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Nanocoating Tackles Soil Toxins

Tuesday, December 11, 2012

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Seek and destroy. That's how nanoparticles in a new coating could potentially rid soil of dangerous toxins, a Canadian researcher has found.

Iron nanoparticles encapsulated in a rust-preventing polymer coating could be the future to cleaning up groundwater contaminated with toxic chemicals, a leading water expert says.


Dr. Denis O'Carroll and colleagues have tested iron nanoparticles at two contaminated sites in Ontario.

Dr. Denis O'Carroll, a visiting academic at the University of New South Wales, sees a new approach in cleaning up contaminants using metal nanoparticles 500 to 5,000 times narrower than a human hair.

Historical Mistakes, Innovative Future

"Toxic contamination of soils is an historical problem," said O'Carroll, who is visiting UNSW Water Research Lab from the University of Western Ontario in Canada.

"Until the 1970s, people wrongly believed that if we put these toxins into the ground, they would simply disappear—that the subsurface would act as a natural filtration unit."

However, chemical contaminants from spilled gas and solvents seep through microscopic soil cracks into the earth where they accumulate and can eventually reach the groundwater table.

For years, people have tried different ways to clean toxins out of groundwater. Usually, water is either pumped out and cleaned or a special cleansing solution is used to flush out toxins. However, both techniques are limited by locating and accessing contaminated groundwater deep in the ground.

The idea involves using tiny nanoparticles of zero valent iron, or iron that has no electrons to share, to form covalent bonds with other substances. When these particles come in contact with groundwater toxins, it causes a redox reaction where electrons are transferred between the particle and the pollutant, changing the oxidation level of the pollutant, and making it less toxic.

"The possibility of this waste polluting the environment, and potentially contaminating groundwater resources and remaining there for decades was ignored," he said.

The Technology

With the new technology, the iron particles are injected directly into contaminated soil where the reaction changes the oxidation state of the pollutant and diminishes its overall toxicity to safe levels, said O'Carroll.

The nanoparticles are up to 5,000 times narrower than a human hair.

Since iron particles are not very mobile and dissolve quickly, they are particularly safe for use in the environment. However, this also limits the nanoparticles' ability to seek out and degrade toxins.

To optimize the nanoparticles, O'Carroll is experimenting with different formations of iron and encapsulating the particles in a rust-preventing polymer. This will slow the dissolution process and increase mobility without adverse environmental impacts.

Successful Field Trials

In November 2010 and February 2011, two contaminated sites in Ontario were used for field trials.

At the first field experiment, 1,000 liters of a nanoiron solution were injected into a very contaminated region in the subsurface. Continued site monitoring found considerable decreases in subsurface contaminants.

The second field trial was equally successful.

"Significant degradation of the contaminants at both sites has been observed," said O'Carroll.

About the Water Research Lab

WRL is an international consulting and research laboratory and a major group within the University of New South Wales Water Research Centre. WRL houses academic staff alongside a commercial projects team. The projects team offers commercial services of expert advice to industry and government, while the academic staff carries out research programs and supervises postgraduate students.

WRL takes on problems in engineering relating to water, the coast, the environment, and groundwater.


Tagged categories: Cleanup; Nanotechnology; Polymers; Research; Site/field testing

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