CaO In Slag Research Articles

Electrical Conductivity Measurements in Ternary SiO2–PbO–CaO Slags

Electrical Conductivity Measurements in Ternary SiO2–PbO–CaO Slags

Solidification behavior of the FeOt-SiO2-CaO-Al2O3-(ZnO) slag system

Slag solidification behavior significantly influences the tapping of the Zn fuming process and slag valorization. In this work, the effect of ZnO and CaO concentration on slag solidification was investigated under a pO2 of approximately 10−10 atm using confocal laser scanning microscopy (CLSM) at various cooling rates. It was concluded that in the low CaO slag, the ZnO increased the onset formation temperature of the fayalite phase. An increase in CaO concentration facilitated wustite precipitation and prevented spinel formation in the slag at cooling rates exceeding 1 °C/s, while it enhanced melilite generation and inhibited fayalite precipitation in the slag at cooling rates below 1 °C/s. Furthermore, the slag mineralogy was studied as a function of equilibration temperature and CaO concentration of the slag through water quenching experiments under the Ar atmosphere. When slags with a CaO concentration of 3–20 wt% were quenched from 1050 to 1200 °C, the amorphous and spinel phases were observed in all quenched slags, whereas the wustite phase was only identified in slags with a CaO concentration above 10 wt%. Additionally, the fayalite phase was detected in slags containing 3–5 wt% CaO, quenched at temperatures of 1150–1050 °C. Notably, as the quenching temperature decreases and the CaO concentration increases, the observed phases in the quenched slag become more complex, and the solid particles grow coarser. The FeOt-SiO2-(4.7–5.7 wt%)ZnO-(8.3–10.1 wt%)Al2O3–CaO-1.3 wt%MgO-1.1 wt%Cr2O3 (FeO/SiO2 = 1.44) slags with a CaO concentration of below 20 wt% is suggested to be quenched from 1150 °C or 1200 °C to prevent the precipitation of a SiO2-containing phase and coarse wustite.

Research on thermodynamic characteristics of metallurgical slag

This article uses Sn as the metal flux and CaF2-CaO as the reference slag to experimentally measure the activity of CaO at T = 1773∼1873 K. The effects of different w(Al2O3) and temperature(T) on CaO activity were investigated. The results are as follows: when w(MgO) = 6%, R(w(CaO)/w(SiO2)) = 1.20, w(Al2O3) = 12%, 14%, 16% and 18%, with the increase of w(Al2O3), the activity and activity coefficient of CaO in slag gradually decrease; with the increase of temperature (T), the activity and activity coefficient of CaO in slag gradually increase; the activity coefficient of Ca in Sn decrease with increasing temperature.

Slag chemistry, element distribution behaviors, and metallurgical balance of e-waste smelting process

The co-smelting of electronic waste (e-waste) in copper/lead pyrometallurgical processes is widely recognized as the preferred solution for sustainable development. However, aluminum and halogen elements in e-waste causes new challenges. To address this, the slag chemistry of high Al2O3-containing slag was studied, and the distribution behaviors of Au, Ag, Sn, and other elements in the copper alloy/slag/gas system were investigated in the presence of halogen elements (F/Cl/Br) using the equilibration method. The industrial practice of electronic waste smelting was modeled using METSIM, and the material and energy balances of one industrial process were obtained. Under the conditions of electronic waste smelting, the solubility of Al2O3 in the FexO–SiO2–Al2O3–CaO slag system decreased with increasing CaO content. When the CaO content was 20 wt%, and the Fe/SiO2 mass ratio was 0.62–0.95, the solubility of Al2O3 in the slag reached 20 wt%. When 1%–10% CaF2 was added, 93% of Au entered the metal phase. When the same amount of CaCl2 or CaBr2 was added, up to 32% Au entered the gas phase. When CaF2 was added to the system, 22%–49% of Ag entered the gas phase. However, when CaCl2 or CaBr2 was added, 3%–34% of Ag entered the gas phase. The proportion of tin in the gas and slag phases increased with increasing temperature or the addition of halides. The METSIM simulation results showed that under optimized conditions, the crude copper contained more than 90 wt% copper, the discharged slag contained approximately 0.5 wt% copper, and the recovery rates of copper, gold, and silver were ≥98%. The heat generated from raw materials and fuel accounted for the largest part of the heat income, representing 65.32% of the total.

