Development and progress on hydrogen metallurgy

Hydrogen metallurgy is a technology that applies hydrogen instead of carbon as a reduction agent to reduce CO2 emission,and the use of hydrogen is beneficial to promoting the sustainable development of the steel industry.Hydrogen metallurgy has numerous applications,such as H2reduction ironmaking in Japan,ULCORED and hydrogen-based steelmaking in Europe;hydrogen flash ironmaking technology in the US;HYBRIT in the Nordics;Midrex H2TM by Midrex Technologies,Inc.(United States);H2FUTURE by Voestalpine(Austria);and SALCOS by Salzgitter AG(Germany).Hydrogen-rich blast furnaces(BFs)with COG injection are common in China.Running BFs have been industrially tested by AnSteel,XuSteel,and BenSteel.In a currently under construction pilot plant of a coal gasification–gas-based shaft furnace with an annual output of 10000 t direct reduction iron(DRI),a reducing gas composed of 57 vol%H2 and 38 vol%CO is prepared via the Ende method.The life cycle of the coal gasification–gas-based shaft furnace–electric furnace short process(30 wt%DRI+70 wt%scrap)is assessed with 1 t of molten steel as a functional unit.This plant has a total energy consumption per ton of steel of 263.67 kg standard coal and a CO2 emission per ton of steel of 829.89 kg,which are superior to those of a traditional BF converter process.Considering domestic materials and fuels,hydrogen production and storage,and hydrogen reduction characteristics,we believe that a hydrogen-rich shaft furnace will be suitable in China.Hydrogen production and storage with an economic and large-scale industrialization will promote the further development of a full hydrogen shaft furnace.

Effect of MgO content in sinter on the softening–melting behavior of mixed burden made from chromium-bearing vanadium–titanium magnetite

The effect of sinter with different MgO contents on the softening-melting behavior of mixed burden made from chro- mium-bearing vanadium-titanium magnetite was investigated. The results show that with increasing MgO content in the sinter, the softening interval and melting interval increased and the location of the cohesive zone shifted downward slightly and became moderately thicker. The softening-melting characteristic value was less pronounced when the MgO content in the sinter was 2.98wt%-3.40wt%. Increasing MgO content in the sinter reduced the content and recovery of V and Cr in the dripped iron. In addition, greater MgO contents in the sinter resulted in the generation of greater amounts of high-melting-point components, which adversely affected the permeability of the mixed burden. When the softening-melting behavior of the mixed burden and the recovery of valuable elements were taken into account, proper MgO con- tents in the sinter and slag ranged from 2.98wt% to 3.40wt% and from 11.46wt% to 12.72wt%, respectively, for the smelting of burden made from chromium-bearing vanadium-titanium magnetite in a blast furnace.

不锈钢粉尘和红土镍矿碳热还原新工艺多目标协同优化

采用基于响应面法的中心复合设计,通过碳热还原实现不锈钢粉尘和红土镍矿中Fe、Cr和Ni金属回收的多目标协同优化,获得高金属回收率和高品位Fe-Cr-Ni-C合金颗粒。结果表明,红土镍矿的配入量和还原温度对金属回收率有显著影响,还原产物中金属Fe、Cr和Ni的回收率之间存在显著的交互作用。通过模型优化得到的最优工艺参数为:红土镍矿配入量5.47%、还原温度1428.02℃、还原时间23.10 min和碳氧比(FC/O)0.85。该模型的Fe、Cr和Ni的回收率预测结果分别为93.15%、91.63%和92.70%。

Metalizing reduction and magnetic separation of vanadium titano-magnetite based on hot briquetting

