Longterm leaching of natural radionuclides from uranium mill tailings material: comparison of indoor and outdoor column experiments

Abstract

27Uranium / Tailings / Leaching / Laboratory columns / 28 Outdoor columns 29 Summary. The leaching of natural radionuclides from the 30 material of a uranium mill tailing at Crossen/Saxony was in-31 vestigated using eight columns (20 cm diameter, 50 cm 32 height). Six columns were irrigated in the laboratory by syn-33 thetic rainwater of pH 6, 3 and 2, two columns were exposed 34 outdoor to natural meteorological conditions. In the effluent 35 of the columns, the concentrations of the radionuclides were 36 measured periodically. With exception of the initial phase after 37 installation of the columns (ca. 0.4 y), the leaching rates of 38 radionuclides decreased slowly within the observation period 39 of 4.5 years. Due to the buffering capacity of the tailings 40 material, acidifying the irrigation water of the laboratory col-41 umns did not effect the effluent concentrations of the radio-42 nuclides. However, significant differences were observed be-43 tween laboratory and outdoor columns : outdoor, the concen-44 tration of 235 U in the effluents was for the first two years sub-45 stantially smaller than in the laboratory. As a consequence, 46 the accumulated leached activity of 235 U during 4.5 years was 47 19.0 Ϯ 0.9 % of the inventory for the laboratory columns, but 48 only 10.9 Ϯ 0.6 % for the outdoor columns. While uranium thus 49 proved to be rather soluble, the concentration of 226 Ra in the 50 effluents was quite small (Ͻ1 Bq/l). Thorium was retained 51 completely in the columns.52

Vertical migration of 60Co, 137Cs and 226Ra in agricultural soils as observed in lysimeters under crop rotation

“…For 226 Ra and 60 Co, however, no data appropriate for a comparison were found in the literature: in the case of 226 Ra, only studies in connection with uranium mining and tailings were performed (e.g. Klingel et al, 1995;Schimmack et al, 2000), while in the case of 60 Co, the only migration rates published were obtained by column experiments (Schimmack and Bunzl, 1992) and refer to forest soils with pH values of about 3 as compared to 5-7 in the present study. Most migration data are available for 137 Cs, and many of them were determined by field experiments in nearly all regions of the world.…”

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“…The rare earth isotopes 153 Sm and 166 Ho can be produced 38 by neutron irradiation of samarium and holmium oxides respectively. Similarly the longer lived 186 Re isotope can be made 38 by neutron capture in rhenium oxide (both 185 & 187 Re undergo the n,g reaction but 188 Re decays more quickly). Double neutron capture by 186 W leads to 188 W which can be used 39 in a generator as a source of 188 Re.…”

“…Similarly the longer lived 186 Re isotope can be made 38 by neutron capture in rhenium oxide (both 185 & 187 Re undergo the n,g reaction but 188 Re decays more quickly). Double neutron capture by 186 W leads to 188 W which can be used 39 in a generator as a source of 188 Re. 186 Re can also be made from 186 W either by proton [ 186 W(p,n) 186 Re] or by deuteron 40 [ 186 W(d,2n) 186 Re] irradiation.…”

“…Double neutron capture by 186 W leads to 188 W which can be used 39 in a generator as a source of 188 Re. 186 Re can also be made from 186 W either by proton [ 186 W(p,n) 186 Re] or by deuteron 40 [ 186 W(d,2n) 186 Re] irradiation. The bombardment of a tantalum target with 11 B 4+ ions leads to the formation 41 of 187 & 188 Pt and 187 & 188 Ir whilst slightly heavier isotopes are formed, 188 & 189 Pt and 188 & 189 Ir, if a beam of 12 C 6+ ions is used instead.…”

“…184 When all else fails look to the bugs. Bacilli have been identified 185 that can extract uranyl cations from groundwater near uranium mine spoil heaps 186 whilst others have been found 187 that will reduce both uranium(VI) and rhenium(VII) (and by implication Tc(VII) too) to insoluble species.…”