Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D11/00—Solvent extraction
  • B01D11/04—Solvent extraction of solutions which are liquid
  • B01D11/0415—Solvent extraction of solutions which are liquid in combination with membranes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D11/00—Solvent extraction
  • B01D11/04—Solvent extraction of solutions which are liquid
  • B01D11/0488—Flow sheets
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
  • B01D61/24—Dialysis ; Membrane extraction
  • B01D61/246—Membrane extraction
  • B01D61/2461—Membrane extraction comprising multiple membrane extraction steps
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
  • B01D61/38—Liquid-membrane separation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D63/00—Apparatus in general for separation processes using semi-permeable membranes
  • B01D63/02—Hollow fibre modules
  • B01D63/032—More than two tube sheets for one bundle
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
  • B01D69/14—Dynamic membranes
  • B01D69/141—Heterogeneous membranes, e.g. containing dispersed material; Mixed matrix membranes
  • B01D69/142—Heterogeneous membranes, e.g. containing dispersed material; Mixed matrix membranes with "carriers"
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
  • C22B3/04—Extraction of metal compounds from ores or concentrates by wet processes by leaching
  • C22B3/06—Extraction of metal compounds from ores or concentrates by wet processes by leaching in inorganic acid solutions, e.g. with acids generated in situ; in inorganic salt solutions other than ammonium salt solutions
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
  • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
  • C22B3/26—Treatment or purification of solutions, e.g. obtained by leaching by liquid-liquid extraction using organic compounds
  • C22B3/32—Carboxylic acids
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
  • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
  • C22B3/26—Treatment or purification of solutions, e.g. obtained by leaching by liquid-liquid extraction using organic compounds
  • C22B3/38—Treatment or purification of solutions, e.g. obtained by leaching by liquid-liquid extraction using organic compounds containing phosphorus
  • C22B3/384—Pentavalent phosphorus oxyacids, esters thereof
  • C22B3/3842—Phosphinic acid, e.g. H2P(O)(OH)
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
  • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
  • C22B3/26—Treatment or purification of solutions, e.g. obtained by leaching by liquid-liquid extraction using organic compounds
  • C22B3/38—Treatment or purification of solutions, e.g. obtained by leaching by liquid-liquid extraction using organic compounds containing phosphorus
  • C22B3/384—Pentavalent phosphorus oxyacids, esters thereof
  • C22B3/3844—Phosphonic acid, e.g. H2P(O)(OH)2
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
  • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
  • C22B3/26—Treatment or purification of solutions, e.g. obtained by leaching by liquid-liquid extraction using organic compounds
  • C22B3/40—Mixtures
  • C22B3/408—Mixtures using a mixture of phosphorus-based acid derivatives of different types
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B59/00—Obtaining rare earth metals
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• the present invention relates to methods for separating rare earth elements that have been recovered from scrap permanent magnets and other end-of-life products.
• Rare earth magnets are strong permanent magnets made from alloys of rare earth elements. It is estimated that over ten thousand tons of scrap permanent magnets of hard disk drives containing Nd, Dy, and Pr, are available for recycling. Rare earth magnets are typically not recycled however. In the case of hard drives, more than 500 million hard drives are manufactured annually. Disposal operations primarily include shredding hard drives with e-waste recyclers. Steel and aluminum are typically electromagnetically sorted from the shredded material stream for recycling. The remaining components, including the rare earth magnets, are treated as waste. [0005] The content of Dy in scrap permanent magnets varies significantly in their applications. For example, while hard disk drives contain about 1-3 wt.
• Dy is an essential component of almost all types of permanent magnets including laptop hard disk drives, hybrid/electric cars, and wind turbines due to their very specific properties such as coercivity, high temperature tolerance, and corrosion resistance.
• the demand for Dy is estimated to increase every year and will exceed 800 tons in 2020, which is nearly double the amount used in 2011. While the demand of Dy is continuously increasing, its supply, however, is uncertain because most of its production is limited to a single source in southern China, and the amount of Dy available in mines is also limited.
• Dy has high criticality and commands almost a four-fold higher market value compared to Nd and Pr.
• the limited production and supply and the high economic rewards demand the recovery, separation and purification of Dy from mixed rare earth oxides recovered from scrap permanent magnets.
