Liquid phase formation and phase equilibrium analysis of sintering with high-iron concentrate proportion at Ansteel

Sintering with a high-iron concentrate proportion serves as a vital way to improve the utilization efficiency of domestic self-produced iron concentrate resources. The Anshan-Benxi area in Liaoning Province hosts the largest iron ore deposits in China. Ansteel intends to carry out sintering production with a high-iron concentrate proportion of over 70%, whereas systematic theoretical researches on high-iron concentrate proportion sintering are still insufficient. Based on the actual raw materials applied in the sintering plant of Ansteel, the thermodynamic software FactSage 8.1 was adopted to systematically investigate the liquid phase behavior and phase evolution mechanism of the sintering system with the mass fraction of iron concentrate ranging from 50% to 100%. The results show that when the iron concentrate proportion increases from 50% to 100%, the initial liquid phase formation temperature rises from 1 150 ℃ to 1 200 ℃, and the liquid phase content in the low-temperature zone presents a gradually decreasing trend. The liquid phase viscosity of the system drops significantly with the increase of temperature, and reaches the maximum value of 0.06-0.10 Pa·s in the low-temperature zone of 1 100-1 200 ℃. With the increase of iron concentrate proportion, the liquid phase viscosity in the low-temperature zone decreases due to the increased FeO content and the reduced polymerization degree of silicate networks. The area of the liquid phase region expands first and then contracts with the rising iron concentrate proportion. The sintering system presents the optimal thermodynamic conditions for liquid phase formation at the iron concentrate proportion of 80%, with the largest liquid phase region area and the lowest initial liquid phase formation temperature. When the mass fraction of iron concentrate exceeds 80%, the liquid phase region shrinks obviously and the spinel phase region expands, which restricts the formation of calcium ferrite liquid phase and sinter mineralization. It is necessary to regulate the liquid phase composition and bonding behavior of sintering by adjusting raw material structure and sintering process parameters. Further analysis of the isothermal sectional phase diagram verifies that the liquid phase region expands remarkably at 1 300 ℃ under the 80% iron concentrate proportion condition. The calcium ferrite phase melts and decomposes, while the dicalcium silicate phase exists stably and provides skeletal support for sinter ores. This study clarifies the thermodynamic essence of mineral phase transformation during high-iron concentrate proportion sintering, and provides a significant theoretical basis for optimizing the process parameters of high-iron concentrate proportion sintering.