Recycling of Rare Earth Magnet Scraps Part III Carbon Removal from Nd Magnet Grinding Sludge under Vacuum Heating

Abstract

The removal of the carbon from Nd magnet scraps is indispensable for high-quality recycling by the induction melting method as a preliminary process. The Nd magnet scraps can be decarburized to a level of less than 0.03 mass% by using an oxygen source at high temperatures, as reported in Part 1. The decarburized Nd magnet scraps can then be deoxidized by using the Ca reduction to a level that allows commercial melting in an induction furnace, as reported in Part II. However, the undesirable iron oxide (Fe 2 O 3 ) which causes a disadvantage for Ca reduction is inevitably generated by using an oxygen source at high temperatures. The aim of this work is to investigate an economical decarburization method in which only the carbon sources in Nd magnet scraps are decarburized, without generating iron oxide. The grinding sludge as Nd magnet scraps is effectively decarburized to a level of less than 0.03 mass% without generating any iron oxide by heating at above 1073 K under a pressure of less than 5.32 × 10 −2 Pa. The amount of oxygen in the decarburized powder is about 8 mass%, which is lower in comparison with its value in Part 1. In this report, the decarburization mechanism under reduced pressure using the grinding sludge, and its economic significance prior to the decarburizing method described in Part 1, are discussed.

Phase equilibrium of the system Ag–Fe–Nd, and Nd extraction from magnet scraps using molten silver

“…The latter pyrometallurgical process is simple and fast; however, it is difficult to prevent neodymium (Nd) oxidation during the remelting process, and the physical separation of metal from slag is currently a serious technical problem. In the recent years, Suzuki and co-workers [8][9][10] investigated a new recycling process for the Nd-Fe-B magnet scrap using calcium metal and CaCl 2 flux. In principle, this technique is based on the calcium halide flux deoxidation technique for rare earth metals [11,12].…”

Review of High-Temperature Recovery of Rare Earth (Nd/Dy) from Magnet Waste

“…On reducing the oxygen partial pressure at 1350 K, NdFeO(s) dissociates to Fe(s) and Nd 2 O 3 (s). [9,35,37] studied the removal of carbon and oxygen from magnet scrap. In principle, the technique was based on the calcium halide flux deoxidation technique for RE metals.…”

“…The recycling process, although involving several steps, can be considered as a simple process utilizing basic reduction methods and is easy to operate. The decarburization of the sludge has also been found to be possible under vacuum, with most of the oxygen source coming from the sludge itself [35]. Hydrogenation of the decarburized scraps is done to reduce the Ca consumption in the second stage reduction because iron oxide hinders the subsequently Ca reduction-more Ca is required for reduction of Fe 2 O 3 , increasing the recycling cost, and the Fig.…”

Recycling of rare earth magnet scraps: Carbon and oxygen removal from Nd magnet scraps

“…The second is the oxygen removal process by a combination of hydrogen-reduction and reduction-and-diffusion (RD) method using Ca and CaCl 2 . In our previous work, the carbon and oxygen content could reach a level of 0.01% and 0.70%, respectively [5][6][7]; however, further removal of oxygen is required to promote practical application. * Corresponding author.…”