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Slag fuming process is used to extract zinc from the lead blast furnace slags and recently for the extraction of multiple elements from the complex primary and recycling feed streams, making the thermochemistry of the process challenging. To meet new challenges, computer models with predictive powers outside of the range of normal process conditions are necessary. These models cannot rely exclusively on sets of existing process data and must have a foundation in thermodynamics combined with reasonable kinetic factors. The accuracy of predictions largely depends on the quality of thermodynamic data, including phase equilibria, elemental distributions, and calorimetry measurements. Present study demonstrates the recent developments of the self-consistent thermodynamic model for the gas/slag/matte/metal/speiss/solid phases within the Cu-Pb-Zn-Fe-Ca-Si-O-S-Al-Mg-As-Sb system, applied to zinc fuming, with attention to the phase equilibria and partitioning of minor elements in the process. As a demonstration of calculations far outside of normal operations, the use of ammonia as an alternative to coal is investigated. It was shown that from the thermodynamic point of view the process can reach the same final concentration of zinc and the heat balance of the reactor in the same amount of time when coal is replaced in the process by ammonia.

The combined effects of Al2O3, CaO and MgO slagging components on phase equilibria and thermodynamics in the basic Cu–Fe–O–S–Si system have been evaluated at 1473 K (1200 ºC) and p(SO2) = 0.25 atm for a range of oxygen partial pressures and matte compositions. The experimental technique included high-temperature equilibration of the samples on a spinel substrate under controlled gas atmosphere (CO/CO2/SO2/Ar), followed by rapid quenching and subsequent measurement of the equilibrium phase compositions using Electron Probe X-ray Microanalysis (EPMA). The experimental data have been compared with the results of thermodynamic calculations undertaken using FactSage software and an internal thermodynamic database. Both the experimental results and the calculations results revealed that the presence of Al2O3, CaO and MgO reduced both the sulphur and copper concentrations in the slag phase for a given set of process conditions. The data have been used for further optimisation of the parameters of the thermodynamic database describing multicomponent metallurgical systems. The resulting thermodynamic database is capable of predicting, with high accuracy, the phase equilibria and the distribution of all elements between the phases in the Cu–Fe–O–S–Si–(Al, Ca, Mg) system. Graphical Abstract

The experimental study of the phase equilibria between calcium ferrite slag, metallic copper, spinel and/or dicalcium ferrite in the Cu2O-FeO x -CaO system has been carried out. Effects of temperature, oxygen partial pressure and Fe/CaO ratio on phase assemblages and compositions have been estimated. The advanced experimental technique including high-temperature equilibration on primary phase substrates, rapid quenching of the samples and quantitative measurements of equilibrated phase compositions using electron probe X-ray microanalysis has been applied. Spinel and dicalcium ferrite substrates have been specially designed to study phase equilibria at certain primary phase fields. Obtained experimental results have been compared with thermodynamic assessment of the Cu2O-FeO x -CaO system and available literature data.

Magnesium oxide-based refractory materials are used industrially to contain the chemically aggressive slags present in lead smelting systems. In the present study an integrated experimental and thermodynamic modeling approach was taken to provide fundamental information on the chemical reactions taking place in these systems. New experimental phase equilibria and liquidus data were obtained for the PbO–MgO–SiO2 system in air in the temperature range 750 °C to 1740 °C. In the MgO–SiO2 binary, new experimental results were obtained at 1550 °C to 1740 °C and compared to the available thermodynamic data in the literature. The experiments were carried out using the high-temperature equilibration of oxide powder mixtures followed by rapid quenching of the samples. Electron probe X-ray microanalysis (EPMA) was used to determine the compositions of the solid and liquid phases present at equilibrium conditions. Phase equilibria and liquidus isotherms in the cristobalite and tridymite (SiO2), pyroxene (protoenstatite MgSiO3), olivine (forsterite Mg2SiO4), barysilite (Pb8MgSi6O21), massicot (PbO) and periclase (MgO) primary phase fields were measured, and the extent of the high-silica two-liquid immiscibility gap in equilibrium with cristobalite was determined. The experimental results were used to optimize the parameters in a thermodynamic database that was subsequently used to describe this multi-component, multi-phase system and predict the liquidus for the PbO–MgO–SiO2 system. The new data were used to characterize the chemical interactions of magnesia-based refractory with PbO–MgO–SiO2 slags.

Phase equilibria of the PbO-“FeO”-SiO2 and PbO-“FeO”-CaO-SiO2 slags with liquid Pb metal, solid or liquid Fe metal and solid oxides [cristobalite and tridymite SiO2, wustite (Fe,Ca)O1+x, olivine (Fe,Ca)2SiO4, dicalcium silicate (Ca,Fe)2SiO4, wollastonite (Ca,Fe)SiO3 and lime (Ca,Fe)O] were investigated at 1100-1689 °C. These conditions correspond to the minimum solubility of PbO in slag in presence of Pb and Fe metals at reducing conditions and represent the limit of lead smelting and slag cleaning process. High-temperature equilibration on silica or iron foil substrates, followed by quenching and direct measurement of Pb, Fe, Ca, and Si concentrations in the phases with the electron probe x-ray microanalysis (EPMA) was used to accurately characterize the system. Present results provide important basis for improvement of the thermodynamic models for all phases in this system.

The CaO·3(Al,Fe)2O3, (C(A,F)3), phase forms a solid solution in the FeO-Fe2O3-CaO-Al2O3 system and is an end member of the SFCA (Silico-Ferrite of Calcium and Aluminum) suite of solid solutions observed in industrial iron ore sinters. SFCA acts as a bonding phase in these sinter materials so an accurate description of the phase equilibria and thermodynamic properties of this phase can be used to assist in the design and operation of Fe-sintering and Fe-making processes. New experimental data are reported on the liquidus and sub-liquidus phase equilibria in the iron-rich region of the FeO-Fe2O3-CaO-Al2O3 system in air. The study was undertaken using equilibration/quenching and microanalysis techniques enabling the compositions of the liquid and solid phases in equilibrium at high temperature to be directly and accurately measured. The compositional limits of the C(A,F)3 phase and associations with the primary phase fields of CA [CaO·(Al,Fe)2O3], CA2 [CaO·2(Al,Fe)2O3], CA6 [CaO·6(Al,Fe)2O3], Hematite [(Fe,Al)2O3], Spinel [(Fe,Ca)O·(Fe,Al)2O3)], C2F [2CaO·(Fe,Al)2O3], C2F3A (2CaO·3Fe2O3·Al2O3), CF [CaO·(Fe,Al)2O3], and CF2 [CaO·2(Fe,Al)2O3] have been determined in the high-iron, low-melting temperature region of the system. The C(A,F)3 is found to be stable over a wide range of temperatures (1213 °C to 1400 °C) and alumina compositions (3.3 to 33.6 mol pct AlO1.5). The solid-phase C2F3A (2CaO·3Fe2O3·Al2O3), which is isostructural to SFCA-I indicated by previous researchers, has been found to be stable up to 1225 °C in the FeO-Fe2O3-CaO-Al2O3 system in air.

