Method for recovering permanent magnets and valuable metals from hard disks

Abstract

The invention relates to a method for recovering NdFeB-type permanent magnets from waste electrical and electronic equipment, comprising the following successive steps: - subjecting demagnetised permanent magnets to a first magnetic separation in a 400 G drum; - recovering a first magnetic phase (1FM); - subjecting the first magnetic phase (1FM) to a first magnetic separation on an overband separator, so that a second non-magnetic phase (2FNM) resulting from the first overband magnetic separation is enriched with demagnetised magnets; and - recovering the second non-magnetic phase (2FNM).

Description

Process for recovering permanent magnets and valuable metals from hard drives

[0001] 1 – Technical field of the invention

[0002] The invention relates to a method for recovering permanent magnets of the NdFeB type from waste electrical and electronic equipment (WEEE), and in particular hard drives from WEEE. The invention also relates to a method for extracting metals such as rare earths, aluminum, copper, gold, silver, platinum and palladium, from WEEE.

[0003] 2 - State of the art

[0004] The growing use of rare earths (REs) in many recent technological innovations has led to a sharp increase in their demand. Green technologies, which help reduce environmental impacts due to their reduced energy consumption and are particularly fond of these elements, contribute significantly to this sustainable demand. In this context, Europe has placed recycling, in its "Raw Materials" strategy, as one of the main pillars for securing part of its supplies of strategic metals, including rare earths. Rare earth recycling operations on an industrial scale remain relatively few in number, although they offer many advantages compared to the exploitation of primary resources:

[0005] - Europe is one of the largest regions for rare earth consumption through its high value-added industries. It has also accumulated consumer goods over decades which, when they reach the end of their life, constitute secondary resources from which rare earths can be extracted.

[0006] - European and French dependence on resources from foreign countries could be reduced through the recycling of post-consumer waste.

[0007] - The processing of secondary resources for the production of rare earths would not entail health and environmental risks, whereas the exploitation of primary deposits presents such risks, linked to the presence of radionuclides in the primary deposits.

[0008] - The production of metallic resources by exploitation of secondary resources is most often done with energy consumption much lower than that observed for the exploitation of primary resources.

[0009] Furthermore, the production volume of Neodymium has increased dramatically since the development of powerful magnets (Nd–Fe–B) in 1980. This development has significantly improved the performance of small motors and reduced the size and weight of portable electronic devices. For example, most mobile phones use miniaturized motors built on the basis of small Nd-based magnets for their vibration functions. These magnets are also very widely used in computer hard drives where they constitute the motor that ensures the positioning of the read / write heads. They significantly improve the performance of this storage device and contribute to the reduction in size of computers. The technological revolution in developed countries has led to supply deficits and tensions that have resulted in soaring prices since January 2010.

[0010] However, the recycling of permanent magnets contained in WEEE categories comes up against numerous obstacles such as those mentioned below.

[0011] - The WEEE deposit is heterogeneous and it is difficult to obtain representative samples.

[0012] - Rare earths are dispersed in the WEEE deposit.

[0013] - The rare earth content of the flow of small mixed devices (SMD) and central units is unknown.

[0014] - The magnetic property of permanent magnets constitutes a technical obstacle during recycling operations; in fact, these magnets “stick” in crushing and sorting equipment.

[0015] - The WEEE entering the process is general waste, at the base of the process, and its nature is therefore variable.

[0016] - The efficiency of unit operations for crushing and sorting from complex matrices is questioned. For example, a hard drive is made up of 80% aluminum, 7% electronic circuit board, 8% scrap metal, 1% plastics, 3% magnets and 1% other metals.

[0017] - The separation of rare earths from the metals constituting the coatings of the magnets in the fraction below 80 µm obtained after grinding is difficult.

[0018] However, in Japan, rare earths from permanent magnets are already being recycled. Recycling is mainly carried out through extractive metallurgy.

[0019] In France, current discussions focus on the recycling of magnets contained in wind turbines and hybrid or all-electric vehicles.

