Carbonatation

Field of application

Sugar industry.

Description of techniques, methods and equipment

Carbonatation is the introduction of milk of lime (calcium hydroxide) and carbon dioxide gas (CO2) into a liquid to form calcium carbonate and to precipitate and remove impurities. The effect of lime and CO2 is the precipitation of insoluble calcium salts, the flocculation of colloidal components, the chemical degradation of other molecules such as invert sugar and amides, and the absorption of non sugars on precipitated calcium carbonate. Lime and CO2 are normally produced in lime kilns by the thermal dissociation of limestone. CO2 can also be stored as liquefied gas.
Any non-sugar components contained in the raw sugar juice after extraction from the beet make the subsequent stages in the sugar process impossible to perform. Therefore, the raw juice must be purified in order to allow further processing. This is achieved by continuously adding milk of lime and carbon dioxide from the lime kiln to precipitate most of the non-sugars. The product after filtration contains calcium carbonate and the non-sugars and is used in agriculture as a liming material to improve the structure of arable soil and to regulate soil acidity. Sugar factory lime may also be used for site recovery (for example filling quarry ditches) and for producing bricks or cement. (For aspects relating to lime kilns, see reference document on ‘Best Available Techniques in the Cement and Lime Manufacturing Industries’.)