Orthogonal Array Design for the Optimization of Silver Recovery from Waste Photographic Paper

Abstract

An orthogonal array design (OAD), OA₉, was employed as a chemometric method for the optimization of the silver recovery from waste photographic paper using external electrolysis. In this work, silver was recovered from photographic paper by dissolving the silver compounds with ammonia solution. The external electrolysis method was carried out using a brass electrode as cathode and a carbon electrode as anode. Similarly, external electrolysis was carried out without adding ammonia solution. The effects of four parameters: electrolysis time, ammonia concentration as chelating agent, solution temperature, and electrolysis voltage on the amount of recovered silver were investigated. The effects of these factors on the recovery of metallic silver were quantitatively evaluated by the analysis of variance (ANOVA). The results showed that silver can be effectively extracted from various sources, such as waste photographic paper and jewellery scrap, by dissolution in ammonical solutions with the aid of external electrolysis. Finally, the optimum conditions for silver recovery by electrolysis using ammonia as chelating agent were proposed. The results of ANOVA showed that 7.5‐hr electrolysis time, 1.3359 mol/L ammonia concentration, and 4.5 V electrolysis voltage are optimum conditions for the silver recovery procedure.

Keywords:

• Orthogonal array design
• Taguchi method
• Silver recovery
• External electrolysis
• Ammonia solution
• Photographic paper