Aluminium is the most abundant metal in the Earth’s crust, occurring as bauxite which contains aluminium oxide. The first step in producing aluminium is mining this ore. Bauxite occurs mainly in tropical and sub-tropical areas, like Africa, the Caribbean, South America and Australia.
Australia is the largest producer of bauxite, with five large mines supplying around 30 per cent of global production.
Bauxite mining has five steps:
- preparation of the mining area;
- bauxite mining;
- ore transport; and
Preparation of Mining Area
Pre-Mining Surveys are conducted in all new mining areas, to provide information on flora and fauna, to map the extent of any disease, such as dieback, and to identify any significant cultural heritage sites. If rare or protected species or significant sites are present, they are avoided, or management plans are developed to minimise the impact of mining on them.
Scrapers and small excavators are used to remove the remaining overburden and expose the caprock. Depending on the depth of the caprock, it can be broken by blasting, or simply removed with scrapers and excavators.
The bauxite is then mined using excavators or loaders to load the bauxite onto haul trucks and transported to the crusher. Several pits are usually mined simultaneously in order to produce a consistent grade of ore.
A crusher is used to break the ore down to a smaller size suitable for transport. The crusher is made up of a number of components that include a vibrating screen, a jaw crusher and sizers. Fine material drops through the vibrating screen while larger material passes over the screen to the jaw crusher that breaks up the large rocks. The material that passes through the vibrating screen and jaw crusher is collected and passed through the sizer that further reduces the size of the material before it is transported via conveyor or ship to a refinery. The final size of the crushed bauxite ore is approximately 7.5cm or less in diameter.
The crushed bauxite is transported via conveyor belts and railway systems, either to the refinery or shipping terminal.
After mining, the edges of the pit are smoothed. Topsoil and overburden are returned to the site and the earth is prepared to prevent soil erosion and for seeding and planting. The logs and rocks that were put aside during clearing are then returned to provide shelter and nesting sites for animals.