Raw materials
The raw materials for smelting ferrosilicon include silica, carbonaceous reducing agent and iron raw materials.
Silica
Requires SiO2>97%, Al2O3<1.0%, CaO<0.5%, P2O5<0.03%. Silica does not burst during heating and has a high softening temperature. Before smelting into the furnace, it must be washed with water to remove attached soil and debris.
Carbonaceous reducing agent
The carbonaceous reducing agent is required to have high fixed carbon, low ash and volatile matter, high specific resistance, large porosity, good chemical reaction activity, good high-temperature thermal stability, and certain mechanical strength. Commonly used carbonaceous reducing agents include metallurgical coke, gas coal coke, petroleum coke, bituminous coal, dry distillation coal, etc. Using bituminous coal as part of the reducing agent can improve smelting operations and reduce furnace condition fluctuations. Through the comprehensive combination of multiple reducing agents, the furnace operating resistance, input electric power and electric efficiency can be improved. (See electric carbon heating method)
Iron raw materials
There are two commonly used iron raw materials: (1) Steel shavings. It is ordinary carbon steel shavings, the length of the coil is no more than 100mm, the iron content should be >95%, and alloy steel shavings, non-ferrous metal shavings and pig iron shavings cannot be mixed. (2) Iron ore. Iron ore used for smelting 75% Si ferrosilicon contains Fe≥60%, CaO≤1.0%, SiO2≤10%, P≤0.1%, S≤0.01%, preferably iron ore concentrate pellets, or rolled steel oxidation Iron sheet: Iron silicate can also be used to smelt ferrosilicon with Si≤50%.
Smelting reaction When smelting ferrosilicon, silicon dioxide is reduced by carbon to form intermediate products silicon monoxide and silicon carbide:
SiO2+C=SiO+CO↑
SiO2+3C=SiC+2CO↑
Silicon monoxide is in a gaseous state at high temperatures. It rises slowly in the material layer and interacts with the carbon in the charge to generate silicon or silicon carbide:
SiO+C=Si+CO↑
SiO+2C=SiC+CO↑
Silicon monoxide also undergoes a disproportionation reaction to produce silicon and silicon dioxide:
2SiO=Si+SiO2
At high temperatures, silicon carbide reacts with silicon dioxide or silicon monoxide to form silicon:
2SiC+SiO2=3Si+2CO↑
Or SiC+SiO=2Si+CO↑
The produced silicon carbide, when iron is present, can react with iron at a lower temperature to form iron silicide:
SiC+Fe=FeSi+C
The silicon produced by the reaction is also dissolved in the iron.
