Determination of silver in silver-containing spent catalysts by coulometric titration with acid-dissolution oxidation

The accurate determination of silver (Ag) content in silver-containing spent catalysts is of great significance for resource recovery. In this study, Ag in spent catalysts was leached with HNO₃-H₂O₂ system. Ag/AgCl electrode-platinum wire electrode was used as the working electrode pair, and Ag electrode-double salt bridge saturated calomel electrode was used as the indicator electrode pair in experiments. KNO₃ solution was selected as the electrolyte. The content of Ag⁺ in leachate was titrated by Cl^- generated in electrolysis. The potential jump was used to indicate the titration end point. The content of Ag was determined by coulometric titration. Consequently, the method for determination of Ag in Ag-containing spent catalysts by coulometric titration with acid-dissolution oxidation was established. The experimental parameters were systemically optimized, including the liquid-solid ratio, volume ratio of HNO₃ to H₂O₂, leaching temperature, leaching time, stirring speed, as well as the electrolyte concentration, current intensity, and anti-interference performance. The results showed that the optimal conditions were as follows: the liquid-solid ratio was 4∶1 mL/g, the volume ratio of HNO₃ to H₂O₂ was 1∶6, the leaching temperature was 50 ℃, the leaching time was 60 min, the stirring speed was 400 r/min, the electrolyte was 1.5 mol/L KNO₃ solution, the current intensity was 10-20 mA, and the coexisting metal ions had no interference. The content of Ag in Ag-containing spent catalysts was determined according to the experimental method, and the spiked recoveries were between 97.4% and 100.9%. The proposed method was applied for the determination of Ag in 4 Ag-containing spent catalyst samples, the relative standard deviations (RSD, n=5) of determination results were between 0.64% and 1.3%. The t-test revealed that there was no significant difference between the results obtained by this method and those by potentiometric titration. The proposed method had the advantages of simple operation, high efficiency and good accuracy, which could meet the recovery and detection requirements of Ag-containing spent catalysts.