Reaction crystallization of struvite in a continuous draft tube magma (DTM) crystallizer with a jet pump driven by recirculated mother solution

Reaction 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 298 K assuming stoichiometric conditions. Struvite crystals of mean size L-m from 4 to 22.4 mu m were produced depending on pH (pH from 9 to 11) and mean residence time of suspension in a crystallizer vessel (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 7.15.10(-9) m/s (pH 9, 900 s) to 1.16.10(-9) m/s (pH 11, tau 3600 s). Nucleation rate changed within the 9.3.10(8) - 9.0-10(9) 1/(sm(3)) range. Crystal product of the best formed crystals, which maximal sizes reached 90 mu m while content of crystals of sizes below 3 mu m was ca. 12%, corresponded to pH 9 and mean residence time of suspension in a crystallizer 3600 s. (C) 2012 Published by Elsevier Ltd. Selection under responsibility of the Congress Scientific Committee (Petr Kluson)