A combined experimental and thermodynamic study has been carried out to determine the CaO effect on the equilibria between slag/matte/metal (Fe or Cu)/tridymite phases in the Cu-Fe-O-S-Si-Ca system at 1473 K (1200 °C). The experimental methodology included equilibration of the mixtures at high temperatures on substrates made from the primary phase, followed by rapid quenching of the samples and direct measurement of the condensed phase compositions using the Electron Probe X-ray Microanalysis (EPMA) technique. New experimental results have been obtained for fixed concentrations of CaO in slag phase (1.5, 6, 9, and 18 wt pct). All results have been plotted as functions of the copper concentration in the matte phase and provides information about the effect of CaO on the oxygen and sulfur concentration in the matte phase; the Fe/SiO2 ratio in slag; and dissolved copper and sulfur in slag. The experimental research is part of integrated experimental and thermodynamic study aimed to development and optimisation a thermodynamic database for copper-containing systems of non-ferrous metallurgy.

Rising concentrations of impurities are expected at copper fire-refining stage due to lower availability of high-quality copper concentrates and due to increasing recycling of electronics and other secondary materials in primary copper smelting. Extra steps involving the removal of impurities from copper into the slag phase may provide a solution, but better understanding of thermochemistry is needed to evaluate the feasibility of changes in the process. In the present study, the distribution coefficients of Pb, Bi, and Ag between the fayalite or calcium ferrite slags and copper-based metal at 1250 °C were measured experimentally, using high-temperature equilibration, rapid quenching, and electron probe X-ray microanalysis (EPMA). The experiments were undertaken in a closed system using a modified substrate support technique, at relatively high oxidizing conditions typical for copper refining. The improved substrate technique enables the measurement of distributions coefficients for slags in equilibrium with solid spinel (Fe3O4) or dicalcium ferrite (Ca2Fe2O5). Experimental results of the present study and the literature data were analyzed together using thermodynamic modeling. As a result, thermodynamic database has been developed and used to predict the effects of oxygen partial pressure, wt% Cu in slag, temperature, and Fe/SiO2 and Fe/CaO in slags on the distribution coefficients of Pb, Bi, and Ag for the fayalite and calcium ferrite slag systems.

New experimental measurements have been made to determine liquidus isotherms, univariant and invariant equilibria in the FeO-Fe2O3-CaO-SiO2, CaO-SiO2 and FeO-Fe2O3-SiO2 systems in air at temperatures between 1190 °C and 1730 °C. The study was undertaken using equilibration/quenching and microanalysis techniques, enabling the compositions of the liquid and solid phases in equilibrium at temperature to be accurately measured. The data have been used to define liquidus in the primary phase fields of hematite (Fe2O3), spinel [(Fe,Ca)O·Fe2O3], lime (CaO), tridymite or cristobalite (SiO2), dicalcium ferrite (2CaO·Fe2O3, C2F), pseudo-wollastonite (CaO·SiO2, CS), rankinite (3CaO·2SiO2, C3S2), dicalcium silicate (2CaO·SiO2, C2S), tricalcium silicate (3CaO·SiO2, C3S) and the two liquids miscibility gap. These data obtained in the present study provide a more complete and more accurate description of the multi-component Fe-Ca-Si-O-Al-Mg-Cu-S system directly relevant to applications in the cement, the ferrous and non-ferrous metallurgical industries.

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.

Silico-ferrite of calcium and aluminum (SFCA) is the major bonding phase in iron ore sintering process and is critical to enhancing the sinter properties, such as reducibility and mechanical strength in subsequent blast furnace operations. The phase relations foundations of the alumina-free silico-ferrite of calcium (SFC) have been previously experimentally investigated in air by the authors (Chen et al. ISIJ Int 59:795–804, 2019, Cheng et al. Metall Mater Trans B 51:1587–1602, 2020) and in 1 atm CO2 (Chen et al. ISIJ Int, 59:805–809, 2019). Present investigation using equilibration and quenching followed by electron probe X-ray microanalysis (EPMA) technique, follows those previous works on the SFC, with the focus on the effects of: (i) Al2O3 (in the “Fe2O3”-CaO-Al2O3 and the “Fe2O3”-CaO-SiO2-Al2O3 system in air), and (ii) the effect of $$ p_{{{\text{O}}_{2} }} $$ (the “Fe2O3”-CaO-Al2O3 in 1 atm CO2 atmosphere), to investigate the thermodynamic stability of the C(A, F)3 [Ca(Al, Fe)6O10] solid solution in the “Fe2O3”-CaO-Al2O3 system in both air and pure CO2 atmospheres between 1150 °C and 1250 °C; and the silico-ferrite of calcium and aluminum (SFCA) solid solution with 1, 2 and 4 wt pct of Al2O3 in bulk compositions in the “Fe2O3”-CaO-SiO2-Al2O3 system at temperatures in the range between 1255 °C and 1340 °C. Present study shows that C(A, F)3 is stable over a wide range of Al2O3 concentration (8.8 to 26.7 wt pct Al2O3, or 12.5 to 34.8 mol pct AlO1.5). It also becomes less stable in terms of both the temperature and the compositional stability range as the oxygen partial pressure is reduced. The SFCA phase in the “Fe2O3”-CaO-SiO2-Al2O3 system is found to be present in the range of 1 to 4 wt pct Al2O3 bulk compositions selected in air. The relative stability of this phase increases with increased Al2O3 in the bulk material. Tie-lines joining the SFCA and the corresponding liquid and hematite phases are constructed over the range of composition investigated at sub-liquidus temperatures. The new experimental measurements show that the CaO/SiO2 ratio in the SFCA phase is almost identical to that in the liquid. The distribution ratio of Al2O3 between SFCA and liquid is in the range 2/1 to 3/1.

