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

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

► This study focused on the Ag recovery from waste fixer solutions by electrolysis.
► 99.55% of silver recovery was obtained with electric current of 3 A during 2.5 h.
► The purity of silver was 98.62% with electric current of 3 A.
► Higher removal efficiency of COD by employing distillation was obtained.