Clay Schists from Barrancos (Portugal): An Approach Toward Sustainable Ceramic Raw Material Use

This study presents a comprehensive mineralogical, chemical, and technological characterization of clay schist samples from Barrancos (southern Portugal), aiming to evaluate their suitability for sustainable ceramic production. The work integrated X-ray diffraction (XRD), X-ray fluorescence (XRF), thermal analysis (TGA, DTA, and dilatometry), and other assays. After simple dry milling, the clay schist samples’ texture supported their use in plastic ceramic pastes but indicated a need for blending with coarser materials to meet extrusion requirements. Mineralogical analysis confirmed a dominance of illite (82%–85%), with minor kaolinite and chlorite. Chemical composition revealed significant Al2O3 (21.65%–28.24%) and SiO2 (52.27%–58.99%) contents, while Fe2O3 (4.41%–8.89%) supported their use in red ceramics. The presence of K2O (up to 5.43%) and Na2O (up to 1.63%) contribute to the fluxing capacity, promoting vitrification. Cation exchange capacity and specific surface area were low, consistent with the mineralogy dominated by illite and kaolinite. Thermal analysis confirmed the formation of mullite after firing at 1100 and 1150 °C, alongside residual quartz and hematite. The ceramic bodies exhibited progressive densification and strength enhancement with increasing temperature. The mixture of two selected samples showed good mechanical properties and lower porosity, with no efflorescence observed. These results underscore the potential of these schists as sustainable raw materials for ceramic production, promoting regional economic valorization and reducing environmental impact by utilizing local resources.