Aluminium hydroxide

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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
Aluminium(3+) trioxidanide
Other names
Aluminic acid

Aluminic hydroxide
Aluminium(III) hydroxide
Aluminium hydroxide
Aluminum trihydroxide
Hydrated alumina

Orthoaluminic acid
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.040.433
KEGG
RTECS number BD0940000
UNII
Properties[1][2]
Al(OH)3
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
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)
  • US: B (No risk in non-human studies)
Hazards
Safety data sheet External MSDS
GHS pictograms GHS-pictogram-exclam.svg
H319, H335
P264, P261, P280, P271, P312, P304+340, P305+351+338, P337+313
NFPA 704
Flammability code 0: Will not burn. E.g., waterHealth code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentineReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
0
1
0
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
>5000 mg/kg (rat, oral)
Related compounds
Other anions
None
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 verify (what is ☑Y☒N ?)
Infobox references

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 in nature, 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.

Nomenclature[edit]

The naming for the different forms of aluminium hydroxide is ambiguous and there is no universal standard. All four polymorphs have a chemical composition of aluminium trihydroxide (an aluminium atom attached to three hydroxide groups).[5]

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, 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 nordstrandite and doyleite.[5]

Properties[edit]

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.[6][7]

Aluminium hydroxide is amphoteric. In acid, it acts as a Brønsted-Lowry base by picking up hydrogen ions and neutralizes the acid, yielding a salt:[8]

3HCl + Al(OH)3 → AlCl3 + 3H2O

In bases, it acts a Lewis acid by taking an electron pair from the hydroxide ions:[8]

Al(OH)3 + OH → Al(OH)4

Polymorphism[edit]

Four polymorphs of aluminium hydroxide exist, all based on the common combination of one aluminium atom and three hydroxide molecules into different crystalline arrangements that determine the appearance and properties of the compound. The four combinations are:[5]

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.[5]

Production[edit]

Virtually all the aluminium hydroxide used commercially is manufactured by the Bayer process[9] 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 pH of 13.[10]

Uses[edit]

One of the major uses of aluminium hydroxide is as a feedstock for the manufacture of other aluminium compounds: speciality calcined aluminas, aluminium sulfate, polyaluminium chloride, aluminium chloride, zeolites, sodium aluminate, activated alumina, and aluminium nitrate.[7]

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.[citation needed]

Fire retardant[edit]

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.[11][12][13][14][15] 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.[16]

Pharmaceutical[edit]

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,[17][18] 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.[19] Some such products (such as Maalox) are formulated to minimize such effects through the inclusion of equal concentrations of magnesium hydroxide or magnesium carbonate, which have counterbalancing laxative effects.[20]

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.[21][22]

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.[23][full citation needed] 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", which properly refers to aluminium potassium sulfate.[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.[24] 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,[25] nor is it useful when the antigen is peptide-based.[26]

Potential adverse effects[edit]

In the 1960s and 1970s it was speculated that aluminium was related to various neurological disorders, including Alzheimer's disease.[27][28] Since then, multiple epidemiological studies have found no connection between exposure to aluminium and neurological disorders.[29][30][31]

References[edit]

  1. ^ For solubility product: "Archived copy". Archived from the original on 15 June 2012. Retrieved 2012-05-17. 
  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. Retrieved 2017-07-01. 
  3. ^ Zumdahl, Steven S. (2009). Chemical Principles (6th ed.). Houghton Mifflin Company. ISBN 0-618-94690-X. 
  4. ^ Black, Ronald A.; Hill, D. Ashley (2003-06-15). "Over-the-Counter Medications in Pregnancy". American Family Physician. 67 (12): 2517–2524. ISSN 0002-838X. Retrieved 2017-07-01. 
  5. ^ a b c d Karamalidis, AK; Dzombak DA (2010). Surface Complexation Modeling: Gibbsite. John Wiley & Sons. pp. 15–17. ISBN 0-470-58768-7. 
  6. ^ Wells, A.F. (1975), Structural Inorganic Chemistry (4th ed.), Oxford: Clarendon Press 
  7. ^ a b Evans, KA (1993). "Properties and uses of aluminium oxides and aluminium hydroxides". In A. J. Downs. Chemistry of aluminium, gallium, indium, and thallium (1st ed.). London; New York: Blackie Academic & Professional. ISBN 9780751401035. 
  8. ^ a b Boundless (2016-07-26). "Basic and Amphoteric Hydroxides". Boundless Chemistry. Retrieved 2017-07-02. 
  9. ^ Hind, AR; Bhargava SK; Grocott SC (1999). "The Surface Chemistry of Bayer Process Solids: A Review". Colloids Surf Physiochem Eng Aspects. 146: 359–74. doi:10.1016/S0927-7757(98)00798-5. 
  10. ^ "Hungary Battles to Stem Torrent of Toxic Sludge". BBC News Website. 5 October 2010. 
  11. ^ 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. 
  12. ^ Hollingbery, LA; Hull TR (2010). "The Thermal Decomposition of Huntite and Hydromagnesite - A Review" (PDF). Thermochimica Acta. 509: 1–11. doi:10.1016/j.tca.2010.06.012. 
  13. ^ 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. 
  14. ^ 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. 
  15. ^ 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. 
  16. ^ Huber Engineered Materials. "Huber Non-Halogen Fire Retardant Additives" (PDF). Retrieved 2017-07-03. 
  17. ^ 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. 
  18. ^ 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. 
  19. ^ Washington, Neena (2 August 1991). Antacids and Anti Reflux Agents. Boca Raton, FL: CRC Press. p. 10. ISBN 0-8493-5444-7. 
  20. ^ Bill, Robert L. (2016-09-01). Clinical Pharmacology and Therapeutics for Veterinary Technicians - E-Book. Elsevier Health Sciences. p. 105. ISBN 9780323444026. 
  21. ^ Plumb, Donald C. (2011). "Aluminum Hydroxide". Plumb's Veterinary Drug Handbook (7th ed.). Stockholm, Wisconsin; Ames, Iowa: Wiley. pp. 36–37. ISBN 9780470959640. 
  22. ^ Lifelearn Inc. (2010-11-01). "Aluminum Hydroxide". Know Your Pet. Retrieved 2017-06-30. 
  23. ^ "About Brenntag Biosector - Brenntag". www.brenntag.com. Retrieved 19 April 2018. 
  24. ^ Kool, M; Soullié T; van Nimwegen M; Willart MA; Muskens F; Jung S; Hoogsteden HC; Hammad H; Lambrecht BN (2008-03-24). "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 2807488Freely accessible. PMID 18362170. 
  25. ^ Petrovsky N, Aguilar JC (2004). "Vaccine adjuvants: current state and future trends". Immunol Cell Biol. 82 (5): 488–96. doi:10.1111/j.0818-9641.2004.01272.x. PMID 15479434. 
  26. ^ 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 1-59259-399-2. 
  27. ^ "Alzheimer's Myth's". Alzheimer's Association. Retrieved 2012-07-29. 
  28. ^ Khan, A (2008-09-01). "Aluminium and Alzheimer's disease". Alzheimer's Society. Retrieved 2012-03-08. 
  29. ^ 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 4764671Freely accessible. PMID 12222737. 
  30. ^ 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. 
  31. ^ 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 1757634Freely accessible. PMID 9861186. 

External links[edit]