Exploring Lower Cretaceous Karst Bauxite from South-Central Pyrenean Unit (NE Spain): Genesis and Ceramic Potential

This study investigates a karst bauxite deposit from NE Spain with a dual objective incorporating the novel aspect of directly linking genetic processes to industrial ceramic performance. First, the bauxite is mineralogically and texturally characterized using X-ray diffraction and field emission scanning electron microscopy. Second, the mineralogical and textural transformations of the bauxite during firing at 1000, 1200 and 1300 °C are analyzed, together with their effects on the physical properties of the fired products. The Lower Cretaceous bauxite is autochthonous, shows a pisolithic structure, and formed in situ under tropical monsoon conditions through intense chemical weathering involving dissolution–crystallization processes. For ceramic testing, the bauxite was mixed with illitic–kaolinitic clays in a 90/10 proportion. During firing, kaolinite and illite destabilize and transform into mullite, initially by solid-state reactions at 1000 °C and subsequently by crystallization from a vitreous phase at higher temperatures, producing larger crystals and composition closer to the empirical mullite formula. The formation of vitreous phase and mullite leads to reduced porosity and increased density and linear shrinkage, particularly between 1000 and 1200 °C. Specimens fired at 1300 °C show higher mechanical strength, related to higher mullite content and a larger size of its crystals. The results demonstrate the potential interest of these bauxites for ceramic manufacturing.