Anhydrous sodium sulfate is a salt of sulfuric acid. It is a white, hygroscopic solid that has a density of 2.664 grams per cubic centimetre. Sodium sulfate is widely used as an inert drying agent in organic solutions. This compound is also used in the manufacture of paperboard and Kraft paper. The compound is also used in the dyeing of textiles.
Sodium sulfate has a melting point of 884 degrees Celsius, which makes it insoluble in ethanol and water. Sodium sulfate is an important raw material for the production of sodium sulfide. Sodium sulfate is also used in the manufacturing of glass. In the glass industry, sodium sulfate removes small air bubbles from the molten glass.
Sodium sulfate decahydrate is a very high-density substance, forming a thick deposit layer on its surface. When it is hydrated, the crystal changes to an anhydrous liquid. Sodium sulfate decahydrate has a heat of fusion of 252 kJ/kg. Sodium sulfate has been proposed to store heat in passive solar heating systems.
In the US, the Kraft process is the largest use of sodium sulfate. During this process, organics present in the “black liquor” are burned to produce heat. The heat is then supplied to the pulp to hydrate it. Other uses of sodium sulfate in the US include sizing fabrics, in the production of synthetic detergents and as a mordant in the printing industry.
Sodium sulfate is one of the world’s most widely produced compounds, with about 6 million tonnes of the substance being produced annually. Half of the production is from natural sources. Almost all of the remaining production is as a by-product of chemical processes.