Isolation and characterisation of scale and turbid particles in beet sugar processing and the quality of granulated sugar

The objective of this work is to unveil the nature of scale and of particles responsible for turbidity in white beet sugar. Different techniques such as scanning electron microscopy (SEM) and X-ray diffraction (XRD) were applied for identification of the structure of scale and turbid particles. Results clearly showed that sugar turbidity is mainly constituted of fine crystals of calcium oxalate dihydrate (COD). These turbid particles were found comparable to the scale observed in the last effects of evaporation station. The role of anti-scale agents was studied. It was found that the chelating of calcium by anti-scales prevents the formation of calcium oxalate in evaporators. However, this chelating is temporary and the problem posed by the precipitation of oxalate particles is delayed to the crystallisation step where it was identified as responsible for stored syrup precipitate and granulated sugar turbidity.