Abstract :

Metallurgical slags generated from ironmaking, steelmaking, ferroalloy production, and molten salt electrolysis are increasingly recognized as secondary resources for critical raw materials, particularly rare earth elements (REEs) such as scandium, yttrium, and light REEs, which are incorporated into complex silicate, aluminate, and fluoride phases formed at high temperatures. This review critically evaluates hydrometallurgical routes for REE recovery across a wide range of slag systems, including blast furnace, basic oxygen furnace, electric arc furnace, bauxite residue–derived, FCC catalyst, and molten salt electrolytic slags, covering direct leaching approaches (acidic, alkaline, and ammoniacal), hybrid roast–leach processes (sulfation, chlorination, and alkali roasting), and downstream separation techniques such as selective precipitation and solvent extraction. Particular emphasis is placed on the role of slag mineralogy, phase assemblage, and glassy matrices in controlling leaching kinetics, selectivity, and impurity co-dissolution, with silicate-rich slags identified as the most challenging systems due to their polymerized structure, which limits reagent accessibility and often requires thermal pretreatment to achieve recoveries above 80–90%, typically at high reagent consumption (>50–300 kg/t). Comparative evaluation reveals that reported performance is frequently dominated by recovery metrics, while key parameters such as selectivity, reagent intensity, and process integration remain underreported, such that high extraction efficiencies do not necessarily translate into industrial feasibility. The main limitations across existing approaches include silica gel formation, extensive co-dissolution of matrix elements, and the generation of secondary residues, all of which negatively impact process stability and economic viability; moreover, most reported systems remain constrained by poor selectivity, high reagent intensity, and lack of continuous pilot-scale validation, limiting their industrial transferability. Future progress, therefore, depends on shifting from isolated process optimization to integrated, mineralogy-driven process design, supported by reduced reagent consumption, simplified separation flowsheets, and validation under industrially relevant conditions, positioning metallurgical slags as strategic secondary resources capable of supporting diversified and resilient REE supply chains within circular economy systems.

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Keywords :

Rare earth elements; Metallurgical slags; Hydrometallurgy; Scandium recovery; Thermal pretreatment; Circular economy.

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References :

1. Abhilash, Hedrich, S., Meshram, P., Schippers, A., Gupta, A., & Sen, S. (2022). Extraction of REEs from blast furnace slag by Gluconobacter oxydans. Minerals, 12(6), 701. https://doi.org/10.3390/min12060701
2. Akcil, A., Ibrahim, Y. A., Meshram, P., Panda, S., & Abhilash. (2021). Hydrometallurgical recycling strategies for recovery of rare earth elements from consumer electronic scraps: A review. Journal of Chemical Technology & Biotechnology, 96(7), 1785–1797. https://doi.org/10.1002/jctb.6739.
3. Akl, H. M., Kandil, A. E.-H. T., Tilp, A. H., Cheira, M. F., Gado, H. S., & Salah, B. A. (2024). Development of a process for extracting rare earth elements from phosphogypsum by dissolving them in deep eutectic solvent. Separation Science and Technology, 59(17–18), 1739–1755. https://doi.org/10.1080/01496395.2024.2401577
4. Anawati, J., & Azimi, G. (2022). Separation of rare earth elements from a South American ionic clay lixivium by sequential precipitation. Hydrometallurgy, 213, 105946. https://doi.org/10.1016/j.hydromet.2022.105946.
5. Asubonteng, D., Mahtar, A., Zaidi, S.T.H. et al.Advancements in Rare Earth Elements Leaching and Separation Process: A Review. Mining, Metallurgy & Exploration (2026). https://doi.org/10.1007/s42461-026-01477-4.
6. Binnemans, K., Jones, P.T., Manjón Fernández, Á. et al.Hydrometallurgical Processes for the Recovery of Metals from Steel Industry By-Products: A Critical Review.  Sustain. Metall. 6, 505–540 (2020). https://doi.org/10.1007/s40831-020-00306-2.
7. Botelho Junior, A. B., Espinosa, D. C. R., Vaughan, J., & Tenório, J. A. S. (2022). Extraction of rare-earth elements from silicate-based ore through hydrometallurgical route. Metals, 12(7), 1133. https://doi.org/10.3390/met12071133
8. Botelho Junior, A.B., Espinosa, D.C.R. & Tenório, J.A.S. Extraction of Scandium from Critical Elements-Bearing Mining Waste: Silica Gel Avoiding in Leaching Reaction of Bauxite Residue.  Sustain. Metall.7, 1627–1642 (2021). https://doi.org/10.1007/s40831-021-00434-3.
9. Cesaro, A. (2024). Microbial Leaching Strategies for Extraction of Rare Earth Elements from Primary and Secondary Resources. In: Panda, S., Mishra, S., Akcil, A., Van Hullebusch, E.D. (eds) Biotechnological Innovations in the Mineral-Metal Industry. Advances in Science, Technology & Innovation. Springer, Cham. https://doi.org/10.1007/978-3-031-43625-3_4.
