Phase evolution of cement raw meal in a high-CO2 atmosphere

Abstract

This study investigates the effects of a high-CO₂ atmosphere on phase evolution, burnability, and clinker mineral formation in cement raw meals using high-temperature X-ray diffraction (HT-XRD). The cement industry is a significant CO₂ emitter, primarily from limestone decomposition and fuel combustion. Innovative solutions such as carbon capture and storage (CCS) are critical, with electrification and oxy-fuel combustion showing promise. Electrification using plasma technology, which employs CO₂ as a carrier gas, offers a pathway to near-zero emissions.

Four industrial raw meals from northern Europe were analyzed under conventional (20% CO₂) and high-CO₂ (95% CO₂) conditions. Chemical composition, particle size distribution, and coarse fraction analyses preceded HT-XRD data collection across temperatures up to 1500 °C. High-CO₂ conditions delayed calcite decomposition, reducing free-CaO availability and altering burnability. The timing of calcite decomposition relative to C₂S formation suggests a reaction pathway in which free CaO, released from calcite, rapidly reacts with thermally activated SiO₂ to form C₂S. Additionally, spurrite decomposition released reactive CaO and C₂S, enhancing C₃S formation at 1300–1400 °C in spurrite-rich samples. Above 1400 °C, melt formation promoted further C₃S development, leading to similar final levels in both tested atmospheres.

These findings indicate that high-CO₂ conditions significantly influence clinker phase evolution and reactivity. Practical implications include optimizing raw meal composition and kiln temperature profiles in electrified and oxy-fuel systems to enhance burnability while minimizing operational issues such as spurrite-induced kiln buildup. Future research should further explore industrial scalability and raw material adjustments to enhance CO₂ efficiency during clinkerization.