Papers by Author: Paula C. Oliveira

Abstract: In electronic appliances, printed circuit boards (PCB) represent an important component, containing high grade of valuable metals, besides organic resins and some ceramic materials. Copper is the major metal in PBC’s composition (normally higher than 20% w/w) but many other secondary and minor metal elements, including precious metals, are found in PCB’s. Recycling of PCB´s involves firstly the shredding operation, which is crucial in order to liberate particles from different materials, allowing its further processing by other mechanical, physical and chemical technologies. An efficient shredding operation is difficult to achieve due to the high heterogeneity of these wastes involving materials with different mechanical properties and complex assemblies. This paper presents results from laboratorial studies of shredding of PCB’s and the evaluation of size reduction efficiency as well as the chemical characterization of the obtained shredded fractions. Results showed that an efficient size reduction (characteristic average diameter d50=1.0mm) is obtained using two shredding stages of PCB’s, the first one with a grab shredder and the second one with a cutting mill. Chemical analysis of shredded PCB’s indicated that copper is the principal metal present (28%) followed by Sn, Zn, Pb and Al (3-5%) and many other minor elements. The fine fractions were rich in plastic materials while the metals were essentially present in the intermediate fractions (0.3-1.5 mm). These results can lead to guidelines regarding further design of the physical separation steps in the recycling processes.

Abstract: Sludges generated in leather tanning processing are very complex wastes with potential deleterious effect on the environment and its management constitutes a high cost for the companies. In this work, sludges from a Portuguese tanning company were characterized and leached with acid solutions in order to evaluate the metals removal yields. The sludges contain, as main metals, 15% Ca, 5% Fe and 2.2 % Cr, in a dry basis. Other minor elements namely Al, Ti, Zn, Pb and Cu were also detected. The leaching experiments were carried out with two types of acids – hydrochloric and sulfuric – and the effects of the reaction time, temperature and leachant concentration were evaluated. The reaction conditions strongly affected the chromium leaching yields, being temperature and acid concentration highly significant (confidence level above 99.9%). About 90% of Cr was leached using the higher levels of the factors (4h, 80°C and 2M H+, with both acids). Concerning the other major metals, iron leaching was very efficient (yields usually above 90%) whatever the conditions tested while calcium behaviour was quite different, depending on the type of acid used for the same H+ concentration: H2SO4 leaching efficiency was generally lower than HCl, probably due to the formation of less soluble calcium sulfate. The maximum calcium removal achieved was near 75%. The leaching process developed can be useful not only as a decontamination step of the tanning sludges, but also as a process for metals recovery to be potentially applied in an integrated recycling system, where several metal wastes from different sources could be processed.