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| Names | |
|---|---|
| Preferred IUPAC name Aluminium hydroxide | |
| Systematic IUPAC name Trihydroxidoaluminium | |
Other names
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| Identifiers | |
3D model (JSmol) | |
| ChEBI | |
| ChEMBL | |
| ChemSpider |
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| DrugBank | |
| ECHA InfoCard | 100.040.433 |
| KEGG | |
| RTECS number |
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| UNII | |
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| Properties[1][2] | |
| Al(OH)3 | |
| Molar mass | 78.003 g·mol−1 |
| Appearance | Whiteamorphous powder |
| Density | 2.42 g/cm3, solid |
| Melting point | 300 °C (572 °F; 573 K) |
| 0.0001 g/(100 mL) | |
Solubility product (Ksp) | 3×10−34 |
| Solubility | soluble inacids andalkalis |
| Acidity (pKa) | >7 |
| Isoelectric point | 7.7 |
| Thermochemistry[3] | |
Std enthalpy of formation(ΔfH⦵298) | −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) | |
| 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 | |
Otheranions | None |
Related compounds | |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Aluminium hydroxide,Al(OH)3, is found in as the mineralgibbsite (also known as hydrargillite) and its three much rarerpolymorphs:bayerite,doyleite, and nordstrandite. Aluminium hydroxide isamphoteric, i.e., it has bothbasic andacidic properties. Closely arealuminium oxide hydroxide, AlO(OH), andaluminium oxide or alumina (Al2O3), the latter of which is also amphoteric. These compounds together are the major components of the aluminiumorebauxite. Aluminium hydroxide also forms a gelatinous precipitate in water.
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] Fourpolymorphs are recognized.[7] All feature layers ofoctahedral aluminium hydroxide units, withhydrogen bonds between the layers. The polymorphs differ in terms of the stacking of the layers. All forms ofAl(OH)3 crystals are hexagonal[disputed –discuss]:
Hydrargillite, once thought to be aluminium hydroxide, is analuminium phosphate. Nonetheless, bothgibbsite andhydrargillite refer to the same polymorphism of aluminium hydroxide, withgibbsite used most commonly in the United States andhydrargillite used more often in Europe. Hydrargillite is named after theGreek words for water (hydr[o-]) and clay (argillos).[citation needed]
Aluminium hydroxide isamphoteric. Inacid, it acts as aBrønsted–Lowry base. It neutralizes the acid, yielding a salt:[9]
In bases, it acts as aLewis acid by binding hydroxide ions:[9]
Virtually all the aluminium hydroxide used commercially is manufactured by theBayer process[10] which involves dissolvingbauxite 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 ofsodium aluminate. This aluminium hydroxide can be converted toaluminium oxide or alumina bycalcination.[citation needed]
The residue orbauxite tailings, which is mostly iron oxide, is highly caustic due to residual sodium hydroxide. It was historically stored in lagoons; this led to theAjka 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 theDanube. While the mud was considered non-toxic due to low levels of heavy metals, the associated slurry had a pH of 13.[11]
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 ofhuntite andhydromagnesite 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 a 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 inpolyesters,acrylics,ethylene vinyl acetate,epoxies,polyvinyl chloride (PVC),rubber,[19] as well as in wood-based products.[20][21][22]
Aluminium hydroxide is used as filler in someartificial stone compound material, often inacrylic resin.[citation needed]
Aluminium hydroxide is afeedstock for the manufacture of other aluminium compounds:calcined aluminas,aluminium sulfate, polyaluminium chloride,aluminium chloride,zeolites,sodium aluminate, activated alumina, andaluminium nitrate.[6]
Freshly precipitated aluminium hydroxide formsgels, which are the basis for the application of aluminium salts asflocculants in water purification. This gel crystallizes with time. Aluminium hydroxide gels can be dehydrated (e.g. using water-miscible non-aqueous solvents likeethanol) to form an amorphous aluminium hydroxide powder, which is readily soluble in acids. Heating converts it to activated aluminas, which are used asdesiccants,adsorbent in gas purification, andcatalyst supports.[12]
Under the generic name "algeldrate", aluminium hydroxide is used as anantacid in humans and animals (mainly cats and dogs). It is preferred over other alternatives such assodium bicarbonate becauseAl(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,[23][24] which may relieve the symptoms ofulcers,heartburn ordyspepsia. Such products can causeconstipation, because the aluminium ions inhibit the contractions ofsmooth muscle cells in the gastrointestinal tract, slowingperistalsis and lengthening the time needed for stool to pass through thecolon.[25] Some such products are formulated to minimize such effects through the inclusion of equal concentrations ofmagnesium hydroxide ormagnesium carbonate, which have counterbalancinglaxative effects.[26]
This compound is also used to controlhyperphosphatemia (elevatedphosphate, 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 theintestines and reduce the amount of phosphorus that can be absorbed.[27][28]
Precipitated aluminium hydroxide is included as anadjuvant in somevaccines (e.g.anthrax vaccine). One of the well-known brands of aluminium hydroxide adjuvant is Alhydrogel, made by Brenntag Biosector.[29][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 theimmune system by inducing the release ofuric acid, an immunologicaldanger signal. This strongly attracts certain types ofmonocytes which differentiate intodendritic cells. The dendritic cells pick up the antigen, carry it tolymph nodes, and stimulateT cells andB cells.[30] It appears to contribute to induction of a goodTh2 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,[31] nor is it useful when the antigen ispeptide-based.[32]
In the 1960s and 1970s it was speculated that aluminium was related to variousneurological disorders, includingAlzheimer's disease.[33][34] Since then, multipleepidemiological 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.[35][36][37]
Neural disorders were found in experiments on mice motivated byGulf War illness (GWI). Aluminium hydroxide injected in doses equivalent to those administered to the United States military, showed increased reactive astrocytes, increasedapoptosis of motor neurons andmicroglial proliferation within the spinal cord and cortex.[38]
