 | |
|
|
What is In-situ Recovery (ISR)?
ISR is an environmentally-friendly process by which uranium can be extracted from the ground with minimal disturbance to the surface environment.
How many "pounds in the ground" of uranium do you need to make an ISR mine feasible?
Because ISR is so much cheaper than many conventional mining techniques (see "How much does it cost?" below) an ISR mine doesn't require as many "pounds in the ground" of uranium to make a mine economically viable. An ISR mine may require as little as 6 million pounds in the ground to go into production.
Does Target's Shirley Basin Project have enough "pounds in the ground" of uranium to make an ISR mine feasible?
An initial drill program has been planned for this summer/fall, which will be the first step in moving towards confirming the historic resource. Following the drill program, Target will release a 43-101 compliant resource calculation. Because an ISR mine can go into production with as little as 6 million pounds, Target expects to have the pounds required to go into production in the near future.
How soon can an ISR mine go into production?
An ISR mine can be constructed within as little as 18 months after being licensed, while it can take at least 3 or 4 years for a conventional mine to be permitted and built.
How much does it cost?
An ISR processing plant costs between US$10 million and US$35 million and can produce between 1 and 2 million pounds of uranium per year at an operating cost of ~ US$25/lb. On the other hand, conventional mines cost between $US130 million to $US150 million at an operating cost of ~ US$80/lb, but can produce 5 to 8 million pounds per year.
How does ISR work?
At some point in the history of the orebody, a solution with dissolved uranium flowed through the sandstone unit where it encountered a change in the chemical conditions (reducing conditions) of the surrounding environment. This change caused the uranium to precipitate out of the solution and onto the grains of sand in the sandstone unit. ISR simply reverses those chemical conditions, causing the uranium to be redissolved into solution.
Groundwater with dissolved oxygen and carbon dioxide is injected into the sandstone hosting the orebody via injection wells. This water provides the oxidizing conditions to reverse the precipitation process. The water frees the uranium from around the grains of sand and this solution is drawn out by production wells. The more pressure the water in the orebody is under, the more oxygen can be dissolved in the water and the more uranium that can be dissolved.
The solution is then pumped into a centralized ion-exchange facility. The uranium is concentrated using a process called ion exchange, where the uranium is passed through an ion exchange resin which has a preference for uranium. To free the uranium from the resin a small amount of salt solution is added, which strips the uranium away. Effectively the resin has a greater chemical affinity for the uranium than the groundwater solution, but the salt has a greater chemical affinity for the resin than the uranium. So initially the uranium sticks to the resin, but then the salt that would rather stick to the resin is added, freeing the uranium.
After the uranium is concentrated, it is precipitated from yellowcake slurry following filtering, dewatering, and drying into yellowcake
Approximately 70% of the uranium in the ore is recovered in a typical ISR operation.
Is ISR safe?
Monitoring wells are frequently sampled to ensure that all fluids are returned to the area surrounding orebody and for quality control purposes. Uranium is deposited in sandstone when water carrying the uranium is depleted of oxygen through naturally occurring chemical reactions with surrounding minerals and organic materials. ISR simply reverses the natural process by which the uranium was concentrated in the first place.
The United States has very strict guidelines for ensuring the safety and health of its citizens. The Department of Environmental Quality ensures that following ISR mining, a company must return groundwater to background chemical levels (levels prior to when mining began), even though the groundwater is not used for any other purposes.
What are the limitations of ISR?
Although more than 25% of uranium is produced through ISR, only certain orebodies are suitable candidates for this method. The deposits must be hosted in rock types that are porous enough to allow water to be pumped through it (e.g. sandstone) and located in area that will not contaminate groundwater far away from the orebody. However, the lower cost of extracting uranium using the ISR method means lower grade deposits can be developed. Average grades of sandstone-hosted deposits range from 0.05% to 0.40% U3O8.
Sources:
www.uic.com.au
www.ccnr.org
www.world-nuclear.org
| |
| |
