By Joseph Caleb Chappell Three Groups of Fluorapatite from the Mont
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ABSTRACT CHEMICAL AND STRUCTURAL CHARACTERIZATION OF FLUORAPATITE FROM THE POUDRETTE PEGMATITE, MONT SAINT-HILAIRE, QUEBEC, CANADA by Joseph Caleb Chappell Three groups of fluorapatite from the Mont Saint-Hilaire igneous complex in Quebec, Canada have been analyzed with scanning electron microscopy (SEM), electron probe microanalyses (EPMA), single-crystal X-ray diffraction (SCXRD), Fourier transform infrared spectroscopy (FTIR), and magic angle spinning nuclear magnetic resonance (MAS-NMR) to fully characterize the chemical and structural details of fluorapatite from one of the most mineralogically diverse locales on Earth. SEM and EPMA revealed these fluorapatites to be enriched in Th, Y, and Na, while FTIR showed substantial concentrations of carbonate substituting for phosphate at the tetrahedral site. The Th contents observed in these fluorapatites are the highest ever observed for natural samples, and have implications for designing new solid nuclear waste forms. SCXRD refinements revealed the dissymetrization of two of the three groups from the classic P63/m space group to the P space group due to the elevated Y and Na contents. Lastly, the FTIR and NMR data show the presence of the long debated C-F bond the observation of which has important implications for the incorporation of carbonate groups into apatites, and is the first time this bond has been observed in any natural mineral. CHEMICAL AND STRUCTURAL CHARACTERIZATION OF FLUORAPATITE FROM THE POUDRETTE PEGMATITE, MONT SAINT-HILAIRE, QUEBEC, CANADA A Thesis Submitted to the Faculty of Miami University In partial fulfillment of The requirements for the degree of Master of Science. Department of Geology and Environmental Earth Science. by Joseph Caleb Chappell Miami University Oxford, Ohio. 2019 Advisor: John Rakovan Reader: Claire McLeod Reader: Mark Krekeler ©2019 Joseph Caleb Chappell This thesis titled CHEMICAL AND STRUCTURAL CHARACTERIZATION OF FLUORAPATITE FROM THE POUDRETTE PEGMATITE, MONT SAINT-HILAIRE, QUEBEC, CANADA by Joseph Caleb Chappell has been approved for publication by The College of Arts and Science and Department of Geology and Environmental Earth Science ____________________________________________________ John Rakovan ______________________________________________________ Claire McLeod _______________________________________________________ Mark Krekeler Table of Contents List of Tables…………………………………………………………………………………….iv List of Figures……………………………………………………………………………….……v Dedication……………………………………………………………………………...…….…..vi Acknowledgments……………………………………………………………...………...….….vii Introduction……………………………………………………………………………………....1 Occurrence…………………………………………………………….………………………….2 Analytical Methods………………………………………………………………………………3 Scanning Electron Microscopy……………........................................................................3 Electron Probe Microanalysis…………………………………………………………….3 Single Crystal X-ray Diffraction…………………………………………………………..3 Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy………………...4 Magic Angle Spinning-Nuclear Magnetic Resonance…………………………………….4 Results Scanning Electron Microscopy……………………………………………………………5 Electron Probe Microanalysis…………………………………………………………….5 Single Crystal X-ray Diffraction…………………………………………………………..6 Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy………………...6 Magic Angle Spinning-Nuclear Magnetic Resonance…………………………………….7 Discussion Sodium in the fluorapatite structure………………………………………………………7 Thorium in the fluorapatite structure……………………………………………………..8 Yttrium in the fluorapatite structure………………………………………………………9 Solid solution with belovite group minerals……………………………………………..10 3- Carbonate in the fluorapatite structure and evidence for the CO3F molecule…………10 Conclusions……………………………………………………………………………………...11 References……………………………………………………………………………………….12 Tables……………………………………………………………………………………………16 Figures……………………………………………………………………………………...........20 Supplemental Data……………………………………………………………………………...32 iii List of Tables Table 1. SCXRD Experimental Details from group 2………………….………………………..17 Table 2. Atomic positions, etc, for group 2……………………………………...………………18 Table 3. Selected mean bond lengths from group 2…………………………………….….…….18 Table 4. SCXRD Experimental Details from group 3…………………………….……….…….19 Table 5. Atomic positions, etc, for group 3…………………………………………….…..……20 Table 6. Selected mean bond lengths from group 3……………………………………….……..20 iv List of Figures Figure 1. Geologic map of Mont Saint-Hilaire……………………………………………...…..21 Figure 2. Picture if the Poudrette pegmatite………………………………………………...…..22 Figure 3. XEDS spectrum of the Mont Saint-Hilaire fluorapatite………………………………23 Figure 4. SEM image of fluorapatite……………………………………………………………24 Figure 5. Mean EPMA analyses for all fluorapatites……………………………………………25 Figure 6. CIF of refined group 2 fluorapatite crystal structures…………………………...