Effect of By-Product-Derived Low-Melting-Point Additive on Mineralogical and Metallurgical Properties of Iron Ore Sinter

Reducing solid fuel consumption in iron ore sintering is an important strategy for lowering fossil fuel use and associated CO2 emissions. However, insufficient heat input can limit liquid-phase formation and compromise sinter quality. In this study, a by-product-derived low-melting-point additive (LMA) was used under reduced-fuel sintering condition, and the resulting mineralogical characteristics, pore structural, and metallurgical properties were evaluated. Preformed Ca–Fe–O phases accounted for 46.2 wt.% of the quantified crystalline phase assemblage in the LMA. Differential scanning calorimetry revealed a thermal event near 1200 °C, interpreted as being associated with the onset of liquid-phase formation. In sinter pot tests, the LMA-containing reduced-fuel condition (RFL) exhibited a lower maximum bed temperature than the conventional reference condition (STD), decreasing from 1375 to 1339 °C. With the mean STD values normalized to 100%, the relative mean reducibility index, tumble index, and reduction disintegration index of RFL were 104.7%, 101.8%, and 100.3%, respectively, indicating that these quality indices remained broadly comparable despite the reduced fuel input. Rietveld refinement indicated a higher magnetite fraction and a lower SFCA-I fraction in RFL, suggesting that the higher mean reducibility could not be explained by bulk mineralogy alone. Optical microscopy of entire specimen cross-sections revealed a lower pore area fraction and a more consolidated structure in RFL, whereas mercury intrusion porosimetry indicated that mercury-accessible pore volume associated with pore-entry sized below 50 μm was largely maintained. Overall, these findings suggest that the combined use of LMA and reduced fuel input can maintain sinter quality at a lower maximum bed temperature. The pore-structure results provide a possible explanation for the higher mean reducibility despite the mineralogical changes, although a causal relationship has not been established.