| Effective Eectrochemical and Physical Reprocessing of Nd-Fe-B and Sm-Co Permanent Magnets, Approaching the Zero Waste Economy|
Kristina Zuzek Rozman1; Xuan Xu1; Awais Ikram1; Farhan Mehmood1; Richard Sheridan2; Allan Walton2; Muhammad Awais2; Anas Eldosoukey3; Spomenka Kobe4; Saso Sturm5;
1JOZEF STEFAN INSTITUTE, Ljubljana, Slovenia; 2UNIVERSITY OF BIRMINGHAM, Birmingham, United Kingdom; 3MAGNETI LJUBLJANA, D.D., Ljubljana, Slovenia; 4JOSEF STEFAN INSTITUTE, Ljubljana, Slovenia; 5HEAD OF DEPARTMENT FOR NANOSTRUCTURED MATERIALS, Ljubljana, Slovenia;
PAPER: 189/SISAM/Regular (Oral)
SCHEDULED: 17:10/Thu. 24 Oct. 2019/Dr. Christian Bernard
Currently, less than 1% of the rare-earth elements (REEs) that reach the end of their useful lives are recycled. This is a very small percentage, especially if we consider that the recycling of end-of-life (EoL) (Dy, Nd)-Fe-B magnets is an important strategy for reducing the environmental dangers associated with rare-earth mining, and overcoming the well-documented supply risks associated with the REEs. We report on possibilities of direct electrochemical recycling and electrochemical reprocessing of Nd-Fe(B)-based magnets. Previous attempts to deposit alloys of rare earths from solutions at mild temperatures have met little success. Excitingly, in this investigation, we were able to electrodeposit Nd-Fe from the 1-ethyl-3-methylimidizolium dicyanamide ([EMIM][DCA]) ionic liquid. We observed that Nd(III) cannot be reduced independently, although it can be co-deposited inductively as substrate with the addition of Fe(II), proven by electron-energy-loss spectroscopy. Further, we propose a new concept of recycling the sintered (Dy, Nd)-Fe-B magnets by directly recovering the (Dy, Nd)<sub>2</sub>Fe<sub>14</sub>B matrix phase. Via an electrochemical etching method, we are able to recover pure individual(Dy, Nd)<sub>2</sub>Fe<sub>14</sub>B grains that can be re-used for new types of magnet production. In terms of energy consumption, the proposed electrochemical recycling route is comparable to the established direct re-use methods. These direct methods are considered as the most economical and ecological ways for recycling the sintered (Dy, Nd)-Fe-B magnets. In the frame of physical reprocessing, we have successfully synthesised new magnets out of hydrogen-recycled stocks with contemporary sintering technique of pulsed electric current sintering. The SmCo<sub>5</sub> magnets for recycling were first decrepitated by hydrogen gas to produce the powder. The sample sintered at 900°C showed the best internal coercivity (jHc) of higher than 1500 kA/m with high remanence (Br) value of 0.47 T. The optimal SPS conditions yielded fully dense Nd-Fe-B magnets with the coercivity Hc = 1060 kA/m, which was boosted to 1160 kA/m after the post-SPS thermal treatment. The Br and Hc were tackled further, and increased applied pressures of 100-150 MPa resulted in Br = 1.01 T. Via the addition of DyF<sub>3</sub>, 17.5% higher coercivity than the optimally SPS-ed magnet was obtained due to Dy substituting the Nd in the matrix Nd<sub>2</sub>Fe<sub>14</sub>B phase. We showed that with a fine tune of the SPS and post annealing, together with variations in Br and Hc, it is possible to revitalize the recycled Nd-Fe-B and Sm-Co magnets.