Utilization of fly ash for CO2 capture through mineral carbonation: An experimental study with Indonesian coal fly ash

Fly ash, a by-product of coal combustion, holds significant potential as a reactive feedstock for CO 2 mineral carbonation, presenting a viable method for permanent CO 2 sequestration. Despite its high availability and cost-effectiveness advantages, fly ash typically exhibits low carbonation rates and efficiency. This research examines the carbonation behavior and underlying mechanisms of fly ash, using a process in which CO 2 is first captured in KOH to form K 2 CO 3 , providing a uniform distribution of carbonate ions that enhances Ca 2+ dissolution and accelerates CaCO 3 precipitation. Semi-batch carbonation experiments investigated the impact of solid-to-liquid ratio, temperature, and reaction time on overall carbonation efficiency, while multi-cycle carbonation experiments assessed process repeatability and solvent regeneration potential. Results indicated that calcium-bearing phases in fly ash, such as lime, anhydrite, and brownmillerite, react effectively with CO 3 2– , leading to the formation of CaCO 3 . Higher solid-to-liquid ratios and elevated reaction temperatures enhanced sequestration rates and carbonation efficiency. The pre-loaded K 2 CO 3 solvent, free from gas–liquid mass transfer limitations, enabled efficient carbonation even at high solid-to-liquid ratios by shifting the rate control to mineral dissolution, offering a scalable and low-energy alternative to direct CO 2 bubbling. Multi-cycle experiment results confirmed effective CaCO 3 precipitation and solvent regeneration at ambient pressure and temperature, supporting a sustainable and economically viable carbonation process. This study provides critical insights into optimizing fly ash mineral carbonation, contributing to enhanced CO 2 capture strategies in coal-based power generation. • Indonesian coal fly ash achieved up to 19.6% carbonation efficiency for CO 2 sequestration via mineralization. • Pre-loaded potassium-based solvent avoids gas-liquid transfer limits of direct CO 2 bubbling, allowing high carbonate availability for efficient carbonation. • The method operates well without pressurization or heating, enabling repeatable carbonation and regeneration cycles without high energy cost. • Solvent regeneration and by-product reuse offer potential pathways for scalable and sustainable CO 2 mitigation.