Sodium Sulphate

Sodium sulphate Product

Sodium sulphate with formula Na2SO4 is an inorganic compound,, it is also known as salts of sulfuric acid. White in color and high solubility in water is widely used chemical commodity. It is widely used by chemical industry and is also called as Glaubers salt, in its decahydrate form, known as the mineral mirabilite [discovered by Johann Rudolf Glaubers in 1625]. In its anhydrous form, known as mineral thenardite, it is used as a drying agent in organic synthesis. Anhydrous sodium sulphate occurs in arid environments as the mineral thenardite and it slowly turns to mirabilite in damp air.

Generally sodium sulphate is traded in there forms salt cake, Glauber’s salt and niter cake. In areas where the rainfall is very low sodium sulphate is called as white alkali in contrast to sodium carbonate , which is termed as black alkali on account of its corrosive action on vegetation.
When the sodium sulphate is form of salt cake, used in the manufacture of wood pulp by the sulphate process, plate glass, window glass.
Glauber’s salt is used in the industries involves dyeing, tanning and medicine, treatment of cattle.
Niter cake is used as a alternate for sulphuric acid for many purposes as in metal picking, absorbing ammonia and in production of fertilizers
Sodium Sulphate is an inorganic solid present in anhydrous and hydrate forms. It is a major commodity chemical widely applied in textile, detergent, glass and paper manufacturing. The demand for sodium sulphate is expected to witness strong growth in the near future. Global sodium sulphate market is expected to show stable growth mainly driven by Asia Pacific (China, Indonesia, India, South Korea, Malaysia, etc.) and Latin America regions (Brazil, Argentina, Mexico). Mexico and Spain were the world's main producers of natural sodium sulphate with Russia, USA and Canada following after. However in recent years china has been main producer of the same.


In tunnels, caves and covered spots, lavas, white coatings powders, efflorescence haves the traces of sodium sulphates, which are frequently observed. Granite and igneous rocks are rarely free from pyrites and other sulphides, these sulphides when they are exposed they were oxidized to sulphuric acid, which gives basic oxides, producing soluble suphates. They can be found in the areas where there is no outlets for water bodies which evaporates regularly forms these salts.Some of the places where we can see sodium sulphate deposits are lakes in Utah, western Canada, steppes in the Minussinsk and Abakansk, lakes Altai, beisk and Domoshakovo which are underlain by solid Glauber’s salt. There is a soda lake near Omsk fairly rich in sodium sulphate. Some traces can be found in the east side of Caspian Sea.


Sodium sulphate was discovered by Johann Rudolf Glauber who named it sal mirabilis (miraculous salt), because of its medicinal properties. Since the 18th century it began to be used in Soda Ash production due to the continuous demand.


The demand for sodium sulphate for export greatly stimulated the search for deposits of the natural salt. It occurs in nature as Glauber's salt, which is known as Mirabilite in its mineral form, and as the anhydrous sulphate, Thenardite. Sodium sulphate deposits result from high evaporation rates of ponded or seepage waters that contain dissolved minerals. In tunnels, caves, and covered spots in recent lavas, white coatings, powders, and efflorescence consisting largely of calcium and sodium sulphates are dissolved by rain waters furnishing sodium sulphate to drainage systems. Glauber's salt is a common constituent of efflorescence on clays in dry regions.

About half of the production of Sodium Sulphate is as a by-product in many industrial production processes such rayon, battery acids, hydrochloric acid production etc.

Manufacturing Process

Sodium chloride is treated with sulfuric acid in the Mannheim process. This reaction produces sodium sulfate(called the salt cake) and hydrogen chloride:
2 NaCl + H2SO4 → Na2SO4 + 2 HCl
Sodium sulfate is an intermediate of the Leblanc process.
Sodium sulfate has unusual solubility characteristics in water. Its solubility in water rises more than tenfold between 0 °C to 32.384 °C, where it reaches a maximum of 49.7 g/100 mL. At this point the solubility curve changes slope, and the solubility becomes almost independent of temperature. This temperature at 32.384 °C, corresponding to the release of crystal water and melting of the hydrated salt, serves as an accurate temperature reference for thermometer calibration.

About one third of the world's sodium sulfate is produced as by-product of other processes in chemical industry. Most of this production is chemically inherent to the primary process, and only marginally economical. By effort of the industry, therefore, sodium sulfate production as by-product is declining.
However, sodium sulfate is found abundantly as the mineral deposit mirabilite which forms naturally.

Natural Sources

Two thirds of the world’s Glauber’s salt production is from harvesting the natural deposits of minerals in the form of mirabilite. Mirabilite can be found in lake beds, around saline springs and along saline playa lakes. Playa lakes are dried lakes which used to contain a standing surface of water but have dried of as evaporation rates exceeded the refill rates. The floor of the dried lake containing the salts is know as a salt flat.

In 1990, Mexico and Spain were the world's main producers of natural sodium sulfate (each around 500,000 tonnes), with Russia, United States and Canada around 350,000 tonnes each. Natural resources are estimated at over 1 billion tonnes.

About half of the production of Sodium Sulphate is as a by-product in many industrial production processes such rayon, battery acids, hydrochloric acid production etc.

By-product of Viscose Fiber production:

Viscose rayon is produced worldwide with an annual production of millions of tons. Sodium sulphate is produced in large quantities by the viscose process. In the production step the wood pulp raw material is immersed in sodium hydroxide to convert it to alkaline cellulose. A solution of carbon disulfide is added to form cellulose xanthate. The crumbs are dissolved in sodium hydroxide to obtain a viscous solution called “viscose”.The sodium salt results from the acidification of the alkaline viscose by sulphuric acid, the acid and the salt being the uniform ingredients of the spin-bath liquor. The salt is extracted from the liquor further by the processes of filtration, evaporation, crystallization. Crystallization facilitates the removal of sodium sulphate from other chemicals and is further purified using calcination and centrifugation.

