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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Reck, B. K. & Graedel, T. E. Challenges in metal recycling. Science 337, 690–695 (2012).
Liu, G., Bangs, C. E. & Müller, D. B. Stock dynamics and emission pathways of the global aluminium cycle. Nat. Clim. Change 3, 338–342 (2013).
Cullen, J. M. & Allwood, J. M. Mapping the global flow of aluminum: from liquid aluminum to end-use goods. Environ. Sci. Technol. 47, 3057–3064 (2013).
Løvik, A. N., Modaresi, R. & Müller, D. B. Long-term strategies for increased recycling of automotive aluminum and its alloying elements. Environ. Sci. Technol. 48, 4257–4265 (2014).
Gaustad, G., Olivetti, E. & Kirchain, R. Improving aluminum recycling: a survey of sorting and impurity removal technologies. Resour. Conserv. Recycl. 58, 79–87 (2012).
Capuzzi, S. & Timelli, G. Preparation and melting of scrap in aluminum recycling: a review. Metals 8, 249 (2018).
Hatayama, H., Daigo, I., Matsuno, Y. & Adachi, Y. Evolution of aluminum recycling initiated by the introduction of next-generation vehicles and scrap sorting technology. Resour. Conserv. Recycl. 66, 8–14 (2012).
Nakajima, K. et al. Thermodynamic analysis of contamination by alloying elements in aluminum recycling. Environ. Sci. Technol. 44, 5594–5600 (2010).
Hiraki, T. et al. Thermodynamic analysis for the refining ability of salt flux for aluminum recycling. Materials 7, 5543–5553 (2014).
Kosai, S., Matsui, K., Matsubae, K., Yamasue, E. & Nagasaka, T. Natural resource use of gasoline, hybrid, electric and fuel cell vehicles considering land disturbances. Resour. Conserv. Recycl. 166, 105256 (2021).
Shaffer, B., Auffhammer, M. & Samaras, C. Make electric vehicles lighter to maximize climate and safety benefits. Nature 598, 254–256 (2021).
International Aluminium Institute. https://international-aluminium.org/ (2021).
Graedel, T. E., Reck, B. K. & Miatto, A. Alloy information helps prioritize material criticality lists. Nat. Commun. 13, 150 (2022).
American Society for Testing and Materials. Annual Book of ASTM Standards: 2013: Section 2: Nonferrous Metal Products (ASTM International, 2013).
Reuter, M. A., van Schaik, A., Gutzmer, J., Bartie, N. & Abadías-Llamas, A. Challenges of the circular economy: a material, metallurgical, and product design perspective. Annu. Rev. Mater. Res. 49, 253–274 (2019).
Kondo, M., Maeda, H. & Mizuguchi, M. The production of high-purity aluminum in Japan. JOM 42, 36–37 (1990).
Schwarz, V. & Wendt, H. Electrorefining of aluminium scrap from chloride melts. J. Appl. Electrochem. 25, 34–40 (1995).
Wu, B., Reddy, R. G. & Rogers, R. D. in Recycling of Metals and Engineered Materials (eds Stewart, D. L. et al.) 845–856 (John Wiley & Sons, 2000).
Kamavaram, V., Mantha, D. & Reddy, R. G. Electrorefining of aluminum alloy in ionic liquids at low temperatures. J. Min. Metall. B 39, 43–58 (2003).
Kamavaram, V., Mantha, D. & Reddy, R. G. Recycling of aluminum metal matrix composite using ionic liquids. Electrochim. Acta 50, 3286–3295 (2005).
Pradhan, D., Mantha, D. & Reddy, R. G. The effect of electrode surface modification and cathode overpotential on deposit characteristics in aluminum electrorefining using EMIC–AlCl3 ionic liquid electrolyte. Electrochim. Acta 54, 6661–6667 (2009).
Pradhan, D. & Reddy, R. G. Dendrite-free aluminum electrodeposition from AlCl3-1-ethyl-3-methyl-imidazolium chloride ionic liquid electrolytes. Metall. Mater. Trans. B 43, 519–531 (2012).
