[en] Process for recovering at least one metallic element selected from within the group composed of uranium, molybdenum, vanadium, copper, selenium and germanium contained in kerogeniferous ores. In particular, it relates to a process for the more complete recovery of the uranium contained in certain sedimentary ores. It involves: - grinding the ore down to the mesh that will release the kerogen particles, - separating the kerogen from the carrying ores by flotation, - modifying the kerogen by heating, - processing the residue for extraction of the elements it contains

[en] The experimental study of the uranium-lignite association has been investigated at different temperatures from 20 to 400⁰C. Fixation of uranyl species by the lignite (45 to 250⁰C) and reduction of them to uraninite (120 to 400⁰C) were observed. The reduction of uranium is accompanied by dehydrogenation of the lignite

[en] Organo-metallic complexes formed by fixation (chemisorption) of various metallic cations (UO₂²⁺, Cu²⁺, Ni²⁺, Zn²⁺, Pb²⁺, Co²⁺, Mn²⁺) on a recent sedimentary organic material of algal origin were submitted to thermal treatments of increasing intensity. The ensuing decomposition of the products results in: (a) the appearance of various crystallized mineral phases (oxides, sulfides, carbonates, native metals); (b) the appearance of polar organic compounds (bitumens) with part of the metals (and sometimes a large part) is associated; (c) the reduction of some metallic species and of the sulfate sulfur. In sediments, these three processes can result in the reconcentration of some metallic elements at the expense of the organo-metallic complexes, either in situ, or at some distance

[en] The geological study of three French Permian basins is reported: the Aumance basin (Allier), the Autun basin (Saone-et-Loire) and the Carentan basin (Manche). For the Aumance basin, after a presentation of the geological context, the study of oil shales is reported (thickness, extension), as well as the presence of uranium, and a geological, geochemical and mineralogical study of uranium sediments. For the Autun basin, after a presentation of the geological context, a sedimentological study is reported, as well as a location study of samples and sample studies and analyses. For the Carentan basin, the reports addresses the geological structure, the presence of a Permian volcanism, the limits of the Permian basin, and proposes a paleo-geographical sketch

[en] Published in summary form only

[en] The reactivity of lignite towards soluble uranyl species in an aqueous medium is experimentally investigated as a function of temperature (between 20⁰C and 400⁰C). The fixation process starts near 45⁰C, with reduction beginning around 120⁰C. The fixation process leads to the formation of chemically and thermally stable organo-uranyl species. The reduction of free uranyl species is accompanied by a stoichiometric (2:1) liberation of protons into the medium. These protons originate from the organic matter which thus undergoes dehydrogenation. The general evolution of the carbonaceous residue in the course of this reaction shows that alcoholic and aliphatic hydrocarbon groups are responsible for the reduction. This chemical dehydrogenation could explain the low hydrogen content of natural organic materials associated with uraniferous deposits. The kinetics of the reduction step have been studied at 180⁰C, 190⁰C and 200⁰C. The kinetic parameters determined over this temperature range, and the extrapolation made to 20⁰C, show that reduction can be a crucial process in the geochemical behaviour of uranium especially in the thermal conditions in which sedimentary basins evolve

[en] Interactions between lignite and soluble uranyl species have been investigated experimentally at different temperatures from 20 deg to 400 deg C. Fixation of uranyl species by lignite and their reduction to uraninite were observed. The fixation of uranyl species by lignite results in the formation of stable organo-uranyl compounds. The reduction of uranyl species by lignite results in a stoichiometric liberation of H⁺ in the solution medium and in a dehydrogenation of lignite. This dehydrogenation can be attributed to two different processes. The first is an oxidation of alcohol functional groups into aldehyde or ketone functions accompanied by a simultaneous reduction of uranyl species. The second is a dehydrogenation of hydrocarbonaceous aliphatic moieties induced by the uranium species. The molecular hydrogen produced during this process is subsequently used for an additional reduction of uranyl species. (author)

[en] A sedimentological study of a 755 cm length core sampled in the middle of a marshy depression surrounded by a cloud forest in the central Andes reveals that this site has recorded important environmental variations during the last 50 000 years. For the most part (625 cm) the core is composed of detrital rich sediments deposited during the Upper Pleistocene. The highest amount of detrital influx underlines the Last Glacial Maximum which ranges from ca 29,000 ¹⁴C yr B.P. to ca 16,000 ¹⁴C yr B.P. (ca 18,500 cal yr B.P.), between two relatively humid phases. The sedimentation of the present Interglacial, starting at ca 12,500 ¹⁴C yr B.P. (14,500 cal yr B.P.), is mainly organic, as a consequence of the great development of soils and the forest vegetal cover the catchment area. The maximum extension of this vegetal cover ranging from 12,500 to ca 10,500 ¹⁴C yr B.P. (14,500 and 12,400 cal yr B.P.) is followed from 10,500 to 8,000 ¹⁴C yr B.P. (12,400 and 8,800 cal yr B.P.) by a drier period is revealed by the occurrence of micro-charcoals in the sediment. Between ca 8,000 and 4,000 ¹⁴C yr B.P. (8,800 and 4,500 cal yr B.P.), the sharp increase of micro-charcoals content, likely related to palaeo-fires, underlines an intensification of this dry trend. (authors)