Study On Mechanism And Suppression Of Reduction Swelling Of Bayan Obo Iron Concentrate Briquetting

Due to the Bayan Obo iron concentrate contains K₂O+Na₂O and CaF₂,it is easy to cause abnormal or even malignant swelling of the pellets during the reduction process,which will adversely affect the smelting production of the blast furnace,and MgO can improve the reduction swelling performance of pellets.In this paper,the low K,Na,F content of the Australian ore is added with MgO,K₂CO₃+Na₂CO₃,CaF₂ pure reagent,mixed,briquetting,roasting,reduced in three stages?Fe₂O₃?Fe₃O₄,Fe₃O₄?FeO,FeO?Fe?,calculate the swelling rate of each stage,combine the mineral phase microscope and scanning electron microscope to observe the morphology of the briquetting,and analyze it to find out the influence mechanism of K₂O+Na₂O,CaF₂ and MgO on the reduction swelling of the briquetting.Then add the MgO pure reagent into the Bayan Obo concentrate to prepare a fluxing briquetting,and carry out experimental research to provide a theoretical basis for improving the reduction swelling performance of the Bayan Obo iron concentrate,and develop the Baotou self-produced mine and rationally utilize Bayan Obo iron concentrate pellets have scientific guiding significance.The Australian ore was added with 0%,0.3%and 0.6%K₂O+Na₂O?K₂O:Na₂O was 1:1?.The results showed that K₂O+Na₂O increased the melting point of the slag phase during the roasted process,and the slag phase content decreased,the increase of5.41%to 9.07%and 13.88%,hindered the development of hematite continuous crystals and refined the crystal structure of the roasted pellets.The first stage briquetting reduction swelling ratio was 12.36%,9.58%and 8.12%,respectively,the reduction swelling rate is reduced at this stage;the second stage reduction temperature is 1000°C,and the low melting point slag phase containing K and Na is deformed,the FeO oriented growth ability is strong during reduction,and the reduction swelling ratio increases from 4.27%to 6.03%and 7.91%,promotes the reduction swelling of the briquetting;with the reduction of iron oxide,K₂O+Na₂O is solid dissolved in the FeO crystal,causing crystal defects to increase the diffusion coefficient of Fe²⁺,promoting the growth of the third stage iron whisker,resulting in briquetting reduction swelling rate increased from 15.61%to 25.37%and 27.85%,causing malignant swelling of the briquetting.The Australian ore was added with 0%,0.3%and 0.6%CaF₂ pure reagent to prepare the briquetting.When roasted,CaF₂ reacted with SiO₂ to form CaO and SiF₄gas.The porosity of the roasted briquetting increased from 35.51%to 37.27%and40.47%,which hindered the the development of hematite continuous crystals,the first stage reduction swelling rate is 12.36%,9.15%and 8.83%,respectively,reducing the reduction swelling rate at this stage;the second reduction stage,the briquetting reduction swelling rate is 4.27%,5.98%And 7.36%,the increase of the porosity of the briquetting promotes the directional growth of the flourite,resulting in an increase in the swelling ratio of the briquetting;the reduction swelling ratio of the third stage increases from 15.61%to 20.33%and 24.72%,and Ca²⁺and FeO are formed the solid solution,which causes lattice distortion and promotes the growth of iron whiskers,resulting in a significant increase in the reduction swelling ratio.The Australian ore is added with 0%,2%and 4%of MgO pure reagent to prepare the briquetting.During roasted,MgO promotes the formation of magnesium-containing magnetite in the briquetting,and stabilizes the crystal lattice structure of the magnetite.The reduction swelling ratio of the briquetting is 12.36%,and the reduction swelling ratio of the briquetting added with 4%MgO is only 3.85%.MgO obviously inhibits the reduction swelling rate at this stage;the second reduction stage is due to the solid solution of MgO in the FeO lattice.The lattice defects were reduced,and the reduction swelling rates were 4.27%,3.80%and 2.12%,respectively;MgO stabilized the FeO lattice,thereby inhibiting the growth of iron whiskers,and the swelling rate of the third reduction stage decreased from 15.61%to 10.91%.8.22%,which reduces the reduction ratio of the briquetting at this stage.The fluxing briquetting was prepared by adding MgO pure reagent to the Bayan Obo iron concentrate.The experimental results show that the melting point of the slag phase after the addition of MgO during roasting increases,the slag phase decreases,and a stable magnesium-containing magnetite is formed.The swelling rate of the three reduction stages of the briquetting is reduced.The total swelling rates of the three stages are:54.33%,28.09%and 22.25%,respectively,especially inhibiting the growth of the iron whiskers.and the reduction swelling of the third reduction stage of the briquetting.The reduction swelling properties of the fluxing briquettig of Bayan Obo iron concentrate are good.