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Plasma Fusion Center advances in hazardous waste disposal work

MIT scientists report significant progress on two techniques that could convert a variety of hazardous wastes into harmless or less noxious compounds.

Recently the researchers began operation of a new furnace that melts solid wastes such as contaminated soils into glassy blobs while vaporizing and decomposing any volatile chemicals present. "We fed in simulated waste soil continuously, it was processed in the furnace, and it came out as a lava-like material that solidified into a glass," said Daniel R. Cohn, acting assistant director of the Plasma Fusion Center and director of the PFC program on waste remediation.

The new furnace is capable of ultimately processing up to 700 pounds of waste per hour (a smaller version tested last year handled only 40 pounds per hour).

On another front, the researchers are currently loading a second type of unit onto a tractor trailer that they'll be ready to drive out to the DOE Hanford Reservation in Washington state within the next few weeks. There they'll use the unit in field tests to clean up large amounts of hazardous solvents such as carbon tetrachloride that contaminate the soil.

Both techniques use plasma-the same electrically charged gas found in lightning bolts and fluorescent lightbulbs-to break the chemical bonds of certain solid and gaseous wastes.

In the furnace, a plasma arc discharged between two graphite electrodes melts the material in question, which could include contaminated soils, incinerator ash, hospital wastes, or other materials with high melting temperatures that are difficult to process with other techniques. Temperatures in the plasma can run to about 10,000 degrees C.

In tests last year with a smaller furnace, the scientists found that the resulting glassy blobs are stable and won't leach into water supplies. "They could be suitable for landfills or possibly as a material for construction," said Dr. Cohn.

The furnace project is a good example of a collaboration between a national lab (Battelle Pacific Northwest Laboratories), industry (T&R Associates and Electro-Pyrolysis, Inc.), and a university (MIT). Jeffrey E. Surma of Pacific Northwest Labs has overall responsibility for the project; the furnace design was developed by Charles H. Titus of T&R Associates. At MIT, Paul Thomas, a PFC technical supervisor, heads up facility operation; Paul P. Woskov, a PFC principal research engineer, is in charge of the development of diagnostics to measure and monitor byproducts from the process.

The second technique destroys gaseous organic compounds, converting them into harmless byproducts like carbon dioxide and salt. Here a beam of electrons is shot into a sample of gases containing the hazardous gas of interest. In the process, which can run at room temperature and at atmospheric pressure, extremely reactive secondary electrons-the plasma-are created.

These in turn attack the hazardous gas molecules, breaking them up into mainly chlorine, carbon dioxide and hydrochloric acid. These byproducts are then sent to a scrubber that converts them to the final byproducts of carbon dioxide and salt.

At the Hanford site the PFC researchers will test the electron-beam reactor on organic solvents after pumping them out of the ground as gases.

The e-beam work is led by Richard M. Patrick, a PFC research engineer. The team includes Kamal Hadidi, a PFC visiting scientist; Dr. Cohn; Leslie Bromberg, a PFC principal research scientist; Paul Falkos, a PFC research engineer, and Matthew P. Schuetze, a graduate student in nuclear engineering.

Both the furnace and e-beam projects, which have been underway for about three years, are funded by the DOE.

A version of this article appeared in the September 21, 1994 issue of MIT Tech Talk (Volume 39, Number 5).

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