MATERIALSDECODED
Aluminium · Mining

From Bauxite to Metal: Two Chemical Steps, Not a Smelter Alone

Aluminium is made in two distinct chemical steps, the Bayer process and the Hall-Heroult process, and the second one consumes enormous amounts of electricity.

Bauxite mining itself is conventional open-pit work, stripping and excavating near-surface lateritic soil, covered on this material’s geology page. What makes aluminium genuinely distinctive is what happens after the ore leaves the ground: two separate, real chemical processes, not one smelting step.

Step one: the Bayer process

Bauxite is digested in hot sodium hydroxide, which dissolves the aluminium hydroxide minerals while leaving iron oxides and other impurities (the residue called red mud) behind:

Al2O3⋅xH2O+2NaOH→2NaAlO2+(x+1)H2OAl_2O_3 \cdot xH_2O + 2NaOH \rightarrow 2NaAlO_2 + (x+1)H_2O
The Bayer process digestion reaction. Bauxite's aluminium hydroxide dissolves as sodium aluminate, leaving iron oxide and other impurities behind as insoluble red mud. Cooling and seeding the solution then precipitates pure aluminium hydroxide, which is calcined to alumina (Al2O3).

Step two: the Hall-Heroult process

Alumina does not melt and pour like iron ore reduced in a blast furnace. It is electrolysed, dissolved in molten cryolite and split into aluminium metal and oxygen by passing a very large direct current through the cell, a process that consumes roughly 13 to 15 megawatt-hours of electricity per tonne of metal produced, one of the most electricity-intensive industrial processes that exists at scale.

~4 t
Bauxite needed per tonne of metal
~14 MWh
Electricity per tonne of aluminium
2
Separate chemical processes
Bayer, then Hall-Heroult

Why this makes electricity the real input, not bauxite

This is exactly why smelter location follows cheap power rather than bauxite deposits, covered on this material’s geology page, and why the industry talks about aluminium as “congealed electricity” almost as much as a metal. A country or region’s aluminium output is, in practice, a function of its power grid’s cost and availability, not its mineral endowment.

Sources: Bayer and Hall-Heroult process chemistry and energy intensity draw on standard extractive metallurgy references (International Aluminium Institute, USGS); production figures reference the production data elsewhere on this site.