Sodium Metabisulfite (Na₂S₂O₅) 7681-57-4

Sodium Metabisulfite (Na₂S₂O₅), also known as sodium pyrosulfite, is a white to yellowish crystalline powder with a molecular weight of 190.11 g/mol. It is highly soluble in water and releases sulfur dioxide when dissolved. It is widely used as a food preservative, water treatment chemical, and industrial reducing agent.

Sodium metabisulfite (E223) is used as a preservative in dried fruits, wine, beer, fruit juices, and other food products. It releases sulfur dioxide, which prevents enzymatic browning, inhibits microbial growth, and acts as an antioxidant. It helps maintain color, flavor, and shelf life. However, some individuals are sensitive to sulfites, and products containing sulfites must be labeled accordingly.

In water treatment, sodium metabisulfite serves as an effective dechlorination agent, removing excess chlorine and chloramines from treated water. It is widely used in reverse osmosis pretreatment, boiler feed water, and wastewater treatment to protect downstream equipment from chlorine corrosion. It also functions as an oxygen scavenger in boiler water systems.

In gold mining, sodium metabisulfite is used to precipitate gold from aqua regia and other gold-bearing chloride solutions. When added to a gold chloride solution, SO₂ gas released from Na₂S₂O₅ reduces dissolved gold ions to metallic gold powder. This is a widely used method for recovering gold in small to medium-scale refining operations.

Sodium metabisulfite should be stored in a cool, dry, well-ventilated area in tightly sealed containers away from moisture, heat, and acids. Upon contact with acids, it releases toxic sulfur dioxide gas. It is sensitive to moisture and oxidation. Under proper storage conditions in sealed containers, shelf life is 12 months. Avoid storing near oxidizers, acids, or in humid environments.