Liquid Slag Phase Research Articles

Thermodynamic re-optimization of the CaO-FeO-Fe2O3 system integrated with experimental phase equilibria studies (Part II – Thermodynamic optimization)

The Ca-Fe-O system is essential for understanding the chemical equilibria involved in copper production using calcium ferrite slags. It forms a core component of a complex 20-component Cu-Pb-Zn-Fe-Ca-Si-O-S-Al-Mg-Cr-Na-As-Sn-Sb-Bi-Ag-Au-Ni-Co system developed for diverse applications in ferrous and non-ferrous metallurgy. This study re-evaluates the Ca-Fe-O system using recent experimental phase equilibrium data acquired by the authors (Cheng et al., 2024) [1] through advanced equilibration, quenching, and Electron Probe X-ray Microanalysis (EPMA) techniques. Thermodynamic properties of solid phases have been revised in accordance with the recommendations for the third generation of Calphad databases. Liquid endmember heat capacities have been refined to describe glass transition behaviour in supercooled liquids. The updated properties of liquid endmembers significantly extend the applicability of the database, enabling lower-temperature applications related to toxic element leaching from amorphous and partially crystallized slags. The revised, higher melting temperature of CaO enhances predictive accuracy in multicomponent systems. Liquid slag phase has been modelled within the Modified Quasichemical Formalism to account for short-range ordering phenomena. Recent advances in modelling and optimization technique made it possible to assess experimental data within the Ca-Fe-O system as an integral part of a large multicomponent dataset, applicable for industrial conditions.

Analysis of magnesia-carbon bricks erosion in vanadium extraction converters: Insights from dynamic experiments and interface characterization

This paper uses a rotary furnace to simulate the dynamic erosion behavior of various magnesia-carbon bricks within a vanadium extraction converter, focusing on the effects of carbon content and antioxidants on erosion. The results indicate that vanadium-rich slag primarily consists of oxide solid solutions, iron vanadium spinel, and metallic Fe. Adding aluminum and silicon powders to the bricks reduces apparent porosity, increases body density, and improves slag erosion resistance. However, an increase in carbon content (12.54 wt% to 18.59 wt%) within magnesia-carbon bricks correlates with decreased high-temperature strength, exacerbating the reaction propensity with slag and consequent structural damage. Analysis of the interface phase between magnesia-carbon bricks and vanadium slag reveals a predominance of metal phase, spinel phase, and liquid slag phase. Thermodynamic calculations suggest an initial reaction between MgO and C on the brick surface, yielding Mg vapor and CO gas, while C reacts with slag to produce Cr and V elements, leading to surface structure degradation. Subsequent slag encasement and dissolution of remaining MgO via decarburization channels further erode magnesia-carbon bricks. Cumulative erosion iterations ultimately culmi nate in performance failure of magnesia-carbon bricks.

Thermodynamic re-optimization of the CaO–SiO2 system integrated with experimental phase equilibria studies

CaO–SiO2 is the key system in ferrous and non-ferrous metallurgy, ceramic manufacture, cement production, and other applications. A number of discrepancies and gaps in knowledge has been identified and resolved since the last thermodynamic optimization of this system. This study reports new experimental phase equilibria data measured using recent advances in equilibration, sample quenching, and Electron Probe X-ray Microanalysis (EPMA) technique. An updated self-consistent set of thermodynamic model parameters is provided. Most importantly, these updates are integrated with a complete re-assessment of the 20-component Cu–Pb–Zn–Fe–Ca–Si–O–S–Al–Mg–Cr–Na–As–Sn–Sb–Bi–Ag–Au–Ni–Co system directly relevant to applications in the ferrous and non-ferrous metallurgical industries. To obtain a large single set of model parameters, significant advances were made in the computational approach, with a focus on simultaneous parallel optimization of binary and ternary model parameters using an experimental dataset combining binary, ternary, and multicomponent information. The Modified Quasichemical Formalism is used for the liquid slag phase. Thermodynamic properties of solid phases and liquid endmembers are completely revised following the recommendations for the third generation of CALPHAD databases. Other notable changes include the revision of the melting temperature of CaO, justified by extrapolations from the multicomponent systems, as well as a physically realistic heat capacity function for metastable SiO2 below the glass transition temperature. These updated properties expand the areas of application of the database to amorphous and partially crystallized slags at ambient temperatures, such as thermodynamics and kinetics of leaching of toxic elements in an aqueous environment. The fundamental limitations of the existing Modified Quasichemical Formalism are also discussed, along with strategies for addressing them.