• the separation of Dy from other rare earth elements is of significant commercial interest.
• separation of Dy from mixed rare earth oxides, particularly NdPrDy will lead to two pure products including Dy and NdPr, which have significant market values in their individual form. If Dy can be separated in its pure form, it can be added to any rare earth oxide mixture to meet end-user specifications for various applications for recycling and reuse of recovered rare earth elements from scrap magnets.
• a system and method for the separation of recovered rare earth elements include the supported membrane solvent extraction of rare earth elements and rare earth element oxides that have been recovered from permanent magnets and other electronic waste.
• an organic phase consisting of an extractant and an organic solvent is immobilized in the pores of hollow fibers.
• An aqueous feed solution and a strip solution flow along the shell side and the lumen side of the hollow fibers, respectively.
• the extractant functions as a carrier to selectively transport certain rare earth metals from the feed side to the strip side.
• the rare earth metals are back- extracted in the strip solution, allowing processing to proceed continuously without equilibrium limitations.
• the permeable hollow fibers are hydrophobic polypropylene hollow fiber membrane modules that are oriented in a common direction between opposing tubesheets.
• the hollow fibers can include a bundle assembly with several thousands of fibers having an inner diameter of about 0.24 mm, and outer diameter of about 0.30 mm, a pore size of about 30 nm, and membrane area of about 1.4 m 2 .
• the immobilized organic phase includes a solvent and an extractant.
• the organic phase can include an isoparaffinic hydrocarbon solvent and a phosphorous-based chelating extractant and with a ratio by volume of between 1:1 and 3:1 or any other combination.
• the feed solution can include a pH maintained between 0 and 2.0, further optionally between 1.0 and 1.5.
• Figure 1 is an illustration of a system for supported membrane solvent extraction for the separation of rare earth elements.
• Figure 2 is an illustration of a supported membrane solvent extraction module including porous hollow fibers.
• Figure 3 is an illustration of a multi-stage system for supported membrane solvent extraction.
• Figure 4 is a flow diagram of a method for supported membrane solvent extraction for the separation of rare earth elements.
• Figures 5A to 5F are graphs illustrating the stage-one recovery of Dy from mixed rare earth element oxides.
• Figures 6 A to 6F are graphs illustrating the stage-two recovery of Dy from mixed rare earth element oxides.
• Figures 7 A to 7F are graphs illustrating the stage-three recovery of Dy from mixed rare earth element oxides.
• Figure 8 is an X-ray diffraction (XRD) analysis of Dy obtained from the strip solution after third stage recovery, with standard Dy2(3 ⁇ 4 as a reference.
• XRD X-ray diffraction
• Figure 9 is an illustration of a system for membrane solvent extraction of REEs and the subsequent separation of Dy from Nd and Pr.
• Figures 10A to 10F are graphs illustrating Dy separation from rare earth elements recovered from scrap magnets using the system of Figure 9. DETAILED DESCRIPTION OF THE CURRENT EMBODIMENTS
• the system includes supported membrane solvent extraction for the separation of heavy rare earth elements from light rare earth elements, each having been collectively recovered from scrap permanent magnets as mixed rare earth element oxides in substantially pure form (e.g., greater than 90%, optionally greater than 99.5%, by weight of rare earth element oxides).
• the system generally includes a feed line 12, a strip line 14, and a hollow fiber membrane module 16.
• the hollow fiber membrane module 16 includes a bundle assembly of hollow fibers oriented in a common direction between opposing tubesheets.
• the REE feed solution is contained within a feed reservoir 18 and is mixed to ensure a uniform concentration.
• the feed solution is circulated through the hollow fiber membrane module 16 in a closed loop under pressure from a first pump 20, for example a peristaltic pump, optionally ensuring the feed line pressure is greater than the strip line pressure.
• the strip line 14 includes a reservoir 22 and a pump 24, for example a peristaltic pump, to ensure a continuous flow of strip solution through the module 16.
• a pump 24 for example a peristaltic pump, to ensure a continuous flow of strip solution through the module 16.
• Both of the feed line 12 and the strip line 14 are shown as a closed circuit in Figure 1, such that the feed solution and the strip solution are in continuous recirculation. However, in other embodiments the feed line and/or the strip line form an open circuit.
