Sodium Sulphate

Sodium sulphate Product

product1Sodium sulphate with formula Na2SO4 is an inorganic compound, 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.

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.

BRIEF OVERVIEW

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.

NATURAL OCCURRENCE

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.

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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 of Hydrochloric Acid production

The Mannheim and Hargreaves 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.

Mannheim Process

Owing 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

Textile

Textile production
Sodium sulphate plays an important role in reactive dyeing by improving the affinity of the dyestuff towards the fibre, acceleration of the dyestuff’s association and lowering its solubility. The presence of chlorine ion in the common salt may cause corrosion of the equipment. Hence, Sodium Sulphate is always preferred 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.

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Detergent

detergent production1. 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.

Glass

glass production
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

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 labor 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.

Product Identification

CAS No.497-19-8
Molecular formulaNa2SO4
SynonymsGlauber’s Salt
H.S. Code2833.11.00
PropertyUnitsValue
AppearanceWhite powder
Na2SO4%99.2(min)
NaCL%0.2(max)
Insoluble in water%0.2(max)
Feppm20
Water content%0.1(max)