Synthesis and Characterization of Carbonated Calcium and Lead Apatite Minerals
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Apatites constitute a diverse family of minerals, which are found in the environment and as the major mineral constituent of bone and teeth. They have the generic stoichiometry M10(PO4)6X2, where M is a divalent cation and X is a halide, hydroxide, or carbonate. The apatite structure is vulnerable to ionic substitution. Substitutions significantly alter the physical and chemical properties of the minerals. Calcium and lead apatites of various carbonate contents were prepared in aqueous media by a method of reagent addition intended to yield apatites with maximized and controllable amounts of incorporated carbonate. The samples’ identities and changes in crystallinities upon carbonation were determined by XRD, ATR-IR, micro-Raman spectroscopy, and petrographic microscopy. Carbonate content was determined by carbon elemental analysis. The data demonstrate that the synthetic method used is reproducible and able to yield calcium and lead apatites with up to 18 and 5 wt % carbonate, respectively. Moreover, structural data demonstrate that increased carbonate incorporation dramatically lowers the crystallinity of the samples. In addition, theoretical calculations, employing our simple salt approximation of the lattice enthalpy of complex minerals, predict that the solubilities of calcium and lead apatites increase with increasing carbonate. These results were tested experimentally using atomic absorption spectroscopy and Visual Minteq ® multiple equilibrium software. This work is among the first investigations of the chemistry of carbonated lead apatites, which have important environmental and biological consequences.
Franklin and Marshall College Archives, Undergraduate Honors Thesis, 2008. Permission to access this thesis electronically (via Scholars Square) has not been granted by the author. To access this thesis in print, please visit the Archives & Special Collections Reading Room, Franklin & Marshall College, Lancaster, PA.
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