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The heat of arc plasma is the primary energy source of the electric arc furnace (EAF) for high-titania slag smelting. A unified model of fluid flow, heat transfer, and arc-slag interaction is developed by taking magnetohydrodynamic (MHD) equations into account. The model is first validated by comparing the calculated results with the previous experimental data. The dynamic variations of the concavity of the molten pool surface are tracked by using the volume of fluid (VOF) model to investigate the interaction between the arc and the molten pool. Moreover, the model is applied to investigate the influence of slag viscosity and arc length on the flow behavior of the interface and the arc plasma characteristics. Based on the simulation results, the low viscosity and short arc length result in deeper and narrower concavity of the interface, which may lead to the splashing of molten slag and influence the stability of the arc. For cost savings and efficiency improvement, the position of electrodes and the temperature distribution in the EAF ought to be monitored and controlled to maintain proper arc length and viscosity during the production process. [ABSTRACT FROM AUTHOR]

Blast furnace–basic oxygen furnace (BF–BOF) process is the predominant method for smelting vanadium titano-magnetite (VTM) in China. Hydrogen-rich (H2-rich) gas injection in BF is considered as an important way to reduce CO2 emission under the background of low carbon metallurgy. In this paper, the softening–melting behaviors of VTM sinter in H2–rich gases were investigated by the method of determination of its reduction softening drippinger performance under load. The experimental results indicated that the permeability of VTM sinter during the softening–melting process was improved by increasing the H2 content of the reducing gases. The maximum pressure drop of the burden decreased gradually from 29.76 kPa to 19.97 kPa, and the total characteristic value (representing the comprehensive softening–melting property) also decreased obviously from 2357.52 kPa·°C to 630.94 kPa·°C with the increase in H2 content. The softening interval of the samples was widened, while the melting–dripping interval increased firstly and then decreased. In that case, the position of the melting–dripping zone in BF would move downwards, which was beneficial to smelting smoothly. The thermodynamic analysis indicated that Ti- and Fe-bearing phases were more difficult to be reduced than iron oxides, and H2-rich gas is beneficial to the reduction of that kind of oxides. Titano-magnetite will be reduced stepwise to form Fe2TiO4, and then in the order of FeTiO3→TiO2→Ti(C,N). Wustite (FeO) was an important component during the slag-forming process, whose content increased firstly and then decreased. Perovskite and silicate were the main phases in the dripping slag samples. [ABSTRACT FROM AUTHOR]

A structure-based viscosity model has been developed for the CaO-MgO-FeO-SiO2-Al2O3 system and its subsystems. A critical analysis of the experimental data for iron oxide aluminosilicate systems has been conducted and used in the optimization of a model, which provides a link between the viscosity and the structures of the melts. The structural characteristics of aluminosilicate melt can be described by four types of oxygen: bridging oxygen Oi0, non-bridging oxygen Oj-, free oxygen O2−, and excess bridging oxygen O*. The present model is capable of predicting the viscosities in the CaO-MgO-FeO-SiO2-Al2O3 system and its subsystems over wide ranges of composition and temperature above the liquidus within experimental uncertainties, and the average of relative errors for this model was found to be 19.94 pct. This model includes FeO-SiO2, CaO-SiO2-FeO, Al2O3-SiO2-FeO, MgO-SiO2-FeO, CaO-SiO2-MgO-FeO, CaO-SiO2-Al2O3-FeO, and CaO-MgO-SiO2-Al2O3-FeO. It was found that the effects of different metal cations on the viscosity can be determined, and the ability to reduce viscosity in the silicate melts follows the order: FeO > CaO > MgO. In the present model, the predicted viscosity decreased when CaO was initially initial added to the Al2O3-MgO-FeO-SiO2 system at a fixed SiO2 content because Ca2+ has the highest priority for charge compensation and FeO is the strongest modifier for this slag. [ABSTRACT FROM AUTHOR]

