TRLFS study on the speciation of uranium in seepage water and pore water of heavy metal contaminated soil |
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Authors: | Nils Baumann Thuro Arnold Martin Lonschinski |
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Institution: | (1) Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiochemistry, 01328 Dresden, Germany;(2) Friedrich-Schiller University, Institute of Geosciences, 07743 Jena, Germany |
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Abstract: | In situ leaching of uranium ores with sulfuric acid during active uranium mining activity on the Gessenheap has caused longstanding
environmental problems of acid mine drainage and elevated concentrations of uranium. To study there remediation measures the
test site Gessenwiese, a recultivated former uranium mining heap near Ronnenburg/East Thuringia/Germany, was installed as
a part of a research program of the Friedrich-Schiller University Jena to study, among other techniques, the phytoremediation
capacity of native and selected plants towards uranium. In the first step the uranium speciation in surface seepage and soil
pore waters from Gessenwiese, ranging in pH from 3.2 to 4.0, were studied by time-resolved laser-induced fluorescence spectroscopy
(TRLFS). Both types of water samples showed mono-exponential luminescence decay, indicating the presence of only one major
species. The detected emission bands were found at 477.5, 491.8, 513.0, 537.2, 562.3, and 590.7 nm in case of the surface
water samples, and were found at 477.2, 493.2, 513.8, 537.0, 562.4, and 590.0 nm in case of the soil water samples. These
characteristic peak maxima together with the observed mono-exponential decay indicated that the uranium speciation in the
seepage and soil pore waters is dominated by the uranium (VI) sulfate species UO2SO4(aq). Due to the presence of luminescence quenchers in the natural water samples the measured luminescence lifetimes of the UO2SO4(aq) species of 1.0–2.6 μs were reduced in comparison to pure uranium sulfate solutions, which show a luminescence lifetime of
4.7 μs. These results convincingly show that in the pH range of 3.2–4.0 TRLFS is a suitable and very useful technique to study
the uranium speciation in naturally occurring water samples. |
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