(162at) Molecular Modifiers Suppress Struvite Formation through Unique Mechanisms

The crystallization of struvite (MgNH₄PO₄·6H₂O) is relevant for nutrient (nitrogen and phosphorus) recovery in water purification and scale formation in pipelines, and it is a primary component of so-called infection stones arising from urinary tract infections. Research efforts have focused on understanding the effects of different parameters (e.g., supersaturation, pH, inhibitors) on crystallization of struvite; however, prior studies have only focused on the use of bulk techniques and have not provided mechanistic insights into these controls.

Herein, we present a comprehensive approach to evaluate struvite formation at both macroscopic and microscopic length scales in the absence and presence of various inhibitors. We conducted in situ kinetic measurements to estimate the extent of inhibition posed by each inhibitor on struvite formation. To this end, we employ a microfluidic platform to track the anisotropic growth rates of struvite crystals under various conditions, including comparisons of solutions with and without the presence of modifiers¹. Furthermore, we elucidate the mechanism of inhibitory action by probing the surface dynamics in real time via in situ atomic force microscopy (AFM), which has proven to be a powerful technique to elucidate molecular level details of crystallization^2,3. The results reveal unique mechanisms facilitating complete inhibition of growth and in select cases the unprecedented suppression of nucleation, which is not commonly observed for even the most potent modifiers of mineralization. Collectively, our findings identify highly efficient and commercially available modifiers that inhibit struvite formation. This study also uncovers a new class of inhibitory mechanisms that have potentially broader applicability to other minerals, thus establishing new paradigms for the prevention of commercial scale.

1. Kim, D., Olympiou, C., McCoy, C. P., Irwin, N. J., & Rimer, J. D. (2020). Time‐Resolved Dynamics of Struvite Crystallization: Insights from the Macroscopic to Molecular Scale. Chemistry–A European Journal, 26(16), 3555-3563.
2. Chung, J., Granja, I., Taylor, M. G., Mpourmpakis, G., Asplin, J. R., & Rimer, J. D. (2016). Molecular modifiers reveal a mechanism of pathological crystal growth inhibition. Nature, 536(7617), 446-450.
3. Farmanesh, S., Ramamoorthy, S., Chung, J., Asplin, J. R., Karande, P., & Rimer, J. D. (2014). Specificity of growth inhibitors and their cooperative effects in calcium oxalate monohydrate crystallization. Journal of the American Chemical Society, 136(1), 367-376.