Thermodynamic Behaviour of Chlorine in CaO‐SiO2‐MgO‐Al2O3(‐CaF2) Slags

The solubility of chlorine in CaO‐SiO₂‐Al₂O₃‐MgO(‐CaF₂) slag was measured at 1673 ‐1823 K. By estimating the chloride capacity of slags, thermodynamic behaviour of chlorine in the molten slag was investigated. Chloride capacity increased with increasing CaO / SiO₂ ratio (C/S). An increase in MgO content decreased chloride capacity at C/S≥1.0 because it lowered the activity of Ca²⁺ which seemed to have strong affinity with Cl^? in molten slag. Also, the chloride capacity decreased with increasing Al₂O₃ content. The affinity between the Ca²⁺ and Cl^? ions was confirmed by measuring the infrared spectra of slags. The dissolution reaction of chlorine into slag was exothermic and its molar enthalpy was evaluated from the experimental results at 1673 ‐ 1823 K. Based on the result obtained in the present study, the quantitative prediction of chlorine distribution during the blast furnace process was performed. It was estimated that almost all chlorine in the blast furnace would be absorbed into molten slag even if the PCI ratio was increased or low quality coal with chlorine content less than 1.0 mass% was injected.     

Fundamental research on phosphorus behaviour in the smelting reduction process

The behaviour of phosphorus in the smelting reduction process was investigated in this paper. Experiments were carried out under the conditions of smelting reduction: the phosphate reduction in molten slag by solid carbon, liquid iron saturated with carbon and CO gas, respectively. Furthermore, experiments on the phosphate reduction in pre-reduced iron ore by liquid iron saturated with carbon were carried out respectively when liquid iron was in permanent contact with molten pre-reduced iron ore, and when powders of the pre-reduced iron ore were injected into the iron bath from the bottom. The results showed that there was considerable unreduced P₂O₅ in the slag. Part of the reduction product of phosphorus escaped from the bath, while the other part was absorbed by liquid iron. The pig iron with low content of phosphorus can be obtained by smelting reduction in comparison with blast furnace. In the process of liquid iron bath with coal-oxygen-ore injection, the phosphorus content in liquid iron could be kept constant in 100 kg scale tests.     

Oxidation and Characterization of As‐Cast TRIP Steel Surfaces

This paper presents recent results from a collaborative study between the Department of Ferrous Metallurgy at RWTH‐Aachen University and the Department of Materials Science and Engineering at Carnegie Mellon University on high temperature oxide scale formation of Al and Si containing as cast TRIP steel surfaces under conditions similar to that of continuous casting and hot rolling. A combination of experimental studies consisting of (i) electron microprobe analysis and metallographic studies of the cast steel surface, (ii) direct visualization of the oxide formation through high temperature confocal scanning microscopy and (iii) Tammann furnace oxidation tests were carried out. It was found that internal oxidation of Al and Si takes place along the inter‐dendritic boundaries, where Al and Si were found to have been enriched after casting. The scale formed on the steel surface was a complex mixture of solid fayalite ((FeO_n)₂(SiO₂)), wüstite (FeO_n), magnetite (Fe₃O₄), hematite (Fe₂O₃), and Fe‐particulates and the rate of scale growth appears to have been controlled at high temperatures by the formation of a liquid slag layer that allows for rapid oxygen transport to the steel/scale interface.     

Activity of VO1.5 in CaO‐SiO2‐MgO‐Al2O3 Slags at Low Vanadium Contents and Low Oxygen Pressures

In the present work, the gas‐slag equilibration technique was employed for the measurement of the thermodynamic activity of vanadium oxide. The vanadium‐containing slag kept in a platinum crucible was equilibrated with a gas mixture of CO, CO₂ and Ar, with well‐defined oxygen partial pressure at a pre‐determined temperature. The slag sample was quenched and the composition of the final slag was determined by chemical analysis. From the value of the oxygen partial pressure, the thermodynamic activity of VO_1.5 could be calculated using the value for the activity of vanadium in V‐Pt alloy. The measurements were carried out in the temperature range 1823～1923K and the oxygen partial pressures employed were 10^‐3, 10^‐4, 10^‐5 Pa. The present results show that the activity of vanadium(III) oxide in slag exhibits a negative deviation from ideality in the present composition range. With increasing basicity of the slag, the final content of vanadium oxide in the slag was found to show an initial increase followed by a constant content. The activities of vanadium(III) oxide did not exhibit any significant change with increasing temperature. The activity coefficient of vanadium(III) oxide decreased sharply with slag basicity approximately up to a basicity of 1, beyond which it showed a near–constant value. Increase in basicity was found to cause a change in the distribution of vanadium between the slag and the alloy phases even though this effect was less pronounced. From the present results, a mathematical relationship for estimating the vanadium content in slag for a given activity of vanadium in the molten metal phase was developed.     

