APPLICATION OF RIETVELD REFINEMENT-BASED METHODS FOR QUANTITATIVE MINERALOGY IN THE CHARACTERISATION OF BAUXITE RESIDUES

Bauxite residue is a saline, alkaline mixture of minerals from both the parent bauxite and the Bayer alumina refining process. With the high volumes of bauxite residue generated globally there is a need to improve our understanding of bauxite residue mineralogy in order to further improve management of environmental impacts associated with these tailings, and possibly improve process efficiency and thus decrease the quantities of residue being generated. This study compared methods for quantitative mineralogical characterisation of bauxite residues, and identified major sources of error in these methods. Although alternative techniques exist for the quantification of mineral concentrations in bauxite residues, Rietveld refinement-based quantitative phase analysis is likely to be more accurate and precise than methods based on chemical extraction, normative calculation, or single X-ray diffraction peaks. The problems of microabsorption, caused by both heavy and light X-ray absorbing minerals being present in a sample and non-ideal mineral compositions (such as those of desilication product minerals), are particularly difficult and impractical to eliminate completely. Careful sample preparation and analysis, and further characterization of the structures of desilication product minerals, may reduce the effect of these issues on quantification of mineral concentrations in bauxite residues.