The individual effects of Al2O3, CaO and MgO on gas/slag/matte/spinel equilibria in the Cu-Fe-O-S-Si-(Al, Ca, Mg) system at 1473 K (1200 °C) and p(SO2) = 0.25 atm. have been experimentally measured for a range of oxygen partial pressures and matte compositions. The experimental methodology has included the high temperature equilibration of individual samples on a spinel primary phase substrate under controlled gas atmospheres (CO/CO2/SO2/Ar), followed by rapid quenching of the equilibrium condensed phases and direct measurement of the phase compositions using electron probe x-ray microanalysis. The experimental results show that the presence of Al2O3, CaO and MgO reduce the iron, sulphur and copper concentrations in the slag phase. Present study is undertaken as part of an integrated approach involving thermodynamic modelling and experimental measurements. The experimental data are compared with predictions obtained using the current thermodynamic database for the Cu-Fe-O-S-Si-(Al, Ca, Mg) system in order to further improve thermodynamic parameters.

To address the increasing complexity of feed materials to pyrometallurgical processes, an integrated experimental and thermodynamic modeling research program is in progress to accurately characterize the multi-phase gas-slag-matte-speiss-metal-solids 17-component Cu/Pb-(Cu2O-PbO-ZnO-CaO-FeO-Fe2O3-SiO2)-(Al2O3-MgO)-S-(As-Bi-Sb-Sn-Ag-Au-Ni) system. New experimental data are used to continuously improve the thermodynamic database using FactSage. An example is provided on the slag-matte distributions of Bi, Pb, and Zn in equilibrium with tridymite in the Cu-Fe-O-S-Si system under copper smelting conditions. A closed system equilibration experimental technique with rapid quenching was used. Major element concentrations in phases were measured with electron probe x-ray microanalysis. A laser ablation inductively coupled plasma mass spectrum technique was used for determination of Bi, Pb, and Zn concentrations in slag. New experimental data contributed to the optimization of thermodynamic model parameters. Improved thermodynamic databases can be used to accurately predict the elemental distributions in multi-component systems; an example is given for the minor element distributions between slag and matte for industrial conditions.

New experimental data are reported on the liquidus and sub-liquidus phase equilibria in the FeO-Fe2O3-CaO-SiO2 system in air. The study was undertaken using equilibration/quenching and microanalysis techniques enabling the compositions of the liquid and solid phases in equilibrium at temperature to be accurately measured. The limits of stability and associations of the primary phase fields of hematite (Fe2O3), dicalcium silicate (Ca2SiO4), silico-ferrite of calcium solid solution (SFC), dicalcium ferrite (Ca2Fe2O5), calcium ferrite (CaFe2O4), calcium diferrite (CaFe4O7) have been characterized in the high iron, high CaO/SiO2, low melting temperature region of the system. The full extent of the primary phase field of SFC has been determined, as have the conjugate lines joining the SFC and the corresponding liquid phase over the range of SFC compositions at sub-liquidus temperatures.

Thermodynamic modeling of the Pb-S and Cu-Pb-S systems is presented. All available experimental data in these systems are collected, assessed and used to optimize the model parameters. For the liquid phase, a solution (CuI, PbII, SII) is developed using the modified quasichemical model in pair approximation. Liquid copper, liquid lead metal, as well as matte phases are described using single solution with miscibility gaps. Earlier thermodynamic assessments available in the literature did not include all the data on the solubility of Cu and S in liquid Pb at low temperatures, 900 °C (1123 K), a significant discrepancy among different sets of literature data and existing thermodynamic assessments is revealed. Preliminary experiments are performed with the goal to understand the nature of the problem and to develop the methodology based on high-temperature equilibration, rapid quenching and electron probe x-ray microanalysis. The results of this study help to select accurate literature results in the optimization of model parameters. The resulting database is applicable to calculate slag/matte/metal distribution of lead in copper smelting and converting, as well as for predictions in the lead smelting and fire refining.

The effect of temperature, CaO, MgO and Al2O3 on important technological copper smelting parameters, such as the chemically dissolved copper in slag and the composition of the liquid phase in equilibrium with tridymite, are experimentally characterised as a function of copper concentration in matte. Two series of experiments for the gas/slag/matte/tridymite equilibria in the Cu-Fe-O-S-Si system at p(SO2) = 0.25 atm have been carried out. The effect of CaO at 1573 K (1300 °C), and the combined effect of Al2O3 + CaO + MgO at 1473 K (1200 °C) and 1573 K (1300 °C) have been measured in the first and second series of experiments respectively. The experimental methodology involves high temperature equilibration of samples on a substrate made from the primary phase under controlled gas atmosphere (CO/CO2/SO2/Ar), followed by rapid quenching of the equilibrium condensed phases and direct measurement of the phase compositions using the Electron Probe x-ray Microanalysis. The resulting data are used in the optimization of the thermodynamic database for the copper-containing systems.

Phase equilibria in the ZnO-“CuO0.5”-SiO2 system have been investigated at 1403-1948 K (1130-1675 °C) for oxide liquid in equilibrium with Cu-Zn metal (> 99% Cu) and solid oxide phases: (a) tridymite or cristobalite SiO2; (b) willemite Zn2SiO4; (c) zincite ZnO; and (d) cuprite Cu2O. Two-liquid immiscibility range in the high-SiO2 slags has also been studied. High-temperature equilibration on primary phase (SiO2, Cu2O), inert metal (platinum-iridium wire), or ceramic (Al2O3 for high-Cu2O slags) substrates, followed by quenching and direct measurement of Zn, Cu, Si and possible impurities (Al, Pt, Ir) concentrations in the phases with the electron probe x-ray microanalysis (EPMA) has been used to accurately characterize the system in equilibrium with metal. All results are projected onto the ZnO-“CuO0.5”-SiO2 plane for presentation purposes.