Phase Equilibria and Thermodynamic Modelling of the PbO-ZnO-FeO-FeO1.5-SiO2 system and its subsystems in equilibrium with air/metallic lead/iron

The phase equilibria of the ZnO-“FeO1..5”, ZnO-“FeO1.5”-SiO2, PbO–ZnO-“FeO1.5” and PbO–ZnO-“FeO1.5”-SiO2 slag systems in equilibrium with air or metallic lead/iron were studied as part of the investigation of the 19-component PbO–ZnO–Cu2O–FeO–Fe2O3–CaO–SiO2–Al2O3–MgO–S-(As, Sn, Sb, Bi, Ag, Au, Ni, Cr, Co as minor elements) slag/matte/metal/speiss/gas system, supporting the operation/development of existing and emerging pyrometallurgical processes. In the experimental part of the study, samples underwent high temperature equilibration followed by quenching, and the direct measurement of the lead, zinc, iron and silicon concentrations in the liquid slag, solid oxide, and metal phases by electron probe microanalysis (EPMA). The a) massicot (PbO), b) spinel ((Zn, Fe)Fe2O4), c) zincite ((Zn,Fe)O1+x, 2 polymorphs), d) lead ferrite (Pb2+xFe2O5+x), e) plumboferrite (Pb4Fe22-xZnxO37), f) magnetoplumbite (Pb(Fe2O3,PbFeO2,PbZnO2)Fe10O16), and g) W-ferrite (PbZn2-xFe16+xO27) primary phase fields of the PbO–ZnO-“FeO1.5” system in equilibrium with air were studied between 780 and 1300 °C. The ZnO-“FeO1.5”, ZnO-“FeO1.5”-SiO2 and PbO–ZnO-“FeO1.5”-SiO2 systems in equilibrium with air were studied up to 1745 °C, significantly improving the availability of information on the composition range of the high- and low-Fe zincite ((Zn,Fe)O1+x) phases, and on the liquid slag composition at the boundaries of their primary phase fields. Lastly, the solubilities of iron in larsenite (Pb(Zn,Fe)SiO4) and melilite (Pb2(Zn,Fe)Si2O7) in equilibrium with air or metal were studied between 700 and 800 °C. The newly obtained and existing experimental data were used to develop a self-consistent set of thermodynamic parameters describing all phases in the system using the FactSage computer package.

Experiment and thermodynamic modelling of phase equilibria in PbO−“CuO0.5” and PbO−“CuO0.5”−“FeO1.5” slag systems with metal

The phase equilibria of the PbO−“CuO0.5” and PbO−“CuO0.5”−“FeO1.5” slag systems in equilibrium with solid metallic copper and/or liquid metallic lead−copper alloy were studied as part of the investigation of the 19-element PbO−ZnO−Cu2O−FeO−Fe2O3−CaO−SiO2−Al2O3−MgO−S−(As, Sn, Sb, Bi, Ag, Au, Ni, Cr, Co as minor elements) multicomponent slag/matte/metal/speiss system, supporting the operation and development of the existing and emerging pyrometallurgical processes. In the experimental portion of this study, samples underwent high temperature equilibration followed by quenching, after which the compositions in the liquid slag, solid oxide and metallic phases were directly measured by electron probe microanalysis (EPMA). Phase equilibria data on the massicot (PbO), spinel ((Fe, Cu)Fe2O4), cuprite (Cu2O), lead ferrite (Pb2+xFe2O5+x), magnetoplumbite (Pb1+xFe12−xO19−x), copper plumbite (Cu2PbO2), and delafossite (CuFeO2) primary phase fields were obtained between 688 and 1000 °C. A key finding of the experimental study of the PbO−“CuO0.5” subsystem was that the copper plumbite (Cu2PbO2) phase melted incongruently, contradicting previous studies that suggested it apparently decomposed below the binary eutectic temperature to form massicot (PbO) and cuprite (Cu2O). Based on the results of past and present experimental studies, a self-consistent set of thermodynamic model parameters describing all phases in the system was derived using the FactSage software package.