[0020] WO2017 / 079183 also proposes a method for recycling magnets containing rare earths from manufactured articles. This method involves aligning the manufactured articles in a predetermined orientation, then separating the magnets from the manufactured articles, and then heating to demagnetize, or demagnetize, the magnets. Finally, the demagnetized magnets are separated from the residual parts of the manufactured articles. This method therefore requires a special installation, particularly for aligning the articles. It is a long and economically cumbersome process, with a low yield.

[0021] The Fraunhofer Institute has developed a process for recycling magnets from electric motors and generators by melting the magnets in an induction furnace at 1000°C. One drawback of this type of melting process is the high energy consumption, which leads to high costs. In addition, the efficiency of this process needs to be improved, and the quality of the resulting product also needs to be improved.

[0022] Finally, it has also been proposed to recover hard drive magnets through mechanical sorting. In WEEE devices, such as hard drives, which consist of a complex matrix including a lot of aluminum, electronic cards, scrap metal, magnets, plastics, and other metals, only mechanical sorting currently allows the magnets to be separated from other components. Magnets demagnetized by heat treatment are recovered using fragmentation, classification, and magnetic separation. In this process, a magnet-rich fraction is recovered from the magnetic fraction. Thus, in this process, the magnets are recovered with other magnetic objects, such as scrap metal. To purify the magnets, they must then be separated from these other magnetic objects. The efficiency of this process is therefore not optimal.Thus, in document JP5797603, the hard disk is subjected to manual mechanical sorting, which allows the motor containing the magnet to be separated from other components such as the hard disk casing, then the demagnetized motor is subjected to magnetic separations to recover the magnet.

[0023] Description of the invention

[0024] The invention aims in particular to propose an alternative method for recovering permanent magnets, which does not have all or part of these drawbacks.

[0025] To this end, the invention relates to a method for recovering permanent magnets of the NdFeB type from waste electrical and electronic equipment. The method comprises the following successive steps: - subjecting demagnetized permanent magnets to a first 400 G drum magnetic separation, - recovering a first magnetic phase, - subjecting the first magnetic phase to a first magnetic separation on an Overband separator, so that a second non-magnetic phase resulting from the first Overband magnetic separation is enriched in demagnetized magnets, - recovering the second non-magnetic phase.

[0026] Due in particular to their iron alloy content, demagnetized permanent magnets, when subjected to magnetic separation, are drawn into the magnetic fraction. Surprisingly, the inventors have developed a method for separating, by magnetic separation, the demagnetized magnets from the rest of the magnetic fraction, which includes, for example, scrap metal. There is therefore no need for an additional step to separate the magnets from the scrap metal. The method according to the invention has an improved yield. Furthermore, when the recovered magnets are used to obtain rare earths, it is particularly advantageous to limit the presence of iron because this will then have to be separated from the rare earths.

[0027] Overband magnetic separators are traditionally used in waste treatment systems. For example, in document FR2962924, an Overband separator ensures the extraction of ferrous residues dissociated from other materials during a previous crushing. The Overband comprises a fixed magnetic system around which a discharge belt rotates. It is placed above or below a conveyor and allows magnetic particles to be drawn off the conveyor and non-magnetic particles to pass through. The Overband magnetic field intensity is typically between 380 and 400 G.

[0028] The invention avoids a long and expensive step of manual mechanical sorting to separate the magnets from other components of these devices, such as aluminum, electronic cards, scrap metal, plastics and various metals.

[0029] The iron contained in the device can be in the form of an alloy such as cast iron or steel.

[0030] The particle fraction up to 16 mm and larger than 5 mm is preferably richer in magnets than the other fractions. Thus, this fraction is enriched in magnets and it is this magnet-rich fraction that is subjected to the first 400 G drum magnetic separation.

[0031] After each magnetic separation, the term "magnetic phase" refers to the fraction that has been retained by the separator, and the term "non-magnetic phase" refers to the fraction that has not been retained by the magnetic separator.

