Formation and transformation of struvite and newberyite in aqueous solutions under conditions similar to physiological
The precipitation of magnesium phosphates in the system MgCl2-NH4H2PO4-NaOH-H2O was studied at a wide range of reactant concentrations at 37°C and an initial pHi of 7.4. Precipitates were aged for 24 h and characterized by means of optical and scanning electron microscopy, x-ray diffractometry, FT-IR spectroscopy and thermogravimetry. Struvite was found to precipitate in nearly the whole concentration region investigated. Pure newberyite and a mixture of struvite and newberyite were obtained in a narrow range only with a pH24 h<6.4. The transformation of struvite into newberyite was studied by following changes in the liquid and solid phases. Thus, the changes of pH and the content of struvite in the precipitate as a function of time were recorded. The influence of the initial pHi and temperature on the transformation process is discussed. Analysis of the experimental data suggests a solution mediated transformation process as a possible mechanism of struvite transformation.
KeywordsStruvite Newberyite Precipitation Transformation
We wish to thank Dr. Sc. Damir Kralj for useful discussions and Dr. Sc. Andreja Gajović for taking the SEM micrographs. This research has been sponsored by the Ministry of Science and Technology of the Republic of Croatia (Project no. 0098061).
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