Aluminium Hydroxide
Aluminium Hydroxide
Aluminium hydroxide is an inorganic compound represented by the chemical formula Al(OH)3. It is primarily found in nature as the mineral gibbsite, also known as hydrargillite, and exists in several polymorphic forms. Aluminium hydroxide is closely related to bauxite, an important ore of aluminium, which is utilized extensively in industrial processes.
Chemical Structure and Properties
Aluminium hydroxide is composed of aluminium cations and hydroxide anions. The hydroxide anion is a diatomic entity, consisting of one oxygen and one hydrogen atom bound covalently. The compound presents itself as a white, gelatinous substance that is amphoteric in nature, meaning it can act both as an acid and as a base.
Polymorphs
Aside from gibbsite, aluminium hydroxide has three additional polymorphs: bayerite, doyleite, and nordstrandite. These polymorphs differ in their crystalline structure and are less common compared to gibbsite.
Applications
Aluminium hydroxide is widely used in various applications, thanks to its properties.
- Flame Retardant: It is used as a flame retardant filler in plastics due to its ability to release water vapor when heated, which helps in suppressing flames.
- Antacid: In the pharmaceutical industry, aluminium hydroxide is used as an active ingredient in antacid formulations. It neutralizes stomach acid and is often combined with magnesium hydroxide to balance side effects.
- Water Purification: It plays a role as a coagulant in water purification processes, helping to remove impurities through precipitation.
Industrial Significance
The significance of aluminium hydroxide extends to its role in the production of aluminium metal. It is a precursor in the Bayer process, where it is dissolved in sodium hydroxide to form sodium aluminate, which is then precipitated to recover aluminium hydroxide. This process is crucial in refining bauxite into alumina, subsequently used to produce aluminium metal through the Hall-Héroult process.
Environmental and Health Aspects
In terms of environmental impact, aluminium hydroxide is considered less harmful. However, it should be handled with care in industrial settings to prevent dust inhalation. In medical applications, while generally safe, it can cause side effects such as constipation when used in excess.