Evading the refining-induced trade-off between performance enhancement and alloy composition deviation in Fe-based amorphous alloys

Understanding the slag-metal reactions in Fe-based amorphous alloys is of paramount importance to evade the refining-induced trade-off between performance enhancement and alloy composition deviation. In this study, the B2O3 and B2O3–CaO slags refining-induced alloy composition deviation was theoretically and experimentally verified in Fe83Si2B12P3 (at.%) amorphous alloy, and a quaternary SiO2–B2O3–CaO–Al2O3 slag suitable for FeSiBP amorphous alloy was designed after the careful calculation of slag-metal equilibrium, slag viscosity and melting point. After refining with simple B2O3 and B2O3–CaO slags, the enrichment of B element and depletion of Si element in the FeSiBP amorphous alloy was confirmed due to the oxidation of constituent Si element and the reduction of B2O3 in the slag. The refining-induced alloy composition deviation can be effectively alleviated by using our designed slags, and the 20%SiO2–55%B2O3–10%CaO–15%Al2O3 (wt.%) slag is effective in removing the impurities and enhancing the glass-forming ability (GFA). In terms of the removal of impurities, the high activity of B2O3 in slag is crucial for the oxidation and removal of Mn, Al, Ti impurities. These results are quite vital for the design of refining slags suitable for Fe-based amorphous alloys and pave the way for the large-scale production of high-performance soft magnetic materials.

Improved Settling Mechanisms of an Industrial Copper Smelting Slag by CaO Modification

A significant source of copper losses from pyrometallurgical copper extraction is attributed to dissolved and entrained copper in discarded slag. Entrained copper can be recovered via pyrometallurgical slag cleaning in a settling furnace, where the slag viscosity and copper droplet size distribution (CDSD) are critical parameters. Reduced copper losses suggest improved raw material efficiency, and the slag becomes a more environmentally safe byproduct. In this study, iron silicate slags from a smelting furnace are industrially CaO modified in a fuming furnace to contain a CaO content between 8 and 18 wt.%. The viscosity of slags with and without CaO modifications is evaluated in the temperature range from 1423 to 1723 K. The influences of the CaO modifications on the CDSD, slag matrix copper content, and total copper content were determined. The results show that the slag viscosity decreases with increasing CaO concentrations in the slag. In addition, the copper content decreases in the slag phase, and the CDSD shifts to contain relatively larger droplets. The effect of CaO slag modification reveals a linear relationship between the overall copper recovery and viscosity, which increased from 63 to 88% when the viscosity in the respective batch was 0.51 and 0.25 Pa·s.Graphical

Influence of Slag and Refractory Materials on Inclusions during the Ladle Refining of Low Carbon Aluminum Killed Steel

The evolution of inclusions in low carbon Al killed steel during ladle refining of was studied based on industrial experiments, in which high basicity slag was used. The results showed that inclusions experienced the changes from Al2O3 → MgO-Al2O3 → CaO-MgO-Al2O3 → CaO-Al2O3. Without calcium treatment, MgO-Al2O3 inclusion in steel were largely transformed into CaO-MgO-Al2O3 or CaO-Al2O3. With the aim to decrease MgO-Al2O3 inclusions and to clarify the effects of refining slag and refractory materials on inclusions, laboratory experiments were performed with lower basicity refining slag (lower basicity slag theoretically helps reduce spinel-type inclusions) in MgO and Al2O3 crucibles. The results indicated that, the dissolved Al in liquid steel would react with MgO and CaO in slag or in refractory at 1600 °C. Hence, [Mg] and [Ca] would be supplied into bulk steel. Due to the large contact area between MgO-based refractory and steel, as well as the higher activity of MgO in the refractory, Mg can be more easily reduced, which accounts for the easy modification of Al2O3 into MgO-Al2O3. By contrast, because of the limited supply of [Ca] to steel, modification of MgO-Al2O3 into CaO-MgO-Al2O3 or CaO-Al2O3 was incomplete. With the use of Al2O3-based refractory and reefing slag basicity of about 2.45, MgO-Al2O3 inclusions were obviously decreased.

