Effect of fluxing agents on reduction degradation behaviour of hematite pellets

Abstract

During induration at a high temperature, a considerable amount of slag/melt phase forms inside the iron ore pellets, comprising SiO 2 , Al 2 O 3 , CaO, MgO and FeO. After cooling, the slag phase solidifies and acts as an important bonding phase in the finished pellets and influences their room temperature as well as high temperature properties, especially reduction degradation. Fluxing agents play an important role in forming these bonding phases depending on the type and amount of flux. In the present study, the effect of different fluxing agents, namely, limestone, dolomite, magnesite and pyroxenite, on melt formation and microstructure during induration and on reduction degradation behaviour during reduction was examined. From the results, it was understood that to reduce the disintegration during reduction it is essential to increase the amount and distribution of bonding phases like silicates, which are more stable as compared to oxide phases like hematite. Acid pellets exhibited highest reduction degradation due to the presence of more hematite bonds and less silicate bonds. In limestone fluxed pellets, reduction degradation index dropped considerably with increasing CaO content due to the formation of more amount of bonding phase. Dolomite-pyroxenite pellets, on the other hand, showed lower reduction degradation index up to 0.4 basicity, and beyond that, higher degradation was observed due to the increased pore size, which resulted in poor strength of the reduced pellet matrix and hence more degradation. Low reduction degradation observed in pyroxenite and magnesite fluxed pellets could be due to the formation of magnesioferrite and silicate melt, which are more stable phases compared to hematite.

Review of pellets and blast furnace slag research progress: the effects of MgO on metallurgical properties

“…The large-scale utilization of high basicity sinter is based on its high reducibility and good softening performance [53]. Generally speaking, the reducibility of acid pellets is poor [54,55], while the reducibility of MgO-bearing pellets has been improved to a considerable extent [56][57][58]. The addition of MgO improves the reducibility of pellets, while excessive MgO produces silicate melt in the reduction process, which is not good for reducibility.…”

Phase transition mechanism of high-silica fluxed pellets during consolidation

“…And the preheating time was also found to play an important role in the extent of oxidation and calcination. Dwarapudi et al [9,10] studied carbon-containing fluxed pellets in the range of basicity (CaO/SiO 2 ) (0–0.8) and MgO content (0–1.5) and the effect of pellet basicity (CaO/SiO 2 ) and MgO content on pellet quality during hardening. And microstructure effects.…”

Effects of magnesium olivine on the mineral structure and compressive strength of pellets

“…Many scholars have prepared pellet by adding different types of additives, such as dolomite, light burned dolomite, magnesium fines, high magnesium olivine and so on [9][10][11][12]. Dwarapudi et al [13][14][15][16] studied the effect of MgO source, MgO content and basicity on the reducing performance of hematite pellets, such as reduction swelling index, reducibility and microstructure, and found that RSI could be promoted with the addition of MgO. A series of works had also been done by to investigate the addition of magnesium olivine on the reduction behaviour of magnetite pellets and interaction between iron ore and olivine under different temperatures.…”