Fundamental Research On Reduction-Efficient Separation Of Bayan Obo Hematite Ore

Bayan Obo ore is famous for its rare mineral paragenesis of iron, rare earth, niobium, thorium et al, in which26kinds of elements could be comprehensively utilized. But owing to complex minerals composition, close paragenesis, fine and uneven dissemination and so many useful component, the recoveries of iron minerals and rare earth minerals during mineral processing are very low. So it is of great theoretical and practical significance to improve separation efficiency of banyan obo Hematite ore.According to the complex feature of bayan obo Hematite ore, a new technique combined with beneficiation and smelting, called reduction-efficient separation was put forward in this thesis, breaking through the conventional concept of mineral processing-sintering-blast furnace smelting. By reduction, iron minerals in banyan obo Hematite ore was fully reduced into metallic iron particle, while minerals, such as rare earth, niobium and manganese were reduced to different degree. After that, the deeply reduced product was separated effectively. Iron, rare earth and niobium in the ore were separated and enriched effectively by systemic experiments. The mechanism of deep reduction was also studied.In this thesis, systemic experiments were carried out to investigate the effects of reducing temperature, reducing time, carbon additive, particle size of coal powder on reduction. The results were evaluated by chemical and image analysis technique, with metallization rate of reduced materials, particle size of metallic iron and grade of iron powder as index, The results showed that separation efficiency mainly depended on metallization rate and particle size of metallic iron, which was determined by reducing temperature, reducing time and carbon additive. The optimum conditions for reduction determined by experiments were that reducing temperature was1225℃, reducing time was30min, carbon additive was2, the particle size of coal powder was1.5mm and the particle size of hematite was2mm. Reduced materials with iron grade35.30%, content of metallic iron33.05%and metallization rate93.63%were obtained under this condition. According to the poor grindability of deeply reduced material, combined flowsheet of low intensity magnetic separation-shaking table was adopted for pre-decarburization. Then after the process of stagewise grinding and respective treatment of course and fine fraction, a good index with iron powder grade92.02%, recovery93.27%and metallization rate94.18%was obtained when the two stage grinding fineness were57.18%and85.66%respectively. The production could be directly used as the raw materials for steel making.Optical microscope, X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy was used to analyse the mineralogical properties of the materials both before and after reduction, including chemical and mineral composition of and crystal size. Combining with the study on dynamics of nucleation and growth of metallic iron grain, the mechanism of deep reduction was investigated thoroughly. The iron minerals were reduced in the sequence of Fe2O3�'Fe3O4�'FeO�'Fe. The main reaction was the indirect reaction between carbon and iron oxide, with iron being generated in short time. The speed of the whole reduction process was determined by the nucleation and growth of the metallic iron crystal grain, which can be divided into3steps, namely, reduction and nucleation, reduction、coarsening of iron grain. The dynamics of nucleation and growth of metallic iron grain could be depicted by Avrami-Erofeev model.The research on reduction properties of other element showed that, the reduction temperature had an important influence on the reduction property and enrichment and migration of different minerals. At the same time, occurrence of minerals such as rare earth, niobium and manganese etc. were discovered after deep reduction, which can pave the way for further separation and comprehensive utilization of these minerals. Under the proper reduction conditions determined in this thesis, most of rare earth minerals, hamartite (REFCO3) and monazite (REPO4), gradually converted to rare earth phase (CaO2RE2O3·3Si02). During magnetic separation,97.18%rare earth element reported to tailings, which had a grade of15.10%and can be used as the raw material for rare earth separation;25.93%niobium and18.29%manganese mixed into iron powder after reduction, with the rest reporting to tailings as oxide; harmful elements phosphorus and sulfur, with41.89%and21.94%respectively were mixed into iron powder,18.11%phosphor and26.08%sulfur became gas phase and volatilized together with CO, and the rest was tailings in the form of phosphate or sulfate.By means of artificial blending, TG-DSG and reduction research were carried out on ores of different CaF2content. The results showed that, CaF2could not only decrease the smelting temperature of raw ore obviously, but also can decrease the viscosity of slag. Thus, it was beneficial to improve the metallization rate of the reduced material and the growth of iron grain. With reference of Ionization Theory of Melting Slag, the action mechanism of CaF2was studied and discussed.The research by this paper can not only provide a new technique method for highly effective utilization of Bayan Obo Hematite Ore, but also make a theoretical basis for practical application.