Slag optimization to control CaO increase in inclusions during vacuum degassing of high carbon chromium-bearing steel

ABSTRACT The impacts of slag composition on the CaO content in inclusions during vacuum degassing(VD) treatment are presented. Industrial trials and thermodynamic calculations are used to test, analyze and identify proper optimization method. After optimization, the CaO content of inclusions after VD treatment decreases from 11.3mass% to 7.4mass%. Furthermore, the quantity of CaO containing inclusions in hot-rolled bar decreases from 146 to 41 as well. It is found that the ideal kinetic conditions and the evaporation of Ca during VD process combined trigger and are expected to further enhance the reaction between Al in liquid steel and CaO in slag. Some of the Ca generated from slag will further react with the inclusions which leads to the increase of CaO content in inclusions and equivalent circle diameter of the inclusions. The mathematical correlations among the components of slag in equilibrium with that of liquid steel is obtained by thermodynamic calculations.

Design of Refining Slag Based on Structural Modifications Associated with the Boron Removal for SoG-Si.

Solar grade silicon (SoG-Si) is the core material of solar cells. The removal of boron (B) has always been a challenge in the preparation of high purity Si. Slag refining has always been considered as one of the effective methods to remove B, but the design of refined slag has been limited by the cognition of the relationship between slag structure and impurity removal, and can only rely on the apparent basicity and oxygen potential adjustment of slag based on a large number of conditional experiments. In order to clarify the B removal mechanism of slag refining from Si, nuclear magnetic resonance (NMR) and Raman vibrational spectroscopy were used to investigate in detail the behavior and state of B and aluminum (Al) in the SiO2–CaO–Al2O3–B2O3 slag. The role of the degree of B–Si cross linking on the B activity in slag was highlighted by comparing the partition ratio (LB) between slag and Si. Q2 structural unit of slag is an important site for capturing B. BO4 (1B, 3Si) species is the main form of connection between B and silicate networks, which determines the activity of B in the slag. The addition of Al2O3 into SiO2–CaO slag can change the relative fraction of Q2 and BO4 (1B, 3Si). Increasing Al2O3 content from 0 to about 20 wt% can lead to the overall increase of Q2 population, and a tendency to decrease first and then increase of BO4 (1B, 3Si) fraction under both basicity conditions (0.6 and 1.1). When Al2O3 content is less than 10 ± 1 wt%, the decrease of BO4 (1B, 3Si) population plays a major role in deteriorating the connectivity between B and aluminosilicate network, which leads to a higher activity of B. When the Al2O3 content is greater than 10 ± 1 wt%, B is incorporated into the silicate network more easily due to the formation of more Q2 and BO4 (1B, 3Si), which contributes to a rapid decline in activity of B in slag.

Determination of the Partial Contributions to the Electrical Conductivity of TiO2-SiO2-Al2O3-MgO-CaO Slags: Role of the Experimental Processing Conditions

The electrical transport properties of molten TiO2–SiO2–Al2O3–MgO–CaO slags were determined as a function of temperature and oxygen partial pressure. To avoid the corrosion of crucible materials by this slag at ultra high temperatures, the pendant droplet technique was used inside a modified floating zone furnace. Electronic and ionic transference numbers were estimated using stepped-potential chronoamperometry experiments to quantify the contribution of the electronic/ionic conductivity to the total electric conductivity. The results show that these slags are mixed conductors, where current is carried by ionic and electronic carriers. The oxygen partial pressure dependence of the electronic transference numbers, t_e, indicated a semiconducting mechanism in the molten slag. The ratio of the different valences of the transition metal ions had a predominant effect on the t_e. The {{text{TiO}}_{2}} content also favoured electronic conduction, while the effect of temperature and structure was less noticeable within the temperature and composition range studied.

