Uranium In-Situ Recovery
In-situ recovery (ISR) is a means of extracting uranium from underground ore bodies and pumping it to the surface.
Uranium ore deposits suitable for ISR occur in permeable sand or sandstones, confined above and below by relatively impermeable strata, and are below the water table.
Before recovery begins, well pump tests are performed to define the hydrological characteristics of the ore zone, obtain information about the ground water flow, and determine if the surrounding strata are suitable to prevent movement of the recovery solution into underlying or overlying aquifers.
Before and throughout the recovery process, aquifer water samples are taken near the uranium ore to document water quality.
Land grading and trenching will prepare the earth above the ore deposit for placement of wells and piping.
A series of injection and production wells are drilled into the ore body.
The injection wells pipe water at a neutral pH, which contains oxygen and sodium bicarbonate (baking soda) into underground uranium deposits.
The nearby pumping extraction wells draw the solution through the ore in a closed recovery process.
The recovery solution naturally dissolves the uranium in the ore sandstone and is pumped to the surface through the production well to an on-site processing facility.
At the on-site facility, an ion-exchange process separates the uranium from the recovery solution by causing it to adhere to resin beads. The resin is then transported away from the mining site to a central processing plant for further processing.
Through a recycling process, the remaining water is then re-pressurized, recharged with oxygen and sodium bicarbonate, and re-injected as recovery solution into the ore to continue mining.
Yellowcake (U3O8) Production
At a central processing plant, the uranium is stripped from the loaded resin, precipitated and dried, yielding a uranium oxide product (U3O8) with a rich yellow color, called "yellowcake".
By-Products of ISR
During mining, in the underground strata, the recovery solution also dissolves other naturally-occurring elements that react to oxidizing solutions. These elements can include selenium, molybdenum, vanadium and arsenic. In addition, some portion of the naturally-occurring radioactive elements such as radon and radium can go into solution and can be brought to the surface. Because the elements are not attracted to the ion exchange resin, they are recycled to the subsurface ore horizon. During production, companies often process the flow stream after uranium removal to extract other dissolved elements. These elements are precipitated in either tanks or a small, double-line pond. At the conclusion of production, all solid residue is drummed and disposed of in an NRC-licensed disposal site.
Radon will be measured during the baseline data collection period and potential radon
emissions from the proposed ISR operation will be calculated. Until this information is available, there can be no definitive determination of how radon will be addressed. However, Powertech will handle radon emissions in a manner that will satisfy the applicable regulatory requirements and be protective of human health and the environment.
During operations, a small waste stream or 'bleed' is directed to a small surface retention pond. This is typically only one to three percent of the production solution. The sludge from the pond is recovered, dried, packaged and transported to an NRC approved disposal site.
A cone of depression in the aquifer is maintained during the groundwater restoration process to assure no metals or salts are released from the recovery area.
The company will obtain sufficient water rights to provide for complete restoration without affecting surrounding well owners.
Following the mining phase is the groundwater restoration phase, which entails pumping any remaining oxidized and soluble metals and salts to the surface; treating the water flow to remove these residues and "flushing" the depleted ore zone to return the water quality to baseline conditions, or class of use, as appropriate. During this process the mined sandstone returns to a reduced state, thus stabilizing metals and salts in-situ.
Decommissioning a uranium in-situ recovery site calls for wells to be sealed or capped, process facilities removed, including any evaporation pond(s). The site is then graded, topsoiled and revegetated, and the land can readily revert to its previous use(s).
This diagram illustrates the processes involved in the in-situ recovery of sedimentary uranium ore.
Through the use of water wells, oxygenated groundwater is injected into the ore-bearing sandstone.
These fluids are controlled by impermeable units above and below the host sandstone and dissolve uranium as they pass through the ore zone.
The pregnant solutions are brought to the surface by production well and are run through ionic exchange columns where the uranium is extracted.
The stripped fluids are again oxygenated and reinjected into the wellfield.
This recycling of fluids through the wellfield is an efficient, non-consumptive use of groundwater and can recover up to 90% of the in-place uranium.
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