Experimental study and thermodynamic optimization of the ZnO–FeO–Fe2O3–CaO–SiO2 system
Introduction
A thermodynamic “optimization” of a system using the CALPHAD approach involves critical evaluation of all available phase equilibria and thermodynamic data to obtain one set of model equations for the Gibbs energies of all phases as functions of temperature and composition [[1], [2], [3]]. The thermodynamic properties and the phase diagrams can then be back-calculated from the model equations to ensure that all data have been reproduced within the experimental error limits. Thermodynamic property data, such as activity data, can aid in assessing the phase diagram, and phase diagram measurements can be used to derive the thermodynamic properties. If a discrepancy in the available data is found during the development of the model, new experimental measurements are undertaken to provide the data essential for further refinement of the model equations. The present thermodynamic optimization was performed using FactSage thermodynamic software package [4] as part of the development of the self-consistent thermodynamic database for the seven-component gas-slag-solid-metal PbO–ZnO–FeO–Fe2O3–Cu2O–CaO–SiO2 system for zinc/lead/copper smelting and recycling industries by integrated experimental and thermodynamic modelling studies. For the molten slag phase, a modified quasichemical model has been used [[5], [6], [7], [8]]. Spinel, melilite and olivine are described with compound energy formalism [[9], [10], [11], [12]]; lime and wustite (monoxide), zincite, calcium-zinc ferrites Ca2Fe2O5-“CaZnO2” and CaFe4O7-“ZnFe4O7”, α- and α′-dicalcium silicate, tricalcium silicate, and silicoferrite of calcium (SFC) are described within Bragg-Williams formalism.
Section snippets
Literature review
The following data are available for the selection of model parameters for the thermodynamic database. The CaO–ZnO and CaO–ZnO–SiO2 systems have been recently reassessed [13] based on new experimental data [14,15]. The FeO–Fe2O3–CaO and FeO–Fe2O3–CaO–SiO2 systems are taken from Hidayat et al. [16,17] with minor modifications described below. The ZnO–FeO–Fe2O3–SiO2 system has been reoptimised by the authors [18].
Liquidus of the ZnO-“Fe2O3”-CaO system in air has been studied by the authors in air
Experimental technique and results
The technique used for experiments are the same as in the previous study by the authors [19,27]. Initial mixtures were made by mixing high-purity powders of Fe2O3 (99.945 wt% purity), ZnO (99.8 wt% purity), CaCO3 (99.9–99.99 wt% purity), SiO2 (99.9 wt%) supplied by Alfa Aesar, MA, USA. Pt foil (>99.9% purity, 0.05 mm thickness, provided by Johnson Matthew, Australia) envelope substrates were used for all experiments. Synthetic samples were equilibrated at controlled conditions, quenched in H2
Thermodynamic optimization
In the present study, the Modified Quasichemical model (MQM) is used to describe the liquid phase in the binary, ternary and multicomponent systems. The liquid oxide phase is assumed to form an ionic liquid where Zn2+, Fe2+, Fe3+, Ca2+ and Si4+ cations mix on one sublattice, while oxygen anions occupy the other sublattice. The model has been described in detail by Pelton and co-workers [[5], [6], [7], [8]].
The CaO–ZnO–Fe2O3, CaO–ZnO–FeO, and CaO–FeO–SiO2 parameters of the liquid slag are
Modelling results and discussion
Optimized thermodynamic properties of the liquid slag solution and the solid phases (stoichiometric compounds and solutions) are listed in Table 2.
The optimized thermodynamic model calculations are compared to the experimental results for the pseudo-ternary liquidus ZnO-“Fe2O3”-CaO in air and ZnO-“FeO”-CaO in equilibrium with metallic Fe in Fig. 2, Fig. 3. The calculated ZnO-“Fe2O3”-CaO diagram in air is an improved version of the diagram published in Ref. [19].
The CaO-“Fe2O3”-SiO2 phase
Conclusions
A critical evaluation of phase equilibria and thermodynamic data for the ZnO–FeO–Fe2O3–CaO–SiO2 system has been carried out using previous as well as most recent experimental data, the latter produced by the authors as part of the integrated research program. The modified quasichemical model is used to describe the Gibbs energy of the slag phase. The new model parameters reproduce the available data within experimental error limits. The optimized database can be used as a basis for the
Data availability
The raw/processed data (thermodynamic parameters) required to reproduce these findings are provided in supplementary file.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors would like to thank Nyrstar (Australia), Outotec Pty Ltd (Australia), Aurubis AG (Germany), Umicore NV (Belgium), and Kazzinc Ltd, Glencore (Kazakhstan), and Australian Research Council Linkage project LP150100783 for their financial support for this research. The authors are grateful to Prof. Peter C. Hayes (UQ) for valuable comments and suggestions.
References (49)
- et al.
Thermodynamic optimisation of the systems CaO-Pb-O and PbO-CaO-SiO2
Can. Metall. Q.
(1998) - et al.
FactSage thermochemical software and databases - recent developments
Calphad
(2009) Some properites of the compound energy model
Calphad
(1996)The compound energy formalism
J. Alloys Compd.
(2001)- et al.
Parameters in the compound energy formalism for ionic systems
Calphad
(2009) - et al.
Thermodynamic optimization of the binary CaO-ZnO and ternary CaO-ZnO-SiO2 system
Calphad
(2020) - et al.
Experimental liquidus study of the binary PbO-ZnO and ternary PbO-ZnO-SiO2 systems
Ceram. Int.
(2019) - et al.
Thermodynamic optimization of the binary systems PbO-SiO2, ZnO-SiO2, PbO-ZnO, and ternary PbO-ZnO-SiO2
Calphad
(2019) - et al.
Thermodynamic reevaluation of the Fe-O system
Calphad
(2015) A general "geometric" thermodynamic model for multicomponent solutions
Calphad
(2001)