Al_(2)O_(3)and MgO serve as the primary gangue components in sintered ores,and they are critical for the formation of CaO-Fe_(2)O_(3)-xAl_(2)O_(3)(wt%,C-F-xA)and CaO-Fe_(2)O_(3)-xM gO(wt%,C-F-xM)systems,respectively.I...Al_(2)O_(3)and MgO serve as the primary gangue components in sintered ores,and they are critical for the formation of CaO-Fe_(2)O_(3)-xAl_(2)O_(3)(wt%,C-F-xA)and CaO-Fe_(2)O_(3)-xM gO(wt%,C-F-xM)systems,respectively.In this study,a nonisothermal crystallization thermodynamics behavior of C-F-xA and C-F-xM systems was examined using differential scanning calorimetry,and a phase identification and microstructure analysis for C-F-xA and C-F-xM systems were carried out by X-ray diffraction and scanning electron microscopy.Results showed that in C-F-2A and C-F-2M systems,the increased cooling rates promoted the precipitation of CaFe_(2)O_(4)(CF)but inhibited the formation of Ca_(2)Fe_(2)O_(5)(C2F).In addition,C-F-2A system exhibited a lower theoretical initial crystallization temperature(1566 K)compared to the C-F system(1578 K).This temperature further decreases to 1554 K and 1528 K in the C-F-4A and C-F-8A systems,respectively.However,in C-F-xM system,the increased MgO content raised the crystallization temperature.This is because that the enhanced precipitation of MF(a spinel phase mainly comprised Fe_(3)O_(4)and MgFe_(2)O_(4))and C2F phases suppressed the CF precipitation reaction.In kinetic calculations,the Ozawa method revealed the apparent activation energies of the C-F-2A and C-F-2M systems.Malek's method revealed that the crystallization process in C-F-2A system initially followed a logarithmic law(lnαor lnα2),later transitioning to a reaction order law((1-α)-1or(1-α)^(-1/2),n=2/3)or the lnα2function of the exponential law.In C-F-2M system,it consistently followed the sequencef(α)=(1-α)^(2)(αis the crystallization conversion rate;n is the Avrami constant;?(α)is the differential equations for the model function of C_(2)F and CF crystallization processes).展开更多
High-alumina iron ores(Al_(2)O_(3) content>3.0wt%)are widely utilized in sinter production due to their economic benefits,yet their high alumina content challenges the performance of sinter and the stability of bla...High-alumina iron ores(Al_(2)O_(3) content>3.0wt%)are widely utilized in sinter production due to their economic benefits,yet their high alumina content challenges the performance of sinter and the stability of blast furnaces.This study focuses on the application of high-alumina composite calcium ferrites(SFCA)in the sintering of high-alumina iron ores.By prefabricating calcium ferrites,we aimed to substitute phase adjustment for compositional tuning,particularly examining its effects on enhancing sinter quality at 30wt%,50wt%,and 100wt%replacement ratios of Al_(2)O_(3).Previous work developed two types of high-alumina SFCA(A-type and B-type),with A-type demonstrating superior experimental performance.Our results indicate that increasing the proportion of A-type SFCA in the raw materi-als leads to higher calcium ferrite and composite calcium ferrite contents,while decreasing the proportions of Al_(2)O_(3),CaO,SiO_(2),calcium silicate,and calcium alumino-ferrite(CaAl_(x)Fe_(2-x)O_(4)).Scanning electron microscopy(SEM)and mineralogical analyses reveal that sinter substituted with A-type SFCA primarily consists of SFCA and calcium ferraluminate(CFA),with increasing calcium ferrite content and decreasing porosity and silicate content as the substitution ratio increases.Complete substitution of Al_(2)O_(3) with A-type SFCA enhances the compressive strength of the sinters to 22.57 MPa,a 6.76 MPa improvement over traditional methods.With 100wt%substitution,the redu-cibility reaches 0.85,a 0.33 increase over the baseline(A-type and B-type SFCA are not added).A cost-effective method for SFCA pro-duction using high-alumina ores,hazardous waste,and iron-calcium-based solid waste is proposed to lower production costs and promote the recycling of industrial solid waste.A-type SFCA exhibits significant advantages in mechanical properties,reducibility,and melting characteristics,validating its potential in optimizing sinter performance and reducing carbon emissions,thereby laying a theoretical and practical foundation for the industrial application of high-alumina SFCA.展开更多
