Alumiinaates

Alumiinates are a class of chemical compounds containing aluminum in which the aluminum atom is bonded to oxygen atoms. In ionic compounds, these are typically salts containing the aluminate anion. The most common and simplest aluminate anion is the tetrahedral [Al(OH)4]− ion, also known as tetrahydroxoaluminate. This anion is found in minerals like tobermorite and in alkaline solutions of aluminum salts. In more complex structures, aluminum can also form octahedral [Al(OH)6]3− anions or other polyanionic species.

Alumiinates are formed when aluminum compounds react with bases, particularly in aqueous solutions. For example, aluminum oxide (alumina) dissolves in strong bases like sodium hydroxide to form sodium aluminate, which contains the aluminate anion. This reaction is significant in the Bayer process for refining bauxite ore into alumina, the precursor to aluminum metal. The solubility of alumina in alkaline solutions is a key step in separating it from impurities.

Beyond simple hydroxoaluminates, there are also oxyaluminates where aluminum is bonded to oxygen atoms in various structural arrangements. These are often found in ceramic materials and glasses. For instance, calcium aluminate, with the formula CaAl2O4, is an important component of cement. These compounds exhibit a wide range of properties depending on their composition and structure, finding applications in refractories, catalysts, and as additives in various industrial processes. The term "aluminate" can also sometimes refer to organoaluminum compounds where aluminum is bonded to carbon atoms, though this usage is less common and often specified as organoaluminates.