[en] Phosphogypsum (PG) is a by-product of the phosphate fertilizer industries that contains relatively high concentrations of uranium series radionuclides. The US-EPA regulates the agriculture use of PG, attending to its ²²⁶Ra content and to the ²²²Rn exhalation rate from inactive stacks. Measurements of ²²²Rn exhalation rates in PG stacks typically show a large and still poorly understood spatial and temporal variability, and the published data are scarce. This work studies an inactive PG stack in SW Spain of about 0.5 km² from where PG can be extracted for agriculture uses, and an agriculture soil 75 km apart, being representative of the farms to be amended with PG. Activity concentrations of ²²⁶Ra, ²³⁸U and ²¹⁰Po have been measured in 30 PG samples (0-90 cm horizon) allowing for the construction of maps with spatial distributions in the PG stack and for the characterization of the associated PG inputs to agriculture soils. Averaged ²²⁶Ra concentrations for the stack were 730 ± 60 Bq kg^-1 (d.w.), over the US-EPA limit of 370 Bq kg^-1. ²²²Rn exhalation rate has been measured by the charcoal canister method in 49 sampling points with 3 canisters per sampling point. Values in PG stack were under the US-EPA limit of 2600 Bq m^-2 h^-1, but they were one order of magnitude higher than those found in the agriculture soil. Variability in radon emissions has been studied at different spatial scales. Radon exhalation rates were correlated with ²²⁶Ra concentrations and daily potential evapotranspiration (ETo). They increased with ETo in agriculture soils, but showed an opposite behaviour in the PG stack.

[en] In this work, radiological, chemical, and also morphological characterization was performed in phosphate rock and phosphogypsum samples, in order to understand the behavior of toxic elements. Characterization was carried out using X-ray diffraction (XRD), X-ray fluorescence (XRF), gamma spectrometry and scanning electron microscopy with energy-dispersive X-ray analysis (SEM-EDX). Our results show that the phosphate rock was mainly composed of fluorapatite, calcite, perovskite, quartz, magnetite, pyrite and kaolinite, whereas phosphogypsum only exhibited dihydrated calcium sulfate. The activity concentration of U-series radioisotopes in phosphate rock was around 1640 Bq/kg. ²²⁶Ra and ²¹⁰Pb tend to be distributed into phosphogypsum by up to 80%, whereas the fraction of U-isotopes is 10%. The most abundant trace elements in phosphate rock were Sr, Cr, V, Zn, Y, Ni and Ba. Some elements, such as Ba, Cd, Cu, La, Pb, Se, Sr, Th and Y, were enriched in the phosphogypsum. This enrichment may be attributed to an additional input associated to the sulfuric acid used for the phosphoric acid production. Furthermore, results from SEM-EDX demonstrated that toxic elements are not distributed homogeneously into phosphogypsum. Most of these elements are concentrated in particles <20 μm of high porosity, and could be easily mobilized by leaching and/or erosion.

[en] This meeting of the French Geological Society (SGF) was organized with the joint contribution of Areva, CNRS-INSU, PACEN, GUTEC, IDES, and Paris-Sud University. This document gathers the abstracts of the following 40 presentations: 1 - Uranium deposits of 'Intrusive'-type; 2 - U deposits beneath discordance: analogy with F-Ba-Pb-Zn(Ag) 'Basin Hosted'-type deposits?; 3 - Clays and related minerals as guides for uranium deposits prospecting: status of recent advances; 4 - Hudsonian Uranium mineralizations in the Western part of the Trans-Hudsonian orogen (Saskatchewan, Canada): a source for the formation of discordance-type deposits?; 5 - U-Th elements mobilization during the Panafrican metamorphism: implication on the formation of Cu-Co-(U) deposits, Solwezi dome, NW Zambia; 6 - Fractures network characterization by seismic and electrical anisotropy; 7 - study of uranyl speciation by Raman spectroscopy in chlorinated solutions (LiCl = 0.5 to 15 M) up to 350 deg. C. Metallogenic consequences and perspectives; 8 - Experimental weathering of natural monazite in the conditions of formation of Oklo and discordance-type uranium deposits; 9 - Disturbance of the U-Th-Pb chronometers during the low temperature weathering of monazite: synergy between irradiation damages and dissolution-precipitation; 10 - U(VI) interaction with humic substances: speciation and application to independent data; 11 - Preparation and characterization of Th_1-xU_xSiO₄ solid solutions: towards the understanding of coffinite formation?; 12 - A new geochemical tool for the study of U deposits: the anions in uraninite; 13 - Tectonics in the Unegt basin (E-Gobi, Mongolia): deformation stripes, hydrocarbons migration and U mineralizations; 14 - Study of U sources in the Erlian Basin (China); 15 Thermodynamic data acquisition for uranyl phosphates and vanadates: from synthetic analogues to natural samples; 16 - U speciation in Nopal I opals: geochemical consequences for the end of the deposit genesis; 17 - U distribution and valence in phosphorites; 18 - Nuclear industry and a 'uranium peak'?; 19 - Geologic context of the primary U deposits of the Damara orogenic belt (Namibia): from the migmatitic source to the plutonic deposit; 20 - U distribution in an Archean granite: from the batholith to the thin section; 21 - Mineralogical, geochemical and hydrochemical zoning of a roll-front in Kazakhstan: recent data and interpretations; 22 - Carbonated facies in silico-clastic series of roll-type U deposits of Kazakhstan: mineralogical, geochemical and isotopic data; 23 - 3D modeling of Muyunkum uraniferous deposit, Kazakhstan; 24 - From the stratigraphic model to the 3D geologic modeling of roll-front systems in Kazakhstan; 25 - U deposits in the tectonic-sedimentary evolution of the Franceville basin (Gabon); 26 - From Talak to Teleflak (Madaouela, Arlit Niger): analysis of the key events for the understanding of the evolution of the region during the Visean and of the related mineralizations in the Guezouman; 27 - Contribution of clays in the understanding of the sedimentary context at the base of the Athabasca basin in the Shea Creek deposit area (W Athabasca, Saskatchewan, Canada); 28 - Clayey weathering and related uraniferous mineralizations along the Kiggavik-Andrew Lake structural cluster (Nunavut, Canada); 29 - About the U deposits of rhyolitic origin: Xiangshan /Jiangxi (China), Sierra Pena Blanca/ Chihuahua (Mexico) and Lodeve/Herault (France); 30 - U and Th L/L extraction: role of water in their solvation sphere in organic environment; 31 - New uranium concentrate precipitation process to increase the bulk concentrate density; 32 - Grain-size study of natural phosphates from Morocco 'Oulad Abdoun Basin': distribution, quantifying of natural radionuclides and genesis implication; 33 - Phosphoric acid uranium content valorization; 34 - Development of a direct coupling system between an instrumented column and an ICP-MS: application to uranium migration in a sand column in the presence of humic acids; 35 - U speciation and stability factors in the Cominak mining wastes (Niger); 36 - IMOURAREN - leaching tests and analcimes specificity; 37 - Modeling of U ore acid leaching tests, application to in-situ recovery; 38 - Role of detrital pyrites in U concentration in the meso-Archean Pongola basin (2.9 Ga, South Africa); 39 - The role of black chert pebbles in uranium mineralisation in conglomerates of the basal Mozaan Group (Pongola basin, South Africa); 40 - U hydrothermal alteration and leaching in the Questembert granite (Massif Armoricain, France)

