Change of the 234U Content in Uranium Obtained by Underground Leaching at the Dalmatovskoye Deposit

Abstract

The results of a determination of the 234 U content in various samples obtained at the Dalmatovskoye deposit are presented: samples of ores, solutions from technological wells, and concentrate obtained at the deposit. It is shown that underground leaching increases the 234 U content in the uranium obtained. The 234 U concentration in the concentrate exceeds 0.0070%, which is 1.3 times higher than the equilibrium content in ore (0.0054%). The reasons for the change in the isotopic composition of uranium on leaching from ore using sulfuric-acid solutions are discussed.The 234 U content in two samples of uranium ores from the Dalmatovskoye deposit, which were obtained from the geological-mineralogical museum of All-Russia Scientific-Research Institute of Chemical Engineering, was determined in [1]. Similar measurements were performed in 2003 for uranium concentrate obtained from the Dalur company. These latter results do not agree with previous results (Table 1). The 234 U content in the ore samples is somewhat lower than the equilibrium value 0.00534% [1], while in the concentrate it is much higher. The lower 234 U content could be due to partial washing out of the easily soluble 234 U-enriched U(VI) from the main ore bodies by ground water. The ore samples may have been obtained from such bedrock. However, the reasons for the large discrepancy between the results reamined unclear. Consequently, it was decided to determine additionally the 234 U content in various uranium samples taken directly from the Dalmatovskoye deposit: ore samples, samples of solutions from service wells, and a concentrate sample.Characteristics of the Dalmatovskoye Deposit. The trans-Ural uranium region is currently known to contain three uranium deposits with average reserves: Dalmatovskoye -explored and currently in operation; Dobrovol'skoye -preliminary exploration completed; and, Khokhlovskoye -in the assessment stage. The predicted resources of the entire region are estimated to be 115,000 tons.The Dalmatovskoye deposit is an exogenic infiltration uranium deposit in paleozoic valleys. The uranium mineralization lies in clayey, sandy, sand-gravel, and gravel deposits. The uranium-bearing minerals -uraninite and coffinite -are distributed approximately in equal ratios. The ore bodies lie at depths 410-440 m. The average uranium content in the ore is 0.039%. For economic reasons, the deposit is being developed by underground well leaching, for which a 1-1.2% solution of sulfuric acid (10-12 g/liter) is used.The deposit underwent experimental-commercial development in 1984-