Aluminium: Extraction

How tropical weathering makes the ore

Bauxite forms when tropical weathering leaches silica from rock, leaving aluminium-rich laterite near the surface. It is strip-mined from shallow pits, chiefly in Guinea, Australia, China and Brazil. Refineries dissolve it in caustic soda by the Bayer process to make alumina. As a rule, 4 tonnes of bauxite make 2 tonnes of alumina, which make 1 tonne of metal (USGS). Smelters then split alumina electrolytically, using so much power that traders call aluminium congealed electricity (Blas & Farchy). Some bauxite operations also yield gallium as a by-product (Tilton & Guzmán).

Primary aluminium passes through three plants: a bauxite mine, an alumina refinery and a smelter. Refineries sit near mines in Australia, Brazil, Guinea and India, or near ports in China that import bauxite. Smelters sit where electricity is cheap and reliable, because power is the largest variable cost. China adapted refineries to its own diaspore-rich bauxite with an extra sintering step and now imports most of the world's traded bauxite (Humphreys 2015). Secondary aluminium, made by remelting scrap, needs a fraction of the energy and supplies roughly a third of total metal use. Ingot is priced on the LME plus regional premiums.

Methods compared

How each method works

Bauxite, a weathered tropical laterite, lies close to the surface. Overburden is stripped, the ore layer dug by excavators, sometimes crushed and washed, and railed or trucked to a refinery or port. Land is rehabilitated in strips behind the mining face.

Low-cost, high-volume mining, but deposits are in tropical areas with land-use, community and political risks (Guinea revoked a foreign firm's licences in 2025).

Crushed bauxite is digested in hot caustic soda under pressure. Alumina dissolves, impurities settle out as bauxite residue (red mud), and aluminium hydroxide is precipitated and calcined to alumina. Chinese refineries added a sintering stage to use high-diaspore local bauxite.

Mature and efficient, but uses caustic soda and energy and leaves large volumes of residue that must be stored safely.

Alumina is fed into pots of molten cryolite. Direct current passes from carbon anodes to the cathode, releasing oxygen as CO2 at the anode and depositing molten aluminium, which is siphoned off and cast. Potlines run continuously; a power cut of a few hours can freeze the pots.

Only commercial route to primary metal; output is tied to power cost and carbon intensity, which ranges from low (hydro) to very high (coal).

New scrap from rolling, extrusion and stamping and old scrap such as used beverage cans, cars and window frames is sorted, de-coated and remelted, then alloyed and cast. Can-to-can loops are the most closed.

Far lower energy and emissions than primary metal, but alloy mixing limits which scrap can make which product.

Share produced as a by-product

Who does it: global

Who does it: India

India is the second-largest aluminium producer, with about 4.2 Mt of smelter output, 8.2 Mt of alumina and 25 Mt of bauxite in 2025 (USGS), and supplied 8.5% of world unwrought aluminium exports by value in 2024 (UN Comtrade). Coal-fired captive power keeps costs low but carbon intensity high.