……26 Figure 7. CIF of refined group 3 fluorapatite crystal structures…………………………….…..27 Figure 8. ATR-FTIR spectrum of group 2 fluorapatite……………………………………...….28 Figure 9. ATR-FTIR spectrum of group 3 fluorapatite…………………………………...…….29 Figure 10. ATR-FTIR zoom of C-F signal region for group 2 fluorapatite……………………..30 Figure 11. ATR-FTIR zoom of C-F signal region for group 3 fluorapatite……………………..31 Figure 12. 19F MAS-NMR spectrum of group 3 fluorapatite……………………………….…...32 v Dedication This body of work is dedicated to my wife Hillary and our two cats Halpert and Beesly who we adopted right as I was beginning this Master’s degree. Beesly unfortunately passed away quite suddenly, just days after the defending this thesis, but he will always hold a special place in our hearts. vi Acknowledgments This work would not have been possible without the mentoring of my adviser John Rakovan and his expertise in the field of apatite chemistry. The collection of the FTIR data by Andy Sommer in the Department of Chemistry at Miami University is greatly appreciated, as is the NMR data collection by Brian Phillips in the Department of Geoscience at Stony Brook University. Lázslo and Elsa Horváth originally provided the samples to be studied, and without them this entire project would not have begun. vii Introduction Fluorapatite (Ca5(PO4)3F) is the most common phosphate mineral on Earth, and its accommodating crystal structure allows for nearly half the elements on the periodic table to substitute into one of 4 distinct sites (Hughes & Rakovan 2015). The M1 site is 9-fold coordinated and generally accommodates cations slightly larger than Ca, while the M2 site is 7-fold coordinated and generally incorporates cations slightly smaller than Ca, though this is not always the case (Fleet & Pan 1997). The tetrahedrally coordinated site, where P5+ sits in end member fluorapatite, can accommodate cations such as Si4+, C4+, , As5+, V5+, and S6+. And lastly the X site, or anion column site, is often occupied by more than one constituent with the most to least common being F, OH, Cl, and C. Because of this flexible crystal structure and crystal chemistry, fluorapatite has been studied extensively for a variety of applications, including biomedical, environmental remediation, and multiple materials science applications (Rakovan & Pasteris 2015). Because of its ubiquity in rock forming environments, large stability field, and affinity for many trace elements including lanthanides and actinides, fluorapatite has long been used in geochronologic and petrogenetic studies (Piccoli & Candela 2002, Braund et al. 2017, Chakhmouradian et al. 2017). These same characteristics are reasons for interest in using apatite as a sequestration agent for heavy metals and as a solid nuclear waste form (Ewing & Wang 2002, Luo et al. 2011, Rigali et al. 2016, Li et al. 2017). Naturally occurring fluorapatite has been found with significant quantities of U and Th, up to 0.40wt %, and perhaps most notably Pu at the Oklo natural reactor in Gabon (Bros et al. 1996, Horie et al. 2004). Both studies concluded that fissiongenic LREE and nucleogenic Pu were selectively trapped in the fluorapatite grains while the reactor was at its peak and have remained in the crystal structure over the last ~2.0Ga years (Bros et al. 1996, Horie et al. 2004). The retention of these elements within the apatite grains is especially interesting when considering the dissolution of uraninite during this time span. Studies such as Rakovan and Hughes (2000), Rakovan et al. (2002), Luo et al. (2009), and Luo et al. (2011) have utilized single-crystal X-ray diffraction (SCXRD) and extended X-ray absorption fine structure (EXAFS) techniques to assess the site preference of fissiongenic elements such as U and Th in the apatite structure, and have yielded significant insight into the accommodation of these elements by the fluorapatite structure. 2- Substitution of the CO3 ion into apatite has also been of great interest and debate, mainly among those studying apatite for biomedical applications (Reigner et al. 1994, Fleet & Liu 2003, Fleet 2017). Because of the often-small size of natural and synthetic apatite crystals that are heavily 2- 2- substituted by the CO3 ion, samples which do contain significant CO3 content and have crystals of large enough size for single-crystal X-ray diffraction studies are of considerable interest to those studying this aspect of apatite crystal chemistry (Fleet 2014). A suite of 12 apatite group minerals from the Poudrette Quarry in the Mont Saint-Hilaire igneous complex have been examined with electron probe microanalyses, single-crystal X-ray diffraction, Fourier transform