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Calcium ferrite containing aluminum (CFA) is a precursor of the low-temperature bonding phase in the sintering process of iron ore fines for blast furnace ironmaking. Thus, improving the formation of CFA at lower temperature is very important for saving energy, improving efficiency and production. In this paper, the formation process of CFA was investigated at 1200 °C by reactions of alumina (Al₂O₃), respectively with a mixture of calcium oxide (CaO) and hematite (Fe₂O₃) and monocalcium ferrite (CF) as a recognized initial product, as well as reaction of Al-containing hematite (H_ss) with CF. The result confirmed that CF is an intermediate product formed easily in the sintering process, and it may react with excessive Fe₂O₃ to generate an alpha-calcium iron oxide (Ca₂Fe_15.50O₂₅) as a new phase. It was found that CFA can be formed directly by reactions of CF with H_ss and Ca₂Fe_15.50O₂₅ with Al₂O₃, while the reaction of CF with Al₂O₃ is more helpful in generating Ca₂Fe_15.5O₂₅ rather than CFA, simultaneously forming a calcium aluminum oxide (CaAl₂O₄, CA; CaAl₄O₇, CA₂). It was revealed that the appearance of CA and CA₂ is a main reason to hinder CFA formation in the sintering process of iron ore fines.