Investigating the crystallization pathways of struvite using in-situ liquid-phase and cryogenic transmission electron microscopy
Final Report Abstract
The controlled crystallisation of struvite (MgNH4PO4 6H2O) is a viable means for the recovery and recycling of phosphorus (P) from municipal and industrial wastewaters. However, an efficient implementation of this recovery method in water treatment systems requires a fundamental understanding of struvite crystallisation mechanisms, including the behaviour and effect of metal contaminants during struvite precipitation. Our findings on struvite crystallisation in the presence of Co2+ revealed an amorphous-to-crystalline transformation. These findings contribute to the ongoing general discussion about the mechanisms of crystal formation. From a practical point of view, these results have significant implications for the recovery of phosphate from wastewaters and the fate of metals during struvite crystallization. In this context, even if metal-bearing struvite is not the only final crystalline phase, the precipitation of other solid phases is beneficial for metal remediation from wastewater. This because the in situ formation of struvite launches a “cascade” of reactions, yielding easy-to-remove solids. In addition to waste-water treatment, we can use struvite for other applications. Mesoporous phosphates are a group of nanostructured materials with promising applications, particularly in biomedicine and catalysis. However, their controlled synthesis via conventional template-based routes presents a number of challenges and limitations. We showed how to synthesize a mesoporous magnesium phosphate with a high surface area and a well-defined pore structure through thermal decomposition of a crystalline struvite (MgNH4PO46H2O) precursor. We showed that the thermal decomposition of struvite at temperatures below 100 °C leads to a pseudomorphic transformation into a mesoporous Mg-phosphate featuring a well-defined pore structure and high surface area. The so produced mesoporous material is a prime candidate for use in biomedical applications considering that magnesium phosphate is a widely used, non-toxic substance that has already shown excellent biocompatibility and biodegradability.
Publications
- A template-free and low temperature method for the synthesis of mesoporous magnesium phosphate with uniform pore structure and high surface area. Nanoscale 11, 6939-6951 (2019)
Jörn Hövelmann, Tomasz M. Stawski, Rogier Besselink, Helen M. Freeman, Karen M. Dietmann, Sathish Mayanna, Brian R. Pauwe, Liane G. Benning
(See online at https://doi.org/10.1039/C8NR09205B) - Struvite Crystallisation and the Effect of Co2+ Ions. Minerals 9(9), 503 (2019)
Jörn Hövelmann, Tomasz M. Stawski, Helen M. Freeman, Rogier Besselink, Sathish Mayanna, Jeffrey Paulo H. Perez, Nicole S. Hondow, Liane G. Benning
(See online at https://doi.org/10.3390/min9090503)
