aluminium hydroxide

{{chem2|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.{{Wells4th}}{{Cite book | editor=A. J. Downs | last=Evans | first=K. A. | title=Chemistry of aluminium, gallium, indium, and thallium | chapter=Properties and uses of aluminium oxides and aluminium hydroxides | location=London; New York | date=1993 | edition=1st | publisher=Blackie Academic & Professional | isbn=9780751401035}} Four polymorphs are recognized.{{cite book | last = Karamalidis | first = A. K. |author2=Dzombak D. A. | year = 2010 | publisher = John Wiley & Sons | url = https://books.google.com/books?id=XULsOFSipsgC&pg=PA15 | pages=15–17 | title = Surface Complexation Modeling: Gibbsite | isbn = 978-0-470-58768-3 }} 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 {{chem2|Al(OH)3}} crystals are hexagonal {{Disputed inline|date=October 2020}}:

• gibbsite is also known as γ-{{chem2|Al(OH)3}} {{Cite book|last1=Wefers|first1=Karl|url=http://worldcat.org/oclc/894928306|title=Oxides and hydroxides of aluminum|last2=Misra|first2=Chanakya|date=1987|publisher=Alcoa Research Laboratories|pages=2|oclc=894928306}} or α-{{chem2|Al(OH)3}} {{Citation needed|date=October 2020}}
• bayerite is also known as α-{{chem2|Al(OH)3}} or β-alumina trihydrate{{citation needed|date=March 2021}}
• nordstrandite is also known as {{chem2|Al(OH)3}}
• 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 ({{lang|grc-Latn|hydr[o-]}}) and clay ({{lang|grc-Latn|argillos}}).

Aluminium hydroxide is amphoteric. In acid, it acts as a Brønsted–Lowry base. It neutralizes the acid, yielding a salt:{{Cite web |url=https://www.boundless.com/chemistry/textbooks/boundless-chemistry-textbook/acids-and-bases-15/acid-base-properties-of-oxides-114/basic-and-amphoteric-hydroxides-469-6403/ |title=Basic and Amphoteric Hydroxides |last=Boundless |date=2016-07-26 |work=Boundless Chemistry |access-date=2017-07-02 |archive-url=https://web.archive.org/web/20170822135614/https://www.boundless.com/chemistry/textbooks/boundless-chemistry-textbook/acids-and-bases-15/acid-base-properties-of-oxides-114/basic-and-amphoteric-hydroxides-469-6403/ |archive-date=22 August 2017 |url-status=dead }}

:{{chem2|3 HCl + Al(OH)3 → AlCl3 + 3 H2O}}

In bases, it acts as a Lewis acid by binding hydroxide ions:

:{{chem2|Al(OH)3 + OH− → [Al(OH)4]−}}

File:Bützflethermoor Rotschlammdeponie Luftaufnahmen 2012-05-by-RaBoe-478-1.jpg 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{{cite journal|last=Hind|first=AR|author2=Bhargava SK|author3=Grocott SC|title=The Surface Chemistry of Bayer Process Solids: A Review|journal=Colloids Surf Physiochem Eng Aspects|year=1999|volume=146|issue=1–3|pages=359–74|doi=10.1016/S0927-7757(98)00798-5}} which involves dissolving bauxite in sodium hydroxide at temperatures up to {{convert|270|C}}. 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.{{cn|date=February 2024}}

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 {{convert|40|km2}} 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.{{cite news|title=Hungary Battles to Stem Torrent of Toxic Sludge|url=https://www.bbc.co.uk/news/world-europe-11475361|newspaper=BBC News Website | date=5 October 2010}}

