A process for leaching mineral values from an underground formation in situ, applicable particularly to uranium. In accordance with known practice, an aqueous solution of a leaching agent (alkaline or acid) is delivered into the formation, where it remains for a prolonged period, and then is pumped out with dissolved mineral values. Some minerals occur naturally in a relatively insoluble form, and can be leached only if first oxidized to a more soluble form. An example is uranium oxide, which occurs naturally in the plus-four valance state (UO2) and must be oxidized to the plus-six valance state (UO3) to enable it to be leached. Invention is to introduce oxygen to the leaching solution at a substantial depth within the injection well where the head of solution thereabove increases the solubility of oxygen in the solution.
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