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 (licensees) 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.
The ISL method involves these steps:
- 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 for uranium recovery.
- At the surface, the recovered injection solution is passed through an ion-exchange column. The uranium is adsorbed 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.
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 one year of baseline 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.)
- Periodically, usually once per quarter, sample the monitoring wells, local air, and local soils to make sure that no significant amount of radioactive material is escaping. (This measure prevents any exposure to individuals living near the site.)
- After ISL is complete:
- Remove all radiological hazards and restore the groundwater of the now-depleted uranium capture zone back to pre-ISL conditions. [Title 30, Section 331.107(b)].
- The aquifer restoration must meet the technical requirements of the uranium company’s Underground Injection Control (UIC) permit.
- The restoration table in the permit establishes the values for key constituents that meet the pre-exisiting conditions for groundwater of the mining zone. (30 TAC 331.104).
Conventional uranium recovery involves open pits or tunnels. 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 that 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, see 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.
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