The solubility of water vapour in CaO‐SiO2‐Al2O3‐MgO slag system

The solubility of water vapour in the CaO‐SiO₂‐Al₂O₃‐MgO quaternary slag system was measured using an inert gas fusion technique with thermal conductivity detection. The slags were equilibrated with argon‐water vapour mixture corresponding to 0.157 bar of water vapour pressure at 1873 K. The slag solubility of water vapour is proportional to the square root of vapour pressure. Since the hydroxyl capacity of slag, C_OH shows an independence on the relative amount of CaO or MgO in slag, the contributions of CaO and MgO on the hydroxyl capacity are equivalent on a molar basis. Whereas, Al₂O₃ shows a better effect on the hydroxyl capacity than SiO₂. A linear relationship between hydroxyl capacity and slag basicity in logarithmic scale was obtained with the slope of 1/2, confirming the water vapour dissolution reaction into a basic slag as (O^2‐) + H₂O(g) = 2(OH^?). The correlation between hydroxyl capacity and slag components was derived in terms of their contributing weight factors. The measured values of C^'_OH agree well with the calculated ones using the interaction energies of α_H‐Al = ?38300 and α_H‐Mg = ?22700 J determined with the aid of the regular solution model. In addition, the correlation between hydroxyl capacity and sulphide capacity was empirically derived as a formula of logC_OH = 1/2logC_S + (4.38 ± 0.25) through the thermodynamic expression of both capacities by virtue of the common oxygen ion activity.     

Viscosities of the Quaternary Al2O3‐CaO‐MgO‐SiO2 Slags

Viscosities of some quaternary slags in the Al₂O₃‐CaO‐MgO‐SiO₂ system were measured using the rotating cylinder method. Eight different slag compositions were selected. These slag compositions ranging in the high basicity region were directly related to the secondary steel making operations. The measurements were carried out in the temperature range of 1720 to 1910 K. Viscosities in this system and its sub‐systems were expressed as a function of temperature and composition based on the viscosity model developed earlier at KTH. The iso‐viscosity contours in the Al₂O₃‐CaO‐MgO‐SiO₂ system relevant to ladle slags were calculated at 1823 K and 1873 K for 5 mass% MgO and 10 mass% MgO sections. The predicted results showed good agreement with experimental values and the literature data.     

Activity of Chromium Oxide in CaO‐SiO2 based Slags at 1873 K

Thermodynamic properties of chromium oxides in molten slags are very important for optimization of stainless steel refining processes as well as reduction processes of chromium ores. The solubility of chromite into molten slags has been found to vary drastically with oxygen partial pressure and slag composition in the former studies by the authors. In the present study, activity data and redox equilibria of chromium oxides measured under moderately reducing conditions, P_O2= 6.95×10^?11 atm, at 1873 K are summarized. For the CaO‐SiO₂‐CrO_x system, the activity coefficient of chromium oxide increased with increasing basicity and the optimized slag composition for stainless steel refining is assessed as that saturated with CaCr₂O₄ and Cr₂O₃ using the phase relations determined. On the other hand, the presence of MgO and Al₂O₃ brings about different behaviour of chromium oxide activity and redox equilibria and the 44 mass per cent CaO ‐ 39 mass per cent SiO₂ ‐11 mass per cent Al₂O₃ ‐ 6 mass per cent MgO slag is recommended to reduce the chromium oxidation loss in the practical stainless steel refining process at 1873 K.     

Progress in Technologies of Vanadium‐Bearing Titanomagnetite Smelting in PanGang

The smelting of vanadium‐bearing titanomagnetite by blast furnace was very difficult because the content of TiO₂ of blast furnace slag could amount to 20‐25%. After long term development and continuous improvement, special intensified smelting technologies for vanadium‐bearing titanomagnetite by blast furnace were obtained and improved gradually. With the improvement of beneficiated material and equipment, smelting intensity has been increasing gradually and the highest comprehensive smelting intensity that is fuel comsumption per unit useful volume per day reached 1.45t/(m³·d). Technical‐and‐economic indexes of blast furnace have also been increasing remarkably. The highest monthly utilization coefficient exceeded 2.7t/(m³·d) on the condition that the burden total ferrum grade was only about 50%.     