10. Chanturia, V.A., Minenko, V.G., Samusev, A.L. et al.Stimulation of Leaching of Rare Earth Elements from Ash and Slag by Energy Impacts. J Min Sci 58, 278–288 (2022). https://doi.org/10.1134/S1062739122020119.
11. Chen, J., Sun, S., Tu, G., & Xiao, F. (2023). Review of efficient recycling and resource utilization for rare earth molten salt electrolytic slag. Minerals Engineering, 204, 108425. https://doi.org/10.1016/j.mineng.2023.108425
12. Chen, L., Xu, J., Yu, X., Tian, L., Wang, R., & Xu, Z. (2021). Thermodynamics and kinetics of sulfuric acid leaching transformation of rare earth fluoride molten salt electrolysis slag. Frontiers in Chemistry, 9, 574722. https://doi.org/10.3389/fchem.2021.574722.
13. Chen, Z., Peng, R., Xiang, Z., Liu, F., Wang, J., & Chen, X. (2024). Low-acid leaching for preferential lithium extraction and preparation of lithium carbonate from rare earth molten salt electrolytic slag. Metals, 14(11), 1303. https://doi.org/10.3390/met14111303.
14. Cheng, S., Vaughan, J., Wang, G., Ma, X., Lyu, X., & Peng, H. (2026). Slag to product: Unlocking titanium-bearing slag value via selective leaching of amorphous titanium phase. Minerals Engineering, 235(Part 1), 109846. https://doi.org/10.1016/j.mineng.2025.109846.
15. Deblonde, G. J.-P., Chagnes, A., & Cote, G. (2022). Recent advances in the chemistry of hydrometallurgical methods. Separation and Purification Reviews, 52(3). https://doi.org/10.1080/15422119.2022.2088389.
16. de Oliveira, R.P., Vinhal, J.T., Yamane, L.H. et al.Extraction of Yttrium from Light-Emitting Diode Waste by Alkali Fusion Followed by Acid Leaching.  Sustain. Metall. 10, 625–636 (2024). https://doi.org/10.1007/s40831-024-00814-5.
17. Ding, W., Bao, S., Zhang, Y., & Xiao, J. (2022). Efficient selective extraction of scandium from red mud. Mineral Processing and Extractive Metallurgy Review. https://doi.org/10.1080/08827508.2022.2047044.
18. Dodbiba, G., & Fujita, T. (2023). Trends in extraction of rare earth elements from coal ashes: A review. Recycling, 8(1), 17. https://doi.org/10.3390/recycling8010017.
19. Dong, Z., Mattocks, J. A., Deblonde, G. J.-P., Hu, D., Jiao, Y., Cotruvo, J. A., & Park, D. M. (2021). Bridging hydrometallurgy and biochemistry: A protein-based process for recovery and separation of rare earth elements. ACS Central Science, 7(11), 1798–1808. https://doi.org/10.1021/acscentsci.1c00724.
20. Duan, W., Wang, D., Wang, Z. et al.Hydrometallurgical Leaching Behavior and Kinetic Modeling of Blast Furnace Slag in Hydrochloric Acid.  Sustain. Metall. 8, 170–185 (2022). https://doi.org/10.1007/s40831-021-00473-w.
21. Foppiano, D., Jonsson, E., Bao, S., Skår, Ø., Slagstad, T., Kumar, P., Wallin, M., Mervič, K., Šala, M., & van der Eijk, C. (2026). Exploring the potential of secondary resources: LA-ICP-MS for critical raw materials characterization. Talanta, 303, 129478. https://doi.org/10.1016/j.talanta.2026.129478
22. Gao, J., Xu, H., Lan, X., & Guo, Z. (2022). Phase equilibrium of the CaO–SiO₂–Al₂O₃–Ce₂O₃ system: A basis for recovering REEs from RE-containing slag. Ceramics International, 48(23), 34907–34914. https://doi.org/10.1016/j.ceramint.2022.08.080.
23. Gkika, D. A., Chalaris, M., & Kyzas, G. Z. (2024). Review of methods for obtaining rare earth elements from recycling and their impact on the environment and human health. Processes, 12(6), 1235. https://doi.org/10.3390/pr12061235.
24. Gontijo, V. L., Teixeira, L. A. V., & Ciminelli, V. S. T. (2023). The effect of iron- and calcium-rich waste rock’s acid baking conditions on the rare-earth extraction. Minerals, 13(2), 217. https://doi.org/10.3390/min13020217.
25. Guo, L., Xu, L., Mei, Y., Gao, J., Lan, X., & Guo, Z. (2023). Extraction of the cefluosil from rare earth slag by pressurized filtration. Separation and Purification Technology, 327, 124829. https://doi.org/10.1016/j.seppur.2023.124829.
