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Abstract

Magnesium values are leached from a fragmented mass containing combusted oil shale particles. Magnesium is leached selectively with respect to calcium compounds and silicates with aqueous solutions of a mixture of purgeable, acid-forming gases such as carbon dioxide with a minor proportion of sulfur dioxide. A two-stage leaching process can employ leachant with dissolved carbon dioxide and sulfur dioxide in a first stage and with a carbon dioxide containing solution in the substantial absence of sulfur dioxide in the second stage. An enriched solution containing magnesium values is withdrawn from the fragmented mass and magnesia is recovered from such enriched solution. In one embodiment a fragmented permeable mass of formation particles containing oil shale and carbonates of calcium and magnesium is formed in an in situ oil shale retort. A combustion zone is advanced through the fragmented mass, whereby kerogen in oil shale in the fragmented mass is decomposed in a retorting zone on the advancing side of the combustion zone to produce gaseous and liquid products including shale oil, and particles containing retorted oil shale are combusted for converting magnesium values to more leachable form such as magnesium oxide. Such a process is also used for leaching combusted oil shale from above ground retorting and combustion.

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First Claim