Effect of MgO on the liquid/spinel/matte/gas equilibria in the Si–Fe–Mg–O–Cu–S system at controlled P(SO2) 0.3 and 0.6 atm

In this study, the effect of MgO on the phase equilibria of iron silicate slags in equilibrium with Fe₃O₄ spinel and matte of fixed 72 wt % Cu were identified at controlled P(SO₂) 0.3 and 0.6 atm. The experimental process includes equilibration, quenching and Electron Probe X-ray Micro Analysis (EPMA). Spinel (Fe₃O₄) substrates were applied to confirm the equilibrium was achieved in the primary phase field of spinel. It was found that the presence of MgO increases the liquidus temperature of slag under a constant SiO₂ content, i.e., more SiO₂ is required to be fluxed to keep a stable smelting temperature with MgO. The effects of CaO and MgO on the liquidus of the system were further compared and found that the influence of MgO is stronger than CaO at 1250 °C under the same weight content while opposite situation occurs at 1200 °C, which is different from the FactSage predictions. Thus, the present study provides important information not only for the industrial smelting process but also for the thermodynamic modelling.     

Experimental studies of liquid/spinel/matte/gas equilibria in the Si-Fe-O-Cu-S system at controlled P(SO2) 0.3 and 0.6 atm

In the present study, the phase equilibria in the “FeO”-SiO₂ system in equilibrium with matte at controlled P(SO₂) 0.3 and 0.6 atm and fixed matte grade 72 wt% Cu were experimentally investigated. The high-temperature equilibration using primary phase material as the substrate, quenching and Electron Probe Micro-analysis (EPMA) were applied in the experiments where the P(O₂) and P(SO₂) were accurately controlled by CO/CO₂/SO₂ gas mixtures. The correlations between oxygen partial pressure and the matte grade were determined at P(SO₂) 0.3 and 0.6 atm to obtain the target matte grade in the samples. The liquidus temperatures of this “FeO”-SiO₂ system in equilibrium with matte at controlled P(SO₂) 0.3 and 0.6 atm and fixed matte grade 72 wt% Cu were also reported. The present experimental results were also compared with the FactSage predictions and show the differences. The present results are expected to be useful for the copper smelting operations and also provide reliable information for the thermodynamic database.     

Phase equilibria of the Cu–Zr–Si system at 750 and 900 °C

Phase equilibria in the ternary Cu–Zr–Si system at 750 and 900 °C have been experimentally investigated via electron probe micro-analyzer (EPMA) and X-ray diffraction (XRD) analysis on the equilibrated alloys. The results show the presence of eight three-phase regions at 750 °C and seven three-phase regions at 900 °C. Four ternary phase: τ₁ (Zr₃Cu₄Si₆, tI26-Zr₃Cu₄Si₆), τ₄ (Zr₃Cu₄Si₄, oI22-Gd₃Cu₄Ge₄), τ₅ (ZrCuSi, oP12-Co₂Si), and τ₆ (Zr₃Cu₄Si₂, 2hP9-Fe₂P) were confirmed to exist in the Cu–Zr–Si ternary system at 750 and 900 °C. At 900 °C, the dark gray phase, the chemical composition of which is close to η-Cu₃Si, is confirmed to be the liquid phase. Moreover, the solubilities of Cu in ZrSi₂, SiZr and Zr₃Si₂ are considerably small. The solubility of Zr in η-Cu₃Si is determined to be negligible. The newly determined phase equilibria of the Cu–Zr–Si system in this work can provide important experimental data for the thermodynamic assessment of the Cu–Zr–Si system and to develop the Cu–Zr–Si alloys and related transition metal silicides.     

Thermodynamic assessment of the CaO–Cu2O–FeO–Fe2O3 system

Thermodynamic assessment of the CaO–Cu₂O–FeO–Fe₂O₃ system is presented. Effects of temperature and P(O₂) on the phase equilibria involving slag, solubility of copper and the Fe³⁺/Fe²⁺ ratio in slag have been modeled using available experimental data. Subsolidus phase equilibria and concentration of iron in liquid copper were evaluated as well. Different ways of representing phase equilibria in a quaternary system are illustrated. The slag model, [Ca²⁺, Cu⁺, Fe²⁺, Fe³⁺][O²⁻], was developed using the Modified Quasichemical Model (MQM). Liquid metal phase is modeled using the MQM, but as a separate solution, (Cu^I, Fe^II, O^II). Spinel phase is modeled using the Compound Energy Formalism (CEF) and takes into account the solubility of copper and calcium. A thermodynamic database produced in the present study can be used for predictions in pyrometallurgical processing of copper involving calcium ferrite slags. The database is internally consistent with the binary and ternary sub-systems published earlier, as well as with higher-order systems. It works in the environment of FactSage, ChemApp, ChemSheet and SimuSage software packages.     

