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