Aluminium hydroxide, Al(OH)
3, is found in nature as the mineral
gibbsite (also known as hydrargillite) and its three much rarer
polymorphs:
bayerite
Gibbsite, Al(OH)3, is one of the mineral forms of aluminium hydroxide. It is often designated as γ-Al(OH)3 (but sometimes as α-Al(OH)3.). It is also sometimes called hydrargillite (or hydrargyllite).
Gibbsite is an important ore of aluminiu ...
,
doyleite, and nordstrandite. Aluminium hydroxide is
amphoteric
In chemistry, an amphoteric compound () is a molecule or ion that can react both as an acid and as a base. What exactly this can mean depends on which definitions of acids and bases are being used.
One type of amphoteric species are amphiprot ...
, i.e., it has both
basic
BASIC (Beginners' All-purpose Symbolic Instruction Code) is a family of general-purpose, high-level programming languages designed for ease of use. The original version was created by John G. Kemeny and Thomas E. Kurtz at Dartmouth College i ...
and
acidic
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
properties. Closely related are
aluminium oxide hydroxide
Aluminium hydroxide oxide or aluminium oxyhydroxide, AlO(OH) is found as one of two well defined crystalline phases, which are also known as the minerals boehmite and diaspore. The minerals are important constituents of the aluminium ore, bauxite. ...
, AlO(OH), and
aluminium oxide or alumina (Al
2O
3), the latter of which is also amphoteric. These compounds together are the major components of the aluminium
ore
Ore is natural rock or sediment that contains one or more valuable minerals, typically containing metals, that can be mined, treated and sold at a profit.Encyclopædia Britannica. "Ore". Encyclopædia Britannica Online. Retrieved 7 April ...
bauxite
Bauxite is a sedimentary rock with a relatively high aluminium content. It is the world's main source of aluminium and gallium. Bauxite consists mostly of the aluminium minerals gibbsite (Al(OH)3), boehmite (γ-AlO(OH)) and diaspore (α-AlO(OH ...
. Aluminium hydroxide also forms a gelatinous precipitate in water.
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.
Four
polymorphs are recognized.
All feature layers of
octahedral
In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at ea ...
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 :
*
gibbsite is also known as γ-Al(OH)
3 or α-Al(OH)
3
*
bayerite
Gibbsite, Al(OH)3, is one of the mineral forms of aluminium hydroxide. It is often designated as γ-Al(OH)3 (but sometimes as α-Al(OH)3.). It is also sometimes called hydrargillite (or hydrargyllite).
Gibbsite is an important ore of aluminiu ...
is also known as α-Al(OH)
3 or ''β-alumina trihydrate''
*
nordstrandite is also known as Al(OH)
3
*
doyleite
''Hydrargillite'', once thought to be aluminium hydroxide, is an
aluminium phosphate
Aluminium phosphate is a chemical compound. In nature it occurs as the mineral berlinite. Many synthetic forms of aluminium phosphate are known. They have framework structures similar to zeolites and some are used as catalysts, ion-exchangers o ...
. 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 (') and clay (').
Properties
Aluminium hydroxide is
amphoteric
In chemistry, an amphoteric compound () is a molecule or ion that can react both as an acid and as a base. What exactly this can mean depends on which definitions of acids and bases are being used.
One type of amphoteric species are amphiprot ...
. In
acid
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
, it acts as a
Brønsted–Lowry base. It neutralizes the acid, yielding a salt:
: 3 HCl + Al(OH)
3 → AlCl
3 + 3 H
2O
In bases, it acts as a
Lewis acid
A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...
by binding hydroxide ions:
: Al(OH)
3 + OH
− → Al(OH)
4−
Production
Virtually all the aluminium hydroxide used commercially is manufactured by the
Bayer process
The Bayer process is the principal industrial means of refining bauxite to produce alumina (aluminium oxide) and was developed by Carl Josef Bayer. Bauxite, the most important ore of aluminium, contains only 30–60% aluminium oxide (Al2O3), th ...
which involves dissolving
bauxite
Bauxite is a sedimentary rock with a relatively high aluminium content. It is the world's main source of aluminium and gallium. Bauxite consists mostly of the aluminium minerals gibbsite (Al(OH)3), boehmite (γ-AlO(OH)) and diaspore (α-AlO(OH ...
in sodium hydroxide at temperatures up to . The waste solid,
bauxite tailings
Bauxite is a sedimentary rock with a relatively high aluminium content. It is the world's main source of aluminium and gallium. Bauxite consists mostly of the aluminium minerals gibbsite (Al(OH)3), boehmite (γ-AlO(OH)) and diaspore (α-AlO(OH ...
