Patent Description:
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 <NPL>) and the <NPL>), the 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 <NUM>-<NUM>, decarbonization (for removal of resin) by combustion at <NUM>-<NUM> under air or oxygen flow, and deoxidization by hydrogen reduction[<NUM>-<NUM>]. The main process (separation of rare earth metals and iron) begins after these preliminary stages. Several wet processes: acid dissolution [<NUM>], solvent extraction, and the oxalate method [<NUM>] are used too for recovery of the neodymium. These wet chemical methods have poor yield from the acid dissolution and effluent treatment steps, which requires a multiple-step process resulting in high cost. It is important that the recovery process for the rare earth metals from magnet scrap has as low cost and as few steps as possible, because recovery of the magnets from the product is itself a multi-step process.

Several works were carried out on the chlorination of magnets with various reagents: NH<NUM>Cl [<NUM>], FeCl<NUM> [<NUM>], MgCl<NUM> [<NUM>], and chlorine gas with carbon [<NUM>]. The use of NH<NUM>Cl, FeCl<NUM>, and MgCl<NUM> as chlorinators led to the formation of neodymium chloride and iron and boron alloy remained in the solid metallic form. The resulting mixture of the neodymium chloride and Fe-B metal residue was then separated by vacuum distillation or magnetic separation. The chlorination method is low-cost, simplifies the overall process, and reduces the amount of effluent requiring treatment as a dry process. A method for chlorinating magnets with chlorine and carbon addition at a temperature of <NUM>-<NUM> with preliminary oxidation treatment was proposed in [<NUM>].

It was shown that preliminary oxidation sintering in an air stream with the conversion of all metals to oxides (Fe<NUM>O<NUM>, FeNdO<NUM>, Nd<NUM>O<NUM>) dramatically reduces the degree of sublimation of iron and boron during chlorination with pure chlorine. When carbon is added to the chlorination process (carbochlorination process), the degree of sublimation of iron and boron chlorides increases. It is known [<NUM>] that the Gibbs energy of the chlorination reaction of metal oxides by chlorine gas is a significant positive value; therefore, successful chlorination of them with pure chlorine is practically impossible. Chlorination of metal oxides showed to be effective with the addition of a reducing agent and the addition of carbon during the chlorination of oxides which dramatically increased the efficiency of the chlorides sublimation process [<NUM>].

One of the biggest challenges associated with the recycling of magnets is how to separate efficiently the magnets from the other components.

The present invention provides a method for electrolytic atomic hydrogen decrepitation of a ferromagnetic alloy, wherein the method comprises an electrolytic reaction by providing an applied potential between an anode and a cathode, wherein the ferromagnetic alloy is connected to the cathode, producing atomic hydrogen at the cathode, wherein the ferromagnetic alloy is scattered by the atomic hydrogen to obtain a ferromagnetic alloy powder. The present invention is defined by claim <NUM>.

In an embodiment, the electrolytic atomic hydrogen decrepitation is carried out at room temperature.

In an embodiment, the cathode comprises copper, nickel, steel, titanium, or a combination thereof.

In an embodiment, the anode comprises lead, nickel, steel or a combination thereof.

This invention also provides a method for recovery of at least one rare earth metal from ferromagnetic alloy, the method comprising: pre-treatment of the ferromagnetic alloy by the atomic hydrogen decrepitation treatment, followed by:.

thereby recovering said at least one rare earth metal.

In an embodiment, the at least one chlorine-containing gas in step (a) is present in an amount of <NUM> - <NUM> of chlorine per <NUM> of ferromagnetic alloy.

In an embodiment, the air flow to the volatile iron-containing chloride product of step (b) is present in an amount of <NUM> - <NUM> of air per <NUM> of volatile iron-containing chloride product.

In an embodiment, the 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).

The present invention provides a method for electrolytic atomic hydrogen decrepitation of a ferromagnetic alloy, wherein the method comprises an electrolytic reaction by providing an applied potential between an anode and a cathode, wherein the ferromagnetic alloy is connected to the cathode, producing atomic hydrogen at the cathode, wherein the ferromagnetic alloy is scattered by the atomic hydrogen to obtain a ferromagnetic alloy powder.

In other embodiments, the decrepitation is performed at room temperature. 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 an embodiment, the recovery of spent neodymium magnets by chlorine treatment does not require pre-treatment of magnets. After treatment at <NUM>, a clinker consisting of rare earth metals chlorides and sublimates consisting of iron oxide and iron chlorides were obtained. The resulting rare earth metals chlorides can be easily processed by electrolysis of the molten salts for rare earth metals production [<NUM>, <NUM>].

When referring to a ferromagnetic (can be 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 persistent magnetic field. These metals include the elements iron, nickel and cobalt, rare-earth metals, naturally occurring minerals (such as lodestone) and any combination 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).

