Боксит: Құрамы, өндірісі және экологиялық салдары

Sedimentary rock rich in aluminium
the ore

Bauxite ('/b//ɔː//k//s//aɪ//t/) is a sedimentary rock with a relatively high aluminium content. It is the world's main source of aluminium and gallium. Bauxite consists mostly of the aluminium minerals gibbsite (|Al(OH)3), boehmite (γ AlO(OH)) and diaspore (α AlO(OH)), mixed with the two iron oxides goethite (FeO(OH)) and haematite (|Fe2O3), the aluminium clay mineral kaolinite (|Al2Si2O5(OH)4) and small amounts of anatase (|TiO2) and ilmenite (|FeTiO3 or |FeO*TiO2). Bauxite appears dull in luster and is reddish brown, white, or tan. In 1821, the French geologist Pierre Berthier discovered bauxite near the village of Les Baux in Provence, southern France. Bauxite extraction and refining has numerous negative consequences to the environment and to people. The negative impacts are well documented and there are many examples from all over the world. These impacts include the destruction of the environment, water, and air soil pollution and soil degradation.

Australia is the largest producer of bauxite, followed by Guinea and China. Bauxite is usually strip mined because it is almost always found near the surface of the terrain, with little or no overburden. Increased aluminium recycling, which requires less electric power than producing aluminium from ores, may considerably extend the world's bauxite reserves.

as of 2010, approximately 70% to 80% of the world's dry bauxite production is processed first into alumina and then into aluminium by electrolysis. Bauxite rocks are typically classified according to their intended commercial application: metallurgical, abrasive, cement, chemical, and refractory. Bauxite ore is usually heated in a pressure vessel along with a sodium hydroxide solution at a temperature of At these temperatures, the aluminium is dissolved as sodium aluminate (the Bayer process). The aluminium compounds in the bauxite may be present as gibbsite(Al(OH)3), boehmite(AlOOH) or diaspore(AlOOH); the different forms of the aluminium component will dictate the extraction conditions. The undissolved waste, bauxite tailings, after the aluminium compounds are extracted contains iron oxides, silica, calcia, titania and some un reacted alumina. After separation of the residue by filtering, pure gibbsite is precipitated when the liquid is cooled, and then seeded with fine grained aluminium hydroxide. The gibbsite is usually converted into aluminium oxide, Al2O3, by heating in rotary kilns or fluid flash calciners to a temperature in excess of This aluminium oxide is dissolved at a temperature of about in molten cryolite. Next, this molten substance can yield metallic aluminium by passing an electric current through it in the process of electrolysis, which is called the Hall–Héroult process, named after its American and French discoverers. Prior to the invention of this process, and prior to the Deville process, aluminium ore was refined by heating ore along with elemental sodium or potassium in a vacuum. The method was complicated and consumed materials that were themselves expensive at that time. This made early elemental aluminium more expensive than gold.

As a bulk cargo, bauxite is a Group A cargo that may liquefy if excessively moist. Liquefaction and the free surface effect can cause the cargo to shift rapidly inside the hold and make the ship unstable, potentially sinking the ship. One vessel suspected to have been sunk in this way was the MS Bulk Jupiter in 2015. One method which can demonstrate this effect is the "can test", in which a sample of the material is placed in a cylindrical can and struck against a surface many times. If a moist slurry forms in the can, then there is a likelihood for the cargo to liquefy; although conversely, even if the sample remains dry it does not conclusively prove that it will remain that way, or that it is safe for loading.

Bauxite is the main source of the rare metal gallium. During the processing of bauxite to alumina in the Bayer process, gallium accumulates in the sodium hydroxide liquor. From this it can be extracted by a variety of methods. The most recent is the use of ion exchange resin. Achievable extraction efficiencies critically depend on the original concentration in the feed bauxite. At a typical feed concentration of 50 ppm, about 15 percent of the contained gallium is extractable. Bauxite is also a potential source for vanadium.

The social and environmental impacts of bauxite extraction are well documented. Most of the world's bauxite deposits can be found within 1 to 20 meters of the earths surface. Strip mining is the most common technique used for extracting shallow bauxite. It contains several elements such as sodium aluminoscilicate, calcium titanate, monohydrate aluminium, and trihydrate aluminium that do not break down in nature. When improperly stored, red mud can contaminate soil and water, which can result in local extinction of all life. Red mud was responsible for killing all life in the Marcal River in Hungary after a spill occurred in 2010. When red mud dries, it turns into dust that can cause lung disease, cancer and birth defects. Between 2015 and 2018, new bauxite mining operations in the Boké Region of Guinea have caused in 35 conflicts which include movements of revolts and road blockades. These conflicts have resulted in the loss of human life, the destruction of heavy machinery, and damage to government buildings. The forest reserve is one of the only two upland evergreen forests in Ghana, and makes up a significant portion of the remaining 20% of forested habitat left in Ghana. The Atewa range falls under the jurisdiction of Akyem Abuakwa Traditional Area and is overseen by the king known as Okyenhene. These tribal lands are densely populated and home to over 100 million Indigenous Indian peoples. The mountain summits located on these lands act as a source of water and greatly contribute to the regions fertility. The Indian bauxite industry is interested in developing this land for aluminum production, which poses great risk to the terrestrial and aquatic ecosystems. Historically, the Indigenous peoples living on these lands have shown resistance to development, and oppose any new bauxite mining projects in the area. This has led to violent conflicts between Indigenous communities and police. On December 16, 2000, police killed three Indigenous protestors and wounded over a dozen more during a protest over a bauxite project in the Kashipur region.