To achieve high efficiency utilization of Panzhihua vanadium titano-magnetite, a new process of metalizing reduction and magnetic separation based on hot briquetting is proposed, and factors that affect the cold strength of the hot-briquetting products and the efficiency of reduction and magnetic separation are successively investigated through laboratory experiments. The relevant mechanisms are elucidated on the basis of microstructural observations. Experimental results show that the optimal process parameters for hot briquetting include a hot briquetting temperature of 475°C, a carbon ratio of 1.2, ore and coal particle sizes of less than 74 μm. Additionally, with respect to metalizing reduction and magnetic separation, the rational parameters include a magnetic field intensity of 50 mT, a reduction temperature of 1350°C, a reduction time of 60 min, and a carbon ratio of 1.2. Under these above conditions, the crushing strength of the hot-briquetting agglomerates is 1480 N, and the recovery ratios of iron, vanadium, and titanium are as high as 91.19%, 61.82%, and 85.31%, respectively. The new process of metalizing reduction and magnetic separation based on hot briquetting demonstrates the evident technological advantages of high efficiency separation of iron from other valuable elements in the vanadium titano-magnetite.

Effects of smelting parameters on the slag/metal separation behaviors of Hongge vanadium-bearing titanomagnetite metallized pellets obtained from the gas-based direct reduction process

Smelting separations of Hongge vanadium-bearing titanomagnetite metallized pellets（HVTMP）prepared by gas-based direct reduction were investigated,and the effects of smelting parameters on the slag/metal separation behaviors were analyzed.Relevant mechanisms were elucidated using X-ray diffraction analysis,FACTSAGE 7.0 calculations,and scanning electron microscopy observations.The results show that,when the smelting temperature,time,and C/O ratio are increased,the recoveries of V and Cr of HVTMP in pig iron are improved,the recovery of Fe initially increases and subsequently decreases,and the recovery of Ti O_2 in slag decreases.When the smelting Ca O/Si O_2 ratio is increased,the recoveries of Fe,V,and Cr in pig iron increase and the recovery of Ti O_2 in slag initially increases and subsequently decreases.The appropriate smelting separation parameters for HVTMP are as follows：smelting temperature of 1873 K;smelting time of 30–50 min;C/O ratio of 1.25;and Ca O/Si O_2 ratio of 0.50.With these optimized parameters（smelting time：30 min）,the recoveries of Fe,V,Cr,and Ti O_2 are 99.5%,91.24%,92.41%,and 94.86%,respectively.

Effects of MgO/Al2O3 ratio on viscous behaviors and structures of MgO-Al2O3-TiO2-CaO-SiO2 slag systems with high TiO2 content and low CaO/SiO2 ratio

The effects of MgO/Al2 O3 ratio on the viscous behaviors of MgO-Al2 O3-TiO2-CaO-SiO2 systems were investigated by the rotating cylinder method.Raman spectroscopy was used to analyze the structural characteristics of slag and Factsage 7.0 was adopted to demonstrate the liquidus temperature of slag.The results show that the viscosity and activation energy for viscous flow decrease when the MgO/Al2O3 ratio increases from 0.82 to 1.36.The break point temperature and liquidus temperature of slag initially decrease and subsequently increase.The complex viscous structures are gradually depolymerized to simple structural units.In conclusion,with the increase of MgO/Al2O3 ratio,the degree of polymerization of slag decreases,which improves the fluidity of slag.The variations of liquidus temperature of slag lead to the same changes of break point temperature.

Preparing high-purity iron by direct reduction?smelting separation of ultra-high-grade iron concentrate

A new process for preparing high-purity iron(HPI)was proposed,and it was investigated by laboratory experiments and pilot tests.The results show that under conditions of a reduced temperature of 1075°C,reduced time of 5 h,and CaO content of 2.5wt%,a DRI with a metallization rate of 96.5%was obtained through coal-based direct reduction of ultra-high-grade iron concentrate.Then,an HPI with a Fe purity of 99.95%and C,Si,Mn,and P contents as low as 0.0008wt%,0.0006wt%,0.0014wt%,and 0.0015wt%,respectively,was prepared by smelting separation of the DRI using a smelting temperature of 1625°C,smelting time of 45 min,and CaO content of 9.3wt%.The product of the pilot test with a scale of 0.01 Mt/a had a lower impurity content than the Chinese industry standard.An HPI with a Fe purity of 99.98wt%can be produced through the direct reduction?smelting separation of ultra-high-grade iron concentrate at relatively low cost.The proposed process shows a promising prospect for application in the future.

