Characterization of bauxite pisoliths

Bauxite mainly consists of the major minerals gibbsite, boehmite, diaspore, kaolinite, quartz, goethite and hematite. Large quantities of bauxite often occur in the form of small balls (pisolites). Mineralogical analyses of ores can be complicated, especially when minerals of very similar elemental composition are present and sophisticated techniques such as bulk x-ray diffraction (XRD) are usually required to accurately identify the types of minerals present. Bulk x-ray diffraction (XRD) is however time consuming, prohibiting large scale routine analysis. In this context, Fourier Transform Infra-Red (FTIR) imaging has emerged as a valuable technique for the examination of various mineral phases and for phase mapping. In this paper, we present results on FTIR imaging of bauxite in the form of complex pisoliths. Synchrotron FTIR results were used to validate the results of FTIR imaging. General Area Diffraction Detector System (GADDS) was also used to map boehmite in bauxite pisoliths. Boehmite inclusions in the size of 5 to 20 microns were easily detected by FTIR imaging and the results were further confirmed by Synchrotron FTIR and the general area micro x-ray diffraction technique. FTIR mapping was also able to reveal the two dimensional location and mineralogical association of the mineral phases in bauxite pisoliths.