Post-mortem analysis of Cr2O3-Al2O3-ZrO2 refractory bricks used in an industrial opposed multi-burner gasifier

Periodical relining of the gasifier due to refractory corrosion and failure is a major cost driver in the coal gasification industry. In the present work, the failure mechanisms of Cr2O3-Al2O3-ZrO2 refractory bricks taken from different areas of an industrial opposed multi-burner (OMB) gasifier were investigated by post-mortem analysis. The results demonstrated that a densified (Mg, Fe)O-n(Al, Cr)2O3 complex spinel layer was attained on surface of refractory, which inhibited the further infiltration of slag. The SiO2 and CaO in slag were the main corrosive components and infiltrated into the refractory through pores and cracks. Damage of used bricks was mainly due to crack growth as well as structural spalling caused by different thermal expansion coefficient of de-zirconium layer, infiltration layer and original brick layer. In addition, the failure mechanisms of refractory bricks in different areas were also different owing to unique flow field and structure of OMB gasifier. The dome brick has the smallest wear, which was mainly destroyed by thermal corrosion, the strong scouring of upward flow unit and folded back flow unit. The sidewall brick was damaged by the scouring of high-speed airflow, chemical corrosion and high temperature creep. The damage of lower cone brick was mainly caused by strong mechanical scouring and structural spalling, which has the shortest service life.

Direct microalloying of steel with cerium under slags of СаО–SiO 2 – Ce2O3– 15 % Al2O3 –8 % MgO system with additional reducing agents

An assessment of the possibility of steel direct microalloying with cerium was performed using thermodynamic modeling of cerium reduction from slags of CaO– SiO2– Ce2O3 system containing 15 % Al2O3 and 8 % МgO, additional additives of reducing agents (aluminum or ferrosilicoaluminium), at temperatures of 1550 and 1650 °C using the HSC 6.1 Chemistry (Outokumpu) software package. Depending on the additional additives of aluminum or ferroglycoaluminium, metal temperature, slag basicity and content of cerium oxide, 0.228 to 40.5 ppm of cerium transfers into the metal. With an additional additive of aluminum from slag (Y1) containing 1.0 % of cerium oxide, 0.228 ppm of cerium is transferred to the metal at 1550 °C. An increase in the system temperature to 1650 °C is accompanied by a slight increase in cerium content, reaching no more than 0.323 ppm. When added to ferrosilicoaluminium metal, cerium content in the metal is higher and amounts to 0.402 and 0.566 ppm at 1550 and 1650 °C, respectively. When concentration of cerium oxide in the slag (Y2) increases to 7.0 %, more signifcant increase in cerium content in the metal is observed, reaching in temperature range of 1550 – 1650 °C, 1.65 – 2.31 ppm with aluminum additives and 2.90 – 4.05 ppm with ferrosilicoaluminium additives. The most noticeable increase in cerium content in the metal is observed with an increase in slag basicity. During formation of slags with basicity of 2 – 3, containing 1 – 7 % Ce2O3, the equilibrium concentration of cerium in the metal varies from 0.5 to 4 ppm with aluminum additives and 1 – 7 ppm with ferro­silicoaluminium additives at 1550 °C. Slags transfer to the increased (up to 3 – 5) basicity is accompanied by an increase in the equilibrium content of cerium in the metal to 4 – 12 ppm with aluminum additives and 7 – 20 ppm with ferrosilicoaluminium additives at Ce2O3 content of 3 – 7 % and, as a result, an increase in efciency of cerium reduction process.

Settling of Copper Phases in Lime Modified Iron Silicate Slag

Copper in discarded slag decreases the profits and copper recovery during the pyrometallurgical extraction processes. The copper losses to slag can be reduced by using a settling furnace, in which mechanically entrained copper droplets separate from the slag under the action of gravity. The settling rate of entrained droplets can be increased by modifying the slag composition and, thus, the slag properties, which are known to influence the settling rate. The knowledge of industrial CaO slag modification in a reduced iron silicate slag with a Fe/SiO2 ratio close to unity is limited. An industrial trial was thus conducted in an electric settling furnace, where the slag had been pretreated in a fuming furnace, to investigate the effect of CaO slag modification on the final slag copper content. Slag samples were collected from the ingoing and outgoing slag and from within the furnace of batches modified with CaO up to about 16 wt %. The trial was evaluated by comparing the final slag copper content and the copper recovery in the settling furnace. The results indicate that the settling becomes more efficient with the CaO modification as the final slag copper content decreased with increasing CaO content.

