Análise comparativa da utilização de ácido orgânico versus ácido inorgânico na recuperação de neodímio presente em hard disk drives (HDs): uma abordagem técnica, ambiental e econômica

Abstract

The improvement of electrical and electronic equipment (EE) and its growing demand has brought an alert regarding the increase in the consumption of raw materials and the generation of solid waste. Rare earth elements (REEs) are essential and irreplaceable in the production of this equipment. Therefore, solid waste of this nature is considered potential sources of recovery of secondary raw materials, thus enabling the reintroduction of these elements in the production chain. One of the most used REEs is neodymium (Nd), which is prominent in the production of neodymium-iron-boron (NdFeB) magnets used in computer Hard Disk Drives (HDs). Thus, the objective of the work presented here was to compare the use of hydrochloric acid (HCl) with acetic acid (CH3COOH) in the recovery of Nd from magnets from post-consumer HDs, from a technical, environmental and economic point of view. The study was divided into 5 stages: characterization and sample preparation, leaching, environmental assessment, economic assessment and compilation of results. The efficiency of the processes was evaluated through the leaching of magnets previously demagnetized, ground, sieved (<0.25mm) and roasted. This process was carried out with the leaching agents HCl 0.5M and CH3COOH 1.0M at room temperature and 95°C. After 5 hours of leaching, vacuum filtration was performed to remove the solid phase, followed by pH adjustment of the filtrate with 37% HCl and subsequent selective precipitation of Nd through the addition of oxalic acid (H2C2O4), forming Nd oxalate. The Nd oxide was obtained by roasting the oxalate at 850°C. The hot CH3COOH process showed the highest yield, followed by the hot HCl process. The processes carried out without heating showed the lowest yields. The environmental assessment was carried out through a simplified LCA study that highlighted electric energy as responsible for more than 90% of the potential environmental impacts in the evaluated impact categories: scarcity of fossil resources, GWP (global warming potential) and terrestrial ecotoxicity. Excluding energy consumption and making a new assessment, the greatest potential environmental impacts were identified in the leaching agents (HCl 0.5M and CH3COOH 1.0), HCl 37% and H2C2O4. The global analysis indicated that the greatest potential environmental impacts are associated with the hot CH3COOH process. The economic evaluation indicated that electric energy was responsible for more than 90% of the costs of the processes, and the hot HCl process was the one that best fit the condition of economic viability. Considering a global view of the results, it can be said that the process in which 0.5M HCl was used is the best option for Nd recovery under the conditions presented in this study. The great influence and contribution of energy consumption in the evaluated processes can also be highlighted.