Conversion of hazardous waste into calcium sulfoaluminate cement: effect of alkalinity modulus on mineral composition and Fe2O3 incorporation in Ye'elimite

The production of calcium sulfoaluminate (CSA) cement using hazardous wastes can enhance its sustainability and economic benefits. Incorporating Fe 2 O 3 into ye'elimite can reduce the Al 2 O 3 demand in waste-based CSA cement, while the influence of alkalinity modulus (Cm) on this incorporation remains unclear. This study synthesised CSA cement clinker from hazardous wastes with varying Cm. Results show that forming inert phases like C 2 AS and Fe 2 SiO 4 hinders the synthesis of hydraulically active minerals, requiring a higher Cm of 1.10 to attain the highest 28-day compressive strength of 76.4 MPa. Additionally, increasing Cm reduces the Fe/(Al + Fe) ratio in ye'elimite, particularly in low-aluminium clinkers. This contributes to the transformation of C 4 A 3 S ¯ -o to C 4 A 3 S ¯ -c and the slowed hydration. However, facilitated ye'elimite formation under higher Cm and increased Al 2 O 3 content in feedstock leads to more Fe 2 O 3 being incorporated into ye'elimite. This study provides guidance on regulating Fe 2 O 3 incorporation in the production of waste-based CSA cement clinker. • Calcium sulfoaluminate cement is synthesised from more than 80 % hazardous wastes. • Formation of inert phases like C 2 AS and Fe 2 SiO 4 restricts strength development. • Low availability of CaO in WIFA necessitates a Cm of 1.10 to maximise strength. • Fe/(Al + Fe) ratio in ye'elimite decreases as Cm increases. • Increasing Cm leads to more Fe 2 O 3 incorporated in ye'elimite.