Model studies with DU to assess the mobilisation and speciation of U in soils


Model studies with DU to assess the mobilisation and speciation of U in soils

Geipel, G.; Baumann, N.; Arnold, T.; Bernhard, G.; Gerstmann, U.; Schimmack, K.; Read, D.

Since the 1990th, depleted uranium (DU) was used in several conflict regions as 'penetrator' in munition rounds designed to pierce battle tanks. Lots of this amunition undergo wheatering processes under environmental conditions. One goal of our studies was the determination of the binding forms of uranium, if the DU is exposed to several environmental conditions.
The formed uranium species were detected by time-resolved laser-induced fluorescence spectroscopy (Geipel 2005). By use of spectroscopic databases including U(VI)-oxides, U(VI)-hydroxides, U(VI)-sulphates and U(VI)-phosphates the different formed uranium species in solution as well as solid species can be clearly assigned.
In a first series disks of DU were treated with a calcium phosphate solution at ambient temperature for 182 days. The weathering solution contained 2.49 mM calcium and 1.05 mM phosphate, representing enhanced pore water concentrations of agricultural soils. The TRLFS results clearly show that metaautunite, a U(VI) phosphate, has formed during low temperature alteration of the DU disc. The TRLFS spectrum is characterized by six fluorescence emission bands at 486, 501, 522, 546, 573, and 601 nm, and two fluorescence life times of 50±5 ns and 700±25 ns (Baumann et.al., 2006).
In a second experiment the corrosion and leaching of depleted uranium (DU) was investigated for three years in a column with a soil core. The columns were installed in a laboratory with controlled temperature of (21 ± 1) °C and a relative humidity of (55 ± 10) %. The columns were irrigated weekly with 16 mm synthetic rainwater of pH 6 consisting mainly of 0.09 mM NH4NO3, 0.08 mM (NH4)2SO4 and 0.05 mM CaSO4.
The luminescence spectrum of a yellow material, which was crystallized at the soil surface was measured and the comparison with the TRLFS database assigned this luminescence spectrum clearly to be the mineral sabugalite AlH(UO2)(PO4)4 x 16(H2O).
In contrast to the luminescence spectra of the solid material the spectra of the uranium species in the dissolved samples could only obtained at temperatures below 220 K. From the shape of the spectrum and the emission maxima of the luminescence of seepage water samples it could be clearly concluded that the solution species are mostly uranyl carbonate species UO2(CO3)34- (Schimmack et.al.submitted, Schimmack et.al. 2007).

Keywords: Depleted uranium; binding form

  • Invited lecture (Conferences)
    International Symposium Protecting Water Bodies from Negative Impacts of Agriculture, 04.-06.06.2007, Braunschweig, Germany

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