Metal silicon, also known as industrial silicon or crystalline silicon, is usually made by reducing silicon dioxide with carbon in an electric furnace. Metallic silicon is a product made of quartz and coke by smelting in an electric furnace. The content of silicon as the main component is about 98% (in recent years, 99.99% of Si is also included in metallic silicon). The remaining impurities are iron, aluminum and calcium. It is mainly used as an additive for non-ferrous alloys and as a starting material for the production of semiconductor silicon and organosilicon.
In China, metallic silicon is usually classified according to the content of iron, aluminum and calcium. According to the percentage content of iron, aluminum and calcium in metal silicon, metal silicon can be divided into 553, 441, 411, 421, 3303, 3305, 2202, 2502, 1501, 1101 and other different brands. (about the source of metal silicon number: the first and second codes represent the percentage content of iron and aluminum, and the third and fourth digits represent the content of calcium. For example, 553 represents the content of iron, aluminum and calcium, which is 5%, 5%, and 3%; 3303 represents the content of iron, aluminum and calcium, which is 3%, 3%, and 0.3%)
The production of metallic silicon adopts carbothermal method, that is, smelting in submerged arc furnace with silica and carbonaceous reducing agent. The purity of the silicon thus obtained is 97% - 98%, and such silicon can generally be used for metallurgical purposes. If higher grade silicon is to be obtained, it needs to be refined to remove impurities and obtain metallic silicon with purity of 99.7% ~ 99.8%.
Smelting metallic silicon with quartz sand as raw material includes several steps, such as making blocks with quartz sand, preparing furnace charge and smelting in submerged arc furnace.
Generally speaking, high-quality quartz sand will be directly used to produce high-grade quartz glass products, and even processed into gem grade products such as crystal and tourmaline. Those with slightly poor grade but large reserves, slightly better mining conditions and cheaper surrounding power are suitable for producing metallic silicon.
At present, the production process route of carbothermal method for producing metallic silicon in China is that silica is generally used as raw material, petroleum coke, charcoal, wood chips, low ash coal, etc. are used as reducing agents, and metal silicon is reduced from silica by high-temperature smelting in a mine thermal power furnace, which is a slag free submerged arc high-temperature smelting process.
