A methodology to enhance ye'elimite in calcium sulfo-aluminate ferrite clinker from bauxite residue

Calcium sulfoaluminate-ferrite (CSA-F) clinkers were prepared using the alumina production waste bauxite residue (BR) as one of the raw materials, next to limestone, kaolin, and gypsum. A complementary approach was employed, aiming to maximize the desired ye’elimite phase. This consisted of thermodynamic modelling and computational statistics via response surface modelling, which enabled the identification of the best raw meal by varying the proportions of the chosen raw materials and the optimal clinkering conditions by unraveling the interaction between clinkering temperature and time. The optimal parameters were for a raw meal consisting of 38 wt% BR, 42 wt% limestone, 5 wt% kaolin, and 15 wt% of gypsum, fired for 60 min at 1300 °C. The accuracy of the model was assessed experimentally on a clinker synthesized at a temperature range of 1250–1300 °C for 30 and 60 minutes, followed by rapid cooling. Based on the characterization results, firing at 1300 °C for 60 minutes was the optimal set of conditions to maximize ye'elimite formation, which was in accordance with the response surface model. In addition, clinker 1300_60 exhibited the highest 28d compressive strength of 33 MPa due to the presence of Ternesite phase. In conclusion, the combined methodology endorsed and presented herein is a pragmatic and relatively accurate methodology for producing low-CO2 clinkers from bauxite residue and can likely be transferred to other unexploited secondary raw materials.