Aluminium smelting

Aluminium smelting

Aluminium smelting is the process of extracting aluminium from its oxide alumina, generally by the Hall-Héroult process. Alumina is extracted from the ore Bauxite by means of the Bayer process at an alumina refinery.

This is an electrolytic process, so an aluminium smelter uses prodigious amounts of electricity; they tend to be located very close to large power stations, often hydro-electric ones, and near ports since almost all of them use imported alumina.

Layout of an aluminium smelter

An aluminium smelter consists of a large number of pots, steel containers lined with carbon, in which the electrolysis takes place; smelting is run as a batch process, with the aluminium metal deposited at the bottom of the pots and periodically drained off. Power must be constantly available, since the pots have to be repaired at significant cost if the liquid metal solidifies.

The anodes are made of carbon, generally derived from pitch.

A typical smelter contains about 300 pots, each of which produces about a ton of aluminium a day, though the largest proposed smelters are up to five times that capacity.

Environmental issues of aluminium smelters

The process produces a quantity (as small as 0.5 kg per ton of aluminium in the best plants in 2007, up to 4 kg per ton of aluminium in older designs in 1974) of fluoride waste: perfluorocarbons and hydrogen fluoride as gases, and sodium and aluminium fluorides and unused cryolite as particulates. Unless carefully controlled, these fluorides tend to be very toxic to vegetation around the plants.

The Soderburgh process produces significant emissions of polycyclic aromatic hydrocarbons as pitch is baked to form the electrodes.

The linings of the pots end up contaminated with cyanide-forming materials; Alcoa has a process for converting spent linings into aluminium fluoride for reuse, synthetic sand usable for building purposes and inert waste.

Example aluminium smelters

* Alcan Lynemouth Aluminium Smelter, powered by the coal-fired Lynemouth Power Station in north-east England
* Anglesey Aluminium, powered by Wylfa nuclear power station in north-west Wales
* The Valco aluminium smelter in Ghana, powered by the Akosombo Dam hydro-electric dam
* Fjarðaál in Iceland, to be powered by the Kárahnjúkar dam
* Jharsuguda in Orissa, India, to be powered by its own 1215 MW coal-fired power station.
* Alcoa's Point Henry smelter near Geelong, Australia, powered by its own brown coal fueled power station and grid electricity.

ee also

*List of aluminium smelters

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