• a membrane module containing a fiber bundle is illustrated in Figure 2 and generally designated 16.
• the membrane module 16 includes an outer casing 26 defining a feed input port 28, a feed output port 30, a strip input port 32, and a strip output port 34.
• the plurality of fibers 36 are potted to first and second tubesheets 38, 40 at opposing ends thereof, such that the fibers 36 extending in a common direction within the module 16.
• Each fiber 36 includes a lumen side 42 and a shell side 44.
• the lumen side 42 is illustrated in Figure 2 as being exposed to the strip solution, however in other embodiments the lumen side 42 is exposed to the feed solution.
• the shell side 44 is illustrated in Figure 2 as being exposed to the feed solution, however in other embodiments the shell side 44 is exposed to the strip solution.
• the “lumen side” includes the interior surface that defines a channel extending longitudinally through the length of the hollow fiber
• the “shell side” includes the exterior surface of the fiber, such that the lumen side and the shell side are spaced apart from each other by the thickness of the membrane sidewall.
• the side in contact with the feed solution defines the “feed interface,” and the side in contact with the strip solution defines the “strip interface.” Consequently, the lumen side is the feed interface in some embodiments and is the strip interface in other embodiments.
• the shell side is the strip interface in some embodiments and is the feed interface in other embodiments.
• the REE feed solution includes rare earth elements that have been previously separated from non-rare earth elements.
• the feed solution can be extracted according to the membrane assisted solvent extraction process set forth in U.S. Patent 9,968,887 to Bhave et al, in which rare earth elements (such as Nd, Dy, and Pr) are recovered from commercial scrap magnets (also containing non-rare earth elements as Fe and B).
• the feed solution includes, as a first component, a dry mixture of two or more different rare earth element oxides (e.g., in a composition of greater than 90%, optionally greater than 99.5%, by weight of rare earth element oxides), and, as a second component, a solution of dilute nitric acid, for example 0.02 M nitric acid.
• Example rare earth element oxides include Nd2(3 ⁇ 4, Pr2(3 ⁇ 4, RGbOii, and Dy2(3 ⁇ 4, though other rare earth element oxides can be used in other embodiments.
• the feed solution can include a mixture of two or more different rare earth elements not in oxide form, but with a purity of at least 90% by weight, optionally at least 99.5% by weight, in combination with a solution of dilute nitric acid.
• the pH of the feed solution is generally maintained at between 0 and 2.0, consistent with the best operating mode for the cationic extractant, further optionally between 1.0 and 1.5.
• the strip solution is generally selected to strip heavy rare earth element complexes that have diffused from the feed interface to the strip interface.
• the strip solution can include HNO3, HC1, or H2SO4, for example, at a higher molar concentration than in the feed solution.
• the strip solution can include 3.0 M HNO3 in comparison to the feed solution of 0.02 M HNO3.
• the strip solution is contained within a second reservoir 22 and is circulated through the hollow fiber membrane module 16 in a closed loop under pressure from a second pump 24.
• the hollow fiber membrane module 16 includes an organic phase consisting of an extractant and an organic solvent immobilized in the pores of the hollow fibers.
• the extractant is a phosphorous-based chelating extractant in the current embodiment, for example Cyanex 572 by Cytec Industries, Inc.
• the extractant can be a neutral extractant, for example tetraoctyl diglycolamide (“TODGA”).
• TODGA tetraoctyl diglycolamide
• other extractants such as trialkyl phosphine oxide, 2-ethylhexyl phosphonic acid mono-2-etylhexyl ester, carbamoyl phosphoryl oxides, sec-octyl phenoxy acetic acid or Cyanex 272 can be used in other embodiments.
• the organic solvent includes an isoparaffinic hydrocarbon solvent, for example Isopar L from ExxonMobil Chemical, however other solvents such as tributyl phosphate, xylene, hexane, octanol or kerosene can be used in other embodiments.
• the pores of the hollow fibers are pre-impregnated with the organic phase, consisting of the isoparaffinic hydrocarbon solvent and the phosphorous-based chelating extractant, with a ratio by volume of between 3 : 1 and 1:1, further optionally 2:1.
