Rusen, AydinChoubi, HanaeKarakaya, Muazzez CelikKarakaya, Necati2025-11-102025-11-1020252524-34622524-3470https://doi.org/10.1007/s42461-025-01352-8https://hdl.handle.net/20.500.13091/10975Red mud is an iron-rich by-product generated during alumina production and typically stored in waste ponds, where it poses significant environmental challenges. However, its enrichment in critical elements-particularly rare earth elements (REEs) such as Sc, Ce, and La, as well as V and Ga-makes it a promising secondary resource. Therefore, this study proposes two methods for the recovery of the REEs from red mud:(i) sulfation with sulfuric acid followed by roasting and water leaching (S-R-WL), and (ii) roasting with ammonium sulfate followed by water leaching (R-WL). In the S-R-WL process, red mud, water, and sulfuric acid were mixed in a 1:1:2 ratio. For the R-WL route, red mud and ammonium sulfate were combined in a 1:1 ratio. The effects of roasting temperature and solid-to-liquid ratio (S/L) on extraction efficiency were systematically investigated. The R-WL method achieved up to 71% Sc, 56% La, 57% Ce, and over 70% for heavy REEs (Y, Er, Yb, Ho, Dy) with extended leaching times (up to 96 h). In contrast, the S-R-WL method provided a higher Sc recovery (similar to 79%), and comparable recovery rate of Ce (similar to 57%) and La (similar to 50%) under low roasting temperatures (650 & ring;C, 1:10 S/L). Recovery of heavy REEs also exceeded 70% after prolonged leaching. Notably, roasting above the optimum temperature led to diminished yields of REEs, while the solid-to-liquid ratio proved critical to overall extraction performance. As a result, both methods demonstrated effective REE extraction from red mud, with the R-WL method favoring heavy REEs and the S-R-WL method yielding superior Sc recovery. Also, it was determined that both sulfating agents were effective on recovery of REEs with gains over %70 under the optimum conditions: roasting temperature of 700 degrees C, roasting time 60 min, leaching temperature 25 degrees C, leaching duration 96 h, initial solid/liquid ratio is 1:20 g/ml. Given the high environmental cost of producing critical elements from primary ores, valorizing secondary waste streams such as red mud offers sustainable pathway for critical metal recovery in the aluminum industry.eninfo:eu-repo/semantics/closedAccessReesRed MudRecoveryAmmonium SulfateSulfation-RoastingLeachingArticle10.1007/s42461-025-01352-82-s2.0-105019101012