PORTLAND, Ore. A "universal elixir" brewed from nanoscale technologies is being promoted as a fast, cost-effective way to clean up hazardous waste.
The curious marriage of high technology and heavy industry, researchers at Lehigh University said, would attack large-scale toxic wastes with injection wells that employ highly reactive nanoparticles of iron. The slurry would simultaneously neutralize and "fix" in place all known contaminants.
Such an approach, the researchers said, contrasts with those of organizations like the U.S. Department of Environmental Protection's trillion-dollar Superfund, which clean up sites of contaminated soil and groundwater by treating them with agent-specific neutralizers, one shovel at a time.
"It used to be just the federal agencies," said Wei-xian Zhang, principal investigator of the project and assistant professor of civil and environmental engineering at Lehigh (Bethlehem, Pa.). "But now, we're working with big pharmaceutical firms, semiconductor manufacturers and many other companies, all of which are interested in cleaning up sites," said Zhang. "Iron's cleansing power is the key, which stems from the simple fact that it rusts, or oxidizes-not just the familiar patina of brick-red iron oxide, but when metallic iron oxidizes in the presence of contaminants such as trichloroethene, carbon tetrachloride, dioxins, or PCBs, these organic molecules get caught up in the reactions and broken down into simple carbon compounds that are far less toxic."
Likewise, "rusting"-the slang for iron oxidation-can neutralize dangerous heavy metals such as lead, nickel, mercury and even nuclear contaminants like uranium, by transforming them into the insoluble form that stays locked in place rather than migrating along with ground water. By injecting the 1- to 100-nanometer-diameter particles of iron into groundwater channels, their curative powers can also migrate along the same paths as the contaminants-eliminating the need to dig up hidden contamination.
Environmentally friendly companies already pretreat their industrial wastes with a crude form of iron filings powder to purify them before releasing them into the environment, Zhang said. Iron is also already abundant in the environment in rocks, soil and water, and has no known toxic effect. But most of all, nanoparticles of iron can be suspended in a slurry that can be pumped straight into the heart of a contaminated site.
Downsizing iron filings powder to the nanoscale, Zhang said, makes the particles from one to three orders of magnitude (10- to 1,000-fold) more reactive than usual, basically because the molecular-sized nanoparticles present vastly more surface area to "rust."
Unlike rival in-place biological treatments using genetically engineered bacteria that metabolize the toxins, iron is not affected by biological requirements for nutrients, mild temperature and low acidity. Also, because nanoparticles are 10 to 1,000 times smaller than most bacteria, the tiny iron crystals can slip between soil particles rather than be blocked by them.
Laboratory and field tests confirm that formulas for iron nanoparticles can lower contamination to acceptable levels within a few days of injection, Zhang said, and can completely neutralize the seepage fields of spills within a few weeks of treatment so that the site can meet federal groundwater quality standards.
Decontaminating an area of about 100 meters2 using a single injection of iron nanoparticles would require about 12 kilograms at a cost of $50 per kilogram. After the area had been neutralized, any remaining unused nanoscale iron will continue to work its way through groundwater paths until it is completely dissolved, becoming undetectable against the much higher background of naturally occurring iron.
Zhang's recent case for nanoscale iron is the culmination of his eight-year-long pioneering research on downsizing iron to the nanoscale with studies. The work was partially funded by the National Science Foundation. More recently, Zhang's research was a part of the United States' 16-agency National Nanotechnology Initiative. He is currently forming a company to manufacture iron nanoparticles.
"We're entering a phase of exponential growth," said Zhang. "There are thousands and thousands of contaminated sites out there. And, hopefully, this will be a cost-effective way to deal with many of them."
Today the trillion-dollar Superfund has yet to treat more than 1,000 large-scale sites in the United States. There are also more than 150,000 domestic underground storage tanks slowly seeping toxins and nearly 1 million landfills, abandoned mines and industrial sites.