TAGRA 2025

This study investigates the structural, compositional, and thermal transformations of Perna viridis (PVS) shells heated at 100, 500, and 1000 °C using FTIR, XRD, and TGA/DTG analyses. The FTIR spectra of the raw shell reveal the presence of adsorbed water, organic matrix components, and calcium carbonate in the aragonite form. Heating at 500 °C induces a clear phase transition from aragonite to calcite. Calcination at 1000 °C results in the appearance of CaO, Ca(OH)₂, and residual CaCO₃, reflecting the decomposition of CaCO₃ followed by the rapid rehydration and re-carbonation of CaO upon exposure to atmospheric moisture and CO₂. XRD patterns corroborate these observations, showing predominantly aragonite in the raw sample, calcite at 500 °C, and portlandite as the major phase at 1000 °C, with a minor amount of calcite. TGA/DTG analysis reveals three main weight-loss events corresponding to the release of adsorbed water, the decomposition of organic components, and the major thermal decomposition of CaCO₃ between 531–916 °C. Overall, the combined FTIR, XRD, and TGA findings demonstrate significant mineralogical transformations in Perna viridis shells upon high-temperature treatment, highlighting their potential as a biogenic precursor for CaO production and related calcium-based material applications.