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Turning Magnetic Scrap Into Valuable Alloy.

Researchers at the U.S. Department of Energy's Ames (Iowa) Laboratory have refined a process that makes it commercially viable to recover a valuable rare-earth element from tons of stockpiled magnetic scrap. High-energy neodymium-iron-boron magnets are used extensively in automotive, consumer electronics, and biomedical applications with sales exceeding $2,000,000,000 per year. The superior performance of Nd-Fe-B magnets allows manufacturers to make electric motors smaller, more powerful, and more efficient, so everything from portable CD players and cordless drills to the motors driving automotive power windows can be lighter in weight and less draining on batteries.

The Nd-Fe-B material is quite brittle, so manufacturers wind up with a substantial amount of waste beyond the amount normally generated during machining and handling. Although this magnet scrap contains about 29% neodymium (by weight), the rare-earth element is valued at $30 per kilogram (or just slightly less per ounce than the price of silver), so it's worth recovering. The problem has been how to recover it.

"The magnet material oxidizes when heated to its melting point," notes Scott Chumbley, Ames Laboratory metallurgist and lead researcher on the project. "So it is not a simple matter to recycle. But it's too valuable to throw away, so there are literally warehouses full of 55-gallon drums of the stuff waiting to be recycled."

Until now, the best separation method available was to dissolve the Nd-Fe-B scrap in acid, then perform a series of chemical extraction and reduction steps. However, the complexity and expense of such a method was impractical for large-scale, commercial recycling. Chumbley focused on using molten magnesium to extract the neodymium from the magnet scrap. Neodymium is soluble in liquid magnesium. In fact, the magnesium casting industry routinely adds neodymium and other rare-earth elements to make alloys that are corrosion-resistant and offer improved weldability.

The recovery process is relatively simple. After receiving a solvent bath to remove machining lubricant residue, crushed pieces of Nd-Fe-B magnet scrap are immersed in liquid magnesium at 800 [degrees] C, which leaches the neodymium from the scrap particles. The liquid magnesium-neodymium solution can then be poured off, leaving behind the iron-boron particles.

The resulting magnesium alloy is enriched in neodymium, making it perfect for use as feed material for the magnesium casting industry, at a substantially lower cost. Currently, a typical magnesium alloy casting contains just two percent neodymium by weight, yet the neodymium accounts for 40% of the raw materials cost.

"It would give them a product that is exactly what they're already used to using," Chumbley says. "They wouldn't have to retool or change any of their processes." In addition, the leftover iron-boron scrap could be recycled as well, particularly for low-grade iron castings where composition isn't critical.
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Title Annotation:process developed at Department of Energy's Ames Laboratory
Publication:USA Today (Magazine)
Article Type:Brief Article
Geographic Code:1USA
Date:Jun 1, 2001
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