Aluminates are compounds containing an oxyanion of aluminum. Since aluminum lives at the border between metallic and non-metallic elements on the periodic table, compounds of aluminum often have unique properties. Aluminum oxide is amphoteric and dissolves in both bases and acids. When dissolved in bases it forms the aluminate ion. Minerals like chrysoberyl are sometimes called aluminates, although they are usually classified as mixed oxides. As minerals, aluminates are much less common than aluminosilicates.
Sodium aluminate finds applications in a number of settings, including in water treatment and in the papermaking industry. However, the majority of sodium aluminate produced is used for the manufacture of sodium aluminosilicates or titanium dioxide for use in pigments and coatings, a process which improves the pigment's resistance to ultraviolet light. 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 used in the paper industry for fire brick production and alumina production.
Potassium aluminate can replace sodium aluminate for applications with Sodium sensitivity. Potassium aluminate is a basic coagulant as a result its use in acidic wastewaters lowers the cost of the treatment compared to the use of other coagulants. Potassium aluminate is also used as a dyeing and printing mordant and as an accelerant in the setting of concrete.
Calcium aluminates are used in the manufacture of refractories and cements. Due to its relatively high cost calcium aluminate is used in cements only under specific circumstances: when rapid strength development is required at low temperatures, when high chemical resistance is necessary, when refractory concretes need to maintain strength at high temperatures, or when as a component in blended cement require ultra-rapid strength development and controlled expansion.