Nanotechnology Used to Study Environment

Nanotechnology, normally used for work with the crystal structures of silicone chips and pure oxides, is being used for something a little more dirty at the Lawrence Berkeley Lab, like learning how to clean up environmental contaminants like nuclear waste.

Researchers Glenn Waychunas and Carl Steefel are using techniques that allow them to study the environment at the nanoscale as part of the new Center for Environmental Kinetics Analysis (CEKA) program, based at Pennsylvania State University.

The goal of the program is to gain insight into the kinetics, or rates, of reactions that occur at the earth's surface using a nanoscale approach that better models what happens in the real world as opposed to in the lab.

"We are conducting pore scale flow reaction experiments to determine the kinetics of reactions in the pore scale environment. The rate found in beakers is completely different than the one you find in the field," Steefel said.

Waychunas explains that lab experiments are often inadequate for describing real-world kinetics, citing the example of an aquifer in Cape Cod where the silica sand reacted much differently than lab experiments had predicted because the coatings on the sand were absent on the pure sand used in the lab.

"The devil's in the details," Waychunas said. "In order to understand what's happening in the aquifer, you have to know what's happening with the coatings."

The CEKA program uses a multidisciplinary approach to studying environmental kinetics including the rates of reaction on mineral surfaces, using the newest nanotech methods and computer models to study rates at a very small scale, from nanometers up.

Waychunas and Steefel are working on the reactions that take place on the pore scale, like the flow of water through the minerals in an aquifer.

"What has been left out is determining rates at the pore scale, we're measuring rates at different scales to see how biogeochemical and microbial reactions scale up," Steefel said.

This can have implications for transport of contaminants, especially of radioactive materials. Researchers seek to determine reaction rates to determine how long it would take for a plume of pollutant to spread through different mineral substrates.

"You can do a field scale experiment or a lab experiment, but you don't understand why the rate is the way it is. You need to go down to the pore scale to understand what's happening through the different scales, physical, geochemical, microbiological," Steefel said.

Steefel is working on a model of nanopores, using a scanning transmission x-ray microscope to look at a single pore, about 100 nanometers in diameter. The work will then scale up to the micron level using microtomography and computerized tomography, methods of imaging at the microscale.

The next scale is supercomputer modeling, according to Waychunas.

"This will model chemical reactions and integrate fluid flow through pore structures, using more complicated fluids and soils. Then we'll apply them to real systems, like the Yucca Mountains, natural aquifers, oil recovery, ore recovery, and natural gas," Waychunas said.

Besides geochemists Waychunas and Steefel at the lab, the CEKA program also includes chemists, biochemists, soil scientist and engineers at Penn State.

"Chemists and physicists have developed these techniques, and now we're bringing these methods to earth science. Earth science used to be an isolated field that didn't take advantage of new chemistry and physics, but to be a quantitative field, you have to use these new types of instruments," Steefel said.

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