Bauxite

Bauxite



Mixture of Iron and Aluminium Hydroxides/Oxides
Al, Fe, O, OH

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.




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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.

Formula
Al2O3 + SiO2 + TiO2 + Fe2O3

Typical Chemical Properties Available

Purities available from 98% (industrial grade) to 99.999% (high purity grade).

Typical Physical Properties Available

Physical properties vary widely according to the mine source. Granulations available include: 50 mm by down lumps, crushed coarse sizes (-3 mesh, -6 mesh, -8 mesh and -12 mesh) and ground powder sizes (-100 mesh, -200 mesh and -325 mesh).

Nominal Physical Constants:

Molecular Weight (g/mol.) -
Apparent Density (g/cm3) 3.08
Bulk Density (g/cm3) 3.1
Calcination Temperature(°C) 1650
Boiling Point (°C) -
Specific Surface Area (m2/g) -
Thermal Conductivity (cal/s-cm-°C) -
Mohs Hardness @20°C -
Specific Gravity 2.45- 3.25
Apparent Porosity (%) 8.4
L.O.I. (%) 0.1

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.

Bauxite mining
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.

Traditional uses of bauxite

Blast Furnaces
Iron/Steel Ladles
Torpedo Cars
Electric Arc furnaces
Tundishes
Soaking Pits
Reheat/Soaking Pits
Open Hearth
Cement
Aluminum
World Bauxite Mine Production, Reserves, and Reserve Base
(x1000 tonne)
Mine production Reserves Reserve base
2000 2001

Australia 53,800 53,500 3,800,000 7,400,000
Brazil 14,000 14,000 3,900,000 4,900,000
China 9,000 9,200 720,000 2,000,000
Guinea 15,000 15,000 7,400,000 8,600,000
Guyana 2,400 2,000 700,000 900,000
India 7,370 8,000 770,000 1,400,000
Jamaica 11,100 13,000 2,000,000 2,500,000
Russia 4,200 4,000 200,000 250,000
Suriname 3,610 4,000 580,000 600,000
United States NA NA 20,000 40,000
Venezuela 4,200 4,400 320,000 350,000
Other countries 10,800 10,200 4,100,000 4,700,000
World total (rounded) 135,000 137,000 24,000,000 34,000,000



The Major Producers
China
Today, exportable refractory-grade bauxite (essentially all diasporitic) is mined mainly from two provinces in China-Shanxi and Guizhou. Shanxi reportedly exports two-thirds of the total.

The Guizhou and Shanxi materials have similar characteristics, however, Guizhou has the disadvantage of higher TiO2 (3.7% typical vs. 4.2) and alkalies (0.2% typical vs. 0.6).

Although there have been unconfirmed reports of higher bulk densities in Guizhou, the two provinces are essentially the same in principle, with Shanxi possibly having the edge. In this case, chemistry is a minor influencing factor (lower alkali content, higher Al2O3 in Southern Shanxi), meaning bulk densities in China are primarily a function of the calcining equipment and process.

With residence time as a primary factor, their minimum control rudimentary shaft kilns are limited to maximum range BSGs (3.20-3.25). Rotary kilns can produce up to the 3.30 range and the Chinese round kilns can produce up to 3.35 by means of a special 18th century burning procedure.

It is estimated that 50% of Chinese refractory-grade bauxite is produced in updraft shaft kilns, with the remainder split between round and rotary.

The Chinese bauxite supply picture is complicated because there are ~300 bauxite mines in China, with the exported product rarely representing a single mine source. When ISO-9000 comes to refractory-grade bauxite in China, it will be with some difficulty.

The supply of Chinese refractory-grade bauxite has improved during the past 20 years-in part due to the installation of several controlled processing plants in Tianjin. However, the basic supply from the mine to the kiln to the port still involves considerable rudimentary control and consequent quality variations. This could improve significantly if experienced third parties get involved in the mining and calcining of the material.

Despite numerous complaints that the Chinese producers have been dumping, it does not appear to be probable. In any case, recent export and provincial taxes will now force the Chinese prices somewhat closer to world market levels. This will tend to promote a switch back to South American bauxites.

Refractory-grade bauxite also is used to produce brown-fused alumina, a significant product in China. Total current production there is reportedly in excess of 300,000 tpy.

Brazil
The MSL Minerais (CAEMI) operation is the new supplier on the block. Despite some apparent built-in disadvantages, it has managed to develop a niche market and justify the installation of a second rotary kiln in 1994. Thus, increasing total productive capacity to ~140,000 tpy.

Although the bauxite vein at CAEMI is only 1-3 m thick, the relatively 8-12 m thick overburden is within an acceptable proportion. Therefore, mining costs should be relatively low. The crude ore must be beneficiated, first by crushing (10 mm maximum) washing and screening, then with a heavy media process to remove iron. After calcining, the material goes through eight iron-removing magnetic separators. Despite the relatively high SiO2 content (approaching 10%), the beneficiation costs and relatively higher fuel costs for calcining, the finished product is priced lower than Guyana RASC, and has gained significant market share-particularly in Europe.

The higher SiO2 and lower alkalies in the MSL bauxite, together with a uniform fine kiln feed size, contributes to the higher level of mullite (and lower corundum) in the final product. TiO2 is a low 2.2%, tielite a low 0-2%.

Guyana
Bauxite was first identified in Guyana in the period 1897-1910. Although Alcoa Industrial Chemicals began alumina-grade bauxite production in Guyana in 1917, and Alcan took over in 1929, it was not until 1938 that refractory-grade bauxite was separately identified and produced. The typical processing of Guyanese bauxite is straightforward: Bauxite is crushed to -9 cm, washed and screened, crushed to -4 cm, rewashed, then rotary kiln calcined, with some final de-ironing before shipment.

Refractory-grade bauxite from Guyana presently falls into two separate geographic sourcings: the original Linmines' home of the traditional world standard RASC bauxite; and the Berbice/Bermine operation, the latter primarily a source of abrasive- and chemical-grade bauxite.

Reserves at Linmines are substantial. Ongoing improvements to operating practices and costs began five years ago, with the consequent gradual improvement to a global competitive marketing position.

A privatization program now in progress in Guyana should contribute to an improved bauxite product, availability and costs.