Catalytic selective recovery of silver from dilute aqueous solutions and e-waste leachates

Abstract

The two-step catalytic process is proposed for the recovery of silver ions from aqueous solutions. First, the Ag+-containing solution is enriched with hydrogen gas and recirculated through the Pt-loaded activated carbon (Pt/AC). The Ag+ ions are reduced into the metal particles at ambient temperature and H2 gauge pressure of 1 atmosphere. Next, the Ag particles precipitated on the Pt/AC are oxidized by air to form the pure Ag+ concentrate and to regenerate the catalyst. The process was studied using pure AgNO3 solutions at varied pH values (0.0, 1.5 and 3.9) in a batch mode system that was operated with Pt/AC particles loaded with 0.1–1.0% of Pt metal. The complete removal of Ag+ ions was achieved within<2 h of hydrogenation of 1-liter AgNO3 solutions with an initial concentrations of 100–1000 mgAg/L. The hydrogenation rate was not influenced by the pH value. Increasing the Pt load in the Pt/AC media above 0.25% did not result in an increase in the Ag+ hydrogenation rate. Next, the process was applied for the separation of Ag+ ions from H2SO4 leachates of Ag2O-Zn batteries. Finally, it was shown that due to a large difference in standard reduction potentials the silver and the copper ions can be “kinetically” separated within the hydrogenation and the oxygenation steps of the process.