Carbonatation

[1] The carbon dioxide in the air reacts with the alkali in the cement and makes the pore water more acidic, thus lowering the pH.

It involves the introduction of limewater (milk of lime - calcium hydroxide suspension) and carbon dioxide enriched gas into the "raw juice" (the sugar rich liquid prepared from the diffusion stage of the process) to form calcium carbonate and precipitate impurities that are then removed.

Carbonatation involves the following effects: The target is a large particle that naturally settles rapidly to leave a clear juice.

The non-sugar solids are incorporated into the calcium carbonate particles and removed by natural (or assisted) sedimentation in tanks or clarifiers.

it may undergo pH adjustment with soda ash and addition of sulfur ("sulfitation") prior to the next stage which is concentration by multiple effect evaporation.