Behavior And Role Of Boron-magnesium In Agglomeration Of Fine Iron Ore

The agglomeration before ironmaking is a main energy-consuming procedure for iron and steel enterprises. Magnetite is main iron ore resources in China, but there are many problems on the agglomeration of iron ore powders, such as the ore being of the low iron and high SiO2 contents and the poor pelletizing performance, and the sinter being of the low strength, the poor metallurgical performance and easily pulverizing. Considering these problems, this thesis has synthesized a lot of references, and mastered the developments in the agglomeration of the iron ore powders at home and abroad, especially in the present situation and the existing problems of boron and magnesium additives used in the agglomeration of the iron ore powders. According to these problems, a systemic study has been made to seek for some new methods of solving them.This thesis mainly studies the rules of the boron and magnesium distributions in the sinter, the formation mechanism of calcium ferrite and dicalcium silicate and the effects of boron and magnesium in the sintering process of the magnetite, the effects of boron and magnesium on the formation and composition of the glassiness, the mechanism in which boron and magnesium affect the baking temperature and the oxidation rate of the pellet etc. In this thesis, the analysis instruments such as mineral phase microscope, scanning electron microscope attached with X-ray energy dispersive spectrum and X-ray diffractionmeter are used.In the course of the study, two breadthroughs on the experimental methods have been made. On the one hand, the static process of an interrupted sintering method used hi the experiment simulates the instant dynamic process of the reaction at a high temperature. On the other hand, the total boron content in the sinter and the boron contents in the different separated mineral phases have been successfully measured by Beryllium reagent III spectrophotometer showing non-color, which solves a difficult problem that can not be solved by physical methods.After studying the behaviors and effects of boron and magnesium in the agglomeration of the iron ore powders, we find that the most of boron in the sinter is in the glassiness and the distribution of magnesium in the sinter relates to the type of the additive and the basicity of the sinter. The distribution rules of magnesium in the sinter are different when the different additives and basicity of the sinter are used. The formation mechanism of both calcium ferritie and dicalcium silicate in the sintering processes of magnetite is different from those in the sintering processes of hematite. The primary liquidphase in the sintering processes of the magnetite is from FeOn-Si02 system instead of CaO-Fe2O3 system in the sintering processes of the hematite. The addition of boron and magnesium improve the homogenous degree in the mixing of the raw material and the ability in the pelletizing, and decrease the melting point of the sinter and the viscidity of the primary liquid phase, which favor the formation of the calcium ferrite and restrain the formation of the dicalcium silicate. Meanwhile, boron can activate magnesium in the state of inert in the sintering process, the monticellite is formed because of the isomorphism reaction resulted from the dissolution of magnesia into the dicalium silicate instead of the calcium silicate. In addition, the changing trends in the glossiness composition and the formation mechanism of the low concave area in the relationship between strength and basicity of the sinter are found. The additions of boron and magnesium together in the sinter can alter the structure and physical properties of the glossiness, increase the strength of the glassiness and improve the quality of the sinter. Magnesium and boron play very different roles in affecting the baking temperature and the oxidation rate of the pellet. The addition of magnesium in the pellet enhances the stability of the magnetite and restrains its oxidation, which result in its incomplete oxidation, the decrease in the strengt...