General Knowledge of Bauxite

The earliest discovered bauxite

We usually refer to the industrially usable ore with gibbsite, boehmite or diaspore as the main minerals as bauxite, which has been discovered as far back as 1821. It was first mined in France in 1873. The production of alumina from bauxite began in 1894, using the Bayer process.

Aluminum industry chain

The aluminum industry chain is mainly composed of four links: bauxite mining, alumina refining, primary aluminum production and aluminum processing. The first is bauxite mining, and then through the processes of dissolving, filtering, acidizing and burning bauxite to extract alumina, and then preparing electrolytic aluminum by electrolytic melting. 

Electrolytic aluminum can be further processed into various aluminum materials, aluminum alloys and aluminum powder after remelting and purification.

The aluminum industry chain continues to extend in the process of technological upgrading, from the initial simple casting, rolling and extrusion to the field of precision processing, and continues to expand the field of aluminum applications. It is currently widely used in emerging fields such as high-speed rail, urban rail, solar panels, electric vehicles, nuclear power, etc. .

The highest-tech aluminum deep processing is high-voltage electronic aluminum foil and brazing foil used in electronic equipment, automobiles and aerospace.

Application of bauxite

It is mainly applied to both metal and non-metal. More than 90% of the world's total bauxite output is used in metal aluminum; non-metal uses are relatively rare.

It is mainly used as raw material for refractory materials, abrasive materials, chemicals and high-alumina cement. It is also used in papermaking, water purification, ceramics, oil refining, pharmaceuticals, dyes, rubber and glass manufacturing.

Bauxite has various uses:

(1) Aluminum smelting industry. Used in national defense, aviation, automobiles, electrical appliances, chemicals, daily necessities, etc.

(2) Precision casting. The bauxite clinker is processed into fine powder to form a mold and then precision cast. Used in military industry, aerospace, communications, instrumentation, machinery and medical equipment departments.

(3) Used in refractory products. High bauxite clinker has a refractoriness of up to 1780°C, strong chemical stability and good physical properties.

(4) Aluminum silicate refractory fiber. It has the advantages of light weight, high temperature resistance, good thermal stability, low thermal conductivity, small heat capacity and mechanical vibration resistance. Used in various industries such as steel, non-ferrous metallurgy, electronics, petroleum, chemical industry, aerospace, atomic energy, and national defense.

(5) Using magnesia and bauxite clinker as raw materials, adding appropriate binders, the effect is very good for castables.

(6) Manufacturing alumina cement, abrasive materials, various compounds that can be made of aluminum in the ceramic industry and the chemical industry.

Among the most important uses are: extraction of metallic aluminum in the aluminum industry, as refractory materials and abrasive materials, and as raw materials for high-alumina cement.

More than 85% of bauxite mined globally is used to produce alumina, which in turn produces metallic aluminum. 10% is used to produce alumina for non-metallic use, and the remainder is used for non-smelting bauxite applications.

Material elements in bauxite

In practical applications, the index for evaluating the quality of bauxite is mainly the content of available alumina and reactive silica for gibbsite.

Effective alumina refers to the alumina that can be dissolved from the ore into the solution under certain dissolution conditions.

Active silicon oxide refers to silicon oxide that can react with alkali during the production process to cause the loss of aluminum oxide and sodium oxide.

Because these two oxides can exist in ore with a variety of mineral forms, some minerals can react with alkaline solutions under certain dissolution conditions, and some cannot.

Diaspore cannot dissolve under the conditions of trihydrate dissolution and cannot be included in the effective aluminum.

Silicon in the form of quartz is inert silicon that cannot react with alkali under this condition, and is not counted as active silicon oxide.

However, under the conditions of monohydrate ore dissolution, the aluminum oxide in the ore can be regarded as all effective, and the silicon can be regarded as all active.

Iron oxide has little effect on production under the Bayer process, just only increases the amount of red mud;

However, part of the iron minerals in laterite-type sanhydrate bauxite and boehmite exist in the form of goethite and aluminum goethite, which has an adverse effect on the dissolution rate, red mud sedimentation performance and alkali loss. .

Other harmful impurities in the ore such as sulfur, carbonate and organic matter, the lower the content, the better.

Judge the quality of bauxite

To measure the quality of bauxite, the following points should generally be considered:

(1) The aluminum to silicon ratio of bauxite. The ratio of aluminum to silicon refers to the mass ratio of the content of aluminum oxide in the ore to the content of silicon dioxide. It is generally expressed by A/S. The higher the ratio of aluminum to silicon, the better.

(2) The content of aluminum oxide. The higher the content, the more beneficial the production.

(3) The mineral type of bauxite has a great influence on the dissolution performance of alumina. The alumina in gibbsite-type bauxite is most easily dissolved out by caustic alkali solution, followed by boehmite, and diaspore is the most difficult.

China's bauxite reserves

China's bauxite reserves are about 1 billion tons, ranking fifth in the world, behind Guinea, Australia, Vietnam, Brazil and other countries. The resources are relatively concentrated in the four provinces (regions) of Shanxi, Henan, Guizhou and Guangxi. As of the end of 2015, China had a total of 553 bauxite mining areas, with identified resource reserves (ore volume) of 4.706 billion tons, of which Shanxi accounted for 32.4% of the country, Henan accounted for 22.7%, Guangxi accounted for 18.5%, and Guizhou accounted for 17.8% , The four provinces (regions) together account for 91.4% of China.