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Aluminium hydroxide

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Title: Aluminium hydroxide  
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Subject: Aluminium sulfate, Antacids, Bayer process, Sodium hydroxide, Aluminium
Collection: Aluminium Compounds, Antacids, Hydroxides, Inorganic Compounds, Phosphate Binders
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Aluminium hydroxide

Aluminium hydroxide
Unit cell ball and stick model of aluminium hydroxide
Sample of aluminium hydroxide in a vial
Preferred IUPAC name
Aluminium hydroxide
Systematic IUPAC name
Aluminium(3+) trioxidanide
Other names
Aluminic acid

Aluminic hydroxide
Aluminium(III) hydroxide
Aluminium hydroxide
Hydrated alumina

Orthoaluminic acid
ATC code A02

A02 (algeldrate)
ChemSpider  Y
Jmol-3D images Image
RTECS number BD0940000
Molar mass 78.00 g/mol
Appearance White amorphous powder
Density 2.42 g/cm3, solid
Melting point 300 °C (572 °F; 573 K)
0.0001 g/100 mL (20 °C)
Solubility soluble in acids, alkalis, HCl, H2SO4
Acidity (pKa) >7
−1277 kJ·mol−1[2]
Safety data sheet External MSDS
Irritant (I) Xi
R-phrases R36 R37 R38
S-phrases S26 S36
NFPA 704
Flash point Non-flammable
Related compounds
Other anions
Related compounds
Sodium oxide,
aluminium oxide hydroxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
 N  (: Y/N?)

Aluminium hydroxide, Al(OH)3, is found in nature as the mineral gibbsite (also known as hydrargillite) and its three much rarer polymorphs: bayerite, doyleite and nordstrandite. Closely related are aluminium oxide hydroxide, AlO(OH), and aluminium oxide (or alumina), Al2O3. These compounds together are the major components of the aluminium ore bauxite. Freshly precipitated aluminium hydroxide forms gels, which are the basis for the 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, as an adsorbent in gas purification, as a Claus catalyst support for water purification, and as an adsorbent for the catalyst during the manufacture of polyethylene by the Sclairtech process.


  • Nomenclature 1
  • Properties 2
    • Polymorphism 2.1
  • Production 3
  • Uses 4
    • Fire retardant 4.1
    • Pharmaceutical 4.2
      • Potential adverse effects 4.2.1
  • References 5
  • External links 6


The naming for the different forms of aluminium hydroxide is ambiguous and there is no universal standard. All four polymorphisms have a chemical composition of aluminium trihydroxide (an aluminium atom attached to three hydroxide groups).[3]

Gibbsite is also known as hydrargillite, named after the Greek words for water (hydra) and clay (argylles). The first compound named hydrargillite was thought to be aluminium hydroxide, but was later found to be aluminium phosphate; despite this, both gibbsite and hydrargillite are used to refer to the same polymorphism of aluminium hydroxide, with gibbsite used most commonly in the United States and hydrargillite used more often in Europe. In 1930 it was referred to as α-alumina trihydrate to contrast it with bayerite which was called β-alumina trihydrate (the alpha and beta designations were used to differentiate the more- and less-common forms respectively). In 1957 a symposium on alumina nomenclature attempted to develop a universal standard, resulting in gibbsite being designated γ-Al(OH)3 and bayerite becoming α-Al(OH)3 and nordstrandite being designated Al(OH)3. Based on their crystallographic properties, a suggested nomenclature and designation is for gibbsite to be α-Al(OH)3, bayerite to be designated β-Al(OH)3 and both nordstrandite and doyleite are designated Al(OH)3. Under this designation, the α and β prefixes refer to hexagonal, close-packed structures and altered or dehydrated polymorphisms respectively, with no differentiation between nordstrandiate and doyleite.[3]


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.[4]

Aluminium hydroxide is amphoteric. It dissolves in acid, forming [Al(H2O)6]3+ (hexaaquaaluminium) or its hydrolysis products. It also dissolves in strong alkali, forming [Al(OH)4] (tetrahydroxidoaluminate).


Four polymorphs of aluminium hydroxide exist, all based on the common combination of one aluminium atom and three hydroxide molecules into different crystaline arrangements that determine the appearance and properties of the compound. The four combinations are:[3]

All polymorphs are composed of layers of octahedral aluminium hydroxide units with the aluminium atom in the centre and the hydroxyl groups on the sides, with hydrogen bonds holding the layers together. The polymorphisms vary in how the layers stack together, with the arrangements of the molecules and layers determined by the acidity, presence of ions (including salt) and the surface of the minerals the substance forms on. Under most conditions gibbsite is the most chemically stable form of aluminium hydroxide. All forms of Al(OH)3 crystals are hexagonal.[3]


Virtually all the aluminium hydroxide used commercially is manufactured by the Bayer process[5] which involves dissolving bauxite in sodium hydroxide at temperatures up to 270 °C (518 °F). The remaining solid, which is a red mud, is separated and aluminium hydroxide is precipitated from the remaining solution. This aluminium hydroxide can be converted to alumina by calcination.

