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Jennifer Boecker and Criztel Navizaga

Spectroscopic and Microscopic Identification of the Reaction Products and Intermediates during the Struvite Formation from Magnesium Oxide and Magnesium Carbonate Microparticles

Department: Chemical and Biomolecular Engineering
Advisor: Jonas Baltrusaitis

Abstract:
The mineral struvite (magnesium ammonium phosphate hexahydrate, MgNH4PO4·6H2O) is a crystalline material that occurs naturally in decomposing organic materials and been observed in sludge derived from the anaerobic digestion of animal farming liquid wastes and treated wastewater sludge. Our objectives were to examine the potential of low solubility, naturally abundant magnesium inorganic materials (MgO and MgCO3) for the utilization of nutrient recovery from wastewater via time-resolved ex situ XRD, ATR-FTIR and Raman analyses, and SEM measurements to identify reactive intermediates and use spectroscopic data for kinetics analysis. Our data suggest that a common reactive intermediate between homo- and heterogeneously nucleated struvite exists that is due to the amorphous magnesium hydroxide structural units. The presence of low coordination O4C–H, O3C–H, and O1C–H surface hydroxyl groups, associated with the surface steps, edges, and kinks, is proposed to enhance struvite formation, thus an increase in their abundance and stabilization are suggested for the preparation of MgO and MgCO3 before the struvite recovery. Two different crystal morphologies (needle and rhomboidal) were observed for reactions with 600 and 4000 ppm of (NH4)2HPO4, which were proposed to form due to the kinetic control of the reaction at higher concentrations. Finally, Raman spectroscopy was used to measure the relative kinetics of struvite formation utilizing the relative populations of the magnesium carbonate and struvite, as obtained from the area under the 950 and 1125 cm−1, respectively, peaks providing a spectroscopic method to monitor reactive solid magnesium source conversion into struvite.

About Jennifer Boecker:
Jennifer Boecker is a junior at Lehigh University majoring in Chemical Engineering. Outside of academics, she is an active member of Alpha Omega Epsilon and is in the process of starting a club to help bring STEM to the nearby middle school. She was also part of the GREEN Program over winter break 2016-2017. Her main passion is sustainability, which her research is focused on; she hopes to continue pursuing this passion after graduation.

About Criztel Navizaga:
Criztel Navizaga is a junior at Lehigh University pursuing BS in Chemical and Biomolecular engineering with a minor in Earth and Environmental Science. She has been involved in Professor Jonas Baltrusaitis’s Research lab since the spring of 2014 with the focus of creating useful fertilizer from waste byproducts. She has collaborated with other graduate and undergraduate students in the publication of several articles for the ACS Sustainable Chemistry and Engineering Journal including works on the conversion of dairy waste water to chelated biodegradable Zn micronutrient fertilizers, the production of urea phosphate fertilizers for sustainable phosphorus and nitrogen use and the formation of struvite crystal fertilizers from magnesium oxide and magnesium carbonate micro particles.