Aluminium hydroxide

This article is about Al(OH)₃. For AlOH, see aluminium monohydroxide.

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. Aluminium hydroxide is amphoteric, i.e., it has both basic and acidic properties. Closely related are aluminium oxide hydroxide, AlO(OH), and aluminium oxide or alumina (Al₂O₃), the latter of which is also amphoteric. These compounds together are the major components of the aluminium ore bauxite. Aluminium hydroxide also forms a gelatinous precipitate in water.

Aluminium hydroxide

Names
Preferred IUPAC name Aluminium hydroxide
Systematic IUPAC name Trihydroxidoaluminium
Other names Aluminic acid Aluminic hydroxide Alumanetriol Aluminium(III) hydroxide Aluminium hydroxide Aluminium trihydroxide Hydrated alumina Orthoaluminic acid
Identifiers
CAS Number	21645-51-2^Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:33130^Y
ChEMBL	ChEMBL1200706^N
ChemSpider	8351587^Y
DrugBank	DB06723
ECHA InfoCard	100.040.433
KEGG	D02416
PubChem CID	10176082
RTECS number	BD0940000
UNII	5QB0T2IUN0^Y
CompTox Dashboard (EPA)	DTXSID2036405
InChI InChI=1S/Al.3H2O/h;3*1H2/q+3;;;/p-3^Y Key: WNROFYMDJYEPJX-UHFFFAOYSA-K A02AB02 (WHO) (algeldrate)^N InChI=1/Al.3H2O/h;3*1H2/q+3;;;/p-3 Key: WNROFYMDJYEPJX-DFZHHIFOAJ
SMILES [OH-].[OH-].[OH-].[Al+3]
Properties^[1]^[2]
Chemical formula	Al(OH)3
Molar mass	78.003 g·mol^−1
Appearance	White amorphous powder
Density	2.42 g/cm^3, solid
Melting point	300 °C (572 °F; 573 K)
Solubility in water	0.0001 g/(100 mL)
Solubility product (Ksp)	3×10^−34
Solubility	soluble in acids and alkalis
Acidity (pKa)	>7
Isoelectric point	7.7
Thermochemistry^[3]
Std enthalpy of formation (ΔfH^⦵298)	−1277 kJ·mol^−1
Pharmacology^[4]
ATC code	A02AB01 (WHO)
Hazards
GHS labelling:
Pictograms
Hazard statements	H319, H335
Precautionary statements	P261, P264, P271, P280, P304+P340, P305+P351+P338, P312, P337+P313
NFPA 704 (fire diamond)	1 0 0
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)	>5000 mg/kg (rat, oral)
Safety data sheet (SDS)	External MSDS
Related compounds
Other anions	None
Related compounds	Boric acid Gallium(III) hydroxide Indium(III) hydroxide Thallium(III) hydroxide Scandium(III) hydroxide 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 verify (what is ^YN ?) Infobox references

Structure

Al(OH)₃ is built up of double layers of hydroxyl groups with aluminium ions occupying two-thirds of the octahedral holes between the two layers.^[5][6] Four polymorphs are recognized.^[7] All feature layers of octahedral aluminium hydroxide units, with hydrogen bonds between the layers. The polymorphs differ in terms of the stacking of the layers. All forms of Al(OH)₃ crystals are hexagonal^{[disputed ]}:

• gibbsite is also known as γ-Al(OH)₃ ^[8] or α-Al(OH)₃^{[citation needed]}
• bayerite is also known as α-Al(OH)₃^[8] or β-alumina trihydrate^{[citation needed]}
• nordstrandite is also known as Al(OH)₃^[8]
• doyleite

Hydrargillite, once thought to be aluminium hydroxide, is an aluminium phosphate. Nonetheless, both gibbsite and hydrargillite refer to the same polymorphism of aluminium hydroxide, with gibbsite used most commonly in the United States and hydrargillite used more often in Europe. Hydrargillite is named after the Greek words for water (hydra) and clay (argylles).

Properties

Aluminium hydroxide is amphoteric. In acid, it acts as a Brønsted–Lowry base. It neutralizes the acid, yielding a salt:^[9]

3 HCl + Al(OH)₃ → AlCl₃ + 3 H₂O

In bases, it acts as a Lewis acid by binding hydroxide ions:^[9]

Al(OH)₃ + OH⁻ → [Al(OH)₄]⁻

Production

 

Red mud reservoirs (this one in Stade, Germany) contain the corrosive residues from the production of aluminium hydroxide.

Virtually all the aluminium hydroxide used commercially is manufactured by the Bayer process^[10] which involves dissolving bauxite in sodium hydroxide at temperatures up to 270 °C (518 °F). The waste solid, bauxite tailings, is removed and aluminium hydroxide is precipitated from the remaining solution of sodium aluminate. This aluminium hydroxide can be converted to aluminium oxide or alumina by calcination.

