Geochemical and ceramic evaluation of Permian alteritic clays (Paraná Basin, Brazil)

Research was conducted to identify and characterise alteritic plastic clay deposits from the Palermo/Rio Bonito and Teresina formations of the Paraná Basin, São Paulo State, Brazil, and to evaluate their suitability as raw materials for ceramic tile production. The deposits are predominantly composed of pelitic facies, represented by plastic claystones and siltstones with fine- to medium-grained textures. Samples from the Palermo/Rio Bonito Formation are characterized by high SiO₂ and Al₂O₃ contents and low concentrations of alkaline oxides, reflecting the predominance of quartz and kaolinite. In contrast, samples from the Teresina Formation contain higher K₂O contents (average 2.79 wt%), resulting in a more fluxing behaviour during firing. The ceramic tests revealed marked differences between the two formations. Palermo/Rio Bonito samples exhibited a more refractory behaviour, with an average fired flexural strength of 16.2 MPa and water absorption of 11.8%, whereas Teresina samples reached an average fired flexural strength of 33.3 MPa and water absorption of 2.8%, with some samples presenting values below 0.5%. The results indicate that these clays are suitable for use in ceramic tile bodies, particularly in stoneware formulations, while their application in porcelain stoneware is mainly constrained by the relatively high iron oxide contents.