By-product Hydrochloric Acid production:

The Mannheim angreaves process are the other popular processes where sodium sulphate is obtained as a by-product. These processes are used by companies other than fiber manufacturers .Owning to the easy availability of sulphuric acid and salt, this is one of the cheaper processes for the production of sodium sulphate. The acid and salt are heated in a furnace, forming hydrochloric gas and sodium hydrogen sulphate. The sulphate paste is separated and heated at a high temperature with additional salt resulting in salt cake. The purity of salt cake is about 90-99%. This is further concentrated using different unit operations.

2 NaCl + H2SO4 → 2 HCl + Na2SO4

Hargreaves process:

In the Hargreaves process, salt is heated with sulphur dioxide gas, steam and oxygen in iron retorts. The complete conversion takes place in about 15-20 days of continuous process. When Sulphur dioxide is exhausted, the hydrochloric acid is recovered separately and salt cake is removed. This is then further processed for various applications.

4 NaCl + 2 SO2 + O2 + 2 H2O → 4 HCl + 2 Na2SO4


Sodium sulphate plays an important role in reactive dyeing by improving the affinity of the dyestuff towards the fiber, acceleration of the dyestuff’s association and lowering its solubility. The presence of gas particle within the common salt might cause corrosion of the instrumentation. Hence, sulfate is usually most popular over common salt.

Function of Sodium Sulphate in dyeing:

1.To drive dye into textile during the dyeing process in textile. 2.Use of sodium sulphate leads to maximum exhaustion of dye molecules during dyeing process in textile. 3.It is used as an electrolyte for migration, adsorption and fixation of the dyestuff to the cellulose material. In textile industry, sodium sulphate acts as a catalyst. The textile substrate and dye molecule has non-homogeneous characteristics, so it becomes difficult for them to combine with each other. In such cases, we require catalyst to facilitate dyeing action on fabric.


1. Sodium sulphate is used in powdered detergents as filler because phosphates, which were traditionally used as fillers in powder detergents. 2. Sodium Sulphate is added to change the consistency of the detergent, to make it more pourable, more soluble and to help it disperse evenly. 3. Sodium sulphate is added to make the detergent powder flow freely. Without it, the detergent would stick together and become one big block. 4. Sodium sulphate is widely used as desiccant which are able to bind multiple molecules of water, forming “hydrates”. This effectively locks up any moisture that enters the detergent, maintaining a dry, free-flowing powdered detergent.


1. Sodium sulphate is used in making bottle, sheet, and plate glass in order to provide the necessary alkali base and because it is cheaper than soda ash, which is the standard source of alkali. 2. Sodium sulphate prevents scum formation in the molten glass during refining, and also fluxes the glass. 3. Also acts as a fining agent in molten glass, removing small air bubbles and imperfections during the blowing and casting processes. 4. In making glass the several ingredients, such as sand, soda ash, salt cake, coke, and niter, are weighed out in the proper proportions, mixed in mixing machines, and transferred to the pots in furnaces heated by gas. 5. Glassmakers desire salt cake with less than 1 per cent of either sodium chloride or sulphuric acid, less than 0.4 % of iron and aluminium oxide, less than 0.5 % of matter insoluble in water, and less than 0.2 % of magnesium sulphate.

Paper and Pulp:

Sodium Sulphate is used in manufacturing of pulp in Kraft process. 1. The sulphate process of reducing wood to pulp is so named because it involves the use of sodium sulphate, but this substance is used only in making the sodium sulphide that is one of the active chemicals in the process, the other being sodium hydroxide. 2. The process might more properly be called the sulphide process. It is used in treating all the long-fibered woods. 3. As a matter of fact, however, sulphate pulp can be more easily bleached than soda pulp. The cost of labour in the sulphate process is slightly higher than in the soda process, on account of the smelting operation; on the other hand, the raw material is cheaper. 4. Salt cake for this process should be ground and should contain at least 95 per cent of anhydrous sodium sulphate.

Commodity Industry

Sodium sulfate is still used in the Kraft process for the manufacture of wood pulp in a reduced rate, due to advances in thermal efficiency of the process.

The glass industry provides another significant application for sodium sulfate, as second largest application in Europe. Sodium sulfate is used as a fining agent, to help remove small air bubbles from molten glass. It fluxes the glass, and prevents scum formation of the glass melt during refining.

Sodium sulfate is important in the manufacture of textiles, particularly in Japan, where it is the largest application. Sodium sulfate helps in "levelling", reducing negative charges on fibres so that dyes can penetrate evenly. Unlike the alternative sodium chloride, it does not corrode the stainless steel vessels used in dyeing.

Food industry

Sodium sulfate is used as a diluent for food colours, the E number additive E514.



Thermal storage

Sodium sulfate has a high heat storage capacity in its phase change from solid to liquid. This makes this material especially appropriate for storing low grade solar heat for later release in space heating applications. In some applications the material is incorporated into thermal tiles that are placed in an attic space while in other applications the salt is incorporated into cells surrounded by solar–heated water.

Product identification
CAS No.497-19-8
Molecular formulaNa2SO4
SynonymsGlauber’s Salt
H.S. Code2833.11.00
Appearance-White powder
Insoluble in water%0.2(max)
Water content%0.1(max)