Aluminium Production Process

Bauxite ore is converted to alumina, then an electrolysis process converts alumina into metal in a carbon-lined container. Rows of these "pots" connected in series form a "potline" which can be more than a kilometre long.

In 1886, Charles Hall of the USA and Paul L.T. Heroult of France discovered that molten cryolite (a sodium aluminium fluoride mineral) could be used to dissolve alumina and that the resulting chemical reaction would produce metallic aluminium. They found that by passing an electrical current through the cryolite/alumina mixture they could bring about the chemical reaction that converts the alumina to metallic aluminium. The Hall-Heroult process, as it is now known, remains in use today.

Production of primary aluminium metal using the Hall-Heroult process involves electrolytic reduction of alumina in cells or pots. The electrolyte is made up of molten cryolite and other additives and is contained in a carbon and refractory lining inside a steel potshell. 

The cathode for the electrolytic process is a carbon lining made up of pre-formed carbon cathode blocks. Other carbon materials line the sides of the pot and refractory materials generally sit between the carbon cathode and the steel potshell. Over the typical three to ten year life of a pot, materials such as alumina, molten aluminium, calcium, fluorides and sodium infiltrate the cathode lining and cause it to deteriorate. After a defined period, or when indicators determine that the lining is at risk, the lining material is replaced and what is removed from the pot is called Spent Potlining or SPL. Regain recovers and processes the Spent Potlining. 

The anode for the electrolytic process is a large carbon block held by a metal frame and suspended in the molten cryolite/alumina mixture to conduct the current. Most of the anode is consumed in the production process. At the end of its service, the remaining carbon anode "butt" is removed and cleaned of residues and a large proportion of the butt is recycled to make new carbon anode blocks. Some of the anode carbon and cleaning residues are however not re-usable. Regain recovers and processes this otherwise unusable anode carbon. 

Below are links to further information about aluminium production. Please note that the content and performance of these external links is not guaranteed by Regain to be accurate or consistent.

Overview of Reduction Process (world-aluminium.org)

Recent technical advances in aluminium smelting (Journal of Metals (JOM))