Equilibria between gas/slag/matte/spinel phases in the Cu-Fe-O-S-Si system have been experimentally studied at 1523 K (1250 °C), P(SO2) = 0.25 atm, and a range of oxygen partial pressures. The experimental technique involved high temperature equilibration using spinel substrates in controlled gas atmospheres (CO/CO2/SO2/Ar), rapid quenching of the equilibrated phases, and direct measurement of phase compositions using Electron Probe X-ray Microanalysis. The influence of temperature on the gas/slag/matte/spinel equilibria has been analyzed. Comparisons with previous studies on the gas/slag/matte/tridymite equilibria and the most recent thermodynamic database have been provided. This is the first systematic study on the influence of temperature on the gas/slag/matte/spinel equilibria in the Cu-Fe-O-S-Si system at P(SO2) = 0.25 atm.

Fundamental experimental investigations have been conducted to study the effect of Al2O3 on the equilibria between the gas phase (CO-CO2-SO2-Ar) and slag-matte-tridymite phases in the Cu-Fe-O-S-Si-Al system at 1573 K (1300 °C) and P(SO2) = 0.25 atm. The experimental technique used is based on equilibration, rapid quenching and electron probe x-ray microanalysis. New experimental data have been obtained for the four-phase gas-slag-matte-tridymite equilibria system for a range of alumina concentrations up to 20.4 mass% in the slag phase as a function of matte grade, including the concentrations of dissolved sulphur and copper in slag, and Fe/SiO2 ratios in slag. The results obtained for 1573 K (1300 °C) are also used to analyse the effect of temperature on phase equilibria in the range of conditions investigated to that of reported for 1473 K (1200 °C) in the literature. The results obtained show that the concentrations of sulphur, copper and “FeO” in slag decrease with increase of Al2O3 concentration in slag while it has no detectable effect on concentration of sulphur in matte for a given matte grade. The new data provided in the present study are of direct relevance to the pyrometallurgical processing of copper and will be used as an input for optimisation of the FactSage thermodynamic database for the copper-containing, multi-component multi-phase system.

Understanding the significance of magnesia as a common component in copper processing slags is essential for optimisation of the industrial copper production. Fundamental experimental studies have been undertaken to determine the effect of MgO on the equilibria between the gas phase (CO-CO2-SO2-Ar) and slag-matte-tridymite phases in the Cu-Fe-O-S-Si-Mg system at 1473 K (1200 °C) and 1573 K (1300 °C), and P(SO2) = 0.25 atm. The experimental methodology used was based on equilibration, quenching and microanalysis. New experimental data have been obtained for the four-phase gas–slag–matte–tridymite equilibria system for a range of MgO concentrations up to 3.1 wt pct in the slag phase as a function of matte grade, including the concentrations of dissolved sulphur and copper in slag, and Fe/SiO2 ratios in slag. The results are also used to analyse the effect of temperature on phase equilibria in the range investigated. The results obtained showed that dissolution of sulphur, copper and “FeO” in slag decreases with increase of MgO in slag while it has no detectable effect on concentration of sulphur in matte. Also, dissolved copper and sulphur in slag increases when temperature increases while the Fe/SiO2 ratio in slag is greater at 1473 K (1200 °C) than 1573 K (1300 °C). The new data provided in the present study are of direct relevance to the pyrometallurgical processing of copper and will be used as an input for optimization of the FactSage thermodynamic database for the copper-containing multi-component multi-phase system.

The present article continues the series reviewing the thermochemistry of complex multicomponent pyrometallurgical systems. The recovery of multiple metals through the Pb-based primary and recycling processes is an economic driving force for the circular economy of the future. In this study, equilibrium distributions of Ag, Au, Bi, and Zn between PbO–FeO–Fe2O3–SiO2 silica saturated slag and Pb metal phases were investigated experimentally, using high-temperature equilibration followed by rapid quenching. The measurement of phase compositions was done using microanalytical methods. Electron Probe X-ray Microanalysis (EPMA) was applied for those elements which present at relatively high concentrations. The Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) was used to measure very low concentrations of Ag and Au in slag. The starting mixtures of materials were planned using FactSage software and preliminary thermodynamic database to target specific proportions of phases and concentrations of Pb in slag after the achievement of equilibrium. Measured slag/metal distribution coefficients follow the sequence Zn ≫ Ag > Bi ≫ Au. Newly obtained results were critically assessed and used to improve the thermodynamic database. Integration between experiments and thermodynamic database development permits cross-analysis of distribution coefficients obtained in the present study with the parallel measurements of distribution in copper-based systems. The liquid slag phase was described using a two-sublattice Modified Quasichemical Model (MQM). Single sublattice MQM was applied for the liquid metal phase.

Phase equilibria in the CaO-ZnO-Fe2O3 system have been investigated at 1483-1673 K (1210-1400 °C) for oxide liquid in equilibrium with air and solid oxide phases: (a) zincite (Zn,Fe,Ca)O1+x; (b) spinel (Zn,Fe,Ca)Fe2O4; (c) lime (Ca,Zn)O; (d) calcium ferrites dissolving zinc oxide: brownmillerite Ca2(Fe,Zn)2O5−x, and calcium diferrite (Ca,Zn)Fe4O7. High-temperature equilibration on inert metal (platinum) substrates, followed by quenching and direct measurement of the Ca, Zn and Fe concentrations in the phases with the electron probe x-ray microanalysis (EPMA) has been used to accurately characterize the system in equilibrium with air. All results are projected onto the CaO-ZnO-“FeO1.5” plane for presentation purposes. The present paper presents systematic characterization of liquidus over a wide range of compositions in this system in equilibrium with air.

Assessment of literature data, experimental study and thermodynamic modeling of the Pb-As and Cu-Pb-As systems are presented. These chemical systems are of importance for metallic lead refining at 330-500 °C (603-773 K), and for separation of copper from lead in complex polymetallic processes at 1000-1150 °C (1273-1423 K). Few studies are available for the solubility of solid copper arsenide in lead at low temperature. At high temperature, significant discrepancies between available experimentally measured limits of two-liquid miscibility gap exist in the Cu-Pb-As system. Experimental investigation of the present study aimed to fill the gaps and resolve the discrepancies. It consists of equilibration, quenching and electron probe microanalysis. Thermodynamic modeling helped to analyze the results and provided a database of model parameters. Present study is a part of a larger research program aimed at characterization of phase equilibria, heat balance and distribution of elements during complex copper and lead smelting, refining and recycling.

