Compositional Properties and Colorimetric Characterization of Calcined Clays from the Central-West Region of Paraná and Their Application as Sustainable Pigment in Paints.

This study investigated two clays from the Guarapuava region, Paraná, Brazil, which were calcined at different temperatures. Their compositional and structural properties were evaluated using diverse characterization techniques, and their colorimetric analysis was performed using the CIELab* system. Significant changes in the structural and granulometric properties of the clays were observed, as well as colorimetric changes in the samples that occurred due to calcination at temperatures of 200, 400, 600, 800, and 1000 °C. The clays were tested as pigments in colorless and white acrylic paints and applied to plaster blocks. Among the two clay samples, one (designated GC) exhibited a high quartz content and showed no significant structural changes even after calcination at 1000 °C, as confirmed by XRD analysis. In contrast, the sample designated BC, which presented the highest iron content via EDXRF analysis, demonstrated the most significant structural alterations and phase changes in XRD, TGA, and particle size tests. Furthermore, BC yielded more pronounced color variations due to changes in the phases of its iron compounds, indicating its greater potential for use as a pigment.