Silver recovery and chemical oxygen demand (COD) removal from waste fixer solutions

Wei-Ting Chen, Chin-Chi Ma, Ming-Hsun Lee, Yung-Chuan Chu, Lung-Chang Tsai and Chi-Min Shu

Applied Energy, 2012, vol. 100, issue C, 187-192

Abstract: This study focused on the silver recovery from waste fixer solutions by electrolysis under different experimental conditions. During an 8h electrolysis procedure, the silver recovery efficiencies were 10.57%, 11.75%, 45.5%, 62.68%, and 83.88% for electric currents of 0.1A, 0.3A, 0.5A, 0.7A, and 0.9A, respectively. Thus, the most efficient recovery factor of silver was found for a current of 0.9A. Additionally, the pH values of the waste fixer solutions were adjusted prior to treatment by electrolysis, and the silver recovery was 100% for a solution with pH 8 that underwent electrolysis for 8h at an electric current of 0.9A. The recovery efficiency of silver was 88.64% for an electric current of 3A and a duration of 3.5h, but the recovery efficiency of silver decreased to 83.72% for an electrolytic time of 6h. Furthermore, the recovery efficiency of silver increased to 99.55% with a decreased electrolysis time of 2.5h when the solution was adjusted to pH 8 at an electric current of 3A. These results suggest that the most suitable experimental conditions were an electric current of 3A, pH 8, and 2.5h of electrolysis. The treated waste fixer solutions still had high concentrations of chemical oxygen demand (COD) after electrolysis. The addition of 30mL of sulfuric acid to 1000mL of waste fixer solution resulted in a COD removal efficiency of 42%. Furthermore, when the waste fixer solutions were treated by distillation to remove COD, the removal efficiency of COD was 99.3%. Although a higher COD removal efficiency was obtained by employing distillation, the cost of the distillation treatment was more expensive.

Keywords: Silver recovery; Waste fixer solutions; Electrolysis; Chemical oxygen demand (COD); Distillation (search for similar items in EconPapers)
Date: 2012
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DOI: 10.1016/j.apenergy.2012.06.026

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