Swelling Mechanism Of Bayan Obo Iron Concentrate Pellets In The Progressive Reduction Process

In order to explore the reduction swelling process of Bayan Obo iron concentrate pellets,based on the theory of iron oxide reduction of pellets,the volume swelling behavior of Bayan Obo iron concentrate pellets was studied in stages during reduction process.The reduction products of each stage are able to analyze by XRD and SEM-EDS,the crystal parameters of reduction products are able to calculate and the reduction swelling mechanism of Bayan Obo iron concentrate pellets is able to deeply explain.The results show that the reduction swelling index of Bayan Obo iron concentrate pellet is as high as 35%.Among them,the third stage is the largest,which is 24%.The reduction swelling in three stages is caused by the crystal transformation,the effect of the slag phase,and the formation of iron whiskers.With the gradual reduction reaction,the crystallite size of iron oxide increases,the degree of microcrystalline increases,and the crystallite structure gradually tends to be orderly,which creates conditions for the directional growth of iron whiskers.Simultaneously,the crystal plane index value of Fe₂O₃?Fe decreases gradually,the crystal plane spacing increases,and the binding force between the two crystal planes decreases,so that the swelling index increases.Reduction of Bayan Obo iron ore concentrate pellets in the three stages is analyzed by experiments and kinetic calculations.The causes of abnormal swelling of pellets prepared from Bayan Obo iron ore concentrate are able to analyze from the perspective of reduction kinetics.The results show that carbon deposition occurs in the first stage of reduction of Bayan Obo iron ore concentrate pellets.Reduction of pellets in the second stage is controlled by the interfacial diffusion reaction,and the activation energy is 117.99k J/mol.The higher the reaction energy barrier,the slower the reaction speed.In the second stage,the reduction swelling index of pellets is low.Reduction of pellets in the third stage is controlled by internal diffusion reaction.The reaction activation energy is 15.9k J/mol,and the reaction is intense.Therefore the reduction swelling of pellets in the third stage is the most serious.