Precipitation and Crystallization of Struvite from Synthetic Wastewater under Stoichiometric Conditions

Anna Kozik, Nina Hutnik, Krzysztof Piotrowski, Agata Mazienczuk, Andrzej Matynia

Silesian University of Technology, Department of Chemical & Process Engineering, M. Strzody Gliwice, Poland.
Wroclaw University of Technology, Faculty of Chemistry, Wybrzeze Wyspianskiego, Wroclaw, Poland.

DOI: 10.4236/aces.2013.34B004                

Abstract

Phosphate (V) ions were continuously removed from synthetic wastewater containing inorganic impurities using magnesium and ammonium ions. The product was magnesium ammonium phosphate (V) hexahydrate, struvite, MgNH₄PO₄ × 6H₂O. Research ran in stoichiometric conditions in DT MSMPR type crystallizer with internal circulation of suspension. Increase in process environment pH from 9 to 11 resulted in 3-time decrease of mean struvite crystals size (from 40.1 to12.6mm). Elongation of mean residence time of suspension in a crystallizer up to 3600 s resulted in improvement of the product quality. Mean size of struvite crystals enlarged up to50.2mm. Based on kinetic calculations results (SIG MSMPR model) it was concluded, that linear struvite crystal growth rate varied within 5.04 × 10^–9 – 1.69 × 10^{–8 m/s range, whereas nucleation rate within 1.4} × 10⁷ – 1.7 × 10¹⁰ 1/(s m³) limits. In solid product, besides struvite, also all impurities present in wastewater were identified analytically as hydroxides, phosphates and other salts.

Keywords

Struvite; Precipitation; Continuous Reaction Crystallization; Phosphate(V) Ions; Impurity Ions; Continuous DT MSMPR Crystallizer; Crystal Size Distribution; Kinetics

Conflicts of Interest

The authors declare no conflicts of interest.

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