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.{{Ullmann |doi=10.1002/14356007.a01_557|title=Aluminum Oxide|year=2000|last1=Hudson|first1=L. Keith|last2=Misra|first2=Chanakya|last3=Perrotta|first3=Anthony J.|last4=Wefers|first4=Karl|last5=Williams|first5=F. S.|isbn=3527306730}} Magnesium hydroxide and mixtures of huntite and hydromagnesite are used similarly.{{cite journal | last = Hollingbery | first = LA |author2=Hull TR | url = http://clok.uclan.ac.uk/1432/1/2._The_fire_retardant_behaviour_of_huntite_and_hydromagnesite_-_A_review.pdf | title = The Fire Retardant Behaviour of Huntite and Hydromagnesite - A Review | journal = Polymer Degradation and Stability | volume = 95 | issue = 12 | year = 2010 | pages = 2213–2225 | doi=10.1016/j.polymdegradstab.2010.08.019}}{{cite journal | last = Hollingbery | first = LA |author2=Hull TR | url = http://clok.uclan.ac.uk/1139/1/1._The_thermal_decomposition_of_huntite_and_hydromagnesite_-_A_review.pdf | title = The Thermal Decomposition of Huntite and Hydromagnesite - A Review | journal = Thermochimica Acta | volume = 509 | issue = 1–2 | year = 2010 | pages = 1–11 | doi=10.1016/j.tca.2010.06.012}}{{cite journal | last = Hollingbery | first = LA |author2=Hull TR | url = http://clok.uclan.ac.uk/3420/1/Fire%20retardant%20effect%20of%20huntite%20and%20hydromagnesite.pdf | title = The Fire Retardant Effects of Huntite in Natural Mixtures with Hydromagnesite | journal = Polymer Degradation and Stability | volume = 97 | issue = 4 | year = 2012 | pages = 504–512 | doi=10.1016/j.polymdegradstab.2012.01.024}}{{cite journal | last = Hollingbery | first = LA |author2=Hull TR | url = http://clok.uclan.ac.uk/3414/1/The%20Thermal%20Decomposition%20of%20Natural%20Turkish%20Huntite%20and%20Hydromagnesite.pdf | title = The Thermal Decomposition of Natural Mixtures of Huntite and Hydromagnesite | journal = Thermochimica Acta | volume = 528 | year = 2012 | pages = 45–52 | doi=10.1016/j.tca.2011.11.002}}{{cite journal | last = Hull | first = TR |author2=Witkowski A |author3=Hollingbery LA | url = http://clok.uclan.ac.uk/2963/1/Hull_MineralFillersPDSAcceptedManuscript.pdf | title = Fire Retardant Action of Mineral Fillers | journal = Polymer Degradation and Stability | volume = 96 | issue = 8 | year = 2011 | pages = 1462–1469 | doi=10.1016/j.polymdegradstab.2011.05.006| s2cid = 96208830 }} These mixtures start to decompose at temperatures around {{convert|180|C}} to {{convert|220|C}} (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 a reported maximum rate at {{convert|250|C}}.{{Cite web |title=Aluminium Hydroxide |url=https://www.chembk.com/en/chem/Aluminium%20Hydroxide |access-date=2024-10-20 |website=www.chembk.com |language=en}}

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), rubber,{{Cite web|url=https://www.hubermaterials.com/userfiles/files/PFDocs/Huber%20Non-Halogen%20Fire%20Retardant%20Additives.pdf|title=Huber Non-Halogen Fire Retardant Additives|author=Huber Engineered Materials|access-date=2017-07-03}} as well as in wood-based products.{{cite journal | last=Martinka | first=Jozef | last2=Mantanis | first2=George I. | last3=Lykidis | first3=Charalampos | last4=Antov | first4=Petar | last5=Rantuch | first5=Peter |author2-link=George Mantanis | title=The effect of partial substitution of polyphosphates by aluminium hydroxide and borates on the technological and fire properties of medium density fibreboard | journal=Wood Material Science & Engineering | volume=17 | issue=6 | date=2022-11-02 | issn=1748-0272 | doi=10.1080/17480272.2021.1933175 | pages=720–726}}{{cite journal | last=Uddin | first=Mezbah | last2=Alabbad | first2=Maitham | last3=Li | first3=Ling | last4=Orell | first4=Olli | last5=Sarlin | first5=Essi | last6=Haapala | first6=Antti | title=Novel Micronized Mica Modified Casein–Aluminum Hydroxide as Fire Retardant Coatings for Wood Products | journal=Coatings | publisher=MDPI AG | volume=12 | issue=5 | date=2022-05-14 | issn=2079-6412 | doi=10.3390/coatings12050673 | doi-access=free | page=673}}{{cite journal | last=Wang | first=Nana | last2=Fu | first2=Yanchun | last3=Liu | first3=Yongzhuang | last4=Yu | first4=Haipeng | last5=Liu | first5=Yixing | title=Synthesis of aluminum hydroxide thin coating and its influence on the thermomechanical and fire-resistant properties of wood | journal=Holzforschung | publisher=Walter de Gruyter GmbH | volume=68 | issue=7 | date=2014-02-07 | issn=1437-434X | doi=10.1515/hf-2013-0196 | pages=781–789}}

