Bauxite of Metallic Minerals
Bauxite
Bauxite is the most common ore of aluminium. Extraction of aluminium metal takes place in three main stages: mining of bauxite ore, refining the ore to recover alumina, and smelting alumina to produce aluminium. Other raw materials are mined as aluminium ore, but their use is minor compared with bauxite.
Typically between two and three tonnes of bauxite must be refined to produce one tonne of alumina.
Waste from the refining process, so called “red mud”, is stored in large dams designed to prevent leakage of, and environmental damage from, the still highly caustic contents.
Typical Bauxite Mining Process
- Vegetation is cleared and top soil is removed and set aside for rehabilitation
- Scrapers and excavators are used to remove the remaining overburden and expose the cap rock. Depending on the depth of the cap rock, it can be broken by blasting, or simply removed with scrapers and excavators
- The bauxite is then mined using excavators or loaders. Off road haul trucks transported the bauxite to the crusher. Several pits are usually mined simultaneously in order to supply the refinery with a consistent grade of ore.
- The mined out area is backfilled with the removed over burden, the set aside top soil is redeposited, then re vegetated with plants indigenous to the area.
Schematic of a typical mining process for lateritic bauxites
Bauxite comminution, beneficiation and transport
Comminution
- Crushing and grinding are used to break the ore down to a smaller size suitable for transport and or beneficiation.
Beneficiation
- Most bauxites considered economic require minimal or no beneficiation.
- Beneficiation of lateritic materials may involve dry screening to remove fine particles with higher silica contents, or simple washing to remove adherent clay minerals. More sophisticated beneficiation involving dense media separation and spirals has been practiced in Brazil.
- Froth flotation for silica removal is practiced in at least one refinery in China.
Transport
- Bauxite is transported by any number of means including off and on road trucks, rail, conveyor systems, ships and even as piped slurries.
Typical mining and transport equipment
The Haul trucks emptying run of mine (ROM) bauxite into crushers for the initial stages of comminution
Crushed bauxite transport via a covered conveyor