Ionic liquids as novel electrolytes for electrolytic aluminum production

Abstract

Aluminum (Al) is among the most widely used materials in a variety of industries. However, as a major producer of Al, China pays a heavy toll in terms of environmental destruction and public health risks. Given the serious drawbacks of the traditional Hall–Héroult method of electrolytic Al production, the aim of this study is to introduce a novel, more environmentally friendly technique, using ionic liquids as the electrolyte in the production of Al. This process is more energy-efficient, with low (i.e., practically zero) pollution. In this study, an optimal imidazole ionic liquid electrolyte (ILE) system was developed. In particular, the electrodeposition behavior of Al in different ILE systems and the effect of the electrolysis conditions on the morphology of the Al deposition layer were investigated, using a variety of electrolysis methods. A compound ILE system was also developed by mixing two imidazole ionic liquids ([Emim]Cl/AlCl₃ and [Bmim]Cl/AlCl₃) with various volume ratios, followed by an investigation into the Al electrodeposition process. The experiments illustrate the advantages of compound ILEs for potential practical implementation. In addition, when benzene or toluene was added to the system as additives, the morphology and quality of the Al deposition layer were optimized further. In order to improve the potential of this technology for future industrial applications, polydimethylsiloxane was applied as an electrolyte liquid seal, allowing the electrolytic Al process to occur in an ambient atmosphere (i.e., at room temperature and under high humidity). Using the best-performing compound ILE system from the study, the electrolytic refining process of Al using the ILE system was carefully analyzed, while the effects of electrolysis temperature, current density, and stirring on the refining process were also investigated. The cathode Al deposition layers were also characterized using scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. An Al deposition layer with a purity higher than 99.9% was obtained via the electrolytic refining of five Al alloys. Thus, the electrolytic refining process of Al can be realized at a low temperature with low energy consumption, high efficiency, and greater environmental protection. The Al electrolysis and refining technique studied in this thesis represents an environmentally friendly approach, with the advantages of low-temperature operation and low energy consumption. Thus, a reduction in emissions and energy requirements can be achieved at the production source, which is of great importance for the future innovation of electrolytic Al production technology.

Date of Award	2020
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology