Synthesis of Ag nanoparticles from waste printed circuit board

The amount of waste from electrical and electronic equipment has been growing every year. The printed circuit boards contained in this waste include metals that can be recovered through urban mining, adding value to this waste and minimizing environmental impacts with its incorrect disposal or treatment. In this work, memory boards obsolete with 0.053 wt% Ag were used. The extraction of all metals studied (Ag, Al, Cu, Fe, Ni, Sn, and Zn) involved the evaluation of the Pourbaix and speciation diagrams to identify the pH and redox potential conditions, considering the possible species formed with leaching agents: sulfuric, nitric, and hydrochloric medium. After the definition of the leaching agent, the extraction routes by hydrometallurgical processing were proposed from the parameters of temperature, s/l ratio, and reaction time previously studied. Route A was composed of sequential stages (the first leaching in a sulfuric medium and the second in an oxidizing sulfuric medium) and obtained 100% of Ag recovery. Route B consisted only of leaching in an oxidizing sulfuric medium, obtained about 94% of the Ag recovery, and could not contribute to the subsequent purification steps (if necessary) of this solution, as all metals would also be in the solution. These two routes showed that Ag can only be recovered in an oxidizing sulfuric acid medium, according to the conditions studied. Ag recovered in the leach liquor of the second stage of Route A was purified by chemical precipitation with NaCl, and the AgCl was solubilized in an NH4OH solution. This solution was used to synthesize silver nanoparticles by the Turkevich method in 25 min. The spherical nanoparticles synthesized an average size distribution of 67 nm.