The recycling of aluminium scrap today utilizing a remelting technique downgrades the quality of the aluminium, and the final sink of this downgraded recycled aluminium is aluminium casting alloys1,2,3,4,5,6,7,8,9. The predicted increase in demand for high-grade aluminium as consumers choose battery-powered electric vehicles over internal combustion engine vehicles is expected to be accompanied by a drop in the demand for low-grade recycled aluminium, which is mostly used in the production of internal combustion engines2,7,10,11. To meet the demand for high-grade aluminium in the future, a new aluminium recycling method capable of upgrading scrap to a level similar to that of primary aluminium is required2,3,4,7,11. Here we propose a solid-state electrolysis (SSE) process using molten salts for upcycling aluminium scrap. The SSE produces aluminium with a purity comparable to that of primary aluminium from aluminium casting alloys. Moreover, the energy consumption of the industrial SSE is estimated to be less than half that of the primary aluminium production process. By effectively recycling aluminium scrap, it could be possible to consistently meet demand for high-grade aluminium. True sustainability in the aluminium cycle is foreseeable with the use of this efficient, low-energy-consuming process.
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We thank Y. Sasaki (Tohoku University) and E. Webeck (TEQED) for their input to the discussions. We thank K. Kobayashi and K. Watanabe for their experimental assistance. We also thank W. Takayanagi (LAIMAN) for illustration of graphic images. Financial support was provided by the Grant-in-Aid for Scientific Research, JSPS KAKENHI grant nos. 20H02492, 20K15069, 21H04610 and 21K17918, and the New Energy and Industrial Technology Development Organization, NEDO grant no. P21003. The cooperation of Hoei Metal Co. Ltd. is also gratefully acknowledged.
The authors declare no competing interests.
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Extended data figures and tables
Extended Data Fig. 1 Results for the electrolysis of the AC2A casting alloy in the molten LiCl-KCl-5mol%AlF3.
(a) The anode and cathode potentials and (b) the cell voltage during the recycling of aluminium casting alloy (AC2A) using SSE (electrolyte: LiCl-KCl-5 mol%AlF3; electrolysis temperature: 500 °C). EPMA results of (c) the initial aluminium casting alloy (AC2A) and (d) the anode slime, showing the elemental distribution.
Extended Data Fig. 2 Results for the electrolysis of the AD12 die-casting alloy in the molten LiCl-KCl-5mol%AlF3.
(a) The anode and cathode potentials and (b) the cell voltage while recycling the aluminium die-casting alloy (AD12) using SSE (electrolyte: LiCl-KCl-5 mol%AlF3; electrolysis temperature: 500 °C). (c) The composition by ICP analysis and (d) XRD results of the initial aluminium die-casting alloy (AD12), anode slime and the cathode deposition. EPMA results of (e) the initial aluminium die-casting alloy (AD12) and (f) the anode slime, showing the elemental distribution.
(a) The controlled current, (b) the electrode potential, and (c) the expansion of the black square area in (b).
The fabrication, use, scrap processing and metallurgical processes are shown in blue and the products are shown in yellow. Process losses are shown in grey. Internal combustion engine vehicles are abbreviated as ICEVs. Hybrid electric vehicles are abbreviated as HEVs. Battery electric vehicles are abbreviated as BEVs. End-of-life is abbreviated as EoL.
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Lu, X., Zhang, Z., Hiraki, T. et al. A solid-state electrolysis process for upcycling aluminium scrap. Nature 606, 511–515 (2022). https://doi.org/10.1038/s41586-022-04748-4
Frontiers of Environmental Science & Engineering (2023)