• the pore size is selected based on capillary forces necessary to hold the organic phase into the pores of the membrane fibers, for example between approximately 0.01 micron and approximately 1.0 micron, or about 30 nm in the present embodiment.
• the separation of heavy rare earth elements (e.g., Dy) from light rare earth elements (e.g., Nd and Pr) can occur in multiple stages.
• the first stage separation is conducted for a first predetermined time period, for example twenty four hours, where the feed solution and the strip solution are continuously recirculated through the membrane module 16.
• the feed solution containing REOs are previously recovered from scrap magnets dissolved in 0.02 M nitric acid feed solution.
• the pH of the feed solution can be maintained at 0 to 2.0.
• the pH of the Dy, heavy REE-enriched strip solution from the first stage is adjusted (increased) to between 0 and 2.0, optionally 1.5, using ammonium hydroxide and is used as the feed solution for the second stage.
• the strip solution can be filtered to remove any precipitated salts.
• the second stage of separation can occur over a second predetermined time period, optionally less than the first predetermined time period, for example ten hours, where the feed solution and the strip solution are continuously recirculated through the membrane module 16.
• the pH of the Dy, heavy REE-enriched strip solution can be adjusted (increased) to between 1.0 and 2.0, optionally 1.5.
• the third stage of separation can occur over a third predetermined time period, for example ten hours, where the feed solution and the strip solution are continuously recirculated through the membrane module 16.
• the membrane module 16 includes an organic phase of Cyanex 572 (33 v/v%) and Isopar L (67 v/v%), or other combination of the organic phase constituents, and the strip solution includes 3.0 M nitric acid or other appropriate concentration based on feed solution conditions.
• the heavy rare earth element Dy is in substantially pure form, optionally greater than 99.5% by weight, being separated from lighter rare earth elements, for example Nd and Pr.
• the system includes supported membrane solvent extraction for the separation of heavy rare earth elements from light rare earth elements, each having been collectively recovered from scrap permanent magnets as mixed rare earth element oxides in substantially pure form (e.g., greater than 90%, optionally at least 99.5% by weight of rare earth element oxides).
• a flow chart illustrating supported membrane solvent extraction in accordance with one embodiment is presented in Figure 4.
• the method can include the following steps: a) recovering mixed rare earth element oxides from scrap permanent magnets or other electronic waste (50), b) pre impregnating the pores of the plurality of permeable hollow fibers with an organic phase including an extractant and an organic solvent (52), c) applying a continuous flow rate of an acidic aqueous feed solution including dissolved rare earth element oxides along the lumen side or the shell side of the plurality of permeable hollow fibers (54), d) applying a continuous flow rate of an acidic strip solution along the other of the lumen side or the shell side of the plurality of permeable hollow fibers (56), and e) after a predetermined time period, repeating steps c) and d) for a further stage of rare earth element separation using the strip solution from the immediately preceding stage as the feed solution for the subsequent stage (58).
• the steps of applying a feed solution at step c) and applying a strip solution at step d) are simultaneous to provide simultaneous extraction (by the organic phase) and stripping (by
• the step of recovering mixed rare earth element oxides at step a) can be performed in accordance with the method for membrane assisted solvent extraction set forth in U.S. Patent 9,968,887 to Bhave et al, resulting in mixed rare earth element oxides in substantially pure form (e.g., a mixture of substantially 90% by weight, optionally at least 99.5% by weight, of two or more rare earth element oxides).
• Pre-impregnating the pores of the plurality of hollow fibers with an organic phase at step b) can include wetting the pores with an isoparaffinic hydrocarbon solvent and a phosphorous-based chelating extractant, with a ratio by volume of between 3:1 and 1:1, further optionally 2:1, or any other combination.
• Applying a continuous flow rate of an acidic aqueous feed solution along the lumen side or the shell side of the plurality of permeable fibers at step c) can include providing an acidic aqueous feed solution including dissolved rare earth elements from post-consumer products, end-of-life products, and other sources of rare earth elements.
• the acidic aqueous feed solution can include HNO3, HC1, or H2SO4 or other mineral acids for example, at the desired molar concentration.
