Description
Aluminum hydroxide is a metal salt with amphoteric properties. It occurs in nature in the composition of some minerals such as gibbsite, bayerite, nordstrandite and doyleite; However, aluminum hydroxide together with aluminum oxide hydroxide (AlO(OH)) and aluminum oxide or alumina (Al2O3) construct the main part of the aluminum ore bauxite. In the manufacturing line, bauxite is dissolved in sodium hydroxide at temperature near 270°C and aluminum hydroxide is precipitated from the solution. Newly precipitated product forms gels but it will crystallize over time. Aluminum hydroxide gel have remarkable applications in different fields.
In the field of pharmaceuticals, aluminum hydroxide is the best known antiacid prescribed in treatment of stomach ulcers, heartburn and dyspepsia. The advantage of this compound over the other antiacid medicines returns to insolubility of aluminum hydroxide in stomach fluid so it does not enhance the pH above 7 and prevent excess acid secretion from stomach parital cells. Furthermore, it neutralizes the abnormal acidity in stomach due to its amphoteric nature.
As a phosphate binder, aluminum hydroxide is an effective medicine for control hyperphosphatemia in patients with kidney failure; In these patients, phosphate is accumulated in blood because their kidney does not able to filter and excrete phosphate from blood. But oral aluminum hydroxide gels can decrease phosphate absorbtion into blood through binding to phosphate in the intestine.
Aluminum salts are also used as pharmaceutical excipients in the formulation of some buffered analgesics to help their active substance dissolve effectively; Among NSAIDs, acidic compounds such as ibuprofen, diclofenac and aspirin need aluminum hydroxide in their dosage form in order to have better release from the formulation and reach to the blood stream. Al(OH)3 creates a neutral micro-environment in the stomach so that the drug substance could be released faster and to higher amount; This buffering property of aluminum hydroxide limits the local adverse effects of NSAIDs on the gastrointestinal mucosa.
As an adjuvant, aluminum hydroxide is used in several human and veterinary vaccines, toxoids and allergen injectants. These aluminum hydroxide-containing componds not only stimulate humoral and cellular immune system but also it stabilizes the vaccine formulation during storage and prevents the protein vaccine from precipitation or attachment to the container because Al(OH)3 efficiently absorbs protein molecules.
Recently aluminum hydroxide gel has found wonderful application as flocculants in water purification.
In the field of polymer technology, aluminum hydroxide is used as fire-retardant filler. This colorless compound disintegrates at about 180 °C, soaks up a huge amount of heat from the reaction and releases off water vapour. It serves also as a smoke suppressant in the process of some polymers including polyesters, acrylics, ethylene vinyl acetate, epoxies, polyvinyl chloride (PVC) and rubber.