[0032] To obtain demagnetized magnets, WEEE is first heated, preferably to between 325°C and 450°C, i.e., above its Curie temperature. For example, one ton of hard drives is treated for at least 2 hours in a furnace. The WEEE is then shredded, preferably in an autogenous shredder.

[0033] Depending on other optional features of the magnet recovery process, taken alone or in combination:

[0034] - The Overband separator comprises a fixed magnetic system placed above or below a conveyor to convey the demagnetized magnets, and the magnetic system is located at a distance ranging from 7 to 15 cm, preferably from 8 to 10 cm, more preferably about 9 cm. At this distance, the demagnetized magnets are driven into the non-magnetic fraction. To move the magnets into the non-magnetic fraction, one could have thought, for example, of varying the intensity of the magnetic field. Intervention at the distance level makes it possible to move the demagnetized magnets into the non-magnetic fraction in a simple and effective way.

[0035] - Demagnetized magnets are obtained by grinding and then selecting the fraction of particles whose size goes up to 16 mm. By selecting these particle sizes, the magnets are concentrated because it is visually identified that the majority of the magnets are found in this fraction.

[0036] - Particles larger than 5 mm are selected. In fact, the fraction of particles smaller than 5 mm is poorly suited to magnetic separation and the passage of these particles smaller than 5 mm through magnetic separators risks polluting the phases obtained at the end of the separations, as these small particles do not necessarily have the expected behavior. Furthermore, the fraction smaller than 5 mm does not contain many magnets.

[0037] - Permanent magnets are recovered from hard drives from waste electrical and electronic equipment. Among this waste, hard drives systematically contain permanent magnets. This concentrates the permanent magnets on which the recovery process will be implemented.

[0038] - The method further comprises at least one of the following successive steps:. recovery of a first non-magnetic phase at the end of the first 400 G drum magnetic separation,. second 400 G drum magnetic separation of the first non-magnetic phase, to obtain a third magnetic phase,. second Overband magnetic separation of the third magnetic phase, and. recovery of a fourth non-magnetic phase. Advantageously, these additional steps are combined together and make it possible to recover magnets which had not passed into the magnetic phase at the end of the first 400 G drum magnetic separation.

[0039] - The process also includes a preliminary step of demagnetization by heating the waste electrical and electronic equipment to between 325°C and 450°C. For example, one ton of hard drives is heated to between 325°C and 450°C for 2 hours in an induction furnace.

[0040] - The process also includes a preliminary step of releasing the demagnetized magnets by crushing. For example, 50 kg of hard disks are subjected to crushing for 45 minutes in an autogenous crusher, at a rotation speed of 25 rpm. In the autogenous crusher, the crushing is solely or mainly due to the impacts between the blocks of material introduced into the crusher. The autogenous crusher allows the opening and disassembly of WEEE waste. The autogenous crusher is, for example, supplied by KM Key Machinery GmbH in Sulzberg, Germany.

[0041] The invention also relates to the products obtained directly from the magnet recovery process according to the invention and their subsequent use, particularly in the field of electronics.

[0042] The invention also relates to a method for extracting metals such as rare earths, aluminum, copper, gold, silver, platinum and palladium, from permanent magnets of the NdFeB type of waste electrical and electronic equipment, incorporating a method for recovering magnets as described above.

[0043] The invention also relates to the products obtained directly from the rare earth extraction process according to the invention and their subsequent use, particularly in the field of electronics.

[0044] The invention also relates to a method for manufacturing permanent magnets from NdFeB type permanent magnets from waste electrical and electronic equipment, incorporating a method for recovering magnets as described above.

