Sodium hydroxide, also known as caustic soda and lye is a highly caustic compound and alkali that decomposes proteins at ordinary ambient temperatures and may cause severe chemical burns. It is highly soluble in water and readily absorbs moisture and carbon dioxide from the air. Worldwide production in 2004 was approximately 60 million tonnes, while demand was 51 million tonnes.
Sodium hydroxide is also widely used in pulping of wood for making paper or regenerated fibres. Along with sodium sulphide, sodium hydroxide is a key component of the white liquor solution used to separate lignin from cellulose fibres in the sulphate process. It also plays a key role in several later stages of the process of bleaching the brown pulp resulting from the pulping process.
Sodium hydroxide is sometimes used during water purification to raise the pH of water supplies. Increased pH makes the water less corrosive to plumbing and reduces the amount of lead, copper and other toxic metals that can dissolve into drinking water.
Cements, mortars, concretes and grouts
Sodium hydroxide is used in some cement mix plasticisers. This helps homogenise cement mixes, preventing segregation of sands and cement, decreases the amount of water required in a mix and increases workability of the cement product, be it mortar, render or concrete.
Sodium hydroxide is frequently used as an industrial cleaning agent where it is often called “caustic”. It is added to water, heated, and then used to clean process equipment, storage tanks, etc. It can dissolve grease, oils, fats and protein-based deposits. It is also used for cleaning waste discharge pipes under sinks and drains in domestic properties.
Food uses of sodium hydroxide include washing or chemical peeling of fruits and vegetables, chocolate and cocoa processing, caramel colouring production, poultry scalding, soft drink processing.