absolute quantitative predictions. The use of this dataset was selected based on accessibility and reproducibility considerations, as comprehensive industrial thermodynamic databases (e.g., full FactSage cement or metallurgical databases) require specialized licenses and were beyond the scope of this study. 3. RESULTS The primary feedstock in this study was bauxite residue from Alumina d.o.o. (Zvornik, Bosnia-Herzegovina). The chemical composition was determined by ICP-OS, and the mineral composition by XRD (Table 1). The materials are dry solids, finely grained (<100 µm), making them suitable for thermal processing and subsequent leaching. The BR sample displays a (normalized) composition of ~50% FeO, 10-20% Al₂O₃, 3% TiO₂, along with significant amounts of Na₂O, CaO, SiO₂ and minor rare metals (Table 1). X-ray diffraction (XRD) analysis of the starting material revealed a complex and heterogeneous mineralogical composition typical of bauxite residue (Table 1). The preliminary study identified predominant crystalline phases included hydrogarnet, hematite, magnetite, ilmenite, gibbsite, perovskite, cancrinite, and coesite. The previous research from Stopic et al., 2024 identifies hematite and goethite (iron phases), cancrinite and hydrogarnet (Na-Ca-Al silicates), gibbsite/boehmite (alumina phases), and anatase/ilmenite/perovskite as Ti-bearing phases. Most of the primary phases were identified as well in our study, as displayed in Table 1. Stopic et al., 2024 discusses that a portion of Ti in the raw BR is already present as perovskite (CaTiO₃), owing to the lime additions during Bayer processing, and as ilmenite (FeTiO₃). This affirmation is consistent with our results (Table 1). Following hydrogen reduction, significant mineralogical transformations were observed, with the formation of metallic α-iron as a major reduction product, alongside silicate and titanate phases such as perovskite, and nepheline. Due to the complexity and multiphase nature of the BR, no Rietveld refinement was possible, and the analyses should be interpreted as semi-quantitative (from a nondimensional point of view), which is appropriate for identifying phase evolution and reaction pathways under the investigated reduction conditions. The non-dimensional comparison between phases before and after calcination is collected in Table 2.
RkJQdWJsaXNoZXIy MTM0Mzk2