Research And Application Of Metallogenic Mechanics For Fine Grinding Magnetite Sintering

Magnetite is main iron resource in China. Magnetite is chief sintering raw material in some sintering plants in the north of China. In recent years, the technique of improving iron and decreasing silicon has been implemented to iron concentrate in China. Many sintering plants have adopted the technique of high-iron and low-silicon, and mainly used magnetite as sintering raw materials with addition of sane high-quality hematite overseas. It is very important to study metallogenic mechanics and technical conditions of improving production and quality of sintered ores.Solid phase consolidation of iron ore particles, sintering reactivity of single iron ore, sintering reactivity behavior of magnetite with addition of hematite and sintering behavior of particles were studied on the basis of characteristics of fine magnetite mixture and hematite. Besides, effects of improving production and quality of sintered ores dominated fine grinding magnetite were tested. Results are as follows:(1)Solid phase consolidation rate of magnetite particles which are consolidated by crystallization and oxidization crystallization is faster under oxidization atmosphere. Iron ore particle size is fine and the particles are contacted with each other, which is good for diffusion and bonding. Content of FeO is also a factor of affecting solid consolidation. Oxidization heat of magnetite is advantageous for diffusion of mass point and accelerates particles bonding. In addition, magnetite and SiO₂ will form low-melting compound when magnetite is not oxidized completely, which will strengthen particles bonding .So SiO₂ content is also a factor of affecting particles consolidation. Hematite particles keep original shapes and do not contact with each other at 1200℃.Crystal particles grow up and form initial attachment bridges, when temperature is over 1280℃.(2)Early sintering liquid phase is CaO-Fe₂O₃ system when hematite is sintered.Hematite particles are enclosed and ablated gradually, at last formed interlaced texture between hematite and calcium ferrite. Sintering mechanics of fine grinding high-iron and low-silicon magnetite is different from that of hematite. Formation of calcium ferrite is little and main consolidation shapes are magnetite oxidization recrystallization and magnetite recrystallization. Magnetite is oxidized to form calcium ferrite, which is blended with magnetite and hematite. Magnetite easily consolidates with Ca2+ and Mg2+,then forms iron ores containing calcium and magnesium.(3)Coarse particles in mixture (e.g. Australian ore)enclosed by liquid phase calcium ferrite can provide framework for the briquette. Some large particles are prior to soft melt or form low melting point minerals during roasting process (e.g. returning ores). Limestone mineralizes with other minerals to forme fluid phase quickly after decomposed. Dolomite mineralization needs higher roasting temperature and longer roasting time in the mixture. It is enclosed by magnetite after decomposed, and formed interlaced texture between magnoferrite and periclase.(4) Studies on improving the yield and quality of the fine grinding magnetite sintering in the sintering cup assay have been performed in this paper. The results indicate that: the mixture of full concentrate sintering is weak in permeability, and the sintering utilization index is low. Adding the compound binder F and catalyst J can improve the sintering quality. The dosage of compound binder F, from 0% to 1.0%, has obvious effects on granulation of the mixture. The granularity composition of-lmm is low and permeability index is improved in the mixture. The vertical sintering velocity is improved from 16.95 mm/min to 21.05 mm/min, and the utilization index is obviously improved from 1.352 t/(m2.h) to 1.729 t/(m2.h), which shows adding catalyst J has obvious effects on improving tumble index and utilization index. Especially, the catalyst had obvious effect on reducing the solid fuel consumption.When the fine grinding magnetite is mainly sintered with some addition ofhematite, the sintering yield and quality are both better than those of sintering by full concentrate. On the base of that, it was studied that the effects of alkalinity, MgO and the quantity of calcined limes on the sintering yield and quality. The alkalinity has obvious effect on the tumble index of sintering. When the alkalinity is improved form 1.6 to 2.0, the tumble index is obviously increased from 57.60% to 69.60%. MgO content in the sintering ores decreased from 2.3% to 1.4%, and the sintering utilization index increased from 1.629 t/(m2h) to 2.031 t/(m2.h), but the tumble index has no obvious change. Calcined limes can effectively improve the granulation effect of the mixture, and the material bed permeability is markedly improved, the vertical sintering velocity is instinctly accelerated, the utilization index increases, moreover, the tumble index is improved a little.