Electrochemical Formation of Pr–Ni Alloys in LiF–CaF₂–PrF₃and NaCl–KCl–PrCl₃Melts

Abstract

For the establishment of a process for the electrochemical recovery of rare earth elements from used magnet scraps, the electrochemical formation of Pr-Ni alloys in molten LiF-CaF 2 -PrF 3 and NaCl-KCl-PrCl 3 salts at 1123 K and 973 K, respectively, was investigated.Cyclic voltammetry and open-circuit potentiometry indicated the formation of several phases of Pr-Ni alloys. Alloy samples were prepared by one-or two-step potentiostatic electrolysis using a Ni plate electrode at various potentials. Scanning electron microscopy observations and X-ray diffraction measurements confirmed the formation of PrNi 2 , PrNi 3 , Pr 2 Ni 7 , and PrNi 5 . The formation potential for each Pr-Ni alloy phase was determined from experimental results. In addition, the optimum electrolysis conditions for the separation of Nd, Dy, and Pr are discussed.Rare earth (RE) metals have several superior characters such as electric, magnetic, and fluorescence properties and are therefore indispensable as industrial materials throughout the world. Among the many applications of RE metals, the use of neodymium-ironboron (Nd-Fe-B) magnets-the so-called neodymium permanent magnets-has been remarkably increasing recently. Neodymium permanent magnets composed of a Nd 2 Fe 14 B main phase have several advantages such as superior magnetic properties and high mechanical strength, and are used for voice coil motors in hard disk drives (HDDs), magnetic resonance imaging (MRI), speakers/vibrators in cell phones, and motors in electric vehicles (EVs) and hybrid electric vehicles (HEVs). Since praseodymium (Pr) and Nd have similar chemical properties, they are found in nature in the same ores and their separation is difficult. Thus, in some applications including permanent magnets, a Nd-Pr alloy called didymium (Di) is sometimes utilized. On the other hand, Nd-Fe-B magnets have the drawback of a relatively low Curie temperature of ∼583 K. In order to maintain its superior coercive force even at high temperatures (above 473 K), where high-performance motors in EVs and HEVs operate, dysprosium (Dy) is necessary as an additive.One of the concerns pertaining to RE magnets is the uneven distribution of RE resources: in 2011, China had 50% of the proven RE reserves and produced over 97% of the global RE supply. 1 In 2010-2012, the price of REs increased sharply, causing supply problems for the magnets. While the present RE production capacity satisfies the demand and their price has lowered, there remains the potential for RE shortage in the future.On the basis of these supply circumstances, it can be concluded that the recycling or waste management of Nd-Fe-B magnet scraps is currently an urgent task. The conventional wet processes for RE recycling from Nd-Fe-B magnet scraps have several disadvantages such as their multistep and complicated processes, high environmental loads, and large energy consumption. As new recycling methods, pyrometallurgical processes such as chemical vapor transport, 2 selective reduction, 3 molten salt electrolysis, 4 and ionic liquid e...

Selective Formation of Rare-Earth–Nickel Alloys via Electrochemical Reactions in NaCl–KCl Molten Salt

“…Table 1 Formation reactions and corresponding potentials for RE-Ni alloys and RE metals in molten NaCl-KCl-0.50 mol%RECl 3 at 973 K (RE = Pr, Nd, and Dy). [13][14][15]…”

“…salts at 1123 K [10][11][12]15 and molten NaCl-KCl-RECl 3 salts at 973 K. [13][14][15] Concerning the LiF-CaF 2 eutectic melt, Nourry et al also reported the formations of Nd-Ni alloys. 16,17 For the application of the process, investigations not only of the behaviors of each element but also of the separation between Pr, Nd, and Dy are essential.…”

Electrochemical Synthesis and Thermodynamic Properties of Pr‐Ni Intermetallic Compounds in a LiCl‐KCl‐NiCl2‐PrCl3 Melt

“…The first one is the formation of different RE‐iron group(IG) alloys for preparation of magnetic materials . Nohira et al ,. investigated the electrochemical formation and phase control of Pr−Ni alloys in LiCl‐KCl‐PrCl 3 melts, LiF‐CaF 2 ‐PrF 3 and NaCl‐KCl‐PrCl 3 melts.…”

Selective Formation of Rare Earth-Nickel Alloys via Electrochemical Reactions in NaCl-KCl Molten Salt

“…We have proposed a new separation and recovery process for RE elements from magnet scraps using molten salt electrochemistry utilizing an alloy diaphragm. [9][10][11][12][13][14][15] In the proposed process, two molten salt electrolytes are separated by an RE-iron group (IG) alloy diaphragm. Scraps of RE magnets are used as an anode to dissolve RE elements into the molten salt in the anode chamber, and then, Pr, Nd, and Dy are separated using the differences in both the formation potentials and formation rates of the RE-IG alloys.…”

“…salts at 1123 K [10][11][12]15 and molten NaCl-KCl-RECl 3 salts at 973 K. [13][14][15] Concerning the LiF-CaF 2 eutectic melt, Nourry et al also reported the formations of Nd-Ni alloys. 16,17 For the application of the process, investigations not only of the behaviors of each element but also of the separation between Pr, Nd, and Dy are essential.…”