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Aluminium Hydroxide

 
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Aluminium hydroxide
 
 
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Aluminium hydroxide, Al(OH)3, is the most stable form of aluminium
Aluminium

Aluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13....
 in normal conditions. It is found in nature as the mineral gibbsite
Gibbsite

Gibbsite, Al3, is one of the mineral forms of aluminium hydroxide. It is often designated as ?-Al3 . It is also sometimes called hydrargillite ....
 (also known as hydrargillite) and its three, much more rare, polymorphs: bayerite, doyleite and nordstrandite. Closely related are aluminium oxide hydroxide
Aluminium oxide hydroxide

Aluminium hydroxide oxide or aluminium oxyhydroxide is found as one of two well defined crystalline phases, which are also known as the minerals boehmite and diaspore....
, AlO(OH), and aluminium oxide
Aluminium oxide

Aluminium oxide is an amphoteric oxide of aluminium with the chemical formula 23. It is also commonly referred to as alumina or aloxite in the mining, ceramic and materials science communities....
, Al2O3, differing only by loss of water. These compounds together are the major components of the aluminium ore
Ore

An ore is a type of Rock that contains minerals such as gemstones and metals that can be extracted through mining and refined for use. Samples of ore in the form of exceptionally beautiful crystals, exotic layering visible when sectioned or polished or metallic presentations such as large nuggets or crystalline formations of metals suc...
 bauxite
Bauxite

Bauxite is the most important aluminium ore. It consists largely of the minerals gibbsite Al3, boehmite ?-AlO, and diaspore a-AlO, together with the iron oxides goethite and hematite, the clay mineral kaolinite and small amounts of anatase TiO2....
.






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Aluminium hydroxide, Al(OH)3, is the most stable form of aluminium
Aluminium

Aluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13....
 in normal conditions. It is found in nature as the mineral gibbsite
Gibbsite

Gibbsite, Al3, is one of the mineral forms of aluminium hydroxide. It is often designated as ?-Al3 . It is also sometimes called hydrargillite ....
 (also known as hydrargillite) and its three, much more rare, polymorphs: bayerite, doyleite and nordstrandite. Closely related are aluminium oxide hydroxide
Aluminium oxide hydroxide

Aluminium hydroxide oxide or aluminium oxyhydroxide is found as one of two well defined crystalline phases, which are also known as the minerals boehmite and diaspore....
, AlO(OH), and aluminium oxide
Aluminium oxide

Aluminium oxide is an amphoteric oxide of aluminium with the chemical formula 23. It is also commonly referred to as alumina or aloxite in the mining, ceramic and materials science communities....
, Al2O3, differing only by loss of water. These compounds together are the major components of the aluminium ore
Ore

An ore is a type of Rock that contains minerals such as gemstones and metals that can be extracted through mining and refined for use. Samples of ore in the form of exceptionally beautiful crystals, exotic layering visible when sectioned or polished or metallic presentations such as large nuggets or crystalline formations of metals suc...
 bauxite
Bauxite

Bauxite is the most important aluminium ore. It consists largely of the minerals gibbsite Al3, boehmite ?-AlO, and diaspore a-AlO, together with the iron oxides goethite and hematite, the clay mineral kaolinite and small amounts of anatase TiO2....
. Freshly precipitated aluminium hydroxide forms gel
Gel

A gel is a solid, gelatin material that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute crosslinked system, which exhibits no flow when in the steady-state....
s, which is the basis for application of aluminium salts as flocculants
Flocculation

Flocculation is a process where a solute comes out of solution in the form of floc or flakes. The action differs from Precipitation in that the solute coming out of solution does so at a concentration generally below its solubility limit in the liquid....
 in water purification. This gel crystallizes with time. Aluminium hydroxide gels can be dehydrated (e.g., with the utility of water-miscible non-aqueous solvents like ethanol) to form an amorphous aluminium hydroxide powder, which is readily soluble in acids. Heat-dried aluminium hydroxide powder is known as activated alumina and is used in gas purification, as a catalyst support and an abrasive.

Production

Aluminium hydroxide is an intermediate product in the Bayer process
Bayer process

The Bayer process is the principal industrial means of refining bauxite to produce alumina.Bauxite, the most important ore of aluminium, contains only 30-54% alumina, Al2O3, the rest being a mixture of silica, various iron oxides, and titanium dioxide....
. In this process, bauxite
Bauxite

Bauxite is the most important aluminium ore. It consists largely of the minerals gibbsite Al3, boehmite ?-AlO, and diaspore a-AlO, together with the iron oxides goethite and hematite, the clay mineral kaolinite and small amounts of anatase TiO2....
 is dissolved in hot sodium hydroxide
Sodium hydroxide

Sodium hydroxide , also known as lye, caustic soda and sodium hydrate, is a caustic metallic Base . Sodium hydroxide forms a strong alkaline solution when dissolved in a solvent such as water, however, only the hydroxide ion is basic....
 solution, and insolubilities are filtered off. On cooling, aluminium hydroxide precipitates. The aluminium hydroxide is further calcined to give alumina, which may be smelted in the Hall-Héroult process
Hall-Héroult process

The Hall-H?roult process is the major industrial process for the production of aluminium. It involves dissolving alumina in molten cryolite, and electrolysing the solution to obtain pure aluminium metal....
 in order to produce aluminium.

