High-purity ferrosilicon, as a special metallic material, plays an irreplaceable role in the production of electromagnetic steel, aerospace, and high-end special steels. Its core quality indicator is extremely low aluminum and calcium impurity content. However, in traditional ferrosilicon smelting processes, oxides such as alumina and calcium oxide in the raw materials are difficult to completely reduce, resulting in high residual aluminum and calcium levels in the alloy. To overcome this bottleneck, ladle refining technology has become a key step in reducing impurities. By combining physical separation with selective chemical oxidation, the purity of ferrosilicon can be significantly improved.
Slag refining is one of the most widely used ladle refining technologies in high-purity ferrosilicon production. Its principle involves adding a synthetic slag composed of raw materials such as quartz, limestone, and dolomite to the molten ferrosilicon at high temperatures. By adjusting the slag composition, a low-melting-point, low-density slag layer is formed. During the refining process, the synthetic slag reacts chemically with impurities such as aluminum and calcium in the ferrosilicon, generating high-melting-point compounds such as calcium aluminate and calcium silicate. These compounds gradually float to the slag layer due to their density difference and are eventually separated by tipping or skimming. The key to this method lies in the precise control of the slag ratio. The proportions of calcium oxide, silicon dioxide, and alumina need to be dynamically adjusted according to the raw material composition and the content of target impurities to optimize the physicochemical properties of the slag and enhance the impurity removal effect.
The oxygen refining method removes impurities by blowing oxygen or oxygen-enriched air into the ferrosilicon melt, utilizing the principle of selective oxidation. Under high-temperature conditions, impurities such as aluminum and calcium have a significantly higher affinity for oxygen than silicon, and are preferentially oxidized to form oxides such as alumina and calcium oxide. These oxides either dissolve in the slag or precipitate as solid particles, which are then removed through subsequent separation processes. To enhance refining efficiency, modern processes often employ bottom-blowing oxygen technology, using permeable bricks to evenly blow gas into the interior of the melt, creating a strong stirring effect and promoting the oxidation reaction of impurities. Meanwhile, some companies combine synthetic slag refining with the simultaneous addition of flux during oxygen blowing to further reduce slag viscosity and improve impurity separation.
Chlorination refining, with its strong selective impurity removal capability, has become a core technology for the preparation of ultra-high-purity ferrosilicon. This process introduces chlorinating agents such as chlorine gas or silicon tetrachloride into the ferrosilicon melt, causing impurities such as aluminum and calcium to generate volatile chlorides. For example, aluminum reacts with chlorine gas to produce aluminum trichloride gas, while calcium forms calcium chloride vapor. These chlorides rapidly escape from the melt at high temperatures and are collected by a dust removal system, thus removing the impurities. Chlorination refining has extremely high aluminum removal efficiency, reducing the content to very low levels, and also has a significant removal effect on impurities such as titanium and boron. However, the strong corrosiveness and toxicity of chlorine gas impose stringent requirements on equipment materials and operational safety, necessitating the use of closed refining units and tail gas treatment systems, which limits its large-scale application.
To address the limitations of traditional chlorination processes, the industry has developed a composite refining technology that combines chlorination refining with slag refining or oxygen refining to form a multi-stage impurity removal system. For example, chlorination refining first rapidly reduces aluminum and calcium content, then slag refining removes residual oxides and chlorides, and finally oxygen refining further decarburizes and adjusts the alloy composition. This composite process not only improves impurity removal efficiency but also reduces the side effects of single refining methods, such as silicon oxidation loss or secondary chloride pollution. Furthermore, some companies have introduced inert gas protection technology, introducing argon or nitrogen during the refining process to suppress excessive reactions between silicon and oxygen or chlorine, ensuring alloy yield.
High-purity ferrosilicon's ladle refining technology is evolving towards green and intelligent processes. The development of new environmentally friendly fluxes, such as low-pollution synthetic slag and chlorine-free chlorinating agents, reduces waste emissions during refining. The application of intelligent control systems, through real-time monitoring of melt temperature, composition, and gas flow, enables dynamic optimization of refining parameters, improving process stability and product consistency. In the future, with breakthroughs in materials science and metallurgical technology, ladle refining technology will further break through the limits of impurity removal, promoting the widespread application of high-purity ferrosilicon in high-end fields such as semiconductors and new energy.
