Roasting Characteristics And Reduction Behaviors Of Fluxed Brazilian Hematite Oxidized Pellets

With the progresses of iron-making technologies in China, the production of pellets has been promoted greatly. In2011, the production of pellets gets to160million tons. Particularly, with the development of large-scale grate-kiln process, the growing shortage of the magnetite concentrate with high grade iron, fine particle size and good firing behaviors become more serious. The utilization of imported hematite concentrate is an effective way for sustainable development of pellets industry in our country. Though Brazilian specularite is characterized by poor firing behaviors, it has gained world-wide recognition as an indispensable charge to replace magnetite for pelletizing plant due to its high grade iron and abundant. Therefore, the studies on the pelletizing of specularite concentrate and the reduction behaviors of hematite pellets will be of practical significance for Chinese iron and steel enterprises.In this paper, process of preparation of fluxed hematite pellets by blending Brazilian PFFT hematite with limestone and magnesite and their reduction behaviors in blast furnace have been systematically studied. The optimum process parameters are as follows:bentonite dosage is1.2%, balling for12min, at about8.3%moisture, preheating at1100℃, for10min, roasting at1250℃, for lOmin. In these conditions, the indicators of green balls with varying basicity and MgO are in line with the requirements of industrial production.At the nature basicity (0.06) and nature MgO content (0.08%), the hematite pellets process a high RDI-3.15mm of12.75%, RSI of12.93%, RI of62.22%, and poor high temperature properties with softening temperature1009℃, dropping temperature1272℃, and compressive strength is2400N/pellet.At natural MgO content (0.08%), the compressive strength and RI increases, the RSI climes firstly and then drops with an increase in the basicity, the maximum RSI occurs at0.4-0.6basicity, the RDI-3.15mm decreases and the softening temperature increases a little with the elevation of basicity. Due to the high RSI, the properties of hematite pellets can’t be all improved by the elevation of basicity only. At natural basicity (0.06), the compressive strength decreases obviously, the RI augments, the RSI declines slightly, the RDI-3.15mm decreases, respectively when the MgO content is elevated. Because of the decrease of compressive strength, only increasing MgO content can’t improve all of the properties of hematite pellets.In order to take the advantages of basicity and MgO and avoid disadvantages of them on properties of pellets, basicity and MgO content was adjusted at the same time to produce pellets with good properties. At fixed MgO content, the compressive strength and RI increases, the RSI climes firstly and then drops with an increase in the basicity, the maximum RSI occurs at0.4-0.6basicity, the RD-3.15mm decreases and the softening temperature increases a little with the elevation of basicity. At fixed basicity, the compressive strength decreases obviously, the RI augments, the RSI declines significantly, the RDI-3.15mm decreases, respectively when the MgO content is elevated. When basicity is1.0and MgO content3.0, or, basicity is1.2, MgO content is equal or greater than1.0%, the RSI can be controlled below15%, and the RI, DRI and Softening-melting characteristics are improved significantly.