This red mud is damaging to the environment and highly toxic. It is usually stored in large artificial lakes: this led to the Ajka alumina plant accident in 2010 in Hungary, killing nine people and injuring 122. The dam holding back the red mud burst, allowing it to contaminate large areas of land and waterways.[6]


Annual production is some 100 million tonnes, over 90% of which is converted to aluminium oxide (alumina) that is used in the manufacture of aluminium metal.

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.

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.[7][8][9][10][11] It decomposes at about 180 °C (356 °F), 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.


Under the generic name algeldrate, aluminium hydroxide is used as an antacid. Brand names include Alu-Cap, Aludrox, Gaviscon or Pepsamar. It reacts with excess acid in the stomach, reducing the acidity of the stomach content,[12] which may relieve the symptoms of ulcers, heartburn or dyspepsia. It can however 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.

Precipitated 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 sometimes mistakenly called "alum": "alum" properly refers to aluminium potassium sulfate.

Vaccine formulations containing aluminium hydroxide stimulate 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 dendritic cells pick up the antigen, carry it to lymph nodes, and stimulate T cells and B cells.[13] 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,[14] nor is it useful when the antigen is peptide-based.[15]

Potential adverse effects

In the 1960s and 1970s it was speculated that aluminium was related to various neurological disorders including Alzheimer's disease.[16][17] Since then, multiple epidemiological studies have found no connection between exposure to aluminium and neurological disorders.[18][19][20]


  1. ^
  2. ^ Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company.  
  3. ^ a b c d Karamalidis, AK; Dzombak DA (2010). Surface Complexation Modeling: Gibbsite.  
  4. ^ Wells, A.F. (1975), Structural Inorganic Chemistry (4th ed.), Oxford: Clarendon Press 
  5. ^ Hind, AR; Bhargava SK; Grocott SC (1999). "The Surface Chemistry of Bayer Process Solids: A Review". Colloids Surf Physiochem Eng Aspects 146: 359–74. 
  6. ^ "Hungary Battles to Stem Torrent of Toxic Sludge". BBC News Website. 5 October 2010. 
  7. ^ Hollingbery, LA; Hull TR (2010). "The Fire Retardant Behaviour of Huntite and Hydromagnesite - A Review". Polymer Degradation and Stability 95: 2213–2225.  
  8. ^ Hollingbery, LA; Hull TR (2010). "The Thermal Decomposition of Huntite and Hydromagnesite - A Review". Thermochimica Acta 509: 1–11.  
  9. ^ Hollingbery, LA; Hull TR (2012). "The Fire Retardant Effects of Huntite in Natural Mixtures with Hydromagnesite". Polymer Degradation and Stability 97: 504–512.  
  10. ^ Hollingbery, LA; Hull TR (2012). "The Thermal Decomposition of Natural Mixtures of Huntite and Hydromagnesite". Thermochimica Acta 528: 45–52.  
  11. ^ Hull, TR; Witkowski A; Hollingbery LA (2011). "Fire Retardant Action of Mineral Fillers". Polymer Degradation and Stability 96: 1462–1469.  
  12. ^ Galbraith, A; Bullock, S; Manias, E. Hunt, B. & Richards, A. (1999). Fundamentals of pharmacology: a text for nurses and health professionals. Harlow: Pearson. p. 482. 
  13. ^ Kool, M; Soullié T; van Nimwegen M; Willart MA; Muskens F; Jung S; Hoogsteden HC; Hammad H; Lambrecht BN (2008-03-24). "T-helper 1 and T-helper 2 adjuvants induce distinct differences in the magnitude, quality and kinetics of the early inflammatory response at the site of injection". J Exp Med 205 (4): 869–82.  
  14. ^ Petrovsky N, Aguilar JC. (2004). "Vaccine adjuvants: current state and future trends".  
  15. ^ Cranage, MP; Robinson A (2003). Robinson A; Hudson MJ; Cranage MP, ed. Vaccine Protocols - Volume 87 of Methods in Molecular Medicine Biomed Protocols (2nd ed.).  
  16. ^ "Alzheimer's Myth's".  
  17. ^ Khan, A (2008-09-01). "Aluminium and Alzheimer's disease".  
  18. ^ Rondeau V (2002). "A review of epidemiologic studies on aluminum and silica in relation to Alzheimer's disease and associated disorders". Rev Environ Health 17 (2): 107–21.  
  19. ^ Martyn CN, Coggon DN, Inskip H, Lacey RF, Young WF (May 1997). "Aluminum concentrations in drinking water and risk of Alzheimer's disease". Epidemiology 8 (3): 281–6.  
  20. ^ Graves AB, Rosner D, Echeverria D, Mortimer JA, Larson EB (September 1998). "Occupational exposures to solvents and aluminium and estimated risk of Alzheimer's disease". Occup Environ Med 55 (9): 627–33.  

External links

  • International Chemical Safety Card 0373
  • "Some properties 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
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