Silver recovery from an effluent generated by plating industry using a rotating cylinder electrode (RCE)

This paper concerns silver recovery from simulated rinse wastewater from the electrolytic cyanide silver process (1300 and 23,000 ppm of Ag(I) and CN−, respectively, at pH 13 and 150 mS cm−1 conductivity) using a laboratory scale RCE. Rotating disk electrode (RDE) studies revealed that at −1.35 ≤ E ≤ −1.15 V vs. SCE, the Ag(I)/Ag process is limited by mass transport. Global mass transport data were obtained by monitoring the (first order) concentration decay of Ag(I). The electrolyses were performed by maintaining a potential of −1.2 V vs. SCE and varying the Reynolds numbers between 7600 ≤ Re ≤ 45,400. Based on the Sh = aRebSc0.356 correlation, the value of the constant a, associated with transport properties, shape and cell dimensions, was 0.11; the constant b exhibited a value of 0.99 attributed to rough silver deposits on RCE interface. The best electrolysis in terms of Ag(I) removal reached 8 ppm in 90 minutes, at Re = 45400 with a 98% current efficiency, and energy consumption of 1.5 KW h m−3. The metallic silver and treated solution can be recycled back through the same electrolytic cyanide silver process.