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[en] Weathering of uranium ores and migration of radionuclides were studied in the area of 450 years old waste rock dump Geister II after silver mining in Joachimsthal. The dump shows significant contents of uranium series radionuclides and the site can be regarded as an analogue of modern uranium waste rock dumps from 20th Century. It is likely to provide valuable information about process of weathering and washing of radionuclides away from it due to its long-term exposure to oxidizing conditions. Samples of the dump horizons for laboratory scintillation gamma spectrometry were collected in digged well and also bores made with engine drilling. Alpha-autoradiography using LR 115, type 2 film detectors was employed to study of distribution of radioactive micro-objects in the profile. Electron microanalysis does not provide Ra concentration measurements, but localization of the active centres to the rims appointed indicates the possibility of radium bound to grain surfaces and layered silicates. A series of secondary uranyl phosphates samples from the site in a different stage of weathering was studied. XRD was employed for determining a mixture of uranyl phosphates. Mineral samples were studies using an optical microscopy with UV light. In several grains a transition zone between the fluorescent part and non-fluorescent part was visible. Those grains were studied by electron microanalysis in detail. It was determined that the corroded rims of the grains were depleted with Ca, U and P and enriched with Fe. Moessbauer spectroscopy was used for distinguishing of different types of Fe bond in studied samlpes and amount of phase with certain oxidation state in each sample. Goethit was determined in the mixture of secondary minerals. By means of alpha spectrometry was found out that the studied bassetite from the dump upper layer are not in a significant radioactive disequilibrium (U∼Ra), but it shows a high microporosity (Rn escape) in compare with unaltered meta-autunite. The performed research showed that uranium is redeposited from the waste rock to fossil soils under the dump. In the subsoil it is bound mainly to decomposed organic matter remainders and lesser amount is adsorbed on porous hydrated Fe3+ oxides, which play the role of an effective geochemical barrier. In the horizon of fossil soil the uranium concentration can reach up to 0.25 wt. %. Radium, however, is still bound in a horizon of active dump material and comes under a partial redeposition controlled by biological processes. It is possible to establish that the studied model mirrors the late stage of uranium migration. Leaching of uranium ore in the surface oxidizing conditions proceeded more than 450 years. Nearly total leaching of uranium from waste rock and its washing away from the dump occurred. It seems very probable, that a similar process will happen in the time horizon of several hundreds years in case of modern waste rock dumps after intensive uranium mining in other mining districts, as well. It is only a question, if there will be present effective geochemical barriers for its retain
[en] This chapter covers on industries that related to Naturally Occuring Radioactive Material (NORM) such as ore and mineral mining, ore melting and also natural gas. In this topic, the authors explained on ore processing, products of mineral processing industry which consist thorium, uranium and non radioactive material. The uranium and thorium sources will only increase if there is more ore and mineral which contain reasonable radioactive materials concentration been procesed.
[en] The crystal structures of two autunite-group minerals have been solved recently. The crystal structure of bassetite, Fe"2"+[(UO_2)(PO_4)]_2(H_2O)_1_0, from the type locality in Cornwall, United Kingdom (Basset Mines) was solved for the first time. Bassetite is monoclinic, space group P2_1/n, a = 6.961(1), b = 20.039(2), c = 6.974(1) Aa and β = 90.46(1) . The crystal structure of saleeite, Mg[(UO_2)(PO_4)]_2(H_2O)_1_0, from Shinkolobwe, Democratic Republic of Congo, was also solved. Saleeite is monoclinic, space group P2_1/n, a = 6.951(1), b = 19.942(1), c = 6.967(1) Aa and β = 90.58(1) . The crystal structure investigation of bassetite (R_1 = 0.0658 for 1879 observed reflections with vertical stroke F_o vertical stroke ≥ 4σ_F) and saleeite (R_1 = 0.0307 for 1990 observed reflections with vertical stroke F_o vertical stroke ≥ 4σ_F) confirms that both minerals are topologically identical and that bassetite contains ten water molecules per formula unit. Their structure contains autunite-type sheets, [(UO_2)(PO_4)]"-, consisting of corner-sharing UO_6 square bipyramids and PO_4 tetrahedra. Iron and magnesium are surrounded by water molecules to form Fe(H_2O)_6 or Mg(H_2O)_6 octahedra located in interlayer, between the autunite-type sheets. Two isolated independent water molecules are also located in interlayer. Energy-dispersive X-ray spectroscopy analysis confirmed the chemical composition obtained from structure refinement. These new data prompt a re-assessment of minerals of the autunite and meta-autunite groups.
[en] Weathering of 450 years old mine wastes after silver mining at Geister vein in the Jachymov ore district (Czech Republic) and migration of uranium were studied. Specific gamma-ray activity of 226Ra, measured by field gamma-ray spectrometry, varies from 38 Bq/kg (3 ppm eU) to 3816 Bq/kg (309 ppm eU) in the observed area. The most active material forms the top layer of the dump. The gamma-ray activity of the top layer is caused mainly by 226Ra. Uranium is leached from upper layer and accumulated in fossil soils beneath. U-micas were studied using X-ray powder diffraction and EDA. The following succession of supergene alteration was found: autunite → meta-autunite → bassetite →- oxidized bassetite. (author)
[en] Microanalytical techniques are described which allow rapid determinations of secondary species associated with uranium. They consist in exposing the constituent elements of the ores by means of characteristic microchemical reactions. Because of their rapidity and the small amount of apparatus needed, these techniques can be used either in the field or in the laboratory. (author)
[fr]Les techniques de microanalyse decrites dans cet ouvrage permettent la determination rapide des especes secondaires d'uranium. Elles consistent a mettre en evidence les elements constitutifs des mineraux par des reactions microchimiques caracteristiques. En raison de leur rapidite et du peu de materiel qu'elles necessitent, ces techniques peuvent etre utilisees aussi bien sur le terrain qu'au laboratoire. (auteur)