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Geochemical modeling of reactive minerals associated with in situ recovery of uranium

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Résumé

Dissolution of uraninite and pyrite in the presence of oxidants and SO4 2- derived from H2SO4 are important geochemical processes taking place during in situ recovery (ISR) of uranium worldwide. During ISR of uranium using H2SO4, pH values of 3 or less are typically achieved depending on the buffering capacity of reactive (intermediate kinetic) minerals. Reactions involve significant dissolution of uraninite and primary silicate minerals. Possible precipitation of secondary minerals (gypsum, alunite, and jurbanite) can also occur under localized acidic conditions. Geochemical modeling using PHREEQC and CHESS was conducted to quantify dissolution and redox reactions. The preextraction geochemistry is built, in agreement with observations, by equilibrating groundwater with primary phases (uraninite, pyrite, K-feldspar, hematite, calcite, kaolinite, Mg-montmorillonite, and Canontronite). Acidification results in early-stage dissolution of Fe(III) minerals, which initiates oxidative and irreversible dissolution of uraninite and pyrite. Surface-controlled dissolution of K-feldspar, kaolinite, and Mg-montmorillonite with intermediate kinetics produces an acidic, mixed solute [Al-Ca-Fe(II)-SO4] composition, enhancing precipitation of alunite and jurbanite. 2D simulations were then performed to study mixing effects, particularly near the production wells. Flow velocities can be much smaller for longer streamtubes allowing for slower kinetic reactions to be effective. The amount of buffering by calcite increases along these flow paths characterized by increasing pHbuffering capacity.
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Dates et versions

hal-00624658 , version 1 (19-09-2011)

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  • HAL Id : hal-00624658 , version 1

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Patrick Longmire, Vincent Lagneau. Geochemical modeling of reactive minerals associated with in situ recovery of uranium. Goldschmidt, Aug 2011, Prague, Czech Republic. ⟨hal-00624658⟩
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