A crystallizer with fluidized bed and mixing suspension zone and with internal circulation forced by jet pump fed with a mother soln. (vol. 1.2 L) was used for pptn. of MgNH4PO4 center dot 6H(2)O from phosphate fertilizers-contg. industry wastewater (pH <4) with Mg and NH4 ions. The wastewater contained phosphate(V) ions (0.445% by mass) and impurities (Al, Ca, Cu, Fe K, Mg, Ti, Zn, fluorosilicate, fluoride and SO4 ions). The tests were carried out at 298 K under stoichiometric conditions at 20% excess of Mg ions in relation to the amount of PO4 and NH4 ions. Medium sized struvite crystals (19-31 mu m) were obtained. Largest size and satisfactory homogeneity of the crystals were obtained at 20% excess of Mg ions, pH 9 and residence time 3600 s. The linear crystal growth rate was 3.7.1(09) m/s, according to the size independent growth, mixed suspension mixed product removal model. The concn. of PO4 ions decreased from 0.445% by mass in a feed solution down to 19.2 mg/kg in the postprocessed mother soln. The product contained struvite (65-75% by mass) as well as some amts. of amorphous Ca-3(PO4)(3) and impurities.