Optimization of silver recovery from waste X-ray radiographic films by oxalic acid extraction with response surface methodology

Abstract

Waste X-ray radiographic films contain an appreciable amount of silver (Ag) that can be recovered and reprocessed. Most of the existing methods of Ag recovery from waste radiographic films are expensive and harmful to the environment. In this study, the extraction of Ag from waste radiographic films was done using oxalic acid solution heated at 90–100 °C. XRD and SEM results reveal that the recovered residue contains pure metallic Ag spherical microparticles. According to the response surface methodology (RSM) based on three-level, three-factorial Box-Behnken design, the optimized stripping conditions are oxalic acid concentration of 9.97% w/v, extraction temperature of 99.51 °C, and extraction time of 16.62 min. The predicted and actual % Ag recovery are of 94.94 and 90.07%, respectively. Reusability study confirms that the oxalic acid solution can be reused for several runs of Ag extraction. Initial Ag recovery of ~68.9% decreased to ~28.2% after 4 cycles of reusing the extraction solution.