Aluminium hydroxide
[CAS# 21645-51-2]

Identification

• Classification: API >> Digestive system medication >> Acid and gastric mucosal protective drugs
• Name: Aluminium hydroxide
• Molecular Formula: Al(OH)₃
• Molecular Weight: 78.00
• CAS Registry Number: 21645-51-2
• EC Number: 244-492-7
• SMILES: [OH-].[OH-].[OH-].[Al+3]

Properties

• Density: 2.40
• Water solubility: insoluble

Safety Data

• Hazard Symbols: GHS07 Warning
• Hazard Statements: H319
• Precautionary Statements: P305+P351+P338

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Eye irritation	Eye Irrit.	2	H319
Specific target organ toxicity - single exposure	STOT SE	3	H335
Skin irritation	Skin Irrit.	2	H315
Acute hazardous to the aquatic environment	Aquatic Acute	1	H400
Chronic hazardous to the aquatic environment	Aquatic Chronic	1	H410
Specific target organ toxicity - single exposure	STOT SE	3	H336Aerosols

Discovory and Applicatios

Aluminum hydroxide, with the chemical formula Al(OH)₃, is a versatile compound that plays an important role in a variety of industrial, medical, and environmental applications. Its discovery dates back to early studies of aluminum compounds, and it remains an essential material in a wide range of fields today.

The discovery of aluminum hydroxide is closely tied to the history of aluminum itself. In the early 19th century, scientists began to isolate aluminum from aluminum ores, leading to the identification of various aluminum compounds, including aluminum hydroxide. One of the first important discoveries was made by German chemist Friedrich Wöhler in 1827, who isolated aluminum by reducing anhydrous aluminum chloride with potassium. During this period, the precipitation of aluminum hydroxide from aqueous aluminum salt solutions was also observed and studied.

Aluminum hydroxide is amphoteric, meaning it reacts with both acids and bases. It appears as a white crystalline powder and has several allomorphs, including gibbsite, bayerite, and Nordstrandite. It has a relatively low solubility in water, but can dissolve in both acidic and alkaline solutions to form aluminates or aluminum salts, respectively.

One of the main uses of aluminum hydroxide is as a raw material for the production of aluminum metal. Bauxite is refined into alumina (aluminum oxide) through the Bayer process, and aluminum hydroxide is an intermediate product of the process. The Bayer process involves dissolving bauxite in sodium hydroxide, precipitating aluminum hydroxide, and then calcining to obtain aluminum oxide.

In addition to its role in aluminum production, aluminum hydroxide is used as a flame retardant for various materials such as plastics, rubber, and textiles. When heated, it decomposes to release water, which helps cool the material and dilutes the flammable gases, thereby reducing the spread of fire. This property makes it a valuable additive in fireproof materials and coatings.

Aluminum hydroxide is widely used in the pharmaceutical industry, especially as an antacid to neutralize stomach acid and relieve symptoms of heartburn, indigestion, and peptic ulcers. It works by reacting with hydrochloric acid in the stomach to form aluminum chloride and water, thereby increasing the pH of the stomach contents. Aluminum hydroxide is also used as an adjuvant in vaccines, enhancing the immune response to the vaccine antigen.

In water treatment, aluminum hydroxide plays an important role as a coagulant. It is used to remove impurities from water, causing suspended particles to aggregate into larger particles, which can then be easily filtered out. This process is essential for producing clean drinking water and treating wastewater.

In addition, aluminum hydroxide is used to treat industrial wastewater and remove phosphates from water bodies, helping to control algae blooms and improve water quality.

While aluminum hydroxide is generally considered safe for use in a variety of applications, it must be handled with care to avoid inhaling dust, which can irritate the respiratory system. In medical applications, long-term use of antacids containing aluminum hydroxide can lead to phosphate depletion and should be monitored to prevent potential side effects.