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Aluminium hydroxide

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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
Unit cell ball and stick model of aluminium hydroxide
Sample of aluminium hydroxide in a vial
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
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.040.433 Edit this at Wikidata
KEGG
RTECS number
  • BD0940000
UNII
  • InChI=1S/Al.3H2O/h;3*1H2/q+3;;;/p-3 checkY
    Key: WNROFYMDJYEPJX-UHFFFAOYSA-K
    A02AB02 (WHO) (algeldrate) ☒N
  • InChI=1/Al.3H2O/h;3*1H2/q+3;;;/p-3
    Key: WNROFYMDJYEPJX-DFZHHIFOAJ
  • [OH-].[OH-].[OH-].[Al+3]
Properties[1][2]
Al(OH)3
Molar mass 78.003 g·mol−1
Appearance White amorphous powder
Density 2.42 g/cm3, solid
Melting point 300 °C (572 °F; 573 K)
0.0001 g/(100 mL)
3×10−34
Solubility soluble in acids and alkalis
Acidity (pKa) >7
Isoelectric point 7.7
Thermochemistry[3]
−1277 kJ·mol−1
Pharmacology[4]
A02AB01 (WHO)
Hazards
GHS labelling:
no GHS pictograms
no hazard statements
P261, P264, P271, P280, P304+P340, P305+P351+P338, P312, P337+P313
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
0
0
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
>5000 mg/kg (rat, oral)
Safety data sheet (SDS) External MSDS
Related compounds
Other anions
 None
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Structure

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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 – discuss]:

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).[citation needed]

Properties

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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

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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.[citation needed]

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

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Filler and fire retardant

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Aluminium hydroxide 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] These mixtures start to decompose at temperatures around 180 °C (356 °F) to 220 °C (428 °F) (depending on the type of aluminium hydroxide used), absorbing a considerable amount of heat in the process and giving off water vapour. The decomposition rate of aluminium hydroxide increases with an increase in temperature, with an reported maximum rate at 250 °C (482 °F).[18]

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.[19]

Aluminium hydroxide is used as filler in some artificial stone compound material, often in acrylic resin.[citation needed]

Precursor to Al compounds

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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

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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,[20][21] 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.[22] 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.[23]

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.[24][25]

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.[26][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.[27] 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,[28] nor is it useful when the antigen is peptide-based.[29]

Safety

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In the 1960s and 1970s it was speculated that aluminium was related to various neurological disorders, including Alzheimer's disease.[30][31] 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.[32][33][34]

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.[35]

References

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  1. ^ For solubility product: "Solubility product constants". 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. ^ a b 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. ^ a b c Wefers, Karl; Misra, Chanakya (1987). Oxides and hydroxides of aluminum. Alcoa Research Laboratories. p. 2. OCLC 894928306.
  9. ^ a b Boundless (26 July 2016). "Basic and Amphoteric Hydroxides". 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. ^ a b 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. ISBN 3527306730.
  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. ^ "Aluminium Hydroxide". www.chembk.com. Retrieved 20 October 2024.
  19. ^ Huber Engineered Materials. "Huber Non-Halogen Fire Retardant Additives" (PDF). Retrieved 3 July 2017.
  20. ^ 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.
  21. ^ 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.
  22. ^ Washington, Neena (2 August 1991). Antacids and Anti Reflux Agents. Boca Raton, FL: CRC Press. p. 10. ISBN 978-0-8493-5444-1.
  23. ^ Bill, Robert L. (1 September 2016). Clinical Pharmacology and Therapeutics for Veterinary Technicians - E-Book. Elsevier Health Sciences. p. 105. ISBN 9780323444026.
  24. ^ Plumb, Donald C. (2011). "Aluminum Hydroxide". Plumb's Veterinary Drug Handbook (7th ed.). Stockholm, Wisconsin; Ames, Iowa: Wiley. pp. 36–37. ISBN 9780470959640.
  25. ^ Lifelearn Inc. (1 November 2010). "Aluminum Hydroxide". Know Your Pet. Retrieved 30 June 2017.
  26. ^ "About Brenntag Biosector - Brenntag". brenntag.com. Retrieved 19 April 2018.
  27. ^ Kool, M; Soullié T; van Nimwegen M; Willart MA; Muskens F; Jung S; Hoogsteden HC; Hammad H; Lambrecht BN (24 March 2008). "Alum adjuvant boosts adaptive immunity by inducing uric acid and activating inflammatory dendritic cells". J Exp Med. 205 (4): 869–82. doi:10.1084/jem.20071087. PMC 2807488. PMID 18362170.
  28. ^ 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.
  29. ^ 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.
  30. ^ "Alzheimer's Myth's". Alzheimer's Association. Retrieved 29 July 2012.
  31. ^ Khan, A (1 September 2008). "Aluminium and Alzheimer's disease". Alzheimer's Society. Archived from the original on 11 March 2012. Retrieved 8 March 2012.
  32. ^ 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.
  33. ^ 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.
  34. ^ 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.
  35. ^ 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.
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