Comparative analysis of non-isothermal decomposition kinetics in Chrysotila carterae (Haptophyta) culture: Effects of coccolith removal

The cement industry is a major contributor to global CO₂ emissions, necessitating sustainable alternatives. Biocement production using microalgae-derived calcium carbonate (CaCO₃) offers a promising solution. Coccolithophores, a group of calcifying microalgae, naturally produce CaCO₃, which can be extracted and utilized in biocement production to reduce the industry's carbon footprint. This study investigates the thermal degradation of Chrysotila carterae biomass before and after coccolith removal to assess its thermal stability. Thermogravimetric analysis (TGA) confirmed effective coccolith extraction via acid treatment. Isoconversional models (Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, and Starink) were applied at multiple heating rates (5, 10, 25 °C/min) to determine the activation energy (Ea). The coccolith-free biomass exhibited significantly higher Ea values (3441.2 ± 4.3 kJ/mol) than biomass with coccoliths (536.4 ± 4.8 kJ/mol), indicating improved heat resistance. Further kinetic modeling using Coats-Redfern and Malek methods identified the three-way transfer model as the best fit. These results provide crucial insights into the thermal behavior of C. carterae, facilitating its optimal use in biocement production. Additionally, understanding its thermal decomposition enhances the feasibility of utilizing the residual biomass in other applications, including bioenergy. This study contributes to advancing sustainable cement alternatives and biomass valorisation.