Aluminium hydroxide is used as filler in some artificial stone compound material, often in acrylic resin.{{cn|date=February 2024}}

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.

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.

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 {{chem2|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,{{cite book |author1=Galbraith, A |author2=Bullock, S |author3=Manias, E |author4=Hunt, B |author5=Richards, A | year = 1999 | title = Fundamentals of pharmacology: a text for nurses and health professionals | location = Harlow | publisher = Pearson | pages = 482}}{{Cite book | last=Papich | first=Mark G. | title=Saunders Handbook of Veterinary Drugs | chapter=Aluminum Hydroxide and Aluminum Carbonate | location=St. Louis, Mo | date=2007 | edition=2nd | publisher=Saunders/Elsevier | isbn=9781416028888 | pages=15–16}} 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.{{cite book|last1=Washington|first1=Neena|title=Antacids and Anti Reflux Agents|date=2 August 1991|publisher=CRC Press|location=Boca Raton, FL|isbn=978-0-8493-5444-1|page=10}} 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.{{Cite book | last=Bill | first=Robert L. | title=Clinical Pharmacology and Therapeutics for Veterinary Technicians - E-Book | date=2016-09-01 | publisher=Elsevier Health Sciences | isbn=9780323444026 | page=105 | url=https://books.google.com/books?id=0Hf2DAAAQBAJ&pg=PA105}}

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.{{Cite book | last=Plumb | first=Donald C. | title=Plumb's Veterinary Drug Handbook | chapter=Aluminum Hydroxide | location=Stockholm, Wisconsin; Ames, Iowa | date=2011 | edition=7th | publisher=Wiley | isbn=9780470959640 | pages=36–37}}{{Cite web | author=Lifelearn Inc. | title=Aluminum Hydroxide | work=Know Your Pet | access-date=2017-06-30 | date=2010-11-01 | url=https://vcahospitals.com/know-your-pet/aluminum-hydroxide}}

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.{{cite web|url=http://www.brenntag.com/biosector/en/biosector/about-brenntag-biosector/index.jsp|title=About Brenntag Biosector - Brenntag|website=brenntag.com|access-date=19 April 2018}}{{full citation needed|date=June 2017}}{{Dead link|date=January 2021}} 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|date=October 2018}}

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.{{Cite journal | last = Kool | first = M |author2=Soullié T |author3=van Nimwegen M |author4=Willart MA |author5=Muskens F |author6=Jung S |author7=Hoogsteden HC |author8=Hammad H |author9=Lambrecht BN | title = Alum adjuvant boosts adaptive immunity by inducing uric acid and activating inflammatory dendritic cells| journal = J Exp Med | volume = 205 | issue = 4 | pages = 869–82 | date = 2008-03-24 | doi = 10.1084/jem.20071087| pmc=2807488 | pmid=18362170}} 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,{{cite journal |vauthors=Petrovsky N, Aguilar JC | title = Vaccine adjuvants: current state and future trends | journal = Immunology & Cell Biology | year = 2004 | volume = 82 | issue = 5 | pages = 488–96 | doi = 10.1111/j.0818-9641.2004.01272.x | pmid = 15479434| s2cid = 154670 }} nor is it useful when the antigen is peptide-based.{{cite book |title = Vaccine Protocols - Volume 87 of Methods in Molecular Medicine Biomed Protocols | last = Cranage | first = MP | editor = Robinson A |editor2=Hudson MJ |editor3=Cranage MP |author2=Robinson A | edition = 2nd | publisher = Springer | year = 2003 | isbn = 978-1-59259-399-6 | url = https://books.google.com/books?id=kCk9BUyEaLkC&pg=PA176|page= 176 }}

