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| Titel |
New Insights into Struvite Formation: Relevance for Phosphorus Recovery from Wastewaters |
| VerfasserIn |
Jörn Hövelmann, Christine V. Putnis, Tomasz M. Stawski, Rogier Besselink, Liane G. Benning |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250148284
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| Publikation (Nr.) |
 EGU/EGU2017-12527.pdf |
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| Zusammenfassung |
| The mineral struvite is a magnesium ammonium phosphate hexahydrate [MAP,
MgNH4PO4⋅6H2O] that is a common component of kidney stones [1] and a prime scale
forming mineral in sewage and wastewater treatment systems [2]. At present, struvite
formation is being widely investigated as a possible way to recover phosphorus (P) from
wastewater streams [3]. Such P-recovery approaches are highly attractive because struvite can
be used as a slow-release fertilizer and substitute for conventional fertilizers, thus
helping to reduce the environmental impact of excess P release into aquatic systems
and the demand on rock phosphate, whose resources are slowly but surely running
out.
Considering the relevance of struvite in such diverse and multidisciplinary fields like
biomineralization, and industrial and environmental technologies, it is not surprising
that numerous studies aim to elucidate its crystallization behaviour. Yet, a detailed
understanding of the early crystallization stages is still lacking although such knowledge
would help control and manipulate struvite precipitation reactions that are crucial in
these diverse systems and applications. In an attempt to fill this knowledge gap
we employed a set of in situ characterization techniques enabling us to directly
follow (i) the heterogeneous and (ii) homogeneous crystallization of struvite at
high spatial and temporal resolution. Firstly, by using atomic force microscopy
(AFM) in connection with a fluid cell, we imaged the initial stages of heterogeneous
struvite formation on a dissolving brucite (Mg(OH)2) substrate acting as a Mg source
[4]. Our results demonstrate that brucite dissolution and struvite precipitation are
closely coupled within a thin fluid boundary layer at the solid-fluid interface. We
further show that the heterogeneous crystallization of struvite occurs via a continuous
process involving (i) the formation of surface (inner-sphere) complexes and (ii)
the subsequent nucleation and growth of primary nanoparticles, followed by (iii)
their continuous aggregation, fusion and possible transformation to a crystalline
phase.
Secondly, we followed the homogeneous formation of struvite through in situ and
time-resolved, synchrotron-based X-ray scattering experiments. Our results from small
and wide-angle X-ray scattering (SAXS, WAXS) and pair distribution function
analysis (PDF) indicate that struvite formation is preceded by the fast precipitation
of apparently non-crystalline nanoparticles (up to 50 nm in diameter) that later
self-assemble and crystallize to struvite. Our work is the first to report that both the
heterogeneous and homogeneous formation of struvite occurs through non-classical,
particle-mediated crystallization pathways. This new knowledge contributes to the discussion
regarding the early stages of crystal formation in general and may provide a key in
designing novel struvite-based fertilizers or developing more effective struvite-scaling
inhibitors.
[1] Coe et al. (1992). New Engl. J. Med., 327(16), 1141-1152. [2] Ohlinger et al.
(1998). Water Res., 32(12), 3607-3614. [3] Kataki et al. (2016). Waste Manage., 49,
437-454. [4] Hövelmann and Putnis (2016). Environ. Sci. Technol. 50, 13032-13041. |
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