Key Takeaways & Executive Findings
- •• Slag formation in Si/FeSi furnaces is more substantial than traditionally assumed, with slag accumulating in inactive zones. • Slag forms from reactions between SiO2 and other oxides (e.g., CaO, Al2O3) introduced via raw materials or fluxes, with composition influenced by equilibrium or kinetics. • Trace elements like K2O significantly lower slag viscosity and liquidus temperature, promoting slag formation and affecting furnace operation. • The study provides experimental data on slag formation mechanisms, including grain boundary reactions, composition gradients, and wettability, which are critical for optimizing raw material selection and process control.
Abstract
In Si and FeSi production, slag formation is traditionally considered minimal, but industrial furnace excavations reveal substantial slag accumulation. This study investigates slag formation from reactions between SiO2 and sources of limestone or iron. Experimental analysis focused on slag formation at grain boundaries and interfaces, composition gradients, slag composition within quartz cracks, effects on element dissolution, role of minor elements, wettability, and slag viscosity. The work uses industrial quartz, limestone, lime, iron source, and pure FeO to isolate effects. Findings indicate that slag forms when other oxides react with quartz, and its composition is influenced by equilibrium or kinetic factors. Trace elements like K2O lower slag viscosity and liquidus temperature, enhancing slag formation. The study provides insights into reaction mechanisms, equilibrium conditions, and kinetics, aiding in better understanding of slag formation in industrial furnaces.
1. Introduction
In Si and FeSi production, the processes are traditionally considered slag-free with minimal slag formation expected. However, excavations of industrial furnaces reveal that substantial slag can accumulate inside the furnace, often found in inactive areas. This slag typically consists of SiO2–CaO–Al2O3 in various proportions. Observations show that a layer of liquid slag and SiC particles may encase silicon within the tap hole channel. Calcium and aluminum, introduced either as trace elements in raw materials or as separate fluxes, are largely tapped alongside the liquid metal, suggesting that significant slag buildup may occur gradually over time.
In Si/FeSi production, both solid and molten SiO2 from quartz are typically present throughout the furnaces. Additionally, molten SiO2 formed through the condensation of SiO gas often exists within the furnace, mixed closely with Si and/or SiC. These forms of SiO2 are not regarded as slag. For material to be classified as slag in this context, it must contain over 10 wt% of other oxides in addition to SiO2. Slag forms when other compounds react with, coalesce with, or dissolve in quartz, and its composition changes as either quartz or other oxides are introduced. The composition of the formed slag may be determined by equilibrium among all compounds under furnace conditions or by kinetic factors. There is limited information on slag formation in Si and FeSi processes. Due to the high viscosity of quartz at low temperature, it is likely that equilibrium between quartz and the slag phase is not reached. However, when slag mixes with additional components, both its liquidus temperature and viscosity decrease rapidly. Trace elements in the gangue minerals within quartz, such as K2O, will also help lower slag viscosity and liquidus temperature, potentially enhancing slag formation.
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Unknown (2025). Slag Formation in Si and FeSi Production: Reactions Between SiO2 and Limestone or Iron Sources. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-024-3052-z
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Frequently Asked Questions
What is the main focus of this study?
The study investigates slag formation in Si and FeSi production, specifically from reactions between SiO2 and sources of limestone or iron, to understand reaction mechanisms, equilibrium conditions, and kinetics.
Why is slag formation important in Si/FeSi furnaces?
Slag formation can affect furnace operation, product quality, and refractory lining life. Understanding it helps optimize raw material selection and process control.
What raw materials were used in the experiments?
Industrial quartz (Qz47 and Qz54), limestone, lime, iron source, and pure FeO were used to isolate the effects of impurities and study slag formation under controlled conditions.
How does K2O affect slag formation?
K2O lowers slag viscosity and liquidus temperature, which can enhance slag formation by promoting reactions and wetting of quartz.
What are the key findings of this study?
Key findings include that slag forms at grain boundaries and interfaces, composition gradients extend towards pure quartz, and trace elements like K2O significantly influence slag properties. The study also provides insights into wettability and viscosity of slag.
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