[0045] The invention also relates to the products obtained directly from the process for manufacturing magnets according to the invention and their subsequent use, particularly in the field of electronics. Brief description of the figures

[0046] The invention will be better understood on reading the following description, given solely by way of example and with reference to the appended drawings in which:

[0047] schematizes a metal recovery process, including the steps of the permanent magnet recovery process according to the invention;

[0048] is a photograph of the fraction greater than 40 mm obtained after the classification step of a magnet recovery method according to the invention;

[0049] is a photograph of the 20 to 40 mm fraction obtained after the classification step of a magnet recovery method according to the invention;

[0050] is a photograph of the fraction less than 5 mm obtained after the classification step of a magnet recovery method according to the invention;

[0051] is a photograph of the 5 to 16 mm fraction obtained after the classification step of a magnet recovery method according to the invention;

[0052] is a photograph of the fraction obtained in step 9 of a method for recovering magnets according to the invention. Detailed description

[0053] The diagram shows a process for recovering metals, including rare earth extraction. This process includes the steps of the permanent magnet recovery process according to the invention (steps 1 to 10 of the schematic process). In the process according to the invention, the magnets are recovered from WEEE waste. In the example described below, the permanent magnets are more specifically recovered from hard drives from WEEE.

[0054] Example 1

[0055] In the first stages 1 and 2, the magnets are recovered from the hard drives and demagnetized. They are then released by crushing in stage 3. The rare earths contained in the magnets are then selectively recovered hydrometallurgically in stages 9 and 10. The other metals separated from the magnets are shredded and recovered by extractive metallurgy in stages 11 to 15.

[0056] In step 1, a batch of used hard drives collected from a manufacturer's site was collected. In a well-known manner, manufacturers collect used hard drives using two techniques, namely manual dismantling and mechanical dismantling of small mixed devices (SMD) using a rotating drum with lifters to release the computer components.

[0057] In step 2, a ton of hard drives were then heated to between 325°C and 450°C (Curie temperature) to demagnetize the magnets, also known as demagnetization. Specifically, the magnets were heated to 350°C for 2 hours in an induction furnace.

[0058] In stage 3, approximately 415 kg of hard disks from stage 2 were introduced into an autogenous mill to free the magnets from the hard disks. The hard disks were grouped in batches of 50 kg. Each batch was placed in the autogenous mill for 45 minutes at a rotation speed of 25 rpm.

[0059] In step 4, the ground material from step 3 was classified by sieving into different particle size classes: size greater than 40 mm, 20 to 40 mm, 16 to 20 mm, 5 to 16 mm and size less than 5 mm. The particle size fraction less than 40 mm was sieved at 5, 16 and 20 mm. The fractions of size less than 5 mm, 5 to 16 mm, 16 to 20 mm and size greater than 20 mm represented 14.2%, 19.9%, 8.2% and 57.7% by weight respectively.

[0060] Figures 2, 3, 4 and 5 show photographs of the size fraction greater than 40 mm, the fraction from 20 to 40 mm, the fraction less than 5 mm and the fraction from 5 to 16 mm respectively.

[0061] It is visually identified that the magnets are more present in the two fractions 5 - 16 mm and smaller than 5 mm. Thus the classification allows to concentrate the permanent magnets to be recovered.

[0062] Permanent magnets from hard drives recovered after the classification step were subjected to qualitative chemical analysis by scanning electron microscopy – energy dispersive spectroscopy (SEM EDS). In scanning electron microscopy, the magnets have a granular structure. They consist of Nd2Fe phase crystals 14 B sintered in the presence of an intergranular phase. The analysis was carried out on the crystals.

[0063] The following table shows the distribution of the chemical elements detected.

[0064] element% by massNd2Fe 14 Theoretical BNd28,127,0Fe69,672,0Dy2,31,0

[0065] Thus in Nd2Fe phase crystals 14In sintered B, Fe is predominant and Nd is well represented. In the intergranular phase, the emission lines of Nd and Pr are particularly identified. Thus, the magnets contain an alloy of Nd / Fe / B as a matrix and other rare earths such as Dy and Pr in the form of oxides are present in the interfaces.

[0066] Steps 5 to 8 of the process were carried out using the 5 - 16 mm fraction from classification step 4.

