STUDIES ON THE INTERACTIONS OF CALCIUM OXALATE MONOHYDRATE AND SILICA SCALE COMPONENTS

The current knowledge gap for scale control is due to the fact that conventional studies involve single-component systems and so do not adequately address the mechanisms associated with multi-component (i.e. composite) systems which exist in chemical industries. This paper describes composite fouling characteristics of calcium oxalate monohydrate (COM) and amorphous silica (SiO2) in aqueous solutions under conditions similar to those of sugar mill evaporators. To complement these studies, a number of clarification experiments were carried out on 4th effect syrup. Results are presented for the fouling resistances of COM, SiO2 and COM/SiO2 mixtures and the physicochemical properties of the scale. The amount of composite scale deposited and the scale texture is dependent on the initial COM and SiO2 concentrations and their supersaturation ratios. The results also show that the presence of oxalate ions affects SiO2 solubility. The implication of these results is that the variability in scaling rates that occurs during the season and between seasons may well be dependent on the COM and SiO2 ratios.