MINERALOGICAL AND GEOCHEMICAL CHARACTERISTICS OF 2 BAUXITIC PROFILES,FRIA, GUINEA-REPUBLIC

Bauxite deposits of the Fria district, Guinea, have been exploited sin ce 1960. These lateritic bauxites, located on the upper parts of plate aus, result from weathering of paleozoic schists. The ores are compose d of gibbsite associated with pyrophyllite, Al-substituted goethite, a nd kaolinite. Pyrophyllite and Al-substituted goethite may contain up to 9% of the total Al2O3 content of the bauxite; this cannot be recove red through the Bayer process because these phases are insoluble in th e leaching solutions. Kaolinite is soluble under Bayer leaching but th is dissolution induces precipitation of sodium alumino-silicates, whic h apart from loss of further alumina results in decreasing efficiency of the process through scale formation. Detailed knowledge of the dist ribution of the different ore types and their mineralogical compositio n is necessary for efficient processing.