DOE Lab Cooks Up Rare Earth Recycling With Molten Metals
October 26, 2012 9:48 AM
New process could help combat rare Earth resource shortage
Money and global conflict have long been the core drivers of innovation.
I. What is Old, is New Again
So with rare earth metal prices at an all time high, and U.S. buyers irked by the fact that rare earth metals
, the pressure to find alternatives or to reuse existing stocks is extreme.
That backdrop has driven the
U.S. Department of Energy
-- a research institution tied to the
Iowa State University
a process it developed in the 1990s, repurposing it for molten rare earth metal recycling.
The process looks to extract neodymium, which is one of the most commonly used rare earth metals. Only 20,000 tons of neodymium is produced per year, while demand is around 22,350 tons [
]. The scarce resource is primarily used in powerful magnets that are used to regenerate power in
hybrid electric vehicles
or to generate power in wind turbines.
Slowly China came to dominate rare earth metal production, a realm once dominated by the U.S. (neodymium magnets pictured) [Image Source: Doug Kanter/Bloomberg]
Prices on neodymium have relaxed slightly, but still sit at around $150 USD/kg [
]. And a greater looming problem is that prospecting only estimates global reserves of the resource to be at around 8 million tons [
The original Ames Lab project in the 1990s merely looked to extract neodymium from neodymium-iron-boron magnet scrap, using liquid magnesium. The idea was that the neodymium would strengthen the resulting alloy. At the time rare earth prices were low, so this was the most attractive use of the scrap method.
Neodymium from Chinese-owned Inner Mongolia Baotou Steel Rare-Earth Hi-Tech Co. factory in Baotou, Inner Mongol [Image Source: Nelson Ching/Bloomberg]
But with rare earth prices soaring, Ames Lab researchers began to think about repurposing the method to extract the neodymium. The crucial question was whether the resulting yields would retain the same attractive magnetic properties as the original magnets.
II. Molten Extraction
worked with colleague
, also of Ames Lab. Professor Ott describes the process, commenting, "We start with sintered, uncoated magnets that contain three rare earths: neodymium, praseodymium and dysprosium. Then we break up the magnets in an automated mortar and pestle until the pieces are 2-4 millimeters long."
The magnet scraps go in a mesh screen box within a steel crucible and magnesium chunks are added. Heated by radio waves, the magnesium in the vessel is melted, while the magnet scraps remain solid. Magnesium has a relatively low melting point of 923 K, 650 °C (Neodymium's melting point is 1297 K, 1024 °C).
The magic is that the rare earths then diffuse out of the magnet scraps. Professor Ott describes, "The iron and boron that made up the original magnet are left behind."
The rare earth metals are extracted via diffusion into molten magnesium.
[Image Source: Ames Lab]
The magnesium + rare earths combination is cast into an ingot and cooled. Finally, the magnesium is boiled off, leaving behind only the neodymium, praseodymium and dysprosium in a smaller ingot of pure rare earths.
Early tests show the material properties of the extracted metals compare "favorably" with those of unprocessed materials. The next step will be to refine the extraction process and demonstrate it on a large industrial scale.
Comments Professor Ott, "We’re continuing to identify the ideal processing conditions. We want to help bridge the gap between the fundamental science and using this science in manufacturing. And Ames Lab can process big enough amounts of material to show that our rare-earth recycling process works on a large scale."
The research is being funded by an agreement with the
Korea Institute of Industrial Technology
(KIIT). South Korea, like the U.S., is a top electronics manufacturer and uses a lot of rare earths, so the research should prove mutually beneficial.
It's possible similar molten magnesium extraction methods could be applied to other rare earth alloys to recycle them. If the process could be perfected it could mean that the electronics, automotive, and green power industries could have a modest supply of rare earth metals for millennia to come.
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