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July 23, 2003 – It was the industrial age that brought increased exposure to dangerous heavy metals like lead, mercury or arsenic as factories dumped contaminated wastewater into rivers and oceans. It is the nanotechnology age that could mark the end of this particular toxic chapter.
Barring a return to a purely agricultural society, heavy metals are here to stay, since they are produced by such essential sectors as the steel and electricity industries. That keeps the health industry busy, though, because most heavy metals are not normally found in the human body and a buildup can cause anemia, hypertension, infertility, miscarriages and damage to the nervous system or kidneys, depending on the metal.
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As governments crack down on contamination, industries are always on the lookout for ways to improve wastewater treatment before returning it to the water supply or reusing it in the manufacturing process.
A team of scientists and manufacturers from Germany, Ireland and the United Kingdom has developed a process that uses nanoparticles to draw heavy metals out of industrial wastewater with a little help from simple magnetism.
The secret lies in the iron oxide nanoparticles that scientists at the Institute for New Materials (INM) in Saarbrücken, Germany, have set in a glass matrix to create superparamagnetic composite particles (SPMC) — micron and submicron-size particles with magnetic properties that heavy metals simply find irresistible.
The SPMC are introduced into wastewater and attract the heavy metals present there. Then the water is passed through a magnetic field and the fully laden SPMC are drawn out of the flow. Think back to those old elementary school experiments with metal shavings bunching around a horseshoe magnet.
After removal from the water, the heavy metals can be detached from the SPMC through a chemical process. The result is a highly concentrated sludge.
“The concept is simple,” said Eoin Byrne, a project manager at Arcon Mines Ltd., an Irish company that tested the process on its own wastewater. “You’re basically dragging the metals out of a solution with a magnet, rinsing the particles and collecting your metals solution to dispose of or even reuse if you want.”
Depending on the heavy metal to be extracted, about a gram of particles is needed per liter of water, according to INM researcher Peter Rogin. With that, his team has been successful in pulling out up to 100 milligrams of heavy metal.
The advantages of the particle treatment method, as opposed to traditional processes like chemical or precipitation treatments, is that it is possible to achieve very high levels of purity at the end. That is especially important when the metals in question are highly toxic ones such as mercury or lead.
“Treatment methods in these cases are very difficult and quite expensive,” Rogin said. “We will be able to offer cost advantages here.”
But don’t run out looking to buy a bucketful of SPMC just yet. He and other team members said that although the process has been shown to work in the lab, it is still some three years away from being ready for industry. The difficulty has been in getting just the right mix in the composite particles, which can be “customized” to pull out different metals according to need.
Another hurdle is cost. “Right now I don’t think it’s appropriate for the whole (waste treatment) industry,” said Horst Suchomel, head of business development at the waste disposal company HIM Technologie, which was also involved in the project.
“But it could be a very good solution for the 5 percent or so of industry which produces high-value metals. And in Germany, companies produce some 150,000 tons of this kind of material every year. In the U.S., the market would be even bigger.”