Patent Application
20240368790
Provided herein is an apparatus for electrolytic atomic hydrogen decrepitation and methods of use thereof.
Rare earth magnets based upon neodymium-iron-boron (NdFeB) are employed in many clean energy and high-tech applications, including hard disk drives (HDDs), motors in electric vehicles and electric generators in wind turbines. In recent years, the supply of rare earth metals has come under considerable strain. This resulted in dramatic price fluctuations for the rare earth metals, in particular, neodymium, praseodymium and dysprosium, the rare earth constituents of NdFeB magnets. According to the EU Critical Materials list (2010, 2014) and the US Department of Energy's energy critical element list (2010), rare earth metals are classified as at greatest risk of supply shortages compared to those of all other materials used for clean energy technologies.
There are several ways in which these material shortages could be addressed including: (a) opening more rare earth mines, (b) using alternative technologies which do not contain rare earths (c) reducing the amount of rare earth metal used in particular applications such as magnets or (d) recycling the existing stock of magnets containing rare earth metals with various types of equipment. However, with regard to option (a), the mining, beneficiation and separation of rare earth elements is energy intensive, results in toxic by-products from acid leaching processes and the primary ores are nearly always mixed with radioactive elements such as thorium. If alternative technologies are employed, as in option (b) or reduction of rare earth metal quantities as in option (c), compared to permanent magnet machines, this often leads to a drop in efficiency and performance.
Recycling of magnet scrap from waste products consists of multiple steps, including preliminary steps; separation of the magnets from the waste product, demagnetization through heat treatment at 300-350° C., decarbonization (for removal of resin) by combustion at 700-1000° C. under air or oxygen flow, and deoxidization by hydrogen reduction. The main process (separation of rare earth metals and iron) begins after these preliminary stages. Several wet processes: acid dissolution, solvent extraction, and the oxalate method are also used for the recovery of neodymium. These wet chemical methods have poor yield from the acid dissolution and effluent treatment steps, which requires a multi-step process resulting in high cost. It is important that the recovery process for the rare earth metals from magnet scraps has as low cost and as few steps as possible, because recovery of magnetic material from the product is itself a multi-step process.
Grinding/milling of Nd-magnet alloy accounts for more than 10% of total recycling costs, while the risk of contaminating the resulting fine powder with grinding media and/or lining material of the milling equipment (jet mills, ball mills) is not negligible. Decrepitation protocols developed for recycling Nd magnets have generally used dry hydrogen gas to produce powdered alloy, at moderately high gas pressure and/or temperature.
One of the biggest challenges associated with the recycling of magnets is how to efficiently separate the magnetic materials from the other components. Specifically, carrying out decrepitation of ferromagnetic alloys at low cost.
In one embodiment, the presently disclosed subject matter provides an electrolysis apparatus for atomic hydrogen decrepitation of at least one rare-earth containing material, the apparatus comprises:
a cathode where the at least one rare-earth material is the cathode itself;
an anode;
an electrolyte in a bath; and
wherein the electrolysis apparatus is configured to carry out an electrolytic reaction to decrepitate said at least one rare-earth-containing material.
In some embodiments the cathode and the ferromagnetic alloy comprise the same material. In one embodiment the cathode and the ferromagnetic alloy are the same material. In one embodiment of the apparatus, the at least one rare-earth-containing material comprises any of the following elements selected from: cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb) and yttrium (Y).
In one embodiment of the apparatus the at least one rare-earth-containing material comprises a ferromagnetic alloy or rare-earth magnet. In another embodiment the rare-earth magnet is selected from a list comprising: Nd2Fe14B, SmCO5, Sm(Co,Fe,Cu,Zr)7, Sr-ferrite, iron bar-magnets or combinations thereof. In one embodiment, iron-containing materials undergo further treatment processes to separate rare-earth materials from iron-containing ones, as detailed herein. In some embodiments, further pre-treatment processes can include milling, grinding, crushing, pulverizing ferromagnetic alloys, before the electrolytic atomic hydrogen decrepitation processes.
In one embodiment the cathode of the apparatus further comprises copper, nickel, steel, titanium or any combination thereof. In one embodiment the electrolyte of the apparatus is a hydroxide. In another embodiment the electrolyte is KOH or NaOH aqueous solution. In one embodiment the cathode further comprises at least one grid adapted to allow decrepitated fragments to pass through it. In one embodiment the grid has holes with a size ranging from 1 to 100 μm in diameter. In one embodiment the at least one grid is comprised of copper, nickel, steel, titanium, ferromagnetic alloy or any combination thereof. In one embodiment the apparatus further comprises at least one additional cathode.
In one embodiment, the presently disclosed subject matter provides a method for electrolytic atomic hydrogen decrepitation of at least one rare-earth-containing materials, the method comprising:
providing an electrolysis apparatus of any of the apparatus' disclosed here, configured to carry out an electrolytic reaction in an electrolyte; and
carrying out an electrolytic reaction by providing an applied potential between said anode and said cathode, producing atomic hydrogen at said cathode.
In on embodiment, the presently disclosed subject matter provides a method for electrolytic atomic hydrogen decrepitation of at least one rare-earth-containing materials, the method comprising:
providing an electrolysis apparatus comprising an anode, cathode and electrolyte, configured to carry out an electrolytic reaction to decrepitate said at least one rare-earth-containing material;
disposing said at least one rare-earth-containing materials onto said cathode; and
carrying out an electrolytic reaction by providing an applied potential between said anode and said cathode, producing atomic hydrogen at said cathode.