[en] Abstracts are provided for the different contributions. They address: The UDEPO database of the IAEA; The availability on the long term of world uranium resources; Interpreting U-Th distribution in the continental crust for radiometric data (NEEDS GeoMac project); The U cycle and the growth-remobilization of continents (NEEDS URCO project); The petrographic and geochemical characterisation of bituminous, sandstone and mud-stone shales in Morocco (analogy with the confinement and storage of radioactive wastes); Recent developments in radiometry (from well logging to measurement in laboratory); Multi-scale approach for the characterisation of emanometry anomalies noticed in the Zoovch Ovoo deposit, Mongolia; A new investigation tool for mining applications (the underground muon tomography, NEEDS ToMuFor project); Contribution of VIS-PIR spectrometry to the study of coffinite in the mining context; Isotopic fractioning of oxygen during processes of precipitation, calcination and reduction of uranium oxides; H₂ production and mobility in uranium deposits associated with a discrepancy; Lixiviation of the hydrogen-bearer Cigar Lake ore; New molecules extracting the uranium present in industrial phosphoric acid; Mechanisms of uranium extraction in ionic liquid media (NEEDS MINION project); Uranium recovery from acid media by using silica-type functionalized solid supports; Damage zone of reactivated Hudsonian faults, a major fluid pathway for large and deep brine percolation in basement rocks of the Athabasca basin (Cigar Lake U deposit, Canada); Is a fertile basement complex a necessary prerequisite to the genesis of high grade U/C-type uranium deposits: source rock clues from the Eastern Athabasca Basin?; Structural analysis of the ductile-brittle fault network in the basement below the Athabasca Basin (Martin Lake, Saskatchewan) - Implications on the controls of uranium-related hydrothermal alteration; Integrated targeting for fault-related basement-hosted uranium deposits: lessons from geologically-constrained 3D gravity inversion modelling and lead isotope geochemistry at the Contact prospect (Kiggavik area, Thelon Basin, Canada); Geology and structural controls in the Contact prospect, Kiggavik uranium project (NE Thelon area, Canada); Synthesis and characterisation of UTi₂O₆ brannerite; Physico-chemical characterisation of natural brannerite samples by scanning electronic microscopy and electronic probe; Assessment of the atmospheric impact of a uranium mine on the recording of radionuclides and metallic trace elements in a mire; Contribution of thermodynamics to UF₆ industrial production; Effects of irradiation on the evolution of mineralogical properties of apatites (NEEDS IrrPO4 project); Prospection guides in searches for uranium mineralizations in the Tim Mersoii Basin; Metallogenic model of uranium deposits associated with the Arlit fault (Tim Mersoii Basin, Niger); Molybdenum valorisation from effluents of a uranium ore treatment plant; Characterisation of the host layer of uranium mineralizations of Mikouloungou (High Ogooue Province, Gabon) - Part 1: Sedimentology, stratigraphy, diagenesis. Geo-dynamic implication on the Francevillian. Part 2: Petrography, dating. Geodynamic implications on the Francevillian