Processing

1.1 Raw Materials

Bauxite is the name of the ore that is the primary source of alumina; bauxite contains gibbsite, y-Al(OH)3, which is the stable phase of Al(OH)3 at ambient temperature and pressure. The structure of alumina and hydrated alumina phases are listed in Table 2.

Lattice Parameters, angle (A)

Designation

Structure

a

b

c

Corundum

Hexagonal

4.758

12.991

(rhombohedral)

Eta

Cubic (spinel)

7.90

Gamma

Tetragonal

7.95

7.79

Delta

Tetragonal

7.97

23.47

Theta

Monoclinic

5.63

2.95

11.86 103° 42′

Kappa

Orthorhombic

8.49

12.73

13.39

Bauxite from the Guianas in South America is low in iron and silica impurities, so it is preferred when purity is important. Other important sources of bauxite are in Brazil, the southern United States, Southeast Asia, West Africa, and India.