In one embodiment of the method the cathode and the ferromagnetic alloy are different materials. In some embodiments of the method the cathode and the ferromagnetic alloy comprise the same material. In one embodiment of the method the cathode and the ferromagnetic alloy are the same material. In one embodiment of the method the electrolytic reaction is carried out at room temperature. In one embodiment of the method the electrolytic reaction is carried out at an elevated temperature. In one embodiment of the method the applied potential is between 4 to 10V. In one embodiment of the method atomic hydrogen is released from the cathode by a reduction reaction of 2 H+(aq)+2e−→2H(g). In one embodiment of the method the H+ is a result of electrolysis of the water (H2O) within the cell. In one embodiment of the method the electrolyte comprises hydroxide. In one embodiment of the method the electrolyte comprises KOH or NaOH aqueous solution.
In one embodiment of the method the cathode further comprises at least one grid adapted to allow decrepitated fragments through it. In one embodiment of the method the at least one grid is comprised of copper, nickel, steel, titanium, ferromagnetic alloy or any combination thereof.
The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which:
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.
In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention.
The presently disclosed subject matter provides an electrolysis apparatus and method for atomic hydrogen decrepitation of ferromagnetic alloys by electrolysis. In some embodiments the method of atomic hydrogen decrepitation can further include pre-treatment steps.
In some embodiments, the electrolysis apparatus comprises a cathode, anode and electrolyte wherein at least one rare-earth containing material is disposed on the cathode. In some embodiments, the terms “ferromagnetic alloy”, “rare-earth-containing material” and “rare-earth magnets” are used interchangeably. In some embodiments, any rare-earth containing material that can be coupled to an electrode for electrolysis can be used for this invention. Rare-earth containing materials can include any material that comprises any number of rare-earth elements and/or other materials e.g., a mineral, an alloy or a magnet. The rare-earth elements referred to herein can include any of the following: cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb) and yttrium (Y). In some embodiments the cathode comprises copper, nickel, steel, titanium or any combination thereof.
In some embodiments the ferromagnetic alloy is attached to the cathode in the electrolysis apparatus. In some embodiments the ferromagnetic alloy is disposed on the cathode wherein the ferromagnetic alloy and the cathode are electronically coupled. In some embodiments the electrolysis apparatus can comprise at least one additional cathode.
In some embodiments the electrolysis apparatus further comprises a grid, containing holes, beneath the ferromagnetic alloy/pieces. The hole size in the grid can be any appropriate size configured to allows ferromagnetic pieces/fragments to pass through it, to achieve a powder of a desired grain size at the base of the electrolysis tank, following electrolytic decrepitation.
In some embodiments the hole size of the grid ranges between 1 to 100 μm in diameter. In some embodiments the hole size of the grid ranges between 1 to 1000 μm in diameter. In some embodiments the hole size of the grid ranges between 1 to 50 μm in diameter. In some embodiments the hole size of the grid ranges between 50 to 100 μm in diameter. In some embodiments the hole size of the grid ranges between 100 to 500 μm in diameter. In some embodiments the hole size of the grid ranges between 500 to 1000 μm in diameter. In some embodiments the hole size of the grid ranges between 1 mm to 5 mm in diameter.
In some embodiments more than one grid, connected to the cathode, is used. With multiple grids, larger pieces may pass through the upper grid, but not through the lower grid. Ferromagnetic alloy fragments get smaller as they decrepitate and pass through subsequent grids with progressively smaller hole sizes. Multiple grids can facilitate a greater surface area of exposure between the ferromagnetic alloy and the electrolyte, as the ferromagnetic alloy is decrepitating. In one embodiment, any grid configuration that allows for a higher surface area of exposure between the ferromagnetic alloy and the electrolyte is within the scope of the invention.
In some embodiments the ferromagnetic alloy, rare-earth-containing material or rare-earth magnet itself is the cathode, that is, atomic hydrogen is released directly on the surface of the ferromagnetic alloy cathode.
In some embodiments, where the ferromagnetic alloy is the cathode itself, the electrolysis apparatus further comprises a grid, connected to the cathode, configured to allow decrepitated fragments to pass through it.
This invention further provides a method for electrolytic atomic decrepitation of at least one rare-earth-containing material. “Atomic hydrogen decrepitation” generally refers to a process using atomic hydrogen to break down rare-earth-containing materials into smaller pieces, generally small fragments or powders. “Electrolytic atomic hydrogen decrepitation” refers to the decrepitation process carried out, at least, by electrolysis. In some embodiments “atomic hydrogen decrepitation” and “electrolytic atomic hydrogen decrepitation” or just “decrepitation” are used interchangeably. As such, terms like “decrepitated” and “decrepitated fragments” are understood in view of the definitions herein. In some embodiments, no pre-treatment step is required before placing ferromagnetic alloys into the electrolysis apparatus.
In some embodiments pre-treatment stages to the atomic hydrogen decrepitation can be included, as will be detailed below.
In one embodiment, ferromagnetic alloy pieces are placed immediately in an electrolysis apparatus to perform electrolytic atomic hydrogen decrepitation forming an alloy powder. Such an alloy power can be separated by any number of additional methods to recover different materials. For example, chlorination treatment to separate iron and rare-earth metals, as described herein.
