Silicon: Emissions
Why coal-powered furnaces make silicon carbon-heavy
What this tab covers The greenhouse-gas footprint of the commodity at a global level, split by lifecycle phase: extraction (or farming), refining and processing, movement, usage, and recycling or end of life. Intensities are per unit of product; the global total combines intensity with world output. Also covers other environmental impacts and the main levers to cut emissions. Emission intensity 11.0 t CO2e per t range 4-15 · derived, indicative: about 3.1-3.7 t process CO2 from reductants plus 11-13 MWh of electricity per tonne; about 4-5 t on Norwegian hydro power, 11-15 t on Chinese coal power Global emissions per year 50.0 Mt CO2e per year 2025 · 4,600 kt silicon metal x about 11 t CO2e/t (derived, indicative); excludes ferrosilicon and the extra power for polysiliconPer t of metallurgical silicon metal (cradle-to-gate; polysilicon covered in notes). Intensity: derived from stoichiometry (SiO2 + 2C) and typical furnace power use (indicative); Conway 2023 on coal reliance in China. Global total: USGS MCS 2026; derived.
Share of footprint by lifecycle phase
Extraction 1% Refining / processing 97% Movement 2%Footprint by lifecycle phase
| Phase | Intensity | Share | Main sources of emissions | Notes | Source |
|---|---|---|---|---|---|
| Extraction | about 0.05 t CO2e/t Si (indicative) | 1% | quarrying and washing quartz or quartzite | Quartz is abundant and needs little processing; about 6 t of raw materials go into each tonne of silicon | Conway 2023; indicative |
| Refining / processing | about 10.5 t CO2e/t on a coal-heavy grid: about 3.3 t from reductants, about 7-8 t from power | 97% | coal, coke and wood chips as reductants; 11-13 MWh per tonne for submerged-arc furnaces (a single furnace draws about 45 MW) | Process CO2 cannot be avoided with carbon reductants even on hydro power; part of it is biogenic where wood chips and charcoal are used. Polysilicon by the Siemens process needs large further power, more than 3,000 times the energy of cement per kg (Smil via Conway) | Conway 2023; derived (indicative) |
| Movement | about 0.1-0.2 t CO2e/t (indicative) | 2% | shipping and trucking of lump silicon; coal and coke inputs | Small next to smelting | indicative |
| Usage | not applicable; strong enabling effect | – | silicon emits nothing in use | Solar-grade silicon becomes panels that avoid far more CO2 over their life than was emitted making them; silicon in aluminium alloys helps light-weight vehicles | content_v2 uses; indicative |
| Recycling / end of life | insignificant today | – | solar panel and wafer-kerf recycling at an early stage | USGS calls silicon recycling insignificant and the EU end-of-life recycling input rate is 0% | USGS MCS 2026; EU CRM 2023 |
Other environmental impacts
Silica fume from furnaces is captured and sold for concrete. Polysilicon plants handle chlorosilanes and HCl. US import bans target forced labour risks in Xinjiang's silicon supply chain (Conway 2023).
Levers to cut emissions
- Smelt on low-carbon power: Norwegian and Icelandic hydro cut the footprint to about 4-5 t CO2e/t (indicative)
- Replace fossil reductants with charcoal and wood chips, which makes part of the process CO2 biogenic (indicative)
- Recover furnace off-gas heat for electricity (indicative)
- Cut polysilicon power use with fluidised-bed reactors and better Siemens reactors (indicative)
- Recycle wafer kerf and end-of-life panels
India
India makes about 59 kt of ferrosilicon but no silicon metal and imports 5.2% of world silicon metal by value (USGS; UN Comtrade 2024); neighbouring Bhutan's 98 kt of ferrosilicon is smelted on hydropower, a lower-carbon source for Indian steel mills (USGS; indicative).
Emission figures are indicative global averages from the life-cycle studies named; actual footprints vary widely by site, energy mix and method.