Effect of anions on electrochemical coagulation for cadmium removal

• Published in: Separation and purification technology Vol. 65; no. 2; pp. 137 - 146
• Main Authors: Huang, Chien-Hung, Chen, Luke, Yang, Chen-Lu
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 23.02.2009; Elsevier
• Subjects: Anodic dissolution; Applied sciences; Cadmium; Chemical engineering; Chloride; Electrochemical coagulation; Exact sciences and technology; Nitrate; Sulfate; Cadmium; Nitrate; Chloride; Sulfate; Electrochemical coagulation; Anodic dissolution; Coagulation; Dissolution; Flocculation reagent; Flocculation; Hydroxyl group; Current efficiency; pH; Parallel plate
• ISSN: 1383-5866; 1873-3794
• DOI: 10.1016/j.seppur.2008.10.029

Solutions of nitrate, sulfate, chloride and their combinations were prepared and tested in a parallel plate electrochemical cell to study their effect on electrochemical processes. Among the parameters studied were conductivity, current, current efficiency, pH change, coagulant formation, and cadmium removal. Nitrate ions were able to sustain a healthy current in the cell. The current dissolved aluminum from the anode, dissociated water molecules on the cathode, and increased pH in the solution. Due to excessive pH, Al(OH) 4 − became the dominating species and therefore no coagulant was observed. In sodium sulfate solutions, the aluminum anode quickly built up an inert film that prevented current from crossing the cell. Due to the lack of current, no reaction was observed throughout the 10-min treatment. In sodium chloride solutions, chloride ions provided electrolytic conductivity to sustain a current in the cell. The current dissolved aluminum, generated hydroxyl groups, increased pH, produced coagulant, and removed cadmium from the solution. In nitrate–sulfate mixtures, a small amount of nitrate ions dominated the performance of the sulfate solution in an electrochemical process. Although no coagulant was produced, the process removed 50% of the cadmium from the solution through cathodic reduction. In a solution of both sulfate and chloride, chloride ions were able to penetrate the inert film formed in a sulfate solution and drew a healthy current across the cell. Cadmium was initially removed by cathodic reduction followed by coagulation. This mechanism was very effective in cadmium removal. A 10-min treatment removed more than 99.5% of the cadmium, even with a substantial amount of sulfate in the solution.