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Geochemistry of Restoration
Published in William J. Deutsch, Groundwater Geochemistry, 2020
At the iron-reducing interface several elements such as Se, As, Mo, and U may be concentrated because of the lower solubility of minerals containing these elements under reducing conditions than under oxidizing conditions.6 The typical uranium mineral present at this interface is uraninite (UO2). The elevated concentration of uranium in the solid phase at this interface is taken advantage of by locating and mining these occurrences, which are called roll-front uranium deposits because of their distinctive pattern. Figure 8-1 shows a cross section of a roll-front deposit with the direction of groundwater flow from the oxidizing to reduced zones of the aquifer. These deposits occur in aquifers straddled by confining units. The shape of the roll-front is due to the relatively high permeability in the mid-region of the aquifer compared with the lower permeability as the confining units with their higher clay content are approached. The majority of the flow is down the middle of the aquifer; therefore oxidizing conditions have moved farther downgradient in the center of the formation comprising the aquifer than at its top and bottom.
Minerals of radioactive metals
Published in Francis P. Gudyanga, Minerals in Africa, 2020
Uranium occurs in nature in low concentrations in soil, rock and water. Uranium-bearing minerals such as uraninite UO2 [766], carnotite, autunite, uranophane, torbernite and cof-finite are the commercial sources of the metal. It also occurs in some substances such as phosphate rock deposits, and in minerals such as lignite and monazite sands. Uranium(VI) forms highly soluble carbonate complexes at alkaline pH leading to an increase in mobility and availability of uranium to groundwater and soil from nuclear waste [767].
The Range of Environmental and Social Concerns
Published in Karlheinz Spitz, John Trudinger, Mining and the Environment, 2019
Karlheinz Spitz, John Trudinger
As the naturally occurring element with the highest atomic number, uranium is 70% more dense than lead. This silver gray metal is weakly radio-active. Three isotopes occur: U234, U235 and U238, of which U238 is the most prevalent accounting for more than 99% of uranium. As for all radioactive metals, the metallic nature is of no concern for the end user -uranium is used as nuclear fuel to produce energy, and 20 kg of uranium produces as much energy as 400,000 kg of coal. U235, the fissile isotope used in nuclear reactions, must be enriched prior to use. Uranium is not particularly rare, being more abundant than tin, mercury or silver. Several types of uranium ore occur; the predominant uranium mineral is uraninite. Uranium is chemically reactive and oxidizes readily. It may accumulate in the bones; its toxicity is of more concern than its radioactivity. Depleted uranium, U238, is used for armaments and other applications requiring a highly dense material.
Extraction of Molybdenum and Uranium from Low-Grade Molybdenum Bearing Ore Containing Uranium through Mechanical Activation Following Acid Leaching
Published in Mineral Processing and Extractive Metallurgy Review, 2023
Yongliang Wang, Congying Wang, Hui Liu, YunSheng Meng
Molybdenum is usually associated with other metals (Essilfie-Dughan et al. 2011), in which uranium is one of the associated minerals, and mainly in the state of uraninite (UO2), pitchblende (collomorph UO2) and coffinite (U(SiO4)1-x(OH)4x), in which uraninite is the really economic ore mineral (Hazen, Ewing, and Sverjenski 2009; Migeon et al. 2018; Smith 1984). In the current industry, sulfuric acid leaching is commonly used to recover uranium from the ore because of its wide availability and low cost (Edwards and Oliver 2000). When the uranium ore is mechanically grinded with oxidant, the encapsulated uranium may be exposed to the acid, which will promote the uranium to dissolve into acid. Meanwhile, the Fe(II) leached from the ore will be oxidized to Fe(III) by the oxidants, which favors the dissolution of uranium as the following reaction (Lottering et al. 2008; Migeon et al. 2018; Venter and Boylett 2009):
Aligning missions: nuclear technical assistance, the IAEA, and national ambitions in Pakistan
Published in History and Technology, 2020
Over the next several years, IAEA experts from North America and Europe oversaw Pakistan’s uranium prospecting. One major event was the identification, by another IAEA expert, the American geologist G. W. Chase, of a paleostream channel in the Baghal Chur basin, a key clue about where the uranium minerals may have distributed over long periods of time. Chase himself an American, having worked on uranium exploration in Oklahoma and elsewhere during the war, and worked for the AEC in the 1950s. Another discovery was the consistent finding of the ‘black’ oxide known as uraninite. Formerly known as pitchblende, the ore contained lead, rare earths, and a great deal of uranium. Although ‘yellow’ uranium oxide had been observed in the area for years, finding black uraninite in such quantities in 1973 was significant news for Pakistan’s uranium future. Project manager J. W. Hoadley (a Canadian geologist) guessed that two of the drilling sites in the Baghal Chur area would contain about 150 tons of uranium. He noted that a new phase of exploration ‘should be carried out with all possible energy and despatch’.43
Laboratory core investigations of sandstone-hosted uranium for in situ recovery
Published in Applied Earth Science, 2020
Micha Zauner, Andreas Weller, Matthias Halisch
Figures 5 and 6 show the modal mineralogy and GXMAP images of the analysed thin sections of selected drill cores, emphasizing rock texture and mineralization style. Both are medium- to coarse-grained arkosic sandstones composed of quartz, feldspar (K-fsp and plagioclase), accessory clay minerals (kaolinite/dickite, illite), and organics/carbonates. The elemental composition represents typical arkosic sandstone, whereas aluminium, sodium, potassium, and calcium are mostly incorporated in residual feldspar. Calcium is also present in accessory carbonates forming a binding component in the cement. The uranium minerals are generally very fine grained (<1 µm) but also form mixed grains or agglomerates up to 100 µm. Since the individual grain size of the single V or U crystal phase is <1 µm, it is below the LOD of the SEM, and thus they are classified as mixed phases (U-V-silicates mixed phases). Other methods are required for unambiguous phase identification. According to local geology, most of the uranium is probably mineralized as coffinite and uraninite. The uranium minerals form coatings around the silicates and occur as fine agglomerates in interstitial pore spaces, as illustrated in Figure 6.