Studies on the precipitation and separation of nonsucrose substances in juice purification

Based on laboratory and factory-scale studies, this paper quantifies the colloid-chemical reactions during juice purification. Particular attention is given to the properties affected by the choice of the preliming temperature and the physical and chemical consequences for juice quality. For the first time, it is possible to quantitatively describe relationships, hitherto in part only qualitatively identified, as, for instance, the effect of alkalinity-determining nonsucrose substances on the location of the optimal flocculation point. Similarly, a critical light is thrown on the negative consequences of the carbonatation sludge concentrate return to preliming practized in many sugar factories for filtration-related reasons. The return negatively affects the purity and colour of the thin juice, and its discontinuance resulted in measurably stronger main liming reactions. The pH value and alkalinity management of the first carbonatation related to the conduct of the preliming operation. However, the chemically optimal pH values of the two juice purification stages may differ substantially in some cases. Nonobservance of the optimal pH value in the first carbonatation leads to higher colorant and lime salt contents and also reduces the purity of the thin juice. Finally, the relationships between the colorant adsorption and desorption behaviour of calcium carbonate and between the preliming temperature and the colour level and colorant groups of the thin juice are described.