Magnet recycling

Abstract

The present invention discloses a method for recovering rare earth particulate material from an assembly comprising a rare earth magnet and comprises the steps of exposing the assembly to hydrogen gas to effect hydrogen decrepitation of the rare earth magnet to produce a rare earth particulate material, and separating the rare earth particulate material from the rest of the assembly. The invention also resides in an apparatus for separating rare earth particulate material from an assembly comprising a rare earth magnet. The apparatus comprises a reaction vessel having an opening which can be closed to form a gas-tight seal, a separator for separating the rare earth particulate material from the assembly, and a collector for collecting the rare earth particulate material. The reaction vessel is connected to a vacuum pump and a gas control system, and the gas control system controls the supply of hydrogen gas to the reaction vessel.

Claims

1. A method for recovering rare earth particulate material from an assembly comprising a rare earth magnet having a coating, the method comprising the steps of: exposing the assembly to hydrogen gas to effect hydrogen decrepitation of the rare earth magnet whereby a rare earth particulate material and coating particles are produced, separating the rare earth particulate material and the coating particles from the rest of the assembly, reducing the particle size of the rare earth particulate material to produce a rare earth powder without substantially changing the particle size of the coating particles, and separating the rare earth powder from the coating particles by passing the rare earth powder through at least one screen.

2. The method according to claim 1, wherein the rare earth particulate material and coating particles resulting from the decrepitation process are separated from the remaining assembly components by shaking, vibration, sieving, tumbling or using centrifugal forces.

3. The method of claim 1, wherein the rare earth magnet is Sm.sub.2Co.sub.17, and the decrepitation process is carried out at a temperature of at least 70 C. and/or a pressure of at least 7 bar.

4. The method of claim 1, wherein the method is for recovering NdFeB or SmCo.sub.5 particulate material from an assembly comprising an NdFeB and/or a SmCo.sub.5 magnet and a Sm.sub.2Co.sub.17 magnet, the method comprising the steps of: exposing the assembly to hydrogen gas at a temperature and pressure sufficient to effect hydrogen decrepitation of the NdFeB and/or the SmCo.sub.5 magnet only, whereby NdFeB and/or SmCo.sub.5 particulate material is produced, and separating the NdFeB and/or SmCo.sub.5 particulate material from the rest of the assembly.

5. The method of claim 1, wherein the decrepitation process is carried out at a temperature of at least 100 C. and/or a pressure of at least 5 bar.

6. The method of claim 1, further comprising damaging the coating prior to the decrepitation process.

7. The method of claim 1, wherein the particle size of the rare earth particulate material is reduced by milling, mechanical agitation, air pressure, centrifugal forces or ultrasound.

Description

(1) The invention will now be described by way of example with reference to the accompanying figures in which:

(2) FIG. 1 is a schematic diagram of apparatus according to an embodiment of the present invention.

(3) FIG. 2a shows a roughly shredded computer hard drive prior to being processed by the method of the present invention;

(4) FIG. 2b shows a voice coil assembly manually removed from a computer hard drive, prior to being processed by the method of the present invention;

(5) FIG. 2c shows a hard drive assembly that has been cut open and then subjected to hydrogen decrepitation to remove the rare earth magnets, in accordance with an embodiment of the present invention;

(6) FIG. 3 shows rare earth particulate material obtained by the method of the present invention.

(7) FIG. 4a is an electron micrograph of a flake of a nickel-copper-nickel coating that has been separated from a NdFeB magnet by decrepitation; and

(8) FIG. 4b is an electron micrograph of a flake of a nickel coating that has been separated from a NdFeB magnet by decrepitation.

(9) FIG. 5 is a schematic diagram of apparatus suitable for carrying out an embodiment of the method of the second aspect of the present invention.

(10) FIG. 6 is a schematic of apparatus suitable for carrying out hydrogen decrepitation of magnets and/or assemblies and separation of coating particles from the rare earth particulate material resulting from the decrepitation process.

(11) FIG. 1 shows apparatus according to an embodiment of the present invention, which is used to recover rare earth magnets from assemblies using hydrogen decrepitation.

(12) The apparatus 10 comprises a reaction vessel 12 which houses a porous container 14 positioned above a heater 16. The reaction vessel 12 is open at its top end 18 so that scrap assemblies can be loaded into the vessel 12. The reaction vessel 12 can be closed by a lid 20 which is secured by a fastener 22, to give a gas tight seal between the vessel top 18 and the lid 20.

(13) The reaction vessel 12 is situated above a collection vessel 24 which is used to collect the rare earth particulate material produced by the decrepitation process. A valve 26 is used to control the flow of particulate material from the reaction vessel 12 to the collection vessel 24.

(14) The reaction vessel 12 is connected to a rotary vacuum pump 28 via tubing 30. The flow of gas through the tubing 30 is controlled by a valve 32.

