Avanços na avaliação do processo de lixiviação sob sonicação para recuperação de lítio e cobalto de baterias de íons de lítio

Abstract

The recycling of metals that make up electronic waste, such as used lithium-ion batteries (LIBs), represents a secondary source of these components, in addition to being an alternative for reducing environmental and health impacts, since when improperly disposed of, they contaminate soils and groundwater. LIBs are valuable sources of recovery materials, particularly lithium and cobalt. Therefore, it is urgent to define an environmentally and economically viable recycling process that offers the return of metals as raw material in sufficient quantity for new LIBs since their consumption has been rising continuously. The purpose of the current study was to address the recovery of Li and Co present in LIBs, investigating the leaching technique by organic acids produced by fermentation to reduce the consumption of sulfuric acid. The battery powder used was composed of the previously ground cathode and anode. The material was characterized by X-ray diffraction, scanning electron microscopy coupled with energy dispersion spectroscopy, and inductively coupled plasma mass spectrometry. For the leaching process, the leaching medium was composed of 1.07 M H2SO4 and 0.93 M organic acids from the fermentation medium, and three particle sizes were compared (d1 ≤ 250 μm, 250 μm < d2 ≤ 500 μm and 500 μm < d3 ≤ 850 μm). In preliminary tests, the leaching efficiency at 70 ± 2 °C for 2.5 h and a solid/liquid ratio (S/L) of 18.5 g/L was compared under sonication (40 kHz and 200 W), magnetic stirring (300 rpm) and without agitation. As these tests showed that the process under sonication enabled higher recoveries of Li and Co, the other experiments were carried out using this leaching system. Aiming to evaluate the effect of particle size on lithium and cobalt recover a central composite design (CCD) was carried out, with the independent variables time (3 to 6 h), S/L ratio (5.55 to 18.5 g/L) and temperature (55 to 75 ºC) for each particle size. As the results of these DCCs showed that the battery quantity range could be expanded and the processing time could be reduced, thus increasing the leaching efficiency, a new DCC was performed using a reaction time of 1.5 to 3.5 hours, an S/L ratio ranging from 20 to 100 g/L, and a temperature between 55 to 75 °C. The results for the optimization of the DCC for the particles of particle size d ≤ 250 μm resulted in recoveries of 99.44 % ± 0.02 % for Li and 99.70 % ± 0.07 % for Co for the optimal conditions of 70 °C, 123.2 g/L and 2.5 h process. For the particles of granulometry 250 µm < d ≤ 500 µm, the optimization consisted of recovery of 98.07 % ± 0.03 % of Li and 97.03 % ± 0.13 % of Co under the optimal conditions of 72 ° C, 120 g/L, and 2.5 h process. The particles of granulometry 500 µm < d ≤ 850 µm presented recovery of 96.70 % ± 0.03 % of Li and 95.17 % ± 0.16 % of Co under the optimal conditions of 71 °C, 118 g /L, and 2.5 h. From the performance of the Tukey Test, the recoveries obtained by the samples of different sizes presented significant differences among themselves. Therefore, a smaller sample size promotes more effective recoveries of the metals of interest when using the conditions evaluated in this study.