Phase equilibria of the Pb-Cu-Si-O system have been investigated in the range 933-1938 K (660-1665 °C) for oxide liquid (slag) in equilibrium with solid Cu metal, liquid Pb-Cu alloy, or both solid and liquid metals, and solid oxide phases: (a) quartz, tridymite, cristobalite (SiO2); (b) cuprite (Cu2O); (c) lead silicates (PbSiO3, Pb2SiO4, Pb11Si3O17); (d) lead oxide (massicot, PbO); and (e) copper plumbite (Cu2PbO2). High-temperature equilibration on silica or copper substrates, followed by quenching and direct measurement of Pb, Cu and Si concentrations in the liquid and solid phases with the electron probe x-ray microanalysis (EPMA) has been used to accurately characterize the system in equilibrium with Cu or Pb-Cu metal. All results are projected onto the PbO-“CuO0.5”-SiO2 plane for presentation purposes. The present study is a continuation of the previous investigation of this system by the authors in a part of the silica and cuprite primary phase fields. Present data were later used to develop the thermodynamic models for all phases in this system.

Phase equilibria of the Pb-Fe-Si-O system have been investigated at 958-1913 K (685-1640 °C) for oxide liquid in equilibrium with air and solid oxide phases: (a) quartz, tridymite or cristobalite SiO2; (b) hematite Fe2O3; (c) spinel Fe3O4+x; (d) complex lead-iron silicates (melanotekite PFS = PbO·FeO1.5·SiO2, barysilite P9−xFxS6 = (9 − x)PbO·xFeO1+y·6SiO2, “P5FS” = 5PbO·FeO1.5·SiO2, and “P6FS” = 6PbO·FeO1.5·SiO2); (e) lead silicates (alamosite PS = PbO·SiO2, P2S = 2PbO·SiO2, P11S3 = 11PbO·3SiO2, P5S = 5PbO·SiO2); (f) lead ferrites (magnetoplumbite PbO·12FeO1.5, plumboferrite PbO·(5 + x)FeO1.5, 1:1 lead ferrite PbO·(1 ± x)FeO1.5); and (g) lead oxide (PbO, massicot). High-temperature equilibration on primary phase or inert metal (platinum, gold) substrates, followed by quenching and direct measurement of Pb, Fe and Si concentrations in the phases with the electron probe x-ray microanalysis (EPMA) has been used to accurately characterize the system in equilibrium with air. All results are projected onto the PbO-“FeO1.5”-SiO2 plane for presentation purposes. The present study is the first systematic characterization of liquidus over a wide range of compositions in this system in equilibrium with air.

To assist in improving the recoveries of gold and silver in both primary production and metals’ recycling, the distributions of Ag and Au between slag, matte, and metal in the Cu–Fe–O–S–Si system have been investigated using an integrated experimental and thermodynamic modeling approach. The experimental technique involved high-temperature equilibration at selected temperatures and gas atmospheres, and rapid quenching followed up by measurement of phase compositions using microanalysis techniques. Electron probe X-ray microanalysis was used to measure the major element concentrations in the condensed phases. The laser ablation inductively coupled plasma mass spectrum technique was used to measure the concentrations of Ag and Au in slag. The experimentally determined distribution coefficient of Ag between matte and slag decreases with the increasing matte grade below approximately 70% Cu, but then increases with the increasing matte grade between 70 and 80% Cu. The experimentally determined distribution coefficient of Au between matte and slag decrease from log L = − 2.8 for approximately 63% Cu to approximately log L = − 3.8 at 76% Cu. Thermodynamic model parameters describing Ag and Au distributions have been derived following consideration of available data on slag/matte, slag/metal, and slag/matte/metal systems.

Al2O3, CaO, and MgO are present as impurities in fayalite-based copper smelting systems. A thermodynamic database has been developed to characterize the effects of these impurities on equilibria among the slag, matte, metal and gas phases, using a progressive integrated approach that combines both experimental measurements and thermodynamic modeling. The approach involves the initial assessment of the existing data, planning and undertaking new critical experiments for selected conditions and using the new data to refine the model parameters of the database. The resulting thermodynamic database is capable of predicting, with improved accuracy, the phase equilibria and the distribution of all elements between all of the phases in the Cu-Fe-O-S-Si-(Al, Ca, Mg) system.

Phase equilibria of the binary PbO-CaO and ternary PbO-CaO-SiO2 systems have been investigated at 870-1655 °C for oxide liquid in equilibrium with air and solid oxide phases: tridymite or cristobalite SiO2, pseudowollastonite CaSiO3, dicalcium silicate (Ca,Pb)2SiO4, tricalcium silicate (Ca1−xPbx)3SiO5 (x

Equilibria among the slag, matte and metal phases in the Cu-Fe-O-S-Si system are critically assessed using thermodynamic modeling. The relationships among matte grade, temperature, partial pressure of SO2, Fe/SiO2 in the slag, and the copper concentration in the slag are described by the model, as well as the concentrations of other elements in all phases. A thermodynamic database is created, which can be used for understanding and improving the pyrometallurgical production of copper. An extensive experimental dataset includes the most recent results obtained by the equilibration/quenching/EPMA analysis technique. These data allow to distinguish the physical entrainment of the matte and solid phases in the slag from chemical solubility. As a result, it is possible to describe the copper solubility in the slag with high accuracy and establish the relationship between copper and sulfur in the slag. The thermodynamic database of the present study is consistent with previously reported thermodynamic evaluations of binary, ternary and quaternary subsystems. The slag phase is modeled using the two-sublattice modified quasichemical model in the quadruplet approximation. The matte and metal liquid phases are modeled as one solution using the single-sublattice modified quasichemical model in the pair approximation.

New experimental data were obtained on the gas/slag/matte/spinel equilibria in the Cu-Fe-O-S-Si system at 1473 K (1200 °C) and P(SO2) = 0.25 atm covering Cu concentrations in matte between 42 and 78 wt pct Cu. Accurate measurements were obtained using high-temperature equilibration and the rapid quenching technique, followed by electron-probe X-ray microanalysis of equilibrium phase compositions. The use of spinel substrates made to support the samples ensures equilibrium with this primary phase solid, eliminates crucible contamination, and facilitates direct gas–condensed phase equilibrium and high quenching rates. Particular attention was given to the confirmation of the achievement of equilibrium. The results quantify the relationship between Cu in matte and oxygen partial pressure, sulfur in matte, oxygen in matte, Fe/SiO2 at slag liquidus, sulfur in slag, and dissolved copper in slag.

