Mineralogical and geochemical characteristics of two bauxitic profiles, Fria, Guinea Republic

Bauxite deposits of the Fria district, Guinea, have been exploited since 1960. These lateritic bauxites, located on the upper parts of plateaus, result from weathering of paleozoic schists. The ores are composed of gibbsite associated with pyrophyllite, Al-substituted gœthite, and kaolinite. Pyrophyllite and Al-substituted gœthite may contain up to 9% of the total Al₂O₃ content of the bauxite; this cannot be recovered through the Bayer process because these phases are insoluble in the leaching solutions. Kaolinite is soluble under Bayer leaching but this dissolution induces precipitation of sodium aluminosilicates, which apart from loss of further alumina results in decreasing efficiency of the process through scale formation. Detailed knowledge of the distribution of the different ore types and their mineralogical composition is necessary for efficient processing.