In some embodiments, the at least one chlorine-containing gas which is used in the methods of this invention (step (a)) is present in an amount of <NUM> - <NUM> of the chlorine per <NUM> of the ferromagnetic alloy (or powder alloy).

In an embodiment, said air flow to the volatile iron-containing chloride product of step (b) is present in an amount of <NUM> - <NUM> of the air per <NUM> of the volatile iron-containing chloride product.

In other embodiments, the electrolysis in step (e) is performed using graphite electrodes (cathode, anode). In some further embodiments, said electrolysis is performed at a temperature range of between about <NUM> to <NUM>. In other embodiments, said electrolysis is performed using potential of between <NUM> to 15V.

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.

The decrepitation of the ferromagnetic alloy was carried out in aqueous <NUM> sodium hydroxide solution at room temperature. Electrolysis was carried out with cathode copper electrode and lead anode electrode. Current density was <NUM>. 1A/cm<NUM>. Uncrushed ferromagnetic alloy was attached to the cathode electrode. The atomic hydrogen that is released at the cathode passes through a layer of pieces of a ferromagnetic alloy and reacted with him. The pieces of a ferromagnetic alloy are scattered by atomic hydrogen reaction with ferromagnetic alloy powder production. <FIG>, <FIG> and <FIG> show the ferromagnetic alloy before and after atomic hydrogen decrepitation.

Used magnet pieces were used as input material.

Content of components presented in the Table <NUM>.

Photo of some magnet pieces is presented in the <FIG>.

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 (<FIG>).

The composition of the material was characterized by energy dispersive X-ray fluorescence spectroscopy (EDS, LEO Supra) (<FIG>).

Calculations of Gibbs energy were performed using a computer program and based on standard values for the pure substances [<NUM>]. The Gibbs energy (ΔG) in the temperature range <NUM>-<NUM> is shown in Table <NUM> for reactions with hydrogen. Group <NUM>- reactions with atomic hydrogen; Group <NUM> - reactions with molecular hydrogen; Group <NUM> - hydrolysis reactions of metal hydrides in the water.

Under the above conditions, the Gibbs energy of the reactions (<NUM>, <NUM>) in Group <NUM> for rare metals were strongly negative (- <NUM>-<NUM> kJ/mole).

Thermodynamic calculations predict that the reactions of Nd and Pr from magnets with atomic hydrogen gas can result in the formation of Nd and Pr hydrides within a wide temperature range, including the range of interest <NUM>-<NUM>. Dysprosium is present in magnets as an additive in the form of oxide Dy<NUM>O<NUM> and can react with atomic hydrogen with metallic dysprosium or DyH<NUM> production (reactions <NUM>, <NUM>). Group <NUM> includes hydrogen treatment reactions between magnet components and molecular hydrogen. The likelihood of reactions (<NUM>, <NUM>) is ensured over the entire temperature range of interest too, with the most negative value being ΔG = -<NUM> kJ/mole for reaction (<NUM>). However, the value of Gibbs energy for reactions (<NUM>, <NUM>) is much lower than for reactions (<NUM>, <NUM>). Dy<NUM>O<NUM> does not react with molecular hydrogen (reactions <NUM>, <NUM>). Iron from a magnet practically does not participate in reactions with hydrogen under our conditions (reactions <NUM>, <NUM>). Group <NUM> includes hydrolysis reactions of the neodymium, praseodymium, and dysprosium hydrides in the water. Under our conditions, the Gibbs energy of the hydrolysis reactions (<NUM>-<NUM>) in Group <NUM> for rare metals is strongly negative (- <NUM>-<NUM> 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 <NUM>-<NUM>.

The chemical decrepitation of magnet described by reactions (<NUM>, <NUM>) showing Gibbs energy of - <NUM>-<NUM> kJ/mole, thereby predicting rapid chemical decrepitation of magnet upon atomic hydrogen treatment. Dy<NUM>O<NUM> can react with atomic hydrogen with metallic dysprosium or DyH<NUM> production (reactions <NUM>, <NUM>). These reactions (<NUM>, <NUM>, <NUM>, <NUM>) lead to the magnet decrepitation to obtain a magnet powder with a particle size of less than <NUM> mesh.

The laboratory setup is described in <FIG>. Test duration was <NUM>-<NUM> hours. Temperature was varied from room temperature to boiling temperature. Potential was <NUM> V, current - <NUM>-15A. Cathode current density was <NUM>-<NUM> A/cm<NUM>.

Glass with one mole/liter KOH solution was used as electrolytic bath. Titanium was used as cathode, nickel plate - as anode. Pieces (<NUM>-<NUM>) of the neodymium magnet (as they are, without demagnetization, crushing and milling) were placed on the titanium grid, connected with cathode. Atomic hydrogen, which was emitted during electrolysis, released on the surface of the magnet pieces, and decrepitated them with powder production. Magnet powder passed through the grid and collected at the bottom of the electrolytic bath. <FIG> shows the Powder X-ray diffraction (XRD) pattern of the magnet powder after decrepitation; and <FIG> shows in a photo and SEM image of the magnet powder after decrepitation.