The wetting behaviors of a TiO2 substrate by calcium ferrite (CF) series slags were investigated using an improved sessile drop method at 1523 K (1250 °C). The initial contact angles were in the range 35 to 50 deg, the final equilibrium apparent contact angles were < 20 deg, and the spreading durations were in the range 75 to 180 seconds. The CF-TiO2 system showed reactive wetting, which was categorized into four dynamic stages. Stage I: physical spreading, stage II: slow linear spreading, stage III: fast linear spreading, and stage IV: equilibrium. Interfacial reactions yielded CaTiO3 during reactive spreading, thereby transitioning TiO2 wetting into CaTiO3 wetting and then forming Fe2TiO5 and FeTiO3 owing to the excess Fe2O3 and FeO that had accumulated in the interfacial zone. Although stage III spreading was faster than stage II spreading, adding MgO to the slag slowed stage III spreading. The interfacial microstructure of the residual slag was roughly divided into three layers owing to the different densities of the slag and solid products. The top layer was composed of CaTiO3 and Fe2O3, the middle one was composed of CaTiO3 and Fe2TiO5, and the bottom one was composed of Fe2TiO5 and FeTiO3. Adding TiO2 to the slag produced a dense CaTiO3-containing interfacial layer, resulting in CF being detected in the residual slag. [ABSTRACT FROM AUTHOR]

The effect of AlO and AlO/SiO ratio on the sulfide capacity of the molten aluminosilicate CaO-SiO-AlO-MgO-TiO slag system with high AlO content was measured at 1773 K (1500 °C) using a metal-slag equilibration method. The sulfide capacity between silicate-based and aluminate-based slag was also compared based on the thermodynamic analysis and structural characteristics of melts. At a fixed CaO/SiO ratio of 1.20, the sulfide capacity decreases with increasing AlO content primarily due to the decrease of free oxygen (FO) and the activity of O. Increasing the AlO/SiO ratio from 0.47 to 0.79 causes a significant increase in the sulfide capacity of the slags, and a slight increase is found when the AlO/SiO ratio is more than 0.79. The effect of the substitution of silica by alumina on the sulfide capacity of the slags was not only due to an increase in the activity of basic oxides ( $$ a_{{{\text{O}}^{2 - } }} $$ ) but also to a decrease in the stability of sulfide ( $$ \gamma_{{{\text{S}}^{2 - } }} $$ ). Moreover, $$ a_{{{\text{O}}^{2 - } }} $$ and $$ \gamma_{{{\text{S}}^{2 - } }} $$ increase in a similar degree, and the weaker binding electronegativity of Al with oxygen atoms results in a slight increase in the final sulfide capacity in the aluminate-based slag system with AlO ↔ SiO substitution. Five different sulfide capacity models were employed to predict the sulfide capacity, and the iso-sulfide capacity distribution diagram based on the Young's model was obtained in the high AlO corner of the diagram. [ABSTRACT FROM AUTHOR]

The high roasting temperature and low leaching efficiency of vanadium from vanadium-bearing converter slag are regarded as the main factors significantly influencing the application of calcification roasting-acid leaching processes in the cleaner production of vanadium. In this study, a mechanical activation treatment was performed to enhance the extraction of vanadium from converter slag. The enhancement effects obtained from mechanical activation were comprehensively evaluated through indices such as the roasting temperature and leaching efficiency. The effects of mechanical activation time, roasting temperature, leaching temperature, solid to liquid ratio, particle size, and acid concentration on the leaching efficiency were investigated. Microstructure morphology and elemental analyses of the raw materials and leaching residue were also investigated using scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results demonstrated that the mechanical activation significantly decreased the optimum roasting temperature from 1173 K to 1073 K (900 °C to 800 °C) and increased the leaching efficiency from 86.0 to 90.9 pct. [ABSTRACT FROM AUTHOR]

To determine the effect of AlO content and AlO/SiO mass ratio on the structure of molten aluminosilicate systems, CaO-SiO-AlO-MgO-TiO systems were investigated by conducting molecular dynamics (MD) simulation and Raman spectroscopy. The capabilities of different elements to attract O on the basis of bond length are ranked as follows: Si > Al > Ca. The CN (approximately 4) and the average CN (approximately 4.09) demonstrate that the [AlO] tetrahedron is not as stable as the [SiO] tetrahedron and that some highly coordinated Al units exist in the slags. Non-bridging oxygen prefers to be coordinated with Si, and Al tends to be localized in polymerized environments as a network intermediate phase. In addition, Ca is more energetically active than Mg as the charge compensation ion. MD results and Raman analysis show that an increase in AlO content complicates the structure at a fixed CaO/SiO ratio. In addition, the viscosity of the sample may increase with increasing AlO content but is also influenced by polymerization strength. The substitution of AlO for SiO simplifies the structure of the slag at a fixed CaO concentration when AlO/SiO is less than 0.92, as indicated by the (Q + Q)/(Q + Q) ratio of Al and the structure complexity. The results of MD and Raman analysis agree with those of viscosity measurement. [ABSTRACT FROM AUTHOR]

