Effect of CaO content in raw material on the mineral composition of ferric-rich sulfoaluminate clinker

Abstract

Ferric-rich calcium sulfoaluminate (FR-CSA) cement is an eco-friendly cement. Fe₂O₃ exists in different minerals of FR-CSA clinker, e.g., Ca₄Al₂Fe₂O₁₀ (C₄AF), Ca₂Fe₂O₅ (C₂F), and Ca₄Al_6-2xFe_2xSO₁₆ (C₄A_3-xF_xS-). The mineral composition depends on the chemical composition of the raw materials and significantly determines the reactivity of FR-CSA cement. To optimize the phase composition of the FR-CSA clinker, chemical reagent raw mixtures with different amounts of CaO were used to prepare the FR-CSA clinker. X-ray diffraction (XRD) analysis, Rietveld quantitative phase analysis (RQPA), Fourier Transform Infrared spectroscopy (FT-IR), and scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS) were used to identify the mineralogical conditions of the FR-CSA clinker. The results indicated that the amounts of CaO in raw materials greatly affected the iron-bearing phase formation in the FR-CSA clinker. With decreasing CaO content involved in calcination reaction, the amounts of Fe₂O₃ incorporated in C₄A_3-xF_xS- increased up to 17.72 wt% (where x = 0.36). The findings make it possible to optimize the mineral composition of the FR-CSA clinker by changing the CaO content in raw materials. Furthermore, low CaO content in the raw material is beneficial to the formation of C₄A_3-xF_xS-, which enables the use of solid wastes containing low calcium for producing FR-CSA cement.