Aluminium hydroxide

About Aluminium hydroxide

Aluminium 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, aluminium hydroxide together with aluminium oxide hydroxide (AlO(OH)) and aluminium oxide or alumina (Al₂O₃) construct the main part of the aluminium ore bauxite. In the manufacturing line, bauxite is dissolved in sodium hydroxide at temperature near 270°C and aluminium hydroxide is precipitated from the solution. Newly precipitated product forms gels which can be more processed and dehydrated to generate amorphous aluminium hydroxide powder with great applications.

In the field of pharmaceuticals, aluminium 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 aluminium 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, aluminium 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 aluminium hydroxide powder can decrease phosphate absorbtion into blood through binding to phosphate in the intestine.

Aluminium 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.

In the field of polymer technology, aluminium 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 vapor. 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.

Finally, aluminium hydroxide powder is an intermediate for the other aluminium species like activated aluminas that have usage as absorbent in gas purification, desiccant and catalyst supports.