In some embodiments, a method of electrolytic atomic hydrogen decrepitation of rare earth metals comprises:
providing any one of the electrolysis apparatuses disclosed herein, generally comprising an anode, cathode, electrolyte and bath;
disposing at least one rare-earth-containing material onto the cathode; and
carrying out an electrolytic reaction by providing an applied potential between the cathode and anode, producing atomic hydrogen at the cathode.
In some embodiments, the method comprises a cathode which is itself made of ferromagnetic alloy fragments, pieces or material.
In some embodiments the method is carried out at room temperature. In some embodiments the method is carried out in ambient conditions. In some embodiments the electrolysis is carried out at an elevated temperature. In some embodiments the elevated temperature is between 20-30° C. In some embodiments the elevated temperature is between 20-40° C. In some embodiments the elevated temperature is between 20-50° C. In some embodiments the elevated temperature is between 30-40° C. In some embodiments the elevated temperature is between 40-50° C. In some embodiments the elevated temperature is between 50-100° C.
In some embodiments, the atomic hydrogen decrepitation comprises an electrolytic reaction, wherein the applied potential is between 4-10 V. In another embodiment the applied potential is between 4-8 V. In other embodiments the range of the applied potential is any one of: 4-5V, 4-6V, 4-7V, 4-8V, 4-9V, 4-10V, 5-6V, 5-7V, 5-8V, 5-9V, 5-10V, 6-7V, 6-8V, 6-9V, 6-10V, 7-8V, 7-9V, 7-10V, 8-9V, 8-10V or 9-10V.
In some embodiments the electrolyte is a hydroxide. In some embodiments the electrolyte is KOH or NaOH aqueous solution. In some embodiment the method further comprises the filtering of decrepitated ferromagnetic fragments through a grid. In some embodiments there is more than one grid.
One advantage of the present invention is in not requiring pre-treatment or a chlorination step. However, some embodiments may use these as additional steps in methods of decrepitation.
This invention further provides a method for atomic hydrogen decrepitation of at least one rare earth metal from a ferromagnetic alloy, further comprising a chlorination step, the method comprises:
In some embodiments, the method of this invention comprises prior to reacting the ferromagnetic alloy with at least one chlorine-containing gas of step (a), a pre-treatment of the ferromagnetic alloy by decrepitation to form a powder alloy using atomic hydrogen decrepitation treatment. In other embodiments, the decrepitation is performed at room temperature. In other embodiments, the atomic hydrogen decrepitation treatment is performed using electrolysis. In other embodiments, the electrolysis is performed using a first electrode (cathode) of copper, nickel, steel, titanium or combination thereof; and a second electrode (anode) of lead, nickel, steel or combination thereof. In other embodiments, the ferromagnetic alloy is attached to said first electrode (cathode).
In some embodiments, for example as depicted in
In some embodiments, this invention provides a method for the recovery of at least one rare earth metal from a ferromagnetic alloy, the method comprising: (i) electrolytic atomic hydrogen decrepitation of said ferromagnetic alloy to form a powder alloy; (ii) magnetic separation of said powder to form a powder alloy having a lower iron content; (iii) reacting said powder alloy having a lower iron content with at least one chlorine-containing gas to obtain volatile iron-containing chloride product and non-volatile at least one rare earth metal chloride; (iv) separating said volatile iron-containing chloride product and non-volatile at least one rare earth metal chloride; (v) cooling said separated non-volatile at least one rare earth metal chloride; (vi) electrolyzing said cooled non-volatile at least one rare earth metal chloride; thereby recovering said at least one rare earth metal.
In other embodiments, the atomic hydrogen decrepitation is performed at room temperature. In other embodiments, the atomic hydrogen decrepitation is performed using electrolysis. In other embodiments, the electrolysis is performed using a first electrode (cathode) of copper, nickel, steel, titanium, or combination thereof; and a second electrode (anode) of lead, nickel, steel or combination thereof. In other embodiments, the ferromagnetic alloy is attached to said first electrode (cathode).
In other embodiments, this invention also provides a method for recovery of spent neodymium magnets by chlorine treatment that does not require pre-treatment of magnets. For example, magnets that were used without demagnetization, crushing and milling. After treatment at 400° C., a clinker consisting of rare earth metal chlorides, sublimates consisting of iron oxide and iron chlorides were obtained. The resulting rare earth metals chlorides are then processed by electrolysis of the molten salts for rare earth metals production.
“Pre-treatment” refers to any process or processes that occur before another process. In one embodiment, pre-treatment may refer to physical processes such as milling and grinding, but may also refer to non-electrolytic atomic hydrogen decrepitation. Other examples of pre-treatment may include, but is not limited to: magnetic separation, demagnetization, heating, chemical processes, etc.
When referring to a ‘ferromagnetic’ (used interchangeably with ‘ferrimagnetic’) alloy it should be understood to encompass any type of source (including spent) of permanent magnet made of a combination of metals that creates its own permanent magnetic field. These metals include, but are not limited to the elements iron, nickel and cobalt, rare-earth metals, naturally occurring minerals (such as lodestone) and any combination thereof. In another embodiment, the ferromagnetic alloy is Nb2Fe14B, (Nb,Pr)Fe14B with Dy2O3 additions. In some embodiments the rare earth metals are sourced from ferromagnetic alloys, magnets comprising rare earth magnets, Nd2Fe14B, SmCO5, Sm(Co,Fe,Cu,Zr)7, Sr-ferrite, iron bar-magnets and combinations thereof.