26. Guzhov, B., Cassayre, L., Barnabé, A., Coppey, N., & Biscans, B. (2023). Selective precipitation of rare earth double sulfate salts from industrial Ni–MH battery leachates: Impact of downstream processing on product quality. Batteries, 9(12), 574. https://doi.org/10.3390/batteries9120574
27. Hamzat, A.K., Murad, M.S., Subeshan, B. et al.Rare earth element recycling: a review on sustainable solutions and impacts on semiconductor and chip industries. J Mater Cycles Waste Manag 27, 3009–3032 (2025). https://doi.org/10.1007/s10163-025-02276-7.
28. Han, K. N. (2020). Characteristics of precipitation of rare earth elements with various precipitants. Minerals, 10(2), 178. https://doi.org/10.3390/min10020178.
29. Holappa, L., Kekkonen, M., Jokilaakso, A. et al.A Review of Circular Economy Prospects for Stainless Steelmaking Slags.  Sustain. Metall. 7, 806–817 (2021). https://doi.org/10.1007/s40831-021-00392-w.
30. Huang, J., Zhang, L., Yu, W., Chen, J., Li, X., Li, Q., Liao, T., & Mo, X. (2025). Recovery of rare earth elements from calciothermic reduction slag by sulfation roasting–water leaching method. Minerals, 15(10), 1025. https://doi.org/10.3390/min15101025.
31. Ilatovskaia, M., Lonski, O., Löffler, M. et al.Phase Relations in the CaO-Nd₂O₃-Al₂O₃ System in Application for Rare Earth Recycling. JOM 75, 1993–2002 (2023). https://doi.org/10.1007/s11837-023-05731-8
32. Kallio, R., Lassi, U., Kauppinen, T., Holappa, E., Christophliemk, M., Luukkanen, S., Tanskanen, P., & Fabritius, T. (2022). Leaching characteristics of Sc-enriched, Fe-depleted acidic slags. Minerals Engineering, 189, 107901. https://doi.org/10.1016/j.mineng.2022.107901.
33. Kanekaputra, M. R., & Mubarok, M. Z. (2023). Extraction of scandium from bauxite residue by high-pressure leaching in sulfuric acid solution. Heliyon, 9(3), e14652. https://doi.org/10.1016/j.heliyon.2023.e14652
34. Karan, R., Rao, A. K., Babu, M. J., Devi, G. R., & Sreenivas, T. (2022). Development of process scheme for recovery of rare earths from leachate of coal fly ash. Cleaner Chemical Engineering, 4, 100078. https://doi.org/10.1016/j.clce.2022.100078.
35. Kim, J., & Azimi, G. (2020). Recovery of scandium and neodymium from blast furnace slag using acid baking–water leaching. RSC Advances, 10, 31936–31946. https://doi.org/10.1039/D0RA05797E
36. Kim, J., Choi, J. & Lee, S. A Review of Rare Earth Elements Recovery from Bastnaesite Ore: From Beneficiation to Metallurgical Processing.  Sustain. Metall. 11, 773–798 (2025). https://doi.org/10.1007/s40831-025-01019-0.
37. Klemettinen, A., Adamski, Z., Chojnacka, I., Leśniewicz, A., & Rycerz, L. (2023). Recovery of rare earth elements from the leaching solutions of spent NdFeB permanent magnets by selective precipitation of rare earth oxalates. Minerals, 13(7), 846. https://doi.org/10.3390/min13070846.
38. Kursunoglu, S. A Review on the Recovery of Critical Metals from Mine and Mineral Processing Tailings: Recent Advances.  Sustain. Metall.11, 2023–2050 (2025). https://doi.org/10.1007/s40831-025-01126-y.
39. Li, C., Deng, W., Lin, Y. et al.Synergetic Utilization of NdFeB Hydrochloric Leaching Residue and Crystalline Silicon Cutting Waste for Preparing Ferrosilicon Alloy and Recovering Rare Earth Elements.  Sustain. Metall. 11, 4153–4166 (2025). https://doi.org/10.1007/s40831-025-01239-4.
40. Li, M., Li, J., Zhang, D., Gao, K., Wang, H., Xu, W., Geng, J., Zhang, X., & Ma, X. (2020). Decomposition of mixed rare earth concentrate by NaOH roasting and kinetics of hydrochloric acid leaching process. Journal of Rare Earths, 38(9), 1019–1029. https://doi.org/10.1016/j.jre.2019.06.012
41. Li, R., Liu, K., Zhang, X., Zhang, H., Li, J., Xie, Y., & Qi, T. (2024). Comprehensive recycling of slag from the smelting of spent automotive catalysts. Separation and Purification Technology, 350, 127661. https://doi.org/10.1016/j.seppur.2024.127661.
