Aluminium Polychloride

Al (OH)a Clb con a+b=3

IUPAC name: n.d.
Other names:  Aluminium polyhydroxychloride, aluminium chlorhydrate, aluminium chloride hydroxide, basic aluminium chloride.
CAS number: 1327-41-9

Aluminium Polychloride is a straw-yellow solution characterised by remarkable stability, even though its alumina content is over twice that of aluminium sulphate (alum) solutions.
Aluminium Polychloride compounds are polymeric compounds of aluminium hydroxides at various levels of chloride content; they are designated by this generic formula: (Aln(OH)mCl3n-m) x. These compounds contain long chains of atoms and therefore have a higher molecular weight and a larger (positive) electrical charge. This implies that upon hydrolysis they generate aluminium polyhydroxides, which also have long molecular chains of larger dimensions and high weight. These properties make Aluminium Polychloride extremely useful in some processes such as papermaking and water clarification.

Manufacture

Aluminium Polychloride is produced by reacting aluminium hydroxide (i.e. alumina) with hydrochloric acid:

x Al(OH)3 + y HCl → y H2O + AlxCly(OH)3x-y

Principal uses

Aluminium Polychloride can be used in a broad pH range, especially between 6 and 9; its flocculation potential is virtually independent of temperature and it is therefore utilised in the treatment of wastewaters of various types: municipal (to improve purification yields and overall purification capacity); animal husbandry (abatement of COD and phosphorous); textile industry (colour, surfactants, and COD removal); mechanical engineering industry (removal of turbidity, oils, COD, phosphorous); tanning industry (abatement of turbidity, COD, and colour). Furthermore, it finds application as a bonding agent and as a drainage aid in the papermaking industry.