, is removed and aluminium hydroxide is precipitated from the remaining solution of
sodium aluminate
Sodium aluminate is an inorganic chemical that is used as an effective source of aluminium hydroxide for many industrial and technical applications. Pure sodium aluminate (anhydrous) is a white crystalline solid having a formula variously given as ...
. This aluminium hydroxide can be converted to
aluminium oxide or alumina by
calcination
Calcination refers to thermal treatment of a solid chemical compound (e.g. mixed carbonate ores) whereby the compound is raised to high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O2 fraction of air), gener ...
.
The residue or
bauxite tailings
Bauxite is a sedimentary rock with a relatively high aluminium content. It is the world's main source of aluminium and gallium. Bauxite consists mostly of the aluminium minerals gibbsite (Al(OH)3), boehmite (γ-AlO(OH)) and diaspore (α-AlO(OH ...
, 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
Ajka () is a city in Hungary with about 35,000 inhabitants. It is situated in the hills of Bakony.
History
Around 1000 BCE, the area was inhabited by Celts. By the second century CE, the territory was conquered by the Romans. The Hungarians occu ...
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 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.
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.
Magnesium hydroxide and mixtures of
huntite
Huntite is a carbonate mineral with the chemical formula Mg3Ca(CO3)4. Huntite crystallizes in the trigonal system and typically occurs as platy crystals and powdery masses. For most of recorded history its main use was as a white pigment. Today ...
and
hydromagnesite
Hydromagnesite is a hydrated magnesium carbonate mineral with the formula Mg5(CO3)4(OH)2·4H2O.
It generally occurs associated with the weathering products of magnesium containing minerals such as serpentine or brucite. It occurs as incrustations ...
are used similarly. It decomposes at about , 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
Polyester is a category of polymers that contain the ester functional group in every repeat unit of their main chain. As a specific material, it most commonly refers to a type called polyethylene terephthalate (PET). Polyesters include natural ...
,
acrylics,
ethylene vinyl acetate
Ethylene-vinyl acetate (EVA), also known as poly (ethylene-vinyl acetate) (PEVA), is the copolymer of ethylene and vinyl acetate. The weight percent of vinyl acetate usually varies from 10 to 40%, with the remainder being ethylene. There are thr ...
,
epoxies
The Epoxies were an American new wave band from Portland, Oregon, formed in 2000. Heavily influenced by new wave, the band jokingly described themselves as robot garage rock. Members included FM Static on synthesizers, guitarist Viz Spectrum, l ...
,
polyvinyl chloride (PVC) and
rubber.
Precursor to Al compounds
Aluminium hydroxide is a
feedstock for the manufacture of other aluminium compounds:
calcined
Calcination refers to thermal treatment of a solid chemical compound (e.g. mixed carbonate ores) whereby the compound is raised to high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O2 fraction of air), gener ...
aluminas,
aluminium sulfate
Aluminium sulfate is a salt with the formula Al2 (SO4)3. It is soluble in water and is mainly used as a coagulating agent (promoting particle collision by neutralizing charge) in the purification of drinking water and wastewater treatment plant ...
, polyaluminium chloride,
aluminium chloride
Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula . It forms hexahydrate with the formula , containing six water molecules of hydration. Both are colourless crystals, but samples are often conta ...
,
zeolites,
sodium aluminate
Sodium aluminate is an inorganic chemical that is used as an effective source of aluminium hydroxide for many industrial and technical applications. Pure sodium aluminate (anhydrous) is a white crystalline solid having a formula variously given as ...
, activated alumina, and
aluminium nitrate
Aluminium nitrate is a white, water-soluble salt of aluminium and nitric acid, most commonly existing as the crystalline hydrate, aluminium nitrate nonahydrate, Al(NO3)3·9H2O.
Preparation
Aluminium nitrate cannot be synthesized by the reac ...
.
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
Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which a f ...
in gas purification, and
catalyst support
In chemistry, a catalyst support is the material, usually a solid with a high surface area, to which a catalyst is affixed. The activity of heterogeneous catalysts is mainly promoted by atoms present at the accessible surface of the material. Cons ...
s.
[
]
Pharmaceutical
Under the generic name "algeldrate", aluminium hydroxide is used as an antacid
An antacid is a substance which neutralizes stomach acidity and is used to relieve heartburn, indigestion or an upset stomach. Some antacids have been used in the treatment of constipation and diarrhea. Marketed antacids contain salts of alum ...
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, which may relieve the symptoms of ulcers
An ulcer is a discontinuity or break in a bodily membrane that impedes normal function of the affected organ. According to Robbins's pathology, "ulcer is the breach of the continuity of skin, epithelium or mucous membrane caused by sloughing o ...
