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Environmental Cleanup Needs Teamwork Between Owners and Regulators.

by Rich Kimura

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This article discusses good stewardship as applied in the engineering, political, and public arenas. It is about a company had allowed 6 million gallons of solar-concentrated chemical and radioactive wastes to accumulate on its site. State and federal regulators were about to shut down the plant as a result. The plants annual revenue was about $250 million, and it employed over 1000 people. This writer was hired to solve the technical problems with cleaning it up. A chemical processing method was developed. Then, a legally binding consent decree was issued, and a tri-party agreement was reached with all regulators on a technical cleanup approach. This article briefly tells how the chemical process worked, and shows that stewardship can be very difficult and complex, taking years to undo prior mismanagement.

The plant site was located in the sagebrush-covered desert of eastern Washington. About 8 acres of land held 7 large surface impoundments, or lagoons, filled with a blue-green solar-concentrated chemical and uranium solution. The lagoons were plastic-lined, were about 6 feet deep, and were between 1/2 and 1 acre in size. They were filled to 3 feet deep. Some soil contamination occurred when the lagoons leaked decades ago, and the lagoons contained a lot of windblown sand and desert debris mixed with the liquid. This writer designed a large-scale uranium recovery and cleanup process that was operated for 7 years. The 6 million gallons of concentrated liquid wastes were eventually eliminated. In addition, over 1 million cubic feet of soil were treated or disposed.

Uranium was selectively recovered from liquids, soils, and sludge containing metal precipitates, inorganic salts, sand and silt fines, debris, other contaminants, and slimes, which are very difficult to de-water. Chemical processes such as nuclear fuel manufacturing and uranium mining generate enriched and natural uranium-bearing wastes.

At the head end of this process was a floating dredge which retrieves liquids, sludge, and slimes in the form of a slurry directly from the surface impoundment at 600 gallons per minute. The dredge was equipped with a 100 horsepower sludge pump. The slurry was screened, passed through a grinder/shredder, and pumped into a 12,000 gallon feed tank. Debris from the screens are collected and disposed. The slurry was mixed in the feed tank with a turbine mixer and re-circulated to further break down the particles and enhance dissolution of uranium.

The brown slurry was then heat treated by direct steam injection, to heat it up to 160F. The uranium was then made soluble by using a mild bleach (sodium hypochlorite) solution) strike that oxidized all of the uranium. The sodium hypochlorite oxidizes and dissolves any U(IV) present by converting it to U(VI). In addition, the heavy metal contaminants are not extracted into the liquid phase as would normally occur with aggressive oxidants such as nitric acid. Cellulose powder had to be added as a non-reactive filter aid to help filter slimy sludge to give body to the slurry. The cellulose did not react with uranium, which occurs with the use of diatomaceous earth or other inorganic filter aids. How did this all get figured out? By hard work and trial and error in the lab! Letting the data speak for itself was the key to success.

The slurry was pumped into 80 cubic foot recessed-chamber filter press that is also pre-coated with cellulose, and was then de-watered by a pressure cycle-controlled double-diaphragm pump. The clear filtrate was pumped through bag filters to a 12,000 gal filtrate collection tank.

The filtrate was processed batch-wise, and uranium was removed from the solution by special precipitation and filtration. The process was a clear success and recovered 3 metric tons of enriched uranium. The dried solids could be safely disposed. The process was patented and can now be used commercially wherever uranium-contaminated soils and sludge exist.

It was a great relief to remove the uranium-contaminated liquids because the groundwater was only 20 feet below the lagoons, and a rupture would have severely contaminated the aquifer. It was also a joy to see the land returned to its natural condition. And, there was a good working relationship with many of the State and Federal regulators.

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