42. Li, W., Zhou, M.-F., Wang, N., & Gu, H. (2025). Selective extraction of scandium from bauxite residue (red mud) utilizing iron sulfate roasting followed by water leaching. Separation and Purification Technology, 359(Part 2), 130634. https://doi.org/10.1016/j.seppur.2024.130634
43. Li, X., Luo, P., Liu, Z., Tang, X., Zhang, B., & Guo, J. (2024). Recovery of rare earths and lithium from rare earth molten salt electrolytic slag by lime transformation, co-leaching and stepwise precipitation. Physicochemical Problems of Mineral Processing, 60(2), 186333. https://doi.org/10.37190/ppmp/186333.
44. Li, X., Xiang, A., Li, Y., Chen, Y., Liu, K., & Liu, Z. (2026). Recovery of rare earths, lithium and fluorine from rare earth molten salt electrolytic slag by selective acid leaching–sodium aluminate roasting conversion. Hydrometallurgy, 242, 106698. https://doi.org/10.1016/j.hydromet.2026.106698.
45. Liu, X., Cao, Z., Zhao, Z., Chen, X., Li, J., He, L., Sun, F., & Zhang, W. (2026). Chlorination-driven phase control for selective REE–Fe separation from NdFeB waste. Journal of Environmental Management, 404, 129260. https://doi.org/10.1016/j.jenvman.2026.129260.
46. Liu, X., Huang, L., Liu, Z., Zhang, D., Gao, K., & Li, M. (2021). A novel, clean, closed-loop process for directional recovery of rare earth elements, fluorine, and phosphorus from mixed rare earth concentrate. Journal of Cleaner Production, 321, 128784. https://doi.org/10.1016/j.jclepro.2021.128784.
47. Liu, Z., Zhou, H., Li, W., Luo, X., Wang, J., & Liu, F. (2022). Separation and coextraction of REEs and Fe from NdFeB sludge by co-leaching and stepwise precipitation. Separation and Purification Technology, 282(Part B), 119795. https://doi.org/10.1016/j.seppur.2021.119795
48. Lohmeier, S., Lottermoser, B. G., Schirmer, T., & Gallhofer, D. (2021). Copper slag as a potential source of critical elements: A case study from Tsumeb, Namibia. Journal of the Southern African Institute of Mining and Metallurgy, 121(3). https://doi.org/10.17159/2411-9717/1383/2021.
49. Mackay, M., Dunbar, S., Holuszko, M., & Golzar Ahmadi, M. (2023). North American steelmaking slags—A source for critical elements. International Journal of Energy for a Clean Environment, 24(8), 129–145. https://doi.org/10.1615/InterJEnerCleanEnv.2023047794.
50. Marcinov, V., Oráč, D., Klimko, J., Takáčová, Z., Pirošková, J., & Jankovský, O. (2024). Selective precipitation of REE-rich aluminum phosphate with low lithium losses from lithium-enriched slag leachate. Materials, 17(20), 5113. https://doi.org/10.3390/ma17205113.
51. Meshram Abhilash, , P., Gupta, A., & Sen, S. (2023). Steel plant wastes as a resource of rare earth elements and rare metals—Characterisation, resource estimation, and economic assessment. Transactions of the Indian Institute of Metals, 76(5), 1321–1330. https://doi.org/10.1007/s12666-022-02794-0
52. Mousavi, S. N., Mousavi, S. M., & Beolchini, F. (2026). Exploring electric arc furnace dust as a new source of rare earth elements: Comparative leaching strategies and two-step selective precipitation. Minerals Engineering, 238, 110060. https://doi.org/10.1016/j.mineng.2026.110060.
53. Mubula, Y., Yu, M., Yang, D., Niu, H., Gu, H., Qiu, T., & Mei, G. (2024). Microwave-assisted atmospheric alkaline leaching process and leaching kinetics of rare earth melt electrolysis slag. Heliyon, 10(11), e32278. https://doi.org/10.1016/j.heliyon.2024.e32278.
54. Mubula, Y., Yu, M., Yang, D. et al.Recovery of Rare Earths from Rare-Earth Melt Electrolysis Slag by Mineral Phase Reconstruction. JOM 76, 4732–4748 (2024). https://doi.org/10.1007/s11837-024-06630-2.
55. Mubula, Y., Yu, M., Yan, H., Niu, H., Xu, K., Zhu, Z., Kuang, J., & Mei, G. (2026). Recovery of rare earths from rare earth molten salt electrolytic slag using atmospheric pressure alkaline leaching enhanced by ultrasonic. Minerals Engineering, 235(Part 1), 109802. https://doi.org/10.1016/j.mineng.2025.109802
56. Mukaba, J.-L., Eze, C. P., Pereao, O., & Petrik, L. F. (2021). Rare earths’ recovery from phosphogypsum: An overview on direct and indirect leaching techniques. Minerals, 11(10), 1051. https://doi.org/10.3390/min11101051
57. Nikoloski, A. N., Singh, P., & Phiri, T. C. (2026). From waste to resource: Critical mineral recovery and environmental impact mitigation in copper smelting slag. Minerals, 16(2), 206. https://doi.org/10.3390/min16020206.