In the 1960s and 1970s it was speculated that aluminium was related to various neurological disorders, including Alzheimer's disease.{{cite web | url = http://www.alz.org/alzheimers_disease_myths_about_alzheimers.asp | title = Alzheimer's Myth's | access-date = 2012-07-29 | publisher = Alzheimer's Association }}{{cite web | url = http://alzheimers.org.uk/site/scripts/documents_info.php?documentID=99 | title = Aluminium and Alzheimer's disease | access-date = 2012-03-08 | date = 2008-09-01 | publisher = Alzheimer's Society | last = Khan | first = A | archive-url = https://web.archive.org/web/20120311205419/http://alzheimers.org.uk/site/scripts/documents_info.php?documentID=99 | archive-date = 11 March 2012 | url-status = dead}} 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.{{cite journal | author=Rondeau V | title=A review of epidemiologic studies on aluminum and silica in relation to Alzheimer's disease and associated disorders | journal=Rev Environ Health | volume=17 | issue=2 | pages=107–21 | year=2002 | pmid=12222737 | doi=10.1515/REVEH.2002.17.2.107 | pmc=4764671 }}{{cite journal |vauthors=Martyn CN, Coggon DN, Inskip H, Lacey RF, Young WF | title=Aluminum concentrations in drinking water and risk of Alzheimer's disease | journal=Epidemiology | volume=8 | issue=3 | pages=281–6 | date=May 1997 | pmid=9115023 | doi=10.1097/00001648-199705000-00009|jstor= 3702254| s2cid=32190038 | doi-access=free }}{{cite journal |vauthors=Graves AB, Rosner D, Echeverria D, Mortimer JA, Larson EB | title=Occupational exposures to solvents and aluminium and estimated risk of Alzheimer's disease | journal=Occup Environ Med | volume=55 | issue=9 | pages=627–33 | date=September 1998 | pmid=9861186 | pmc=1757634 | doi=10.1136/oem.55.9.627 }}

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.{{Cite journal|last1=Shaw|first1=Christopher A.|last2=Petrik|first2=Michael S.|date=November 2009|title=Aluminum hydroxide injections lead to motor deficits and motor neuron degeneration|journal=Journal of Inorganic Biochemistry|volume=103|issue=11|pages=1555–1562|doi=10.1016/j.jinorgbio.2009.05.019|issn=1873-3344|pmc=2819810|pmid=19740540}}

{{Reflist|30em}}

• [https://www.inchem.org/documents/icsc/icsc/eics0373.htm International Chemical Safety Card 0373]
• [https://cdnsciencepub.com/doi/10.4141/cjss65-045 "Some properties of aluminum hydroxide precipitated in the presence of clays", Soil Research Institute, R C Turner, Department of Agriculture, Ottawa]
• [https://cdnsciencepub.com/doi/abs/10.1139/v76-220 Effect of ageing on properties of polynuclear hydroxyaluminium cations]
• [https://cdnsciencepub.com/doi/abs/10.1139/v76-273 A second species of polynuclear hydroxyaluminium cation, its formation and some of its properties]

{{Hydroxides}}

{{Aluminium compounds}}

{{Antacids}}

{{Drugs for treatment of hyperkalemia and hyperphosphatemia}}

{{Molecules detected in outer space}}

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{{DEFAULTSORT:Aluminium Hydroxide}}

Category:Aluminium compounds

Category:Amphoteric compounds

Category:Antacids

Category:Hydroxides

Category:Inorganic compounds

Category:Phosphate binders

Category:Flame retardants