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Titel |
The replacement of Celestine (SrSO4) by Strontianite (SrCO3) studied in situ, spatially resolved, and real-time by Raman spectroscopy |
VerfasserIn |
Michael Sulzbach, Thorsten Geisler |
Konferenz |
EGU General Assembly 2015
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 17 (2015) |
Datensatznummer |
250113064
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Publikation (Nr.) |
EGU/EGU2015-13260.pdf |
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Zusammenfassung |
The replacement reaction of celestine (SrSO4) by strontianite (SrCO3) is one of the most
common ways to obtain pure strontianite that is an important industrial reagent. Thus, the
replacement reaction has been studied extensively over the past decades. In this work the
replacement serves as a model system to study solid-fluid reactions in particular, the
behavior of oxygen isotopes during the reaction. Measurements of isotopically
enriched compounds using Raman spectroscopy showed that oxo-anion groups
perform localized vibrations with distinct frequencies. These vibrations reflect the
oxygen-based isotopologues of the oxo-anion molecule and the relative intensities of
these bands are proportional to the isotopologue fractions in the molecule species
that allows the precise quantification of its isotope composition. Therefore, Raman
spectroscopy provides us with a tool to monitor the behavior of oxygen isotopes at reaction
interfaces and in the fluid. Combining a confocal Raman spectrometer with an
in-house-made Teflon© fluid cell even enables spatially resolved, in situ, and real-time
measurements.
Two different experimental setups were used to obtain general information about the
replacement kinetics using isotopically natural solutions. The first experimental setup
consisted of an in-house-made Teflon© fluid cell (with an internal heating system) filled with
a 1M Na2CO3 solution and an equimolar amount of celestine powder. Grain sizes
ranged between 63 and 125 μm and experimental temperatures were 35Ë C, 40Ë
C, 45Ë C, and 50Ë C. At the start of the experiments the aqueous ν1(CO3) band
could be observed at 1065 cm-1 that lost intensity over the course of the reaction.
Complementary, the aqueous sulfate ν1(SO4) band at 981 cm-1grows in intensity. From the
relative changes between these bands we derived the reaction rates and the activation
energy.
The second experimental setup also consisted of an in-house-made Teflon© fluid cell
(without heating system) filled with 1M Na2CO3 solution and a rectangle rod of celestine (3
x 3 x 9 mm). This setup was used to measure the reaction front between mineral
and fluid over the course of 10 days at room temperature (21±1Ë C). First results
show a fast formation of a strontianite rim, which slows down the consequential
movement of the reaction front into the celestine. In the solution the intensity of
ν1(CO3)aq and ν1(SO4)aq bands show a similar trend to the first experimental
setup but near the fluid-solid interface a notable difference can be observed. The
ν1(SO4)/ν1(CO3) intensity ratio in solution decreases smoothly towards the reation
interface.
Future experiments will then be carried out with 18O-labelled solution, which will allow
studying the oxygen isotope exchange between aqueous carbonate, aqueous sulfate,
and the solid strontianite product, while celestine is being replaced by strontianite. |
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