Study of Boronizing Mechanism of High‐Alumina Slag

As the Al₂O₃ content of the iron‐making raw materials increasing, the Al₂O₃ content in the slag increases as well, which is the certain result in the development of the iron‐making process. Based on the slag which was from the 2# blast furnace in Hebei Qianan of China, 7 different kinds of B compositions were added. The viscosity values of the CaO ‐MgO‐Al₂O₃‐SiO₂‐B₂O₃ system were measured by using the torque. The SEM and EDS apparatus were used to observe the variation characteristics of the boronizing slag of the blast furnace. Viscosity mechanism model of the boronazing high‐alumina slag was got from the analysis of the EDS compositions. These detailed analysis including the influence on the slag forming components result from different B contents which shows the conclusion that the suitable B content makes good to the viscosity, melting temperature and stability of high‐alumina slag.     

Oxidation of titanium-vanadium slags with the participation of Na2O and its effect on the behavior of vanadium

The oxidation of titanium-vanadium slags with the participation of Na₂O is studied by X-ray diffraction. The slags have the following phase compositions: anosovite, anosovite-spinellide, and spinellide. An alkaline component in the form of Na₂CO₃ is introduced into a slag either before oxidizing roasting or during slag production from a concentrate (alkaline slag forms). The general laws of the processes of slag oxidation in the temperature range 600–1100°C and the effect of these processes on the behavior of vanadium are found. The degree of formation of watersoluble vanadium compounds during roasting is shown to depend substantially on the SiO₂ content in the slag. When the slags are roasted, SiO₂ intensely combines with Na₂O to form sodium silicates or aluminosilicates depending on the slag composition, which restricts the formation of sodium vanadates. In anosovite-spinellide slags (with a high Al₂O₃ content), the maximum degree of vanadium oxidation with the formation of water-soluble sodium vanadates is achieved at a temperature of about 1000°C. In anosovite slags (with a low Al₂O₃ content), the maximum degree of formation of water-soluble vanadium compounds is achieved at a temperature below 900°C. At higher temperatures, the major portion of vanadium transforms into an acid-soluble form.     

A Clean and Efficient Method for Recovery of Vanadium from Vanadium Slag: Nonsalt Roasting and Ammonium Carbonate Leaching Processes

A cleaner method has been developed for the extraction of vanadium from vanadium slag. Compared to the traditional alkaline salts roasting followed by the water leaching process, in the nonsalt roasting process because no additives are added, the chromium spinel in the raw vanadium slag will not be converted to carcinogenic chromate salts and exhaust gas will not be produced. The ammonium metavanadate is precipitated from the water leach solution. The wastewater from the vanadate precipitation process can be recycled into the leaching process. The leaching residue can be comprehensively utilized in conjunction with an iron-making process using blast furnace. The nonsalt roasting mechanism was systematically investigated in a laboratory study. The XRD and morphology analysis of roasted vanadium slag showed that the oxidation of vanadium spinel occurred in the following steps: (1) the destruction of vanadium spinel and the formation of solid solution of Fe₂O₃·V₂O₃; (2) the oxidation of solid solution of Fe₂O₃·V₂O₃ to Fe₂O₃·V₂O₄ and a portion of the V(IV) in the Fe₂O₃·V₂O₄ was reacted with basic oxide such as MgO to generate the low-valence vanadate Mg₂VO₄; (3) the formation by further oxidation of highest-valence vanadates Mn₂V₂O₇ and Mg₂V₂O₇. The effects of particle size, oxygen concentration, gas flow rate, and temperature on vanadium recovery were investigated. Simultaneously, the effects of leaching variables, including ammonium carbonate concentration and temperature, were examined. The thermodynamics of the system are also reported.     

Vaporization Studies from Slag Surfaces Using a Thin Film Technique

The investigations of vanadium vaporization from CaO-SiO₂-FeO-V₂O₅ thin film slags were conducted using the single hot thermocouple technique (SHTT) with air as the oxidizing atmosphere. The slag samples were analyzed after the experiments by SEM/EDX. The vanadium content was found to decrease as a function of time. The loss of vanadium from the slag film after 30 minutes of oxidation was approximately 18 pct and after 50 minutes, it was nearly 56 pct. The possible mechanism of vanadium loss would be the surface oxidation of vanadium oxide in the slag, VO _x to V⁵⁺, followed by surface evaporation of V₂O₅, which has a high vapor pressure at the experimental temperature.     