[0067] In step 5, about 80 kg of the 5-16 mm fraction was subjected to low-intensity permanent magnet dry drum magnetic separation (400G), to separate magnetic and non-magnetic products. Visual analysis showed that the obtained 1FM magnetic fraction was rich in magnets.

[0068] In step 6, the magnetic fraction 1FM from step 5 was treated by an Overband magnetic separator. In this step 6, the Overband magnetic separator was spaced 8 to 10 cm from the conveyor belt. Under these conditions, the non-magnetic fraction 2FNM from the Overband separation step 6 was rich in magnets.

[0069] Thus the exemplified recovery process comprises the following successive steps:- subjecting the demagnetized permanent magnets to a 400 G drum magnetic separation,- recovering a 1FM magnetic phase,- subjecting the 1FM magnetic phase to a magnetic separation on an Overband separator, so that a non-magnetic 2FNM phase resulting from the Overband magnetic separation is enriched in demagnetized magnets.

[0070] The non-magnetic fraction 2FNM from step 6, enriched with magnets, was then subjected to steps 9 and 10 which will be described later. Alternatively, the non-magnetic fraction 2FNM is used to manufacture permanent magnets. Indeed, the non-magnetic fraction can follow a "long loop", i.e. a hydrometallurgical treatment to extract rare earths, then possibly manufacture permanent magnets from these rare earths. It can also follow a "short loop", i.e. the non-magnetic phase is used to form magnets again, without going through rare earth recovery steps by a hydrometallurgical process. In the short loop, the magnetic phase is for example reduced to powder, and magnets are again manufactured from this powder. The short loop generally involves a supplementation of materials.

[0071] The 2FM magnetic fraction from step 6 was then subjected to step 15 which will be described later.

[0072] In step 7, the non-magnetic fraction 1FNM from step 5 was subjected to a second magnetic separation under the same conditions as in step 5.

[0073] At the end of step 7, during step 8, the magnetic fraction 3FM was subjected to magnetic separation under the same conditions as in step 6. The non-magnetic fraction 3FNM from step 7 was then subjected to step 15.

[0074] At the end of step 8, the magnetic 4FM and non-magnetic 4NFM fractions were treated respectively as the 2FM and 2FNM fractions at the output of step 6.

[0075] Thus, the method further comprises the following successive steps: recovery of a first non-magnetic phase 1FNM at the end of the first 400 G drum magnetic separation, second 400 G drum magnetic separation of the first non-magnetic phase 1FNM, to obtain a third 3FM magnetic phase, second Overband magnetic separation of the third 3FM magnetic phase, and recovery of a fourth non-magnetic phase 4FNM. These additional steps make it possible to recover magnets that had not passed into the 1FM magnetic phase at the end of the first 400 G drum magnetic separation.

[0076] In total, approximately 32 kg of the magnet-rich fraction (2FNM and 4FNM phases) representing 7.7% by weight of the hard disks subjected to the process were obtained.

[0077] During steps 9 and 10, the magnet-rich fractions, respectively 2FNM from step 6, and 4FNM from step 8, are ground (step 9), as is the fraction less than 5mm (), and are leached to selectively recover the rare earths during step 10, according to the method described in the applicant's document WO 2017207947.

[0078]

[0079] Thus, rare earths were extracted from NdFeB permanent magnets from waste electrical and electronic equipment, using the magnet recovery process described above.

[0080] Alternatively, permanent magnets are manufactured from NdFeB permanent magnets from waste electrical and electronic equipment, using the magnet recovery process described above.

[0081] Steps 11 to 15 list the steps implemented, following step 4 (classification), on fractions larger than 40 mm, 20 to 40 mm, 16 to 20 mm, and on magnetic fractions 2FM and 4FM, to recover other metals contained in hard disks.

