Porosity, Mineralogy, Strength, and Reducibility of Sinter Analogues from the Fe2O3 (Fe3O4)-CaO-SiO2 (FCS) Ternary System

The presence of Ca-ferrite and silico-ferrite-of-calcium-and-aluminium (SFCA) bonding phases is thought to be crucial to maintain sinter quality due to their high reducibility and strength levels. However, new evidence suggests that porosity might be an equally important factor controlling reducibility, in addition to mineralogy. This work aims to fundamentally understand the development of porosity in simple sinter analogues from the Fe2O3-(Fe3O4)-CaO-SiO2 (FCS) ternary system (with no SFCA), and to connect results back to overall sinter mineralogy, strength, and reducibility properties. Laboratory-scale experiments were conducted to simulate the sintering process by firing tablets of magnetite, hematite, lime and silica mixtures under tightly controlled temperature, holding time and atmosphere conditions. Mineralogy of the fired samples was observed using microscopy techniques, porosity was measured by Mercury Intrusion Porosimetry (MIP), strength was determined using laboratory-scale tumble index equipment and reducibility was measured by the weight loss obtained after reaction of the tablets in a reducing atmosphere of CO/N2. The results confirmed that reducibility is strongly influenced by porosity, and highly reducible sinters can be produced without forming SFCA-like phases. Magnetite-containing samples had similar reducibility to hematite-containing samples, suggesting that magnetite-based sinters could potentially be used in the blast furnace.