Ferrosilicon alloys of 50% and 75% (FeSi50 and FeSi75) are produced by carbothermal reduction in a submerged arc furnace. The source of iron is iron ore or waste, and for silicon it is quartz. The main melting reaction is the same as for melting silicon metal.

The melting reaction between silica and carbon characterizes the formation of silicon carbide and SiO gas as intermediate products. Silicon carbide is reacted with SiO2 at the melting temperature to give Si and SiO. The SiO gas passes into the lower temperature range in the furnace and reacts with carbon and silicon carbide. Unreacted SiO gas leaks to the top of the furnace charge and represents a loss of silicon unit. In the melting of 50% and 75% of ferrosilicon alloys, iron reduces the activity of silicon, and this reduces the formation of SiO gas. Therefore, the yield of silicon is higher in 75% and 50% of ferrosilicon alloys than in the metallurgically obtained silicon metal.

The usual offer of this product on the market occurs with 15%, 45%, 75% or 90% silicon content.