Experimental-Computational Approach to Investigate Elastic Properties of Struvite

Magnesium ammonium phosphate hexahydrate, NH₄MgPO₄·6H₂O, known as struvite, has been widely investigated over the last decade for several reasons.

Firstly, struvite can be a problem in sewage and wastewater treatment as it precipitates easily on specific locations, which may clog the system pipes. On the other hand, struvite is potential source of phosphorus, nitrogen and magnesium, and therefore it is the main compound recovered from wastewater and recycled as a useful P-N-Mg-containing fertilizer. Third and the most important reason for which struvite is examined is the fact that it constitutes the main component of the so-called infectious urinary stones.

The presented investigations combine theoretical and experimental research of properties of struvite, such as: elastic constants, in particular modules: Kirchhoff G, Young's E and bulk K. Theoretical calculations of the above properties were carried out by density functional methods. Such calculations are a challenge, because these methods are mainly developed for semiconductors in view of fast development of electronics. However, struvite is a dielectric crystal. Therefore, quantum-chemical calculations for struvite are innovative. In the presented work, we also present the experimental results of the measurement of Young's modulus by the nanoindentation method.

The knowledge of elastic properties of struvite may point the manner by which urinary stones interact with the mechanical stresses produced by extracorporeal shock-wave lithotripsy - one of the most frequently used procedures for treatment the urinary stones. The knowledge of this properties may be also important from the perspective of prevention of struvite deposition in sewage treatment plants.

In the presented work, we also compare the experimentally obtained value of Young's modulus with the calculated theoretical value and on this basis, we draw conclusions regarding reliability of the quantum-chemical methods applied to the dielectric material.

Acknowledgments: The calculations are performed using the PLATON project's infrastructure at Lodz University of Technology Computer Centre.