[0082] Fractions larger than 40 mm, 20 to 40 mm and 16 to 20 mm are sorted by unit operations used in mineral processing: physical sorting techniques (Overband magnetic separation to recover scrap metal, eddy current separation to recover aluminum and electronic cards during step 11). Metallic iron is recovered by magnetic separation and recycled in electric steelworks. CE electronic cards are recovered by optical sorting or by the eddy current separator, and shredded (step 12). The recovered electronic cards are injected into the copper metallurgy furnaces to recover copper and precious metals (step 15). Aluminum and copper wires are recovered by the eddy current separator or by the gravimetric separator. The various metals contained are selectively recovered by extractive metallurgy (step 15).The recovered metals are sent to the smelters.

[0083] The mixed fraction from step 11 is shredded (step 13) to release the various metals and magnets contained.

[0084] The residual magnets are shredded and ground to 80 µm. SEM analyses show that the pulverized product is concentrated in rare earths (27% Nd, 5% Dy and 3% Pr). These rare earths are selectively recovered by conventional hydrometallurgical techniques. As shown in the, the residual magnets can be treated by steps 9 and 10 of the process.

[0085] The mixture (plastics, metals and ceramics) is shredded to release the different compounds, and treated by pyrolysis to remove the resins and concentrate the metals (base and precious) which will be recovered selectively by hydrometallurgical means.

[0086] The aluminum and scrap metal recovered from step 11 are sent to non-ferrous metallurgy and the steel industry respectively.

[0087] The invention is not limited to the embodiments presented and other embodiments will become apparent to those skilled in the art.

Claims

Method for recovering permanent magnets of the NdFeB type from devices made of more than 50% aluminum, comprising one or more electronic cards, iron and plastic, and at least one permanent magnet, the devices being derived from waste electrical and electronic equipment, comprising the following successive steps: - obtaining demagnetized permanent magnets by demagnetizing the devices and crushing then selecting the fraction of particles whose size is up to 16 mm and is greater than 5 mm, - subjecting the demagnetized permanent magnets to a first magnetic separation with a 400 G drum, - recovering a first magnetic phase (1FM), - subjecting the first magnetic phase (1FM) to a first magnetic separation on an Overband separator, so that a second non-magnetic phase (2FNM) resulting from the first Overband magnetic separation is enriched in demagnetized magnets, - recovering the second non-magnetic phase (2FNM). A method of recovering permanent magnets according to the preceding claim, wherein the Overband separator comprises a fixed magnetic system placed above or below a conveyor for conveying the demagnetized magnets, and the magnetic system is located at a distance ranging from 7 to 15 cm, preferably from 8 to 10 cm, more preferably about 9 cm. A method of recovering permanent magnets according to the preceding claim, wherein the magnetic field intensity of the Overband separator ranges from 380 to 400 G. A method of recovering permanent magnets according to any preceding claim, wherein the devices comprise more than 60% aluminum, preferably more than 80% aluminum, and are preferably hard disk drives. A method of recovering permanent magnets according to any one of the preceding claims, further comprising the following successive steps:- recovery of a first non-magnetic phase (1FNM) at the end of the first 400 G drum magnetic separation,- second 400 G drum magnetic separation of the first non-magnetic phase (1FNM), to obtain a third magnetic phase (3FM),- second Overband magnetic separation of the third magnetic phase (3FM), and- recovery of a fourth non-magnetic phase (4FNM). A method of recovering permanent magnets according to any preceding claim, wherein the apparatuses are demagnetized by heating to between 325°C and 450°C. A method of recovering permanent magnets according to any preceding claim, wherein the grinding of the demagnetized magnets is carried out in an autogenous mill. A method of recovering permanent magnets according to any one of the preceding claims, wherein the selection of the fraction of particles up to 16 mm and greater than 5 mm in size is carried out by classifying, preferably by sieving, into a particle size class ranging from 16 to 20 mm, a class ranging from 5 to 16 mm, a class whose size is less than 5 mm, a class whose size is greater than 40 mm and into a class ranging from 20 to 40 mm.

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