Oliver Blume

B.Sc. (Honours) Thesis

Synthetic leaching of uranium from South Mountain Batholith granites and Horton Group siltstones of south central Nova Scotia, using a suite of ionic complexes

(PDF - 3.4 Mb)

Many rock formations in Nova Scotia, particularly granitic rocks and siltstones of Devono-Carboniferous age, may have an impact on the groundwater quality of surrounding areas. These geologic units have locally elevated uranium concentrations. Roll front type mineralization is responsible for the high uranium concentrations found in the Carboniferous Horton Group siltstones that are used in this study. The South Mountain Batholith (SMB) is a suite of peraluminous granitic rocks that contain locally high uranium concentrations in late-stage mica-rich granites and monzogranites. Uranium can also concentrate in late stage fracture and fault structures. Weathering and other geochemical processes can mobilize uranium, which allows the metal to accumulate in groundwater systems in concentrations above recommended guidelines established by Health Canada (20 μg/L).

This laboratory study focuses on the impact of calcium, chloride, carbonate and sulphate complexes on uranium mobilization, with a focus on geochemical conditions such as pH and Eh as well as lithologic characteristics of the samples. A synthetic leaching procedure using extraction fluids created with the ions listed above, is used to simulate natural weathering processes to try and identify the geochemical components that may be liberating uranium specifically from SMB granites and Horton Group siltstones. These experiments confirm the importance of Eh-pH conditions in mobilizing uranium from these rocks. The sulphate extraction fluids leach elevated U concentrations in oxidizing acidic conditions whereas the carbonate extraction fluids leach elevated U concentrations in oxidizing alkaline conditions. In general, the granites leach higher U levels than the siltstones even with lower U concentrations in the whole rock. It is concluded that, under consistently oxidizing conditions, numerous geochemical and geologic factors have an influence on U mobility, but pH, lithology and mineralogy seem to be the major controlling parameters behind U liberation in this study. Key words:

Keywords: Uranium, Carbonate, Sulphate, Extraction, Leachate, pH, Eh, Granite, Siltstone
Pages: 84
Supervisor: Anne-Marie Ryan