Leaching studies for metals recovery from printed circuit boards scrap

In this paper, the leaching behavior of the major metals present in printed circuit boards waste is evaluated, aiming at its recycling by hydrometallurgy. Several leachants were compared (sulfuric, hydrochloric and nitric acids, at 2 M H concentration), at temperatures of 25oC and 90oC and 4 hours of reaction time. Sulfuric acid leaching was not very promising concerning metals dissolution being only effective for iron. Hydrochloric acid allowed the leaching up to 60% of tin and about 50% of lead, as well as the iron. Nitric acid was the most efficient leachant due to its oxidizing properties. Recoveries of 90% or more for copper, iron, nickel and zinc were achieved at the higher temperature. Lead was also dissolved (up to 80%), as well as silver (more than 70%). These results show that the hydrometallurgical recovery of most of the metals present in PCB’s scrap is a technically feasible alternative that shall be considered and evaluated. Introduction Printed circuit boards (PCB’s) are electronic components with special interest due to its high potential economic value and environmental concern. The management of end-of-life PBC’s involves its removal from electronic devices during the dismantling phase, and treatment in process units for metals recovery. Usually PCB’s are shredded being the metal fraction separated by physical methods and then sent to secondary copper smelters. The alternative technology is the hydrometallurgy, in which metals are dissolved, purified in aqueous media and recovered. Due to the high complexity of PCB ́s, which contain numerous chemical elements in their composition, selective leaching using different agents is a possible approach to be considered, since can allow to extract selectively some groups of metals in successive leaching stages, improving and simplifying the following separation steps. In this sense, the solubility of metal ions in the various media (e.g. sulfate, nitrate, chloride) is the starting point for the development of the selective leaching process. As example, silver is practically insoluble in chloride media while lead is very insoluble in sulfate media. Noble metals such as Pd, Pt and Au would be only soluble under extreme conditions such as in aqua regia. Taking in consideration the chemical stability of different species, a multistep efficient leaching process could be developed. In this paper, results of laboratory studies on the leaching of basic metals contained in printed circuit boards in different aqueous acid media are presented and discussed. EBR’09 Electronics & Battery Recycling ’09 (Proc. of 2 Intern. Conf.) June 24 –26, 2009, Toronto, Canada ICM AG, Switzerland