The isothermal crystallization of perovskite in TiO-CaO-SiO-AlO-MgO high-titanium-bearing blast furnace slag was observed in situ at 1698 K (1425 °C) using a confocal scanning laser microscope. The dendrite structure of perovskite (CaTiO) thus obtained showed vividly the primary dendrite trunks and secondary dendrite arms. Furthermore, the dendritic growth of perovskite in liquid slag was clearly observed on line. The results showed that the dendrite arrays in which the primary dendrite trunks observed on slag surface were parallel with each other grew toward the same direction. The secondary dendrite arms grew in the perpendicular direction with the primary trucks and stopped growing when they encounter. The perovskite dendrites showed a linear growth at two stages. The dendrites grew faster at early stage at about 5 to 7 μm/s and grew with a lower growth rate at about 1 to 2 μm/s in later stage. Finally, the growth mechanism of perovskite in melt was analyzed with the solidification theory. Based on the theoretical calculation of equilibrium phases in slag, the initial slag could be considered as a binary component system. One component was perovskite and the other component was the sum of all the other species that did not attend the crystallization of perovskite (included SiO, AlO, and MgO, as well as CaO and TiO that were not involved in the solid formation). The formation of perovskite required the diffusion of CaO and TiO to the solid/liquid interface and the rejection of the other species from the interface. The solid/liquid equilibrium schematic diagram was made based on the calculation. [ABSTRACT FROM AUTHOR]

The crystallisation behaviour of perovskite in liquid synthesised titanium-bearing blast furnace (BF) slag (TiO2-SiO2-Al2O3-MgO-CaO) was observed in situ with a confocal scanning laser microscope (CSLM). Perovskite crystals were dendritic columnar crystals that nucleated on the crucible bottom (and wall) and grew to the centre and surface of liquid slag. The CSLM result that perovskite grew along straight lines through the successive appearances of quasi-particles on slag surface reflected the growth process of dendrites beneath the surface. The formation of perovskite required the diffusion of TiO2 and CaO to the solid interface at the dendrite tips and the rejection of SiO2, Al2O3 and MgO from the interface. [ABSTRACT FROM AUTHOR]

The isothermal phase composition of high-titanium-bearing slag (23 mass pct TiO) under an argon atmosphere during cooling process from 1723 K (1450 °C) was calculated by FactSage.6.3 (CRCT-ThermFact Inc., Montréal, Canada). Three main phases, which were perovskite, titania spinel, and clinopyroxene, could form during the cooling process and they precipitated at 1713 K, 1603 K, and 1498 K (1440 °C, 1330 °C, and 1225 °C), respectively. The nonisothermal crystallization process of perovskite in synthesized high-titanium-bearing slag was studied in situ by a confocal scanning laser microscope (CSLM) with cooling rate of 30 K/min. The results showed that the primary phase was perovskite that precipitated at 1703 K (1430 °C). The whole precipitation and growth process of perovskite was obtained, whereas other phases formed as glass under the current experimental conditions. Perovskite grew along a specific growth track and finally appeared with snowflake morphology. The growing kinetics of perovskite formation from molten slag were also mentioned. [ABSTRACT FROM AUTHOR]

Blast furnace slag is the main byproduct in the ironmaking process, which contains large amounts of sensible heat. In addition, it's the major raw material for cement. However, the sensible heat is wasted not only without any recovery in the traditional water granulation process at this present. The main challenge is to granulate the slag at a high cooling rate while the heat is also being recovered. This paper describes the hot experiments where a rotating multi-nozzle cup atomizer (RMCA) is used to atomize the molten blast furnace slag without water impingement. The atomization process shows good agreement with Rayleigh's mechanism. The particle size of the slag particle is strongly controlled by the rotating speed and the nozzle diameter, and the higher rotating speed and smaller nozzle diameter are beneficial for obtaining smaller and more uniform slag particles. Moreover, the slag particle still has a high content of glass, which is suitable for cement manufacture. [ABSTRACT FROM AUTHOR]

