Formation Mechanism Of SFCA During Iron Ore Sintering

The effects of Al₂O₃ and Mg O on the formation of calcium ferrite in Ca O-Fe₂O₃ binary are studied,and the effects of Al₂O₃ and Mg O in the sintering are analyzed as well.The formation mechanism of calcium ferrite is clarified through analyzing composition and content of sintered ore within different temperatures,the changes of type and content of ore phase during the sintered process and the diffusion path of Al₂O₃ and Mg O in the ore phase.The main conclusions are as follows:1)In the Ca O-Fe₂O₃ binary system,content of Mg O is increased from 0.5% to 1.5%,contributing to the generation of calcium ferrite.MgFe₂O₄ reacts with calcium ferrite,and magnesium compound calcium ferrite is generated.When content of Mg O exceeds 1.5%,and then the content of magnetite increases,which restrains the generation of calcium ferrite.When the content of Al₂O₃ is increased from 1.5% to 3.5%,the sintered phase is changed from calcium ferrate to SFCA,promoting the generation of SFCA.2)During the generating process of CFA,C2 F and CA₂ are generated first;CA₂/C2 F interface is formed by CA₂ and C₂F.When temperature increases to about 800℃,C₂F/CA₂ interface is transformed into CF/CA₂ interface,and CFA（850℃-900℃）is generated by CF,CA₂ and Fe₂O₃;C₂F,Al₂O₃ and Fe₂O₃ can directly generate CFA（900℃-950℃）,and CA₂ nuclear reaction is the limit for the generation of CFA.3)The generation of SFCA is the process that CFA reacts and disappears in the ore phase.Layer of CA₂ and CFA is formed around of Al₂O₃.CFA mainly reacts with Fe₂O₃,MgFe₂O₄ and a small amount of calcium and magnesium silicate in the low temperature to generate SFCA.CFA mainly reacts with Fe₂O₃,calcium and magnesium Silicate and a small amount of MgFe₂O₄ in higher temperature,and then SFCA is generated;in the temperature of 1250℃,SFCA without CA₂ is easy to be decomposed into magnetite,while SFCA with CA₂ is not decomposed.Low content of Si O2 contributes to the reaction of CFA reaction,and promotes the generation of SFCA.