Formation of Calcium Ferrite Containing Aluminum (CFA) in Sintering of Iron Ore Fines

Abstract

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 (Hss) 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 (Ca2Fe15.50O25) as a new phase. It was found that CFA can be formed directly by reactions of CF with Hss and Ca2Fe15.50O25 with Al2O3, while the reaction of CF with Al2O3 is more helpful in generating Ca2Fe15.5O25 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.