Recovery of Nd and Dy from Rare Earth Magnet Scrap

Transcription

1 Recovery of Nd and Dy from Rare Earth Magnet Scrap Sakae Shirayama 1 and Toru H. Okabe 2 1 Department of Materials Engineering, the University of Tokyo, Japan 2 Institute of Industrial Science, the University of Tokyo, Japan

2 Nd Fe B magnet Nd Fe B magnet is a rare earth permanent magnet. main phase: Nd 2 Fe 14 B intermetallics advantage: high magnetic intensity high coercive force abundance of minerals which contains Nd applications: Hard Disk Drive in personal computer motors for air conditioner motors for Hybrid Electronic Vehicle (HEV) Dy addition improves heat-resistance. Fig. Nd-Fe-B magnet MIT_Shirayama_slide 2

3 Resource for Nd and Dy Rare earth deposits Bastnaesite La Ce Nd Ion adsorption ore (ion clay) Y La Nd Other heavy REE mass% Other Pr Sm heavy REE U : mass% Th : 0.14 mass% Nd: 1 ~ 2 mass% Dy: trace Rich in light REE (La, Ce, Pr, Nd) Abundant all over the world Contain U and Th mass% U, Th : Nd Dy Ce Pr Sm : 70 ~ 200 ppm : 40 ~ 120 ppm Dy Rich in heavy REE (Tb, Dy, Ho, Er, Tm, Yb) Distributed only in China No U and Th MIT_Shirayama_slide 3 100

4 Amount of production, w / kt Problems in supply of REE Worlds 97 % supply is dominated by China. Prices of REE are escalating especially for Dy. Other 3 kt (3%) Total 123 kt China 120 kt (97%) Year Change in amount of production of REE. World share in supply of REE in (USGS Mineral Commodity Summaries (2007)) Price US$ / kg Dy Nd Sm Year. Month Change in prices of Nd, Dy, and Sm. (Industrial rare metals (2007)) MIT_Shirayama_slide 4

5 Purpose of this study Supply of Dy has limitation. Production of REE from ore induces environmental pollution. Large amount of Dy-containing Nd Fe B magnet scrap will be produced especially from automobiles. Development of an efficient recovery process of Nd and Dy from Nd Fe B magnet scrap. MIT_Shirayama_slide 5

6 Recovery of Nd and Dy from magnet scrap HDD HEV REE extractant Dy-containing Nd Fe B magnet scrap have a stronger affinity for REE than Fe or easily react with REE Recycling process (Extraction of Nd and Dy) Pure Nd Pure Dy Fe B alloy MIT_Shirayama_slide 6

7 Overview of this study Dy-containing Nd Fe B magnet scrap MgCl2(l) This study Nd and Dy extraction by molten MgCl2 NdClx (l) + DyClx (l) + Mg (l) + MgCl2 (l) + Fe B (s) Solid / liquid separation L S NdClx (l) + DyClx (l) + Mg (l) + MgCl2 (l) Vacuum distillation / separation Fe B (s) MgCl2 (l, g) NdClx (s, l) Refining / reduction Nd (s) DyClx (s, l) Dy (s) Mg (g) Fig. Flow chart of the recovery process by using MgCl 2 as an extracting agent. MIT_Shirayama_slide 7

8 Experimental work Extraction of Nd and Dy by molten MgCl 2 Reaction temperature: 1273 K Reaction time: 3 h, 6 h, 12 h Stainless-steel wire Stainless-steel foil Dy-containing Nd Fe B alloy Fe crucible Molten MgCl 2 Alumina tube Stainless-steel chamber Thermocouple Heating element Stainless-steel basket Ti sponge Fig. Schematic illustration of the experimental setup. 2 Nd (s) + 3 MgCl 2 (l) 2 NdCl 3 (l) + 3 Mg (l) ΔG = kj at 1300 K Dy (s) + MgCl 2 (l) DyCl 2 (l) + Mg (l) ΔG = 57.6 kj at 1300 K MIT_Shirayama_slide 8

9 Experimental result (1)-alloy Intensity, I (a. u.) (a) Initial. (b) After exp. (1273 K, 6 h) Nd 2 Fe 14 B PDF# Fe PDF# Fe obtained Angle, 2θ / degree (Cu-Kα) Fig. XRD patterns of Dy-containing Nd Fe B alloy. Fe was obtained after experiment. MIT_Shirayama_slide 9

10 Experimental result (1)-salt (a) Initial. MgCl 2 NdCl 3 PDF# PDF# Intensity, I (a. u.) (b) After exp. (1273 K, 6 h) NdCl 3 produced Angle, 2θ / degree (Cu-Kα) Fig. XRD patterns the obtained salt. Nd was extracted into molten MgCl 2 as NdCl 3 MIT_Shirayama_slide 10

11 Experimental result (2)-alloy Table Change in mass and composition of Nd-Fe-B alloy. Exp. No. Reaction temp., T / K Reaction time, t / hr Mass of alloy before exp., w alloy / g Mass of alloy after exp. w alloy / g : initial mass of element i in alloy Conc. of element i in Nd-Fe-B alloy, C i (mass%) a initial # 1 # 2 # a: Determined by ICP-AES analysis. REE content ratio, R i alloy/alloy w i 0, alloy w i, alloy i : mass of element i in alloy after exp. : Nd, Dy C Nd C Dy decreased = w i, alloy w i 0, alloy 100 (%) MIT_Shirayama_slide 11

12 REE content ratio, R i alloy/alloy REE content ratio, R i alloy/alloy (%) Reaction time, t / hr Nd Dy 90 % of Nd and 87 % of Dy were removed after reaction for 12 h. Fig. Change of REE content in the magnet alloy. MIT_Shirayama_slide 12

13 Experimental result (2)-salt Table Mass and composition of salt obtained after experiment. Conc. of element i in salt, Reaction temp., Reaction time, Exp. No. T / K t / hr w MgCl2 / g w salt / g C i (mass%) a C Nd C Dy initial 0l 0lll # 1 # 2 # Mass of MgCl 2 before exp., Mass of salt after exp a: Determined by ICP-AES analysis. increased REE extraction ratio, R i salt/alloy w i 0, alloy i w i, salt : initial mass of element i in alloy : mass of element i in alloy after exp. : Nd, Dy = w i, salt w i 0, alloy 100 (%) MIT_Shirayama_slide 13

14 REE extraction ratio, R i salt/alloy Extraction ratio, R i salt/alloy (%) Nd Dy Reaction time, t / hr Fig. Change of extraction ratio to the molten salt. More than 80 % of Nd and Dy were extracted after reaction for 12 h. MIT_Shirayama_slide 14

15 Conclusions Selective extraction of Nd and Dy directly from magnet scrap was investigated utilizing molten MgCl 2. It is possible to extract Nd and Dy into molten MgCl 2 selectively from Nd Fe B magnet alloy. Effective recovery process of Nd and Dy from magnet scrap can be established by utilizing molten MgCl 2. MIT_Shirayama_slide 15

16 Future work Investigate a new gas phase treatment for direct recovery of Nd and Dy from magnet scrap using various extracting agents. Development of a new simultaneous extraction and separation of rare earth elements from magnet scrap. MIT_Shirayama_slide 16