Viability of bauxite deposits from Catalonia (Spain) for ceramic applications

This study provides a characterization of materials from wastes and outcrops of twoinactive bauxite mines located close to Sant Joan de Mediona and Peramola, Spain. Mineralogy wasdetermined via powder X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR).Thermal properties were measured via differential thermal analysis–thermogravimetry (DTA-TG) andgresification tests. The crystalline phases are medium-high crystalline kaolinite and variable amountsof illite, quartz, calcite, boehmite, hematite and rutile/anatase. DTA show two endothermic peaksproduced by the dehydroxylation of minerals: the first peak, at 530–538 C, belongs to boehmite; thesecond peak, at 535–568 C, corresponds to kaolinite. An exothermic peak at 950–978 C is associatedwith mullite crystallization. The optimal sintering temperatures obtained from the gresification curves(firing shrinkage and water absorption) were 970 C for carbonate-poor, illite-rich clays; 1100 C forillite- and carbonate-poor samples; and near 1190 C for carbonate-rich materials. The carbonate-poorsamples fired at 1300 C contain sillimanite and mullite, and the carbonate-rich materials are richin gehlenite, anorthite, and hedenbergite. The mineralogy of these materials is sufficient to obtainceramic materials with suitable properties, but not their low plasticity. They could be used in theformulation of bricks or as part of mixtures to produce refractory ceramics.