Silver recovery from waste radiographic films by cementation and reduction

Waste radiographic films can act as potential source materials for the recovery of valuable silver. In this study, a chemical processing scheme was adopted to recover silver metal from waste radiographic films. The films were dissolved in 1 M nitric acid (HNO₃) solution for 3 hours at 70°C to convert silver into silver nitrate (AgNO_3(aq)). Subsequently, the silver nitrate solution was treated using two different methods. The first involved cementation with fine iron powder and with fine zinc powder. These two well-known cementators were compared to each other with respect to purity of the final product and the recovery efficiency. The second method was sodium hydroxide (NaOH) precipitation. The treatment with Fe powder and Zn powder resulted in the formation of metallic silver powder in just one step. Ag ₂O obtained via NaOH precipitation was then treated using two different methods: a treatment with a mixture of glucose (C₆H ₁₂O₆) and NaOH to yield metallic silver and a heat treatment, in which Ag₂O was converted to silver metal at 500°C. TGA analysis revealed that at 400°C Ag₂O decomposes into silver and oxygen. With the exception of the powder produced by glucose reduction, all the powders would easily find industrial application. In addition, by using relatively inexpensive chemicals these applied processes show promise for further scaling up.