Thermo-oxidative evolution and physico-chemical characterization of seashell waste for application in commercial sectors

•Successful thermally induced conversion of seashells into value-added products.•Isentropic oxidation which requires a large amount of heat causing entropy penalty.•According to XRD patterns CaCO3 is completely transformed into CaO at yet 850 °C.•Recommended high temperature to shifts reaction equilibrium towards decarbonation.•Agglomeration of CaO grains was favored by temperature-enhanced lattice diffusion. Thermo-oxidative degradation of mollusk shells to CaO through intermediate phase of CaCO3 has been investigated using various analytical techniques. Powders of shells species (Dosinia exoleta and Ostrea edulis), with particle size fractions of 0.045 – 0.125 mm, 0.125–0.2 mm, and 0.2–1 mm, were subjected to degradation at the various heating rates (5, 10, 15 and 20 °C min−1). Degradation pathway of this carbonate-rich waste material has not yet been analyzed in detail at particulate level. Understanding transformation process in air should lead to control over yield and morphology of final product. Thermogravimetric analysis (TGA) and X-ray diffraction (XRD) techniques were used to benchmark transformation steps at different heating rates and final decarbonation temperatures, while scanning electron microscope (SEM) was used to analyze the effect of temperature on evolution of morphological changes for particles of different fractions. It was found that sintering in the presence of carbon dioxide (CO2) could be triggered by agglomeration of CaO crystals, enhanced by CO2 adsorption that increases surface energy.