smaller pieces using an agate mortar. Crushing resulted in large agglomeration being broken down into much smaller particles. Material was then homogenized so that a representative sub-sample could be taken from it. Samples prepared were used for various analyses including chemical, mineralogical and microstructural analyses. 2.1.1 Analytical Techniques Standard analytical techniques were used to determine the major oxide, trace element and mineralogical properties of the red mud samples. The bulk chemical composition of the red mud samples was determined by wavelength dispersive x-ray fluorescence (XRF), where the samples were pressed into pellets as per normal geological practices. Trace and rare earth elements were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES), where the samples had been powdered and acid digested prior to analysis. Mineralogical phases were determined by x-ray diffraction (XRD) using Cu Ka radiation and the usual scan parameters. Field Emission Scanning Electron Microscopy (FE-SEM) was used to examine the microstructure of the red mud samples to determine particle size distribution and surface texture. The analytical results were compared against each other and against the literature to identify the relevant compositional variability and technical significance. 3 RESULTS AND DISCUSSION 3.1 Major Chemical Composition The major oxide composition of the red mud samples, shown in Figure 1, indicates there are clearly some variations in the composition of the red mud samples from the three refineries. In all cases, the primary component is iron oxide (Fe₂O₃). The range of Fe₂O₃ concentration is approximately 52 wt% in Refinery A and close to 68 wt% in Refinery B. The higher level of Fe₂O₃ in the red mud samples from Refinery B, when compared to Refinery A and Refinery C. It may be possible due to variations in the mineralogy of the bauxite feedstock or differences in the alumina refining process. The second most common oxide found in all the red mud samples is aluminum oxide (Al2O3). Refinery A and Refinery C have significant changes in Al2O3 (> 22 wt.%) but a significantly lower concentration of the substance can be observed in Refinery B. Such discrepancy is a sign of different levels of recovery of alumina in the process of refining. The amount of alumina that remains in the red mud is also of significance as alumina is a highly reactive solid and thus it might affect the reactivity of the substance and its possible further use. There is a significant difference in the silicon dioxide (SiO2) concentration in the red mud samples. Refinery A has the highest concentration of SiO2 and Refinery B has the least concentration. This difference can be explained by the nature of bauxite input into the refinery and level of desilication attained during the refining process. SiO2 in high concentrations may influence the mineral phases and processing behaviors. In the red mud samples, titanium dioxide (TiO2) is found in moderate and constant amounts. Refinery C presents a higher concentration of TiO2 when compared to the other two refineries. This 119
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