Reversing Mother Nature, Part Three
We talked to North America’s leading In Situ Leach (ISL) uranium mining engineers, and had them explain exactly how ISL worked. Most of the significant ISL operations in the United States were designed and/or constructed by these engineers. They explained how ISL mining is really just reversing the process of Mother Nature. CLEANING UP THE PROJECT Not so fast. Shipping the uranium out of the ISL plant isn’t the final step. The water has to be cleaned up, the property returned to its original condition.
If done properly, then the footprint of the ISL uranium operation should have been nearly erased. In an earlier article, “Wyoming Uranium: Now and the Future,” we talked to Pat Drummond at Smith Ranch about this process: The company is meticulous in restoring the landscape as well. Any restoration work on the surface is called “reclamation.” That can involve farming. “When we start a well field, we have to, by license, remove the topsoil and store it somewhere,” Drummond explained.
“When we go back to reclaim the property, we take all the pipes out, we take the houses down, and cut our wells off. It’s all identified. We put an ID marker on the well. In 50 years time, when Farmer Joe comes around and wonders what was there, the state can say, ‘That was a uranium well.’ From the time we’ve stopped mining, we put everything back to normal.” The one item we did not address at the time was cleaning up the water after the orebody has been mined out. Why is restoring the water back to background important? “In the mining process, you’re basically elevating sulfate,” explained Anthony. “You’re also elevating calcium because you’re lowering the pH a little bit, down to 6.5 to 7. Because you run it across the ion exchange circuits, you get a little leakage of chlorides into the lixiviant.
” Subsequently, the water will have sulfate, chloride, calcium and bicarbonate circulating within it. “When you add carbon dioxide, you’re forming bicarbonate,” Anthony noted. “These are the major ion groups you are elevating during the mining process.” He also added that in some projects, you may get arsenic, vanadium and/or selenium. “They all go into the solution so that at the end of your mining process, these ions will be elevated above their baseline values.” The water will need to undergo a purification process to return them back to a quality consistent with baseline values.” What does the ISL operator do with the water once the facility has mined out the uranium? There are three options, which we discussed with Glenn Catchpole, who has also set up previous ISL operations. In 1996, Catchpole was the General Manager and Managing Director of the Inkai uranium solution mining project in Kazakhstan. He is currently the Chief Executive of Uranerz Energy. “Here’s my order of priority: If you have a receiver formation for deep disposal on your project, that’s my first choice.
” Sometimes, a project may not have access to a deep disposal aquifer, warned Catchpole. The water is sent down the receiver formation, down about 4000 feet. “You’re usually sending this water to a formation that is very briny, a poorer quality than what you’re sending down,” Anthony pointed out. Another option, according to Catchpole, would be operations ponds, or evaporating ponds, where the water is evaporated. A third option is “land applied.” Catchpole explained this was for land application. “You take your waste stream, you treat it to remove the certain level of impurities, according to the government requirement, and then you’re allowed to disperse it on the land surface, as if you were irrigating.” When applied to the land, it is soaking into the land. “It’s growing grass, and it’s going into the groundwater system,” concluded Catchpole, “Whatever water quality standard they allow for you to put that water in the land, they want to ensure it doesn’t accumulate some particular chemical over time that is going to build up and contaminate the land.” Generally, during the restoration process, the water is circulated through the barren orebody about eight times.
It’s another instance of pore volumes – eight more times through the sandstone formation. Anthony explained, “Normally, the first pore volume is evacuated and disposed of via a disposal well.” But he warned, “This will cause an inflow of surrounding native water back into the mine zone. The resulting water is pumped to the surface and processed through a reverse osmosis unit.” Anthony compared this to the desalination of seawater. “The reverse osmosis equipment acts like an ‘ion filter,’ allowing pure water to pass through a membrane and filtering out ions of sulfate, calcium, uranium, bicarbonate and so forth,” Anthony explained. Two streams of water are produced by the reverse osmosis unit. One stream is called “product water,” and is normally consistent with drinking water quality. The smaller stream of water is called “brine.
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