Recycling of silicon from waste PV diamond wire sawing silicon powders: A strategy of Na2CO3-assisted pressure-less sintering and acid leaching

Recycling diamond wire sawing silicon powders (DWSSP) from photovoltaic (PV) silicon wafers production has become an urgent problem. The challenge of recovery is the surface oxidation and contamination of the ultra-fine powder with impurities during the sawing and collection process. In this study, a clean recovery strategy of Na2CO3-assisted sintering and acid leaching was proposed. Due to the Al contamination from the perlite filter aid, the introduced Na2CO3 sintering aid can react with the SiO2 shell of DWSSP to form a slag phase with accumulated impurity Al during the pressure-less sintering process. Meanwhile, the evaporation of CO2 contributed to the formation of ring-like pores surrounded by a slag phase, which can be easily removed by acid leaching. When 15 % Na2CO3 was added, the content of impurity Al in DWSSP could be reduced to 0.07 ppm with a removal rate of 99.9 % after acid leaching. The mechanism suggested that the addition of Na2CO3 can trigger the liquid phase sintering (LPS) process of the powders, and the cohesive force and liquid pressures difference generated during the process facilitated the transportation of impurity Al from the SiO2 shell of DWSSP to the formed liquid slag phase. The efficient silicon recovery and impurity removal of this strategy demonstrated its potential for solid waste resource utilization in the PV industry.

Dissolution mechanism of magnesium aluminate spinel in copper smelting slag based on the shrinking core reaction models of corrosion

MgAl2O4 spinel is a critical raw material in spinel refractory production. However, the dissolution behavior of the spinel and its interactions with Cu smelting slag have not been previously studied in detail in terms of thermodynamics and kinetics. Therefore, to investigate the interactions of MgAl2O4 spinel in Cu smelting slag, MgAl2O4 spinel was simulated in Cu smelting slag using FactSage. Additionally, the dissolution mechanism of MgAl2O4 spinel in Cu smelting slag was studied via a slag immersion method. It was found that the Fe ions of the Cu smelting slag diffused mutually with the Mg2+ and Al3+ in the spinel, and the final products of the spinel reaction with the slag were ASpinel (Mg1-xFexAl2-yFeyO4) solid solution and liquid slag phases. The dissolution mechanism was consistent with the shrinking core reaction models. In the early stage of dissolution, ASpinel (Mg1-xFexAl2-yFeyO4) was generated at the interface, and the dissolution mechanism was controlled by the rate of solid solution phase generation, with an activation energy of E1 = 153.17 kJ/mol. At the later stage of dissolution, the Fe ions continued to diffuse into the spinel through the solid solution phase, while the spinel dissolved into the slag, and the dissolution mechanism was controlled by the rate of boundary migration of the solid solution phase, with an activation energy of E2 = 110.84 kJ/mol. Meanwhile, this interdiffusion behavior led to an increased liquid viscosity compared to that of the original slag that could further slow slag infiltration. The spinel could absorb Fe ions, rendering it a promising candidate for use in the Cu industry in the field of chromium-free refractories.

The Effect of TiO2 in the Ladle Slag on Inclusion in Ti‐Bearing Steel

To improve the castability of Ti‐bearing steel, the knowledge of inclusions formed in liquid steel, affected by the slag composition, must be obtained. In this study, the effect of TiO2 in ladle slag on inclusions in this steel at 1873 K is investigated. Experimental results indicate that Ca–Mg–Al–Ti–O complex inclusions, complex TiN inclusions containing MgO–Al2O3–TiOx cores, Ti–C–S inclusions, and TiC inclusions appear in the steel samples. The cores in TiN inclusions are mainly in the liquid and liquid + spinel fields before slag addition. When the steel reacts with slag containing 0% TiO2 for 1 h, the inclusions in the steel are mostly in the MgO + liquid + spinel and MgO + liquid field and have the highest MgO content. When the steel reacts with slag containing 5%≈20% TiO2 for 1 h, most inclusions are liquid slag + spinel and liquid slag phases. The average liquid fraction in most inclusions is higher than 60%. The ratio of the (mass percentages Ti3+) to (Ti3++mass Ti4+) in most liquid phases is approximately 50%≈70% for these oxide cores. Increasing TiO2 content in slag increases log(), which in turn decreases Mg content in the steel. This decreases MgO content in MgO–Al2O3–TiOx type inclusions.

