What makes bauxite brown

There are several minerals available in the world from which aluminium can be obtained, but the most common raw material is bauxite. Bauxite is a mineral made up primarily of aluminium oxide mixed with some other minerals. Bauxite supplies Confirmed global bauxite supplies are estimated at At the current level of extraction, this should last for more than a hundred years. There is a lot of variation in bauxites. Structurally they can be solid and dense or crumbly. The usual colour is brick red, flaming red or brown because of iron oxide.

If iron content is low, bauxite can be grey or white. But yellow, dark green and even multi-coloured bauxites with bluish, purple, red and black strains occur too. Guinea has the largest supply of bauxites, 5. They're also found very near to the surface, which makes mining them very easy.

The world's largest bauxite producers, The most common way to mine for bauxites is by using open pit mines. Special equipment is used to cut one layer after another off the surface, with the rock then being transported elsewhere for further processing. However, there are places where aluminium ore has to be mined from deep underground which require underground mines to be built to get at it.

One of the deepest mines is the Cheremkhovskaya-Deep mine in the Urals in Russia, its shafts run metres deep. Alumina Production. The next stage in the production chain is the processing of bauxite into alumina, or aluminium oxide - Al 2 O 3 , - a white powder.

The most common process for making alumina from bauxite is the Bayer process, which was first discovered over years ago but is still in wide use today. It's very efficient but it can only be used on high quality bauxite with fairly low content of admixtures, especially silicon. The principle of the Bayer process is as follows: the crystallised aluminium hydrate found in bauxite easily dissolves in concentrated caustic soda NaOH at high temperatures and when the temperature is lowered and the concentration of the solution increases again, aluminium hydrate crystallises but the other elements contained in the bauxite the so called ballast either don't dissolve or recrystallise and settle to the bottom well before aluminium hydrate crystallises.

This means that after aluminium hydrate gets dissolved in caustic soda the ballast can be easily isolated and removed. This ballast is known as red mud. Red Mud Red mud is a thick red-brown paste consisting of silicon, iron, titanium and other compounds.

It's disposed of in special isolated areas, called mud disposal areas. Mud disposal areas are designed to prevent the seepage of alkali contained in the mud into ground water. Once a mud disposal area has been filled up, the territory can be reclaimed by burying it in sand, ash or dirt and planting certain types of trees and plants there. While full reclamation can take years, in the end the territory will return to its original state.

Many experts don't regard red mud as a waste because it can be used as a raw material. For example, scandium can be made from it and then used in aluminium scandium alloys. Scandium makes aluminium alloys extra strong and such alloys can be used in motor vehicles, rockets, sports equipment and in the production of electric wires.

Red mud can also be used in the production of cast iron, concrete and rare earth metals. Large aluminium hydrate particles can be filtered out from the solution with relative ease. They're then washed with water, dried and calcined: i. The bauxite is purified to yield a white powder, aluminium oxide, from which aluminium can be extracted. Known formally as bauxite residue, red mud is the noxious by-product of the Bayer process for extracting aluminum from bauxite ore.

Aluminum mining leaves behind a staggering million metric tons per year of the salty, highly alkaline, heavy-metal-laden material, according to the International Aluminium Institute , a London-based trade organization. The aluminum industry has long tried to find ways to recycle the environmentally problematic red mud. But so far there have been few safe and economical large-scale applications.

In the Bayer process, strip-mined bauxite is treated with hot caustic soda sodium hydroxide , which selectively dissolves aluminum from an array of other mineralized metals.

Bauxite forms when silica in aluminum-bearing rocks that is, rocks with a high content of the mineral feldspar is washed away leached. This weathering process occurs in tropical and subtropical weathering climates. This means that many countries with current tropical climates, or that were once tropical, have the largest reserves of bauxite ore, such as Brazil, Jamaica, Guinea, and Australia.

Alternative sources of aluminum might someday include kaolin clay, oil shales, the mineral anorthosite, and even coal waste. However, as long as bauxite reserves remain plentiful and production costs are low, the technologies to process these alternative sources into alumina or metallic aluminum will likely not progress beyond the experimental stage.

In open pit operations, bauxite is normally extracted from strata typically 4—6 m thick under overburden that may range up to 10 m thick, covered by a thin layer of topsoil with its associated vegetation. At some nonmetallurgical mining sites, the overburden thickness may reach 70 m or more.

Open pit bauxite mining operations may use backhoes, bucket wheel excavators, bulldozers, draglines, power shovels and scrapers for the stripping of overburden from the ore. When fracturing occurs, water and suspended particles known as "proppants" rush into the fractures and push them open. When the pumps are turned off, the fractures close, trapping the proppant particles in the reservoir.

If an adequate number of crush-resistant particles remain in the reservoir, the fractures will be "propped" open, allowing for a flow of oil or natural gas out of the rocks and into the well. This process is known as hydraulic fracturing. Powdered bauxite can be fused into tiny beads at very high temperatures. These beads have a very high crush resistance, and that makes them suitable as a proppant.

They can be produced in almost any size and in a range of specific gravity. The specific gravity of the beads and their size can be matched to the viscosity of the hydraulic fracturing fluid and to the size of fractures that are expected to develop in the rock.

Manufactured proppants provide a wide selection of grain size and specific gravity compared to a natural proppant known as frac sand. World bauxite resources are adequate for decades of production at current rates. Other materials could be used instead of bauxite for alumina production. Clay minerals, alunite, anorthosite, power plant ash, and oil shale could be used to produce alumina but at higher costs, using different processes.

Silicon carbide and synthetic corundum are sometimes used in place of bauxite-based abrasives. Synthetic mullite and magnesium oxide made from magnesite are sometimes used in place of bauxite-based refractories. Bauxite is found in abundance at many locations around the world. Each of these countries has enough reserves for many years of continued production. Some have reserves for over years of production.

Home » Minerals » Bauxite Bauxite Almost all of the aluminum that has ever been produced has been made from bauxite Article by: Hobart M. Physical Properties of Bauxite Color White, gray, sometimes stained yellow, orange, red, pink, or brown by iron or included iron minerals Streak Usually white, but iron stain can discolor Luster Dull, earthy Diaphaneity Opaque Cleavage None Mohs Hardness 1 to 3 Specific Gravity 2 to 2.

Often exhibits pisolitic habit.