissociation and electroconvection.
Highlights
Electrodeposited brass coatings are widely used for decorative purposes, the protection of steel and the promotion of rubber adhesion to steel and other metals [1]
Considering the advantages related to the use of electrodialysis for treating wastewaters and the promising substitution of cyanide by ethylenediaminetetraacetic acid (EDTA) in brass electrodeposition, the present paper aims at employing ED to treat synthetic solutions of the wastewater from brass electrodeposition with EDTA as a complexing agent
The electrodialysis tests were carried out in a home-made five-compartment ED cell made of acrylic, separated by cation- and anion-exchange membranes with an active area of 16 cm2, arranged alternately in a “Cathode-anion exchange exchange membranes (AEMs)-cationcation exchange membranes (CEMs)-AEM-CEM-Anode” configuration
Summary
Electrodeposited brass coatings are widely used for decorative purposes, the protection of steel and the promotion of rubber adhesion to steel and other metals [1]. Some alternative complexing agents already tested in brass electrodeposition are glycerol [4,5], glycine [1,3], sorbitol [6,7], ethylenediaminetetraacetic acid (EDTA) [8,9], citrate [10], pyrophosphate [11], glycine [1,3], sorbitol [6,7], ethylenediaminetetraacetic acid (EDTA) [8,9], citrate [10], pyrophosphate-oxalate [12], triethanolamine [2], glucoheptonate [13], nitrilotriacetic acid [14], pyrophosphate [11], pyrophosphate-oxalate [12], triethanolamine [2], glucoheptonate [13], tartrate [15], choline acetate [16], bis(trifluoromethylsulfonyl)imide [17] and d-mannitol [18]. Among nitrilotriacetic acid [14], tartrate [15], choline acetate [16], bis(trifluoromethylsulfonyl)imide [17] and them, EDTA is interesting since it is widely used as a complexing agent in the electrodeposition of d-mannitol [18]. EDTA is interesting since it is widely used as a complexing agent in metals [19,20] and for separating cations using electrodialysis, exploiting a difference in the solubility the electrodeposition of metals [19,20] and for separating cations using electrodialysis, exploiting a constants of the complexes [21,22]
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