Hong Yu

Mechanisms, thermodynamics and kinetics of composite fouling of calcium oxalate and amorphous silica in sugar mill evaporators—A preliminary study

Abstract Deposition of amorphous silica (SiO 2 ) and calcium oxalate monohydrate (COM) on the calandria tubes of evaporators cause serious processing problems in many cane sugar mills. Previous studies on scale formation have concentrated on fouling of individual compounds and the development of inhibiting methods for each component. Since SiO 2 and COM co-exist in sugar mill evaporators, this paper investigates the mechanisms and behavior of composite fouling of COM and SiO 2 in binary systems. Batch tests conducted at different pH (6–8) and temperatures (60–80°C) show that the presence of SiO 2 in the supersaturated solutions of COM decreased the precipitation rate of COM and as such increased COM solubility. However, the presence of COM in the supersaturated solutions of SiO 2 accelerated SiO 2 polymerization and lowered the level of initial silica supersaturation required for polymerization. The formation of COM–SiO 2 complexes is used to propose the mechanism for the co-precipitation of SiO 2 and COM.