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 Ag metal from waste radiographic films. The films were dissolved in 1 M nitric acid (HNO3) solution for 3 h at 70 degrees C to convert Ag into silver nitrate (AgNO3(aq)). Subsequently, the AgNo3 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 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. Ag2O obtained via NaOH precipitation was then treated using two different methods: a treatment with a mixture of glucose (C6H12O6) and NaOH to yield metallic silver and a heat treatment in which Ag2O was converted to silver metal at 500 degrees C. TGA analysis revealed that at 400 degrees C Ag2O decomposes into Ag and O2. 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. (Authors.)
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 Ag metal from waste radiographic films. The films were dissolved in 1 M nitric acid (HNO3) solution for 3 h at 70 degrees C to convert Ag into silver nitrate (AgNO3(aq)). Subsequently, the AgNo3 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 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. Ag2O obtained via NaOH precipitation was then treated using two different methods: a treatment with a mixture of glucose (C6H12O6) and NaOH to yield metallic silver and a heat treatment in which Ag2O was converted to silver metal at 500 degrees C. TGA analysis revealed that at 400 degrees C Ag2O decomposes into Ag and O2. 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. (Authors.)