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Staff Accomplishments

Toxic Metals Find New Sorbent Method Very Attractive

September 2007
Thanks to magnets, PNNL technology could provide quick and easy way to clean water Mercury and other heavy metals such as lead, cadmium, and arsenic in our waters can harm our health and the environment. At Pacific Northwest National Laboratory (PNNL), researchers have found a new method of protecting our water resources against these contaminants. This unique magnetic sorbent method can rapidly and efficiently remove toxic metals in solutions. New Sorbent Feels the Pull
The researchers found that by combining iron oxide nanoparticles with DMSA, or dimercaptosuccinic acid, they can create a new sorbent that is highly dispersible in solutions, binds to toxic metals in the solution, and separates from the solutions using a magnet. Iron oxide nanoparticles have the size and texture equal to a grain of powdered sugar. Despite their size, iron oxide nanoparticles have a large surface area, which results in more binding sites for the metals. Although the nanoparticles are attracted to a magnetic field, they do not keep their magnetic properties when the magnet is removed. In liquid form, DMSA is used for treating mercury and lead poisoning. By modifying an iron oxide nanoparticle surface with DMSA, the researchers found that this increases the ability of the iron oxide nanoparticles to remove heavy metals. This is the first time they have been used as efficient magnetic sorbent material for metal ions. "We tested how well the DMSA-modified nanoparticles extracted heavy metals from water by using a method similar to most sorbent evaluations," said Dr. Wassana Yantasee. The only difference is that for the magnetic nanoparticles, a magnet was used to remove the nanoparticles from the solutions. For common sorbents, a filter or centrifuge is used. Quick and Easy Method
In terms of binding affinity for target metals, maximum uptake capacity, and uptake rate, the DMSA-modified iron oxide nanoparticles performed as outstanding as Thiol-SAMMStm, a PNNL-patented sorbent, but much better than commercial sorbents. Because the nanoparticles are attracted to a magnetic field, researchers say that they can be separated from a solution within a minute. Enhancing sorbent materials into nanoporous structures has shown to significantly improve their performance in metal removal when compared to conventional sorbent beds. However, such nanomaterials still suffer from issues involving mass transport of large water volumes through the materials. A large volume of liquid could be treated. For example, a bathtub filled with water could be treated using just 1 gram of DMSA-modified nanoparticles. In addition to water treatment, waste can be treated as well. How much liquid waste that can be treated is determined by the concentration of the metal ions in that waste. Next Steps
The researchers have begun putting other organic groups besides DMSA on the magnetic iron oxide nanoparticles, so they can capture other targets such as actinides, lanthanides, and other toxic metal cations and anions. Funding
The project was funded by two National Institute of Health grants as well as funding through PNNL's Laboratory Directed Research and Development program. Citation
Yantasee, W., Warner, C.L., Sangvanich, T., Addleman, R.S., Carter, T.G., Wiacek, T.J., Fryxell, G.E., Timchalk, C., and Warner, M.G. 2007. "Removal of Heavy Metals from Aqueous Systems with Thiol Functionalized Superparamagnetic Nanoparticles." Environ. Sci. Technol., 41: 5114-5119.

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Energy and Environment

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