Optimized use of MgO flux in the agglomeration of high-chromium vanadium–titanium magnetite

The optimized use of MgO flux in the agglomeration of high-chromium vanadium-titanium magnetite was investigated system- atically through sinter and pellet experiments. MgO was added in the form of magnesite. When the content of MgO in the sinter was in- creased from 1.95wt% to 2.63wt%, the low-temperature reduction degradation index increased from 80.57% to 82.71%. When the content of MgO in the pellet was increased from 1.14wt% to 2.40wt%, the reduction swelling index decreased from 15.2% to 8.6%; however, the com- pressive strength of the oxidized pellet decreased dramatically and it was 1985 N with an MgO content of 1.14wt%. This compressive strength does not satisfy the requirements for blast-furnace production. When all of the aforementioned results were taken into account, the sinter with a high MgO content （2.63wt%） matching the pellet with a low MgO content （less than 1.14wt%） was the rational burden structure for smelting high-chromium vanadium-titanium magnetite in blast furnaces.

Multi-objective collaborative optimization of metallurgical properties of iron carbon agglomerates using response surface methodology

Iron carbon agglomerates(ICA)are used to realize low-carbon blast furnace ironmaking.In this study,the central composite design based on response surface methodology was used to synergistically optimize the compressive strength,reactivity,and post-reaction strength of ICA.Results show that the iron ore addition ratio significantly influences the compressive strength,reactivity,and post-reaction strength of ICA.The iron ore addition ratio and carbonization temperature or the iron ore addition ratio and carbonization time exert significant interaction effects on the compressive strength and reactivity of ICA,but it has no interaction effects on the post-reaction strength of ICA.In addition,the optimal process parameters are as follows:iron ore addition ratio of 15.30 wt%,carbonization temperature of 1000℃,and carbonization time of 4.27 h.The model prediction results of compressive strength,reactivity,and post-reaction strength are 4026 N,55.03%,and 38.24%,respectively,which are close to the experimental results and further verify the accuracy and reliability of the models.

Effects of MgO and TiO_2 on the viscous behaviors and phase compositions of titanium-bearing slag

The effects of MgO and TiO_2 on the viscosity, activation energy for viscous flow, and break-point temperature of titanium-bearing slag were studied. The correlation between viscosity and slag structure was analyzed by Fourier transform infrared（FTIR） spectroscopy. Subsequently, main phases in the slag and their content changes were investigated by X-ray diffraction and Factsage 6.4 software package. The results show that the viscosity decreases when the MgO content increases from 10.00wt% to 14.00wt%. Moreover, the break-point temperature increases, and the activation energy for viscous flow initially increases and subsequently decreases. In addition, with increasing TiO_2 content from 5.00wt% to 9.00wt%, the viscosity decreases, and the break-point temperature and activation energy for viscous flow initially decrease and subsequently increase. FTIR analyses reveal that the polymerization degree of complex viscous units in titanium-bearing slag decreases with increasing MgO and TiO_2 contents. The mechanism of viscosity variation was elucidated. The basic phase in experimental slags is melilite. Besides, as the MgO content increases, the amount of magnesia–alumina spinel in the slag increases. Similarly, the sum of pyroxene and perovskite phases in the slag increases with increasing TiO_2 content.

