A Solubility Model for Calcium Oxalate Formation in a Sugar Mill

Abstract THIS paper describes laboratory studies that investigated the solubility product of calcium oxalate in the presence of water and sucrose at different temperatures, pH, and sucrose concentrations. The products obtained from these precipitation studies were examined by X-ray powder diffraction and scanning electron microscopy. A correlation was derived which states that the solubility product of calcium oxalate decreases with increasing temperature and with increasing sucrose concentration, but increases with increasing pH. This solubility model showed good agreement with the situation in those factories examined, in which increasing amounts of calcium oxalate were progressively formed throughout the evaporator set. X-ray powder diffraction and scanning electron microscopy indicated that the main calcium oxalate phases formed were calcium oxalate monohydrate and calcium oxalate trihydrate. Minute amounts of calcium oxalate dihydrate crystals were also detected at sucrose concentrations of 40% and 50%.