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Staff Accomplishments

New material drinks up mercury

April 2004
A nanostructured sorbent material developed by scientists at Pacific Northwest National Laboratory has proven to be an effective and voracious tool for “absorbing” mercury from low-volume waste streams in a variety of real-life situations. Thiol-SAMMS is a simple, inexpensive and easy-to-use technology that absorbs mercury in liquids and can be easily disposed of afterwards. “This technology will result in huge savings to users who are faced with costly disposal of mercury in the waste stream,” said Shas Mattigod, a staff scientist who manages the project for the Laboratory. Thiol-SAMMS, a derivative of Self-Assembled Monolayers on Mesoporous Supports, was developed by PNNL scientist Glen Fryxell and his colleagues in 1996. SAMMS integrates a nanoporous substrate with an innovative method for attaching monolayers, or single layers of densely packed molecules, to the pore surfaces throughout the substrate. “It’s like laying a carpet,” Mattigod said. “Different carpet surfaces have different properties. You can apply a different type of monolayer to SAMMS depending on the contaminant you want to remove. This monolayer will seek out and adsorb specific contaminants.” Not only is thiol-SAMMS inexpensive and easy to dispose of, but it is also fast and effective. According to Mattigod, thiol-SAMMS surpassed developers’ expectations in tests of its mercury-absorbing capabilities at PNNL and at Oak Ridge National Laboratory (ORNL). Recently, scientists used thiol-SAMMS powder on 10 liters of mercury-containing waste solution generated in one of PNNL’s labs, reducing mercury levels in the waste from 145.8 parts per million of mercury to 0.04 parts per million, safely below U.S. Environmental Protection Agency and Washington state limits of 0.15 parts per million. “Because the solution was well below regulatory limits, we were able to save almost $2,000 in disposal costs,” Mattigod said. “Our tests have shown that mercury-laden thiol-SAMMS also passes EPA requirements for land disposal.” At the Applied Process Engineering Laboratory, a research and development facility in Eastern Washington, PNNL scientists tested thiol-SAMMS on 160 liters of waste solution containing about 11 parts per million of mercury. Thiol-SAMMS reduced mercury concentration in the solution to 0.03 parts per million. “We estimate that it will cost about $200, including material, analysis and labor, to treat similar volumes of this waste solution,” Mattigod said. “That would save $3,200 over more traditional disposal methods.” Scientists at ORNL also tested thiol-SAMMS for its ability to remove mercury from vacuum pump oil containing tritium. Mercury in the waste oil was reduced to less than 0.15 parts per million, again below EPA standards. “Using thiol-SAMMS on vacuum pump oil shows that thiol-SAMMS works not just in water solutions, but also in nonaqueous mediums,” Mattigod said. Ninety-nine percent of thiol-SAMMS’ mercury-absorbing action takes place in the first five minutes. “There is no comparison with commercially available sorbents in terms of how fast it works,” Mattigod said. “Thiol-SAMMS can absorb 60 percent of its weight in mercury, making it an efficient scavenger for mercury.” The monolayer can be custom designed to seek out a variety of contaminants. While thiol-SAMMS has been tailored to absorb mercury, silver, lead and cadmium, other SAMMS technology is being developed and tested for removing toxic contaminants such as arsenic, chromium and radionuclides. SAMMS technology, including thiol-SAMMS, can be used in water and non-aqueous solutions. Thiol-SAMMS in powder form is currently available for use on low-volume waste streams. A team of PNNL developers led by Rick Skaggs and Wayne Martin is also working on industrial applications for the technology. “In addition to the powder form, we’re developing an engineered version that will be adaptable for small to large scale systems,” Skaggs said.

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