Principles of juice purification

The raw juice as obtained by juice extraction of sugar beet cossettes contains dissolved and insoluble impurities (nonsugars) which need to be removed as much as possible to enable a cost-effective production of the wanted quality of white crystal sugar. The most commonly used purification approach of beet raw juice is the so-called classical liming process. The aim and principles of the different successive process steps in juice purification will be outlined in this paper. The purification principles comprise several chemical-physical reactions of particular nonsugars in the juice which are initiated at first by the addition of milk of lime to the raw juice in preliming and main liming. Through injection of the carbon dioxide produced in the lime kiln in the 1st carbonatation calcium ions precipitate as calcium carbonate, which is then used as filter aid to remove by sedimentation and/or filtration the formed slurry. The remaining surplus of lime salts are finally removed in the 2nd carbonatation which after filtration results in a clear thin juice.