Investigation On Strengthening Concretion Of Magnesium Pellets And Its Mechanism

BF smelting basis to quality material, with the characteristic of high iron grade, even granule, good strength, pellets is high-quality material. But in China, acid pellets have the problem of high reduction swelling and low softening melting temperature. Adding magnesium additives to produce high MgO content pellets can improve the matallurgical properties, and indicate the future development of pellets.For hematite concentrate and magnetite concentrate, the influence of different magnesium additives on pellets roasting was studied, and the rules of rising MgO content on strength and roasting condition were revealed. On this basis, calcium containing and boron containing strengthening magnesium pellets concretion was studied, and through the research of Mg2+,Fe3+diffusion, the mechanism of magnesium pellets consolidation strengthening was revealed.Based on the study of roasting properties of magnesium pellets, it was found:when serpentine or MgO powder or magnesite was used as additives, the strength of either preheated or roasted pellets made of magnetite concentrate or hematite concentrate or as a mixture of the two decreased with increasing MgO content in the pellets, which indicate MgO content go against pellets consolidation. The main reason of low pellets strength is Fe2O3grains can not grow up. Studying on influence of MgO content on roasting condition, it is found that:the optimum roasting temperature and time intervals became narrower with an increasing MgO content in the pellets.Studying on calcium containing and boron containing materials strengthening magnesium pellets concretion indicate that:using limestone as calcium containing material the strength of preheated and roasted pellets increased first and then decreased with increasing basicity, and the strength reached the maximum value with basicity between0.4and0.5, controlling the bacisity,high strength pellets can be produced, therefore slaked lime prevented the increase of strength for preheated pellets, with increasing boron content, the strength of both preheated and roasted pellets increased.The study on intensified roasting of pellets by containing calcium and boron indicated that:Adding calcium and boron sources could improve the formation of low melting point substances, resulting in the generation of suitable amount of liquid phase which speeded up the diffusion of Mg2+and Fe3+ions and improved the strength of magnesium pellets by facilitating the mineralization of flux containing magnesium and recrystallization of Fe2O3. Without calcium and boron sources, the diffusion velocity of Mg2+and the grain growth rate constants of Fe3+were11.13μm/min and7.67×105(μm)7·min-1, adding calcium and boron sources they improved to17.11um/min, and1.24×106(μm)7·min-1。...