In some embodiments, the present invention provides for the recovery and/or extraction of rare earth metals from any naturally occurring mineral. In some embodiments, the present invention provides for the recovery and/or extraction of rare earth metals from naturally occurring sources of rare earth elements such as, but not limited to: rare earth minerals, aeschynite-(Y or Ce), allanite, apatite, bastnäsite, britholite, brockite, cerite, Dollaseite-(Ce), euxenite, fluocerite, fluorite, gadolinite, laterite clays, loparite, monazite, parisite-(Ce or La), stillwellite, synchysite, titanite, wakefieldite, xenotime, zircon or combinations thereof.
In some embodiments, said at least one rare earth metal is selected from cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb), and yttrium (Y).
Neodymium magnets absorb gaseous hydrogen. Nd15Fe77B8 alloys absorb hydrogen readily at room temperature (provided that the surface is not heavily oxidized), with consequent decrepitation (pulverization) of the bulk material into a friable powder. Friability, being the tendency of a solid substance to break into smaller pieces under duress or contact, especially by rubbing. Absorption of hydrogen is carried out in two stages: hydrogen is first absorbed by the Nd-rich grain boundary material and then by the matrix Nd—Fe—B phase. Due to a large electronegativity difference, the insertion of hydrogen is favored in the vicinity of the rare earth elements (REE). Inter-grain failure may produce single crystal particles; however, these particles are nevertheless brittle and amenable to further reduction in size by ball milling.
This invention is directed to a method of decrepitation of a ferromagnetic alloy using atomic hydrogen (via electrolysis), as opposed to gaseous hydrogen. However, the advantage of using electrolytic atomic hydrogen compared to gaseous hydrogen is in its use of mild conditions, wherein the reaction is conducted at room temperature and eliminates the need of pure hydrogen at high pressure.
In some embodiments, the methods of this invention comprise an atomic hydrogen decrepitation of a ferromagnetic alloy, wherein the method comprises an electrolytic reaction of the ferromagnetic alloy by atomic hydrogen at room temperature, wherein the atomic hydrogen is released from a cathode within an electrochemical cell and reacted with the ferromagnetic alloy to obtain a ferromagnetic alloy powder having grain size ≤50 μm. In some embodiments the atomic hydrogen is released from the cathode by a reduction reaction of 2 H+(aq)+2e−→2H (g). In other embodiments, the H+ is the result of electrolysis of the water (H2O) within the electrolytic cell.
In other embodiment, the atomic hydrogen further forms a gaseous hydrogen (H2) [2H (g) →H2 (g)] in the water electrolytic bath. Atomic hydrogen forms on the metal surface at the cathode and reacts with the ferromagnetic alloy. Its remainder goes into the water solution and forms molecular hydrogen.
In other embodiments, the cathode comprises copper, nickel, steel, titanium or any combination thereof. In another embodiment, the anode comprises lead, nickel, steel or combination thereof.
In some embodiments, the atomic hydrogen decrepitation comprises an electrolytic reaction, wherein the electrolyte is a KOH or NaOH aqueous solution.
In some embodiments, the atomic hydrogen decrepitation comprises an electrolytic reaction, wherein the electrolytic reaction is conducted at room temperature. In another embodiment, the electrolytic reaction is carried out at a temperature of between 20 to 40° C. degrees. In another embodiment, the electrolytic reaction is carried out between 20 to 30° C. degrees. In another embodiment, the electrolytic reaction is carried out between 20 to 35° C. deg.
In some embodiments this process eliminates the need for high temperature equipment or for a pure hydrogen atmosphere at high pressure. The fine grain NdFeB hydride powder may be processed further to form new magnetic materials or to facilitate separation of valuable rare earth metals from the iron-containing components of the magnet
In some embodiments, the atomic hydrogen decrepitation comprises an electrolytic reaction, wherein the electrolytic reaction is performed for a period of between 30 min to 3 hrs. In another embodiment, the electrolytic reaction is performed in 2 hrs.
In some embodiments, the ferromagnetic alloy powder obtained by the atomic hydrogen decrepitation method of this invention comprises grains of size ≤50 82 m. In other embodiments, the ferromagnetic alloy powder obtained by the atomic hydrogen decrepitation method of this invention comprises grains of between 1 μm to 50 μm in size. In other embodiments, the ferromagnetic alloy powder obtained by the atomic hydrogen decrepitation method of this invention comprises grains of between 10 μm to 50 μm in size. In other embodiments, the ferromagnetic alloy powder obtained by the atomic hydrogen decrepitation method of this invention comprises grains of between 30 μm to 50 μm in size. In other embodiments, the ferromagnetic alloy powder obtained by the atomic hydrogen decrepitation method of this invention comprises grains of between 10 μm to 40 μm in size. In other embodiments, the ferromagnetic alloy powder obtained by the atomic hydrogen decrepitation method of this invention comprises grains of between 10 μm to 30 μm in size. In some embodiments the obtained ferromagnetic alloy powder comprises grains shaped as any of the followings: globular, spherical, cylindrical, non-uniform, cuboidal or combinations thereof. In some embodiments the grains are smooth and in others the grains are rough.
In some embodiments, methods for recovery of at least one rare earth metal from ferromagnetic alloys comprise a reaction with at least one chlorine-containing gas. In other embodiments, the reaction is performed at a temperature of between 400° C. and 450° C.
