In Situ Leach and Conventional Uranium-Recovery Methods
From 1972 through 1985, uranium recovery in Texas was dominated by conventional mining and milling. More recently, companies have been using in situ leaching (ISL), a process that makes possible the recovery of uranium without disturbing the natural surface, generating dust, or producing waste known as tailings.
- How In Situ Uranium Recovery Works
- How Conventional Uranium Recovery Works
- Bureau of Economic Geology Paper
- Staff Contact
The ISL method involves these steps (diagram of in situ leaching):
- A solution of oxygen, hydrogen peroxide, or another oxidizing agent in water is injected into an underground zone that bears uranium ore.
- In contact with this injection solution, the uranium dissolves.
- The injection solution containing the dissolved uranium is pumped back to the surface to recover it.
- At the surface, the recovered injection solution is passed through an ion-exchange column. The uranium sticks to the ion-exchange column, and a uranium-free solution flows out. With the addition of an oxidizing agent, this solution can be reused as injection solution in step 1.
- A stripping solution is poured through the ion-exchange column to redissolve the uranium.
- The uranium-bearing solution is chemically treated to turn the uranium into a solid form. This uranium-containing solid is isolated and transported elsewhere for further processing.
As a result, the main impact of ISL is on the characteristics of the porous rock at the depth where the uranium is recovered, the so-called “uranium capture zone.” To monitor and address this impact, the licensee is required to take these steps:
- Before ISL begins:
- Collect enough environmental data on local air, soil, and groundwater to establish a baseline for comparison to later data.
- Drill a set of precisely spaced monitoring wells just outside the uranium capture zone in all directions—around, above, and below.
- During ISL:
- Ensure that there is a net inflow of clean water into the uranium capture zone from outside. (This measure prevents the injection solution from escaping the capture zone and potentially affecting a nearby aquifer.)
- Continually sample the monitoring wells, local air, and local soils to no significant amount of radioactive material escapes. (This measure prevents any effect on individuals living near the site.)
- After ISL is complete, restore the site by removing all radiological hazards and restoring aquifer quality in the now-depleted uranium capture zone back to pre-ISL conditions. This aquifer restoration must meet the technical requirements of the uranium company’s UIC permit, which contains a “restoration table” that sets constituent values for the aquifer.
Conventional uranium recovery involves open pits or funnels. There are additional waste management considerations. For example:
- In conventional mining, the surface of the land is disturbed significantly. Tunnels or open pit mines must be dug to reach and remove the uranium ore.
- Once removed from the earth, the ore must be ground into small particles for further processing. This pulverization process generates dust, and the dust contains naturally-occurring radioactive materials.
- Acids and other strong chemicals must be used to extract the uranium from the pulverized ore.
- Even though much of the uranium has been removed, the spent ore, or “tailings,” still contains some uranium, other heavy metals, and other naturally-occurring radioactive materials. To learn more, read the Nuclear Regulatory Commission’s fact sheet on uranium mill tailings .
Although there are no active conventional uranium mines in Texas, three conventional uranium mills did operate in Texas from 1972 through 1989. These sites, with their tailings impoundments, are now being decommissioned.
Bureau of Economic Geology (BEG), April 2010
View the BEG Study which discusses the South Texas Uranium Province. The province includes about 20 counties, which wraps around a formation known as the Catahoula Formation, from the Mexican border to south of San Antonio. The BEG Study discusses important volcanic episodes which occured more than 20 million years ago, as being the source of uranium deposits, as well as associated elements such as arsenic and selenium.
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