Attractive alloy

Magnetic scraps are converted into valuable alloys

Published: Saturday 04 July 2015

a new process, devised by researchers at the us department of energy has made it commercially viable to recover a valuable rare-earth element from tons of stockpiled magnetic scrap. They have refined high-energy neodymium-iron-boron magnets, which are used extensively in automotive, consumer electronics and biomedical applications. The superior performance of these magnets allows manufacturers to make electric motors smaller, more powerful and efficient. So everything from portable compact disc players and cordless drills to motors driving automotive power windows can be lighter in weight and less draining on batteries.

Magnets are quite brittle, so manufacturers end up with a substantial amount of waste during machining and handling. Though this magnet scrap contains only about 29 per cent neodymium by weight, the rare-earth element is valued at us $30 per kilogramme -- slightly less than the price of silver -- so it's worth recovering. The problem has been in devising an efficient way of recovering it.

"The magnetic material oxidises when heated to its melting point," says Scott Chumbley, metallurgist at Ames Laboratory based in the us and chief researcher on the project. "So it is not easy to recycle it. But, it's too valuable to throw away. Until now, the best separation method available was to dissolve the magnetic 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, instead, used 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.

After removing the lubricant residue, crushed pieces of the magnet scrap are immersed in liquid magnesium at 800 c . The liquid magnesium leaches the neodymium from the scrap particles. The liquid magnesium-neodymium solution can then be poured off, leaving the iron-boron particles behind. 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. A typical magnesium alloy casting contains only two per cent neodymium by weight, yet the neodymium accounts for 40 per cent of the raw materials cost.

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