2567 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 ironbearing 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 phases indicate the inclusion of titanium bearing minerals and desilication products formed during the bauxite treatment in alkali solution. The mineralogical composition of refinery A, refinery B and refinery C are influenced by both the bauxite mineralogy and the refining conditions and post-processing transformations. 4. IMPLICATIONS FOR CRITICAL MINERAL STRATEGY AND MINERAL POLICY The results of this project have significant implications for the critical mineral strategy and mineral policy in economies which have limited access to natural resources and rely heavily on importing primary materials. There are considerable differences in terms of the chemical composition, mineralogy and morphology of red mud samples from various refineries. These differences demonstrate that red mud should not be viewed as a single, homogeneous industrial waste product. Rather, it should be viewed as a secondary resource located at each site. Therefore, its value as a strategic resource will depend upon the origin of the bauxite and the refining processes used at each refinery. Scandium has demonstrated the greatest level of enrichment in all samples with the greatest amount being in Refinery B. Therefore, red mud appears to represent a potential domestic source of valuable critical material; scandium is a critical metal that is important for advanced alloys, aerospace applications and renewable energy systems (Mitrica et al., 2021).
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