Abstract
Factor and cluster analyses as well as the Pearson correlation coefficient have been applied to geochemical data obtained from phosphorite and phosphatic rocks of Duwi Formation exposed at the Red Sea coast, Nile Valley and Western Desert. Sixty-six samples from a total of 71 collected samples were analysed for SiO 2, TiO 2, Al 2O 3, Fe 2O 3, CaO, MgO, Na 2O, K 2O, P 2O 5, Sr, U and Pb by XRF and their mineral constituents were determined by the use of XRD techniques. In addition, the natural radioactivity of the phosphatic samples due to their uranium, thorium and potassium contents was measured by gamma-spectrometry.The uranium content in the phosphate rocks with P 2O 5>15% (average of 106.6 ppm) is higher than in rocks with P 2O 5<15% (average of 35.5 ppm). Uranium distribution is essentially controlled by the variations of P 2O 5 and CaO, whereas it is not related to changes in SiO 2, TiO 2, Al 2O 3, Fe 2O 3, MgO, Na 2O and K 2O concentrations.Factor analysis and the Pearson correlation coefficient revealed that uranium behaves geochemically in different ways in the phosphatic sediments and phosphorites in the Red Sea, Nile Valley and Western Desert. In the Red Sea and Western Desert phosphorites, uranium occurs mainly in oxidized U 6+ state where it seems to be fixed by the phosphate ion, forming secondary uranium phosphate minerals such as phosphuranylite.In the Nile Valley phosphorites, ionic substitution of Ca 2+ by U 4+ is the main controlling factor in the concentration of uranium in phosphate rocks. Moreover, fixation of U 6+ by phosphate ion and adsorption of uranium on phosphate minerals play subordinate roles.
Published Version
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