58. Odimba, N. J., Khalidy, R., Bakhshoodeh, R., & Santos, R. M. (2023). Recovery of critical metals from carbonatite-type mineral wastes: Geochemical modeling investigation of (bio)hydrometallurgical leaching of REEs. Green Processing and Synthesis, 12(1https://doi.org/10.1515/gps-2022-8086
59. Page, M. J., McKenzie, J. E., Bossuyt, P. M., Boutron, I., Hoffmann, T. C., Mulrow, C. D., Shamseer, L., Tetzlaff, J. M., Akl, E. A., Brennan, S. E., Chou, R., Glanville, J., Grimshaw, J. M., Hróbjartsson, A., Lalu, M. M., Li, T., Loder, E. W., Mayo-Wilson, E., McDonald, S., … Moher, D. (2021). The PRISMA 2020 statement: An updated guideline for reporting systematic reviews. BMJ, 372, n71. https://doi.org/10.1136/bmj.n71
60. Pan, J., Vaziri Hassas, B., Rezaee, M., Zhou, C., & Pisupati, S. V. (2021). Recovery of rare earth elements from coal fly ash through sequential chemical roasting, water leaching, and acid leaching processes. Journal of Cleaner Production, 284, 124725. https://doi.org/10.1016/j.jclepro.2020.124725.
61. Pan, J., Zhao, X., Zhou, C., Yang, F., & Ji, W. (2022). Study on solvent extraction of rare earth elements from leaching solution of coal fly ash by P204. Minerals, 12(12), 1547. https://doi.org/10.3390/min12121547
62. Pasechnik, L. A., Skachkov, V. M., Chufarov, A. Y., Suntsov, A. Y., & Yatsenko, S. P. (2021). High purity scandium extraction from red mud by novel simple technology. Hydrometallurgy, 202, 105597. https://doi.org/10.1016/j.hydromet.2021.105597.
63. Pereira, A. C. (2025). Processing technologies for rare earth elements from peralkaline igneous deposits: A systematic review. REMUNOM, 21(2). https://doi.org/10.61164/p8v9aq27
64. Pereira, A. C. (2026a). Recovery of rare earth elements from hard disk drives: Technologies, challenges, and circular economy perspectives. IKR Journal of Multidisciplinary Studies, 2(2). https://doi.org/10.5281/zenodo.19068704
65. Pereira, A. C. (2026b). Application of magnesium sulfate in in-situ leaching of rare earth elements: Mechanisms, performance and environmental implications. International Journal of Current Science Research and Review, 9(3), 1371–1399. https://doi.org/10.47191/ijcsrr/V9-i3-25
66. Rasool, M. H., Ridha, S., Ahmad, M., Shamsuddun, R. A. B., Zahoor, M. K., & Khan, A. (2025). A mineralogical perspective on rare earth elements (REEs) extraction from drill cuttings: A review. Minerals, 15(5), 533. https://doi.org/10.3390/min15050533
67. Rasoulnia, P., Barthen, R., & Lakaniemi, A.-M. (2021). A critical review of bioleaching of rare earth elements: The mechanisms and effect of process parameters. Critical Reviews in Environmental Science and Technology, 51(4), 378–427. https://doi.org/10.1080/10643389.2020.1727718.
68. Roy, P. K., Praneeth, S., Sakr, A. K., Tummala, C. M., Dardona, M., & Dittrich, T. M. (2025). Efficient two-step separation of vanadium, scandium, and heavy rare-earth elements from gallium and germanium in high-value fly ash: Coupling solid-phase and solvent extraction. Separation and Purification Technology, 374, 133713. https://doi.org/10.1016/j.seppur.2025.133713.
69. Rüşen, A., Choubi, H., Karakaya, M.Ç. et al.Comparison of Rare Earth Elements Recovery from Red Mud by Two Different Roasting-Leaching Methods: A Case Study of Seydişehir, Türkiye. Mining, Metallurgy & Exploration 42, 4085–4102 (2025). https://doi.org/10.1007/s42461-025-01352-8.
70. Salman, A. D., Juzsakova, T., Jalhoom, M. G., Abdullah, T. A., Le, P.-C., Viktor, S., Domokos, E., Nguyen, X. C., La, D. D., Nadda, A. K., & Nguyen, D. D. (2022). A selective hydrometallurgical method for scandium recovery from a real red mud leachate: A comparative study. Environmental Pollution, 308, 119596. https://doi.org/10.1016/j.envpol.2022.119596.
71. Salman, A. D., Juzsakova, T., Mohsen, S., Abdullah, T. A., Le, P.-C., Sebestyen, V., Sluser, B., & Cretescu, I. (2022). Scandium recovery methods from mining, metallurgical extractive industries, and industrial wastes. Materials, 15(7), 2376. https://doi.org/10.3390/ma15072376.
72. Samanta, N. S., Das, P. P., Dhara, S., et al. (2023). “An overview of precious metal recovery from steel industry slag: Recovery strategy and utilization.” Industrial & Engineering Chemistry Research, 62(23), 9006-9031.