Phase equilibria of the Pb-Cu-Si-O system have been investigated in the temperature range from 1073 K to 1673 K (800 °C to 1400 °C) for oxide liquid (slag) in equilibrium with solid Cu metal and/or liquid Pb-Cu alloy, and solid oxide phases: (a) quartz or tridymite (SiO2) and (b) cuprite (Cu2O). High-temperature equilibration on silica or copper substrates was performed, followed by quenching, and direct measurement of Pb, Cu, and Si concentrations in the liquid and solid phases using the electron probe X-ray microanalysis has been employed to accurately characterize the system in equilibrium with Cu or Pb-Cu metal. All results are projected onto the PbO-“CuO0.5”-SiO2 plane for presentation purposes. The present study is the first-ever systematic investigation of this system to describe the slag liquidus temperatures in the silica and cuprite primary phase fields.

Fundamental experimental studies have been undertaken to determine the effect of CaO on the equilibria between the gas phase (CO/CO2/SO2/Ar) and slag/matte/tridymite phases in the Cu-Fe-O-S-Si-Ca system at 1473 K (1200 °C) and P(SO2) = 0.25 atm. The experimental methodology developed in the Pyrometallurgy Innovation Centre was used. New experimental data have been obtained for the four-phase equilibria system for fixed concentrations of CaO (up to 4 wt pct) in the slag phase as a function of copper concentration in matte, including the concentrations of dissolved sulfur and copper in slag, and Fe/SiO2 ratios in slag at tridymite saturation. The new data provided in the present study are of direct relevance to the pyrometallurgical processing of copper and will be used as an input to optimize the thermodynamic database for the copper-containing multi-component multi-phase system.

The Cu-Fe-O-S system is the key system for the characterisation of the phase chemistry in high-temperature copper making processes. An experimental study was undertaken to investigate the gas/matte/spinel equilibria in the Cu-Fe-O-S system at 1473 K (1200 °C), P(SO2) = 0.25 atm, and a range of oxygen partial pressures. The experimental methodology involved high temperature equilibration using a primary phase substrate technique in controlled gas atmospheres (CO/CO2/SO2/Ar), rapid quenching of the equilibrated phases, followed by direct measurement of phase compositions using electron probe x-ray microanalysis. Particular attention was given to the analysis of reactions during equilibration and confirmation of the achievement of equilibrium in the present study. The new data provide important information for understanding of the gas/matte/spinel interactions at high temperature and provide an essential foundation for the development of the multicomponent thermodynamic database for copper-containing systems.

Phase equilibria of the Pb-Fe-Si-O system have been investigated at 943 K to 1773 K (670 °C to 1500 °C) for oxide liquid in equilibrium with liquid Pb metal and solid oxide phases: (a) quartz, tridymite, or cristobalite; (b) (fayalite + tridymite) or (fayalite + spinel); (c) spinel (Fe3O4); (d) complex lead-iron silicates (melanotekite PbO·FeO1.5·SiO2, barysilite 8PbO·FeO·6SiO2, 5PbO·FeO1.5·SiO2, and 6PbO·FeO1.5·SiO2); (e) lead silicates (Pb2SiO4, Pb11Si3O17); (f) lead ferrites (magnetoplumbite Pb1+x Fe12−x O19−x solid solution range); and (g) lead oxide (PbO, massicot). High-temperature equilibration on primary phase or iridium substrates, followed by quenching and direct measurement of Pb, Fe, and Si concentrations in the phases with the electron probe X-ray microanalysis, has been used to accurately characterize the system in equilibrium with Pb metal. All results are projected onto the PbO-“FeO”-SiO2 plane for presentation purposes. The present study is the first systematic characterization of liquidus over a wide range of compositions in this system in equilibrium with metallic Pb.

The Kalgoorlie Nickel Smelter (KNS) produces low Fe, low Cu nickel matte in its Peirce–Smith converter operations. To inform process development in the plant, new fundamental data are required on the effect of CaO in slag on the distribution of arsenic between slag and matte. A combination of plant sample analysis, high-temperature laboratory experiments, and thermodynamic modeling was carried out to identify process conditions in the converter and to investigate the effect of slag composition on the chemical behavior of the system. The high-temperature experiments involved re-equilibration of industrial matte-slag-lime samples at 1498 K (1225 °C) and P(SO2) = 0.12 atm on a magnetite/quartz substrate, rapid quenching in water, and direct measurement of phase compositions using electron probe X-ray microanalysis (EPMA) and laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS). A private thermodynamic database for the Ca-Cu-Fe-Mg-Ni-O-S-Si-(As) system was used together with the FactSage software package to assist in the analysis. Thermodynamic predictions combined with plant sample characterization and the present experimental data provide a quantitative basis for the analysis of the effect of CaO fluxing on the slag-matte thermochemistry during nickel sulfide converting, in particular on the spinel liquidus and the distribution of elements between slag and matte as a function of CaO addition.

In an aluminum electrolysis cell, the side ledge forms on side walls to protect it from the corrosive cryolitic bath. In this study, a series of laboratory analogue experiments have been carried out to investigate the microstructure and composition of side ledge (freeze linings) at different heat balance steady states. Three distinct layers are found in the freeze linings formed in the designed Cryolite-CaF2-AlF3-Al2O3 electrolyte system: a closed (columnar) crystalline layer, an open crystalline layer, and a sealing layer. This layered structure changes when the heat balance is shifted between different steady states, by melting or freezing the open crystalline layer. Phase chemistry of the freeze lining is studied in this paper to understand the side ledge formation process upon heat balance shifts. Electron probe X-ray microanalysis (EPMA) is used to characterize the microstructure and compositions of distinct phases existing in the freeze linings, which are identified as cryolite, chiolite, Ca-cryolite, and alumina. A freeze formation mechanism is further developed based on these microstructural/compositional investigations and also thermodynamic calculations through the software—FactSage. It is found that entrapped liquid channels exist in the open crystalline layer, assisting with the mass transfer between solidified crystals and bulk molten bath.

