The influence of impurities on calcium phosphate floc structure and size in sugar solutions

• Non-sucrose impurities affect macro-floc network structures in sugarcane juices.
• High aconitic acid content in sugar juice affect the abilities of flocs to remove impurities.
• X-rays diffraction techniques were used to identify micro-structural changes of flocs.
• Sugarcane trash impurities increased the electrical double layer of juice particles.

Settling, dewatering and filtration of flocs are important steps in industry to remove suspended solids and improve subsequent processing of the aqueous system. The influence of non-sucrose impurities (Ca2+, Mg2+, phosphate and aconitic acid) on the calcium phosphate floc structure (scattering exponent, Sf), size and shape were examined in synthetic and authentic sugar juices using X-ray diffraction techniques. In synthetic juices, Sf decreases with increasing phosphate concentration to values where loosely bound and branched flocs are formed. These types of flocs are effective for the removal of suspended colloidal particles. Ca2+ and Mg2+ ions, and aconitic acid did not affect Sf increasing concentration, although the floc size significantly decreased with increasing aconitic acid concentration, thereby reducing the ability of the flocs to remove particles. In authentic juices, the flocs structures were marginally affected by increasing proportions of non-sucrose impurities. However, optical microscopy indicated the formation of well-formed macro-floc network structures in sugar cane juices containing lower proportions of non-sucrose impurities. These structures are better placed to remove suspended particles in sugar solutions.