Critical assessment and thermodynamic modeling of the Cu–Fe–O–Si system

The present study is the first Calphad-type assessment of the Cu–Fe–O–Si system. All relevant thermodynamic and phase equilibrium data have been critically evaluated to produce a thermodynamic database describing the Gibbs energies of all phases in the system. The predictive range of the database covers all conditions of pyrometallurgical production of copper in terms of temperature and oxygen partial pressure. Liquid oxide slag and liquid metal phases have been described using two separate solution models, both developed within the framework of the Modified Quasichemical Formalism. Slag model is expressed as [Cu⁺, Fe²⁺, Fe³⁺, Si⁴⁺][O^2-] and metal model is expressed as (Cu^I, Fe^II, O^II). They are internally consistent with the models for fcc–Cu, fcc–Fe, bcc–Fe, spinel, wüstite, CuFeO₂, Cu₂O, Fe₂SiO₄, Fe₂O₃ and SiO₂ obtained in the previous optimizations of the Cu–O, Fe–O, Cu–Fe, Cu–Fe–O, Cu–O–Si, Fe–O–Si sub-systems.     

Thermodynamic assessment and database for the Cu–Fe–O–S system

The previously obtained thermodynamic databases for the Cu–Fe–S, Cu–Fe–O, Fe–O–S and Cu–O–S ternary systems have been combined and used to predict thermodynamic equilibria in the quaternary Cu–Fe–O–S system. The available experimental data were compared with model predictions. Minor modifications of model parameters were required to better describe the experimental points in the quaternary system; the effect of these changes was verified in the ternary subsystems. The procedure was developed to calculate the isothermal sections of the phase diagram of the quaternary system inside the tetrahedron. The liquid phase over the whole composition range from metallic liquid to sulfide melt to oxide melt has been described by a single model developed within the framework of the quasichemical formalism. The obtained self-consistent set of model parameters can be used as a basis for the development of a thermodynamic database for simulation of copper smelting and converting.     

Measurements and calculations of solid–liquid equilibria in the quaternary system NaBr–KBr–CaBr2–H2O at 298 K

The solubilities and densities of the quaternary system NaBr–KBr–CaBr₂–H₂O were investigated by the method of isothermal solution saturation at 298 K. On the basis of the experimental data, the phase diagram, water content diagram and the density-composition diagram were plotted, respectively. In the phase diagram of quaternary system NaBr–KBr–CaBr₂–H₂O at 298 K, no complex salt or solid solution was found. There are two invariant points, five univariant curves, and four crystallization fields corresponding to NaBr, NaBr·2H₂O, KBr and CaBr₂·6H₂O. Pitzer's equations based model has been applied to calculate bromide minerals solubilities in the quaternary system NaBr–KBr–CaBr₂–H₂O at 298 K. All binary and mixing ion interaction parameters and solubility products of bromide solids are taken from previously published T-variation model for the system under study, adapted to 298 K. The predicted and experimental solubilities are in a very good agreement up to a very high total concentration of the quaternary system.     

Experimental investigation of phase equilibria in the Co–Fe–La system at 600 and 500 °C

Phase equilibria in the Co–Fe–La ternary system have been studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Isothermal sections at 600 (in the whole concentration region) and 500 °C (in the La-rich region) for this system have been constructed. It was shown that the ternary compound La₂(Co,Fe)₁₇ (τ) (Th₂Zn₁₇-type structure) is stable at 600 °C and has homogeneity range from 67 to 72 at.% Co. It co-exists with the majority of solid phases (αFe,Co), LaCo₁₃, LaCo₅, La₂Co₇ and La₂Co₃ at 600 °C. The LaCo₁₃ phase has the widest homogeneity region and dissolves up to 32.5 at.% Fe at 600 °C. The character of phase equilibria at 500 °C in the studied region is similar to those at solidus temperature. The character of phase equilibria at 600 °C is different from those at the solidus temperature. The main difference involves the fact that the equilibrium τ + LaCo₅ which is present in the Co–Fe–La system at solidus temperature, is absent at 600 °C. Instead, the alternative equilibrium (αFe,Co) + La₂Co₇ is present at 600 °C.     