Stepwise recovery of magnesium from low-grade ludwigite ore based on innovative and clean technological route

A novel and clean technological route for the comprehensive utilization of low-grade ludwigite ore was proposed, inwhich magnesium was extracted by metallizing reduction？magnetic separation, sulfuric acid leaching and ethanol precipitationoperation. Meanwhile, iron-rich product, silicon-rich product and boron-rich product were obtained, respectively. In the process ofmetallizing reduction-magnetic separation, 94.6% of magnesium was enriched in the non-magnetic substance from the ore reducedat 1250 ℃ for 60 min with the ore size of 0.50-2.00 mm and coal size of 0.50-1.50 mm. When the non-magnetic substance wasleached at 90 ℃ for 15 min with the liquid-to-solid ratio of 7：1, 87.4% of magnesium was leached into the liquor separated fromsilicon gathering in leaching residue. The ethanol precipitation was conducted for 30 min with the ethanol-to-original liquid volumeratio of 1.5：1 at room temperature. 97.2% of magnesium was precipitated out with the initial concentration of 0.8 mol/L in the formof MgSO4·7H2O.

Reduction mechanism of high-chromium vanadium–titanium magnetite pellets by H_2–CO–CO_2 gas mixtures

The reduction of high-chromium vanadium–titanium magnetite as a typical titanomagnetite containing 0.95wt% V2O5 and 0.61wt% Cr2O3 by H2–CO–CO2 gas mixtures was investigated from 1223 to 1373 K. Both the reduction degree and reduction rate increase with increasing temperature and increasing hydrogen content. At a temperature of 1373 K, an H2/CO ratio of 5/2 by volume, and a reduction time of 40 min, the degree of reduction reaches 95%. The phase transformation during reduction is hypothesized to proceed as follows： Fe2O3 → Fe3O4 → FeO → Fe; Fe9 TiO 15 ＋ Fe2Ti3O9 → Fe2.75Ti0.25O4 → FeT iO 3 → TiO 2;（Cr0.15V0.85）2O3 → Fe2VO4; and Cr1.3Fe0.7O3 → FeC r2O4. The reduction is controlled by the mixed internal diffusion and interfacial reaction at the initial stage; however, the interfacial reaction is dominant. As the reduction proceeds, the internal diffusion becomes the controlling step.

Novel blast furnace operation process involving charging with low-titanium vanadium–titanium magnetite carbon composite hot briquette

An innovative process of blast furnace （BF） operation involving charging with low-titanium vanadium-titanium magnetite carbon composite hot briquette （LVTM-CCB） was proposed for utilizing LVTM and conserving energy, In this study, the effect of LVTM-CCB charging ratio on the softening, melting, and dripping behaviors of the mixed burden was explored systemically, and the migration of valu- able elements V and Cr was extensively investigated. The results show that with increasing LVTM-CCB charging ratio, the softening inter- val T40 - T4 increases from 146.1℃ to 266.1℃, and the melting interval To - Ts first decreases from 137.2℃ to 129.5℃ and then increases from 129.5℃ to 133.2℃. Moreover, the cohesive zone becomes narrower and then wider, and its location shifts slightly downward. In addi- tion, the recovery ratios of V and Cr in dripped iron first increase and then decrease, reaching maximum values of 14.552% and 28.163%, respectively, when the charging ratio is 25%. A proper LVTM-CCB charging ratio would improve the softening--melting behavior of the mixed burden; however, Ti（C,N） would be generated rapidly in slag when the charging ratio exceeds 25%, which is not favorable for BF op- eration. When considering the comprehensive softening-melting behavior of the mixed burden and the recovery ratios of V and Cr, the rec- ommended LVTM-CCB charging ratio is 20%.

Effect of Cr_2O_3 addition on the oxidation induration mechanism of Hongge vanadium titanomagnetite pellets