73. Shao, D., Song, J., Du, X., Deng, Y., Xue, Z., Yu, H., & Qi, T. (2023). Leaching characteristics and kinetics of scandium from Sc-concentrate of Bayan Obo rare earth tailings in sulfuric acid solution. Journal of Environmental Chemical Engineering, 11(5), 111037. https://doi.org/10.1016/j.jece.2023.111037.
74. Shao, D., Du, X., Yan, Z., Yu, H., & Qi, T. (2024). Recovery of scandium from Sc-bearing aegirine by Na₂CO₃ roasting–water washing–H₂SO₄ leaching process. Journal of Environmental Chemical Engineering, 12(4), 113146. https://doi.org/10.1016/j.jece.2024.113146
75. Shi, B., Qian, G., Pang, S., Sun, Y., Peng, H., Fu, W., Wang, D., & Wang, Z. (2024). Synchronous extraction of Pt, Zr and Ce from spent catalysts via SoG-Si scraps melting collection by regulating Si reduction based on a new fluorine-containing slag. Separation and Purification Technology, 351, 128086. https://doi.org/10.1016/j.seppur.2024.128086.
76. Shoppert, A., Loginova, I., Napol’skikh, J., Kyrchikov, A., Chaikin, L., Rogozhnikov, D., & Valeev, D. (2022). Selective scandium (Sc) extraction from bauxite residue (red mud) obtained by alkali fusion–leaching method. Materials, 15(2), 433. https://doi.org/10.3390/ma15020433.
77. Shoppert, A., Loginova, I., Napol’skikh, J., & Valeev, D. (2022). High-selective extraction of scandium (Sc) from bauxite residue (red mud) by acid leaching with MgSO₄. Materials, 15(4), 1343. https://doi.org/10.3390/ma15041343.
78. Sim, G., Hong, S., Moon, S., Noh, S., Cho, J., Triwigati, P. T., Park, A.-H. A., & Park, Y. (2022). Simultaneous CO₂ utilization and rare earth elements recovery by novel aqueous carbon mineralization of blast furnace slag. Journal of Environmental Chemical Engineering, 10(2), 107327. https://doi.org/10.1016/j.jece.2022.107327
79. Sim, G., Park, Y., Hong, S., Seo, D., Moon, S., Cho, J., & Park, Y. (2025). Alkali fusion-enhanced metal leaching of blast furnace slag for pretreatment of simultaneous carbon mineralization and rare earth elements recovery. Chemical Engineering Journal, 505, 159762. https://doi.org/10.1016/j.cej.2025.159762.
80. Stopić, S., & Friedrich, B. (2021). Advances in understanding of the application of unit operations in metallurgy of rare earth elements. Metals, 11(6), 978. https://doi.org/10.3390/met11060978
81. Swain, B. Challenges and opportunities for sustainable valorization of rare earth metals from anthropogenic waste. Rev Environ Sci Biotechnol22, 133–173 (2023). https://doi.org/10.1007/s11157-023-09647-2.
82. Tang, H., Liao, C., Liu, F., Mao, J., Zhou, Z., & Zheng, Y. (2024). Research on the hierarchical separation of rare earths and lithium from rare earth molten salt slag. Metals, 14(11), 1247. https://doi.org/10.3390/met14111247.
83. Tian, G., Xu, Z., Li, X., Hu, Z., & Zhou, B. (2025). Research progress on the extraction and separation of rare-earth elements from waste phosphors. Minerals, 15(1), 61. https://doi.org/10.3390/min15010061
84. Tian, L., Chen, L., Gong, A., Wu, X., Cao, C., & Xu, Z. (2021). Recovery of rare earths, lithium and fluorine from rare earth molten salt electrolytic slag via fluoride sulfate conversion and mineral phase reconstruction. Minerals Engineering, 170, 106965. https://doi.org/10.1016/j.mineng.2021.106965
85. Tong, Z., Wen, H., & Hu, X. (2022). Extraction of rare earth, lithium and fluorine by acid leaching of roasted product of rare earth electrolytic molten salt slag. Nonferrous Metals Science and Engineering, 13(4), 141–147. https://doi.org/10.13264/j.cnki.ysjskx.2022.04.017.
86. Tong, Z., Hu, X., & Wen, H. (2023). Effect of roasting activation of rare earth molten salt slag on extraction of rare earth, lithium and fluorine. Journal of Rare Earths, 41(2), 300–308. https://doi.org/10.1016/j.jre.2022.02.014.
87. Tsaousi, G. M., Toli, A., Bempelou, A., Kotsanis, D., Vafeias, M., Balomenos, E., & Panias, D. (2023). Control of silica gel formation in the acidic leaching of calcium aluminate slags with aqueous HCl for Al extraction. Sustainability, 15(21), 15462. https://doi.org/10.3390/su152115462.
