Synthetic Clay Could Assist Radioactive Waste Cleanup

A team led by Sridhar Komarneni, professor of clay mineralogy demonstrated that a synthetic clay known as a swelling mica has the ability to separate ions of radium, a radioactive metal, from water. The scientists report their results in the April 12 issue of Nature.

The finding could have implications for radioactive and hazardous waste disposal, particularly in the cleanup of mill tailings left over from the processing of uranium for the nation's nuclear industry. The tailings contain radium and heavy metals that can leach into groundwater and contaminate drinking water supplies.

"This result represents significant progress in developing new ion-separation materials," said Thomas Chapman, manager of NSF's program for separations and purification processes, which funded the research. "With more development, the swelling micas should prove useful in both waste remediation and metals recovery."

The swelling mica tested by Komarneni's team, known as Na-4, is one of a group of clays not found in the natural environment. Created specifically for water treatment purposes, swelling micas expand as they absorb metal ions and then, reaching their capacity, collapse and seal the contaminants inside. The swelling micas are being explored for potential use in separating ions of heavy metals such as lead, zinc and copper as well as other radioactive materials, including strontium, from waste streams. Because they trap the ions, the micas can permanently immobilize the pollutants. They could prove useful for the recovery and recycling of valuable metals as well.

Komarneni has used x-ray diffraction and nuclear magnetic resonance spectroscopy to evaluate the chemical properties of this new class of materials. One of his goals is to determine whether they have a larger capacity for metal uptake than currently available materials. In this recent experiment, he succeeded in synthesizing Na-4 into a fine powder more useful for practical applications than the large crystals previously synthesized.

The research was performed at Penn State's Materials Research Laboratory and Department of Agronomy.