Investigation of biomass, RDF and coal ash-related problems: Impact on metallic heat exchanger surfaces of boilers

The goal of this work was to study the corrosion resistance of boiler steel and protective alloy coatings. Four ashes obtained from wood biomass, straw, refused-derived fuel and coal were analysed. The aggressive components of ash, such as potassium, sodium, sulphur and chlorine, can accelerate the operating problems of heat exchanging surfaces in power boilers, leading to enhanced slagging, fouling, agglomeration of ash, and corrosion. Four boiler steels were chosen for detailed investigation: 16Mo3, P265GH, Inconel 625 and 686. They were covered with ashes, placed in a furnace and heated through 4 months at 750 °C under oxidizing conditions. Multifaceted ash analysis (chemical composition, thermal behaviour, phase composition, and characteristic melting temperatures) was performed. Additionally, both slagging and fouling indices were calculated to predict the sintering properties of the studied ashes. The surfaces of studied steels after the exposure of ash presence were analysed using SEM-EDS technique. The results showed that the corrosive impact of the ashes depended on the aggressive components present in the ash. Furthermore, FactSage thermochemical equilibrium calculations were used to predict the amount of liquid slag and solid phases under the studied conditions and to determine the transformation of the mineral phases of the ash.

Thermodynamic and Experimental Study on Migration Characteristics of Heavy Metals during the Melting Process of Incineration Fly Ash

The migration characteristics of heavy metals during the melting process were one of the key factors for safe treatment and resource utilization of incineration fly ash (IFA). In this paper, the material variation of heavy metal elements of Pb, Zn, Cu, and Fe during the IFA melting process was simulated by HSC 6.0 chemistry software. The effects of melting temperature, alkalinity, atmosphere, chlorine content of raw materials, and an iron bath added to the migration characteristics, and phase transformation of selected heavy metal elements was investigated. The simulation results were also verified by experimental results. The results showed that, with the increase in temperature, the gas phase proportion of Pb, Zn, Cu, and Fe gradually increased. The alkalinity had little effect on the proportion of elements Fe and Cu in the liquid slag (LS) phase and the element Pb in the gas phase, but the increase in alkalinity could inhibit the proportion of element Zn in the gas phase. Zn mainly existed in the gas phase, and the atmosphere had little influence on the distribution of Zn. In reducing atmosphere (RA), elements Fe and Cu, which entered the liquid metal (LM) phase, were promoted, while the volatilization of Pb was restrained, which was conducive to the recovery of heavy metals. The melting process of IFA with water-washing and dechlorination had an inhibitory effect on the volatilization of Zn and Pb, but had little effect on Fe and Cu. The proportion of element Zn in the gas phase reduced from 85.84% to 9.89%. With the iron bath added in the IFA melting process, 98.42% of Cu and 82.28% of Pb entered the LM phase as metal simple substances, and 76.3% of Zn entered the gas phase as Zn (g) and ZnCl2 (g). In the experimental verification, the distribution proportions of the four heavy metals in the gas phase, LS phase, and LM phase were consistent with the simulation results.

Thermophysical properties of synthetic slags of the FeO – MnO – CaO – Al2O3 –– SiO2 system

In the electrometallurgy of manganese alloys, viscosity has an important effect on the production indicators from the physicochemical properties of slag. During the smelting of manganese alloys, the main amount of heat spent on reduction reactions is released due to the current passing through the liquid slag phase, since the resistance of the latter, depending on the composition, affects the completeness of the reduction of manganese from melts. In the case of refined ferromanganese by the silicothermic method, the vast majority of silicon of silicomanganese is refined with higher manganese oxides or it is burned out due to oxygen in the air. The paper presents the results of thermophysical properties of slags representing the FeO - MnO - CaO - Al2O3 - SiO2 system. Laboratory experiments were carried out on synthetic slags by varying the slag basicity CaO / SiО2 = 1.5 - 1.9 and the concentration of Al2O3 = 5 - 15%. As a result, graphs of the dependence of these properties on temperature values are constructed, the activation energies of the viscous flow are calculated and the phase compositions of the experimental slags are determined using a mathematical model of the diagram of the FeO - MnO - CaO - Al2O3 - SiO2 system. Thus, an increase in the concentration of aluminum oxide against its usual level, changing the basicity of the slag, significantly affected the physicochemical properties of the slag and thereby contributes to the adjustment of the parameters of the electric melting process. At the same time, it is advisable to study the interaction of some Physical chemical properties of slags on the melting conditions of manganese ferroalloys in relation to the composition of slags.

