Aluminium chlorohydrate is a group of salts having the general formula AlnCl(3n-m)(OH)m. It is used in deodorants and antiperspirants and as a flocculant in water purification.
In water purification, where it is usually called polyaluminium chloride, this compound is preferred in some cases because the pH value can be varied according to the exact values chosen for the subscripts n and m in the pattern formula. Although many variations are used, an especially important combination is Al12Cl12(OH)24. The actual pH correlates to the formula m/(3n).
1.Structure:
     Aluminium chlorohydrate is best described as an inorganic polymer and as such is difficult to structurally characterise. However, techniques such as gel permeation chromatography, X-ray crystallography and 27Al-NMR have been used in research by various groups including that of Nazar[1] and Laden[2] to show that the material is based on Al13 units with a Keggin ion structure and that this base unit then undergoes complex transformations to form larger poly-aluminium complexes.
2.Synthesis
   Aluminium chlorohydrate can be commercially manufactured by reacting aluminium with hydrochloric acid. A number of aluminium-containing raw materials can be used, including aluminium metal, alumina trihydrate, aluminium chloride, aluminium sulfate and combinations of these. The products can contain by-product salts, such as sodium/calcium/magnesium chloride or sulfate.
   Because of the explosion hazard related to hydrogen produced by the reaction of aluminium metal with hydrochloric acid, the most common industrial practice is to prepare a solution of aluminium chlorohydrate (ACH) by reacting aluminium hydroxide with hydrochloric acid. The ACH product is reacted with aluminium ingots at 100 °C using steam in an open mixing tank. The Al to ACH ratio and the time of reaction allowed determines the polymer form of the PAC n to m ratio.

Poly Aluminium Chloride, Poly Aluminium Chloride PAC, Coagulant