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| Titel |
Pseudomorphic replacement of single cerussite PbCO3 crystals by hydroxylpyromorphite Pb5(PO4)3OH in phosphate solutions |
| VerfasserIn |
M. Kwaśniak-Kominek, M. Manecki, T. Bajda, J. Rakovan |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250067235
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| Zusammenfassung |
| Lead apatite, pyromorphite, can form by replacing lead carbonate, cerussite, under conditions
similar to those found in earth surface environments. This occurs by a process analogous to
the calcium carbonate - calcium apatite system, where during chemical weathering and
natural hydrothermal reactions hydroxylapatite can form by replacing calcium carbonates.
The aim of this study is to experimentally investigate reactions of cerussite with phosphate
solutions to determine the conditions under which pyromorphite can form and the mechanism
of the transformation.
Cerussite can be readily transformed into hydroxylpyromorphite by hydrothermal
treatment in a 2M (NH4)H2PO4 solution. The product of reactions is independent of the
presence of Cl in the solution. Hydrothermal experiments were carried out in order to
produce partially reacted crystals. In both cases, with the presence or absence of Cl, the
cerussite is pseudomorphologically replaced by hydroxylpyromorphite.
The reaction products were studied by scanning electron microscopy (SEM) to determine
the microstructural relationship between the parent and the product phases. X-Ray powder
diffraction (XRD) and infra-red spectroscopy (FTIR) were used for phase determination. The
results show that the new phase was only hydroxylpyromorphite even in the presence of Cl.
Observations of broken crystals show partial replacement of cerussite by polycrystalline
hydroxylpyromorphite, preventing even fine scale surface micromorphology. The features of
replacement of cerussite crystals by hydroxylpyromorphite are similar to pseudomorphic
reactions in a wide range of materials and are consistent with a mechanism described as
interface-coupled dissolution-precipitation.
This project is partially financed by Polish NCN grant No UMO-211/01/M/ST10/06999. |
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