aluminum hydroxide application

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 and hydromagnesite are used similarly It decomposes at about 180 °C (356 °F), 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, acrylics, ethylene vinyl acetate, epoxies, PVC and rubber. 

Precursor to Al compounds

Aluminium hydroxide is a feedstock for the manufacture of other aluminium compounds: speciality calcined aluminas, aluminium sulfate, polyaluminium chloride, aluminium chloride, zeolites, sodium aluminate, activated alumina, and aluminium nitrate.

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 in gas purification, and catalyst supports.

Pharmaceutical

Under the generic name "algeldrate", aluminium hydroxide is used as an antacid 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, heartburn or dyspepsia. Such products can cause constipation, because the aluminium ions inhibit the contractions of smooth muscle cells in the gastrointestinal tract, slowing peristalsis 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 (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 aluminium hydroxide is included as an adjuvant in some vaccines (e.g. anthrax vaccine). 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", 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, an immunological danger signal. This strongly attracts certain types of monocytes which differentiate into dendritic cells. The dendritic cells pick up the antigen, carry it to lymph nodes, and stimulate T cells and B cells. It appears to contribute to induction of a good Th2 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.