Nucleation and Crystal Growth Rates of Struvite in DTM Type Crystallizer with a Jet-Pump of Descending Suspension Flow in a Mixing Chamber

Abstract

The kinetic data concerning reaction-crystallization of struvite from diluted water solutions of Mg²⁺, NH₄⁺ and PO₄^3- ions in a continuous DTM-type liquid jet-pump crystallizer with internal circulation of suspension are presented and discussed. The measurements were performed with the assumption of minimal value of unit power of a jet-pump’s feeding stream, providing thus a minimal level of internal circulation intensity. Nucleation and linear growth rates of struvite crystals were calculated on the basis of population density distributions of product particles. A mathematically convenient kinetic model for MSMPR crystallizer, making allowance for a size-dependent growth (SDG) phenomenon, was adopted for description of a complex process of precipitation integrated with crystals growth. It was concluded, that in the concentration range of magnesium ions in a feeding solution [Mg²⁺]_RM = 0.1-2.0 mass % and, in stoichiometric proportions, phosphate ions [PO₄^3-]_RM = 0.39-7.81 mass % as well as the ammonium ions [NH₄⁺]_RM = 0.074-1.48 mass %, the Rojkowski hyperbolic SDG kinetic model proved to be an equation the best statistically fitted to the own experimental data.