Effect of CaF2 on the Reduction Swelling Properties of Iron Ore Briquettes in Different Reduction Stages

Preparation of briquettes by adding CaF 2 reagent into the Australian iron ore powder. The structure and morphology of iron ore briquettes during various reduction stages (i.e., Fe 2 O 3 →Fe 3 O 4 , Fe 3 O 4 →FeO, and FeO→Fe) were observed via an ore microscope and scanning electron microscopy. The results showed that CaF 2 reacted with SiO 2 to form CaO and SiF 4 gas during the roasting process. The reduction swelling index decreased from 12.36 to 8.83% when the CaF 2 content in the briquettes increased due to CaF 2 -mediated refinement of the hematite grains during the first stage of the reduction process. Lattice distortion resulting from the presence of Ca 2+ in the FeO lattice during the second stage of the reduction process, coupled with an increase in the porosity of the iron ore briquettes and the formation of a low-melting-point slag phase, promoted the anisotropic growth of FeO lamellar crystals, which resulted in an increase in the reduction swelling index from 4.27 to 7.36%. During the third stage of the reduction process, the growth of iron whiskers was promoted by wüstite (FeO) lattice distortion caused by a solid solution of Ca 2+ in the FeO lattice; the reduction swelling index increased from 15.61 to 24.72%, resulting in the catastrophic swelling of the iron ore briquettes.