Aluminato

Aluminato, commonly referred to as aluminates, denotes a class of compounds containing aluminum coordinated to oxygen in a highly oxidized state. In inorganic chemistry, aluminates include salts of aluminic acid and hydroxo-aluminate species formed when aluminum(III) ions are in basic solution. The most familiar examples are sodium aluminate (NaAlO2) and potassium aluminate (KAlO2), which in water exist predominantly as hydroxo-aluminate species such as [Al(OH)4]− or related complexes depending on the pH.

Production and composition: Sodium and potassium aluminates are typically prepared by reacting aluminum hydroxide or alumina with concentrated sodium or potassium hydroxide at elevated temperature, yielding soluble aluminate ions. In aqueous environments, aluminate speciation is strongly influenced by pH; at high pH, tetrahydroxoaluminate species are common, while lower pH levels lead to different hydroxo complexes and, eventually, precipitation of aluminum hydroxide under certain conditions.

Applications: Aluminates are used in water treatment as coagulants and clarification aids, by providing reactive aluminum species that destabilize colloidal contaminants. They also serve as precursors for cementitious materials and refractories, notably certain calcium aluminate phases used for high-temperature resistance. In chemistry and catalysis, aluminates and organo-aluminate species function as catalysts or catalyst supports in various reactions, and specialized organometallic aluminates are employed as initiators or stabilizers in polymer chemistry and epoxy systems.

Speciation and properties: The chemistry of aluminates is pH-dependent and often involves equilibria among [Al(OH)4]− and related hydroxo complexes, with potential formation of solid aluminum hydroxide or oxide phases under changing conditions. Aluminate compounds are typically basic and require appropriate handling due to their caustic nature.

Safety and handling: Aluminates are alkaline materials; appropriate protective equipment and handling procedures are advised to minimize skin and eye irritation. See also: aluminates, calcium aluminate cement, sodium aluminate.