CaSO₄ - white pigment, gypsum and HCl from CaCl₂,
waste from soda ash production

Method of manufacturing of technically pure hydrochloric acid and other chemicals using waste from soda production, Patent App. P-280653, 19.07.1989, B. Borkowski, J. Król-Bogomilski

1. Calcium chloride, the second product in the Solvay method can be used in the chemical industry to reach calcium sulfate - white pigment, gypsum and hydrochloric acid (or gaseous HCl) in a simple industrial unit process.

   
   
   

2. The reaction proceeds at the temperature not exceeding 100°C, according to the equation:
   
   CaCl₂ + H₂SO₄ → CaSO₄ + 2HCl

   
   
   

3. Calcium chloride that is the second product of the Solvay process should be dissolved in water. Then one should add the 20°Be hydrochloric acid to this solution.

   
   
   

4. Concentrated sulfuric acid H₂SO₄ should be added to this solution dropwise.

   
   
   

5. During this reaction the solution should be continuously mixed and cooled down to 20°C.

   
   
   

6. The 20°Be hydrochloric acid is obtained in this reaction in the same reactor. This is the first variant.

   
   
   

7. The sulfate CaSO₄ is washed with a diluted solution of Na₂CO₃ and filtered off or centrifuged. Then one can use it as white pigment. One can also manufacture gypsum from this product.

   
   
   

8. Hydrochloric acid can contain a small amount of calcium salts but it is sufficiently pure for many technical applications and uses.

   
   
   

9. However, there is also a second variant; We can dissolve gaseous hydrogen chloride HCl in the saturated brine.

   
   
   

10. Hydrochloric acid may be also obtained by the well known reaction, using NaCl and concentrated sulphuric acid. However, that reaction requires heating to the temperature of about 600°C. It may be also obtained in the reaction of H₂ with Cl₂, but the temperature of that reaction is 2400°C. It is important that the reaction with CaCl₂ does not require heating. On the contrary, the mixture should be cooled.

    
    
    

11. See another page: Waste calcium chloride as a source of economic possibilities, Ma.E. Bogdan Borkowski and Dr. Jerzy Król-Bogomilski, Chemik, 43 (7), 181, (1990), (in Polish).

    
    
    

12. See also the other page: Method of manufacturing of technically pure sodium bicarbonate, Polish Patent, , Bogdan Borkowski and Jerzy Król-Bogomilski.