Biolixiviação de metais contidos em resíduos de placas de circuito impresso de computadores por acidithiobacillus ferrooxidans e por cultura mista submetida a campo magnético

Abstract

The advancement of technology and the increase in the production of printed circuit boards (PCIs) used in electrical and electronic products, such as computers, increased the amount of waste from these boards and became a source of concern due to their harmfulness and the possibility of recycling resources. The purpose of this equipment is incineration, however, when disposed of in landfills, metals such as lead, cadmium and mercury can be leached, contaminating the soil. Bioleaching in the recovery of metals from PCIs has the following advantages: savings in inputs (acids and oxidizing agents) used in conventional hydrometallurgical processes, low energy requirements, low initial capital and cost investments, in addition to avoiding the emission of pollutants gaseous when compared to the pyrometallurgical process. Stimulation of cellular processes by magnetic fields is of considerable interest in biotechnological processes, as it establishes the basic mechanisms of this interaction, including cell proliferation, enzymatic reactions, biopolymers synthesis and membrane transport, which are changes induced by electromagnetic energy. The present work aimed at the treatment of lead, copper and aluminum metals from PCIs. The plates were separated into two samples (I and II)), which were characterized in terms of metal content by EDS, acid digestions (hydrometallurgy) and by X-ray Flourescence Spectroscopy. After the characterization, the percentages of metals obtained by FRX were 0.12% lead, 3.71% copper and 12.73% aluminum in the PCIs. In all the experiments studied, the amount of powder added resulted in reference values of metal concentration of 273.0 mg / L for aluminum, 74.2 mg / L for copper and 2.55 mg / L for lead. Bioleaching experiments of metals in the PCIs, in sample II, were carried out using mixed culture in bioreactors with and without the presence of a magnetic field at the frequency of 5 Hz. pH throughout the experiment from 4.0 to 7.7, with a 10.28% removal of Pb without a magnetic field and 24.28% with a magnetic field. When performing bioleaching using the bacteria Acidithiobacillus ferrooxidans without the presence of a magnetic field with and without pH adjustment in the inoculum, values of 94.67% for Al, 78.63% for Cu and 93.3% for o Pb. This study also addressed sequential bioleaching with A. ferrooxidans followed by bioremoval of metals bioleached by mixed culture in the presence and absence of magnetic field. Sequential bioleaching experiments of A. ferrooxidans with initial pH adjustment of the inoculum and removal of bioleached metals from the mixed culture without field application, had 100% Al removal, 27.34% for Cu and 96.43% for Pb. The results for the same condition and with application Field tests indicated 100% removal of Al, 83.82% for Cu and 98.27% for Pb. The sequential experiments on the bioleaching of A. ferrooxidans and removal of bioleached metals from mixed culture in bioreactors without adjustment of the inoculum pH of A ferroxidans ns and without field application had 99.74% removal for Cu and 91.92% for Pb. Removal results in the same condition and with field application indicated 100% removal for Cu and 95.76% for Pb. The experiments in bioreactors with the presence of magnetic field showed better removals for all metals analyzed, compared to experiments without field application.