Pemsler, J. P. & Michael, D. Electrorefining of Aluminium NSF/CPE-81012, PB81-243693 (National Science Foundation, 1981).
Xu, J., Zhang, J. & Shi, Z. Extracting aluminum from aluminum alloys in AlCl3-NaCl molten salts. High Temp. Mater. Process. 32, 367–373 (2013).
Xu, J. et al. Current efficiency of recycling aluminum from aluminum scraps by electrolysis. Trans. Nonferrous Met. Soc. China 24, 250–256 (2014).
Huan, S. et al. Recovery of aluminum from waste aluminum alloy by low-temperature molten salt electrolysis. Miner. Eng. 154, 106386 (2020).
Huan, S., Wang, Y., Liu, K., Peng, J. & Di, Y. Impurity behavior in aluminum extraction by low-temperature molten salt electrolysis. J. Electrochem. Soc. 167, 103503 (2020).
Ponweiser, N. & Richter, K. W. New investigation of phase equilibria in the system Al–Cu–Si. J. Alloys Compd. 512, 252–263 (2012).
Villada, C., Ding, W., Bonk, A. & Bauer, T. Engineering molten MgCl2–KCl–NaCl salt for high-temperature thermal energy storage: review on salt properties and corrosion control strategies. Sol. Energy Mater. Sol. Cells 232, 111344 (2021).
Zhou, W. & Zhang, J. Thermodynamic evaluation of LiCl-KCl-PuCl3 system. J. Alloys Compd. 695, 2306–2313 (2017).
Kvande, H. & Haupin, W. Cell voltage in aluminum electrolysis: a practical approach. JOM 52, 31–37 (2000).
Haupin, W. in Light Metals 1998 (ed. Welch, B.) 531–537 (Minerals, Metals, & Materials Soc., 1998).
Zheng, Y., Dong, K., Wang, Q., Zhang, J. & Lu, X. Density, viscosity, and conductivity of Lewis acidic 1-butyl- and 1-hydrogen-3-methylimidazolium chloroaluminate ionic liquids. J. Chem. Eng. Data 58, 32–42 (2013).
Wang, Q., Zhang, Q., Lu, X. & Zhang, S. Electrodeposition of Al from chloroaluminate ionic liquids with different cations. Ionics 23, 2449–2455 (2017).
Zhu, G. et al. Rechargeable aluminum batteries: effects of cations in ionic liquid electrolytes. RSC Adv. 9, 11322–11330 (2019).
Van Artsdalen, E. R. & Yaffe, I. S. Electrical conductance and density of molten salt systems: KCl–LiCl, KCl–NaCl and KCl–KI. J. Phys. Chem. 59, 118–127 (1955).
Huber, R. W., Potter, E. V. & Clair, H. W. ST. Electrical Conductivity and Density of Fused Binary Mixtures of Magnesium Chloride and Other Chlorides. Bureau of Mines Report of Investigation 4858, 1–14 (United States Department of Interior, 1952).
Robelin, C., Chartrand, P. & Pelton, A. D. Thermodynamic evaluation and optimization of the (NaCl+KCl+AlCl3) system. J. Chem. Thermodyn. 36, 683–699 (2004).
Report of Inventory Survey of Scrap Melting https://www.aluminum.or.jp/environment/pdf/2-1.pdf (Japan Aluminum Association, 2007).
Addendum to the Life Cycle Inventory Data and Environmental Metrics for the Primary Aluminium Industry https://international-aluminium.org/resource/life-cycle-inventory-data-and-environmental-metrics/ (International Aluminium Institute, 2018).
Masuko, N. & Masio, K. Present aluminum smelting technology. J. Jpn. Inst. Light Met. 65, 66–71 (2015).
Energy Technology Perspectives 2015, IEA, Paris 45 https://www.iea.org/reports/energy-technology-perspectives-2015. (International Energy Agency, 2015).
Global Aluminum Flow Model 2017 https://alucycle.international-aluminium.org/ (The International Aluminium Institute, 2018).
Hatayama, H. Development of a Material Circulation Analysis Model Considering the Global Economic Development and Changes in Industrial Structure. PhD thesis, No. 126833, Univ. Tokyo (2011).
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