FIELD OF INVENTION:
The invention relates to cheaper method of purifying salt produced from scawater evaporation to remove impurities by washing it with solution of Sodium Carbonate commonly known as Soda Ash. This type of wash with Soda Ash solution not only saves huge cost hut also removes impurities in a better way than the conventional wash with brine and water.
BACKGROUND OF THE INVENTION:
At present, the impurities in the salt like Calcium, magnesium. Sulphate and insolvables result in considerable chemical consumption. Unless these impuritiesv are removed, the salt cannot be used for industrial consumption. The industries which use much salt, though they are washed for removal of impurities and sent by the suppliers, have to do further process of chemical treatment to remove finer impurities. At present the end user mdustries do the further process of purification to remove impurities by chemical treatment. The process not only involves huge cost but also consumes time in as much as the process is being done once again at the user level besides generating trade effluent. Hence a new methodology was developed whereby the salt will be washed with solution

of Sodium Carbonate which at one state reduces Calcium and Sulphate impurities to a great extent but also saves cost to a considerable extent.
DESCRIPTION OF THE INVENTION:
The salt produced from seawater evaporation contains impurities such as calcium, magnesium, sulphate and other insoluble. Tliesc impurities result in consumption of chemicals considerably. It also generates solid waste in Chloralkali industries where such salt is widely used. Of the above. Calcium is present mainly as Calcium Sulphate. Magnesium is present partly as Magnesnim Sulphate and Magnesium Chloride. Though Magnesium impurity can be removed by water wash, it is difficult to remove calcium by such washing. At present, Sulphate is removed by chemical treatent using Barium Carbonate in industries. This method of treatment is very expensive, The main object of this invention is to remove sulphate while the salt is in the crystal form itself using sodium carbonate. In order to avoid the duplication of the process to remove all impurities, mainly Sulphate, as well as to curtail cost to a considerable extent, a new method is invented. In this process, the salt produced from seawater evaporation is washed with water mixed with Sodium Carbonate. In this process, Calcium Sulphate gets converted to Calcium Carbonate and Sodium Sulphate as per the following chemical equation CaSO4 + Na2CO3 -> CaCO3 -> NaSO4

Part of the Calcium Carbonate gets bleached out and part is retained in the salt itself but
does not need further chemical treatment. The Sodium Sulphate will get leached out
during Soda Ash Water solution washing and subsequent water washing.
The process could be understood in a better way through the following example.
A salt produced from seawater evaporation with a volume of 22 meters length, 2 meters
breadth with 5.5 nieters height can be taken. It would contain approximately 200MT.
About 40 cubic meters of water is to be taken in a sump. 1000 Kgs of Soda Ash has to be
dissolved in the water. The Soda Ash solution thus prepared is pumped on the heap of
salt uniformly for over a period of 2 hours. Then, the same heap is washed by way of
spray with 30 cubic meters of fresh water and the water is allowed to seep through. After
this process, the impurities, especially the Calcium and Sulphate would be removed.
This process of removing sulphate using Sodium Carbonate in salt purification can be done even at the point of production of salt before crystallization in the field itself apart from the method of removion in the crystal stage

WE CLAIM
1. The claim for a method and process for purification / removing sulphate and
calcium in the Sodium Chloride salt which is being used as raw materials in various industries like Chloral kali Industries.
'L The claim as made in claim 1 wherein Sodium Carbonate is used to split Calcium Sulphate present in sodium chloride salt into Calcium Carbonate and Sodium Sulphate by Double Decomposition and thier removal subsequently.
3. The claim as made in claim 1 wherein converted Sodium Sulphate is removed from the Sodium Chloride Salt by water washing subsequent to Double decomposition.
4. The claim as made in claim 1 wherein the process of splitting Calcium Sulphate into Calcium Carbonate and Sodium Sulphate by using Sodium Carbonate is achieved even before the crystallization in the field itself in the processes of sodium Chloride salt.