Naslov
Transformation of struvite into newberyite experienced by microscopy

Autori
Babić-Ivančić, Vesna ; Kontrec, Jasminka ; Kralj, Damir ; Brečević, Ljerka

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Proceedings of the 6th Multinational Congress on Microscopy with European Extension / Milat, Ognjen ; Ježek, Davor - Zagreb : Hrvatsko mikroskopijsko društvo, 2003, 499-500

Skup
6th Multinational Congress on Microscopy with European Extension

Mjesto i datum
Pula, Hrvatska, 01.06.2003. - 05.06.2003

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
Struvite; Newberyite; Transformation; Microscopy

Sažetak
Among magnesium phosphates, magnesium ammonium phosphate hexahydrate, MgNH4PO4×6H2O, commonly known as struvite, is of great practical relevance. Apart from being a frequent constituent of renal and vesicle calculi, especially those related to urinary tract infections, this compound also appears naturally as a mineral (guano) and often occurs in scale deposits in the wastewater treatment industry. Due to its importance, struvite has been studied from different points of view and many of its physical and chemical properties have been described. Nevertheless, for a better understanding of the processes in which both struvite and newberyite, MgHPO4×3H2O, are involved, a more systematic physical chemical investigations of struvite precipitation have been undertaken. Thus, the influence of the initial reactant concentrations, initial pH, temperature and ageing time on the spontaneous precipitation of struvite has already been completed [1]. In this work, the kinetics of transformation of struvite into newberyite has been studied, under different initial conditions of temperature (25 °C and 37 °C), pH (5.0Ł pHi ł9.0), and reactant concentrations (c(PO43-)i = c(NH4+)i = 1×10-1 and 4×10-2 mol dm-3, c(Mg2+)i = 2.3×10-1 and 4×10-2 mol dm-3). The progress of transformation was followed both in solid and liquid phases. In the liquid phase, pH was recorded as a function of time. Figure 1 shows a typical pH vs. time curve. During the transformation process, the composition of precipitate (solid phase) was analysed by FT-IR spectroscopy. It was found, that from the initially supersaturated solution (Fig. 1a), a mixture of struvite and some newberyite precipitates (Fig. 1b). Then, the struvite crystals start to disolve, thus transforming into newberyite (Fig. 1c). The final product of this process was pure newberyite (Fig. 1d). An acceleration of the transformation process was achieved by increasing the initial reactant concentrations and the temperature. In order to get more information about changes in the solid phase during the transformation process, a special attention was paid to the observation of changes in morphology. Figure 2 shows optical micrographs of the samples taken in the time intervals shown in Fig. 1. The abrupt fall of pH after mixing the reactant components (Fig. 1a) denotes the formation of a mixture of the rod-like crystals of struvite and the tiny crystals of newberyite (Fig. 2a). With the progress of transformation, the rod-like crystals gradually disappear from the system and the formation of new tiny crystals is evident (Figs. 2b, c). Finally, only small crystals of newberyite remain (Fig. 2d). Dendritic crystals of struvite transform into newberyite in the identical way. FIG. 1: pH as a function of time during the transformation of struvite into newberyite at 25 oC. FIG.2: Optical micrographs of the samples taken during the transformation of struvite into newberyite in the time intervals shown in Fig. 1. (a, b, c) mixture of the rod-like crystals of struvite and the tiny crystals of newberyite ; (d) small crystals of newberyite. REFERENCE [1] V. Babić-Ivančić, J. Kontrec, D. Kralj, Lj. Brečević, Croat. Chem. Acta, 75 (2002) 89. Corresponding author˘s e-mail address: ivancic@rudjer.irb.hr I ACKNOWLEDGE RECEIVING THE STUDENT GRANT WHICH WAS PARTIALLY SUPPORTED BY THE FEICO COMPANY.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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