88. Valeev, D., Shoppert, A., Dogadkin, D., Romashova, T., Kuz’mina, T., & Salazar-Concha, C. (2023). Extraction of Al and rare earth elements via high-pressure leaching of boehmite–kaolinite bauxite using NH₄HSO₄ and H₂SO₄. Hydrometallurgy, 215, 105994. https://doi.org/10.1016/j.hydromet.2022.105994.
89. Wang, J., & Hu, H. (2021). Selective extraction of rare earths and lithium from rare earth fluoride molten-salt electrolytic slag by sulfation. Minerals Engineering, 160, 106711. https://doi.org/10.1016/j.mineng.2020.106711.
90. Wang, L., Xu, Y., Tian, L., Chen, Y., Yang, A., Gan, G., Ma, Y., & Du, Y. (2024). Two-stage method recovery of metals from copper slag: Realize the resource utilization of all components. Minerals Engineering, 206, 108503. https://doi.org/10.1016/j.mineng.2023.108503.
91. Wang, Q., Ma, H., Liu, M., Guo, R., & Liu, G. (2022). A new method of full resource utilization of copper slag. Hydrometallurgy, 212, 105899. https://doi.org/10.1016/j.hydromet.2022.105899.
92. Wang, S., Dube, B., Vaughan, J., Gao, S., & Peng, H. (2023). Silica gel free region and rare earth metal extraction correlations in reprocessing bauxite residue. Minerals Engineering, 199, 108115. https://doi.org/10.1016/j.mineng.2023.108115.
93. Wu, H., Yan, H., Liang, Y., Qiu, S., Zhou, X., Zhu, D., & Qiu, T. (2023). Rare earth recovery from fluoride molten-salt electrolytic slag by sodium carbonate roasting–hydrochloric acid leaching. Journal of Rare Earths, 41(8), 1242–1249. https://doi.org/10.1016/j.jre.2022.07.001.
94. Wu, Y., Zhang, S., Wang, G., Li, T., Xu, X., Pu, Y., Zhou, W., Li, Y., & Jia, Y. (2023). Impurity removal of acid leachates from rare earth slag with sodium hydroxide and ammonium bicarbonate: Mechanism and efficiency optimization. Journal of Cleaner Production, 423, 138782. https://doi.org/10.1016/j.jclepro.2023.138782
95. Xie, B., Liu, C., Wei, B., Wang, R., & Ren, R. (2023). Recovery of rare earth elements from waste phosphors via alkali fusion roasting and controlled potential reduction leaching. Waste Management, 163, 43–51. https://doi.org/10.1016/j.wasman.2023.03.029.
96. Xing, P., Li, H., Ye, C. et al.Recovery of Rare-Earth Elements from Molten Salt Electrolytic Slag by Fluorine Fixation Roasting and Leaching.  Sustain. Metall. 8, 522–531 (2022). https://doi.org/10.1007/s40831-022-00503-1.
97. Yang, D., Yu, M., Mubula, Y., Yuan, W., Huang, Z., Lin, B., Mei, G., & Qiu, T. (2024). Recovering rare earths, lithium and fluorine from rare earth molten salt electrolytic slag using sub-molten salt method. Journal of Rare Earths, 42(9), 1774–1781. https://doi.org/10.1016/j.jre.2023.08.009.
98. Yang, Y., Wei, T., Xiao, M. et al.Rare Earth Recovery from Fluoride Molten-Salt Electrolytic Slag by Borax Roasting-Hydrochloric Acid Leaching. JOM 72, 939–945 (2020). https://doi.org/10.1007/s11837-019-03732-0.
99. Yang, Z., Xiao, F., Sun, S., Zhong, H., & Tu, G. (2024). REEs recovery from molten salt electrolytic slag: Challenges and opportunities for environmentally friendly techniques. Journal of Rare Earths, 42(6), 1009–1019. https://doi.org/10.1016/j.jre.2023.08.010.
100. Yang, Z., Xiao, F., Sun, S., Zhou, Z., Chen, J., Luo, X., Chen, J., Tu, G., Sui, C., & Yu, K. (2025). The recovery of valuable elements from rare earth molten salt electrolytic slag by the fluorination–vacuum distillation method. Sustainable Materials and Technologies, 46, e01670. https://doi.org/10.1016/j.susmat.2025.e01670.
101. Yang, Z., Xiao, F., Sun, S., Tu, G., Zhou, Z., Chen, J., Hong, X., He, W., Sui, C., & Yu, K. (2025). Investigation on the recovery of rare earth fluorides from spent rare earth molten electrolytic slag by vacuum distillation. Materials, 18(7), 1538. https://doi.org/10.3390/ma18071538.
102. Yang, Z., Zhong, H., Sun, S., Xiao, F., Zhou, Z., He, W., Tu, G., Sui, C., & Yu, K. (2025). Recovery of valuable elements from rare earth molten salt electrolytic slag via roasting defluorination with saturated steam. Journal of Environmental Chemical Engineering, 13(3), 116930. https://doi.org/10.1016/j.jece.2025.116930.
