Study of the Mobilization of Uranium Isotopes in a Sandstone Aquifer in Combination with Groundwater Data

Abstract

This work is part of a research project that aims to develop a method for combined radiocarbon and uranium-isotope dating of groundwater. The specific objective of this study was to investigate the mobility of uranium isotopes in the various mineral phases of rocks of an aquifer of sandy-clay deposits of the Vendian in the northwest of Russia, for which a partial extraction procedure was used. Representative aliquots of each core sample were treated with various reagents: distilled water, low mineralized fresh natural groundwater, minopolycarboxylic acid chelating agent (0.05 M EDTA), 0.5M HCl, 15 M HNO 3 , as well as total digestion, and the U isotope data for each procedure are reported in this study. The following mineral phases of core samples were characterized: sorbed material, carbonate minerals, amorphous iron oxides, partially soluble aluminosilicates and crystalline iron oxides, totally digestible aluminosilicates and a clay/quartz resistate. Red-colored siltstones and sandstones were depleted in uranium in relatively readily soluble mineral phases. The concentration of sorbed uranium was established in the range 15.8 ± 2.1-30.5 ± 3.9 µg/kg and carbonate minerals contained even less uranium. For iron hydroxides and the most readily soluble aluminosilicates, uranium concentrations were in the range 168 ± 24-212 ± 28 µg/kg. The most insoluble fraction contained uranium in the range 1.65 ± 0.21-4.32 ± 0.45 mg/kg. In green-colored siltstones, the concentration of sorbed uranium was much higher in the range 106 ± 14-364 ± 43 µg/kg. Carbonate minerals and amorphous iron oxides contained uranium in the range 1.91 ± 0.21-2.34 ± 0.26 mg/kg. In aluminosilicates and a clay/quartz resistate, uranium concentrations were in the range 5.6 ± 0.5-16.8 ± 1.4 mg/kg. Elevated values of 234 U: 238 U activity ratio prevailed in the sorbed material and iron hydroxides. In aluminosilicates and clay/quartz resistate, the values decreased. This indicates the replacement of primary sedimentogenic uranium by secondary hydrogenic uranium sorbed on the surface of minerals and coprecipitation with iron hydroxides. The results obtained made it possible to carry out preliminary quantitative estimates of the retardation factor and recoil loss factor of uranium in the groundwater of siltstones and sandstones of the studied Vendian aquifer.

Dating of groundwater using uranium isotopes disequilibrium in Siwa Oasis, Western Desert, Egypt

“…In the same context, the daughter nuclide ( 234 U) passes most actively from surface coatings (carbonates, iron oxides and clay minerals) into the water, increasing the activity ratio of uranium isotopes in water 56 . The results suggest that the uranium series disequilibrium may be an important tool for tracking the migration of uranium series radionuclides in groundwater from different aquifers 48 .…”

Modeling Changes in the Composition of River Water with Discharged Wastewater: A Case Study in NW Russia

“…As shown in [60][61][62], Vendian siltstones and sandstones do not contain native uranium minerals. The uranium was in a dispersed state and was redistributed by groundwater along its streamlines from the recharge zones of the watersheds to the discharge zones in the river valleys.…”