Radionuclide release from simulated waste material after biogeochemical leaching of uraniferous mineral samples

Biogeochemical mineral dissolution is a promising method for the released of metals in low-grade host mineralization that contain sulphidic minerals. The application of biogeochemical mineral dissolution to engineered leach heap piles in the Elliot Lake region may be considered as a promising passive technology for the economic recovery of low grade Uranium-bearing ores. In the current investigation, the decrease of radiological activity of uraniferous mineral material after biogeochemical mineral dissolution is quantified by gamma spectroscopy and compared to the results from digestion/ICP-MS analysis of the ore materials to determine if gamma spectroscopy is a simple, viable alternative quantification method for heavy nuclides. The potential release of Uranium (U) and Radium-226 (²²⁶Ra) to the aqueous environment from samples that have been treated to represent various stages of leaching and passive closure processes are assessed. Dissolution of U from the solid phase has occurred during biogeochemical mineral dissolution in the presence of Acidithiobacillus ferrooxidans, with gamma spectroscopy indicating an 84% decrease in Uranium-235 (²³⁵U) content, a value in accordance with the data obtained by dissolution chemistry. Gamma spectroscopy data indicate that only 30% of the ²²⁶Ra was removed during the biogeochemical mineral dissolution. Chemical inhibition and passivation treatments of waste materials following the biogeochemical mineral dissolution offer greater protection against residual U and ²²⁶Ra leaching. Pacified samples resist the release of ²²⁶Ra contained in the mineral phase and may offer more protection to the aqueous environment for the long term, compared to untreated or inhibited residues, and should be taken into account for future decommissioning. - Highlights: • Gamma counting showed an 84% decrease in ²³⁵U after biogeochemical mineral leaching. • Chemical digestion/ICP-MS analysis also showed an 84% decrease in total U. • Over 70% of the ²²⁶Ra remained in the host material after biogeochemical leaching. • Bacterial Inhibition offers greater protection against U leaching from host wastes. • Passivation provides greater protection against ²²⁶Ra leaching from waste material