Lime-soda ash softening

[Lan123]

What is the reason behind the carbon dioxide addition prior to non-carbonate hardness removal, but after the carbonate hardness removal, in the Lime-Soda ash process?

Please don't get confused with the the carbon dioxide addition that is done during recarbonation process.

 

[bimr]

Carbon dioxide or acid is fed to lower the pH to prrvent post precipitation in the downstream filter or water softener. See the attachment.