Recovery of Phosphate(V) Ions from Wastewaters of Different Chemical Compositions

摘要

The experimental results concerning continuous removal of phosphate(V) ions with the use of magnesium and ammonium ions from diluted water solutions containing also selected inorganic impurities are presented and discussed. Chemical compositions of these artificial solutions approached typical ions proportions observed in real liquid wastes from mineral fertilizer industry. The research was carried out in a DT MSMPR crystallizer with internal circulation of suspension assuming stoichiometric proportions between PO4 3-, Mg2+and NH4+ions. It was concluded, that with the increase in impurities concentrations in a feed mean product crystal size decreased by ca. 26%, from 39.5 to 29.1 μm at pH 9 and mean residence time of suspension in a crystallizer working volume τ 900 s. Homogeneity within the population of product crystals was unsatisfactory (CV above 100%). Increase in environment's pH up to 11 resulted in additional decrease in mean product crystal size by ca. 65% (to 10.3 μm). Size-homogeneity within the population of product crystals, however, increased (CV ca. 77%). Elongation of mean residence time of suspension in a crystallizer up to τ 3600 s resulted in clear improvement of crystalline product quality. Mean size of struvite crystals increased even to 73.3 μm, while CV coefficient decreased to ca. 60%. On the basis of kinetic calculation results (SIG MSMPR kinetic model) it was concluded, that linear growth rate of struvite crystals varied within the 5.00×10-9 - 2.31×10-8 m/s range, while nucleation rate changed within the 3.7×107 - 1.1×1010 1/(s m3) range.