Abstract—Research results concerning struvite (MgNH4PO4∙6H2O, MAP – Magnesium Ammonium Phosphate) reaction crystallization process from phosphorus mineral fertilizer industry wastewater with the use of magnesium and ammonium ions are presented. Wastewater of pH < 4 contained 0.445 mass % of phosphate(V) ions and impurities: aluminium, calcium, copper, iron, potassium, magnesium, titanium, zinc, fluosilicate, fluoride and sulphate(VI) ions. Laboratory tests were carried out in temperature 298 K, both under stoichiometric conditions and at 20% excess of magnesium ions in relation to phosphate(V) and ammonium ions feed concentrations. Original continuous DTM (Draft Tube Magma) type crystallizer with internal circulation of suspension driven by jet pump fed with compressed air was used. Effect of pH and mean residence time of suspension in a crystallizer on the product crystals quality was determined. Product crystals of mean size from ca. 23 to ca. 40 μm were manufactured. The largest struvite crystals, of acceptable homogeneity, were produced at 20% excess of magnesium ions, pH 9 and for mean residence time elongated up to 3600 s. Concentration of phosphate(V) ions decreased from 0.445 mass % in a feed to 9.0∙10–4 mass % in a postprocessed mother liquor. In a product, besides main component – struvite, also amorphous calcium phosphate(V) (ACP) was detected, accompanied with hydroxides of some metal impurities present in wastewater.
Index Terms—Struvite, industrial wastewater, continuous reaction crystallization, continuous DTM crystallizer, jet pump, compressed air, product quality, phosphorus recycling.
N. Hutnik, A. Kozik, A. Mazienczuk, and A. Matynia are with Faculty of Chemistry, Wroclaw University of Technology, Wroclaw, Poland (e-mail: nina.hutnik@pwr.edu.pl, anna.kozik@pwr.edu.pl, agata.mazienczuk@pwr. edu.pl, andrzej.matynia@pwr.edu.pl).
K. Piotrowski is with Department of Chemical Engineering and Process Design, Silesian University of Technology, Gliwice, Poland (e-mail: krzysztof.piotrowski@polsl.pl).
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Cite: Nina Hutnik, Anna Kozik, Agata Mazienczuk, Krzysztof Piotrowski, and Andrzej Matynia, "Recovery of Struvite from Phosphorus Mineral Fertilizer Industry Wastewater in Continuous Jet Pump Crystallizer," International Journal of Chemical Engineering and Applications vol. 7, no. 1, pp. 36-41, 2016.
