Effect of initial solution pH on solubility and morphology of struvice crystals

Abstract

Struvite is known to form a hard scale in specific areas of wastewater treatment plants. Besides causing problems; struvite can also be used as a fertilizer. Good and reliable solubility data is essential for controlling the crystallisation of struvite. One of the important factors that affect the crystallisation of struvite is solution pH. Therefore, this study was undertaken to investigate initial solution pH on the solubility and morphology of struvite crystals. Methodology used in this study was to dissolve struvite crystals in aqueous solutions at various initial pH. The equilibrium solution pH of struvite dissolution was found to stay within the range of 8 to 11. This pH can be used to predict struvite formation in the solution. A study was also made to investigate of the morphology of the struvite crystals were affected when they were exposed to solutions at different initial pH values. The original struvite crystals and other residual crystals after the solubility test were examined by both SEM and EDS. It was found that the shapes of crystals were amorphous, rhombohedral, and hexagonal for initial pH 3, 7, and 11, respectively, and pH 5 and 9 platelets and spherical resulted, respectively.