Application of Ionic Liquids In the Aluminum Electrorefining

Application of Ionic Liquids in the Aluminum Electrorefining

Yong Zheng, Xingmei Lu *, Suojiang Zhang *

State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, 100190, Beijing, P. R. China

*Corresponding author: xmlu@home.ipe.ac.cn, sjzhang@home.ipe.ac.cn

  The Hall-Heroult process for aluminum production has been widely employed in the past 100 years. According to this technique, the purity of primary aluminum is usually lower than 99.8% and needs to be improved further. At present, there are three main industrial methods applied in the aluminum refining: zone melting, three-layer electrolysis and segregation process. However, these methods suffer from some inherent problems, such as high temperature and energy consumption. Labeled as novel green solvents, ionic liquids have exhibited a series of attracting properties and excellent performance in low-temperature aluminum electrodeposition ^[1,2]. The application of ionic liquids in aluminum electrorefining is worth of investigation.

  In our work, ionic liquid 1-butyl-3-methylimidazolium heptachloroaluminate ([Bmim][Al₂Cl₇]) was prepared and used as electrolyte in the aluminum electrorefining. The electrorefining processes were examined under different temperatures, potentials and current densities. Experimental results shown that the main impurity elements, including Si, Fe, Ti and Na could be efficiently separated from primary aluminum in [Bmim][Al₂Cl₇]. Compact and smooth aluminum deposits with high purity (>99.9%) were obtained at 100 ⁰C, -0.5~-1 V and 10~15 mA/cm² (see Figure 1 and 2). Furthermore, the current efficiency of aluminum electrorefining increased to 98%. And the energy consumption was lower than 5 kWh/kg-Al. As for [Bmim][Al₂Cl₇], it could be recycled and reused after purification. In general, ionic liquids are a class of promising low-temperature electrolytes which open a new way to the aluminum refining.

   

Figure 1. SEM image of the Al deposits             Figure 2. EDAX profile for the Al deposits

Reference

[1]     A. Campion and P. Kambhampati, Chem. Soc. Rev., 1998, 27, 241.

[2]     M. M. Zhang, V. Kamavaram and R. G. Reddy, JOM, 2003, 11, 54.