Recovery of silver in the form of value-added spherical silver powder from spent Ag-Al2O3 catalyst by a novel clean method

Abstract

The spent Ag-Al2O3 catalyst is an important silver secondary resource due to its high content of Ag. However, the most commonly used nitric acid leaching method produces toxic and harmful NOx gases. Herein, a novel clean method was proposed to treat the spent Ag-Al2O3 catalyst using the green leaching agent cerium ammonium nitrate instead of nitric acid to effectively avoid the generation of toxic NOx gases. More importantly, value-added monodisperse micro-sized uniform spherical particles were synthesized directly from the leaching solution by a simple chemical reduction method. The influence of leaching conditions on the leaching ratio of Ag and leaching kinetics were discussed in detail. The response surface methodology was applied to optimize the synthesis parameters of silver powder and explore the interactions between the synthesis process parameters. Under the optimal leaching parameters, the leaching ratio of Ag reached 99.69 %. The leaching kinetic analysis of leaching indicated that the leaching reaction of spent Ag-Al2O3 catalyst was controlled by chemical reaction. By the response surface methodology design, a fitted mathematical model of the particle size for silver powder and the optimum synthesis parameters of silver powder were obtained. The optimum synthesis parameters of silver powder were as follows: [Fe2+] = 1.08 mol/L, [Ag+] = 1.01 mol/L, and dispersant dosage of 2.05 wt%. The average experimental particle size of 1.337 μm was very close to the predicted value of 1.343 μm obtained from the fitted model, indicating that the fitted model of particle size for silver powders was very good. This process not only provides a clean and value-added method for recycling the spent Ag-Al2O3 catalyst, but also helps to promote the balanced and high-value utilization of high-abundance cerium.