Bauxite does not require complex processing because most of the bauxite mined is of an acceptable grade or can be improved by a relatively simple and inexpensive process of removing clay.
The History Says
The first aluminum made in the US. was mined in Bartow and Floyd counties by the present Aluminum Company of America. A local man, Mr. Gibbons, operated these mines and also deposits in Arkansas, where the town near the deposits was named for him. He became a top official of Alcoa. The American Cyanamid Company mined bauxite to make alum. Large foreign deposits caused local mining to cease.
The Present Scenario
Exporting bauxite mines generated about US$1.4m in revenue per hectare mined in 1998 and a typical mine employed about 200 people for each million tonnes/year of bauxite produced or about 11 people per hectare.
BAUXITE is a naturally occurring, heterogeneous material composed primarily of one or more aluminum hydroxide minerals, plus various mixtures of silica, iron oxide, titania, aluminosilicate, and other impurities in minor or trace amounts. The principal aluminum hydroxide minerals found in varying proportions with bauxites are gibbsite and the polymorphs boehmite and diaspore.
Bauxites are typically classified according to their intended commercial application: abrasive, cement, chemical, metallurgical, refractory, etc. The bulk of world bauxite production (approximately 85%) is used as feed for the manufacture of alumina via a wet chemical caustic leach method commonly known as the Bayer process. Subsequently, the majority of the resulting alumina produced from this refining process is in turn employed as the feedstock for the production of aluminum metal by the electrolytic reduction of alumina in a molten bath of natural or synthetic cryolite (Na3AlF6), the Hall-Héroult process.
Bauxite Mining in Forest Areas
The conservation of rain forests is a key concern often voiced with regard to bauxite mining. Only about 6 % of the world’s bauxite mining is today conducted in rain forest regions, affecting a total area of around 1.5 km2 per year. The total area of the globe currently covered by rain forest is about 18 million km2. The original flora and fauna of much of the land involved in bauxite mining is restored once mining operations have ceased.
For all forest areas used for bauxite mining, 80% is returned to native forests, the rest is replaced by agriculture, commercial forest, or recreational area, thereby making the area more productive for the local community. As far as rain forests in particular are concerned, however, the area used for bauxite mining in rain forests is almost totally reverted back to rain forest.
There are numerous bauxite deposits, mainly in the tropical and subtropical regions, but also in Europe. Bauxite is generally extracted by open cast mining from strata, typically some 4-6 metres thick under a shallow covering of topsoil and vegetation. In most cases the topsoil is removed and stored.
Exporting bauxite mines generated about US$1.4m in revenue per hectare mined in 1998 and a typical mine employed about 200 people for each million tonnes/year of bauxite produced or about 11 people per hectare. Usually mines offer relatively well-paid jobs and mining companies tend to provide assistance to their neighbouring communities.
There are attractive commercial and social reasons for the development of a bauxite mine. The mining company wants the ore to use or sell while the local inhabitants want the mine for employment and for the community assistance that the mining company usually offers. National governments want the development for these social reasons and also for the revenue provided by a mining company.
These social benefits are complemented, according to the International Aluminium Institute’s latest “Bauxite Mine Rehabilitation Survey”, by the mining companies’ increasing awareness of environmental factors. Mined areas are being restored to an environmentally stable condition: 92.7% of surveyed operations have formal, written rehabilitation procedures in place. A total of 282km2 (28,245 ha) of land has been rehabilitated to date at 22 operations.
Our survey shows that increasingly mining companies are concerned about environmental matters. Bauxite mining is accompanied by land rehabilitation and environmental control to restore the area to a desirable environmentally friendly condition. It is possible for everyone to gain from mining activities.
Bauxite mining method
Eighty percent of world bauxite production, mainly from large blanket type deposits is from surface mines, with the rest, mainly from Southern Europe and Hungary, from underground excavations. On some surface deposits there is no overburden, and on others, the bauxite may be covered by 70 metres or more of rock and clay. Deposits that are hardened may require blasting in order to release the ore.
Once the bauxite is loosened into manageable pieces it is generally loaded into trucks or railroad cars and transported to crushing or washing plants or to stockpiles. Underground bauxite mines are used to exploit pockets or beds of deposit between layers of carbonic rock. Water in flow is a problem in most underground operations and dewatering shafts are often drilled before mining begins.
Unlike the base metal ores, bauxite does not require complex processing because most of the bauxite mined is of an acceptable grade or can be improved by a relatively simple and inexpensive process of removing clay. In many bauxites, clay is removed by some combination of washing, wet screening and cycloning, even by hand picking or sorting.