Synthesis of Fine Vanadium-Carbide (VC<Subscript>0.88</Subscript>) Powder Using Carbon Nanofiber

The synthesis of fine vanadium-carbide (VC_0.88) powder is considered. To produce the vanadium carbide, vanadium(III) oxide is reduced by means of carbon nanofiber in an induction furnace with an argon atmosphere. The carbon nanofiber is produced by the catalytic decomposition of light hydrocarbons. The specific surface of the carbon nanofiber is very high: ~150000 m²/kg, as against ~50000 m²/kg for soot. The impurity content in the carbon nanofiber is 1 wt %. By analysis of the phase diagram of the V–C system, the batch composition and the upper temperature limit in carbide formation may be determined such that vanadium carbide is formed as powder. Thermodynamic analysis yields the initial temperature at which the vanadium( III) oxide is reduced in a furnace with different CO pressures. The characteristics of the vanadium carbide are determined by the following methods: X-ray phase and elementary analysis; pycnometric analysis; scanning electron microscopy with local energy dispersion X-ray microanalysis (EDX); low-temperature nitrogen adsorption with subsequent determination of the specific surface by the BET method; sedimentation analysis; and synchronous thermogravimetric analysis and differential scanning calorimetry (TG/DSC). The material obtained with optimal reduction parameters consists of a single phase: vanadium carbide VC_0.88. The powder particles are predominantly clumped together in aggregates. The mean size of the particles and aggregates is 9.2–9.4 μm, with a broad size distribution. The specific surface of the samples is 1800–2400 m²/kg. Oxidation of vanadium carbide begins at about 430°C and is practically over at 830°C. Optimal synthesis requires stoichiometric proportions of the reagents in the production of vanadium carbide VC_0.88 at 1500–1600°C, with 20-min holding. In this process, carbon nanofiber effectively produces the carbide as the reduction product. The vanadium(III) oxide is reduced practically completely to VC_0.88.     

Methodological Aspects of Using Blast Furnace Slag for Wastewater Phosphorus Removal

Blast furnace (BF) slag is a by-product of steel plants. The objective of this study was to evaluate experimental methods to determine the phosphorus sorption capacity of BF slag. The handling of BF slag, before usage and clogging were also considered, as well as estimating the phosphorus retention capacity. Agitation and pilot-scale experiments were performed using both wastewater and phosphate solutions. This investigation showed that sorption capacities derived by wastewater experiments were considerably lower compared to those by phosphate solutions. Fresh BF slag briefly exposed to rainfall had a higher phosphorus sorption than weathered BF slag, indicating the importance of handling the slag carefully before usage. The risk for leakage of sulfuric compounds is considerable, especially during the initial operation phase of BF slag filters. Locations of BF slag filter beds for wastewater treatment must be carefully chosen from an environmental point of view.     

Influence of SiO2 Addition on the Properties of Al2O3‐CaO‐CaF2 Slag

The Al₂O₃‐CaO‐CaF₂ slag system is used in making special quality steels by the electro‐slag re‐melting process (ESR). The purpose of our investigation was to analyse ESR slag that contained SiO₂. The slag samples with different SiO₂ fractions (0 ‐ 20 mass %) were examined by chemical analysis, differential thermal analysis, simultaneous thermal analysis, X‐ray diffraction, electron microscopy and wetting angle measurement. With addition of SiO₂ the polymerization of slags was increased due to the formation of new silicate complex compounds that influenced their melting points and wetting angles.     

钒钛高炉渣的流动性

依据承德建龙特殊钢有限公司当前的高炉冶炼情况,以钢厂渣为基准,利用黏度测试装置,分析了钒钛高炉渣的碱度、w(TiO_2)、w(MgO)对高炉渣黏度与熔化性温度的影响。研究结果表明:随高炉渣碱度提高,黏度和熔化性温度先降低,碱度继续提高到1.25时,炉渣黏度与熔化性温度迅速提高;随着高炉渣中w(TiO2)提高,黏度和熔化性温度呈先降低后升高的趋势;w(MgO)提高利于降低炉渣熔化性温度,不同w(MgO)情况下,炉渣熔化性温度最高为1297℃。碱度为1.15~1.20,w(TiO_2)小于10%,w(MgO)在12%~14%时,钒钛炉渣流动性较优。     

Reduction of FeO in EAF Steelmaking Slag by Blends of Metallurgical Coke and End‐of‐Life Tyre

The reduction of FeO‐containing slag by blends of metallurgical coke and end‐of‐life tyres (RT) have been investigated through experiments conducted in a laboratory‐scale horizontal tube furnace. Composite pellets of EAF slag (47.1% FeO) with coke, RT, and blends of coke/RT (in four different proportions) were rapidly heated at 1550°C under high purity argon gas and the off gas was continuously analyzed for CO and CO₂using an online infrared (IR) gas analyzer. The extent of reduction after 10 min, level of carburization and desulfurization, and the total amount of CO₂ emissions were determined for each carbonaceous reductant. The results indicate that the extent of reduction, level of carburization and desulfurization of the reduced metal are significantly improved when coke is blended with RT. Blending of coke with RT resulted in a decrease in direct CO₂ emissions from the reduction reactions.     

