Aplicação de ácidos orgânicos na recuperação de metais a partir de resíduos de baterias de íons de lítio e catalisadores automotivos

Abstract

In the last decades, hydrometallurgical processes have received considerable attention for the recovery of precious metals such as Platinum Group Metals (PGM), as well as recovery of metals with high added value from lithium-ion batteries (LIBs). Hydrometallurgical processes are considered suitable for the recovery of valuable metals due to the low energy requirements, the product obtained with high purity and the minimum emission of pollutants to the atmosphere. However, when a solution strongly acidic is used for the leaching, Cl2, SO3 and NOx are released during this process and the acid residue obtained after leaching is a threat to the environment. Thus, this work is focused on the development of environmentally friendly process to recover metals from spent LIBs and from spent automotive catalysts that do not cause a new environmental threat. The recovery of metals present in LIBs was performed through mechanical processing followed by heat treatment and leaching using malic, citric and formic acids. The techniques of TGA, DSC, XRD, SEM, FT-IR, and EDXRF were used for the characterization. The leaching was carried out in several experimental conditions of temperature, volume of hydrogen peroxide (H2O2), S/L ratio, and extraction time. The leached solutions were analyzed by FAAS. The characterization results showed the efficiency of the heat treatment at 700 °C for 2 hours in the degradation of the graphite and PVDF. The results showed that more than 90% of Co, Li, and Mn can be leached using a solution of DL-malic acid 2 M, 6% (v/v) H2O2, S/L ratio of 1:20 (g/mL), 95 °C, and an extraction time of 60 minutes. The recovery of metals from spent automotive catalysts was performed through mechanical processing, followed by heat treatment and leaching using the malic, citric and formic acids. The techniques employed to characterize the automotive catalyst powder were XRD, SEM/EDS, particle size distribution by laser diffraction, and EDXRF. The parameters of acid concentration, proportion of inorganic acid and organic acids, S/L ratio and extraction time were evaluated. The solutions obtained after leaching were analyzed by ICP-OES. The different techniques confirmed the presence of Pt and Pd, in addition to the different compositions when two automotive catalysts are compared. Through the leaching process with a concentration of HCl of 6 M, S/L ratio of 1:30 and 20% citric acid, more than 90% Pt and Pd can be recovered. Through the use of organic acids, it was possible to develop efficient and environmentally friendly processes for the recovery of metals from spent LIBs and from spent automotive catalysts, replacing (in the case of LIBs) and reducing (in the case of automotive catalysts) acids with harmful effects to the environment and recovering metals with high added value that can be used in the manufacturing of new products.