Characterization of physical properties of struvite crystals grown in gel medium by XRD and FTIR

Magnesium ammonium phosphate (MAP) hexahydrate (MgNH4PO4.6H2O), commonlyknown as struvite is a whitish to brownish rare mineral crystal with high fertilizerproperties due to the concurrent presence of magnesium, nitrogen and phosphorouscontents known to be essential for the growth of crops and plants. Struvite crystals werefirst observed as a nuisance in a wastewater treatment plants in Hamburg, Germany in1939. Struvite stones have been recognized as one of the main constituent of renal calculiof both animals and human. Further and deep study of struvite precipitates and crystalshas absorbed lots of interest amongst the scientists and researchers. However, the study ofstruvite crystals formation in the gel media as it mimics the real situation in humankidneys is of greater importance. In the present study struvite crystallization in silica gelhas been investigated. The effects of different operational conditions like pH (6 to 9) andmolar ratios on struvite crystals size has been studied and reported. For this purposestraight tubes containing sodium metasilicate (SMS) with 1.04 specific gravity (SG) and1M ammonium dehydrogen phosphate (ADP) which forms the gel medium and 1M/2MMg acetate were made. The gel pH was controlled by ADP addition to SMS solution andmagnesium acetate were added drop by drop to gel surface after 2 days that the gel forms.The calculation of the results of the XRD test with Sherrers formula revealed that thesamples prepared with 2M magnesium acetate totally have bigger crystal size. The crystalsize ranges from 0.72 to 7.4 nm while the biggest crystals were reported at samples withpH of 8. The XRD results were analyzed by Xpert highscore software proving theproduced crystals are pure struvite crystals, however the FTIR spectrum peaksreassuringly confirms the XRD test results.

Keywords:

Struvite , crystallization , gel growth , silica gel , fertilizer , wastewater treatment