How Is Silicon Metal Made? From Quartz to Metallurgical-Grade Silicon

What Is Silicon Metal?

Silicon metal, also called metallurgical-grade silicon (MG-Si) or industrial silicon, is a semi-metallic element product with a silicon content of roughly 98-99.7%. It is the base material for aluminium-silicon alloys, silicone polymers, electronic-grade silicon, and photovoltaic polysilicon. Unlike ferrosilicon, which contains iron, silicon metal is essentially pure elemental silicon with trace impurities.

Raw Materials and Preparation

Production starts with high-purity quartz or quartzite containing very low iron, aluminium, and calcium. The carbon reductant is a blend of petroleum coke, charcoal, and coal chosen to give the right reactivity and impurity profile. The quartz is washed, crushed, and sized, and the reductants are dried and blended. Raw material quality is the first control point: impurities in the feed largely end up in the product.

Smelting in the Submerged Electric Arc Furnace

The blended charge is fed continuously into a submerged electric arc furnace with three-phase electrodes. The furnace operates at temperatures above 1800°C, and the core reaction is the carbothermic reduction of silica:

SiO2 + 2C = Si + 2CO

The liquid silicon collects at the furnace bottom and is tapped periodically, while carbon monoxide is combusted or recovered. Power consumption is the dominant operating cost, typically in the range of 11,000-13,000 kWh per tonne of silicon depending on furnace efficiency and raw materials.

Refining, Casting, and Sizing

Tapped silicon contains dissolved aluminium, calcium, and iron. Refining is done by oxygen or air lancing with flux additions, which oxidize aluminium and calcium into a removable slag; iron is controlled mainly through raw material selection. The refined metal is cast into ingots or a continuous slab, cooled, crushed, and screened into product sizes such as 10-100 mm lumps, granules, or powder. Magnetic separation removes any metallic iron pickup from crushing equipment.

Grade System and Specifications

Grade	Fe max	Al max	Ca max	Si min
553	0.5%	0.5%	0.3%	98.5%
441	0.4%	0.4%	0.1%	99.0%
3303	0.3%	0.3%	0.03%	99.3%
2202	0.2%	0.2%	0.02%	99.5%

Applications of the Different Grades

Grade 553: general aluminium alloying and silicone raw material.

Grade 441: cast alloys with tighter iron limits and chemical processes.

Grades 3303 and 2202: higher-value aluminium and chemical applications, and upgrading feedstock toward photovoltaic purity.

How Quality Is Controlled at the Factory

A producing plant controls quality at three stages: incoming raw material analysis, furnace operation parameters (power input, feed balance, tapping schedule), and final product assay by XRF or wet chemistry on every lot. Certificates of analysis report silicon, iron, aluminium, calcium, and additional elements such as phosphorus and boron when required. Buyers should request the lot assay, define sampling rules, and verify particle size distribution on arrival.

FAQ

1. What is the difference between silicon metal and ferrosilicon?

Ferrosilicon is an iron-silicon alloy (typically 15-90% silicon with iron as the balance) used mainly for steel deoxidation and nodular iron inoculation. Silicon metal is nearly pure silicon and is used where iron must not be introduced, such as aluminium alloys and silicones.

2. Why is silicon metal production so energy-intensive?

The carbothermic reduction of quartz requires temperatures above 1800°C sustained electrically. Most of the energy is consumed by the reduction reaction itself and by furnace heat losses, which is why electricity cost largely determines the competitiveness of production regions.

3. Can I use grade 553 for chemical-grade applications?

For many silicone processes, 553 or 441 is suitable. However, chemical-grade specifications also control phosphorus and boron, so confirm the full analysis with the producer rather than relying on the three-digit grade alone.

4. What particle size should I order?

Lumps of 10-100 mm suit furnace additions in aluminium plants; granules of 0.2-6 mm suit wire feeding and chemical dosing. Confirm the fines limit in the contract so the size distribution matches your equipment.

5. How do I verify the quality of a delivered lot?

Compare the certificate of analysis with the contract, check the size distribution by screening, and if necessary commission an independent assay. Keep sealed retained samples from each lot for dispute resolution.