• Applying a continuous flow rate of an acidic strip solution at step d) can include HNO3, HC1, or H2SO4, for example, at a higher molar concentration than in the feed solution. Repeating steps c) and d) is performed after a given time period has elapsed for each separation stage, in which the strip solution for the preceding stage is diluted to increase the pH for use as a feed solution in the subsequent stage.
• An aqueous feed solution was prepared by dissolving REOs previously recovered from scrap magnets in a 0.02 M nitric acid solution.
• the pH of the feed solution 1000 mL was maintained at 1.5 to 2.0.
• the organic phase included Cyanex 572 (33 v/v%) and Isopar L (67 v/v%).
• the organic phase was loaded into the fiber membrane pores through the bottom of the lumen side of the module.
• a volume of 1000 mL of 3.0 M nitric acid was used as a strip solution.
• the feed solution and the strip solution were continuously recirculated through the bottom of the module along the shell and lumen side of the module, respectively.
• the feed and strip flow rates were about 250 mL/min and 70 mL/min, respectively.
• Second stage separation was conducted for 10 hours.
• Third stage separation the pH of the strip solution of the second stage was adjusted to 1.5 by adding ammonium hydroxide and used as the feed for the third stage.
• Third stage separation was conducted for 10 hours. After completing the recovery of Dy from the feed solution, the third stage strip solution was treated with oxalic acid to precipitate the Dy. The Dy was washed with deionized water and dried at ambient temperature overnight. The Dy was annealed at 860°C for 10 hours with a ramp up of 3°C/min to obtain Dy2(3 ⁇ 4.
• the initial feed solution contained 27,000 ppm of Nd, 8,200 ppm of Pr and
• Figures 5A-5F depict the first stage composition of the (A) feed solution (B) strip solution, (C) purity (%) of Dy in the feed solution and the strip solution, (D) Dy separation factor, (E) REE recovery, and (F) REE recovery rates.
• Figures 6A-6F depict the second stage composition of the (A) feed solution (B) strip solution, (C) purity (%) of Dy in the feed solution and the strip solution, (D) Dy separation factor, (E) REE recovery, and (F) REE recovery rates.
• Figures 7A-7F depict the third stage composition of the (A) feed solution (B) strip solution, (C) purity (%) of Dy in the feed solution and the strip solution, (D) Dy separation factor, (E) REE recovery, and (F) REE recovery rates.
• Figure 8 shows the phase and purity of the recovered Dy using XRD.
• the XRD pattern of the feed solution prior to first stage separation
• the XRD pattern of the strip solution (after third stage separation) indicated that the recovered product contained only Dy2(3 ⁇ 4 and the characteristic peaks exactly match with the standard Dy2(3 ⁇ 4 reference data.
• Praseodymium and neodymium oxide species from the starting material were not detected in the product obtained from the strip solution after the third stage.
• the separation and recovery of rare earth elements was also found by the inventors to be dependent on the pH of the feed solution.
• the pH of the feed solution reduces over time due to the hydrogen ion transfer from the strip solution to the feed solution while metal ions are transferred from the feed solution to the strip solution.
• the pH of the feed solution can be maintained between 1.0 and 1.5 by adding ammonium hydroxide solution every three hours, for example. The foregoing pH adjustment was found to lead to a higher recovery of Dy and a higher Dy extraction rate without significantly impacting purity.
• Dy was directly recovered from scrap permanent magnets without intermediate steps (precipitation, annealing, and redissolution in acid) that would otherwise follow from the extraction of mixed REEs from scrap magnets.
• the strip solution (“REE in Strip”) (using a neutral or cationic extractant such as TODGA or Cyanex) was directly applied to the feed solution for separating Dy from Nd and Pr.
• Dy separation was conducted from a solution of Nd of 38,753 ppm, Pr of 11,540 ppm, and Dy of 4,932 ppm, recovered from mixed scrap permanent magnet feedstocks.
• the feed solution (9 wt.
• % of Dy included 1000 mL, 0.02 M HNO3 and the strip solution included 1000 mL, 3.0 M HNO3.
• the recovery, purity, and extraction rate of Dy were 97%, 29.8 wt. %, and 0.31 g/m 2 /hr, respectively, for the first stage. Additional stages of separation can be performed to obtain 100% Dy as shown in Example 1.
• the purity of the Nd Pr remained in the feed solution was 99.6 wt.%.

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