What are poly-aluminium chlorides?
In solutions of poly-aluminium chloride (PAC), aluminium ions have formed into polymers consisting of clusters of ions bridged by oxygen atoms. These polymers only form in solutions of aluminium salts that have been partially neutralised by reaction with a base. As a general rule, the degree of polymerisation increases with the extent of neutralisation. Neutralisation confers basic properties on the solution, and hence the term “basic aluminium chlorides”. Full neutralisation of an aluminium salt results ultimately in precipitation of aluminium hydroxide, with the general formula Al(OH)3, or Al2(OH)6. The simplified formula for Hardman Alchlor®-AC, which is Al2(OH)5Cl, suggests that the solution is 5/6 neutralised, or 5/6 basic, compared to aluminium hydroxide. Unlike aluminium hydroxide however it forms a stable solution in water. As it is highly basic, it is also highly polymerised.
