Sodium sulfate
A cheap, versatile salt used in detergents and paper pulping.
Sodium sulfate, also called sodium sulphate or sulfate of soda, is an inorganic compound with the formula Na₂SO₄. It exists in several hydrated forms, all of which are white solids that dissolve easily in water. The decahydrate form is a major commodity chemical, produced at about 6 million tonnes per year, and is mainly used as a filler in powdered laundry detergents and in the Kraft process for paper pulping.
There are three main forms. Anhydrous sodium sulfate occurs naturally as the rare mineral thénardite and is used as a drying agent in organic synthesis. The heptahydrate is very rare. The decahydrate, known as the mineral mirabilite or Glauber's salt, is widely used in industry.
The decahydrate was named Glauber's salt after the Dutch-German chemist Johann Rudolf Glauber, who discovered it in Austrian spring water in 1625. He called it *sal mirabilis* (miraculous salt) because of its medicinal use as a laxative, a role it served until more advanced alternatives appeared in the 1900s. However, J. Kunckel later claimed it was already used as a secret medicine in Saxony in the mid-1500s. In the 1700s, Glauber's salt became a raw material for making soda ash (sodium carbonate) by reacting it with potash. As demand for soda ash grew, the supply of sodium sulfate had to increase, leading in the 1800s to the Leblanc process, which produced synthetic sodium sulfate as a key intermediate.
Chemically, sodium sulfate is a typical ionic sulfate with electrostatic bonding. Its sulfate ions in solution readily form insoluble sulfates when treated with barium or lead salts, as in the reaction Na₂SO₄ + BaCl₂ → 2 NaCl + BaSO₄. It is unreactive toward most oxidizing or reducing agents. At high temperatures, it can be converted to sodium sulfide via carbothermal reduction (e.g., heating with charcoal): Na₂SO₄ + 2 C → Na₂S + 2 CO₂. This reaction was used in the now-defunct Leblanc process. Sodium sulfate also reacts with sulfuric acid to form sodium bisulfate: Na₂SO₄ + H₂SO₄ ⇌ 2 NaHSO₄. It has a moderate tendency to form double salts. Unlike potassium and ammonium sulfates, which form many stable alums, sodium sulfate only forms alums with aluminum (NaAl(SO₄)₂, unstable above 39 °C) and chromium (NaCr(SO₄)₂). Other double salts include Na₂SO₄·3K₂SO₄ (the mineral aphthitalite), 3Na₂SO₄·CaSO₄, 3Na₂SO₄·MgSO₄ (vanthoffite), and NaF·Na₂SO₄. The reaction of sodium sulfate w
- annual_production
- 5.5 to 6 million tonnes
- main_form
- decahydrate (Glauber's salt)
- discoverer
- Johann Rudolf Glauber (1604–1670)
- discovery_year
- 1625
- natural_mineral
- mirabilite
- anhydrous_mineral
- thénardite
- major_use
- filler in powdered home laundry detergents
Lore & Background
The decahydrate of sodium sulfate is known as Glauber's salt after the Dutch–German chemist and apothecary Johann Rudolf Glauber, who discovered it in Austrian spring water in 1625. He named it sal mirabilis (miraculous salt) because of its medicinal properties; the crystals were used as a general-purpose laxative until more sophisticated alternatives came about in the 1900s. However, J. Kunckel later alleged that it was known as a secret medicine in Saxony already in the mid-16th century.
In the 18th century, Glauber's salt began to be used as a raw material for the industrial production of soda ash (sodium carbonate), by reaction with potash (potassium carbonate). Demand for soda ash increased, and the supply of sodium sulfate had to increase in line. Therefore, in the 19th century, the large-scale Leblanc process, producing synthetic sodium sulfate as a key intermediate, became the principal method of soda-ash production.
Two thirds of the world's production of the decahydrate is from the natural mineral form mirabilite, for example as found in lake beds in southern Saskatchewan. About one third is produced as a by-product of other chemical processes, such as hydrochloric acid production via the Mannheim or Hargreaves processes, or from neutralization of surplus sodium hydroxide by sulfuric acid.
Reader's Guide
Sodium sulfate is significant as a major commodity chemical, with annual production of 5.5 to 6 million tonnes, almost exclusively as the decahydrate. Its largest use is as a cheap filler in powdered home laundry detergents, consuming about 50% of world production. It is also essential in the Kraft process of paper pulping for making highly alkaline sulfides. Historically, it was a key intermediate in the Leblanc process for soda ash production, which drove its large-scale manufacture in the 19th century. The compound has unusual solubility characteristics: its solubility in water rises more than tenfold between 0 °C and 32.384 °C, where it reaches a maximum, and this temperature serves as an accurate reference for thermometer calibration. Natural sources, mainly mirabilite from lake beds, supply two thirds of production, while chemical by-products supply the rest. Despite its low cost (US pricing at $30 per tonne in 1970, up to $130 for better grades), its use in detergents is waning. The compound also has a measurable residual entropy at absolute zero, attributed to its ability to distribute water rapidly.
Did You Know?
- The decahydrate of sodium sulfate is known as Glauber's salt, discovered by Johann Rudolf Glauber in Austrian spring water in 1625.
- Sodium sulfate's solubility in water rises more than tenfold between 0 °C and 32.384 °C, where it reaches a maximum of 49.7 g/100 mL.
- Two thirds of the world's production of the decahydrate comes from the natural mineral mirabilite, found in lake beds in southern Saskatchewan.
- Sodium sulfate is unreactive toward most oxidizing or reducing agents, but at high temperatures it can be converted to sodium sulfide by carbothermal reduction.
More in Sodium Compounds 1-24
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