Softening–melting behavior of mixed burden based on low-magnesium sinter and fluxed pellets

A low MgO content in sinter is conducive to reduce the MgO content in blast furnace slag.This study investigated the effect of MgO content in sinter on the softening–melting behavior of the mixed burden based on fluxed pellets.When the MgO content increased from 1.31 wt% to 1.55 wt%, the melting temperature of sinter increased to 1521℃.Such an increase was due to the formation of the high-meltingpoint slag phase.The reduction degradation index of sinter with 1.31 wt% MgO content was better than that of others.The initial softening temperature of the mixed burden increased from 1104 to 1126℃ as MgO content in sinter increased from 1.31 wt% to 1.55 wt%, and the melting temperature decreased from 1494 to 1460℃.The permeability index(S-value) of mixed burden decreased to 594.46 kPa·℃ under a high MgO content with 1.55 wt%, indicating that the permeability was improved.The slag phase composition of burden was mainly akermarite(Ca_(2)MgSiO_(7)) when the MgO content in sinter was 1.55 wt%.The melting point of akermarite is 1450℃, which is lower than other phases.

Diffusion and reaction mechanism of limestone and quartz in fluxed iron ore pellet roasting process

The increase to the proportion of fluxed pellets in the blast furnace burden is a useful way to reduce the carbon emissions in the ironmaking process.In this study,the interaction between calcium carbonate and iron ore powder and the mineralization mechanism of fluxed iron ore pellet in the roasting process were investigated through diffusion couple experiments.Scanning electron microscopy with energy dispersive spectroscopy was used to study the elements’diffusion and phase transformation during the roasting process.The results indicated that limestone decomposed into calcium oxide,and magnetite was oxidized to hematite at the early stage of preheating.With the increase in roasting temperature,the diffusion rate of Fe and Ca was obviously accelerated,while the diffusion rate of Si was relatively slow.The order of magnitude of interdiffusion coefficient of Fe_(2)O_(3)-CaO diffusion couple was 10^(−10) m^(2)·s^(−1) at a roasting temperature of 1200℃for 9 h.Ca_(2)Fe_(2)O_(5) was the initial product in the Fe_(2)O_(3)-CaO-SiO_(2) diffusion interface,and then Ca_(2)Fe_(2)O_(5) continued to react with Fe_(2)O_(3) to form CaFe_(2)O_(4).With the expansion of the diffusion region,the sillico-ferrite of calcium liquid phase was produced due to the melting of SiO_(2) into CaFe_(2)O_(4),which can strengthen the consolidation of fluxed pellets.Furthermore,andradite would be formed around a small part of quartz particles,which is also conducive to the consolidation of fluxed pellets.In addition,the principle diagram of limestone and quartz diffusion reaction in the process of fluxed pellet roasting was discussed.

High-chromium vanadium-titanium magnetite all-pellet integrated burden optimization and softening-melting behavior based on flux pellets

High-chromium vanadium-titanium magnetite(HVTM)is a crucial polymetallic-associated resource to be developed.The allpellet operation is a blast furnace trend that aims to reduce carbon dioxide emissions in the future.By referencing the production data of vanadium-titanium magnetite blast furnaces,this study explored the softening-melting behavior of high-chromium vanadium-titanium magnetite and obtained the optimal integrated burden based on flux pellets.The results show that the burden with a composition of 70wt%flux pellets and 30wt%acid pellets exhibits the best softening-melting properties.In comparison to that of the single burden,the softening-melting characteristic temperature of this burden composition was higher.The melting interval first increased from 307 to 362℃and then decreased to 282℃.The maximum pressure drop(ΔPmax)decreased from 26.76 to 19.01 kPa.The permeability index(S)dropped from 4643.5 to 2446.8 kPa·℃.The softening-melting properties of the integrated burden were apparently improved.The acid pellets played a role in withstanding load during the softening process.The flux pellets in the integrated burden exhibited a higher slag melting point,which increased the melting temperature during the melting process.The slag homogeneity and the TiC produced by over-reduction led to the gas permeability deterioration of the single burden.The segregation of the flux and acid pellets in the HVTM proportion and basicity mainly led to the better softening-melting properties of the integrated burden.

Improving properties of fluxed iron ore pellets with high-silica by regulating liquid phase

With rapid development of the pellet production under the background of green development,high-quality iron concentrates were gradually exhausted;thus,using high-silica iron concentrates was expected to be a promising way to relieve resource pressure for pellet production.However,increasing the proportion of high-silica acid pellets into the furnace led to worse blast furnace slag,and the metallurgical properties of high-silica pellets were imperfect.To understand the reciprocal effects of basicity(CaO/SiO_(2))and MgO content on the properties of the high-silica pellets,the phase compositions and microstructure were investigated using X-ray diffraction and scanning electron microscope,equipped with energy dispersive X-ray spectrometry.The results indicated that simply increasing MgO content from O to 2.50 wt.%could decrease the reduction swelling index,but the compressive strength rapidly declined due to the formation of magnesioferrite.However,adding CaO to 2.50 wt.%MgO pellets greatly improved the pellet qualities,which could be attributed to a substantial increase in the amount of high-melting-point silicate liquid phase.

Consolidation mechanism of fluxed hematite pellets

Fluxed pellets are becoming a popular burden for the blast furnace in China.The basicity(wCaO/wSiO_(2))ranging from 0.33 to 1.33 was prepared by adding CaO analytical reagent.The phase change of pellets during roasting was analyzed by the FactSage software,and the consolidation mechanism of fluxed hematite pellets was also investigated.The results show that the increase in basicity gradually increases the diameter,volume,and porosity of pellets.The diameter,volume,and porosity of pellets change slightly when the basicity is greater than 0.83.The increase in roasting temperature gradually decreases the volume and porosity of pellets.With the increase in pellet basicity,the compressive strength of pellets reaches the maximum at the basicity of 0.83.The higher the roasting temperature is,the more the slag phase is produced,thereby accelerating Fe^(3+)diffusion and promoting Fe_(2)O_(3) recrystallization.In addition,the consolidation effect of the slag phase after cooling improves the consolidation strength of fluxed pellets.When the basicity is higher than 0.83,the slag phase decreases with the increase in basicity,and the high-temperature solid solution,such as melilite and spinel,increases,thereby hindering Fe2O3 recrystallization.

Effect of quaternary basicity on softening-melting behavior of primary slag based on magnesium flux pellet

It is generally accepted that the softening-melting properties of ferrous burden play a vital role in optimizing the shape and position of cohesive zone.The effect of quaternary basicity and atmosphere on softening,melting and permeation temperatures of primary slag based on magnesium flux pellet was investigated by visualization method.The mechanisms were analyzed utilizing thermodynamic calculation,X-ray diffraction analysis and electron probe microanalysis.The results indicated that the softening and melting temperatures of oxide samples increased by approximately 120℃with increasing quaternary basicity from 0.3 to 1.2 owing to the formation of slag phases with high melting point and solid Fe.Meanwhile,the difference between softening and melting temperatures decreased from 21 to 11℃.The permeation temperature was not affected by the quaternary basicity and fluctuated around a level of 1250 C,given that the permeation temperature depends on the wettability between slag and coke bed.On the other hand,as the ratios of CO/CO_(2) varied from 3/7 to 7/3,there were no significant differences in either the softening or melting temperatures,whereas the permeation temperature was increased from 1239 to 1271℃ since the reduction of FeO-bearing phases to solid Fe could decrease the wettability between slag and coke bed.