With the gradual reduction in high-quality iron ore resources,the global steel industry faces long-term challenges.For example,the continuous increase in the Al_(2)O_(3) content of iron ore has led to a decrease in th...With the gradual reduction in high-quality iron ore resources,the global steel industry faces long-term challenges.For example,the continuous increase in the Al_(2)O_(3) content of iron ore has led to a decrease in the metallurgical performance of sinter and fluctuations in slag properties.Considering calcium ferrite(CF)and composite CF(silico-ferrite of calcium and aluminum,SFCA)play a crucial role as a binding phase in high-alkalinity sinter and exhibit excellent physical strength and metallurgical performance,we propose incorporating excess Al_(2)O_(3) into SFCA to form a new binding phase with excellent properties for high-quality sinter preparation.In the synthesis of high-Al_(2)O_(3) SFCA,two high-Al_(2)O_(3) phases were identified as types A(Al_(1.2)Ca_(2.8)Fe_(8.7)O_(2)0Si_(0.8))and B(Ca_(4)Al_(4.18)Fe_(1.82)Si_(6)O_(26)).Results show that type A SFCA sample had a higher cell density(4.13 g/cm^(3))and longer Fe-O bond length(2.2193Å)than type B(3.46 g/cm^(3) and 1.9415Å),with a significantly greater lattice oxygen concentration(7.86%vs.1.85%),which demonstrates advantages in strength and reducibility.Type A SFCA sample contained a lower proportion of silicates,was predominantly composed of SFCA,and exhibited minimal porosity.Melting point and viscosity simulation tests indicate that type A SFCA sample formed a liquid phase at 880°C with a viscosity range of 0-0.35 Pa·s,which is notably lower than that of type B SFCA sample(1220°C and 0-20 Pa·s).This finding suggests that type A SFCA sample has a low initial melting temperature and viscosity,which facilitates increasing liquid-phase generation and improving flow properties.Such a condition enhances the adhesion to surrounding ore particles.Compressive strength tests reveal that type A SFCA sample(36.83-42.48 MPa)considerably outperformed type B SFCA sample(5.98-12.79 MPa)and traditional sinter(5.02-13.68 MPa).In addition,at 900°C,type A SFCA sample achieved a final reducibility of 0.89,which surpassed that of type B SFCA sample(0.83).In summary,type A SFCA sample demonstrates superior structural,thermophysical,and metallurgical properties,which highlights its promising potential for industrial applications.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.52204331 and 52374315)the Major Industrial Innovation Plan of Anhui Provincial Development and the Reform Commission,China(No.AHZDCYCX-LSDT2023-01)。
文摘Al_(2)O_(3)and MgO serve as the primary gangue components in sintered ores,and they are critical for the formation of CaO-Fe_(2)O_(3)-xAl_(2)O_(3)(wt%,C-F-xA)and CaO-Fe_(2)O_(3)-xM gO(wt%,C-F-xM)systems,respectively.In this study,a nonisothermal crystallization thermodynamics behavior of C-F-xA and C-F-xM systems was examined using differential scanning calorimetry,and a phase identification and microstructure analysis for C-F-xA and C-F-xM systems were carried out by X-ray diffraction and scanning electron microscopy.Results showed that in C-F-2A and C-F-2M systems,the increased cooling rates promoted the precipitation of CaFe_(2)O_(4)(CF)but inhibited the formation of Ca_(2)Fe_(2)O_(5)(C2F).In addition,C-F-2A system exhibited a lower theoretical initial crystallization temperature(1566 K)compared to the C-F system(1578 K).This temperature further decreases to 1554 K and 1528 K in the C-F-4A and C-F-8A systems,respectively.However,in C-F-xM system,the increased MgO content raised the crystallization temperature.This is because that the enhanced precipitation of MF(a spinel phase mainly comprised Fe_(3)O_(4)and MgFe_(2)O_(4))and C2F phases suppressed the CF precipitation reaction.In kinetic calculations,the Ozawa method revealed the apparent activation energies of the C-F-2A and C-F-2M systems.Malek's method revealed that the crystallization process in C-F-2A system initially followed a logarithmic law(lnαor lnα2),later transitioning to a reaction order law((1-α)-1or(1-α)^(-1/2),n=2/3)or the lnα2function of the exponential law.In C-F-2M system,it consistently followed the sequencef(α)=(1-α)^(2)(αis the crystallization conversion rate;n is the Avrami constant;?(α)is the differential equations for the model function of C_(2)F and CF crystallization processes).
基金supported by the National Natural Science Foundation of China(Nos.52204331 and 52374315)Major Industrial Innovation Plan of Anhui Provincial Development and Reform Commission,China(No.AHZDCYCXLSDT2023-01).