The particle size and metallization ratio of iron in reduced ilmenite have an important function in separating the metal from TiO2-rich slag in the electric arc furnace process. In this study, an ilmenite concentrate supplied by Panzhihua Iron and Steel (Group) Co. was reduced at 1380°C in an electric resistance furnace. The effects of Fe-Si addition and reduction time on the particle size and metallization ratio of iron in the reduced sample were analyzed. The metallization ratio of iron significantly increased with increasing Fe-Si amount and reduction time, and reached ≈90% after 40 min. However, the metallization ratio of iron was about 85% without Fe-Si addition. Meanwhile, the iron particle size increased with increasing Fe-Si amount; the growth was obvious with the addition of 1% Fe-Si. Moreover, the growth rate of the iron particle size also increased with increasing reduction time. The TG-DTG curves indicated that the mass loss with Fe-Si addition was less than that without Fe-Si addition, and the temperature at which the maximum rate of mass loss rate was achieved was lower than that without Fe-Si addition. [ABSTRACT FROM AUTHOR]

Blast furnace (BF) slag, which is the main byproduct in the ironmaking process, contains large amounts of sensible heat. To recover the heat, a new waste heat-recovery system-granulating molten BF slag by rotary multinozzles cup atomizer and pyrolyzing printed circuited board with obtained hot BF slag particle-was proposed in this study. The feasibility of the waste heat-recovery system was verified by dry granulation and pyrolyzation experiments. The energy of hot BF slag could be converted to chemical energy through the pyrolysis reaction, and a large amount of combustible gas like CO, H, CH, and CH can be generated during the process. [ABSTRACT FROM AUTHOR]

In order to remove impurity elements from molten aluminum, many processes, such as using inert gas, reactive gas, reactive powders, unreactive powders, slag, or their combinations, have been used during the past 30 years. In the current paper, mathematical models on the removal of impurity elements from molten aluminum for these processes were extensively developed, and validated by industrial measurement from literatures. Special parameters were introduced to express the refining efficiency. Mathematical models for the combined processes like inert gas mixed with reactive gas purging, reactive powders injection with inert gas as carrying gas, were also developed. The removal efficiency of impurity elements for batch reactor and continuous reactor were derived for these processes, either the single method or the combined method. The effects of gas flow rate, impellor rotating speed, fraction of reactive gas, injecting rate of reactive powders, and temperature on the removal of impurity elements were discussed. [ABSTRACT FROM AUTHOR]

• Ab initio molecular dynamics (AIMD) and ab initio lattice dynamics (AILD) simulations are applied to study the properties of CaO SiO 2 Al 2 O 3 slag system. • Density of state (DOS) and electron density difference (EDD) predicts O atoms are more reactive and bonding strength decreases in the order of Si-O>Al O>Ca O. • Bond population analysis indicate that Si-O bonds are stronger than Al O and Ca O bonds due to shorter bond length. • Radial distribution function (RDF) and mean square displacement (MSD) were calculated at 1773 K. • Temperature dependence of diffusion coefficient and viscosity for ternary slag system were investigated in the range of 1350–2100 K. In current first principle studies the electronic, structural and physical properties of CaO SiO 2 Al 2 O 3 ternary slag system were calculated by ab initio molecular dynamics (AIMD) and ab initio lattice dynamics (AILD) simulations, based on density functional theory (DFT). The density of states (DOS) and electrons density difference (EDD) were evaluated to understand the bonding nature of slag network structure. Furthermore, the atomic and bond population analysis shows that the Si O bonds are stronger as compared to Al O and Ca O bonds in molten slag. The radial distribution function (RDF) and mean square displacement (MSD) were obtained at 1773 K, which are used to calculate the diffusion coefficient and viscosity of ternary slag system. Moreover, the temperature dependence of diffusion coefficient and viscosity were investigated in the range of 1350–2100 K. The calculated results indicate that the diffusion coefficient decreases and viscosity increases at high temperature for CSA slag system. [ABSTRACT FROM AUTHOR]

In this paper, the effect of titanium carbonitride (Ti(C,N)) on the viscosity of high-titanium-type blast furnace slags was investigated. The different Ti(C,N) contents were achieved by adjusting the reduction degree of TiO2 to reflect the real characteristics of the high-titanium slag. The results show that the viscosity of the slag increased with the increasing Ti(C,N) content and decreased with the rising temperature. A deviation between the measured and the fitted viscosity appeared as the content of the Ti(C,N) was beyond 4 wt%. Furthermore, the apparent viscous flow activation energy of the slag ranged from 106.13 kJ/mol to 235.46 kJ/mol by varying the Ti(C,N) contents from 0 wt% to 4.97 wt%, which was evidently different from the results of previous studies. The optical microscope and energy dispersive X-ray spectroscopy (EDS) analysis show that numerous bubble cavities were embedded in the slags and the Ti(C,N) particles agglomerated in the solidified samples. This phenomenon further indicates that the high-titanium slag is a polyphase dispersion system, which consists of liquid slag, solid Ti(C,N) particles and bubbles. [ABSTRACT FROM AUTHOR]

