Research On Application Of MHA Binder In Oxidized Pellet Preparation From Specularite Concentrates

With the development of iron ore oxidized pellet industry, the magnetite concentrates characterized by high TFe grade, fine granularity and good roasting performance become more and more shortage in China. Therefore, the development and application of new iron ore resources has provides a new approach for the sustainable development of pellet industry. Specularites are now invoking more and more interests because of their many advantages such as low price, great reserves and high TFe grade, although they are characterized by poor ballability and bad high-temperature reactivity. The reasonable utilization of specularite resources, hence, can play significant role in lightening the shortage of iron ores. Recently, one modified humic substances based binder, named MHA binder, have been patented and proved to be an effective binder for iron ore pellets in China. The MHA binder mainly comprising functional organic polymer is characterized by low residue, low price and good thermal stability. And the presence of MHA binder onto surface of iron ore particles is able to modify the interfacial characteristics of iron ores and improve the green pellet strength. Therefore, the research on application of MHA binder in oxidized pellet preparation from specularite concentrates provides us a novel method and a newdirection for Effective use of specularite.Compared with inorganic bentonite binder, the specularite oxidized pellets are produced by adopting as the MHA binder developed by central south university and Brazilian ORP specularite treated by different pretreatment methods as raw materials. The research results are concluded by the following:The specific surface aera of specularite 1609 cm2/g can be obtained when the process of wet ball grinding combined with high pressure grinding technology is adopted. Under the condition of the dosage of MHA binder 1.0%, balling time 15 min, the moisture wet green pellets 8.0%, the drop strength, the compression strength and the thermal crack temperature of green pellets are respectively 3.7 times/0.5m,12.4 N/P and 330℃. Comparatively speaking, the drop strength, the compression strength and the thermal crack temperature of the green pellets balled with 2.0% bentonite are respectively 3.9 times/0.5m,13.6 N/P and 365℃.Under the optimal experimental conditions of the dosage of MHA binder 1.0%, preheating temperature 980℃, preheating time 10 min, roasting temperature 1280℃and roasting time 10 min, the compression strength of the preheated pellets and the compression strength of the roasted pellets is 401 N/P and 2700 N/P, respectively. Compared with the MHA binder pellets, the compression strength of preheated pellets and the compression strength of the roasted pellets with 2.0% bentonite is 445 N/P and 2709 N/P, respectively. The qualities of the two kinds of pellets are almost close to each other. Compared with the pellets with 2.0% bentonite, the metallurgy performance at high temperature of the pellets with 1.0% MHA binder is better and TFe grade increase by 0.85%.The adsorption experiments show that the MHA binder have a obvious adsorption on the surface of speclarite grains during specularite pelletizing. The adsorption amount of MHA binder is influenced by the specific surface area of specularite, the proportion of MHA binder to specualrite, the adsorption time and so on. Meantimes, MHA improves the surface hydrophilicity of specularite with appearance of MHA binder on the surface of speclarite.The behavior of MHA binder in specularite pellets during preheating and roasting can be involves the following two aspects. (1):combustion and releasing heat of MHA binder. The organic fraction of MHA binder is burned out during heating and partial heat is released. This is helpful to increase the temperature of the core of pellets, and to promote the induration of pellets. (2):reducing action of MHA binder. The reduction reaction of MHA binder takes place on the surface of specularite grains. Fe2O3 is reduced to magnetite or wustite firstly. Thereafter, the secondary magnetite is reoxidized to secondary Fe2O3. The preheating and the roasting processes promote the recrystallization of secondary Fe2O3 grains. Therefore, these changes in the induration process of specularite at high temperature improve the roasting properties of the pellets with MHA binder.