How is silicon metal made
Jul 02, 2025
Silicon metal (also known as industrial silicon or metallurgical-grade silicon) is produced through a high-temperature carbothermic reduction process in an electric arc furnace. Here's a step-by-step breakdown of how it's made:
1. Raw Materials
The primary raw materials used are:
Quartz (SiO₂) – High-purity silica (usually >99% SiO₂) in the form of gravel or crushed rock.
Carbon Sources – Typically coal, coke, or wood chips, which act as reducing agents.
Electrodes – Graphite or carbon electrodes provide the electric arc for heating.
2. Smelting Process (Carbothermic Reduction)
The production occurs in a submerged electric arc furnace at temperatures between 1,700–2,000°C:
Charging the Furnace – Quartz and carbon materials are loaded into the furnace.
Electric Arc Heating – A powerful electric current passes through the electrodes, generating extreme heat.
Chemical Reaction – The carbon reacts with SiO₂ to produce silicon and carbon monoxide (CO) gas:
SiO₂ (quartz)+2C (carbon)→Si (silicon)+2CO (gas)SiO₂ (quartz)+2C (carbon)→Si (silicon)+2CO (gas)
Liquid Silicon Collection – Molten silicon settles at the bottom of the furnace and is tapped off periodically.
Slag Removal – Impurities (like calcium, aluminum, and iron oxides) form a slag layer that is removed.
3. Refining & Casting
The molten silicon is poured into molds and cooled into silicon metal ingots.
After solidification, it is crushed, graded, and purified further if needed.
4. Metallurgical-Grade Silicon (MG-Si)
The resulting silicon is about 98–99% pure, with main impurities being iron, aluminum, and calcium. This grade is used for:
Aluminum alloys (major use)
Silicone chemicals
Solar-grade silicon (after further purification)
Key Points
Energy Intensive: Requires large amounts of electricity (~10,000–14,000 kWh per ton of silicon).
Environmental Controls: CO gas is captured and often burned for energy recovery.
Further Processing: For semiconductor or solar use, MG-Si undergoes additional purification (e.g., Siemens process).
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