In some embodiments, the at least one chlorine-containing gas which is used in the methods of this invention is present in an amount of 0.5-2.0 kg of the chlorine per 1 kg of the ferromagnetic alloy (or powder alloy).
In some embodiments, the air flow to the volatile iron-containing chloride product is present in an amount of 0.5-2.0 kg of air per 1 kg of the volatile iron-containing chloride product.
In other embodiments, the chloride product is a highly pure chloride (both purity and yield >95%).
In some embodiments, the methods for recovery of at least one rare earth metal from ferromagnetic alloys comprise a step of electrolyzing the cooled non-volatile at least one rare earth metal chloride. In other embodiments, the electrolysis is performed using graphite electrodes (cathode, anode). In some further embodiments, the electrolysis is performed at a temperature range of between about 500 to 1500° C. In other embodiments, said electrolysis is performed using a potential of between 10 to 15V.
In some embodiments, this invention provides at least one rare earth metal composition prepared by the methods of this invention. The following non-limiting examples are presented in order to more fully illustrate certain embodiments of the invention. They should in no way, however, be construed as limiting the broad scope of the invention. One skilled in the art can readily devise many variations and modifications of the principles disclosed herein without departing from the scope of the invention.
The decrepitation of the ferromagnetic alloy was carried out in aqueous 1M sodium hydroxide solution at room temperature. Electrolysis was carried out with cathode copper electrode and lead anode electrode. Current density was 0.1 A/cm2. Uncrushed ferromagnetic alloy was attached to the cathode electrode. The atomic hydrogen that is released at the cathode passes through a pieces of ferromagnetic alloy and reacted with it. The pieces of ferromagnetic alloy were scattered by the atomic hydrogen reaction with ferromagnetic alloy powder production.
Used magnet pieces were used as input material.
Content of components presented in the Table 1.
A photo of some magnet pieces is presented in the
Material X-ray diffraction (XRD) was performed on an Ultima III diffractometer (Rigaku Corporation, Japan) with quantitative phase analysis accomplished using Jade_10 (MDI, Cal.) software and the ICSD database (
The composition of the material was characterized by energy dispersive X-ray fluorescence spectroscopy (EDS, LEO Supra) (
Calculations of the Gibbs energy was performed using a computer program and based on standard values for the pure substances. The Gibbs energy (ΔG) in the temperature range 273-473 K is shown in Table 2 for reactions with hydrogen. Group 1—reactions with atomic hydrogen; Group 2—reactions with molecular hydrogen; Group 3—hydrolysis reactions of metal hydrides in the water.
Under the above conditions, shown in Table 2, the Gibbs energy of the reactions (1, 2) in Group 1 for rare metals were strongly negative (−520-570 KJ/mole).
Thermodynamic calculations predicted that the reactions of Nd and Pr from magnets with atomic hydrogen gas resulted in the formation of Nd and Pr hydrides within a wide temperature range, including the range of interest 273-373 K. Dysprosium is present in magnets as an additive in the form of oxide Dy2O3 and can react with atomic hydrogen with metallic dysprosium or DyH2 production (reactions 4, 5). Group 2 includes hydrogen treatment reactions between magnet components and molecular hydrogen. The likelihood of reactions (6, 7) is ensured over the entire temperature range of interest too, with the most negative value being ΔG=−163 KJ/mole for reaction (6). However, the value of the Gibbs energy for reactions (6, 7) is much lower than for reactions (1, 2). Dy2O3 does not react with molecular hydrogen (reactions 8, 9). Iron from a magnet practically does not participate in reactions with hydrogen under the experimental conditions (reactions 3, 8). Group 3 includes hydrolysis reactions of the neodymium, praseodymium, and dysprosium hydrides in the water. Under the experimental conditions, the Gibbs energy of the hydrolysis reactions (11-16) in Group 3 for rare metals is strongly negative (−350-530 KJ/mole). Thermodynamic calculations predict that the hydrolysis reactions of the neodymium, praseodymium, and dysprosium hydrides can result in the formation of Nd, Pr, and Dy hydroxides or oxides within a wide temperature range, including the range of interest 273-373 K.
The chemical decrepitation of the magnet described by reactions (1, 2) showing a Gibbs energy of −520-570 KJ/mole, thereby predicting rapid chemical decrepitation of the magnet upon atomic hydrogen treatment. Dy2O3 can react with atomic hydrogen with metallic dysprosium or DyH2 production (reactions 4, 5). These reactions (1, 2, 4, 5) lead to the magnet decrepitation to obtain a magnet powder with a particle size of less than 200 mesh.
The laboratory setup is described in
A glass vessel with one mole/liter KOH solution (6) was used as an electrolytic bath (1). Titanium was used as the cathode (2), a nickel plate—as anode (5). Pieces (30-40 mm) of the neodymium magnet (3) (as they are, without demagnetization, crushing and milling) were placed on the titanium grid (4), connected with cathode (2). Atomic hydrogen, which was emitted during electrolysis, was released on the surface of the magnet pieces (3) and decrepitated them with producing a powder (7). The magnet powder (7) passed through the grid (4) and collected at the bottom of the electrolytic bath (1).
