Sodium aluminate is an inorganic chemical that is used as an effective source of aluminium hydroxide for many industrial and technical applications. Pure sodium aluminate (anhydrous) is a white crystalline solid having a formula variously given as NaAlO<sub>2</sub>, NaAl(OH)<sub>4</sub> (hydrated), Na<sub>2</sub>O·Al<sub>2</sub>O<sub>3</sub>, or Na<sub>2</sub>Al<sub>2</sub>O<sub>4</sub>. Commercial sodium aluminate is available as a solution or a solid.
Other related compounds, sometimes called sodium aluminate, prepared by reaction of Na<sub>2</sub>O and Al<sub>2</sub>O<sub>3</sub> are Na<sub>5</sub>AlO<sub>4</sub> which contains discrete AlO<sub>4</sub><sup>5−</sup> anions, Na<sub>7</sub>Al<sub>3</sub>O<sub>8</sub> and Na<sub>17</sub>Al<sub>5</sub>O<sub>16</sub> which contain complex polymeric anions, and NaAl<sub>11</sub>O<sub>17</sub>, once mistakenly believed to be β-alumina, a phase of aluminium oxide.
Structure
Anhydrous sodium aluminate, NaAlO<sub>2</sub>, contains a three-dimensional framework of corner linked AlO<sub>4</sub> tetrahedra. The hydrated form NaAlO<sub>2</sub>·5/4H<sub>2</sub>O has layers of AlO<sub>4</sub> tetrahedra joined into rings and the layers are held together by sodium ions and water molecules that hydrogen bond to O atoms in the AlO<sub>4</sub> tetrahedra.
Uses
In water treatment it is used as an adjunct to water softening systems, as a coagulant aid to improve flocculation, and for removing dissolved silica and phosphates.
In construction technology, sodium aluminate is employed to accelerate the solidification of concrete, mainly when working during frost.
Sodium aluminate is also used in the paper industry, for fire brick production, alumina production and so forth.
Sodium aluminate solutions are intermediates in the production of zeolites.
References
See also
- Bayer process
- Bauxite