Because of its potential to achieve a high recovery rate of vanadium, the mechanical activation pretreatment of vanadium-bearing converter slag followed by calcification roasting at low temperature and a two-step leaching process may be a viable alternative to the present roasting and one-step leaching process for vanadium extraction. The object of this study is to enhance the leaching efficiency of vanadium by mechanical activation and two-step leaching methods. The effects of solution acidity, liquid/solid ratio, particle size of the roasted slag, stirring speed, leaching temperature and time were investigated. The first stage leaching liquor was recycled in order to improve vanadium content in the leaching solution and reduce leaching solution consumption and wastewater discharge. Experimental results showed that approximately 81.8% vanadium was dissolved in the first stage of the leaching process with a solution pH of 2.5, and approximately 8.1% vanadium was dissolved in the second stage of the leaching process with a solution pH of 0. In the first stage, the vanadium leaching efficiency was significantly hindered by long recycle times, though this property also increased the content of vanadium in the leaching solution and greatly decreased the water consumption. In addition, mineralography and microstructures of the solid samples were studied by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) to help understand the mechanism. [ABSTRACT FROM AUTHOR]

A cleaner process is tremendously required to deal with the vanadium tailings, which may cause serious environmental problem due to the high content of water soluble hazardous elements such as V and Cr. This problem can be possibly solved by proposed high temperature reduction–magnetic separation process, in which, V, Cr and Fe can be recycled as ferroalloy. The thermodynamic calculation results reveal that a higher temperature (>1127.8 °C) promotes the reduction of Fe, V and Cr, and improves the recovery rates of V and Cr in liquid iron. The reduction behavior of vanadium tailings was investigated using XRD, TG/DSC, SEM, EDS and ICP-OES techniques. The EDS results show that a small portion of V was remained in the slag phase when roasted at 1300 °C, while nearly all of V and Cr can concentrate in ferroalloy at 1400 °C. Approximatly 90% of V and 95% of Cr recovery in magnetic fraction can be obtained for the magnetic separation step. A small portion of V and Cr is remained in the non-magnetic final tailings, however, the hazardous potential assessments results indicate that such kind of tailings can safely use as secondary materials or stockpiled as an end-waste. [ABSTRACT FROM AUTHOR]

In this paper, a novel process was studied for the recovery of iron and titanium from ilmenite concentrate. The ilmenite powders first underwent an oxidation pretreatment and were reduced isothermally at 1350–1450 °C by graphite with the addition of Na 2 SO 4 . The influence of temperature, C/O molar ratio and the dosage of the added Na 2 SO 4 on the metallization ratio, phase transformation and titanium grade were studied. The results demonstrated that Na 2 SO 4 not only significantly promotes the aggregation and growth of metallic iron-grain particles but also enhances the reduction ability. Under the promotion of added Na 2 SO 4 , the highest metallization ratio reached 94%, and the theoretical calculation of the highest grade of titanium dioxide is approximately 75%. The Na 2 SO 4 additive decreases the melting point of the slag and metal, resulting in the effect of semi-melting reduction. The carbothermic reduction order of phase transitions of pre-oxidized ilmenite concentrate was also discussed. [ABSTRACT FROM AUTHOR]

A multistage utilization process was developed to fully recover valuable metals from vanadium-bearing converter slag and reduce the content of hazardous elements, such as vanadium and chromium, in the tailings. A mechanical activation–calcification roasting–acid leaching process was firstly employed to recover vanadium. This process generated two products, viz. a V-bearing solution accounting for ∼95% V recovery and vanadium tailings with Fe and Ti contents of 31.85% and 8.94%, respectively. Then, based on theoretical calculations and physical measurements, a coal–based direct reduction–magnetic separation process and a hydrochloric acid leaching process were employed for the stepwise recovery of iron and titanium, respectively, from the vanadium tailings. Iron was recovered in the form of high chromium–vanadium iron with 81.53% Fe, 1.31% Cr, and 2.04% V, and titanium was recovered as titanium dioxide pigment with 85–90% yield. Such a comprehensive and clean utilization of vanadium-bearing converter slag has great potential for practical application. [ABSTRACT FROM AUTHOR]