from angular to rounded with moderate agglomeration. Particles in Refinery A samples display surface roughness and heterogeneous size distributions, indicating an incomplete breakdown of primary mineral phases during refining. Surface irregularities on the particles in Refinery A may provide increased reactive surface area during leaching. Red mud samples collected from Refinery B contain well defined, compact, densely agglomerated particles with nodular and cluster morphologies. The large size of the agglomerates in Refinery B indicates that the particles are bonded together strongly, which may be the result of the high iron oxide or aluminosilicate content of the red mud. The small form of the agglomerates in Refinery B red mud can create a hindrance to the intrusion of reagents, hence, it can negatively affect the performance of the leaching process. Conversely, samples collected at Refinery C have smaller and more homogeneous particles, and loosely porous agglomerates. This delicately broken morphology and the loosely packed structure suggest that the mineral phases of the red mud have been subjected to a lot of mechanical damage as the refining process goes on. The porosity nature of these agglomerates enables further penetration of fluids to the inside of the agglomerates, and this also may enhance the speed of dissolution of the agglomerates in future hydrometallurgical treatments. Such textural differences are therefore likely to have a massive impact on the performance of subsequent beneficiation processes, and the discerning reclaim of significant components, including scandium and the rare earths. Figure 5 FE-SEM images of red mud from Refinery A, B, and C showing variations in particle morphology and agglomeration. 3.4 Mineralogical Composition The X-ray diffraction (XRD) patterns of the red mud samples were primarily comprised of iron-bearing and aluminosilicate phases. Hematite was the dominant crystalline phase in all the samples. Strong iron oxide enrichment through the Bayer Process confirmed the presence of hematite. Gibbsite and boehmite were found in all samples. The presence of gibbsite and boehmite indicated residual aluminum-bearing minerals due to incomplete alumina extraction. Kaolinite and quartz were present in refinery A as stable aluminosilicate and siliceous phases. Quartz was also found in refinery B and refinery C. The presence of kaolinite and quartz indicate contributions from the bauxite mineralogy and the gangue minerals associated with the bauxite. Goethite and Calcite were also identified in refinery B and refinery C. The presence of goethite in red mud is an indicate the conversion of iron hydroxide during digestion and residue formation (Zhou et al., 2022). The calcite may have been introduced during processing using lime or because of carbonation during the residue storage period. Anatase and sodalite 123
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