Struvite was sepd. by reactive crystn. from aq. solns. of PO43- (0.2-1.0% by mass), SO42- (500-5000 mg/kg), Mg2+ and NH4+ ions at 298 K, pH 9 or 11 and residence time 900-3600 s to det. the rates of crystal growth (4.23.10(-9)-1.67.10(-8) m/s) and nucleation 7.5.10(7)-1.6.10(9) 1/(s.m(3)). The presence and gradual increase of SO42- concn. in crystallizer feed were of disadvantage for the process kinetics while the lower concn. of PO43- and a Mg ion excess as well as elongation of mean residence time were of advantage for the process kinetics.