Al3Kation

Al3Kation typically refers to the aluminium(III) cation, Al3+, the trivalent positively charged ion derived from aluminum. In aqueous environments the Al3+ ion is widely encountered in solution and as a constituent of many aluminum salts and minerals. In water, aluminium is strongly hydrated, forming the hexaaquaaluminium ion [Al(H2O)6]3+ as a common aquated form.

Properties of the Al3+ cation include a high charge density due to its +3 charge and small ionic radius. This leads to strong interactions with water and other donor ligands, making Al3+ a common Lewis acid. In solution, Al3+ readily undergoes hydrolysis, producing various hydroxy species as pH changes. At low to moderate pH, species such as [Al(H2O)6]3+ and [Al(H2O)5(OH)]2+ dominate, while around pH 4–6 aluminum hydroxide precipitates as Al(OH)3. In basic conditions, soluble species like Al(OH)4− can form.

Coordination chemistry of Al3+ is typically octahedral, with six ligands coordinating to the metal center. It forms complexes with a wide range of ligands, including water, hydroxide, fluoride, sulfate, phosphate, and organic chelators such as citrate. The ion’s role as a strong Lewis acid explains its use in various industrial processes and its behavior in environmental systems.

Occurrence and applications: Al3+ occurs in bauxite-derived materials and is released during dissolution of aluminum compounds. It is widely used in water treatment as a coagulant (for example, aluminum sulfate and polyaluminum species) and in papermaking and other chemical processes. Environmental and health considerations relate to its toxicity at elevated concentrations in aquatic systems and to limited absorption in humans.

Safety: Inappropriate concentrations of Al3+ can be harmful to aquatic ecosystems; human exposure is usually limited by low intestinal absorption, though chronic exposure and high levels are subject to regulatory controls.