As part of a research project to develop a novel clean smelting process for the comprehensive utilization of Hongge vanadium titanomagnetite（HVTM）, in this study, the effect of Cr2O3 addition on the oxidation induration mechanism of HVTM pellets（HVTMPs） was investigated in detail. The results showed that the compressive strength of the HVTMPs was greatly weakened by the Cr2O3 addition, mainly because of a substantial increase in the porosity of the HVTMPs. The Cr2O3 addition marginally affected the phase composition but greatly affected the microstructural changes of the HVTMPs. Increased amounts of Cr2O3 resulted in a decrease in the uniform distribution of the hematite grains and in an increase in the Fe–Cr solid solutions（Fe1.2Cr0.8O3 and Fe0.7Cr1.3O3） embedded in the hematite grains. Moreover, the compact hematite was destroyed by forming a dispersed structure and the hematite recrystallization was hindered during the oxidation induration, which adversely affected the compressive strength. On the basis of these results, a schematic was formulated to describe the oxidation induration mechanism with different amounts of added Cr2O3. This study provides theoretical and technical foundations for the effective production of HVTMPs and a reference for chromium-bearing minerals.

Reduction behavior and mechanism of Hongge vanadium titanomagnetite pellets by gas mixture of H2 and CO

Hongge vanadium titanomagnetite（HVTM）pellets were reduced by H2-CO gas mixture for simulating the reduction processes of Midrex and HYL-III shaft furnaces.The influences of reduction temperature,ratio ofφ（H2）toφ（CO）,and pellet size on the reduction of HVTM pellets were evaluated in detail and the reduction reaction kinetics was investigated.The results show that both the reduction degree and reduction rate can be improved with increasing the reduction temperature and the H2 content as well as decreasing the pellet size.The rational reduction parameters are reduction temperature of 1050℃,ratio ofφ（H2）toφ（CO）of 2.5,and pellet diameter in the range of 8-11 mm.Under these conditions（pellet diameter of 11mm）,final reduction degree of 95.51% is achieved.The X-ray diffraction（XRD）pattern shows that the main phases of final reduced pellets under these conditions（pellet diameter of 11 mm）are reduced iron and rutile.The peak intensity of reduced iron increases obviously with the increase in the reduction temperature.Besides,relatively high reduction temperature promotes the migration and coarsening of metallic iron particles and improves the distribution of vanadium and chromium in the reduced iron,which is conducive to subsequent melting separation.At the early stage,the reduction process is controlled by interfacial chemical reaction and the apparent activation energy is 60.78kJ/mol.The reduction process is controlled by both interfacial chemical reaction and internal diffusion at the final stage,and the apparent activation energy is 30.54kJ/mol.

Self-reduction Mechanism of Coal Composite Stainless Steel Dust Hot Briquette

To efficiently recycle valuable metals such as chromium and nickel in stainless steel dust, self-reduction ex- periments were carried out to study the reduction mechanism of metal oxides in coal composite stainless steel dust hot briquette, which is defined as a CCSB here. Self-reduction of CCSB is proceeded by volatile matter and fixed carbon contained within CCSB. Experiments were performed to study the effects of temperature and carbon to oxygen （C/OCoal） ratio on self reduction of CCSB. At 1400 and 1450℃, volatile matter in coal used for experiment could take the place of about 40℃ of fixed carbon in coal. Under the present experimental conditions, reduction product of chromium appears as FeCr2O2, Cr2O3, Cr7C3 , and [Cr] in turn during reduction. To evaluate the formation of met al nuggets in self reduction process of CCSB, metal nuggets containing chromium and nickel were observed in outside of reduction products under various conditions, and thermodynamic equilibrium calculation was carried out for possi hie products and formation of molten metal by fixed carbon. SEM and EDS analyses were made for metal nugget and slag in reduced product. The results reveal that it is reasonable to achieve the metal nuggets at 1450℃, 0.8 of C/OCoal ratio and 20 min of reduction time. The nugget formation can indicate one innovative process for comprehensive utilization of stainless steel dust.

