Can Uranium in Shale Matrix Be Released into Fluids? Insights from Experimental Simulations and Chemical Extraction

Shale is a primary host for both organic matter and uranium within sedimentary basins. Whether uranium within shale can be released from the rock matrix into formation fluids is a critical factor in evaluating its potential as a source of ore fluids for sandstone-hosted uranium deposits, yet it remains a subject of ongoing debate. This study addresses this question by investigating the chemical speciation of uraniuma fundamental determinant of its stabilitythrough thermal simulation experiments and a sequential extraction method. The results demonstrate that uranium release potential strongly depends on its speciation within shale. Weak-acid-extractable and reducible fractions exhibit a heightened tendency to release into fluids, with 80.7% and 63.9% released at temperatures below 100 °C, respectively. Oxidizable species demonstrate partial release (29.4%) at temperatures exceeding 200 °C, whereas residual fractions remain in the solid phase. The released uranium reaches concentrations in aqueous solutions and oil at levels comparable to ore-forming fluids in sandstone-hosted uranium deposits. However, due to the limited understanding ofuranium's mobility potential in oxygen-deficient fluids, its potential as a source for such fluids requires further investigation.