To summarize, the exposure of as-received Nd-magnet fragments (as prepared according to example 4) to chlorine gas for 2 hrs at 673K leaves highly pure REE (rare earth elements) chlorides (both purity and yield >95%) as the clinker in the laboratory furnace. These chlorides are hygroscopic and readily form the hexahydrate when brought into contact with ambient humidity. The volatile components—particularly those which include Fe or B—are removed from the furnace as sublimated oxychlorides and chlorides. The relative amount of these products depends on the rate of air flow at the top of the reactor, while the unreacted chlorine gas is recoverable. The presence of high melting temperature oxides following Nd-magnet alloy decrepitation, does not appear to prevent the formation of REE chlorides.
A ferromagnetic alloy was decrepitated using electrolytic atomic hydrogen decrepitation, producing a ferromagnetic alloy powder. The powder of a ferromagnetic alloy was subsequently treated with chlorine gas at 400-450° C. Chlorination of such a powder increases the rate of chlorination, in comparison to chlorination of pieces of magnets, since the surface area is larger. The material was loaded into the reactor. Chlorine was fed into the reactor, heated to a temperature of 400-450° C. After the reaction, the chlorides of iron and boron were sublimated and removed from the reactor. Iron chloride was captured in a scrubber with water, and boron chloride was removed with gases. Chlorides of rare earth metals remained in the reactor. Iron-containing chloride vapor product (FeCl3) were received in the scrubber and non-volatile neodymium and praseodymium chlorides (NdCl3, PrCl3) in the reactor. Following this step, rare earth chlorides can then be used for electrolysis in the methods described herein.
In this Example, a process for rare-earth extraction did not require pre-treatment of magnets. The magnets that were used did not include demagnetization, crushing and milling pre-treatments. This example relates to rare-earth metal extraction from pieces of magnets whereas example 4 relates to rare-earth metal extraction from powders, using electrolytic atomic hydrogen decrepitation. In this example, after the chlorination treatment of magnets at 400° C., a clinker consisting of rare earth metals chlorides and sublimates consisting of iron oxide and iron chlorides were obtained. It is noted that the rate of chlorination and the completeness of chlorination (where chlorination is required to separate iron from rare-earth metals) is higher for processes that include pre-treatment with electrolytic hydrogen decrepitation.
Used magnet pieces were used as input material. Content of components presented in the Table 3.
Material X-ray diffraction (XRD) was performed on an Ultima III diffractometer (Rigaku Corporation, Japan) with quantitative phase analysis accomplished using Jade_10 (MDI, Cal.) software and the ICSD database (
The composition of the material was characterized by energy dispersive X-ray fluorescence spectroscopy (EDS, LEO Supra) (Table 3 and
Table 3 shows that both magnets are made up of the same elements, but the relationships between the elements are rather different. According to the X-ray diffraction patterns, the first sample (
All the main peaks in
Calculations of the Gibbs energy were performed using a computer program and based on standard values for the pure substances. The Gibbs energy (ΔG) in the temperature range 373-773 K is shown in Table 4 for chlorination reactions with chlorine gas.
In reference to Table 4, under sintering conditions, the Gibbs energy of the reactions (1-, 6, 8) were strongly negative within a wide temperature range, including the range of interest 573-673 K, with the most negative value being ΔG=−(800-900) KJ/mole for reactions (3 and 5). Thus, the highest probability of reactions (1)-(6, 8) can be expected immediately after injection of the chlorine gas. Dysprosium was present in magnets as an additive in the form of oxide Dy2O3 and did not react with chlorine (reaction 7 from Table 4).
Sintering of neodymium magnets with chlorine gas was carried out in a temperature-controlled laboratory furnace at 400° C.: sintering time was 2 hours. The laboratory setup is described in
Pieces (30-40 mm) of the neodymium magnet (as they were, without demagnetization, crushing and milling) were placed in the furnace in a Pyrex glass crucible 9. Prior to heating, the quartz reactor 7 was cleaned under 100 ml/min nitrogen flow, following which the furnace 8 was heated to a given temperature, again under 100 ml/min nitrogen flow. Chlorine gas was fed into the reactor 7 after the latter had reached the designated temperature. All elements (iron, neodymium, praseodymium, and boron) were chlorinated in accordance with reactions (1-6, 8) from Table 4. Dysprosium oxide Dy2O3 did not react with chlorine (reaction 7 from Table 4).
Chlorides of iron and boron were sublimated (Boiling point of the FeCl3 is 316° C., boiling point of the BCl3 is −107° C.) and rare earth metals chlorides remain in the residual clinker (Boiling point of the NdCl3 is 1600° C., boiling point of the PrCl3 is 1710° C.). Rare earth metals chlorides and Dy2O3 were formed of the solid powder clinker (Melting point of the NdCl3 is 758° C., melting point of the PrCl3 is 786° C., melting point of the Dy2O3 is 2408° C.). Air was added 6 to the top part of the reactor for iron chloride oxidation in accordance with reaction (7):
Chlorine was obtained by reaction (7) and could have returned to the Pilot or industrial unit to the chlorination stage, therefore a circulation of chlorine gas can be achieved.
After cooling under nitrogen flow, the crucible 9 was removed from the furnace 7 and broken. The final product 12 (solid NdCl3—PrCl3 clinker) was weighed and analyzed with XRD and EDS. Mixture of the iron chloride and iron oxide was collected from the top part of the reactor and analyzed with XRD and EDS.
