Conductimetric study of struvite crystallization in water as a function of pH

The main objective of this work was to investigate the best pH for phosphorus removal from synthetic aqueous solutions using chemical precipitation of struvite, at constant temperature. The experimental approach, developed in the present study, consisted to precipitate struvite in synthetic wastewater containing PO43−, NH4+ and Mg2+ ions in an equal molar ratio, using a stirred tank with continuous monitoring by conductimetry, at 25 °C. Different laboratory experiments were used to evaluate the effects of pH in the range of 8.5 till 11.8, on size, shape, and purity of the precipitated crystals. Struvite crystals were characterized by Infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The phosphorus conversion rate was determined by spectrophotometric determination of residual phosphorus. The experimental results showed that pH 8.5 provided the best conditions for struvite crystal growth, being obtained a 98% phosphorus to phosphate conversion rate, for an initial concentration of 474 mg/L.