, heartburn
Heartburn, also known as pyrosis, cardialgia or acid indigestion, is a burning sensation in the central chest or upper central abdomen. Heartburn is usually due to regurgitation of gastric acid (gastric reflux) into the esophagus. It is the ma ...
or dyspepsia. Such products can cause constipation
Constipation is a bowel dysfunction that makes bowel movements infrequent or hard to pass. The stool is often hard and dry. Other symptoms may include abdominal pain, bloating, and feeling as if one has not completely passed the bowel movement ...
, because the aluminium ions inhibit the contractions of smooth muscle cells in the gastrointestinal tract, slowing peristalsis
Peristalsis ( , ) is a radially symmetrical contraction and relaxation of muscles that propagate in a wave down a tube, in an anterograde direction. Peristalsis is progression of coordinated contraction of involuntary circular muscles, which ...
and lengthening the time needed for stool to pass through the colon. 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.
This compound is also used to control hyperphosphatemia
Hyperphosphatemia is an electrolyte disorder in which there is an elevated level of phosphate in the blood. Most people have no symptoms while others develop calcium deposits in the soft tissue. Often there is also low calcium levels which can ...
(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.
Precipitated
In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...
aluminium hydroxide is included as an adjuvant In pharmacology, an adjuvant is a drug or other substance, or a combination of substances, that is used to increase the efficacy or potency of certain drugs. Specifically, the term can refer to:
* Adjuvant therapy in cancer management
* Analgesi ...
in some vaccines (e.g. anthrax vaccine
Anthrax vaccines are vaccines to prevent the livestock and human disease anthrax, caused by the bacterium ''Bacillus anthracis''.
They have had a prominent place in the history of medicine, from Pasteur's pioneering 19th-century work with cattle ...
). One of the well-known brands of aluminium hydroxide adjuvant is Alhydrogel, made by Brenntag Biosector. 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
An alum () is a type of chemical compound, usually a hydrated double sulfate salt of aluminium with the general formula , where is a monovalent cation such as potassium or ammonium. By itself, "alum" often refers to potassium alum, with the ...
", a term generally reserved for one of several sulfates.
Vaccine formulations containing aluminium hydroxide stimulate the immune system by inducing the release of uric acid
Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the formula C5H4N4O3. It forms ions and salts known as urates and acid urates, such as ammonium acid urate. Uric acid is a product of the metabolic breakdown o ...
, an immunological danger
Danger is a lack of safety and may refer to:
Places
* Danger Cave, an archaeological site in Utah
* Danger Island, Great Chagos Bank, Indian Ocean
* Danger Island, alternate name of Pukapuka Atoll in the Cook Islands, Pacific Ocean
* Danger Is ...
signal. This strongly attracts certain types of monocytes
Monocytes are a type of leukocyte or white blood cell. They are the largest type of leukocyte in blood and can differentiate into macrophages and conventional dendritic cells. As a part of the vertebrate innate immune system monocytes also infl ...
which differentiate into dendritic cells. The dendritic cells pick up the antigen, carry it to lymph nodes
A lymph node, or lymph gland, is a kidney-shaped organ of the lymphatic system and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. They are major sites of lymphocytes that includ ...
, and stimulate T cells and B cells
B cells, also known as B lymphocytes, are a type of white blood cell of the lymphocyte subtype. They function in the humoral immunity component of the adaptive immune system. B cells produce antibody molecules which may be either secreted or ...
. It appears to contribute to induction of a good Th2
The T helper cells (Th cells), also known as CD4+ cells or CD4-positive cells, are a type of T cell that play an important role in the adaptive immune system. They aid the activity of other immune cells by releasing cytokines. They are considere ...
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, nor is it useful when the antigen is peptide-based.
Safety
In the 1960s and 1970s it was speculated that aluminium was related to various neurological disorders, including Alzheimer's disease
Alzheimer's disease (AD) is a neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in remembering recent events. As ...
. Since then, multiple epidemiological
Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in a defined population.
It is a cornerstone of public health, and shapes policy decisions and evid ...
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.
Neural disorders were found in experiments on mice motivated by Gulf War illness
Gulf War syndrome or Gulf War illness is a chronic and multi-symptomatic disorder affecting military veterans of both sides of the 1990–1991 Persian Gulf War. A wide range of acute and chronic symptoms have been linked to it, including fatigu ...
(GWI). Aluminum hydroxide injected in doses equivalent to those administered to the United States military, showed increased reactive astrocytes, increased apoptosis
Apoptosis (from grc, ἀπόπτωσις, apóptōsis, 'falling off') is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes (morphology) and death. These changes includ ...
of motor neurons and microglial proliferation within the spinal cord and cortex.
References
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
Effect of ageing on properties of polynuclear hydroxyaluminum cations
A second species of polynuclear hydroxyaluminum cation, its formation and some of its properties
{{DEFAULTSORT:Aluminium Hydroxide
Aluminium compounds
Amphoteric compounds
Antacids
Hydroxides
Inorganic compounds
Phosphate binders