Key Takeaways & Executive Findings
- •• The addition of 5wt% Fe3O4 to the CaO–SiO2–TiO2 system at 1400°C in air results in a single liquid region and various liquid–solid and three-phase equilibria, including liquid–tridymite, liquid–rutile, liquid–perovskite, liquid–wollastonite, and liquid–tridymite–rutile and liquid–rutile–perovskite. • The experimental isothermal sections of the CaO–SiO2–TiO2–5wt%Fe3O4 system at 1400°C in air were determined, providing essential thermodynamic data for optimizing the selective crystallization and phase separation (SCPS) process for titanium extraction from titania-bearing slag. • The experimental results show good agreement with FactSage calculations, validating the thermodynamic database for this quaternary system and supporting its use in process modeling. • This study fills a critical gap in thermodynamic data for the CaO–SiO2–TiO2–Fe3O4 system, which is essential for improving the efficiency and sustainability of titanium recovery from blast furnace slag.
Abstract
The equilibrium phase relations of the CaO–SiO2–TiO2–5wt%Fe3O4 system were experimentally investigated at 1400°C in air. High-temperature equilibration-quenching techniques were employed in an electric MoSi2 resistance heated furnace, with phase composition analysis conducted using an electron probe microanalyzer and X-ray diffraction. A single liquid region, liquid–solid phase equilibria regions (including liquid–tridymite, liquid–rutile, liquid–perovskite, and liquid–wollastonite), and three-phase equilibria regions of liquid–tridymite–rutile and liquid–rutile–perovskite were found. The 1400°C isothermal sections of the CaO–SiO2–TiO2–5wt%Fe3O4 system in air were projected. The present experimental results exhibited good agreement with the calculation results obtained from FactSage.
1. Introduction
The comprehensive utilization of secondary resources is a fundamental prerequisite for a circular economy and for fostering environmentally sustainable development. In this respect, titania-bearing slag, a by-product of the blast furnace smelting of vanadium titano-magnetite, has garnered increasing attention as a prototypical secondary resource which is rich in multiple metals [1–3]. Despite originating with a low concentration, approximately 1.5wt% of TiO2 in vanadium titano-magnetite, the smelting process in blast furnaces can enrich it into titania-bearing blast furnace slag, boasting an elevated TiO2 content ranging from 22.0wt% to 25.0wt% TiO2 [4]. However, fine TiO2 particles are widely dispersed within various mineral phases, including perovskite (CaTiO3), anosovite (MgTiO3–Al2TiO5–Ti2O3 solid solution), and rutile (TiO2). This dispersion poses a challenge in terms of effectively extracting titanium [5]. Perovskite and rutile consist of Ti4+, whereas anosovite comprises Ti4+ and Ti3+ [6].
Over the past decades, with the advancement of various titanium extraction processes, the selective crystallization and phase separation (SCPS) method has emerged as a viable approach because of its environmentally friendly and sustainable characteristics [7–9]. Drawing from numerous studies and practical applications conducted on slag, it has been observed that by introducing air into molten slag during the dynamic oxidation process, Ti2+ and Ti3+ components within the slag can be oxidized to Ti4+, with iron oxides oxidized as well [10]. This substantially enriches the Ti component, with a predominant presence in the perovskite phase. Based on the typical compositions of titania-bearing slag, the content of iron oxides is approximately 5.0wt% [1].
Recently, extensive studies have been dedicated to the kinetics and dynamic oxidation of titania-bearing blast furnace slag. However, the examination of thermodynamic data and the impact of variations in the valence state of iron oxides on coexisting liquid–perovskite phase equilibrium relationships have received limited attention. Enhancing the integrity of thermodynamic data serves as the foundation for the advancement and refinement of the SCPS process.
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Junjie Shi, Chenglong Jiang, Yifei Cao, Yumo Zhai, Yuchao Qiu, Hangkai Shi, Maoxi Yao, Jianzhong Li (2025). Effect of 5wt% Fe3O4 addition on the phase equilibria of the CaO–SiO2–TiO2 system at 1400°C in air. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-024-2971-z
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Frequently Asked Questions
What is the main objective of this study?
The main objective is to experimentally investigate the equilibrium phase relations of the CaO–SiO2–TiO2–5wt%Fe3O4 system at 1400°C in air, providing essential thermodynamic data for optimizing titanium extraction from titania-bearing slag.
What experimental techniques were used?
High-temperature equilibration-quenching techniques in an electric MoSi2 resistance heated furnace, with phase composition analysis using electron probe microanalyzer (EPMA) and X-ray diffraction (XRD).
What are the key findings of the phase equilibria study?
The study identified a single liquid region, liquid–solid equilibria (liquid–tridymite, liquid–rutile, liquid–perovskite, liquid–wollastonite), and three-phase equilibria (liquid–tridymite–rutile and liquid–rutile–perovskite). The 1400°C isothermal sections were projected.
How do the experimental results compare with thermodynamic calculations?
The experimental results exhibited good agreement with calculations from FactSage, validating the thermodynamic database for this system.
Why is this study significant for the metallurgical industry?
It provides crucial thermodynamic data for the selective crystallization and phase separation (SCPS) process, which is an environmentally friendly method for extracting titanium from titania-bearing blast furnace slag, thereby supporting sustainable resource utilization.
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