Chemistry

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.

Aluminium hydroxide is amphoteric. It dissolves in acid
Acid

An acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion Activity greater than in pure water, i.e....
, forming Al(H2O)63+ or its hydrolysis
Hydrolysis

Hydrolysis is a chemical reaction during which one or more water are split into hydrogen and hydroxide ions which may go on to participate in further reactions....
 products. It also dissolves in strong alkali
Alkali

In chemistry, an alkali is a Base , Ionic compound salt of an alkali metal or alkaline earth metal Chemical element. Alkalis are best known for being Base s that dissolve in water....
, forming Al(OH)4-.

Pharmacology

Pharmacologically, this compound is used as an antacid
Antacid

An antacid is any substance, generally a Base or basic salt, which counteracts gastric acid. In other words, antacids are stomach acid neutralization ....
 under names such as Alu-Cap, Aludrox or Pepsamar. The hydroxide reacts with excess acid in the stomach, reducing its acidity. This decrease of acidity of the contents of the stomach may in turn help to relieve the symptoms of ulcers
Peptic ulcer

A peptic ulcer, also known as ulcus pepticum, PUD or peptic ulcer disease, is an ulcer of an area of the gastrointestinal tract that is usually acidic and thus extremely painful....
, heartburn
Heartburn

Heartburn or pyrosis is a painful and burning sensation in the esophagus, just below the Sternum usually associated with regurgitation of gastric acid....
 or dyspepsia
Dyspepsia

Dyspepsia , popularly known as indigestion, meaning hard or difficult digestion, is a medical condition characterized by chronic or recurrent pain in the upper abdomen, upper abdominal fullness and feeling full earlier than expected when eating....
. It can also cause constipation and is therefore often used with magnesium hydroxide
Magnesium hydroxide

Magnesium hydroxide is an inorganic compound with the chemical formula Mg2. As a suspension in water, it may be referred to as Milk of Magnesia....
 or magnesium carbonate
Magnesium carbonate

Magnesium carbonate, MgCO3, is a white solid that occurs in nature as a mineral. Several hydrated and Base forms of magnesium carbonate also exist as minerals....
, which have counterbalancing laxative
Laxative

Laxatives are foods, compounds, or drugs taken to induce bowel movements or to loosen the stool, most often taken to treat constipation. Certain stimulant, lubricant, and saline laxatives are used to evacuate the Colon for rectum and bowel examinations, and may be supplemented by enemas in that circumstance....
 effects. This compound is also used to control phosphate (phosphorus) levels in the blood of people suffering from kidney failure.

Aluminium hydroxide is included as an adjuvant
Adjuvant

Adjuvants are pharmacology or immunology agents that modify the effect of other agents while having few if any direct effects when given by themselves....
 in some vaccine
Vaccine

A vaccine is a biological preparation that establishes or improves immunity to a particular disease.Vaccines can be prophylaxis , or Medication ....
s (e.g., Alhydrogel), since it contributes to induction of a good antibody
Antibody

Antibodies are gamma globulin proteins that are found in blood or other bodily fluids of vertebrates, and are used by the immune system to identify and neutralize foreign objects, such as bacterium and viruses....
 (Th2) response. However, it has little capacity to stimulate cellular (Th1) immune responses, important for protection against many pathogens.

Because the brain lesions found in Alzheimer's disease
Alzheimer's disease

Alzheimer's disease , also called Alzheimer disease, Senile Dementia of the Alzheimer Type or simply Alzheimer's, is the most common form of dementia....
 contain aluminium, there is concern that consumption of excess aluminium compounds may cause or contribute to the development of this and other neurodegenerative disease
Neurodegenerative disease

Neurodegenerative disease is a condition in which cells of the brain and spinal cord are lost. The brain and spinal cord are composed of neurons that do different functions such as controlling movements, processing sensory information, and making decisions....
s. In addition, elevated aluminium levels in blood, resulting from kidney dialysis with well water containing high aluminium, result in dementia
Dementia

Dementia is the progressive decline in cognition due to damage or disease in the body beyond what might be expected from normal aging. Although dementia is far more common in the geriatric population, it may occur in any stage of adulthood....
 that is similar to but probably different from that of Alzheimer's disease. However, this hypothesis is controversial.

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