Study offers hope for cleaning radioactive water

US scientists have discovered a new chemical method to immobilise uranium in contaminated groundwater, which could result in better ways to improve water remediation at old nuclear sites.

The researchers hope this information will make it easier to know how and where phosphates can be injected into the ground to render uranium harmless. Phosphates react with calcium in the soil to form calcium phosphate which then immobilises uranium, important as the radioactive material has been linked to increased risks of cancer and liver damage when ingested by humans.

Dr Daniel Giammar, from Washington University in St. Louis, who oversaw the study, said: “A challenge with subsurface remediation is finding the right way to bring the necessary ingredients together in a poorly-mixed system. The solution is to figure out scenarios where it is possible to send the phosphate to where the uranium is, and other scenarios where the phosphate can be added to a location where the natural groundwater flow will bring the uranium into contact with it.”

Previous experiments that injected phosphates into contaminated groundwater struggled with correctly mixing calcium and phosphates in the right proportions. This time, researchers carried out a number of different experiments to find the exact level of calcium in the water. This allowed researchers to add exactly the correct amount of phosphate needed, forming calcium phosphate to neutralise the uranium.

Dr Giammar said: “There will not be a one-size-fits-all approach to using phosphate to remediate uranium-contaminated groundwater.

“With knowledge of the location of the uranium contamination and the composition of the groundwater, we can decide whether to inject phosphate directly into a plume of uranium-contaminated groundwater or to inject phosphate downstream of the uranium to form a calcium phosphate barrier,” he said.