103. Yan, P., Chen, X., Gao, L., & Yang, B. (2024). Recovery of scandium from silicate minerals by high-pressure leaching in sulfuric acid. Journal of Rare Earths, 42(7), 1375–1384. https://doi.org/10.1016/j.jre.2023.02.021 .
104. Yao, L., Liu, Z., Zhao, Z., Li, Q., Li, E., & Lin, H. (2026). Separation and recovery of Fe and REEs from a hydrochloric acid leachate of NdFeB waste using Aliquat 336-based solvent extraction. Separations, 13(2), 70. https://doi.org/10.3390/separations13020070.
105. Yi, W., She, X., Zhang, H., An, Z., Wang, J., & Xue, Q. (2023). Element migration and phase distribution characteristics during crystallization of rare earth phase in rare earth slag. Journal of Rare Earths, 41(5), 780–788. https://doi.org/10.1016/j.jre.2022.08.016.
106. Yu, S., Ao, X., Liang, L., Mao, X., & Guo, Y. (2025). Recovery of rare earth elements from sedimentary rare earth ore via sulfuric acid roasting and water leaching. Journal of Rare Earths, 43(4), 805–814. https://doi.org/10.1016/j.jre.2024.06.006
107. Zhang, B., Liu, J., Jia, X., Xing, T., Liu, C., & Jiang, M. (2024). Mineral phase reconstruction of Bayan Obo tailings by smelting reduction and crystallization control of molten slag containing niobium, rare earth and titanium. Minerals Engineering, 214, 108780. https://doi.org/10.1016/j.mineng.2024.108780
108. .Zhang, M., He, B., Liu, Y., Xu, L., & Liang, Y. (2024). Recovery of rare earth elements from rare earth molten salt electrolytic slag via fluorine fixation by MgCl₂ roasting. Journal of Rare Earths, 42(10), 1979–1987. https://doi.org/10.1016/j.jre.2024.06.010.
109. Zhang, Z., Zeng, Q., Feng, Y., Wang, R., Huang, W., Wang, F., & Liu, Z. (2024). Recovery of valuable elements from copper slag through low-temperature sulfuric acid curing and water leaching. Journal of Environmental Chemical Engineering, 12(6), 114880. https://doi.org/10.1016/j.jece.2024.114880.
110. Zhao, TY., Li, WL., Kelebek, S. et al.A comprehensive review on rare earth elements: resources, technologies, applications, and prospects. Rare Met.44, 7011–7040 (2025). https://doi.org/10.1007/s12598-025-03459-9.
111. Zhi, H., Ni, S., Su, X., Xie, W., Zhang, H., & Sun, X. (2022). Separation and recovery of rare earth from waste nickel–metal hydride batteries by phosphate-based extraction–precipitation. Journal of Rare Earths, 40(6), 974–980. https://doi.org/10.1016/j.jre.2021.04.012.
112. Zhong, S., Chen, J., Weng, W., Lu, Q., Zeng, G., Chen, J., Cai, J., Tan, W., & Chi, X. (2026). Well-tuned filtration performance of the H₂SO₄-leached copper slag pulp and ultrasonic-enhanced leaching of valuable metals. Separation and Purification Technology, 384, 136215. https://doi.org/10.1016/j.seppur.2025.136215.
113. Zhou, J., Ma, S., Chen, Y., Ning, S., Wei, Y., & Fujita, T. (2021). Recovery of scandium from red mud by leaching with titanium white waste acid and solvent extraction with P204. Hydrometallurgy, 204, 105724. https://doi.org/10.1016/j.hydromet.2021.105724.
114. Zhou, L., Peng, T., Sun, H., & Wang, S. (2022). Thermodynamics analysis and experiments on Ti-bearing blast furnace slag leaching enhanced by sulfuric acid roasting. RSC Advances, 12, 34990–35001. https://doi.org/10.1039/D2RA06237B.
115. Zhou, Y., Liu, J., Cheng, G., Xue, X., & Yang, H. (2022). Kinetics and mechanism of hydrochloric acid leaching of rare earths from Bayan Obo slag and recovery of rare earth oxalate and high-purity oxides. Hydrometallurgy, 208, 105782. https://doi.org/10.1016/j.hydromet.2021.105782.
116. Zhu, X., Li, W., Xing, B., & Zhang, Y. (2020). Extraction of scandium from red mud by acid leaching with CaF₂ and solvent extraction with P507. Journal of Rare Earths, 38(9), 1003–1008. https://doi.org/10.1016/j.jre.2019.12.001.
117. Zinoveev, D., Pasechnik, L., Fedotov, M., Dyubanov, V., Grudinsky, P., & Alpatov, A. (2021). Extraction of valuable elements from red mud with a focus on using liquid media—A review. Recycling, 6(2), 38. https://doi.org/10.3390/recycling6020038