Nanosponge soaks up mercury
The first commercial use of a novel sponge-like material dubbed Self-Assembled Monolayers on Mesoporous Supports (SAMMS) began at several sites in May, to remove mercury from effluents. The material boasts two key advantages — very good selectivity for mercury and fast kinetics — says Bob Jones, Atlanta-based vice president of its producer, Steward Environmental Solutions, Chattanooga, Tenn.
SAMMS developer, Pacific Northwest National Laboratory (PNNL), Richland, Wash., granted Steward exclusive worldwide rights to the material for all applications except “produced water” from offshore drilling. Steward started production of thiol-SAMMS powder in March, and now is supplying a number of companies, notes Jones. While some are simply evaluating the material, others already are applying it to organic and aqueous effluents, he says.
Thiol-SAMMS integrates a nanoporous substrate with an innovative method for attaching single layers of densely packed molecules to the pore surfaces throughout the substrate, says Shas Mattigod, a staff scientist at PNNL. “There is no comparison with commercially available sorbents in terms of how fast it works,” he claims, noting that 99% of thiol-SAMMS’ mercury-adsorbing action takes place in the first five minutes. “Thiol-SAMMS can adsorb 60% of its weight in mercury,” he adds. In tests at PNNL, the material reportedly removed 99.9% of mercury in a simulated wastewater, reducing the mercury level to well below EPA discharge limits. Mattigod calls treatment costs an order of magnitude lower than those of the best available alternative technologies. “We estimate that it will cost about $200, including material, analysis and labor, to treat similar volumes of this waste solution,” he says. “This would save $3,200 over the more-traditional disposal methods.”
The material can remove both ionic and elemental mercury and handle both aqueous and organic liquids. The treatment process basically involves pumping effluent into a container, mixing it with SAMMS, and letting the contents sit for a short period, explains Jones. The effluent is then pumped out, with SAMMS subsequently removed by filtration. Because of the strong chemical bond between the material and mercury, mercury-loaded SAMMS is not considered hazardous and so can be disposed of in a conventional industrial landfill, he adds.
The material is 20 times faster at adsorbing mercury than resins, Jones notes, adding that it adsorbs 10 times more of the metal and this higher loading translates into only one-tenth of the volume of spent material for disposal. SAMMS adsorbs about 30 times more mercury than activated carbon, he says.
Jones is talking to companies about applications for gas treatment. However, the current version of SAMMS is limited to temperatures of ambient to 90°C, notes Mattigod.
Besides mercury, the thiol-SAMMS can remove silver, lead and cadmium. Other variants are being developed to handle contaminants such as arsenic, chromium and radionuclides. Mattigod also notes that alternative physical forms such as membrane-sandwich materials for use in fixed beds for higher-volume continuous applications are in the works.