Time-resolved in situ studies of apatite formation in aqueous solutions
-
Olaf Borkiewicz
,
John Rakovan
Abstract
Formation of hydroxylapatite through the precipitation and evolution of calcium phosphate precursor phases under varying conditions of temperature (25-90 °C), pH (6.5-9.0), and calcium to phosphorus ratio (1.0, 1.33, 1.5, and 1.67) comparable to those found in many sediments and soils were studied. The products of low-temperature precipitation were analyzed by ex situ X-ray diffraction and SEM, as well as time-resolved in situ synchrotron X-ray diffraction. Rietveld refinement was used for quantitative evaluation of relative abundances during phase evolution. The results of ex situ investigations conducted at ambient temperature and near-neutral pH indicate formation of amorphous calcium phosphate, which over the course of experiments transforms to brushite and ultimately hydroxylapatite. The results of in situ X-ray diffraction experiments suggest a more complex pathway of phase development under the same conditions. Some of the initially formed amorphous calcium phosphate and/or crystalline brushite transformed to octacalcium phosphate. In the later stage of the reactions, octacalcium phosphate transforms quite rapidly to hydroxylapatite. This is accompanied or followed by the transformation of the remaining brushite to monetite. Hydroxylapatite and monetite coexist in the sample throughout the remainder of the experiments. In contrast to the near-neutral pH experiments, the results from ex situ and in situ diffraction investigations performed at higher pH yield similar results. The precipitate formed in the initial stages in both types of experiments was identified as amorphous calcium phosphate, which over the course of the reaction quite rapidly transformed to hydroxylapatite without any apparent intermediate phases. This is the first application of time-resolved in situ synchrotron X-ray diffraction to precipitation reactions in the Ca(OH)2-H3PO4-H2O system. The results indicate that precursors are likely to occur during the natural or induced (e.g., with application of Ca+PO4 amendments) formation of hydroxylapatite in many sedimentary environments.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Resonant X-ray emission study of the lower-mantle ferropericlase at high pressures
- Uranyl phosphate sheet reconstruction during dehydration of metatorbernite [Cu(UO2)2(PO4)2·8H2O]
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- Electronic structure and local environment of substitutional V3+ in grossular garnet Ca3Al2(SiO4)3: K-edge X-ray absorption spectroscopy and first-principles modeling
- Elbrusite-(Zr)—A new uranian garnet from the Upper Chegem caldera, Kabardino-Balkaria, Northern Caucasus, Russia
- What drives the distribution in nature of 3T vs. 2M1 polytype in muscovites and phengites? A general assessment based on new data from metamorphic and igneous granitoid rocks
- Radiation damage and uranium concentration in zircon as assessed by Raman spectroscopy and neutron irradiation
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- Protracted oceanic subduction prior to continental subduction: New Lu-Hf and Sm-Nd geochronology of oceanic-type high-pressure eclogite in the western Dabie orogen
- Time-resolved in situ studies of apatite formation in aqueous solutions
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- Low-temperature infrared spectroscopic study of OH-stretching modes in kaolinite and dickite
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- Unique crystal chemistry of two polymorphs of topaz-OH: A multi-nuclear NMR and Raman study
- Crystal chemistry of chromian pumpellyite from Osayama, Okayama Prefecture, Japan
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- Crystal chemistry of Cr-spinels from the lherzolite mantle peridotite of Ronda (Spain)
- Lead-tellurium oxysalts from Otto Mountain near Baker, California: I. Ottoite, Pb2TeO5, a new mineral with chains of tellurate octahedra
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- The behavior of the Hf isotope system in radiation-damaged zircon during experimental hydrothermal alteration
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