High-purity ferrosilicon, as a special alloy material, has wide applications in electronics, photovoltaics, and high-end metallurgy. Its impurity content directly affects product performance and downstream processing quality. Synthetic slag injection refining, as a highly efficient ladle refining technology, can significantly improve the purity of high-purity ferrosilicon through the dual effects of physical adsorption and selective chemical reaction, especially in removing key impurities such as aluminum, calcium, and titanium.
The core principle of synthetic slag injection refining lies in utilizing the full contact between high-temperature molten slag and molten ferrosilicon, achieving impurity separation through the selective adsorption of slag components. Considering the characteristics of high-purity ferrosilicon, the synthetic slag typically employs a low-melting-point, high-basicity composite formulation, based on silicates and supplemented with fluorides, calcium oxide, and other components. During the injection process, a carrier gas (such as argon) injects the powdered slag agent at high speed into the molten ferrosilicon pool, creating vigorous stirring and ensuring thorough mixing of the slag agent and molten metal. At this stage, impurities such as aluminum and calcium preferentially react with calcium oxide and fluorides in the slag agent to form low-melting-point compounds such as calcium aluminate and calcium fluoride. These compounds float to the slag layer due to their density difference and are eventually separated mechanically.
Aluminum is one of the most critical impurities in high-purity ferrosilicon, as its content directly affects the conductivity and corrosion resistance of ferrosilicon. Traditional processes primarily rely on oxidation for aluminum removal, but this method has limited efficiency. Synthetic slag injection, by introducing fluorides (such as CaF₂), significantly enhances aluminum removal. Fluorides lower the melting point of calcium aluminate, promoting its rapid flotation while inhibiting silicon oxidation loss. Experiments show that after synthetic slag treatment, the aluminum content in high-purity ferrosilicon can be reduced to extremely low levels, meeting the stringent standards for electronic-grade ferrosilicon (aluminum content <0.01%).
Calcium is another critical impurity, as its presence reduces the mechanical properties and thermal stability of ferrosilicon. Calcium oxide in the synthetic slag can react with calcium in ferrosilicon to form stable calcium silicate, which then enters the slag phase through physical adsorption. Furthermore, fluorides in the slag additive can disrupt the oxide coating of calcium, promoting its migration into the slag layer. The strong stirring effect of the injection process further accelerates this process, significantly improving the calcium removal rate. The calcium content in the treated high-purity ferrosilicon can be controlled within an extremely low range, meeting the requirements of high-end metallurgical additives.
The removal of titanium is one of the challenges in refining high-purity ferrosilicon, as it readily forms a solid solution with silicon, making it difficult to separate using conventional methods. Synthetic slag injection, by introducing components such as alumina and silicates, can alter the form of titanium. At high temperatures, titanium preferentially reacts with alumina to form aluminum titanate, a compound with a high melting point and density, which easily accumulates in the slag layer. Simultaneously, the strong stirring effect generated by injection can break the solid solution structure of titanium, promoting its transfer into the slag phase. After this process, the titanium content in high-purity ferrosilicon can be significantly reduced, meeting the standard for photovoltaic-grade ferrosilicon (titanium content <0.005%).
Synthetic slag injection refining also offers the advantages of improving inclusion morphology and reducing gas content. During the injection process, the slag agent absorbs non-metallic inclusions (such as oxides and sulfides) in the ferrosilicon, causing them to spheroidize or refine, minimizing damage to material properties. Furthermore, the agitation effect of the carrier gas promotes the escape of gases such as hydrogen and nitrogen, reducing the ferrosilicon's porosity and improving its density and processing properties.
Compared to traditional refining processes, synthetic slag injection offers significant efficiency and cost advantages. Its processing cycle is short, down to less than half that of traditional methods; slag agent consumption is low and recyclable; and its flexible operation makes it suitable for the production of high-purity ferrosilicon of various specifications. Furthermore, this process requires minimal equipment and can be easily integrated into existing production lines, offering significant economic benefits and promotional value.
Synthetic slag injection refining, through optimization of slag agent composition and injection process, achieves efficient removal of key impurities such as aluminum, calcium, and titanium from high-purity ferrosilicon. Simultaneously, it improves inclusion morphology and gas content, significantly enhancing product purity and performance stability. This technology provides a reliable guarantee for the large-scale production of high-purity ferrosilicon and promotes its widespread application in high-end fields.