Thermodynamic modeling of CaO-SiO2-VOx system by the generalized central atom model

With the aim of modeling the vanadium partitioning behavior in iron and steelmaking process, the steelmaking slags model/database was extended for covering the vanadium. In this paper, the binary CaO-VOx, SiO2-VOx and ternary CaO-SiO2-VOx systems were assessed and optimized based upon available phase equilibrium and thermodynamic data. The Generalized Central Atom (GCA) Model was used for describing the liquid slag phase while all intermediate vanadium containing solid phases are treated as stoichiometric compounds. During the optimization, effort was focused on the slag liquidus and its primary solid phases. The obtained model parameters can represent the reliable experimental data reasonably well. The sub-solidus regions at low temperature are not well assessed.

Integrated experimental phase equilibria study and thermodynamic modeling of the PbO–SnO–SnO2–SiO2 system in air and in equilibrium with Pb–Sn metal

Phase equilibria of the PbO-SnO-SnO2-SiO2 slags with solid phases (cristobalite, tridymite and quartz SiO2, cassiterite SnO2, massicot PbO, lead stannate Pb2SnO4, and lead-tin silicate Pb3Sn2SiO9) were studied at 800–1730 °C in air and in equilibrium with Pb-Sn metal. High-temperature equilibration on silica, platinum or platinum–iridium foil, or on MgO substrates, followed by quenching and direct measurement of Pb, Sn and Si concentrations in the phases using electron probe X-ray microanalysis (EPMA) was used to accurately characterize the system. Present experimental data were used to obtain a self-consistent set of parameters of the thermodynamic models for all phases in this system using FactSage computer package. The modified quasichemical model with two sublattices (Pb2+, Sn2+, Sn4+, Si4+)(O2-) was used for the liquid slag phase, while all solid phases were described as stoichiometric. A detailed review was done to reevaluate the properties of SnO and SnO2 slag endmembers and the melting point of cassiterite in air. Present study was a part of research program on the characterization of the multicomponent Pb–Zn–Cu–Fe–Ca–Si–O–S–Al–Mg–Cr–As–Sn–Sb–Bi–Ag–Au–Ni system.

Al2O3 and CaO as sintering aids: A strategy to remove impurity boron and SiO2 surface-layer of diamond wire saw silicon waste

Removing the SiO2 surface-layer and impurity boron in diamond wire saw silicon powder waste (DWSSP) are two difficulties in the field of photovoltaic waste recycling. Aiming at the two difficulties, this paper proposes a method of mixing sintering aids to digest the SiO2 layer and remove impurity boron. Firstly, sintering aids Al2O3 and CaO were mixed into DWSSP, and DWSSP-ceramics were prepared by pressure-less sintering. The mixed sintering aids reacted with the SiO2 surface-layer of DWSSP, and the formed liquid slag phase plays a role in promoting the densification of DWSSP-ceramics (the relative density reached 85.97% when sintered at 1300 °C). Secondly, to obtain low-boron silicon, the slag phase was separated from DWSSP-ceramics by smelting treatment. The results showed that an optimal boron removal effect of 45.32% was reached after only 10.11 wt% sintering aids were mixed into DWSSP. The mechanism that the liquid slag phase gathered impurity boron during the sintering process, and then promoted boron to remove from silicon was reasonably deduced. The method of mixing sintering aids to remove the SiO2 surface-layer and impurity boron provides a novel insight into purification and recovery of DWSSP.

Integrated experimental phase equilibria study and thermodynamic modelling of the binary ZnO–Al2O3, ZnO–SiO2, Al2O3–SiO2 and ternary ZnO–Al2O3–SiO2 systems

