THE MECHANISMS OF ADSORPTION OF AG(CN)2- AND AG+ ON TO ACTIVATED CARBON

Silver is adsorbed onto activated carbon from potassium cyanide solution initially in the form of the K+Ag(CN)2- ion pair. Infrared spectra suggest that the cyanide stretching frequency for Ag(CN)2- is shifted to lower wavenumbers upon adsorption, to approximately that of Ag(CN)43-. This may be a result of an aggregation of the species on the carbon surface. Boiling in hydrochloric acid results in the formation of AgCN and AgCl. The presence of AgCN is also indicated on Ag(CN)2--loaded carbons that have been dried at temperatures of 120-degrees-C or higher. Subsequent treatment with hot sodium hydroxide solution results in the reduction of all of the silver on the carbon to the metallic state, with some desorption of Ag(CN)2-. When silver is loaded onto activated carbon from a silver nitrate solution, adsorption takes place via a dual mechanism, with reduction to metallic silver and precipitation of AgCl both taking place on the carbon surface.