Electrorefining of aluminum in urea-imidazole chloride-aluminum chloride ionic liquids

Abstract

The electrochemical behavior of Al(III) in urea-1-butyl-3-methylimidazolium chloride-aluminum chloride (urea-BMIC-AlCl₃) ionic liquids, and the effect of potential and temperature on the characterization of cathode products, current efficiency and energy consumption of aluminum electrorefining have been investigated. Cyclic voltammetry showed that the electrochemical reduction of Al(III) was a one-step three-electron-transfer irreversible reaction, and the electrochemical reaction was controlled by diffusion. The diffusion coefficient of Al(III) in urea-BMIC-AlCl₃ ionic liquids at 313 K was 1.94×10⁻⁷ cm²/s. The 7075 aluminum alloy was used as an anode for electrorefining, and the cathode products were analyzed by XRD, SEM and EDS. The results from XRD analysis indicated that the main phase of the cathode products was aluminum. The results from SEM and EDS characterization revealed that the cathode product obtained by electrorefining −1.2 V (vs. Al) was dense and uniform, and the mass fraction of aluminum decreased from 99.61% to 99.10% as the experimental temperature increased from 313 K to 333 K. In this work, the optimum experimental conditions were −1.2 V (vs. Al) and 313 K. At this time, the cathode current efficiency was 97.80%, while the energy consumption was 3.72 kW·h/kg.

Keywords

ionic liquids / electrorefining / aluminum / cyclic voltammetry

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