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| Fig. 1: Uranium ISL mining method. (Courtesy of the NRC. Source: Wikimedia Commons) |
The United States of America considers In-Situ leach (ISL) to be the most "cost effective and environmentally acceptable" mining method. [1] The process is minimally invasive as uranium ore is extracted directly from the ore body where it is in the ground, hence in-situ. [2] An alkaline or acidic solution is pumped down into the rock where it chemically dissolves the uranium ore. [2] Recovery wells pump up the pregnant solution to the surface. [2] Main trunk lines carry the pregnant solution to a processing plant where the uranium is extracted and the leaching solution is recycled. [2]
Kazakhstan holds the second largest uranium resources in the world behind Australia. [3] To minimize radioactive waste, Kazakhstan evolved from open-pit and underground mines to the ISL mining method. [2] Kazakhstan's environmentally conscious laws require that aquifers be restored to their natural state after the ISL mining operations. [2] To restore the contaminated groundwater to its original chemical condition, Kazakhstan ISL mines experimented with sulfate-reducing bacteria that decreased sulfate content in the sulfuric acid leaching solution from 10 to 0.5g/L. [2] Kazakhstan's ISL mines elect to use much higher acid concentrations than competing Uranium producer Australia, an average of 40 kg/kgU compared to a recorded 7.7 kg/kgU in Australia, as they choose to not apply an oxidizing agent. [1]
To protect residents from contaminated groundwater as a result of acidic solution run-off, Kazakhstan establishes an exclusion zone around the site of 150 by 15 km within which the extraction of drinking water is prohibited. [3] As an added precaution to the run-off problem, monitoring wells are strategically placed around the injection and recovery wells as well as ore body to ensure the chemical solutions and radioactive waste are not leaving the mining site. [4] Fig. 1 shows how the ISL method works by injecting recycled solution down into the sandstone to recover the uranium-containing solution that has run through the ore deposit back up to the surface to then be sent back to the processing plant for extraction and solution recycling. Today, nearly all of Kazakhstan's mines employ the ISL mining method. [5] This is because their uranium deposits are located in sandstone underground and below the water table in a confined aquifer making them amenable to the ISL mining method. [5] Kazakhstan's uranium mining operations are run by national energy company Kazatomprom, making standard mining practices in ISL enforceable and practical. [5] Kazakhstan is a responsible leader in the employment of the ISL mining method leading to great success in becoming the world's leading uranium exporter. [5] I hope the development and implementation of minimally invasive and environmentally responsible resource extraction techniques becomes universal as our planet continues to bare the impact of human exploitation.
© Amir Bashti. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. 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] "In Situ Leach (ISL) Mining of Uranium," World Nuclear Association. June 2009.
[2] G. Taylor et al., "Review of Environmental Impacts of the Acid In-situ Leach Uranium Mining Process," Commonwealth Scientific and Industrial Research Organisation (CSIRO), August 2004.
[3] G. M. Mudd, "Critical Review of Acid In-Situ Leach Uranium Mining: 2. Soviet Block and Asian," Environ. Geol. 41, 404 (2001).
[4] C. Hock, "In-Situ Leach Mining of Uranium," Physics 241, Stanford University, Winter 2017.
[5] E. Sagatov, "Nuclear Power in Kazakhstan," Physics 240, Stanford University, Fall 2010.
