ARS Characteristics of Different Uranium Fractions in Sandstone Uranium Deposit and Their Indication for in-situ Leaching of Uranium

In order to study the indicative function of ²³⁴U/²³⁸U activity ratios (ARS) to in-situ leaching of uranium, taking uranium ore from Xinjiang as an example, sequential extraction test was adopted to separate different uranium chemical fractions, and horizontal column leaching test was applied to obtain pregnant leach solution. ARS in the chemical fractions and the pregnant leach solution were measured by ICP-MS and then uranium concentrations in leaching pregnant solution were measured by TiCl₃ reduction-NH₄VO₃ oxidation titration method. The results show that ARS are higher (1.293-1.348) in exchangeable fraction (F1) and easily acid soluble fraction (F2), which decrease to 1.204-1.229 in acid soluble fraction (F3) and then reduce to the minimum 0.917-0.934 in oxidation fraction (F4). After that ARS increase to 1.018-1.142 in hardly soluble fraction (F5). Three phases of uranium leaching were identified according to the ARS. The first phase was characterized by the relatively high ARS in the range of 1.217-1.318, and the leaching uranium is mainly U(Ⅵ) in fraction F1, F2 and F3. The second phase was represented as the decrease of ARS, up to 1.016, and the leaching uranium is mainly U(Ⅳ) partly in F3 and primarily in F4. The third phase was characterized by the fluctuant ARS of 1.070-1.118, and the few leaching uranium is mainly the hardly soluble uranium in F5.