PURPOSE: To improve the purification efficiency by adding an aqueous solution of NaHCO3 to a crude aqueous solution of NaCl, carrying out the precise filtration and then treating the resultant filtrate with chelate resins.
CONSTITUTION: An aqueous solution of NaHCO3 at 5-6wt.% concentration is added to crude salt water taken out of a raw salt dissolving vessel and the pH is regulated to 7-8. The crude salt water is then passed through a precise filter to separate and remove suspended substances in the salt water. The obtained salt water containing hardness impurities such as Ca, Sr or Mg at hundreds of ppm is subsequently passed through ≥2 chelate resin columns arranged in series at a prescribed superficial velocity. The salt water regulated to slight alkalinity is primarily purified in the first chelate resin column and an aqueous solution of NaOH or Na2CO3 is added thereto according to the kind of hardness impurities in the second chelate resin column to regulate the pH of the salt water to 8-11. Thereby, secondary purification is carried out and the concentration of the hardness impurities is reduced to several ppm or below. The purified salt water is then fed to an electrolytic cell by an ion exchange membrane method. The chelate resins through which the salt water is passed are regenerated by a well-known method for use.
HINO TAKIO
YAMAGUCHI KAZUMICHI
KISHI TAKEMICHI
