Attractive recovery method

Researchers at the US Department of Energy’s Ames 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 billion per year in the US alone.

The Nd-Fe-B material is quite brittle; leaving manufacturers with a substantial amount of waste beyond the amount normally generated during machining and handling. Though this magnet scrap contains around 29 percent neodymium (by weight), the rare-earth element is valued at $30 per kilogram.

‘The magnet material oxidises when heated to its melting point,’ said 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.’

The current method of recovering the material involves dissolving Nd-Fe-B scrap in acid, then performing a series of chemical extraction and reduction steps. However, the complexity and expense of such a method is deemed 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.

The recovery process is said to be 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° C.

The liquid magnesium leaches the neodymium from the scrap particles and the liquid magnesium-neodymium solution can then be poured off, leaving the iron-boron particles behind.

The Ames researchers claim that 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 is said to contain two- percent neodymium by weight, yet the neodymium accounts for 40 percent of the raw materials cost.

‘It would give them a product that is exactly what they’re already used to using,’ said Chumbley. ‘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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