Phase relationship in V2O3-rich region of the V2O3–CaO system between 1573–1773 K at PO2 = 10−10 and 10−11 atm

V₂O₃–CaO system is one of the fundamental systems in the fields of vanadium extraction and vanadium-containing alloys production. Due to the insufficient experimental study, the data of this system was limited. The present study was carried out between 1300 and 1500 °C (1573–1773 K) at the V2O3-rich region (>56 wt% V₂O₃), with the controlled partial pressure of oxygen (PO2) at 10-10 and 10–11 atm. High-temperature equilibration experiments, quenching technique and electron probe micro-analyser (EPMA) were adopted to determine the microstructures and compositions of phases at high temperature. The results of phase compositions obtained were used to plot a sub-solidus phase diagram, which showed a great discrepancy with existing publications, and 4 solid-phase regions with their phase boundaries were identified in the present study. The solubility of CaO in V2O3 was found to increase slightly with the temperature under both PO2. The study is expected to fulfil the gaps of thermodynamics information in the V₂O₃-containing systems.     

Phase Equilibrium studies in the system “FeO”–SiO2–Al2O3–CaO–MgO at 1200 °C and Po2 10-8atm

Iron oxides and silica are the major components of copper smelting slag. The oxides of aluminum, calcium and magnesium are also present in the slag that is introduced through copper concentrate, flux and refractories. Liquidus temperatures of the copper smelting slags are usually controlled by Fe/SiO₂. The concentrations of Al₂O₃, CaO and MgO, and FeO/Fe₂O₃ in the slag can also affect the liquidus temperatures where FeO/Fe₂O₃ is a function of oxygen partial pressure. High temperature equilibration under controlled oxygen partial pressure followed by quenching and electron probe microanalysis were used to determine the compositions of the liquid and solid phases at 1200 °C and Po₂ 10^-8 atm. The experimental results are presented in the forms of pseudo-ternary sections “FeO”-CaO-SiO₂ at fixed 2, 4 and 6 wt pct MgO, and 2 + 2, 4 + 4 and 6 + 6 wt pct MgO + Al₂O₃. Spinel and tridymite are the major primary phases in the composition range investigated. In addition, CaSiO₃, pyroxene, olivine, and melilite are also present. The isotherms in the spinel and tridymite primary phase fields move towards higher SiO₂ concentration directions with increasing CaO, Al₂O₃, and MgO concentrations. The experimentally determined results are compared with the FactSage calculations.     

Thermodynamic assessment of the CaO–P2O5–SiO2–ZnO system with special emphasis on the addition of ZnO to the Ca2SiO4–Ca3P2O8 phase

The CaO–P₂O₅–SiO₂–ZnO system including all binary and ternary sub-systems has been thermodynamically assessed using all available experimental data. Particular attention was given to the phase C2S–C3P which forms a complete solid solution with end-members α-Ca₂SiO₄ and α′-Ca₃P₂O₈. In addition, the present modelling of the phase C2S–C3P allows the inclusion of experimentally determined solubility values of zinc oxide in both end-members of the phase C2S–C3P. The mutual solubility between different crystallographic modifications of calcium and zinc phosphates is also described in this work using available experimental data. 24 phospates as stoichiometric phases have also been included in the database.     

HCO-TERNARY: A FORTRAN code for calculating P–V–T–X properties and liquid vapor equilibria of fluids in the system H2O–CO2–CH4

The equation of state (EOS) for the system H₂O–CO₂–CH₄ was programmed in a FORTRAN code which allows for its utilization in several modes. In one mode, specifically designed for mathematical modeling of two-phase, two-component flow, the code accepts as independent variables (1) pressure and (2) the composition of the gas phase. Other modes allow for the calculation of phase equilibria and/or the molar volumes of H₂O and binary mixtures, with pressure and temperature as the input variables (just pressure in the case of H₂O). Another mode is used to calculate phase equilibria for ternary mixtures, with pressure, temperature and the mole fraction of water in the gas phase as input variables. The algorithms for automatic convergence utilized in each mode are described.The code was tested extensively against experimental data from the literature. Some of these data were applied in the development of the EOS, and others were published subsequently. Analyses of the performance of the code and EOS for the modes described above, in the range 50–1000°C, 0–1000 bar, are presented. P–T–X regions of best applicability of the code and EOS are also identified.