The composition of the material was characterized by energy dispersive X-ray fluorescence spectroscopy (EDS, LEO Supra) (
The resulting rare earth metals chlorides can be easily processed by electrolysis of the molten salts for metallic rare earth metals production.
Quantitative phase analysis of X-ray diffraction patterns of sublimations (
Example 4—Electrolytic Hydrogen Decrepitation of Nd Based Magnets Materials
Fragments of end-of-life rare earth elements-Fe—B (REE-Fe—B) alloy magnets were removed from computer hard disc drives. The magnets had originally been coated with aluminum; however, prior to shipment to Israel, the surfaces were polished, and thereby, part of the surface had corrosion.
X-ray diffraction (XRD) of the as-received magnet fragments was performed on a TTRAX III theta-theta diffractometer while the patterns of the HD (hydrogen decrepitated) powder were measured on an Ultima III theta-theta diffractometer (both diffractometers are products of the Rigaku Corporation, Japan). Phase identification was accomplished using Jade_Pro (MDI, CAL.) software and the Inorganic Crystal Structure Database (ICSD). Cu Kα X-radiation, Bragg-Brentano protocol, diffracted beam monochromator and variable divergence slit widths constituted our standard operating procedure on both diffractometers. Element content of the magnet fragments and HD powders was characterized by energy dispersive (X-ray fluorescence) spectroscopy (EDS) on a LEO Supra scanning electron microscope (SEM). Mass % metal content was quantified by inductively coupled plasma mass spectroscopy (ICP-MS, Agilent 7700s) following dissolution of the magnet or HD powder in aqua regia. 0.65 grams of the as-received magnet fragments were dissolved in 100 ml aqua regia at room temperature with continuous stirring during 24 hours. This solution was diluted to 1000 ml with deionized water to prepare stock solution. 2 ml of stock solution were subsequently diluted to 100 ml with deionized water. 0.86 grams of hydrogen decrepitated powder (following electrolysis, filtration and drying in air at 353K) was dissolved in 100 ml aqua regia with continuous stirring at room temperature for 24 hours. The solution was then diluted to 200 ml with deionized water. Two powder samples were measured. For sample #1, 2 ml of the stock solution was diluted to 1000 ml, and for sample #2, 5 ml of the stock solution was diluted to 1000 ml, both with deionized water.
Details of the laboratory-scale electrolysis cell are shown in
A SQUID magnetometer (MPMS3, L.O.T.-Quantum Design, Inc.) was used in the vibrating (VSM) mode with peak amplitude 2 mm, frequency 13 Hz and averaging time 10 s. The magnetic moment (M, [10−3Am2]) of each sample was measured at ambient temperature (300 K) with field strengths |μoH|≤6T. The temperature dependence of the magnetic moment of the samples was measured at μoH=6T and fit to the modified Bloch law using the Levenberg-Marquardt algorithm for non-linear curve fitting in Origin (OriginLab MA). One fragment of the as-received magnet, and a sample of the fine, electrolytically decrepitated magnet, powder was measured. The mass of the thin, elongated, plate-shaped magnet fragment was 31.0 mg, with approximate dimensions [5×2.8×0.3] mm3. To justify neglecting the demagnetizing factor, the sample was oriented in the magnetometer such that the direction of the magnetic field was parallel to the flat sample surface. Duplicate measurements were made first in a standard brass sample holder and then in a quartz holder. The mass of the fine grain HD powder sample was 10.1 mg. The demagnetizing factor was estimated to be D=0.23, consistent with the size and shape of the powder sample placed in the standard brass holder.
The as-received Nd-magnet fragments appear irregularly shaped, 20-30 mm dimensions and with a partially corroded surface. Whole pattern fitting of the XRD profile to ICSD pattern #48143 measured on a relatively undamaged surface region, gave R-factor of not better than ˜20%, due predominantly to the difficulty in fitting such a highly textured alloy. The CuKα radiation was only able to probe ˜10 micron thick layer at the magnet surface, due to the strong absorption of the RE (rare earth) metals and iron at 8 KeV. A SEM image of the surface and an EDS spectrum are shown in
As a guide for understanding the reaction thermodynamics of each of the metal alloy components with hydrogen, the Gibbs energies for reactions with atomic hydrogen or with hydrogen gas in the temperature range 273-473 K were calculated. Calculations were performed using a computer program based on standard values for the pure substances. The Gibbs energy (ΔG) in the temperature range 273-473 K is shown in Table 6 for reactions with hydrogen: Group 1−reactions with atomic hydrogen and Group 2−reactions with hydrogen gas.
Referring to Table 6, under the conditions of the experiments, the Gibbs energy of reactions (1, 2) in Group 1 for rare earth metals was strongly negative (−520 to −570 KJ/mole). Calculations predict that the reactions of Nd and Pr with atomic hydrogen can result in the formation of Nd and Pr hydrides within a wide temperature range, including the range of interest. Metallic dysprosium may react with atomic hydrogen, producing DyH2 (reaction 3). Group 2 includes reactions between magnet components and hydrogen gas. The likelihood of reactions (7-9) was ensured over the entire temperature range of interest as well. However, the values of Gibbs energy for reactions (7,8) were much less negative than those for reactions (1, 2). Iron participates only marginally in reactions with both atomic hydrogen and hydrogen gas under the experimental conditions (reactions 4, 10). Boron is highly reactive with atomic H but not with hydrogen gas. The resulting B2H6 gas is moderately toxic upon inhalation, but it is readily converted to boric acid by hydrolysis. The damaged aluminum coating remaining on the magnet fragments was not predicted to react with hydrogen gas but should convert to Al hydride via interaction with atomic hydrogen.
