Patent ID: 8273321

Claim:
A method of preparation of an analytical grade sodium chloride from a rock salt sample comprising: (a) dissolving one part of the rock salt in three parts of deionized water and heating the mixture to 65° C. until the rock salt dissolves; (b) filtering the solution in step (a) through filter paper and discarding the precipitate on the filter; (c) concentrating the filtrate in step (b) by heating the solution from step (b) to a concentration of 1.25 to 1.26 g/L to precipitate sodium chloride crystals; (d) separating sodium chloride crystals in step (c) by centrifugation; (e) dissolving the crystals from step (d) using three parts of deionized water to one part of the crystals; (f) measuring the concentration of total sulfates in the solution in step (e); (g) adding barium carbonate in 1:1 molar ratio to the concentration of sulfates in solution from step (f) and heating for 15 minutes at 80° C. to precipitate sulfates as barium sulfate; (h) making a solution of one part of sodium hydroxide and two parts of sodium carbonate by weight in sufficient quantity of deionized water to dissolve both and adding in a ratio of one part of this solution to ten parts of the solution in step (g) with continued heating and stirring for 45 minutes to remove trace metals; (i) adding a 1% polyacrylamide solution in deionized water in equal volume to the solution volume in step (h) to precipitate calcium, magnesium and barium; (j) separating the filtrate by filtering the precipitate in step (i) with filter paper of 0.45 micron pore size; (k) add a 4% sodium hydroxide solution in one to one volume ratio to the filtrate of step (j) to bring the pH of the filtrate to between 9 and 10; (l) passing the solution in step (k) through a weak acid cation exchange resin; (m) passing the solution from step (l) through a strong basic anion exchange resin; (n) heating the solution from step (m) at 85° C. to crystallize sodium chloride; (o) drying the crystals from step (n) at 115° C.