Aluminium hydroxide

Aluminium hydroxide
Preferred IUPAC name Aluminium hydroxide
Systematic name Aluminium(3+) trioxidanide
Other names Aluminic acid Aluminic hydroxide Aluminium(III) hydroxide Aluminum hydroxide Hydrated alumina Orthoaluminic acid
Identifiers
CAS number	21645-51-2 Y
PubChem	10176082 Y
ChemSpider	8351587 Y
UNII	5QB0T2IUN0 Y
ChEBI	CHEBI:33130 Y
ChEMBL	CHEMBL1200706 N
RTECS number	BD0940000
ATC code	A02AB01, A02AB02 (algeldrate)
Jmol-3D images	Image 1
SMILES [OH-].[OH-].[OH-].[Al+3]
InChI InChI=1S/Al.3H2O/h;3*1H2/q+3;;;/p-3 Y Key: WNROFYMDJYEPJX-UHFFFAOYSA-K Y InChI=1/Al.3H2O/h;3*1H2/q+3;;;/p-3 Key: WNROFYMDJYEPJX-DFZHHIFOAJ
Properties
Molecular formula	Al(OH)3
Molar mass	78.00 g/mol
Appearance	White amorphous powder
Density	2.42 g/cm³, solid
Melting point	300 °C, 573 K, 572 °F
Solubility in water	0.0001 g/100 mL (20 °C)
Solubility	soluble in acids, alkalis, HCl, H2SO4
Acidity (pKa)	>7
Thermochemistry
Std enthalpy of formation ΔfHo298	−1277 kJ·mol−1
Hazards
MSDS	External MSDS
EU classification	Irritant (I) Xi
R-phrases	R36 R37 R38
S-phrases	S26 S36
NFPA 704	0 1 0
Flash point	Non-flammable
Related compounds
Other anions	None
Related compounds	Sodium oxide, aluminium oxide hydroxide
N (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Aluminium hydroxide, Al(OH)₃, ATH, sometimes erroneously called Hydrate of alumina, is found in nature as the mineral gibbsite (also known as hydrargillite) and its three, much more rare forms, polymorphs: bayerite, doyleite and nordstrandite. Closely related are aluminium oxide hydroxide, AlO(OH), and aluminium oxide, Al₂O₃, differing only by loss of water. These compounds together are the major components of the aluminium ore bauxite. Freshly precipitated aluminium hydroxide forms gels, which is the basis for application of aluminium salts as flocculants in water purification. This gel crystallizes with time. Aluminium hydroxide gels can be dehydrated (e.g., using water-miscible non-aqueous solvents like ethanol) to form an amorphous aluminium hydroxide powder, which is readily soluble in acids. Aluminium hydroxide powder which has been heated to an elevated temperature under carefully controlled conditions is known as activated alumina and is used as a desiccant, an adsorbent, in gas purification, as a Claus catalyst support, water purification, and an adsorbent for the catalyst during the manufacture of polyethylene by the Sclairtech process.

Chemistry

Gibbsite has a typical metal hydroxide structure with hydrogen bonds. It is built up of double layers of hydroxyl groups with aluminium ions occupying two-thirds of the octahedral holes between the two layers.

Aluminium hydroxide is amphoteric. It dissolves in acid, forming Al(H₂O)₆³⁺ (hexaaquaaluminium(3+)) or its hydrolysis products. It also dissolves in strong alkali, forming Al(OH)₄^- (tetrahydroxidoaluminate(1-)).

Production

Virtually all the aluminium hydroxide used commercially is manufactured by the Bayer process which involves dissolving bauxite in sodium hydroxide as the first step. It is marketed as Alu-Tabs.

Uses

Annual production is some 100 million tonnes,^{[citation needed]} over 90% of which is converted to aluminium oxide^{[citation needed]} (alumina) that is used in the manufacture of aluminium metal.^{[citation needed]}

The major other uses of aluminium hydroxide is as a feedstock for the manufacture of other aluminium compounds: specialty calcined aluminas, aluminium sulfate, polyaluminium chloride, aluminium chloride, zeolites, sodium aluminate, activated alumina, aluminium nitrate.^{[citation needed]}

Fire retardant

Aluminium hydroxide also finds use as a fire retardant filler for polymer applications in a similar way to magnesium hydroxide and mixtures of huntite and hydromagnesite. It decomposes at about 180 °C, absorbing a considerable amount of heat in the process and giving off water vapour. In addition to behaving as a fire retardant, it is very effective as a smoke suppressant in a wide range of polymers, most especially in polyesters, acrylics, ethylene vinyl acetate, epoxies, PVC and rubber.

Pharmaceutical

This compound is used as an antacid under names such as Alu-Cap, Aludrox or Pepsamar. The hydroxide reacts with excess acid in the stomach, reducing its acidity. This decrease of acidity of the contents of the stomach may in turn help to relieve the symptoms of ulcers, heartburn or dyspepsia. It can also cause constipation and is therefore often used with magnesium hydroxide or magnesium carbonate, which have counterbalancing laxative effects. This compound is also used to control phosphate (phosphorus) levels in the blood of people suffering from kidney failure.

Aluminium hydroxide is included as an adjuvant in some vaccines (e.g. anthrax vaccine). One of the well-known brands of aluminium hydroxide adjuvant is Alhydrogel, made by Brenntag. Since it absorbs protein well, it also functions to stabilize vaccines by preventing the proteins in the vaccine from precipitating or sticking to the walls of the container during storage. Aluminium hydroxide is often mis-called "alum" even by researchers; however, "alum" properly refers to aluminium potassium sulphate (alum).

Vaccine formulations containing aluminium hydroxide stimulates the immune system by inducing the release of uric acid, an immunological danger signal. This strongly attracts certain types of monocytes which differentiate into dendritic cells. The DCs pick up the antigen, carry it to lymph nodes, and stimulate T cells and B cells. It appears to contribute to induction of a good Th2 response, so is useful for immunizing against pathogens that are blocked by antibodies. However, it has little capacity to stimulate cellular (Th1) immune responses, important for protection against many pathogens.

On the other hand, in a mouse model of allergen sensitization during pregnancy, while the mother mice had a Th2 response to the allergen plus aluminium hydroxide, the offspring showed lower IgG1 and IgE compared to the offspring of mice treated with the allergen alone or plus a Th1 adjuvant.

Potential adverse effects

It has been speculated that aluminum is related to various neurological disorders including Alzheimer's disease. Despite there being circumstantial evidence linking aluminum with Alzheimer's disease, multiple epidemiological studies have found no connection between exposure to aluminium and neurological disorders and the connection is considered unlikely.

See also

Vaccine controversy

External links

• International Chemical Safety Card 0373
• "SOME PROIPERTIES OF ALUMINUM HYDROXIDE PRECIPITATED IN THE PRESENCE OF CLAYS", Soil Research Institute, R C Turner, Department of Agriculture, Ottawa
• Effect of aging on properties of polynuclear hydroxyaluminum cations
• A second species of polynuclear hydroxyaluminum cation, its formation and some of its properties