(15) The reaction vessel 12 is also connected to gas supply sources 33, 34 through a gas control system 36 via a gas line 38. The gas control system 36 monitors the pressure in the reaction vessel 12 and maintains it at the desired level. A gas line valve 40 and a pressure transducer 42 are situated on the gas line 38 to allow monitoring and control of the gas flow to the reaction vessel 12.

(16) Thermocouples 44 are provided to monitor the temperature inside the reaction vessel 12.

(17) In use, scrap assemblies containing rare earth magnets are comminuted by a shredder or cut open by a cropper (not shown) and manually transferred into the porous container 14. In other embodiments (not shown), the shredded or cropped assemblies 46 are passed along a conveyor to the porous container 14. Depending on the nature and size of the assembly the whole assembly may be subject to hydrogen decrepitation or, alternatively, the assembly may be partially dismantled for processing only a part thereof. For example, the assemblies 46 comprise shredded or cropped computer hard drives and voice coil assemblies, like the ones shown in FIGS. 2a, 2 and 2c. The lid 20 of the reaction vessel 12 is closed and secured by the fastener 22 so that the reaction vessel 12 is gas tight. The reaction vessel 12 is then evacuated through the tubing 30 (through open valve 32) using the rotary vacuum pump 28 to a pressure of 10.sup.2 mbar, as indicated by the pressure transducer 42. The valve 32 is closed and the reaction vessel 12 is backfilled with argon from gas supply source 33 to a pressure of 1 bar, through gas control system 36 and open valve 40 in gas line 36. The gas line valve 40 is then closed and the valve 32 is opened to allow the vacuum pump 28 to evacuate the reaction vessel 12 to a pressure of 10.sup.2 mbar. Valve 32 is then closed and the reaction vessel 12 is backfilled with hydrogen from supply source 34 to a pressure of between 1 and 7 bars. The pressure in the reaction vessel is maintained by the gas control system 36.

(18) The decrepitation process starts once the hydrogen enters the reaction vessel 12 and accesses the assemblies 46, turning the rare earth magnets into a particulate material 48. The assemblies are exposed to the hydrogen gas for 2 to 5 hours.

(19) The porous container 14 is agitated by a vibrator (not shown) during or after the decrepitation process to move the decrepitated magnet particles from the scrap assembly material and through the holes of the porous container 14 so that they collect in the bottom of the reaction vessel 12. Valve 26 is opened to allow the particles to fall from the reaction vessel 12 into the collection vessel 24.

(20) If degassing of the particles is required, the valve 26 is left closed and vibration is not applied. The decrepitated scrap assembly material (including the rare earth particulate material) is heated by the heater 16 to a temperature of 750 C., which is monitored using thermocouples 44 and controlled using a temperature controller (not shown). Degassing is carried out at a pressure of below 1 Bar, ideally under a vacuum of 10.sup.2 Bar The hydrogen removed from the rare earth particulate material can either be pumped into the atmosphere or it can be captured by a metal hydride store 50.

(21) The processing vessel can decrepitate a scrap charge of approximately 300 to 400 shredded/chopped hard disk drives or 1000 to 2000 voice coil assemblies. Processing 400 shredded hard drives results in the recovery of approximately 8 kg of NdFeB particulate material. Processing of 2000 voice coil assemblies results in the recovery of approximately 40 kg of NdFeB particulate material.

(22) FIG. 3 shows a sample of rare earth particulate material produced by the method of the present invention. The sample contains particles 50 with areas of nickel plating 51 present.

(23) Rare earth particulate material recovered from assemblies by the methods of the invention may be further processed, for example by jet milling, and used in a variety of applications. For example, the material is suitable for use in the following processes:

(24) 1. The recycled particles can be put into a refining process, such as fused salt electrolysis, to separate the rare earths from the other components such as iron and boron.

(25) 2. The particles can be jet milled (optional), pressed and then sintered into new magnets.

(26) 3. The particles can be re-melted and melt spun to produce material for bonded magnets.

(27) 4. The particles may be heated in hydrogen and then degassed to produce fine grained material for bonded magnets by mixing with an appropriate bonding agent.

(28) 5. Degassed particles may be directly mixed with a bonding agent such as epoxy and then pressed to make cheap bonded magnets.

(29) If the magnets of the assemblies have a relatively low rare earth content to start with (e.g. near stoichiometric Nd.sub.2Fe.sub.14B), it may be necessary to add extra rare earth to the decrepitated particulate material prior to forming new magnets in order to compensate for rare earth lost to oxidation. During recycling the oxygen content of the rare earth material tends to rise and rare earth oxides form. A certain amount of clean, metallic rare earth rich phase is essential for sintering to full density, giving better magnetic properties and corrosion resistance. The increased oxygen content can make the material more difficult to sinter into new magnets and give a lower density product, hence the addition of small amounts of Nd or NdH.sub.2 to the particulate material. Typically an addition of 1-2 at % has been shown to give the best magnetic properties. If the Nd content of the magnets is sufficiently high to begin with then extra Nd may not be required as a smaller overall percentage of the neodymium will oxidise during processing.