Electrochemical Study on the Reduction of Si and Ti from molten TiO2–SiO2–Al2O3–MgO–CaO Slag

The reduction process during the electrochemical production of titanium via the electrolysis of molten TiO2–SiO2–Al2O3–MgO–CaO slags has been investigated. A laboratory scale, electrolytic cell was designed to study the effect of TiO2 concentration at ultra-high temperatures. Galvanostatic and potentiostatic experiments were performed and results were consistent with thermodynamic predictions using FactSage. We demonstrate the direct production of Si-Ti alloys from the molten oxide mixture. The reduction of Si and Ti ions from the melt on a molybdenum electrode is a complex process that combines electron transfer and chemical phenomena. For the concentrations studied, the extraction of pure metallic Ti directly from ironmaking slag is unlikely without the prior removal of SiO2 or other chemical modifications to the system.

Thermodynamic Modeling of Reduction of Cerium from Slags of CaO–SiO2–Ce2O3–15Al2O3–8MgO by Calcium Carbide Additives

Thermodynamic modeling of the reduction of cerium from slags of the CaO–SiO2–Ce2O3 system containing 15% Al2O4 and 8% MgO, with aluminum dissolved in the metal together with calcium carbide additives at temperatures of 1550 and 1650°C was performed using the HSC 8.03 Chemistry software package (Outokumpu) based on the simplex lattice planning method used to minimize Gibbs energy. The results of thermodynamic modeling are presented in the form of composition-property diagrams (equilibrium content of cerium in the metal) for temperatures of 1550 and 1650°C. It is shown that the formation of slags within a basicity range of 2–3 containing 1–7% Ce2O3 provides an equilibrium concentration of cerium in the metal varying from 1 to 7 ppm at a temperature of 1550°C. The displacement of slags in the area of increased basicity (up to 3–5) is accompanied by an increase in the equilibrium concentration of cerium in the metal up to 7–23 ppm with a content of 3–7% Ce2O3 and as a consequence an increase in the efficiency of the process of cerium reduction. At a temperature of 1650°C, the equilibrium concentration of cerium in the metal within the basicity range of 2–3 and having a Ce2O3 content of 1–7% varies from 2 to 12 ppm. The displacement of slags in the area of increased basicity (up to 3–5) is accompanied by an increase in the equilibrium concentration of cerium in the metal to 7–33 ppm with a Ce2O3 content of 3–7%. The positive influence of the temperature factor basicity of slags and the content of cerium oxide on the process of its reduction is qualitatively explained from the standpoint of the formation of the phase composition of the slags of the studied oxide system and the thermodynamics of chemical reactions of reduction of cerium with aluminum dissolved in the metal, as well as with aluminum dissolved in the metal together with calcium carbide additives.

Experimental Study and Thermodynamic Calculations in the CaO–Cu2O–FeO–Fe2O3–SiO2 System for Applications in Novel Copper-Based Processes

A combination of high-temperature experiments and thermodynamic modeling in the CaO–Cu2O–FeO–Fe2O3–SiO2 system provides the fundamental information necessary to design and improve processes such as WEEE recycling through black copper route, continuous converting of copper matte, copper dross smelting, slag cleaning, and valorization of copper slag. In the experiments, samples were equilibrated on a primary phase substrate or Fe metal foil, then rapidly quenched and studied using the Electron Probe X-ray Microanalysis. The FactSage software was used for calculations, combined with custom developed thermodynamic database. A systematic analysis is provided to select the fluxing strategy and increase the copper recovery in industrial processes. Slag liquidus and concentration of copper in slag were assessed as functions of oxygen partial pressure, temperature, Fe/SiO2 in slag, and wt% CaO in slag.