Table 7 includes hydrolysis reactions of the neodymium, praseodymium, and dysprosium hydrides in water. Under the experimental conditions, the Gibbs energy of reactions (1-6) for rare earth metal hydrides was strongly negative (approx. −340 to −500 KJ/mole). Thermodynamic calculations therefore predicted that hydrolysis reactions of neodymium, praseodymium, and dysprosium hydrides may result in the formation of Nd, Pr, and Dy hydroxides or oxides within a wide temperature range, including the range of interest 273-473 K. Similarly, hydrolysis may result in the oxidation of iron to hematite as well as other iron oxides (Table 7.)
As noted above, the calculated Gibbs energy of reactions of individual REE (rare earth elements) with atomic hydrogen (Table 6) is strongly negative, thereby predictive of rapid chemical decrepitation of the two-phase Nd-magnet within the temperature range of interest. These reactions take place immediately following initiation of atomic hydrogen release at the cathode during electrolysis. Following 2 hr electrolysis at room temperature as described in the Methods Section above, complete magnet decrepitation was observed, producing a powder with particle size of <200 mesh. The powder was filtered from the KOH electrolyte and dried at 353K in air. Subsequent sieving through various sized mesh gave an upper bound of 44 μm for the particle size of the HD powders (
Except for the additional X-ray fluorescence (XRF) peaks identified as being due to Si and Ca, the EDS spectrum in
Phase identification of X-ray diffraction (XRD) peaks from the fine grain HD particles (
The increase in unit cell dimensions reveals that during electrolysis under ambient conditions, atomic H is able to be absorbed into the matrix following absorption into the Nd-rich grain boundary phase. (Table 8).
It is the absorption of H into this electron deficient, intergranular boundary phase that produces the decrepitation of the sintered magnetic alloy. Even in the alloy matrix, H tends to be positioned near Nd atoms, rather than near the Fe or B atoms. X-ray diffraction peaks which cannot be associated with the magnet alloy hydride, have been identified as minor phases of Nd-oxide (Ia-3) (ICSD #191535) and Nd-tri hydroxide (ICSD #398), as well as Pr-oxide (ICSD #75481) and NdFe2 alloy (ICSD #103548). One or more of the various iron oxide phases, including hematite may also be present. This multiplicity of possible minor phases makes quantitative analysis of the electrolytic HD powder XRD pattern very challenging. (* ICSD refers to Inorganic Crystal Structure Database, world's largest database for completely identified inorganic crystal structures).
The magnetic properties of the electrolytic HD powder were characterized as described in the Method Section above. Results are summarized in Table 9 (SQUID magnetometer data are presented in
High levels of oxidation in Nd2Fe14B alloy waste (3000-5000 ppm oxygen) constitute a serious impediment to large-scale recovery and recycling of valuable rare earth metals. Even pristine NdFeB alloy may contain 300-400 ppm oxygen, with a majority of the oxidation reactions occurring within the Nd-rich grain boundaries. Both confocal microscopy and Raman spectroscopy have been used to locate, measure and identify the growth of surface reaction products at room temperature immediately following exposure to air. These measurements demonstrated that significant growth of Nd2O3 occurs at the triple junctions of the Nd-rich grain boundaries. It was furthermore found that oxidized triple junctions do not react with hydrogen to form NdH2, leading to poor redistribution of the Nd-rich phase during subsequent re-sintering. The grain boundary phase no longer melts uniformly due to the very high melting temperature of the RE (rare earth) metal oxides and therefore full mass density cannot be achieved in the recycled magnets. Dispersed Nd2O3 compounds reduce the coercive force of Nd2Fe14B alloys.
HD powders, with a large surface to volume ratio, oxidize rapidly upon exposure to air. Very low magnetic coercivity at 300K, such as we report (Table 9), has also been ascribed to the presence of metallic α-Fe at grain boundaries. This soft magnetic phase is formed as a result of local disproportionation due to the exothermic reaction associated with the formation of neodymium hydride. Upon additional processing of the powder under ambient conditions, the oxygen content will only increase. It is shown that deterioration in sinterability, and hence in the magnetic properties, can be overcome, at least partially, by blending additional Nd in the form of Nd hydride into the HD powder.
Electrolytic hydrogen decrepitation can be an effective procedure for safely and economically pulverizing cm-size, sintered Nd2Fe14B alloy magnet fragments to fine powder (grain size <325 mesh, i.e., <44 μm) under ambient conditions, with 1 M KOH as the aqueous electrolyte of choice. This process eliminates the need for high temperature equipment or for pure hydrogen atmosphere at high pressure. The fine grain NdFeB hydride powder may be processed further to form new magnetic materials or to facilitate separation of the valuable rare earth metals from the iron-containing components of the magnet.
All references referred to (“cited herein”), and all references cited or referenced in this document are hereby or in any document incorporated by reference herein. Along with any manufacturer's instructions, instructions, product specifications, and product sheets for any of the products listed, they can be incorporated herein by reference and used in the practice of the invention. More specifically, all references are incorporated by reference to the extent that each individual reference is specifically and individually indicated to be incorporated by reference.
While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IL2022/050955 | 8/31/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17462047 | Aug 2021 | US |
| Child | 18686465 | US |
