Process for the joint production of sodium carbonate and sodium bicarbonate

Abstract

Process for the joint production of sodium carbonate and sodium bicarbonate crystals, according to which: a solid powder derived from sodium sesquicarbonate, having a mean particle diameter comprised between 0.1 and 10 mm is dissolved in water; the resulting water solution is introduced into a crystallizer, wherein a first water suspension comprising sodium carbonate crystals is produced; the first water suspension is subjected to a separation, in order to produce crystals comprising sodium carbonate on the one hand, which are valorized, and a mother liquor on the other hand; and a part of the mother liquor is taken out of the crystallizer and put into contact in, a gas liquid contactor, with a gas comprising carbon dioxide, in order to produce a second water suspension comprising sodium bicarbonate crystals, which are separated and valorized. A reagent powder comprising sodium bicarbonate crystals made by such process.

We claim: 
     
         1 . A method for reducing the amount of alkali lost in evaporative ponds which are fed with a purge liquor containing such alkali, comprising:
 contacting said purge liquor with a gas comprising carbon dioxide, said purge liquor being a part of a mother liquor taken out of a sodium carbonate crystallizer and comprising at least 175 g/kg sodium carbonate and at least 10 g/kg sodium chloride.   
     
     
         2 . The method according to  claim 1 , wherein the sodium carbonate content in the mother liquor is not more than 250 g/kg. 
     
     
         3 . The method according to  claim 1 , wherein the mother liquor does not contain more than 30 g/kg of sodium bicarbonate. 
     
     
         4 . The method according to  claim 1 , wherein contacting said purge liquor with a gas comprising carbon dioxide produces a water suspension comprising sodium bicarbonate crystals. 
     
     
         5 . The method according to  claim 4 , wherein sodium bicarbonate crystals are separated from the water suspension to form a second mother liquor. 
     
     
         6 . The method according to  claim 5 , wherein the second mother liquor is debicarbonated with vapor and then sent to a pond. 
     
     
         7 . A method for treating a purge stream containing sodium carbonate, comprising:
 treating said purge stream with gaseous carbon dioxide, said purge stream comprising at least 175 g/kg sodium carbonate and at least 10 g/kg sodium chloride.   
     
     
         8 . A method for extending the life of tailings ponds produced from a soda ash purge stream containing sodium carbonate, which method comprises treating said purge stream with gaseous carbon dioxide, wherein said purge liquor is a part of a mother liquor taken out of a sodium carbonate crystallizer and comprising at least 175 g/kg sodium carbonate and at least 10 g/kg sodium chloride. 
     
     
         9 . The method of  claim 8 , wherein the purge stream is treated prior to it being deposited in the tailings pond. 
     
     
         10 . The method according to  claim 1 , wherein said purge liquor comprises at least 20 g/kg sodium chloride. 
     
     
         11 . The method according to  claim 1 , wherein said purge liquor comprises at least 30 g/kg sodium chloride. 
     
     
         12 . The method according to  claim 5 , further comprising drying said sodium bicarbonate crystals. 
     
     
         13 . The method according to  claim 7 , wherein said purge stream comprises at least 20 g/kg sodium chloride. 
     
     
         14 . The method according to  claim 7 , wherein said purge stream comprises at least 30 g/kg sodium chloride. 
     
     
         15 . The method according to  claim 7 , wherein treating said purge stream with said gas comprising carbon dioxide produces a water suspension comprising sodium bicarbonate crystals; wherein sodium bicarbonate crystals are separated from the water suspension to form a second mother liquor; and wherein said sodium bicarbonate crystals are dried. 
     
     
         16 . The method according to  claim 8 , wherein said purge liquor comprises at least 20 g/kg sodium chloride. 
     
     
         17 . The method according to  claim 8 , wherein said purge liquor comprises at least 30 g/kg sodium chloride. 
     
     
         18 . The method according to  claim 8 , wherein treating said purge liquor with said gas comprising carbon dioxide produces a water suspension comprising sodium bicarbonate crystals; wherein sodium bicarbonate crystals are separated from the water suspension to form a second mother liquor; and wherein said sodium bicarbonate crystals are dried.