Oranges versus dirty bombs

Scientists have found a simple, safe way of removing radioactive uranium from structures in the event of a dirty bomb incident. The technique uses citric acid to clean surfaces, soil and incinerator ash.

"Until now, decontamination of radionuclides from buildings and other surfaces left contaminated by radiological incidents has been a major environmental challenge," says Brookhaven (N.Y.) National Laboratory scientist A. J. Francis.

Francis and colleagues Cleveland Dodge and Gary Halada (Stony Brook University) developed an environmentally friendly green-chemistry process that uses only citric acid, common soil bacteria and sunlight.

The process was designed to provide a safe and effective method for decontaminating buildings at former weapons sites.

"However, its use in the case of intentional contamination from a dirty bomb addresses the important issue of how to deal with cleaning up buildings where metal surfaces are rusted, moist and dirty," Halada says.

Currently, removing uranium from contaminated metal surfaces requires sand blasting, chemical extraction and electrochemical dissolution, methods that generate secondary waste streams, compounding the problem. But the new process can also treat the secondary waste generated by the current treatment process, minimizing waste.

"Initial use of mild citric acids to remove radioactive contamination could be performed by remediation crews in the field," Halada says.

Using a synchrotron light source (a source of intense X-rays, ultraviolet and infrared light), the scientists systematically examined the contaminated materials at the molecular level, investigating the association of uranium before and after treatment with the citric acid formulations.

The efficiency of uranium removal ranged from 68% to 94%, depending on the age and extent of corrosion, according to Francis.

Wastewater produced by the process is then subjected to biodegradation, followed by photodegradation, both of which minimize secondary waste and allow the uranium to be recovered. The patented process can also be used to remove toxic metals and radionuclides from contaminated soil, waste and incinerator ash, Francis says.