Characterization Of Pore Reconstruction During Reduction Of Iron-Bearing Minerals

Iron-bearing minerals such as sinter and pellets are all porous media materials,and the pores will change a lot during the reduction process.Since the pore structure of iron-making raw materials directly affects the reducibility and mechanical strength of iron-containing raw materials,a thorough understanding of the changes in pore structure during the reduction process of iron-containing minerals and mastering the pore reconstruction behavior will have a positive effect on improving the reduction and stabilizing the metallurgical properties of the charge.Based on this,this article uses mercury intrusion method and scanning electron microscopy method to physically characterize the pore structure of the pellets.While obtaining the basic parameters of the pellet microstructure,they have a basic understanding of the internal conditions of the pellets;At the same time,a mathematical simulation method is used to construct a pore reconstruction model,to characterize the pore changes during the reduction process of pellets,and to correlate the characterization results with the metallurgical properties(strength,reduction degree)of the pellets,and to explore reasonable pore distribution to improve the metallurgical properties of pellets.The main results of the paper are as follows.(1)By changing the pelletizing process,three pellets with the same composition and size but different initial porosity and compressive strength were prepared,and then the metallurgical properties of the pellets were measured.As the initial porosity increases,the reduction degree of pellets gradually increases,while the strength gradually decreases,which is the same as our understanding of pellets.The increase in porosity represents the increase in pores and the increase in pore size,which increases the diffusion rate of gas and thus increases the degree of reduction;but at the same time it also reduces the structural strength of the porous medium,resulting in a decrease in the compressive strength of the pellets.Therefore,the initial compressive strength and the reduced strength of the pellets should be considered comprehensively,and the degree of reduction should be increased as much as possible on the premise of ensuring the blast furnace to run smoothly and meeting the requirements of blast furnace production.(2)The pore structure of pellets was physically characterized by mercury intrusion method and image method,and the results showed that the characterization result of the change of porosity before and after reduction of pellets with different initial porosity by mercury intrusion method is similar to the characterization result of pore structure by image method.Therefore,the image method is used to characterize the pore distribution state of the porous medium,and the mathematical model characterization method that is consistent with the image method is sought.(3)When constructing the model,four control functions such as single-point probability,two-point probability,linear path and fractal control are introduced to make the constructed model more perfect.Analysis from the research results shows that the absolute error of the linear path function is the smallest,so the linear path function-based characterization method is used.At the same time,it can be seen from the probability curve of each function that when the distance between two points,the length of the line segment,and the side length of the box exceed 100μm,60μm and 15μm respectively,the characterization result of the model includes all the data of the pore structure,so the reconstruction of this article The size of the model is determined to be 100×100μm.(4)The two-dimensional characterization results show that with the progress of the reduction process,the pore sizes of Q2 and Q3 gradually increase,the pore structure changes from the initial uniform pore distribution to the uneven pore distribution,and the pore size gradually increases and is dispersed.At the same time,the partial pore structure distribution law obtained by the characterization results,including pore size,pore distribution,dispersion,etc.,is the same as the reference model,but the pore connectivity in the direction perpendicular to the two-dimensional surface needs to be further studied from the three-dimensional direction.Combined with the actual situation of this research,improvements were made from two aspects of control function probability curve fitting and system search methods,which improved the efficiency and convergence of the algorithm,and made the three-dimensional representation of the model more accurate.(5)After improving the model,perform 3D characterization and skeleton extraction.The characterization results showed that during the reduction process,the matrix phase of the pellets gradually thickened and condensed,and the pore structure of the pellets changed from the uniform distribution of pores in the initial stage to the gradual accumulation of pores into blocks with different shapes.Observation from the characterization result shows that the pores gradually gather toward the center,and the pores at the edge are less and scattered.This is because the three-dimensional accumulation creates a visual illusion.Therefore,it is necessary to extract the skeleton of the image of the above-mentioned characterization result.After extraction,the pore structure is very clear.Q3 has a relatively large pore density and relatively dispersed pore distribution,but its pore connectivity is better,so the strength of Q3 after reduction is poor but the degree of reduction is high.This also realizes the three-dimensional characterization of the pores of the pellet reduction process.