Abstract
Reaction crystallization of struvite in water solutions containing 0.20 mass % of phosphate(V) ions by magnesium and ammonium ions addition was investigated experimentally. Process was carried out in DTM type crystallizer with liquid jet pump device in 298 K assuming stoichiometric conditions. Struvite crystals of mean size Lm 5.2-23.0 μm were produced depending on pH (9-11) and mean residence time of suspension in a crystallizer τ (900-3600 s). Under these conditions linear growth rate of struvite crystals (SIG MSMPR kinetic model) decreased 2-time with the increase in pH and 3-time with the elongation of mean residence time of crystal suspension from 7.11×10-9 m/s (pH 9, τ900 s) to 1.65×10-9 m/s (pH 11, τ3600 s). Nucleation rate varied within the 7.9×108-1.8×1010 1/(sm3) limits. Struvite product of maximal linear size exceeded 100 μm with 10 vol. % of < 3 μm fraction corresponded to pH 9 and τ3600 s.
Highlights
In supersaturated water solutions of magnesium phosphate(V) in presence of ammonium ions—within the 7 < pH < 11 range and at room temperature—the magnesium ammonium phosphate hexahydrate MgNH4PO4·6H2O, struvite, MAP precipitates [1,2]
In modern processes of phosphorus recycling controlled reaction crystallization of struvite is an effect of contacting the magnesium and ammonium ions with preliminary purified secondary phosphorus resources, covering mainly municipal, industrial liquid wastes or liquid manure rich in phosphate(V) ions [3]
Experimental results concerning reaction crystallization of struvite from diluted water solutions of phosphate(V) ions in a continuous DTM type crystallizer with internal circulation of suspension driven by liquid jet pump providing ascending flow of suspension in a mixing chamber are presented [5,13]
Summary
Unique hydraulic arrangement of a jet pump system provides intensive circulation of suspension, its good intrinsic mixing without generation of excessive tensions, influencing favourably the mass and heat transfer processes in a crystallizer. Construction of this apparatus makes removal of suspension of representative crystal size distribution (CSD) possible. Experimental results concerning reaction crystallization of struvite from diluted water solutions of phosphate(V) ions in a continuous DTM type crystallizer with internal circulation of suspension driven by liquid jet pump providing ascending flow of suspension in a mixing chamber are presented [5,13]. The most simplified model of a continuous mass crystallization kinetics in MSMPR crystallizer— SIG (Size Independent Growth) model—assuming linear growth rate of all crystals constant regardless their individual sizes, was applied [12]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
