| In situ leach mining (ISL), also known as | | | | zone. The mined aquifer is surrounded, both |
| in-situ mining or solution mining, was first | | | | laterally and above and below, by monitor |
| used as a means to extract low grades of | | | | wells which are frequently sampled to ensure |
| uranium from ore in underground mines. First | | | | that all mining fluids are retained within |
| used in Wyoming in the 1950s, originally as a | | | | the mining zone. The "bleed" also provides a |
| low production experiment at the Lucky June | | | | chemical bleed on the aquifer to limit the |
| mine, it became a high-production, low cost | | | | buildup of species like sulfate and chloride |
| method of fulfilling Atomic Energy Commission | | | | which are affected by the leaching process. |
| uranium requirements at Utah Construction | | | | The "bleed" water is treated for removal of |
| Company's Shirley Basin mining operations in | | | | uranium and radium. This treated water is |
| the 1960s. Pioneered through the efforts of | | | | then disposed of through waste water land |
| Charles Don Snow, a uranium exploration and | | | | application, or irrigation. A very small |
| mining geologist employed by Utah, many of | | | | volume of radioactive sludge results; this |
| his developments are still used today in ISL | | | | sludge is disposed of at an NRC licensed |
| mining. | | | | uranium tailings facility. |
| | | | |
| What is ISL mining? According to the Wyoming | | | | The ion exchange resin is stripped of its |
| Mining Association website, ISL mining is | | | | uranium, and the resulting rich eluate is |
| explained in the following manner. (We choose | | | | precipitated to produce a yellow cake slurry. |
| Wyoming because it is the birthplace of | | | | This slurry is dewatered and dried to a final |
| "solution mining" as it was originally | | | | drummed uranium concentrate. |
| called.) | | | | |
| | | | At the conclusion of the leaching process in |
| "In-situ mining is a noninvasive, | | | | a well field area, the same injection and |
| environmentally friendly mining process | | | | production wells and surface facilities are |
| involving minimal surface disturbance which | | | | used for restoration of the affected ground |
| extracts uranium from porous sandstone | | | | water. Ground water restoration is |
| aquifers by reversing the natural processes | | | | accomplished in three ways. First, the water |
| which deposited the uranium. | | | | in the leach zone is removed by "ground water |
| | | | sweep", and native ground water flows in to |
| To be mined in situ, the uranium deposit must | | | | replace the removed contaminated water. The |
| occur in permeable sandstone aquifers. These | | | | water which is removed is again treated to |
| sandstone aquifers provide the "plumbing | | | | remove radionuclides and disposed of in |
| system" for both the original emplacement and | | | | irrigation. Second, the water which is |
| the recovery of the uranium. The uranium was | | | | removed is processed to purify it, typically |
| emplaced by weakly oxidizing ground water | | | | with reverse osmosis, and the pure water is |
| which moved through the plumbing systems of | | | | injected into the affected aquifer. This |
| the geologic formation. To effectively | | | | reinjection of very pure water results in a |
| extract uranium deposited from ground water, | | | | large increment of water quality improvement |
| a company must first thoroughly define this | | | | in a short time period. Third, the soluble |
| plumbing system and then designs well fields | | | | metal ions which resulted from the oxidation |
| that best fit the natural hydro-geological | | | | of the ore zone are chemically immobilized by |
| conditions. | | | | injecting a reducing chemical into the ore |
| | | | zone, immobilizing these constituents in |
| Detailed mapping techniques, using | | | | situ. Ground water restoration is continued |
| geophysical data from standard logging tools, | | | | until the affected water is suitable for its |
| have been developed by uranium companies. | | | | pre-mining use. |
| These innovative mapping methods define the | | | | |
| geologic controls of the original solutions, | | | | Throughout the leaching and restoration |
| so that these same routes can be retraced for | | | | processes, a company ensures the isolation of |
| effective in situ leaching of the ore. Once | | | | the leach zone by careful well placement and |
| the geometry of the ore bodies is known, the | | | | construction. The well fields are extensively |
| locations of injection and recovery wells are | | | | monitored to prevent the contamination of |
| planned to effectively contact the uranium. | | | | other aquifers. |
| This technique has been used in several | | | | |
| thousand wells covering hundreds of acres. | | | | Once mining is complete, the aquifer is |
| | | | restored by pumping fresh water through the |
| Following the installation of the well field, | | | | aquifer until the ground water meets the |
| a leaching solution (or lixiviant), | | | | pre-mining use. |
| consisting of native ground water containing | | | | |
| dissolved oxygen and carbon dioxide, is | | | | In situ mining has several advantages over |
| delivered to the uranium-bearing strata | | | | conventional mining. First, the environmental |
| through the injection wells. Once in contact | | | | impact is minimal, as the affected water is |
| with the mineralization, the lixiviant | | | | restored at the conclusion of mining. Second, |
| oxidizes the uranium minerals, which allows | | | | it is lower cost, allowing Wyoming's low |
| the uranium to dissolve in the ground water. | | | | grade deposits to compete globally with the |
| Production wells, located between the | | | | very high grade deposits of Canada. Finally |
| injection wells, intercept the pregnant | | | | the method is safe and proven, resulting in |
| lixiviant and pump it to the surface. A | | | | minimal employee exposure to health risks." |
| centralized ion-exchange facility extracts | | | | |
| the uranium from the barren lixiviant, | | | | ISL mining may be the wave of the future of |
| stripped of uranium, is regenerated with | | | | U.S. uranium mining, or it may become an |
| oxygen and carbon dioxide and recirculated | | | | interim mining measure, in areas where the |
| for continued leaching. The ion exchange | | | | geology is appropriate for IS. Until |
| resin, which becomes "loaded" with uranium, | | | | sufficient quantities of uranium are required |
| it is stripped or eluted. Once eluted, the | | | | by U.S. utilities to fuel the country's |
| ion exchange resin is returned to the well | | | | demand for nuclear energy, ISL mining may |
| field facility. | | | | remain the leading uranium mining method in |
| | | | the United States. At some point, an |
| During the mining process, slightly more | | | | overwhelming need for uranium for the nuclear |
| water is produced from the ore-bearing | | | | fuel cycle may again put ISL mining in the |
| formation than is reinjected. This net | | | | backseat, and uranium miners may return to |
| withdrawal, or "bleed", produces a cone of | | | | conventional mining methods, such as open pit |
| depression in the mining area, controlling | | | | mining. |
| fluid flow and confining it to the mining | | | | |