Phase equilibria of the ZnO–SiO2, Al2O3–SiO2 and ZnO–Al2O3–SiO2 systems at liquidus were characterized at 1340–1740 °C in air. The ZnO–Al2O3 subsolidus phase equilibria were derived from the experiments with the SiO2- and CaO + SiO2-containing slags. High-temperature equilibration on silica or platinum substrates, followed by quenching and direct measurement of Zn, Al, Si and Ca concentrations in the phases with the electron probe X-ray microanalysis (EPMA) was used to accurately characterize the system. Special attention was given to zincite phase that was shown to consist of two separate ranges of compositions: round-shaped low-Al zincite (<2 mol.% AlO1.5) and platy high-Al zincite (4–11 mol.% AlO1.5). A technique was developed for more accurate measurement of the ZnO solubility in the low-ZnO phases (corundum, mullite, tridymite and cristobalite) surrounded by the ZnO-containing slag, using l-line for Zn instead of K-line, avoiding the interference of secondary X-ray fluorescence. Solubility of ZnO was found to be below 0.03 mol.% in corundum and cristobalite, and below 0.3 mol.% in mullite. Present experimental data were used to obtain a self-consistent set of parameters of the thermodynamic models for all phases in this system using FactSage computer package. The modified quasichemical model with two sublattices (Zn2+, Al3+, Si4+) (O2−) was used for the liquid slag phase; the compound energy formalism was used for the spinel (Zn2+,Al3+)[Zn2+,Al3+,Va]2O2-4 and mullite Al3+2(Al3+,Si4+) (O2−,Va)5 phases; the Bragg-Williams formalism was used for the zincite (ZnO, Al2O3); other solid phases (tridymite and cristobalite SiO2, corundum Al2O3, and willemite Zn2SiO4) were described as stoichiometric. Present study is a part of the research program on the characterization of the multicomponent Pb–Zn–Cu–Fe–Ca–Si–O–S–Al–Mg–Cr–As–Sn–Sb–Bi–Ag–Au–Ni system.

Interaction between MgO–C-bricks and ladle slag with a 1:1 CaO/Al2O3 ratio and varying SiO2 content

The interaction between the industrial ladle lining bricks (carbon = 5-13 mass%) and secondary metallurgical slag (CaO/Al2O3 ratio = ~1; SiO2 = 1–20 mass%) was evaluated under laboratory conditions using finger testing between 1550 and 1650 °C. The thermophysical properties, including viscosity, density, and surface tension of the three slags were measured and compared with previously reported data. The experimental investigations were supported by thermochemical modelling (Factsage 7.2). The three lining materials exhibited different wear behaviour when in contact with each of the three slags at different temperatures. The slag with 1 mass% SiO2 was MgO-saturated and had a low viscosity compared to the slags with 10 and 20 mass% SiO2. This slag effectively infiltrated the lining without dissolving it at 1550 °C. With increasing temperature, the MgO saturation in the slag decreased, which led to the dissolution of the MgO grains from the mining bricks into the slag. Further, the carbothermal reaction began to dominate at higher temperatures, which led to carbon oxidation and the formation of new MgO. A solid spinel phase was observed in the slag with 10 mass% SiO2 below 1600 °C and in the slag with 20 mass% SiO2 at all investigated temperatures. Interaction with the lining materials intensified this spinel formation, which slowed or stopped slag infiltration. The high content of impurities in the lining material (e.g. SiO2, CaO, and Fe2O3) led to the formation of a liquid slag phase on the grain boundary, which compromised the strength of the material and caused the loss of MgO grains.

Investigating the effect of chemistry on the flash butt weldability of steels through a combination of experiments and modeling

Flash butt weld process parameters determine the weld quality. The presence of weld defects due to inappropriate process parameters leads to entrapment of oxides in the weld causes premature failure. It was also observed that the flash butt process parameter is dependent on the chemistry of the steel that is processed. The high weight percentage of Mn and Si leads to a higher weight fraction of the oxides during welding. Altering the flashing length and upset length leads to the elimination of weld defects achieving full joint strength. Thermodynamic calculations predict the oxides to be primarily FeO, Fe2O3 (hematite), and SiO2 (cristobalite) along with the presence of MnO, Mn2O3, and Cr2O3. The presence of Mn, Al, and Ti in the oxides at the fractured surface is correlated with the chemical potential of these elements in the liquid steel. It can be inferred from the modeling and experimental results that with an increase in temperature, a more liquid slag phase is formed as compared to solid oxides. Slag is less viscous and can be easily extruded during the upsetting stage as opposed to solid inclusion which can be trapped during the welding operation.

