Anodic Dissolution Behavior in the Electrorefining of Al–Cu Alloys Using an EmImCl–AlCl₃ Ionic Liquid

Abstract

To produce high-purity Al from Al–Cu alloys, the dissolution behaviors of various Al–Cu binary alloy anodes in EmImCl–AlCl3 ionic liquid have been investigated at 323 K. In the anodic polarization measurements, anodic current density peaks were observed at potentials of approximately 0.3 and 0.8 V vs. Al/Al(III) for the Al–5.0%Cu casting alloy. In the constant potential electrolysis of the Al–5.0%Cu casting alloy and cold-rolled plate at 0.3 V, Al atoms in the matrix phase were preferentially dissolved followed by the formation of Al2Cu surface species. The dissolution of both Al2Cu and Al in the alloy matrix occurred during electrolysis at 0.8 and 1.2 V. Moreover, a Cu-rich layer derived from Al2Cu was formed on the cold-rolled plate surface at a potential of 0.8 V. Additionally, Cu was co-deposited on the cathode at the potentials at which Al2Cu dissolved. The dependence of the anodic dissolution behavior of the Al−Cu alloys on the potential in the EmImCl–AlCl3 ionic liquid was analyzed. By controlling the anodic dissolution potential, the dissolution of Cu in Al2Cu into the electrolyte can be suppressed, thus considerably increasing the purity of electrorefined Al.

Anodic Dissolution Behavior of Al Alloys Containing Al6Fe or β-AlFeSi in EmImCl–AlCl3 Electrolyte During Electrorefining

“…The current density peak in the anodic polarization curve of the Al-Cu alloy attributed to the intermetallic compound Al 2 Cu is observed. 25 This suggests that the anodic current density observed for Al-1.5%Fe and Al-1.5%-3.5%Si alloys could be attributed to the anodic dissolution of the respective intermetallic compounds. Furthermore, the casting alloy and cold-rolled alloy showed different electrochemical behavior: in the range below 0.4 V, the peaks of oxidation current density are coincident for Al-Fe alloy, but for Al-Fe-Si alloy, the oxidation current density peak of cold-rolled alloy is higher than that of casting alloy.…”

“…Moreover, as Al can form solid solutions and complex intermetallic compounds depending on the additives used and the manufacturing method, understanding the anodic dissolution behavior for these metallurgical structures is important. In this context, we previously clarified the anodic dissolution and electrorefining behavior of Al-Si, 24 Al-Cu, 25 and Al-Mn 26 alloy anodes. In the case of the Al-Si alloy, Al dissolves preferentially over Si from the anode surface, as Si does not easily dissolve in the electrolyte, resulting in the recovery of high-purity Al on the cathode.…”

“…We previously reported an electrorefining method for recycling Al scrap. [24][25][26] Recycling using the electrorefining method has been reported in attempts using molten salts [27][28][29] or ionic liquids as the electrolyte [30][31][32][33][34] however we focus particularly on methods that use low temperature ionic liquids as an electrolyte. Since this method requires less energy to maintain the bath temperature, the entire process is expected to be an energy-saving electrorefining method.…”

Anodic Dissolution during Electrorefining of Al–Zn Alloys in Lewis Acidic AlCl₃–EmImCl Ionic Liquid

“…The authors proposed a recycling process using electrorefining as one solution to this problem. [17][18][19][20] In electrorefining with scrap Al, understanding the anodic dissolution behavior of additive alloy elements is essential. However, in previous studies on electrorefining methods using molten salts [21][22][23] or ionic liquids, [24][25][26][27] these anodic dissolution behaviors were not clarified.…”

“…However, in previous studies on electrorefining methods using molten salts [21][22][23] or ionic liquids, [24][25][26][27] these anodic dissolution behaviors were not clarified. The authors clarified the processes involved in the anodic dissolution and electrorefining of Al-Si, 17 Al-Cu, 18 Al-Mn, 19 Al-Fe, and Al-Fe-Si alloys 20 as anodes using electrolytes at temperatures ranging from 323 to 423 K. Particularly, AlCl 3 -1-ethyl-3-methyl imidazolium chloride (EmImCl), obtained by mixing AlCl 3 and EmImCl, is capable of Al electrodeposition at room temperature. Therefore, the authors focused on it as an electrolyte for targeted energy-saving electrorefining.…”