A collaborative effort by the Rice lab of chemist James Tour and the Moscow lab of chemist Stepan Kalmykov determined that microscopic, atom-thick flakes of graphene oxide bind quickly to natural and human-made radionuclides and condense them into solids. The flakes are soluble in liquids and are easily produced in bulk.
The experimental results were reported in the Royal Society of Chemistry journal Physical Chemistry Chemical Physics.
The discovery could be a boon in the clean-up of contaminated sites such as the Fukushima nuclear plants damaged by the 2011 earthquake and tsunami in Japan, Tour said. It could also cut the cost of fracking for oil and gas recovery.
Graphene oxide’s large surface area defines its capacity to adsorb toxins, Kalmykov said. ‘So the high retention properties are not surprising to us,’ he explained in a statement. ‘What is astonishing is the very fast kinetics of sorption, which is key.’
Determining how fast was the object of experiments by the Kalmykov group.
The lab tested graphene oxide synthesised at Rice with simulated nuclear wastes containing uranium, plutonium and substances such as sodium and calcium that could negatively affect their adsorption.
Graphene oxide did, however, prove far better than the bentonite clays and granulated activated carbon commonly used in nuclear clean-up.
Graphene oxide introduced to simulated wastes coagulated within minutes, quickly clumping the worst toxins, Kalmykov said, and the process worked across a range of pH values.
Fluid focus
The researchers focused on removing radioactive isotopes of the actinides and lanthanides from liquids, rather than solids or gases.
‘Although they don’t really like water all that much, they can and do hide out there,’ said Steven Winston, an expert in nuclear power and remediation, who is working with the researchers. ‘From a human health and environment point of view, that’s where they’re least welcome.’
Naturally occurring radionuclides are also unwelcome in fracking fluids that bring them to the surface in drilling operations, Tour said.
‘When ground water comes out of a well and it’s radioactive above a certain level, they can’t put it back into the ground. It’s too hot. Companies have to ship contaminated water to repository sites around the country at very large expense,’ he said, adding that the ability to quickly filter out contaminants on site would save a great deal of money.
Tour said that capturing radionuclides does not make them less radioactive — just easier to handle. ‘Where you have huge pools of radioactive material, such as those at Fukushima, you add graphene oxide and get back a solid material from what were just ions in a solution,’ he said. ‘Then you can skim it off and burn it. Graphene oxide burns very rapidly and leaves a cake of radioactive material you can then reuse.’
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