Experimental studies were undertaken to determine the gas/slag/matte/tridymite equilibria in the Cu-Fe-O-S-Si system at 1473 K (1200 °C), P(SO2) = 0.25 atm, and a range of P(O2)’s. The experimental methodology involved high-temperature equilibration using a substrate support technique in controlled gas atmospheres (CO/CO2/SO2/Ar), rapid quenching of equilibrium phases, followed by direct measurement of the chemical compositions of the phases with Electron Probe X-ray Microanalysis (EPMA). The experimental data for slag and matte were presented as a function of copper concentration in matte (matte grade). The data provided are essential for the evaluation of the effect of oxygen potential under controlled atmosphere on the matte grade, liquidus composition of slag and chemically dissolved copper in slag. The new data provide important accurate and reliable quantitative foundation for improvement of the thermodynamic databases for copper-containing systems.

The majority of primary pyrometallurgical copper making processes involve the formation of two immiscible liquid phases, i.e., matte product and the slag phase. There are significant gaps and discrepancies in the phase equilibria data of the slag and the matte systems due to issues and difficulties in performing the experiments and phase analysis. The present study aims to develop an improved experimental methodology for accurate characterisation of gas/slag/matte/tridymite equilibria in the Cu-Fe-O-S-Si system under controlled atmospheres. The experiments involve high-temperature equilibration of synthetic mixtures on silica substrates in CO/CO2/SO2/Ar atmospheres, rapid quenching of samples into water, and direct composition measurement of the equilibrium phases using Electron Probe X-ray Microanalysis (EPMA). A four-point-test procedure was applied to ensure the achievement of equilibrium, which included the following: (i) investigation of equilibration as a function of time, (ii) assessment of phase homogeneity, (iii) confirmation of equilibrium by approaching from different starting conditions, and (iv) systematic analysis of the reactions specific to the system. An iterative improved experimental methodology was developed using this four-point-test approach to characterize the complex multi-component, multi-phase equilibria with high accuracy and precision. The present study is a part of a broader overall research program on the characterisation of the multi-component (Cu-Fe-O-S-Si-Al-Ca-Mg), multi-phase (gas/slag/matte/metal/solids) systems with minor elements (Pb, Zn, As, Bi, Sn, Sb, Ag, and Au).

The phase equilibria information on the Pb-Fe-O system is of practical importance for the improvement of the existing thermodynamic database of lead-containing slag systems (Pb-Zn-Fe-Cu-Si-Ca-Al-Mg-O). Phase equilibria of the Pb-Fe-O system have been investigated: (a) in air at temperatures between 1053 K and 1373 K (780 °C and 1100 °C); (b) in equilibrium with metallic lead at temperatures between 1053 K and 1373 K (780 °C and 1100 °C); and (c) at intermediate oxidation conditions for the liquid slag in equilibrium with two solids (spinel + magnetoplumbite), at temperatures between 1093 K and 1373 K (820 °C and 1100 °C). The high-temperature equilibration/quenching/electron probe X-ray microanalysis technique has been used to accurately determine the compositions of the phases in equilibrium in the system. The Pb and Fe concentrations in the phases were determined directly; preliminary thermodynamic modeling with FactSage was used to estimate the ferrous-to-ferric ratios and to present the results in the ternary diagram.

Phase equilibria and thermodynamic data in the FeO-Fe2O3-SiO2 system were critically reviewed. New experiments were undertaken to resolve discrepancies found in previous data. The liquid oxide/slag phase was described using the modified quasichemical model. New optimized parameters of the thermodynamic models for the Gibbs energies of slag and other phases in the selected system were obtained. The new parameters reproduce all available phase equilibria and thermodynamic data within the experimental error limits from 298 K (25 °C) to above the liquidus temperatures at all compositions and oxygen partial pressures from metal saturation to 1 atm of O2. This study was carried out as part of the development of a self-consistent thermodynamic database for the Al-Ca-Cu-Fe-Mg-Si-O-S multi-component system.

The present study deals with the thermodynamic optimization of the Ca-Fe-O system. All available phase equilibrium and thermodynamic experimental data are critically assessed to obtain a self-consistent set of model parameters for the Gibbs energies of all stoichiometric and solution phases. Model predictions of the present study are compared with previous assessments. Wustite and lime are described as one monoxide solution with a miscibility gap, using the random mixing Bragg-Williams model. The solubility of CaO in the “Fe3O4” magnetite (spinel) phase is described using the sublattice model based on the Compound Energy Formalism. The effect of CaO on the stability of the spinel phase is evaluated. The liquid CaO-FeO-Fe2O3 slag is modeled using the Modified Quasichemical Formalism. Liquid metal phase is described as a separate solution by an associate model.

A complete literature review, critical evaluation, and thermodynamic modeling of the phase diagrams and thermodynamic properties of phases in the Al-Fe-O system at 1 atm total pressure are presented. Optimized model equations for the thermodynamic properties of all phases are obtained, which reproduce all available thermodynamic and phase-equilibrium data within experimental error limits from 298.15 K (25 °C) to above the liquidus temperatures at all compositions and oxygen partial pressures from metal saturation to 1 atm. The complex phase relationships in the system have been elucidated, and discrepancies among the data have been resolved. The database of the model parameters can be used along with software for Gibbs-energy minimization in order to calculate all thermodynamic properties and any type of phase diagram section. The modified quasichemical model was used for the liquid oxide phase. A sublattice model, based upon the Compound Energy Formalism, was developed for spinel, which expands from magnetite, Fe3O4, to hercynite, FeAl2O4. The distribution of cations between octahedral and tetrahedral sites and oxygen nonstoichiometry in spinel are taken into account. The model for metallic liquid assumes random mixing of associates: Fe, Al, O, AlO, and Al2O. It describes well the minimum that is observed on the solubility of oxygen in liquid iron as a function of the Al content. The solid solution between hematite and corundum exhibiting a miscibility gap, as well as a small solubility of Al2O3 in wustite are quantitatively described by a simple Bragg-Williams model.

The Fe-O-S system has been assessed over the whole composition range to produce a self-consistent set of thermodynamic properties of all condensed phases from 298 K to above the liquidus temperatures at ambient pressure. The liquid phase from metallic liquid to sulfide melt to oxide melt is described by a single model developed within the framework of the quasichemical formalism. The model reflects the existence of strong short-range ordering in oxide, sulfide and oxysulfide liquid. Two ranges of maximum short-range ordering in the Fe-O system at approximately FeO and Fe2O3 compositions are taken into account. Parameters of thermodynamic models have been optimized to reproduce all available thermodynamic and phase equilibrium data. The thermodynamic modeling of the Fe-O-S system performed in the present study is of particular importance for the description of the solubility of oxygen in matte.

