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Stabilizing Heavy Metals in Dredged Sediments
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Project Title: Phosphate-Based Heavy Metal Stabilization Technologies for Contaminated Sediments and Dredge Material
Research Locations: Great Bay, NH - Hudson River, NY - Jacques Cousteau, NJ - Narragansett Bay, RI
Last Update: 8-28-01
Contaminated dredged sediments pose a significant threat to coastal environments and to the continued commercial use of harbors and waterways. Heavy metals are prevalent contaminants in these sediments and innovations are needed to help manage them. This project examined the use of phosphorus compounds to stabilize metal contaminants. A second project is currently building upon the success of initial laboratory studies to demonstrate the technology's capabilities in the field. If successful, this project could result in tremendous cost savings for dredged materials management and disposal.
Design Concept
Conventional capping systems inhibit the migration of contaminants by making the capping material physically difficult to pass through. Reactive barriers, on the other hand, inhibit contaminant migration by chemical precipitation within the barrier. (Figure 1 shows how a reactive barrier might be used to stabilize contaminants in an estuarine setting.) CICEET-funded researchers have shown that when heavy metals like lead reach a phosphate-based reactive barrier, they precipitate to form very stable phosphate minerals. Minor disturbances within the barrier materials expose more reactive surfaces, making the system in effect "self repairing."
Results
In lab tests, the phosphate reactive barrier (Figure 2, top graph) greatly decreased the rate at which the metal moved through the phosphate treated sediment as compared to clean sediment without phosphate (Figure 2, bottom graph). In practical terms, this translates into longer lasting landfill caps and confined aquaic disposal sites as well as decreased availability of toxic metals to biological communities.
Cost-effective Solution
The phosphate material used for the reactive barrier is unprocessed mining product and is less expensive than manufactured materials. Reactive barriers may also reduce the amount of clean sediment required to cap the contaminated sediment.
Other Contaminants
Previous work suggests that the reactive barrier will be effective in stabilizing cadmium, chromium, zinc and copper as well as lead. Researchers will also determine the effect, if any, on the retention of organic contaminants (e.g., polynuclear aromatic hydrocarbons, PAHs) often found in contaminated sediments.
Patent Awarded
Methods developed for this project led to the award of a patent. The details of the patent can be found at www.uspto.gov (Patent #6,290,637,).
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Project Coordinator
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Taylor Eighmy University of New Hampshire (603)862-1065 taylor.eighmy@unh.edu |
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Start -End Date:
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09/01/1998 -09/01/2001
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NERR Reserve(s):
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Great Bay, NH - Hudson River, NY - Jacques Cousteau, NJ - Narragansett Bay, RI
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| For more information: |
Dolores Jalbert Leonard Phone: (603) 862-3685 Email: dolores.leonard@unh.edu |