Who knew you could clean up mercury pollution with a sponge?
Not just any sponge, of course — one transformed by nanotechnology, the science of making very, very, very small things.
Researchers at the University of Minnesota reported recently that they have developed a way to use one of the most common of all cleaning tools to remove one of the most toxic and widespread pollutants from contaminated water. Their breakthrough: They permeate the sponge with the natural element selenium by growing it inside from the atom level on up. Soak the sponge in contaminated water, the mercury binds with the selenium, and the water is essentially purified.
“This is the first technology that can remove mercury totally from water,” said Abdennour Abbas, an assistant professor of biosystems engineering at the U and the lead researcher on the project. “You just have to squeeze it.”
So far, it’s been done only in a laboratory, and adapting it to the real world could prove daunting. But already, just weeks after the scientific paper was published, Abbas said he’s getting inquiries from around the globe.
“It could make a massive difference in a place like this,” wrote one woman from the Madre de Dios region of Peru, where illegal gold mining has resulted in extremely high levels of mercury poisoning in local residents.
Now, Abbas and his research team are using the same idea to create nano-sponges that trap other heavy metals such as lead and arsenic, and other pollutants such as nitrates, which contaminate drinking water in Minnesota, and phosphorus, which creates noxious algae blooms in lakes.
“I got very excited about the opportunity to field-test the technology and see how far it can be taken,” said John Tucci, president of Lake Savers, a Michigan company that sells chemicals and equipment to improve lake quality. He said he is especially eager for a sponge that would remove phosphorus, which plagues many of the lake associations and local governments that are his customers.
“The degradation of our lakes is happening at such a fast rate that even if we miraculously change our behavior, it’s going to be too late for a lot of water bodies around the world,” Tucci said.
The mission of Abbas’ division at the U is to solve global problems at the nanoscale. That means, he said, that he has to find problems that are actually solvable. For this project, he was inspired in part by news reports that one in 10 infants born on the North Shore of Lake Superior have unsafe levels of mercury in their blood.
Mercury contamination in water and fish is a significant problem for Minnesota, with its love of the outdoors and the major role it plays in the state’s economy and culture, he said. But the source of mercury is global: It’s produced primarily by coal-fired power plants and moves around the world through the atmosphere, coming back to the Earth with rain.
It’s also a big market: Electric utilities and other industries spend billions of dollars every year trying to remove mercury from their smokestacks.
“We thought, let’s try to solve this problem,” Abbas said.
Turned the sponge red
Selenium was an obvious choice. A natural element produced as a by-product of metals mining, it’s long been known to bind powerfully with mercury. It’s used now in mercury removal technologies and sometimes as a medical treatment for mercury poisoning.
But most of the current technologies are inefficient, slow and expensive.
Other researchers have tried applying selenium to other structures, but none has worked well, Abbas said.
But he came up with the idea of using a sponge, with all its nooks and crannies, and directed Snober Ahmed, a graduate student in his lab, to come up with a way to use nanotechnology to grow selenium on it.
She did it one better, discovering a way to grow selenium throughout the sponge, inside and out. Rather than using the standard practice of dipping the sponge in solution of selenium particles, which didn’t work, she soaked the sponge in an acid form of selenium and then cooked it in the oven for an hour or so. The selenium atoms adhered nicely to the sponge fibers and crystallized to form tiny particles, turning the sponge dark red in the process.
It works, the researchers said, because the tiny particles of selenium — thousands of times smaller than the width of a human hair — create an enormous amount of surface space to bond with mercury.
In practice, it means that if a 68-acre lake like Lake Como in St. Paul were contaminated with mercury at a concentration often found in Minnesota lakes, it could be cleaned up with a selenium sponge the size of a basketball.
And the process renders the mercury inert, making it safe for disposal in landfills.
It wasn’t a exactly a “eureka” moment, Ahmed confessed. It took two years to figure out how to “make it stable and safe,” she explained. Now, the university has three patents on the process, and Abbas and his students are devising ways to use the same idea in other ways.
The solution for phosphorus, Abbas said, is very close.