Raw material for smelting ferrosilicon
Various minerals containing silicon dioxide are the raw materials for the manufacture of ferrosilicon. Silicon dioxide that exists in nature includes crystal, topaz, amethyst, quartz, flint, chalcedony, quartzite, quartz sand, sandstone, etc. However, not all of these minerals are generally used in the manufacture of silicon. Some of them are rare ores. For example, crystal, topaz, and amethyst are not used together. Others, such as sandstone and quartz sand, are not suitable because they are too broken. Smelting ferrosilicon usually uses the cheapest and most common ore, namely quartz, quartzite and chalcedony.
Quartz is a dense crystal with a specific gravity of 2.59-2.65 and a hardness of 7. In most cases it is colorless, white, gray or red, depending on the impurities it contains.
Chalcedony—a long, fibrous, sometimes porous ore with various colors. The specific gravity and hardness are the same as quartz.
Quartzite is a rock composed of quartz grains, and there are sticky terpene substances between the grains, and these binding substances mainly contain silicon dioxide.
These ores are common. When selecting silicon dioxide minerals for smelting ferrosilicon, those deposits containing not less than 95% silicon dioxide and the least amount of miscellaneous materials – steel trioxide, oxonite and crocodile oxide – should be selected. Particular attention should be paid to the content of P.0, which should not exceed 0.02 % in these ores. As for the content of iron oxide, there is no limit, because when making ferrosilicon, these various irons must be added to the fuel. But the production of crystalline silicon is an outlier: its manufacture requires a mineral with a minimum amount of iron oxide.
Special attention should be paid to the mechanical strength of quartzite, and it should not be broken into powder when the crushing industry is heated to the conversion temperature. Quartz and quartz rock used for smelting silicon zirconium must be crushed in advance. Best for industrial furnaces The block degree is 50-100 mm. All the small pieces produced during crushing should be divided into ribs with a hole of 20-30 mm. It is not good for small pieces to enter the furnace, not only because it will reduce the gas permeability of the furnace charge, but also because it contains high impurities. For example, the amount of SiO3 in quartzite is generally not more than 1.5%, but the amount of SiO3 in small pieces may exceed 20%.
2. reducing agent
A variety of carbonaceous materials are used as reducing agents in the production of silicium: charcoal, petroleum coke, metallurgical coke, and sometimes coal. The best reducing agent is charcoal, but due to its high value, it is only used in the manufacture of high silicon content (greater than 90%) silicon or crystalline silicon.
Petroleum coke and sun green coke are good reducing agents. Compared with ordinary coke, The advantages are low ash content (not higher than 1-2%), no harmful impurities, and large porosity.But because of their high price. These reducing agents are only used in the manufacture of crystalline silicon.
Coke or coke sieved from metallurgical enterprises is usually used in the production of silicon. The ash contained in the coke should be as little as possible, because the ash will inevitably bring harmful impurities that promote the formation of slag (such as aluminum oxide, calcium oxide) or damage the alloy (such as phosphorus) into the charge.
In addition to the various ferrosilicon listed above, silicon-containing 18- 25% silicon deficiency.
Ferrosilicon containing up to 45% silicon is mainly used for deoxidation of steel. Ferrosilicon containing 75-90% silicon is used for diffusion deoxidation of steel (through slag), alloying agent for steel and silicon thermal method. The production of silver alloys. Pure silicon used in industry is also used in the smelting of various alloys in nonferrous metallurgy (silicon blue sea bream, silicon pot alloy, etc.)