Effects of Selected Inorganic Impurities Present in Real Phosphate(V)Solutions on the Quality of Struvite Crystals Produced in Continuous Reaction Crystallization Process

摘要

The experimental results concerning influence of selected ionic impurities present in phosphate(V) solutions (0.20 or 1.0 mass % of PO4 3-) on struvite crystals quality are presented and discussed. Influence of each from the following ions: Al3+, Ca2+, Cu2+, Fe2+, Fe3+, K+, Zn2+, F-, NO3 - and SO4 2- at its individually determined concentration in a solution feeding the continuous laboratory DT MSMPR type crystallizer was identified. Reaction crystallization process was carried out in temperature 298 K at pH 9, assuming mean residence time of suspension in a crystallizer working volume τ 900 s. Properly shaped struvite crystals of mean size Lm varied from 27.5 μm to 50.4 μm were produced depending on the feed composition. Impurity ions influenced size-homogeneity within the struvite crystals population significantly (CV from 73.9% to 98.5%), as well as their structure and shape. In the corresponding scanning electron microscope images practically all crystallographic forms of struvite were observed, including characteristic tubular crystal forms. In the crystal products manufactured in the presence of selected ions (mainly Al3+, Ca2+, Fe2+, Fe3+), besides struvite also hydroxides and phosphates(V) of these ions were confirmed with analytical methods.