Understanding the causes of calcium carbonate crystal growth and inhibition during the carbonatation refining of raw sugars

The inhibitory activity of soluble and insoluble starch (0-550 ppm/Brix) in factory raw sugars were investigated using simulated refinery carbonatation clarification reactions to underpin what causes the undesirable formation of CaCO3 crystal fines (≤5 μm). It was found that CaCO3 crystal growth was inhibited mostly by soluble starch by forming starch-Ca2+ metal complexes. Insoluble (granular) starch, however, had a greater affinity for inhibiting CaCO3 crystallization because it retained the carbonatation clarification reactants, i.e., Ca2+and OH−, in the granule interior which caused granule gelatinization and increased viscosity of the melt liquor. Causes for poor press filterability and CaCO3 fines using raw sugar melts were found to be complex and attributed to the combinatorial roles that both soluble and insoluble starch have, among other impurities. More studies are now warranted at the carbonatation refinery to correlate processing characteristics with raw sugars quality attributes to underpin how each impurity impedes carbonatation.