The residue or bauxite tailings, which is mostly iron oxide, is highly caustic due to residual sodium hydroxide. It was historically stored in lagoons; this led to the Ajka alumina plant accident in 2010 in Hungary, where a dam bursting led to the drowning of nine people. An additional 122 sought treatment for chemical burns. The mud contaminated 40 square kilometres (15 sq mi) of land and reached the Danube. While the mud was considered non-toxic due to low levels of heavy metals, the associated slurry had a pH of 13.^[11]

Uses

Fire retardant filler

Aluminium hydroxide also finds use as a fire retardant filler for polymer applications. It is selected for these applications because it is colorless (like most polymers), inexpensive, and has good fire retardant properties.^[12] Magnesium hydroxide and mixtures of huntite and hydromagnesite are used similarly.^{[13][14][15][16][17]} 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, polyvinyl chloride (PVC) and rubber.^[18]

Precursor to Al compounds

Aluminium hydroxide is a feedstock for the manufacture of other aluminium compounds: calcined aluminas, aluminium sulfate, polyaluminium chloride, aluminium chloride, zeolites, sodium aluminate, activated alumina, and aluminium nitrate.^[6]

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. Heating converts it to activated aluminas, which are used as desiccants, adsorbent in gas purification, and catalyst supports.^[12]

Pharmaceutical

Under the generic name "algeldrate", aluminium hydroxide is used as an antacid in humans and animals (mainly cats and dogs). It is preferred over other alternatives such as sodium bicarbonate because Al(OH)₃, being insoluble, does not increase the pH of stomach above 7 and hence, does not trigger secretion of excess acid by the stomach. Brand names include Alu-Cap, Aludrox, Gaviscon or Pepsamar. It reacts with excess acid in the stomach, reducing the acidity of the stomach content,^[19][20] which may relieve the symptoms of ulcers, heartburn or dyspepsia. Such products can cause constipation, because the aluminium ions inhibit the contractions of smooth muscle cells in the gastrointestinal tract, slowing peristalsis and lengthening the time needed for stool to pass through the colon.^[21] Some such products are formulated to minimize such effects through the inclusion of equal concentrations of magnesium hydroxide or magnesium carbonate, which have counterbalancing laxative effects.^[22]

This compound is also used to control hyperphosphatemia (elevated phosphate, or phosphorus, levels in the blood) in people and animals suffering from kidney failure. Normally, the kidneys filter excess phosphate out from the blood, but kidney failure can cause phosphate to accumulate. The aluminium salt, when ingested, binds to phosphate in the intestines and reduce the amount of phosphorus that can be absorbed.^[23][24]

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 Biosector.^{[25][full citation needed][dead link]} 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 called "alum", a term generally reserved for one of several sulfates.^{[citation needed]}

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.^[26] 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,^[27] nor is it useful when the antigen is peptide-based.^[28]

Safety

In the 1960s and 1970s it was speculated that aluminium was related to various neurological disorders, including Alzheimer's disease.^[29][30] Since then, multiple epidemiological studies have found no connection between exposure to environmental or swallowed aluminium and neurological disorders, though injected aluminium was not looked at in these studies.^[31][32][33]

Neural disorders were found in experiments on mice motivated by Gulf War illness (GWI). Aluminium hydroxide injected in doses equivalent to those administered to the United States military, showed increased reactive astrocytes, increased apoptosis of motor neurons and microglial proliferation within the spinal cord and cortex.^[34]

