Identity, Physical and Chemical Properties, Analytical Methods
A compendium is provided of aluminium compounds used in industrial settings, and as pharmaceuticals, food additives, cosmetics and as other household products. Most aluminium compounds are solids exhibiting high melting points. The solubility of aluminium salts is governed by pH, because the aluminium(III)-cation (Al3+) has a strong affinity for the hydroxide ion, which promotes precipitation. Like Mg2+ and Ca2+ ions, Al3+ in most situations seeks out complexing agents with oxygen-atom donor sites such as carboxylate and phosphate groups, including in biological systems. Aluminium oxides, hydroxides and oxyhydroxides occur in numerous crystallographic forms, which exhibit different surface properties. Few compounds of aluminium are classified in Annex 1 of the European Economic Union Council (EEC) Directive 67/1548, with aluminium powder and sodium aluminium fluoride (cryolite) as examples of exceptions, as well as compounds in which the anion renders them reactive such as aluminium phosphide. And finally, the more recent analytical methods available for the study of chemical speciation in solids and solution, and for quantitative analysis, have been applied to the determination of aluminium and the identification of its various forms.