What is Uranium
There are two methods used to mine uranium—conventional mining and the more modern alternative, in-situ recovery. In Wyoming, uranium mining is primarily done through in-situ recovery. However, there are a few conventional mines in the state planned for the future.
Mining is the removal of material from the Earth's interior for the purpose of extracting a commodity of interest (uranium, gold, aluminum, etc.) After mining, uranium ore is processed into yellowcake, a type of uranium concentrate powder obtained from leach solutions. Yellowcake
is further processed, which can then be used in the manufacture of nuclear fuel and for electrical generation. In 2013, Wyoming produced more than 2.5 million pounds of yellowcake, ranking No. 1 the nation.
Wyoming Uranium Mines
- Comeco Resources, Smith Ranch-Highland (Converse County), North Butte operation in Pumpkin Buttes, (Campbell County) (mines with yellowcake processing)
- Uranium One, Inc., Willow Creek, Johnson-Campbell counties (mine and yellowcake processing plant)
- Ur-Energy, Lost Creek mine, Sweetwater County (mine and yellowcake processing plant)
- Uranerz Energy, Nichols Ranch, Johnson County (processing agreement with Cameco)
In-situ recovery or ISR (also referred to as ISL or in-situ leach) is more economical and is considered to have a lower environmental impact than conventional mining. It is the preferred method of uranium mining if the uranium occurs in a shallow deposit hosted in porous and permeable sedimentary rocks.
In-situ recovery is essentially the reverse of the natural geologic processes that originally concentrated the uranium. After natural processes oxidize and leach uranium from
its source rocks, surface water and groundwater transport the uranium to a reducing environment in a porous host rock where the uranium is deposited. In the in-situ recovery process, the uranium minerals are oxidized, remobilized, and pumped to the surface for processing. One of the advantages of this method is that there is very little surface disturbance other than the necessary infrastructure.
History of In-situ Recovery
The in-situ recovery method was developed on an industrial scale in Texas in the 1970s, and since 1993 has been the only uranium extraction method used in Wyoming. The history of in-situ recovery dates back to the early 1960s in the Gas Hills and Shirley Basin uranium districts. Miners found that leaching solutions could be pumped through permeable tailings and through the host rock underground. The in-situ recovery process leaves the host rock in place and removes uranium by pumping a mixture of water and oxidizing agents through the rock, including dissolved gases such as oxygen (O2) or carbon dioxide (CO2).
The mixture, called a lixiviant, consists of water pumped from the orebody aquifer, plus the oxidizing agents added at the surface. In order to remove uranium from its location in the orebody, the lixiviant is pumped into the aquifer through injection wells, through the orebody, and back to the surface through extraction wells. The lixiviant frees the uranium from the orebody and into a solution so that it can be removed at the surface by an ion exchange process. In addition to injection and production/extraction wells, in-situ recovery operations utilize monitor wells, which continually sample the water at the margins of the orebody—laterally as well as above and below—to ensure that the injected water does not migrate away from the targeted ore zone and into adjacent aquifers, an occurrence called an excursion.
Conventional mining involves the physical removal of ore from the ground. The ore is then milled (crushed to a specific grain size) and processed to extract and refine the uranium. Removing the ore from the ground is accomplished by surface (open pit) mining or underground mining.
Surface mining requires removing overburden (topsoil, sand, gravel, etc.) down to the top of the orebody. Then the ore is removed by heavy equipment
and loaded into haul trucks and driven to the mill.
Underground mining involves sinking a vertical shaft from the surface and driving adits (horizontal tunnels)
at depth to reach the ore body. The main factors that determine whether to mine by open pit or underground are depth and cost of production. Ore bodies lying less
than about 500 feet below the surface are typically surface mined as it is much less expensive than underground mining.
After extraction, the uranium ore is transported to a processing plant where it is milled. This process involves crushing the ore, chemically extracting the uranium, and concentrating it into uranium oxide (U3O8) or as yellowcake.
Wyoming’s Uranium Drama: Risks, Rewards and Remorse - WyoHistory.org
The story of uranium in Wyoming is a high-stakes drama whose cast includes engineers and world-class mining companies. Uranium has been part of Wyoming’s economy since it was first discovered when the Cold War began and the U.S. government cornered the domestic uranium supply with a guaranteed price to producers. Read more...
Bob Gregory (307) 766-2286 Ext. 237