Electrochemical Study on the Reduction of Si and Ti from Molten TiO2 - SiO2 - Al2O3 - MgO - CaO Slag

Recently, the electrochemical recovery of metals from molten TiO2 - SiO2 - Al2O3 - MgO - CaO slag has been proven feasible. The use of the largest by-product of the ironmaking process as an electrolyte has the potential of producing titanium metal in a more sustainable and environmentally friendly manner than the current Kroll process. However, a more extensive understanding of the electrochemical behaviour of this complex oxide system in its molten state is paramount for the design of industrial electrolytic cells. In this work, we present the results from molten oxide electrolysis experiments performed above 1500 °C, and we discuss the effect of the experimental processing conditions on the reduction of Si and Ti ions from the melt.

Effect of basicity and chromium oxide on the viscosity of boron-containing slags

The main diluent for chromium-containing slags is CaF2. However, fluorspar disadvantages make it necessary to search for a replacement. As a substitute, boron oxide allows to improve slag physical properties and environmental situation. The paper presents the experimental study results of the chemical composition and temperature influence on viscosity of slags of CaO–SiO2–Cr2O3 system containing 8% MgO, 3% Al2O3 and 6% B2O3. It was found that a slag free of chromium oxide with basicity of 1.0 has a sufficiently high fluidity of 0.2–0.6 Pa·s in a wide temperature range of 1200–1350°C, due to high concentration of low-melting phases, reaching 22%, and only 11 % high-melting. A slag with 18% Cr2O3 and the same basicity retains a low viscosity of 0.1–1.0 Pa·s but at higher temperature of 1450–1570 °C due to increase in high-melting compound content to 27%. The viscosity of a slag with basicity of 2.5 without chromium oxide is 0.07–1.0 Pa·s in a narrow temperature range of 1650–1700°C and 0.14–1.0 Pa·s for a ‘shorter’ slag with 18% Cr2O3 and same basicity in even narrower range of 1650–1670°C. These slags have the highest high-melting phase content of about 50%.

Study of possibility of cerium reduction from slags of CaO-SiO2-Ce2O3–15%Al2O3–8%MgO system

By means of theoretical and experimental studies it is shown that it is possible to reduction cerium from the slags of the CaO–SiO2–Ce2O3 system containing 15%Al2O3 and 8 % MgO, by aluminum dissolved in metal, at temperatures of 1550 and 1650°C. The results of mathematical modeling are presented graphically as ‘composition – equilibrium content of cerium in metal’ diagrams. It is found that depending on temperature of metal, basicity of slag and the content of cerium oxide, from 0.055 to 16 ppm cerium passes into metal containing 0.06 % of carbon, 0.25 % of silicon and 0.055 % of aluminium. Positive influence of the temperature factor, basicity of slags and the content of cerium oxide in a studied range of chemical composition on process of cerium reduction is explained from the perspective of phase structure of formed slags and thermodynamics of reactions of cerium reduction. The possibility of reduction of cerium from slags of CaO–SiO2–Ce2O3 system, containing 15 % Al2O3 and 8 % MgO, has been experimentally confirmed. It has been shown that at basicity of 5 and 4 % of Ce2O3 in slag up to 16 ppm cerium passes into metal during 10 minutes exposure.

Effect of basicity and Al2O3 on viscosity of ferronickel smelting slag

The effect of the Al2O3 content and basicity (the molar ratio of MgO to SiO2) on the viscosity of a SiO2–MgO–FeO–Al2O3–CaO slag was studied to fully understand the smelting process of the ferronickel alloy. Experimental results show that the slag is a mixture of liquid and solid phases at the experimental temperature. The viscosity decreased as the basicity increased and increased as the Al2O3 content increased. To determine the effect of the Al2O3 content and basicity on the structure of the molten slag, Raman spectroscopy was performed on the slag sample, which was quenched from the high temperature with water. The Raman spectra showed that the fractions of the polymerization structural units decreased significantly as the basicity of the slag increased, resulting in a decrease in the apparent viscosity. However, Al2O3 acts as a network former in the slag system, thereby making the slag structure further polymerized and increasing the viscosity.