Nitric acid leaching of base metals from waste PDP electrode scrap and recovery of ruthenium content from leached residues

Abstract

Nitric acid leaching of waste plasma display panel (PDP) electrode scrap was investigated as a part of development for a pre-treatment process to increase Ru content in the scrap. Leaching performance was evaluated in terms of different experimental parameters such as nitric acid concentration, reaction temperature and time. An aqueous nitric acid leaching solution with a concentration range of 1.5 M-3.0 M at 60°C and 1.5 M-4.2 M at 75°C demonstrated as the most effective condition for the selective removal of Pb and Ba from waste PDP scrap powders with about 90% of Pb and 95% of Ba leached in 30 min. The rate of dissolution decreased after a certain level of HNO 3 concentration due to formation of Pb(NO3)2 which has limited solubility in the aqueous solution. Other impurities such as Bi, Zn, Ag and Co were dissolved at the level of 75%-90% at all the leachant concentrations, leaching time and temperatures applied, while Si, Al and Fe showed a poor leachability with only 7%, 30% and 40% dissolution, respectively. Ru and Zr were almost insoluble in an aqueous nitric acid solution. The total concentration of Ru in the undissolved residue (27.96%) of the scrap powder after nitric acid leaching was brought up to 93.8% from the initial concentration (14.43%) of the scrap in the final process. The precipitation behavior of Pb(NO3)2 as well as the solubility of SiO 2 were also investigated. © 2011 The Japan Institute of Metals.