Treatment of the powder of the ferromagnetic alloy with chlorine gas at <NUM>-<NUM>. The material was loaded into the reactor. Chlorine was fed into the reactor, heated to a temperature <NUM>-<NUM>. 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 (FeCl<NUM>) were received in the scrubber and non-volatile neodymium and praseodymium chlorides (NdCl<NUM> , PrCl<NUM>) in the reactor.

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 pretreatments. After treatment at <NUM>, a clinker consisting of rare earth metals chlorides and sublimates consisting of iron oxide and iron chlorides were obtained.

Used magnet pieces were used as input material. Content of components presented in the Table <NUM>.

The composition of the material was characterized by energy dispersive X-ray fluorescence spectroscopy (EDS, LEO Supra) (Table <NUM> and <FIG>).

Table <NUM> shows that both magnets are made up of the same elements, but the relationships between the elements are rather different. According to X-ray diffraction patterns, the first sample (<FIG>) is a well-crystalline material with an average crystal size of about <NUM>, while the second (<FIG>) consists of nanocrystals with a size of about <NUM>.

All the main peaks in <FIG> correspond well to Nd<NUM>Fe<NUM>B and NdPrFe<NUM>B (their peaks have almost identical positions), and the remaining peaks correspond to Dy<NUM>O<NUM>, which were only a few percent. According to the EDS results (Table <NUM>), the two main phases in sample <NUM> had the same amount. In <FIG>, peaks of Nd<NUM>Fe<NUM>B (or NdPrFe<NUM>B), were observed, but they were relatively small. Compounds shown above the main peaks in <FIG> were found, given also in Table <NUM>.

Calculations of Gibbs energy were performed using a computer program and based on standard values for the pure substances [<NUM>]. The Gibbs energy (ΔG) in the temperature range <NUM>-<NUM> is shown in Table <NUM> for chlorination reactions with chlorine gas.

Under sintering conditions, the Gibbs energy of the reactions (<NUM> - ,<NUM>, <NUM>) was strongly negative within a wide temperature range, including the range of interest <NUM>-<NUM>, with the most negative value being ΔG = - (<NUM>-<NUM>) kJ/mole for reactions (<NUM> and <NUM>). Thus, the highest probability of reactions (<NUM>) - (<NUM>, <NUM>) can be expected immediately after injection of the chlorine gas. Dysprosium was present in magnets as an additive in the form of oxide Dy<NUM>O<NUM> and did not react with chlorine (reaction <NUM> from Table <NUM>).

Sintering of neodymium magnet with chlorine gas was carried out in a temperaturecontrolled laboratory furnace at <NUM>: sintering time was <NUM> hour. The laboratory setup is described in <FIG>.

Pieces (<NUM>-<NUM>) of the neodymium magnet (as they were, without demagnetization, crushing and milling) were placed in the furnace in a Pyrex glass crucible. Prior to heating, the quartz reactor was cleaned under <NUM>/min nitrogen flow, following which the furnace was heated to a given temperature, again under <NUM>/min nitrogen flow. Chlorine gas was fed into the reactor after the latter had reached the designated temperature. All elements (iron, neodymium, praseodymium, and boron) were chlorinated in accordance with reactions (<NUM>-<NUM>, <NUM>) from Table <NUM>. Dysprosium oxide Dy<NUM>O<NUM> did not react with chlorine (reaction <NUM> from Table <NUM>).

Chlorides of iron and boron were sublimated (Boiling point of the FeCl<NUM> is <NUM>, boiling point of the BCl<NUM> is -<NUM>) and rare earth metals chlorides remain in the residual clinker (Boiling point of the NdCl<NUM> is <NUM>, boiling point of the PrCl<NUM> is <NUM>). Rare earth metals chlorides and Dy<NUM>O<NUM> were formed of the solid powder clinker (Melting point of the NdCl<NUM> is <NUM>, melting point of the PrCl<NUM> is <NUM>, melting point of the Dy<NUM>O<NUM> is <NUM>). Air was added to the top part of the reactor for iron chloride oxidation in accordance with reaction (<NUM>): <MAT>.

Chlorine was obtained by reaction (<NUM>) 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 was removed from the furnace and broken. The final product (solid NdCl<NUM> - PrCl<NUM> 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) (<FIG> and Table <NUM>).

The resulting rare earth metals chlorides can be easily processed by electrolysis of the molten salts for metallic rare earth metals production [<NUM>-<NUM>].

Claim 1:
A method for electrolytic atomic hydrogen decrepitation of a ferromagnetic alloy, wherein the method comprises an electrolytic reaction by providing an applied potential between an anode and a cathode, wherein the ferromagnetic alloy is connected to the cathode, producing atomic hydrogen at the cathode, wherein the ferromagnetic alloy is scattered by the atomic hydrogen to obtain a ferromagnetic alloy powder.