| In recent years,with carbon peaking and carbon neutralization becoming an important strategy for China’s development,major iron and steel enterprises also began to take low energy consumption and low emission as the development goal,and the rational allocation of blast furnace burden is one of the important methods to achieve this goal.In order to reduce the charging ratio of sinter with high energy consumption and high pollution,it is very important to improve the basicity of pellet.The gangue composition is an important factor affecting the pellet properties.Therefore,it is of great significance to explore the influence of gangue composition on the properties of flux pellets after roasting and reduction.In this paper,the effects of gangue composition on the roasting and reduction properties of pellets are studied from the macro and micro perspectives.As for the experiment of roasting part,this paper presses the pellets with different gangue content and alkalinity by mixing different proportions of analytical pure reagents.After roasting,by measuring its crystallinity,it is found that with the increase of alkalinity,the liquid phase generated in the roasting process will gradually increase,and the increase of liquid phase improves the kinetic conditions of hematite recrystallization,so as to improve the crystallinity of the pellets after roasting.Similarly,Increasing the roasting temperature has the same effect.The increase of Al2O3 content in pellets will reduce the amount of slag phase and Fe element in slag,which will reduce the crystallinity of pellets after roasting,and the phenomenon of Al2O3 inhibiting the formation of slag phase is particularly obvious in high alkalinity pellets.Therefore,in order to improve the pelletizing performance of flux pellets,the content of Al2O3 in pellets must be reduced.For the medium temperature reduction of pellets,by pressing pellets with different gangue components and measuring their reduction rate after roasting and reduction,it is found that Cao and Mg O can improve the medium temperature reduction performance of pellets,while Si O2 can inhibit the reduction of pellets.Then,the microscopic properties of Fe2O3{1 0 4}crystal surface are simulated by DFT.It is found that when the temperature is greater than 1200℃,Mg and Ca will preferentially form replacement defects with Fe2O3{1 0 4},so that they form ionic bonds with surrounding O atoms,while Si forms covalent bonds,and the energy required for covalent bonds to break bonds is higher than that of ionic bonds.Therefore,Ca O and Mg O will improve the reducibility,while Si O2 will inhibit the reduction of pellets.After that,this paper studies the reduction expansibility of pellets.It is found that with the increase of alkalinity,the reduction expansion rate of pellets increases first and then decreases.Through DFT and AIMD to simulate the micro properties and behavior of Fe O{0 0 1}surface,it is concluded that in the reduction process,because Ca has stronger binding ability to electrons,its electrons are not easy to be taken away by surrounding O atoms,so it is easy to form defects in the form of gaps,Moreover,after the defect is formed,an Fe atom will be pushed out of the lattice surface,providing free iron atoms and growth sites for the growth of iron whiskers.When there are more Ca atoms,new metal bonds will be formed between too many Fe atoms overflowing from the surface,making them unable to move freely,and deteriorating the dynamic conditions for the formation of iron whiskers.Therefore,with the increase of alkalinity,the reduction expansion rate first increases and then decreases.For Si O2,at 900℃,Si can effectively inhibit the vibration of Fe O{0 0 1}surface atoms,so that Fe atoms are not easy to break away from binding and become free Fe due to oscillation,so as to inhibit the growth of iron whiskers.For Mg and Al,they will not cause lattice distortion after forming defects,and the defect formation energy of the defects formed by their reaction with Fe O{0 0 1}surface is significantly lower than that of Ca,so they can also inhibit the growth of iron whiskers.In this paper,the effect of reducing atmosphere on reduction expansion is also studied.It is found that the reduction expansion rate of pellets reduced in H2atmosphere is significantly lower than that in CO atmosphere.SEM shows that there is no iron whisker on the surface of pellets reduced in H2 atmosphere.After DFT simulation,it is found that CO can drag the free Fe atom to move at 900℃,which improves the kinetic conditions of iron whisker growth,Thus,the growth of iron whiskers is promoted,while H2 cannot drag the Fe atoms to move.Therefore,no obvious iron whiskers are seen on the reduced surface of pure H2,and the reduction expansion rate is lower than that of CO atmosphere reduction. |
PDF Full Text Request