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Bayuseno, Athanasius P.; Schmahl, Wolfgang W. (December 2020): Thermal decomposition of struvite in water: qualitative and quantitative mineralogy analysis. In: Environmental Technology, Vol. 41, No. 27: pp. 3591-3597
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Struvite (MgNH4PO4 center dot 6H(2)O) is a potential fertilizer mineral that can be obtained from wastewaters. When the ambient temperature changes, struvite may decompose in water and other phosphate-bearing minerals form instead. The wet decomposition may include complex mineralization, as the struvite crystal structure releases both water molecules and ammonia. An in-situ x-ray measurement for the wet transformation of the struvite is needed to get insight into the mineral formed and into the influence of the water temperature on the decomposition/remineralization. In this study, the X-ray diffraction (XRD) sample holder containing struvite and water in a sealed condition was heated to temperatures of 55 to 120 degrees C for 24 h. Later the still sealed sample holder was exposed to the X-ray beam with the Debye-Scherrer transmission technique, and the diffraction pattern was analyzed by the XRD Rietveld method. With increasing temperature (<100 degrees C), struvite first dehydrated to dittmarite (MgNH4PO4 center dot H2O). Moreover, a decomposition of struvite into an amorphous form of magnesium hydrogen phosphate has occurred as the XRD background increased dramatically and showed a structured profile with very broad intensity maxima. Furthermore, struvite transforms into dittmarite, newberyite, and bobierrite when the sample was heated above 100 degrees C. The outcome of this work is expected to add knowledge on the instability of struvite, which may occur in the fields of the wastewater treatment and in the bio-mineralization in the urine of animals and humans.