The researchers described the process of radioactive isotopes entering the water that accompanies the extraction of shale oil and gas. The scientists' findings are described in two scientific articles published in the journal Chemical Geology by a group led by Joshua Landis of Dartmouth College in the United States.
Recall that the production of shale hydrocarbons has been rapidly developing in recent years. Thanks to this technology, the United States has already become a net exporter of natural gas and plans to achieve the same status with respect to oil in the coming years. This is despite the fact that the state with the world's first GDP and the world's third largest population consumes a lot of fossil fuels.
In general terms, the process looks like this. A mixture of water, sand and chemical reagents is pumped into the well with powerful pumps. When the fluid pressure becomes too great, the geological formation breaks and collapses. Figuratively speaking, fuel oozes out of the deformed rock like water from a compressed washcloth.
However, this technology poses an environmental threat. Used reagents partially end up in drinking water and can cause health problems. In addition, the "spent" water is enriched with the radioactive element radium.
Where does it come from? This is what the researchers found out in the first work. They placed shale samples in water enriched with calcium salts. Let us explain that the liquid pumped into the ground, traveling through numerous cracks, inevitably absorbs these substances.
As the researchers found out, such a solution also extracts radium from the surrounding shale. At the same time, there are two sources of the hazardous element, and they have a different ratio of the concentrations of radium-226 and radium-228. The first isotope is relatively stable, with a half-life exceeding one thousand years. The second is very active: for him the same period is less than six years. When radium decays, radiation is emitted, and another radioactive element, radon, is released.
The first source of the hazardous metal was the inorganic mineral part of the shale. It contains one radium-228 atom for only 250 radium-226 atoms. This is a fairly high concentration for the first isotope. The second source is the organic part of the breed. In it, the ratio of radium-228 to radium-226 is 1 in 10,000.
Experiments have shown that in just a few hours more than 14% of the radioactive element contained in the shale passes into solution. For comparison: pure (not enriched with calcium salts) water leaches out only less than 0.5%.
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The second article describes a model of this transfer for different concentrations of salts in solution and different amounts of water bathing the shale. Here the authors used experiment, mathematical modeling and direct measurements of the amount of radium in groundwater at the site of shale hydrocarbon production.
Prior to these studies, experts were not sure whether the shale itself was the source of the radioactive metal. There was a hypothesis that the matter is in the natural accumulations of radium in groundwater, which are sometimes found.
Anatoly Glyantsev