A Study of Some Elemental Distributions Between Slag and Hot Metal During Tapping of the Blast Furnace

This paper investigates the distribution of elements between slag and hot metal from a blast furnace through calculation of distribution coefficients from actual production data. First, samples of slag and hot metal tapped from a commercial blast furnace were taken continually at 10‐minute intervals for a production period of 68 hours. Distribution coefficients of manganese, silicon, sulphur and vanadium were then calculated from the results of the sample analyses. A major conclusion drawn from examination of the results was that the behaviour of the studied elements was as could be expected when approaching the equilibrium reactions from thermodynamic theory. The distributions of the elements in the slag‐metal system showed clear tendencies which did not appear to be influenced by the operational conditions of the furnace. For example, for manganese, vanadium and sulphur, it was found that a higher basicity led to a decreased distribution coefficient L_Mn and L_V, but an increased L_S, which is according to theory. Another observed relationship was that slag basicity increased with an increased carbon content in the hot metal, which indicated that SiO₂ was reduced to [Si] when the oxygen potential decreased. Furthermore, it was found that sulphur and silica behaviour likened that of acidic slag components, while the manganese oxide and vanadium oxide behaviour was similar to that of basic slag components.     

Dissolution of Lime in Synthetic ‘FeO’‐SiO2 and CaO‐‘FeO’‐SiO2 Slags

Dissolution of different CaO samples into molten synthetic ‘FeO’‐SiO₂ and ‘FeO’‐SiO₂‐CaO slags was carried out in a closed tube furnace at 1873 K. The slag was kept stagnant. It was found that the dissolution rate was very fast when CaO rod was dipped into ‘FeO’‐SiO₂ slag. In the case of ‘FeO’‐SiO₂‐CaO slag, the dissolution of CaO rod in the stagnant slag was retarded after the initial period (2 minutes). Only less than 16 percent CaO reacted with the slag, irrespective of the type of lime. Three phase‐regions were identified in the reacted part of the lime rod by SEM‐EDS analysis. The formation of these regions was explained thermodynamically. A dense layer of 2CaO · SiO₂ was found to be responsible for the total stop of the dissolution. It could be concluded that constant removal of the 2CaO · SiO₂ layer would be of essence to obtain a high dissolution rate of lime. In this connection, it was found necessary to study the dissolution of lime in moving slag to reach a reliable conclusion regarding the relevance of the reactivity obtained by water ATSM test to the real reactivity of lime in high temperature slag.     

Thermodynamic behaviours of manganese and phosphorus between CaO‐MgOsat‐SiO2‐Al2O3‐FetO‐MnO‐P2O5 ladle slag and liquid iron

The thermodynamic equilibria of manganese and phosphorus between liquid iron and CaO‐MgO_Sat‐SiO₂‐Fe_tO‐MnO‐P₂O₅‐Al₂O₃ (0–33%) ladle slag have been investigated at 1873 K from the viewpoint of Mn and P yields for the production of high‐strength steels. The equilibrium distribution ratios of Mn and P were found to increase with increasing Fe_tO content; however, these ratios vary with basicity, but they do this the other way round. The addition of alumina into slag at a fixed basicity and Fe_tO content decreases both the equilibrium manganese and phosphorus distributions. The equilibrium distribution ratios were discussed in terms of the variation of activity coefficients of Fe_tO, MnO and PO_2.5, according to the slag basicity and Al₂O₃ content. The quantitative contributions of basicity and (%Fe_tO + %MnO) on L_Mn and L_P were empirically determined and their usefulness was discussed with the aid of plant data: To improve Mn and P yields in the practical RH operation, it is strongly recommended that Fe‐Mn and Fe‐P alloys be added after Al deoxidation treatment inducing relatively high Al₂O₃ in slag and maintaining low Fe_tO content. In addition, a ladle slag composition for the targeted Mn and P contents in liquid iron was substantially estimated using the empirical relationships.