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| Fig. 1: The In-Situ Uranium Recovery Process. [3] Injection wells (1) pump a chemical solution into the layer of earth containing the Uranium. The solution dissolves the Uranium and is then pumped back to the surface through recovery wells (2). Monitoring wells (3) are checked regularly. (Courtesy of the NRC Source: Wikimedia Commons) |
There are a few major mining techniques to harvest uranium. Conventional mining operates similar to surface open-pit coal mines and underground coal mines. Multiple metals can be produced from these mines. Another form, by-product mining, refers to the uranium that would not otherwise be economic to recover. While both these techniques produce uranium in different ways, the most common and direct way of mining uranium is known as in-situ leach (ISL) mining. ISL was first tried on an experimental basis in Wyoming during the early 1960's. Stemming from this, the first commercial in-situ leaching mine began operating in 1974. Today, there are 9 ISL mines in operation in the United States. [1]
Today, most uranium mining in the United States is done now by in situ leach methods, which are also known as in situ recovery (ISR). [2] In-situ mining is a mining process involving minimal surface disturbance, extracting uranium from porous sandstone deposits by reversing the natural processes which deposited the uranium. The uranium is extracted by injecting an acidic or basic aqueous solution, depending upon the underlying geology, into the subsurface through a number of strategically placed injection wells. Injection wells pump a chemical solution into the layer of the Earth containing uranium ore. The solution dissolves the uranium from the deposit in the ground and is then pumped back to the surface through recovery wells and sent to the processing plant to be processed into uranium yellowcake. Monitoring wells are checked regularly to ensure that uranium and chemicals are not escaping from the drilling area (see Fig. 1). [3]
To be mined in-situ, the uranium deposit must occur in permeable sandstone aquifers. These sandstone aquifers provide the plumbing system for both the original emplacement and the recovery of the uranium. [1] The uranium was emplaced by weakly oxidizing ground water which moved through the plumbing systems of the geologic formation. Sandstone hosted uranium deposits are widespread globally and span a broad range of host rock ages. These uranium minerals are usually uraninite (oxide) or coffinite (silicate) coatings on individual sand grains. [1]
© Colton Hock. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] J. Slezak, "Uranium ISL Mining Activities at the International Atomic Energy Agency," in Uranium, Mining and Hydrogeology, ed. by B. J. Merkel and A. Hasche-Berger (Springer, 2008).
[2] Uranium Mining in Virginia (National Academies Press, 2011).
[3] "2013-2014 Information Digest," U.S. Nuclear Regulatory Commission, NUREG-1350, July 2013.
