Develop hydrometallurgical or pyrometallurgical recycling methods to recover valuable rare-earth compounds from various forms of NdFeB magnet scrap.
The U.S. Bureau of Mines (USBM) has developed technology to treat and recycle a variety of wastes containing valuable and strategic metals. As part of this effort, the USBM developed a process to separate neodymium and other valuable rare earths from iron in NdFeB magnet scrap (fig. 1). Since this scrap typically contains nearly 30 weight percent neodymium and since the demand for neodymium is constantly increasing, cost-effective methods for scrap treatment could have a significant impact on industrial expenditure and materials supply in the expanding area of magnet manufacture.
A hydrometallurpical, H2SO4 dissolution-precipitation process provided the most effective treatment for separating rare earths from bulk NdFeB magnet scrap (fig. 2). Precipitation of neodymium-alkali sulfate double salt proved advantageous over direct precipitation of fluoride or oxalate products. This double salt is easily converted to a variety of useful rare-earth compounds, which eliminates, many of the materials handling and economic problems inherent with direct precipitation. Following rare-earth precipitation, dissolved iron was removed from the acid leach solution by precipitation as a jarosite.
Hydromctallurgical techniques also proved successful for processing contaminated fine cutting and grinding particles known as swarf, containing both SmCo5 and NdFeB. Using a simultaneous flotation-leaching technique, the SmCo5 was concentrated in a froth, the grinding media contaminant reported to the tailing, and the NdFeB was dissolved by H2SO4 and later treated to recover both iron and neodymium products.
Pyrometallurgical, selective-oxidation techniques were not effective for treating rare-earth magnet scrap. Although the rare-earth components were preferentially oxidized over the iron, subsequent beneficiation and leaching treatments were found to be ineffective. The extremely fine grain size of the oxidised scrap prevented effective rare-earth recovery by either technique.
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