Three Dimensional Characterization And Microscopic Mechanical Property Analysis Of Pellet's Mineral Phase

The iron ore resources are almost lean ores,there are very less rich ores in China.In the battle of the resources started recently,only relying on the iron ore imported from other country is not a long-time policy.In the mining process of lean ore,it's always milled into powder,then,iron powder will be produced into sinter or pellet.While,the sinter produced from those iron concentrate fines has low strength,high content of FeO,serious reduction degradation,low yield,so it is not suitable to produce good sinter.On the contrary,because of the pellet is solid consolidation,has the advantages of low energy consumption,small and uniform size,high strength,low FeO content,fitting for long-distance transportation,lower pollution and many other advantages,so the iron concentrate fines is more suitable for pelletizing.In the modern blast furnace production,the amount of pellets used in the blast furnace production is increasing due to those advantages.With the increasing ratio of pellet in blast furnace,the operation of BF is facing new challenges.Thus,research on the properties and quality of the pellet was carried out in domestic and overseas,however most of the researchers focused on the ore matching and two-dimensional morphologies of minerals,as for the mineral's 3D morphology and spatial distribution had never been revealed.Therefore,statistical analysis and micro mechanical properties of the pellets and three-dimensional morphology of the different mineral,spatial distribution,the mineral phase and its influence on the pellet strength were carried out in this study.In this paper,the three-dimensional morphology and spatial distribution of main minerals in the pellet were first revealed,which lay a foundation for the study of mineralization mechanism of pellet and give a direction to improve the quality of pellet.Firstly,based on the method of serial slice and modern 3D reconstruction software,the 3D reconstruction of the main mineral phases in the two kinds of pellets with different strength was carried out.The cross-section of each pellet sample was divided into three areas:external zone,intermediate zone and central zone.3D reconstruction results show that,from the outside zone to central zone,the morphologies of hematite are,in order,good interconnected block,loose interconnected block and small particles;while,the shape of magnetite varies from small particles interlaced with hematite,grid intertwined with hematite and layered structure interlaced hematite;but the silicate's shape changes unregularly.The rule of minerals'spatial distribution from the external to the center is that hematite becomes looser and less.On the contrary,magnetite increased and connected with each other gradually from external to internal zone.In addition,most silicates are concentrated in the intermediate zone,while it is less and small in the outer and the center area.At the same time,through the comparison of two kinds of pellets,it can be found that:in the three area,the content of residual magnetite in 1#pellet was obviously higher than that of 2#pellet,the hematite in 2#pellet is almost interconnected with each other;while the hematite in the three circle zone of 1#pellet is mainly particles;the size of silicate and magnetite in 2#pellet is smaller than that of 1#pellet.Based on above results,it can be revealed that,the property of minerals in 2#pellet may be better than that in 1#pellet.Then,Based on the basic principle of area method in mineral stastistics,combined with computer image processing technology,the content of micro mineral phase structure of two kinds of pellet were statisticed and compared.According to the statistic results,it is found that the content of hematite in 2#pellets is more than that of1#pellets,and the porosity is less than that of 1#pellets,the content of magnetite and silicate is less than that of 1#pellets.Through SEM and EDS analysis,the elements distribution of the main minerals in two kind of pellet was obtained.It can be found that,there are few magnesium concentrate in magnetite that weaved with hematite;the Mg²⁺filled the vacancy of Fe²⁺during the magnetite turned into hematite,thus,prevent the oxidation of magnetite,which lead to the formation of the interweaved structure of hematite and magnetite.Based on the SEM-EDS analysis,it was found that,the content of magnesium in 1#pellets was higher than that of 2#pellet,therefore,there are more hematite and magnetite interweaved structure in 1#pellet.Through comprehensive comparison,it was proved that 2#pellet had a better micro structure.Finally,the microhardness and fracture toughness of two kinds of pellets in three different forms of hematite structure had been calculated.The influence of different hematite morphology on micro mechanical property and the macro strength of pellet was studied.The results show that:the hematite in form of large particles has the highest micro hardness,followed by the hematite and magnetite interweaved structure,the interconnected hematite in form of small particles has the lowest microhardness;the fracture toughness of hematite and magnetite interweaved structure is the highest,followed by interconnected hematite in form of small particles,hematite in form of large particles is the lowest.The microstructure and mechanical properties of three forms of hematite structure in 2#pellet are better than that in 1#pellets,this is because the degree of interconnection of hematite is better than that in 2#pellet.There are more hematite in form of big particles in 2#pellet,and the combination way between hematite's crystal is almost hematite-hematite connection and little hematite-magnetite connection;But there are almost hematite-magnetite connection and hematite-silicate connection in 1#pellet.Eventually,all those properties of two kinds of pellets leading to that the compressive strength of 2#pellet is better than1#pellets.