In situ recovery (ISR) uranium mining (aka in situ leaching and solution mining) is one of the most economical and cost effective techniques of mining uranium in the United States. ISR mining was developed in Wyoming during the 1960s and has been the primary of mining uranium in the US since that time. In 2011, the most recent data from the US Energy Information Administration, the five US ISR mines (Crow Butte, Alta Mesa Project, Hobson ISR Plant/La Palangana, Smith Ranch-Highland Operation, and Willow Creek Project) produced about 4.1 million pounds of uranium.
ISR is best done in roll front uranium deposits and involves pumping and circulating groundwater mixed with a bicarbonate solution into the ore body through a series of injection wells leaving the ore in the ground and recovering the uranium by dissolving the minerals and pumping the pregnant solution to the surface through production wells (wellfield design will be a future topic), where it is recovered as yellowcake in a processing plant.
The processing plant of an ISR operation is basically a large water softener. The process of separating the uranium from the pregnant water solution is called ion exchange. The processing facility is primarily composed of large tank that hold resin, regenerating water, and pumps to move the water. Uranium in solution is a negatively charged ion (anion) so the tanks contain anion resin beads. In the ion exchange process, the uranium-in-solution passes over the resin transferring the uranium onto the tiny plastic resin beads. While this is happening, the bicarbonate (a negative ion) transfers off the resin and into the water, completing the ion exchange. With most of the uranium removed, the water is refortified with oxygen and re-injected into the ground repeating the process until most of the uranium has been removed from the deposit.
Image from World Nuclear Association
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