文摘High-alumina iron ores(Al_(2)O_(3) content>3.0wt%)are widely utilized in sinter production due to their economic benefits,yet their high alumina content challenges the performance of sinter and the stability of blast furnaces.This study focuses on the application of high-alumina composite calcium ferrites(SFCA)in the sintering of high-alumina iron ores.By prefabricating calcium ferrites,we aimed to substitute phase adjustment for compositional tuning,particularly examining its effects on enhancing sinter quality at 30wt%,50wt%,and 100wt%replacement ratios of Al_(2)O_(3).Previous work developed two types of high-alumina SFCA(A-type and B-type),with A-type demonstrating superior experimental performance.Our results indicate that increasing the proportion of A-type SFCA in the raw materi-als leads to higher calcium ferrite and composite calcium ferrite contents,while decreasing the proportions of Al_(2)O_(3),CaO,SiO_(2),calcium silicate,and calcium alumino-ferrite(CaAl_(x)Fe_(2-x)O_(4)).Scanning electron microscopy(SEM)and mineralogical analyses reveal that sinter substituted with A-type SFCA primarily consists of SFCA and calcium ferraluminate(CFA),with increasing calcium ferrite content and decreasing porosity and silicate content as the substitution ratio increases.Complete substitution of Al_(2)O_(3) with A-type SFCA enhances the compressive strength of the sinters to 22.57 MPa,a 6.76 MPa improvement over traditional methods.With 100wt%substitution,the redu-cibility reaches 0.85,a 0.33 increase over the baseline(A-type and B-type SFCA are not added).A cost-effective method for SFCA pro-duction using high-alumina ores,hazardous waste,and iron-calcium-based solid waste is proposed to lower production costs and promote the recycling of industrial solid waste.A-type SFCA exhibits significant advantages in mechanical properties,reducibility,and melting characteristics,validating its potential in optimizing sinter performance and reducing carbon emissions,thereby laying a theoretical and practical foundation for the industrial application of high-alumina SFCA.
基金financially supported by the National Natural Science Foundation of China(Nos.52204331 and 52374315)the Major Industrial Innovation Plan of the Anhui Provincial Development and Reform Commission,China(No.AHZDCYCX-LSDT2023-01).
文摘With the gradual reduction in high-quality iron ore resources,the global steel industry faces long-term challenges.For example,the continuous increase in the Al_(2)O_(3) content of iron ore has led to a decrease in the metallurgical performance of sinter and fluctuations in slag properties.Considering calcium ferrite(CF)and composite CF(silico-ferrite of calcium and aluminum,SFCA)play a crucial role as a binding phase in high-alkalinity sinter and exhibit excellent physical strength and metallurgical performance,we propose incorporating excess Al_(2)O_(3) into SFCA to form a new binding phase with excellent properties for high-quality sinter preparation.In the synthesis of high-Al_(2)O_(3) SFCA,two high-Al_(2)O_(3) phases were identified as types A(Al_(1.2)Ca_(2.8)Fe_(8.7)O_(2)0Si_(0.8))and B(Ca_(4)Al_(4.18)Fe_(1.82)Si_(6)O_(26)).Results show that type A SFCA sample had a higher cell density(4.13 g/cm^(3))and longer Fe-O bond length(2.2193Å)than type B(3.46 g/cm^(3) and 1.9415Å),with a significantly greater lattice oxygen concentration(7.86%vs.1.85%),which demonstrates advantages in strength and reducibility.Type A SFCA sample contained a lower proportion of silicates,was predominantly composed of SFCA,and exhibited minimal porosity.Melting point and viscosity simulation tests indicate that type A SFCA sample formed a liquid phase at 880°C with a viscosity range of 0-0.35 Pa·s,which is notably lower than that of type B SFCA sample(1220°C and 0-20 Pa·s).This finding suggests that type A SFCA sample has a low initial melting temperature and viscosity,which facilitates increasing liquid-phase generation and improving flow properties.Such a condition enhances the adhesion to surrounding ore particles.Compressive strength tests reveal that type A SFCA sample(36.83-42.48 MPa)considerably outperformed type B SFCA sample(5.98-12.79 MPa)and traditional sinter(5.02-13.68 MPa).In addition,at 900°C,type A SFCA sample achieved a final reducibility of 0.89,which surpassed that of type B SFCA sample(0.83).In summary,type A SFCA sample demonstrates superior structural,thermophysical,and metallurgical properties,which highlights its promising potential for industrial applications.