(30) Table 1 shows the properties of recycled magnets made from rare earth particulate material produced by the process of the invention, compared to an intact rare earth NdFeB magnet as received, i.e. prior to decrepitation. The as received magnet had a composition of Nd.sub.13.4Dy.sub.0.8Al.sub.0.7Nb.sub.0.3Fe.sub.78.5B.sub.6.3 (at % from ICP). Recycled sintered magnets were made using decrepitated particulate material with no Nd addition and with additions of 1%, 2% and 4% Nd.

(31) TABLE-US-00001 TABLE 1 Density % Br Hcj Bhmax (gcm.sup.3) porosity (mT) (kAm.sup.1) (kJm.sup.3) Intact magnet 7.58 0 1380 860 340 No Nd addition 6.8 10.3 1080 460 195 1at % Nd 7.29 3.8 1060 890 200 2at % Nd 7.48 1.3 1160 925 250 4at % Nd 7.49 1.2 930 1025 155

(32) It was observed that the recycled magnet made with an addition of 2% Nd had the best properties including highest coercivity (Hcj) and highest remanence (Br).

(33) FIGS. 4a and 4b show rare earth particulate material 54 resulting from hydrogen decrepitation of rare earth magnets, which contains flakes of NiCuNi coating 52 or Ni coating 51.

(34) FIG. 5 shows a schematic diagram of a stack of screening sieves which were used for separating rare earth particulate material from coating particles in accordance with an embodiment of the method of the second aspect of the present invention.

(35) Decrepitated NdFeB powder produced from the decrepitation of hard drive units in accordance with the method of GB1020383.4 was collected from the discharge valve at the bottom of the decrepitation vessel. The decrepitated powder comprised a mixture of NdFeB particles and 10% by weight Ni particles, the Ni particles being the debris left from the Ni coating on the NdFeB magnets.

(36) Apparatus 60 comprising stack of screening sieves 62a-e was assembled over a collection tray 63 as shown in FIG. 5. The size of the mesh of the sieves decreased from the top to the bottom of the stack. Screens having the following mesh numbers were used: Sieve 62a: mesh number 10 (2000 m); sieve 62b: mesh number 18 (1000 m); sieve 62c: mesh number 60 (250 m); sieve 62d: mesh number 104 (105 m); and sieve 62e: mesh number 325 (46 m). It will be appreciated by the skilled person that fewer or more sieves, or different mesh sizes, can be used.

(37) The decrepitated mixture 64 comprising NdFeB rare earth particles and Ni coating particles was placed on the uppermost sieve 62a and a lid 66 was placed over the top. A sieve shaker (not shown) was used to shake the sieves to encourage the particles to pass through the mesh. A particle size reducer in the form of 5 mm diameter ball bearings 68 was provided on each of the subsequent sieve screens to fragment the friable NdFeB particles.

(38) The Ni coating particles were unable to pass through the 105 m mesh screen of sieve 62d, and coating particles were retained by all of the sieves 62a-62d. The NdFeB rare earth particles were broken down by the shaking action of the sieve shaker and by the ball bearings 68, producing a fine powder 70. This fine powder 70 passed completely through the 105 m screen 62d. The majority of the powder 70 also passed through the 46 m screen 62e into the collection tray 63.

(39) The Ni content of the NdFeB rare earth powder 70 collected from the collection tray 63 and the 46 m screen 62e was found by chemical analysis to be less than 0.03 wt %. The Ni coating particles captured by the 2000 m sieve 62a were found to be associated with oxidised NdFeB particles, thereby reducing the oxygen content of the resulting powder 70.

(40) Due to its low Ni content, the NdFeB fine rare earth powder 70 produced is suitable for compacting and sintering to form new sintered magnets or for use in bonded magnets.

(41) FIG. 6 is a schematic showing a modified apparatus which can be used for both hydrogen decrepitation of magnets/assemblies and separation of coating particles from the rare earth particulate material resulting from the decrepitation process. The decrepitation vessel 72 contains a rotating drum 74 with perforations 76 into which assemblies comprising coated rare earth magnets are loaded. The vessel is closed with a lid 78 and then filled with hydrogen gas (or a mixture of gases comprising hydrogen) through gas lines (not shown) to start the decrepitation process. As the decrepitation process progresses the drum 74, which is mounted on a shaft 80, is rotated by a motor 82. The rotation of the drum 74 causes the rare earth particulate material magnet and coating particles to fall through the perforations 76 onto a screen 84. The screen 84 comprises a series of sieves of decreasing size and a particle size reducer for reducing the particle size of the rare earth particulate material via mechanical agitation, the particle size reducer including a vibrator and ball bearings on the surface of one or more of the sieves. The combination of vibration and the movement of the ball bearings breaks down the rare earth particulate material, allowing the particles to pass through the sieves into a tapered bottom portion 86 of vessel 72. The resulting rare earth powder is released from the tapered bottom portion 86 of vessel 72 by a valve 88 into a storage vessel 90.