There are 2 major different types of Sodium sulphate, natural and synthetic. The natural Sodium sulphate in decahydrate form also called as mineral mirabilite, and in the anhydrous form also called as mineral thenardite; while the synthetic form is produced by several industrial processes.
1. Natural Sodium Sulphate
2. Sodium Sulphate derived from chemical processes
Sodium Sulphate produced from chemical processes can be differentiated into 4 types based on the production processes :
1. Hydrochloric acid production
2. Viscose/rayon production
3. Sodium dichromate production
4. Laboratory synthesis
Sodium sulphate is widely used chemical commodities, mostly in the following applications :
1. Soap & Detergent industry
2. Pulp & paper industry
3. Glass industry
4. Textile dyeing industry
5. Feed additives – feed grade
A. Hydrochloric acid production
There are 2 available processes to produce sodium sulphate during the hydrochloric acid production. The first process is called the Mannheim process, when sulphuric acid is added to sodium chloride : 2 NaCl + H2SO4 → 2 HCl + Na2SO4 The second process is called the Hargreaves process when sulphur dioxide is added to sodium chloride in the presence of oxygen and water : 4 NaCl + 2 SO2 + O2 + 2 H2O → 4 HCl + 2 Na2SO4 The sodium sulphate produced by these 2 processes is called as salt cake.
B. Viscose/rayon production
In the production process of viscose fiber, sodium sulphate produced as a side product. Hence it is named as sodium sulphate viscose by product or rayon grade based on the production process of the main product which is viscose fiber. Sodium sulphate produced by this process has better grade than salt cake.
C. Sodium dichromate grade
Besides 2 major production of sodium sulphate using above 2 processes, it can also be obtained as a by product from the production process of sodium dichromate when sulphuric acid is added to sodium chromate.
2 Na2CrO4 + H2SO4 → Na2Cr2O7 + Na2SO4 + H2O
D. Laboratory synthesis
Sodium sulphate can be produced from the laboratory synthesis using following methods : 2 NaOH (aq) + H2SO4 (aq) →Na2SO4 (aq) + 2 H2O (l) This method is also applied on large scale production in the production of viscose. Another method used in the laboratory synthesis of sodium sulphate as follows : 2 NaHCO3 + MgSO4 →Na2SO4 + Mg(OH)2 + 2 CO2
A. Soap and Detergents
Sodium sulphate is used in powder detergents as filler to replace the use of phosphates, which were traditionally used as fillers in powder detergents. 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. It is also used to reduce surface tension during the usage of the detergents and increase the solubility of the detergents in the water.
B. Pulp & paper industry
Sodium Sulphate is used in manufacturing of pulp in Kraft process also known as sulphate process. 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. The process might be more properly called the sulphide process. It is used in treating all the long-fibered woods.
C. Glass industry
Sodium sulphate is used in glass industry in order to provide the necessary alkali base and because it is cheaper than soda ash, which is the standard source of alkali. Sodium sulphate prevents scum formation in the molten glass during refining, and also fluxes the glass. Also acts as a fining agent in molten glass, removing small air bubbles and imperfections during the blowing and casting processes.
D. Textile dyeing industry
Sodium sulphate plays an important role in reactive dyeing by improving the affinity of the dyestuff towards the fiber and acceleration of the dyestuff’s association. Sodium sulfate is used as a levelling agent where it reduces the negative charges on fibers. By doing so, it allows dyes to penetrate the textiles evenly and effectively.
E. Feed additives
The feed grade of sodium sulphate can be used in the feed additives industry. It can be used as additives in the animal diet, for monogastrics and ruminants. It helps to improve the absorption and utilization of nitrogen and other nutrients in the feed. Also, the presence of sodium in ruminants feed is needed for saliva production and for pH control of rumen.