Slag freeze linings, the formation of protective deposit layers on the inner walls of furnaces and reactors, are increasingly used in industrial pyrometallurgical processes to ensure that furnace integrity is maintained in these aggressive, high-temperature environments. Most previous studies of freeze-linings have analyzed the formation of slag deposits based solely on heat transfer considerations. These thermal models have assumed that the interface between the stationary frozen layer and the agitated molten bath at steady-state deposit thickness consists of the primary phase, which stays in contact with the bulk liquid at the liquidus temperature. Recent experimental studies, however, have clearly demonstrated that the temperature of the deposit/liquid bath interface can be lower than the liquidus temperature of the bulk liquid. A conceptual framework has been proposed to explain the observations and the factors influencing the microstructure and the temperature of the interface at steady-state conditions. The observations are consistent with a dynamic steady state that is a balance between (I) the rate of nucleation and growth of solids on detached crystals in a subliquidus layer as this fluid material moves toward the stagnant deposit interface and (II) the dissolution of these detached crystals as they are transported away from the interface by turbulent eddies. It is argued that the assumption that the interface temperature is the liquidus of the bulk material represents only a limiting condition, and that the interface temperature can be between T liquidus and T solidus depending on the process conditions and bath chemistry. These findings have implications for the modeling approach and boundary conditions required to accurately describe these systems. They also indicate the opportunity to integrate considerations of heat and mass flows with the selection of melt chemistries in the design of future high temperature industrial reactors.

In design of the freeze-lining deposits in high-temperature reaction systems, it has been widely assumed that the interface temperature between the deposit and bath at steady-state conditions, that is, when the deposit interface velocity is zero, is the liquidus of the bulk bath material. Current work provides conclusive evidence that the interface temperature can be lower than that of the bulk liquidus. The observations are consistent with a mechanism involving the nucleation and growth of solids on detached crystals in a subliquidus layer as this fluid material moves toward the stagnant deposit interface and the dissolution of these detached crystals as they are transported away from the interface by turbulent eddies. The temperature and position of the stable deposit/liquid interface are determined by the balance between the extent of crystallization on the detached crystals and mass transfer across the subliquidus layer from the bulk bath. A conceptual framework is developed to analyze the factors influencing the steady-state deposit/interface temperature and deposit thickness in chemical systems operating in a positive temperature gradient. The framework can be used to explain the experimental observations in a diverse range of chemical systems and conditions, including high-temperature melts and aqueous solutions, and to explain why the interface temperature under these conditions can be between Tliquidus and Tsolidus.

The molten cryolite bath creates chemically a very aggressive environment in the Hall–Heroult cell, and thus, the formation of a protective solid layer (freeze-lining) on the cell wall is essential for the operation of the present cell designs. To provide further information on the formation of the freeze-lining deposit in this system, laboratory-based studies were undertaken using an air-cooled probe technique The effects of process conditions, i.e., time, bath agitation, and superheat on the microstructures, morphologies of the phases, and the phase assemblages adjacent to the deposit/bath interface were investigated. A detailed microstructural analysis of the steady-state deposits shows that a dense sealing primary-phase layer of cryolite solid solution was formed at the interface of the bath deposit for the process conditions examined. The formation of sealing primary-phase layer at the bath/deposit interface explicitly indicates that the deposit/liquid bath interface temperature is equal to that of the liquidus of the bulk bath. The experimentally investigated liquidus temperature and subliquidus equilibria differ significantly from those previously reported.

Slag freeze-lining reactor wall protection is a widely used technology in high temperature reaction systems. An air-cooled probe technique was used to investigate the formation of the freeze-linings in an industrial blast furnace slag. The compositions of the phases and the microstructures within the deposits have been characterized. It has been demonstrated that an industrial air-cooled probe can be used to take bath samples from actual smelter operations. In addition, a laboratory-scale experiment was undertaken to investigate the formation, stability, and bath/deposit interface temperature at steady-state conditions. Importantly, the current study has shown that stable steady-state freeze-linings can be obtained in metallurgical reactors operating below the slag liquidus temperature. In spite of the fact that solids are present in the bulk slag, the deposit thickness remains unaltered due to the dynamic conditions present at the deposit/bath interface. The results are consistent with findings obtained on a number of other different slag systems and the proposed dynamic mechanism of deposit stabilization. The findings demonstrate the basis for, and potential benefits that may follow from, operating the high temperature reactors at temperatures below the liquidus temperature, i.e., with solids present, without a catastrophic build-up of solids. This change in design concept could result in significant decreases in operating temperature, energy, and operating cost savings.

Pyrometallurgical coppermaking processes are operated under intensive reaction conditions; high process temperatures and vigorous bath agitation is used to increase the kinetics of reactions and to achieve high smelter throughput. Slag freeze-lining reactor wall protection is a widely used technology in coppermaking processes, such as flash smelting and converting reactors. Freeze-linings mitigate and resist the effects of thermal and chemical attack by aggressive slags. In this laboratory-based study, a water-cooled probe “cold finger” technique has been used to investigate freeze-lining formation with calcium ferrite slags in equilibrium with metallic copper; the slag composition reflects that used in the industrial copper flash converting furnace of Rio Tinto—Kennecott Utah Copper. The effects of probe immersion times on the thickness and microstructures in the freeze-lining deposits have been investigated. A range of complex oxide solutions and copper-containing phases have been found in the deposits. The phase assemblages formed from the industrial calcium ferrite slag in the steady-state deposit are very complex and information on the phase equilibria of the multi-component systems with addition of minor elements may not be available. Subsolidus and subliquidus phase equilibria in the Cu-Ca-Fe-O system at metallic copper saturation along with interpolated temperature across the deposit, microstructural changes and compositional trends in the phases in the deposit have been used to understand the formation and characteristics of the phases in the steady-state freeze-lining. Also, it has been shown that under steady-state conditions a dense sealing layer consisting primarily of the spinel primary phase is formed at the deposit/liquid interface; however, the interface temperature is below the liquidus temperature. The findings of the study have potentially important implications for the operation of the converting furnace and the design of freeze linings in metallurgical systems.