Regulation of mineral formation of iron-rich calcium sulfoaluminate clinker by controlling SO3 and Fe2O3 contents

This study systematically investigates the effects of SO3 and Fe2O3 variations in the raw mix on the mineral phase formation, transformation and regulation of iron-rich calcium sulfoaluminate (CSA) clinker. The findings reveal that excess SO3 can simultaneously facilitate the formation of C4A3S̅ phase and C2S phase. Moreover, elevated levels of SO3 also enhance ions substitution within different mineral phases. In C4A3S̅ phase and ferrite phases, the substitution rate of Fe3+ for Al3+ gradually increases with rising SO3 content, which contributes to the formation of C4A3S̅-c phase and induces a continuous transformation of ferrite phases through the sequence C4AF → C4A1-yF1+y → C2F → Fe2O3. Essentially, excess SO3 modulates the species and crystalline structures of the mineral phases containing aluminum and iron through strategically directing the fate of Fe2O3 and Al2O3. Furthermore, the increase of Fe2O3 postpones the effect of excess SO3 on mineral phases formation and transformation.