The Research Of Inherited Behavior Of Lanthanum In The Process Of Ferrous Metallurgy Based On Bayan Obo Mine

Bayan Obo mine is the world’s largest symbiotic mine of rare earth resource reserves,which is also one of the main sources of iron ore in Baotou Iron and Steel Group.At the end of the 1990s,Chinese scientists studied the residual trace elements left from iron ore in China.Finally,found that the content of rare earth lanthanum and cerium in the steel which used Bayan Obo iron mine were about 5ppm～10ppm.However,how do the rare earth elements in the iron ore remain in the final steel product during the steel metallurgical process?What are the factors affecting this behavioral process and the law of its influence?Whether the whole process can be controlled,so as to play the role of superior resources?None of the above problems have been systematically studied.In this paper,the inheritance behavior of rare earth lanthanum in steel metallurgy process based on Bayan Obo iron ore has been studied.Firstly,the existence states of rare earth lanthanum in raw materials,the existence states and flow trends in various metallurgical processes were studied and acquired the key process of controlling the behavior of lanthanum.Then,the inheritance mechanism and key influencing factors of lanthanum in key processes and their influence laws have been analyzed.Finally,the direct-alloying utilization of secondary resources of rare earth in the blast furnace slag during steel making process have been explored.The results indicated that:lanthanum exists in tron ore concentrate mainly in two states,bastnaesite and monazite.In sintering and pelletizing,it mainly exists in two states of lanthanum oxide and undecomposed monazite.After the blast furnace iron-making,the lanthanum mainly enters into the blast furnace slag.All of lanthanum remaining iin the molten iron becomes in the form of oxide and floats up into the slag after being blown by the converter.When the deoxidation process of the molten steel was finished,the[La]in the molten steel is increased,and continues to inherit in the molten steel,and finally gradually decreases until it solidifies into continuous castings.The rare earth lanthanum content inherit to the continuous castings which are 0.1～1.1 ppm.The blast furnace iron-making process and the deoxidation process after the completion of the converter blowing process determine the inherited amount of lanthanum in the lolten steel are the key processes in the letallurgical process.In the blast furnace iron-making process,the lanthanum in the sintering and pellets participates in the slagging in the form of oxides which is mainly freely mobile（La₂O₃）based on the silicon oxytetrahedron.Then（La₂O₃）is gradually deoxidized by carbon,and finally reduced to LaC₂,and part of LaC₂ can be dissolved into molten iron.[La]in molten iron is adsorbed by oxygen-containing functional groups on porous graphitized coke which cannot float in molten iron,and finally exists in pig iron in the form of graphite phase,thereby,completing the inheritance process of rare earth lanthanum in the blast furnace iron、making process.The amount of inheritance in the blast furnace iron-making process decreases with the increase of basicity.Increases with the increase of rare earth content in the slag,and the effect is most significant.The increase of furnace temperature helps the reduction reaction,the amount of inheritance increases.After converter blowing,lanthanum in molten steel exists in the form of oxide and floats to slag,which makes it difficult to inherit to the subsequent process.In the deoxidation process of the converter,the oxide of lanthanum which is not completely floated in the molten steel can be reduced to Al₁₁La₃ and La₃Si₂ intermediate compounds by Aland Si,or reduced to La by Ca,and then dissolved into the molten steel to continue the inheritance.In the LF refining process,the rare earth lanthanum in the protective slag exists mainly freely mobile（La₂O₃）based on the silicon oxytetrahedron.After adding aluminum particles to the protective slag,（La₂O₃）in the slag can be reduced to(Ca_0.8La_0.2)Si₂.The inheritance of[La]in LF refining molten steel is mainly affected by the indirect oxidation behavior of（FeO+MnO）in the slag.The higher the content of FeO+MnO in slag,the more difficult it is to inherit in molten steel.Increasing the activity of La₂O₃ in LF refining slag and reducing the activity of（FeO）and（MnO）are beneficial to increase the inherit of rare earth lanthanum in molten steel.The most significant controlling factors are to increase the content of La₂O₃ in the slag and reduce the content of FeO and MnO,The rare earth element in the blast fulnace slag can be gradually reduced by aluminum.First,aluminum can reduce the silicon oxide in the blast furnace slag to silicon.Then,silicon can be used as a reducing agent to reduce calcium and rare earth in the blast furnace slag into(Ca_0.8RE_0.2)Si₂,Thus,blast furnace slag can be directly-alloyed in molten steel.When using blast furnace slag for direct alloying,the importance of influencing factors is ranked as:amount of reducing agent>amount of protective slag>sampling time>amount of blast furnace slag.Among them,the amount of reducing agent and the amount of protective slag are very significant,and the sampling time and the amount of blast furnace slag are significantly affected.