Know More About Aluminium

Aluminium is mainly produced from bauxite.Bauxite consist of 40-60% alumina, as well as earth silicon, ferrous oxide, and titanium dioxide. To separate pure alumina, the Bayer process is applied. First, the ore is heated in an autoclave with caustic soda. It is then cooled and a solid residue — «red mud» — is separated from the liquid. Aluminium hydroxide is then extracted from this solution and calcined to produce pure alumina.

Rare and expensive a century ago, aluminium has since been identified as the mostcommon metal on earth, forming about eight percent of the earth's crust. It is the third most plentiful element known to man. Only oxygen and silicon (sand) exist in greater quantities.

Cryolite is a white translucent, sodium aluminium fluoride material component found in its natural state only in Greenland . Most of the cryolite used in aluminium production today is synthetically produced. Held at 1030°C, the molten cryolite dissolves up to 20% of alumina readily. The electrolytic cell holding the molten cryolite is a tank lined with carbon which serves as one electrode. Large carbon blocks inserted from the top of the bath act as the anode, or other electrode, and a heavy electrical current is passed between these two sets of electrodes through the solution. This current breaks down the alumina into aluminium and oxygen. The molten metallic aluminium collects at the bottom of the cell and is drained off every few days as sufficient metal accumulates. The oxygen combineswith the carbon at the anodes and is given off as carbon dioxide gas. This became the first industrially applied method of making the metal aluminium from alumina, and is the one still in use today.

The immediate effect of the discovery of this process was to send the price of aluminium tumbling from $18 to $4.50 per kg, the first step in a downward course which has today established the selling price in terms of under two dollars per kg. But the discoveries bringing about low-cost production did not lead directly to the widespread use of aluminium. Alumina is produced in a totally separate first stage process from Bauxite ore. This (Bayer) chemical process starts by immersing crushed bauxite into a caustic soda solution which dissolves the alumina to form sodium aluminate liquor. After filtering, the impurities are left behind as a "red mud" and the liquid is treated to precipitate the aluminium content out of the solution which is now in the form of aluminium hydroxide. This material is then separated from the liquor and changed to alumina, which resembles course granulated sugar, by heating in kilns at 1000°C.

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