Boehmite

BOEHMITE (from the name of the German scientist of the 20-th century J. Boehm, J. Bohm * EN: boehmite; DE: Bohmit; FR: boehmite; ES: boehmita; RU: бёмит) is the mineral of the sub-class of hydroxides, g-AlO(OH), one of the main constituent parts of bauxites. It often contains the Fe3+, Ga3+, Sc3+, and other impurities. In terms of composition, it is identical to the diaspore mineral. It crystallizes into the rhombic crystal systems; it is isostructural with the lepidocrocite mineral. The crystal structure is layered, there is within its base the alternation of the packs, which are consisting of the two oxygen (internal) and two hydroxyl (external) layers, with the atoms of aluminium within the voids.

It may be found in the form of the crypto-crystalline, oolitic, earthy, with porcelain appearance, sometimes finely scaled aggregates; small crystals are rare. It is colourless or white; it is often coloured by the mechanical impurities into the yellowish, pinkish, greenish colours. It is transparent, or translucent. It is brittle. The hardness is 3.5-4. The density is approximately 3100 kilograms per cubic metre.

Boehmite is mainly sedimentary mineral, it forms itself also within the crusts of weathering. Together with the diaspore mineral, boehmite forms bauxites, which are developing themselves on the carbonatic rocks, and with the gibbsite mineral, it forms bauxites on the major siliceous rocks. As the major component of bauxites, boehmite is used for the obtainment of alumina. The beneficiation includes the gravity (jigging, and concentration on the tables) and magnetic (polygradient separation) methods, the flotation by the fatty acids with the addition of hydrocarbons, and the chemical beneficiation (roasting with subsequent leaching).