Reaction Crystallization of Struvite in a Continuous Draft Tube Magma (DTM) Crystallizer with a Jet Pump Driven by Recirculated Mother Solution

AbstractReaction crystallization of struvite from water solutions containing 1.0 mass % of phosphate(V) ions by means of magnesium and ammonium ions action was investigated experimentally. The process was carried out in a DTM type crystallizer with liquid type jet pump in temperature 298K assuming stoichiometric conditions. Struvite crystals of mean size Lm from 4 to 22.4μm were produced depending on pH (pH from 9 to 11) and mean residence time of suspension in a crystallizer vessel (τ from 900 to 3600 s). In such process conditions linear growth rate of struvite crystals, calculated with SIG MSMPR kinetic model, decreases 2-time with the increase in pH level and 3-time with the elongation of mean residence time of suspension in a crystallizer, namely from 7.15 x 10–9 m/s (pH 9, τ 900 s) to 1.16 x 10–9 m/s (pH 11, τ 3600 s). Nucleation rate changed within the 9.3 x 108 – 9.0 x 109 1/(sm3) range. Crystal product of the best formed crystals, which maximal sizes reached 90μm while content of crystals of sizes below 3μm was ca. 12%, corresponded to pH 9 and mean residence time of suspension in a crystallizer 3600 s