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Browsing by Issue Date, starting with "2009-11-10"

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  • Physical and chemical processing of printed circuit boards waste
    Publication . Oliveira, Paula; Taborda, F. Charters; Margarido, F.; Nogueira, Carlos
    A recycling process for PCB’s is being studied, based on physical processing and hydrometallurgical treatment. PCB’s waste was shredded in a lab cutting mill, resulting a grinded material with 90% (weight) with particle size less than 2.1 mm and an average particle diameter of 1.2 mm. Chemical analysis of granulometric fractions showed that the base metals like Cu, Zn, Pb and Sn concentrated mainly in intermediate size fractions (0.4-1.7 mm) being fines very rich in epoxy resin composite. About 80-90% of the principal metals were recovered in that size range. The first step of chemical treatment was the acid leaching of metals. The use of nitric acid solutions at appropriate conditions allowed the efficient solubilization of base metals like Cu, Ni, Zn, Pb and Ag. More than 90% recovery of Cu, Zn and Ni were achieved at 90ºC using 1 M HNO3. Dissolution of silver required higher concentrations (only 70% yield using 2 M HNO3). Tin leaching was inefficient in nitric media, being always lower than 20%. The leaching conditions here reported were adequate to the base metals solubilization, allowing further processing of leachates for separation and recovery using hydrometallurgical operations. Precious metals recovery would be attained in a subsequent leaching step using highly concentrated acidic solutions.
    2009-11-10Conference object Open access Show more
  • Leaching behavior of several zinc rich residues in a hydrometallurgical recycling process
    Publication . Pedrosa, Fátima; Cabral, Marta; Nogueira, Carlos; Margarido, F.
    The leaching of metals contained in spent Zn-MnO2 batteries and electric arc furnace (EAF) dusts using sulfuric acid solutions was studied, in order to evaluate the feasibility of simultaneous treatment of both wastes by a hydrometallurgical process. In both residues, a substantial quantity of zinc was solubilized (about 100% in batteries and 70-80% in EAF dusts) in diluted acid solutions and room temperature, corresponding to the reaction of zinc oxide species. Other species were more refractory to the chemical attack, namely the manganese (III or IV) oxides in batteries and the zinc ferrite in dusts, requiring higher temperatures (e.g. 90ºC) and higher leachant concentrations. Lead present in EAF dusts was not solubilized in sulfate media, thus remaining in the leach residue. Results seem to confirm the possibility of treatment of both zinc-containing residues by the same hydrometallurgical process, eventually involving two leaching stages – diluted acid leaching and hot acid leaching – followed by solution purification through iron precipitation and Zn/Mn separation and recovery. Concerning lead, a second leaching circuit in chloride media could be developed for its potential recovery.
    2009-11-10Conference object Open access Show more