References

1. For solubility product: . Archived from the original on 15 June 2012. Retrieved 17 May 2012.
2. For isoelectric point: Gayer, K. H.; Thompson, L. C.; Zajicek, O. T. (September 1958). "The solubility of aluminum hydroxide in acidic and basic media at 25 ?c". Canadian Journal of Chemistry. 36 (9): 1268–1271. doi:10.1139/v58-184. ISSN 0008-4042.
3. Zumdahl, Steven S. (2009). Chemical Principles (6th ed.). Houghton Mifflin Company. ISBN 978-0-618-94690-7.
4. Black, Ronald A.; Hill, D. Ashley (15 June 2003). "Over-the-Counter Medications in Pregnancy". American Family Physician. 67 (12): 2517–2524. ISSN 0002-838X. PMID 12825840. Retrieved 1 July 2017.
5. Wells, A. F. (1975), Structural Inorganic Chemistry (4th ed.), Oxford: Clarendon Press
6. Evans, K. A. (1993). "Properties and uses of aluminium oxides and aluminium hydroxides". In A. J. Downs (ed.). Chemistry of aluminium, gallium, indium, and thallium (1st ed.). London; New York: Blackie Academic & Professional. ISBN 9780751401035.
7. Karamalidis, A. K.; Dzombak D. A. (2010). Surface Complexation Modeling: Gibbsite. John Wiley & Sons. pp. 15–17. ISBN 978-0-470-58768-3.
8. Wefers, Karl; Misra, Chanakya (1987). Oxides and hydroxides of aluminum. Alcoa Research Laboratories. p. 2. OCLC 894928306.
9. Boundless (26 July 2016). . Boundless Chemistry. Archived from the original on 22 August 2017. Retrieved 2 July 2017.
10. Hind, AR; Bhargava SK; Grocott SC (1999). "The Surface Chemistry of Bayer Process Solids: A Review". Colloids Surf Physiochem Eng Aspects. 146 (1–3): 359–74. doi:10.1016/S0927-7757(98)00798-5.
11. "Hungary Battles to Stem Torrent of Toxic Sludge". BBC News Website. 5 October 2010.
12. Hudson, L. Keith; Misra, Chanakya; Perrotta, Anthony J.; Wefers, Karl; Williams, F. S. (2000). "Aluminum Oxide". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a01_557.
13. Hollingbery, LA; Hull TR (2010). "The Fire Retardant Behaviour of Huntite and Hydromagnesite - A Review" (PDF). Polymer Degradation and Stability. 95 (12): 2213–2225. doi:10.1016/j.polymdegradstab.2010.08.019.
14. Hollingbery, LA; Hull TR (2010). "The Thermal Decomposition of Huntite and Hydromagnesite - A Review" (PDF). Thermochimica Acta. 509 (1–2): 1–11. doi:10.1016/j.tca.2010.06.012.
15. Hollingbery, LA; Hull TR (2012). "The Fire Retardant Effects of Huntite in Natural Mixtures with Hydromagnesite" (PDF). Polymer Degradation and Stability. 97 (4): 504–512. doi:10.1016/j.polymdegradstab.2012.01.024.
16. Hollingbery, LA; Hull TR (2012). "The Thermal Decomposition of Natural Mixtures of Huntite and Hydromagnesite" (PDF). Thermochimica Acta. 528: 45–52. doi:10.1016/j.tca.2011.11.002.
17. Hull, TR; Witkowski A; Hollingbery LA (2011). "Fire Retardant Action of Mineral Fillers" (PDF). Polymer Degradation and Stability. 96 (8): 1462–1469. doi:10.1016/j.polymdegradstab.2011.05.006. S2CID 96208830.
18. Huber Engineered Materials. "Huber Non-Halogen Fire Retardant Additives" (PDF). Retrieved 3 July 2017.
19. 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.
20. Papich, Mark G. (2007). "Aluminum Hydroxide and Aluminum Carbonate". Saunders Handbook of Veterinary Drugs (2nd ed.). St. Louis, Mo: Saunders/Elsevier. pp. 15–16. ISBN 9781416028888.
21. Washington, Neena (2 August 1991). Antacids and Anti Reflux Agents. Boca Raton, FL: CRC Press. p. 10. ISBN 978-0-8493-5444-1.
22. Bill, Robert L. (1 September 2016). Clinical Pharmacology and Therapeutics for Veterinary Technicians - E-Book. Elsevier Health Sciences. p. 105. ISBN 9780323444026.
23. Plumb, Donald C. (2011). "Aluminum Hydroxide". Plumb's Veterinary Drug Handbook (7th ed.). Stockholm, Wisconsin; Ames, Iowa: Wiley. pp. 36–37. ISBN 9780470959640.
24. Lifelearn Inc. (1 November 2010). "Aluminum Hydroxide". Know Your Pet. Retrieved 30 June 2017.
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27. Petrovsky N, Aguilar JC (2004). "Vaccine adjuvants: current state and future trends". Immunology & Cell Biology. 82 (5): 488–96. doi:10.1111/j.0818-9641.2004.01272.x. PMID 15479434. S2CID 154670.
28. Cranage, MP; Robinson A (2003). Robinson A; Hudson MJ; Cranage MP (eds.). Vaccine Protocols - Volume 87 of Methods in Molecular Medicine Biomed Protocols (2nd ed.). Springer. p. 176. ISBN 978-1-59259-399-6.
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30. Khan, A (1 September 2008). . Alzheimer's Society. Archived from the original on 11 March 2012. Retrieved 8 March 2012.
31. 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. doi:10.1515/REVEH.2002.17.2.107. PMC 4764671. PMID 12222737.
32. 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. doi:10.1097/00001648-199705000-00009. JSTOR 3702254. PMID 9115023. S2CID 32190038.
33. 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. doi:10.1136/oem.55.9.627. PMC 1757634. PMID 9861186.
34. Shaw, Christopher A.; Petrik, Michael S. (November 2009). "Aluminum hydroxide injections lead to motor deficits and motor neuron degeneration". Journal of Inorganic Biochemistry. 103 (11): 1555–1562. doi:10.1016/j.jinorgbio.2009.05.019. ISSN 1873-3344. PMC 2819810. PMID 19740540.

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^{[permanent dead link]}
• Effect of ageing on properties of polynuclear hydroxyaluminium cations
• A second species of polynuclear hydroxyaluminium cation, its formation and some of its properties