Behavior of phosphorus enrichment in dephosphorization slag at low temperature and low basicity

At low basicity and low temperature, the dephosphorization behavior and phosphorus distribution ratio (LP) between slag and molten steel in the double slag and remaining slag process were studied with a 180 t basic oxygen furnace industrial experiment. The dephosphorization slags with different basicities were quantitatively analyzed. At the lower basicity range of 0.9–2.59, both LP and dephosphorization ratio were increased as the basicity of dephosphorization slag increased. Dephosphorization slag consisted of dark gray P-rich, light gray liquid slag, and white Fe-rich phases. With increasing basicity, not only did the morphologies of different phases in the dephosphorization slag change greatly, but the area fractions and P2O5 content of the P-rich phase also increased. The transfer route of P during dephosphorization can be deduced as hot metal → liquid slag phase + Fe-rich phase → P-rich phase.

Distribution Behavior of Phosphorus in 2CaO·SiO2-3CaO·P2O5 Solid Solution Phase and Liquid Slag Phase

In this paper, the CaO-SiO2-FetO-P2O5 dephosphorization slag system during the premier and middle stage of the converter process was studied, the effect of slag composition on the distribution ratio and activity coefficient of P in the n·2CaO·SiO2-3CaO·P2O5 (recorded as nC2S-C3P) solid solution phase and liquid slag phase in the slag system was studied used by the high temperature experiment in laboratory, the theoretical calculation of thermodynamics, and the scanning electron microscope and the energy dispersive spectrometer (recorded as SEM/EDS). The research results show that when the FeO content in the liquid slag increases from 32.21% to 50.31%, the distribution ratio of phosphorus (recorded as LP) in the liquid slag phase increases by 3.34 times. When the binary basicity in the liquid slag increases from 1.08 to 1.64, the LP in the liquid slag phase decreases by 94.21%. In the initial slag, when the binary basicity increases from 2.0 to 3.5, the LP decreases by 70.07%. When FeO content increases from 38.00% to 51.92%, the LP increases by 6.15 times. When P2O5 content increases from 3.00% to 9.00%, the LP increased by 10.67 times. When the FeO content in the liquid slag increases from 32.21% to 50.31%, the activity coefficient of P2O5 in the liquid slag phase (recorded as γP2O5(L)) increases by 54.33 times. When the binary basicity in the liquid slag increases from 1.08 to 1.64, γP2O5(L) decreases by 99.38%. When the binary basicity increases from 2.0 to 3.5, the activity coefficient of P2O5 in the solid solution phase (recorded as γP2O5(SS)) in the solid solution phase decreases by 98.85%. When P2O5 content increases from 3.00% to 9.00%, γP2O5(SS) increases by 1.14 times. When the binary basicity decreases from 3.5 to 2.0, n decreases from 0.438 to 0.404. When the FeO content increases from 38.00% to 51.92%, n decreases from 0.477 to 0.319. When the P2O5 content increases from 3.00% to 9.00%, n decreases from 0.432 to 0.164. The decrease of binary basicity and the increase of FeO and P2O5 content in the initial slag can reduce the value of n and enrich more phosphorus in the solid solution phase. The results can not only provide a theoretical basis for industrial production, but also lay a theoretical foundation for finding more effective dephosphorization methods.

Thermodynamic optimization of the binary PbO–CaO and ternary PbO–CaO–SiO2 systems

Liquidus phase equilibrium data from the recent study for the PbO–CaO and the PbO–CaO–SiO2 systems (as a part of research program on the characterization of the multicomponent PbO–ZnO–FeO–Fe2O3-“Cu2O”-CaO-SiO2 system), combined with phase equilibrium and thermodynamic data from the literature, have been used to obtain a self-consistent set of parameters of the thermodynamic models for all phases: liquid, (Ca,Pb)2SiO4, (Ca,Pb)3SiO5, (Ca,Pb)SiO3 (wollastonite and pseudowollastonite), Pb3(Ca,Pb)2Si3O11 (ganomalite) solutions, SiO2 (quartz, tridymite, cristobalite), Ca3Si2O7 (rankinite), CaO (lime), PbSiO3 (alamosite), Pb2SiO4, Pb11Si3O17, Pb5SiO7 lead silicates, PbO (massicot), Ca2PbO4, Pb8CaSi6O21 (barysilite), PbCa2Si3O9 (margarosanite) and Pb3Ca12Si5O25 compounds. Analysis of available data has shown the lack of data in the two immiscible liquids range over cristobalite, where several new experiments were done to support the model. The modified quasichemical model is used to describe the liquid slag phase. From these model parameters, the optimized ternary phase diagram is back calculated.