Optimization of BF Slag for High Cr_2O_3 Vanadium-titanium Magnetite

In order to clarify the slag system of high Cr2O3 vanadium-titanium magnetite smelting in BF （blast furnace）, the melting properties of slag samples prepared by analytically pure reagents were measured. By means of orthogonal test synthetic weighted score method, the optimal slag for high Cr2O3 vanadium-titanium magnetite was obtained, which contained 10% MgO, 8% TiO2 and 15% Al2O3, with the binary basicity being 1.15. In addition, the effects of basicity, MgO, TiO2 and A12 03 on slag melting properties were investigated by single factor test, and the results showed that, with increasing the basicity or TiO2 content, melting temperature （Tin） increased, whereas initial vis- cosity （r/0） and high temperature viscosity （r/h） decreased. With increasing the MgO content, Tm decreased firstly and then increased. With increasing the Al2 O3 content, Tm increased, and η0 and r/h decreased firstly and then increased.

Comprehensive Utilization of Ludwigite Ore Based on Metallizing Reduction and Magnetic Separation

With the aim of high-efficiency utilization of Dandong ludwigite ore, a new process of metallizing reduction and mag- netic separation was proposed, and the effects of reduction temperature, reduction time, carbon ratio, ore size and coal size on the efficiency of the process were investigated in details, and relevant mechanisms were elucidated by SEM and EDS. The optimum technological parameters for metallizing reduction and magnetic separation on ludwigite ore were obtained as reduction tempera- ture of 1 250 ℃, reduction time of 60 min, carbon ratio of 1.4, ore size of 0.500-2.000 mm, and coal size of 0.50-1.50 mm. After adopting the optimum parameters, the iron content and recovery ratio of iron in magnetic substance are 87.78% and 88.02%, re- spectively, while the recovery ratios of boron, magnesium and silicon in non-magnetic substance are 88.86%, 94.60% and 98.66%, respectively. After metallizing reduction and magnetic separation, valuable elements of ludwigite ore could be separated and uti- lized in subsequent steelmaking process and hydrometallurgy process.

Analysis of Gas Thermodynamic Utilization and Reaction Kinetic Mechanism in Shaft Furnace

The technology of coal gasification in shaft furnace is an effective way to develop direct reduction iron in China. In order to clarify the process of the reduction of oxidized pellets in shaft furnace by carbon monoxide or hydrogen in two ways, i.e. thermodynamics and kinetics, the gas utilization and reaction mechanism were studied by theoretical computations and isothermal thermogravimetric experiment. The results showed that the gas utilization increased with the rise of temperature when xH2/xco≥1 and with the increase of xco/（xH2 ＋xco） when temperature is less than 1073 K. The water-gas shift reaction restrains efficient utilization of gas, particularly in high tem- perature and hydrogen-rich gas. The gas utilization dropped with increase of carburization quantity of direct reduction iron （DRI） and oxygen potential of atmosphere. With the increase of both temperature and content of H2 in inlet gas, the reaction rate increased. At 100% Hz atmosphere, the interfacial chemical reaction is the dominant reaction re- stricted step. For the H2-CO mixture atmosphere, the reduction process is controlled by both interfacial chemical reaction and internal diffusion

Effect of basicity on metallurgical properties of magnesium fluxed pellets

Magnesium fluxed pellets are the focus of blast furnace burden research for reducing environmental load.The pelletizing,roasting and metallurgical properties of a Chinese fine magnetite ore with the addition of magnesium flux were experimentally tested,and the effects of basicity on the consolidation behavior,compressive strength,and reducibility of magnesium fluxed pellets were systematically clarified.Then,the mechanisms were analyzed by means of thermodynamics calculation and scanning electron microscopy-energy-dispersive spectrometry analysis methods.The results show that the consolidation behavior of magnesium fluxed pellets during roasting process was obviously promoted with increasing the basicity of the magnesium fluxed pellets.The compressive strength increased firstly and then decreased,reaching the maximum value of 2352 N/pellet with the basicity of 1.0.The reduction degree increased gradually with enhancing the basicity owing to the fact that the decomposition of the added CaCO^could increase the porosity of pellets,thereby increasing the CO diffusion in pellet during reduction.Simultaneously,the reduction swelling index was improved with increasing the basicity because the generated calcium feirite could effectively suppress the growth of iron whiskers.