From alumina to metal using the Hall-Héroult method

The molten electrolysis method of producing aluminium was discovered in the mid 1880s, marking the beginning of the aluminium age in the industrial world.
The full name of the method is the Hall-Héroult method, after its discoverers, and it is still used today.
The principle of operation involves melting alumina in molten cryolite at a temperature of about 965 °C, and then using electric current to reduce it to the metal. The pot consists of a cathode in the form of a carbon-lined iron shell and a carbon anode. The process works as follows:

1. Alumina is tipped into the pot and dissolved in the molten cryolite.
2. A heavy direct current is passed through the bath. The voltage and the electrical energy input are controlled by increasing or decreasing the separation between the anode and cathode.
3. The alumina is broken down into molten aluminium and oxygen. The metal falls to the bottom of the furnace, while the oxygen rises and reacts with the carbon anode to carbon dioxide.

Once a day, the molten metal is tapped off. In the Sundsvall No. 1 smelter, which is one of the most modern and efficient primary smelters in the world, each pot (56) produces about 1150 kg of metal per day. In the No. 2 smelter, each pot (262) produces about 800 kg/day. The pots in No. 1 smelter have 16 prebaked anodes. The anodes are progressively consumed in the process and are replaced at regular intervals.

All pots in the plant have their own computers which monitor and control the process. The Söderberg pots in No.2 smelter use one paste anode instead of prebaked anodes. The anode material, which is produced in the on-site anode plant, consists of petroleum coke and pitch.
As the anode is consumed, new briquettes are applied to the top. The heat melts the blocks and carbonises them to produce a solid anode.

Alumina + electricity + coke and pitch products = Aluminium

1.9 kg of alumina + 13.3 kWh of electrical energy (equivalent to the energy in 19 car batteries) + 330 g of petroleum coke + 70 g of pitch constitute the recipe for 1 kg of primary aluminium, using the most modern technology.

Next to alumina, electrical energy is the most important raw material to produce aluminium. It cannot be replaced by anything else, so Kubal is totally dependent on reliable supplies of electricity. It was the availability of electrical energy that originally determined siting of the smelter in Sundsvall: adequate supplies of cheap electrical energy were available from hydro power.

In recent years, Kubal has made substantial investments in order to reduce its use of electricity. Today, the company uses approximately the same quantity of electrical energy as a large pulp or paper mill. Development aimed at reducing the energy input per tonne of aluminium never stops.

Despite the relatively high energy input for primary production, aluminium can nevertheless be regarded as a low-energy material. This is due to the major energy savings resulting from use of the material. The energy input is reduced dramatically when aluminium is recycled and remitted. Secondary production of aluminium requires only about 5 per cent of the electrical energy needed for primary production.

Swedish aluminium from equatorial bauxite

Aluminium has a metallic ring, but is essentially a natural product.
About 8 per cent of the earth´s crust consists of aluminium. Metallic aluminium is produced from the raw material, bauxite. As Sweden has no bauxite deposits, the alumina that is produced from it must be imported from bauxite mining countries around the equator. Most of the alumina that Kubal uses comes from Spain, Ireland and Jamaica. In Spain and Ireland, bauxite from Africa is used to produce alumina.

Today, bauxite mining and alumina manufacture are carried out in such a way as to minimise their environmental impacts.

The processes are controlled by legislation in the respective countries. One of the effects of this is that mining areas are reinstated to bring back both their animal and plant life.