Uptake of aqueous Pb by Cl-, F–, and OH– apatites: Mineralogic evidence for nucleation mechanisms
-
Maciej Manecki
and
Samuel J. Traina
Abstract
Apatites provide a mechanism for in-situ remediation of Pb-contaminated sites, by supplying phosphate which combines with dissolved Pb to form highly insoluble pyromorphite. This study expanded upon previous research using hydroxylapatite (HAP), to focus on how the surface properties of natural chlorapatite (CAP) and fluorapatite (FAP) affect pyromorphite nucleation and growth, when aqueous Pb2+ ([Pb] < 50 mg/L as PbCl2) is reacted with apatite at pH = 4.2, 22 °C. A combination of atomic force microscopy (AFM), scanning electron microscopy (SEM), optical microscopy, energy dispersive X-ray fluorescence spectroscopy (EDS), infrared spectroscopy (FTIR), and X-ray diffraction (XRD) was used for in-situ and ex-situ examination of the interface and the reaction products.
A variety of experiments were performed, and pyromorphite [PY = Pb10(PO4)6Cl2] was the only identified reaction product. PY nucleated both homogeneously (directly from solution) and heterogeneously on CAP and FAP; relationship between PY and HAP could not be determined definitively. The nucleation mechanism was sensitive to initial experimental conditions, which suggests that care should be taken to consider initial conditions in designing sorption and nucleation experiments. Heterogenous nucleation on FAP and CAP showed strong evidence for epitaxy. Epitaxial crystals of PY on CAP and FAP grew away from the substrate surface, which was the only source of phosphate available for crystal growth. Epitaxial crystals showed distinctly different morphologies from homogeneously nucleated crystals, and appeared to grow by a spiral growth mechanism.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Application of new experimental and garnet Margules data to the garnet-biotite geothermometer
- Volumes of mixing in aluminosilicate garnets: Solid solution and strain behavior
- Cerium anomaly and Th/U fractionation in the 1.85 Ga Flin Flon Paleosol: Clues from REE- and U-rich accessory minerals and implications for paleoatmospheric reconstruction
- Os solubility in silicate melts: New efforts and results
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- TEM observations on the P1̄ -I1̄ phase transition in feldspars along the join CaAl2Si2O8-SrAl2Si2O8
- Phase transitions induced by solid solution in stuffed derivatives of quartz: A powder synchrotron XRD study of the LiAlSiO4-SiO2 join
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- The transformation of andalusite to mullite and silica: Part II. Transformation mechanisms in [100]A and [010]A directions
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- The equation of state of lawsonite to 7 GPa and 873 K, and calculation of its high pressure stability
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- Molecular modeling of the structure and dynamics of the interlayer and surface species of mixed-metal layered hydroxides: Chloride and water in hydrocalumite (Friedel’s salt)
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