Systems and methods of extracting rare earth metals from waste

Abstract

A method of extracting rare earth metals from a rare earth metal-iron alloy waste can include providing a particulate rare earth metal-iron alloy-containing waste and mixing the particulate waste with an extraction solution. This can solubilize metals in the particulate waste to form a solubilized metal solution. The extraction solution can include an acid, a chelator having a coordination number of at least 2, and a volatile salt. An iron compound can be precipitated from the solubilized metal solution to form an iron precipitate in a rare earth metal solution. The iron precipitate can be separated from the rare earth metal solution.

Description

[0001] SYSTEMS AND METHODS OF EXTRACTING RARE EARTH METALS FROM WASTE

[0002] PRIORITY DATA

[0003] This application claims the benefit of United States Provisional Patent Application Serial No. 63 / 520,331, filed August 17, 2023, which is incorporated by reference.

[0004] BACKGROUND

[0005] Rare earth metals are used in a variety of applications, such as rare earth magnets, cellular telephones, hard drives, electric vehicles, flat screen displays, lasers, and others. The rare earth metals include the fifteen lanthanides and scandium and yttrium. Rare earth metals are often included in alloys with other metals. For example, neodymium magnets include the rare earth metal neodymium in an alloy with iron and boron. Many of the products that include rare earth metals have a limited life space. A significant amount of rare earth metals are discarded in magnetic waste and electronic waste. Because of the many uses for rare earth metals, it would be useful to recycle the rare earth metals contained in such waste. However, separating rare earth metals from alloys with other metals can be difficult. In particular, previous methods for separating rare earth metals from iron have often been expensive or environmentally unfriendly.

[0006] SUMMARY

[0007] A method of extracting rare earth metals from a rare earth metal-iron alloy waste can include providing a particulate rare earth metal-iron alloy-containing waste. The particulate waste can be mixed with an extraction solution to solubilize metals in the particulate waste to form a solubilized metal solution. The extraction solution can include an acid, a chelator having a coordination number of at least 2, and a volatile salt. The method can also include precipitating an iron compound from the solubilized metal solution to form an iron precipitate in a rare earth metal solution. The iron precipitate can be separated from the rare earth metal solution.

[0008] Another method of separating a rare earth metals from a rare earth metal-iron alloycontaining waste can include dissolving metals from a particulate rare earth metal-iron alloy-containing waste using an acid. Iron can be chelated from the particulate rare earth metal-iron alloy-containing waste using a chelator. Undissolved solids can be filtered. Then, iron can be converted to an iron precipitate, and the iron precipitate can be flocculated. The flocculated iron precipitate can be filtered out. The remaining dissolved metals can be dried to form a dried rare earth metal-containing solid. The dried solid can then be heated to vaporize organic material and to form a rare earth metal oxide.

[0009] A system for extracting rare earth metals from a rare earth metal-iron alloy water can include a dissolution vessel. The dissolution vessel can contain a particulate rare earth metal-iron alloy-containing waste in an extract solution. The extract solution can include an acid to dissolve metals from the particulate waste, a chelator having a coordination number of at least 2 to chelate iron from the particulate waste, and a volatile salt. The system can also include an agitator to agitate the extraction solution in the dissolution vessel; a precipitating reactant to precipitate iron when added to the extraction solution; a filter having a particle retention size from about 0.05 mm to about 1 mm to filter out an iron precipitate from the extraction solution, and a heater to heat the extraction solution. The heater can dry dissolved rare earth metals, vaporize organic material, oxidize rare earth metals, or a combination thereof.

[0010] Additional features and advantages of these principles will be apparent from the following detailed description, which illustrates, by way of example, features of the invention.

[0011] BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a flowchart illustrating an example method of extracting rare earth metals from a rare earth metal-iron alloy waste in accordance with an example of the present technology.

[0013] FIG. 2 is a flowchart illustrating another example method of extracting rare earth metals from a rare earth metal-iron alloy waste in accordance with an example of the present technology.

[0014] FIG. 3 is a flowchart illustrating another example method of extracting rare earth metals from a rare earth metal-iron alloy waste in accordance with an example of the present technology.

[0015] FIG. 4 is a schematic of an example system for extracting rare earth metals from a rare earth metal-iron alloy waste in accordance with an example of the present technology. It should be noted that the figures are merely exemplary of several embodiments and no limitations on the scope of the present invention are intended thereby. Further, the figures are generally not drawn to scale, but are drafted for purposes of convenience and clarity in illustrating various aspects of the invention.

[0016] DETAILED DESCRIPTION

[0017] Reference will now be made to exemplary embodiments and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Alterations and further modifications of the inventive features described herein, and additional applications of the principles of the invention as described herein, which would occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of the invention. Further, before particular embodiments are disclosed and described, it is to be understood that this invention is not limited to the particular process and materials disclosed herein as such may vary to some degree. It is also to be understood that the terminology used herein is used for the purpose of describing particular embodiments only and is not intended to be limiting, as the scope of the present invention will be defined only by the appended claims and equivalents thereof.

[0018] Definitions

[0019] In describing and claiming the present invention, the following terminology will be used.

[0020] The singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. Thus, for example, reference to “a particle” includes reference to one or more of such structures, “a metal” includes reference to one or more of such materials, and “a mixing step” refers to one or more of such steps.

[0021] As used herein, “soluble” refers to a material that dissolves in a particular solvent in an amount of at least 5 wt%. Similarly, “insoluble” refers to a material that does not dissolve at all in a particular solvent or dissolves slightly in an amount less than 5 wt%. As used herein, “solubilize” refers to an action of increasing the solubility of a material, or in other words, making the material more soluble.

[0022] As used herein, “substantial” when used in reference to a quantity or amount of a material, or a specific characteristic thereof, refers to an amount that is sufficient to provide an effect that the material or characteristic was intended to provide. The exact degree of deviation allowable may in some cases depend on the specific context. Similarly, “substantially free of” or the like refers to the lack of an identified element or agent in a composition. Particularly, elements that are identified as being “substantially free of’ are either completely absent from the composition, or are included only in amounts which are small enough so as to have no measurable effect on the composition.

[0023] As used herein, “about” refers to a degree of deviation based on experimental error typical for the particular property identified. The latitude provided the term “about” will depend on the specific context and particular property and can be readily discerned by those skilled in the art. The term “about” is not intended to either expand or limit the degree of equivalents which may otherwise be afforded a particular value. Further, unless otherwise stated, the term “about” shall expressly include “exactly,” consistent with the discussion below regarding ranges and numerical data.

[0024] Concentrations, dimensions, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited, including express support therefor. For example, a range of about 1 to about 200 should be interpreted to include not only the explicitly recited limits of 1 and 200, but also to include individual sizes such as 2, 3, 4, and sub-ranges such as 10 to 50, 20 to 100, etc. This same principle applies for open-end ranges. For example, a numerical range of below 100 should be interpreted to include and provide express support for each number below 100 (e.g. 99, 98, 97 4, 3, 2, 1, etc.) as well as any and all sub-ranges, such as 50-90, 0-25, etc.)

[0025] As used herein, the term “at least one of’ is intended to be synonymous with “one or more of.” For example, “at least one of A, B and C” explicitly includes only A, only B, only C, and combinations of each.

[0026] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary.

[0027] Methods of Extracting Rare Earth Metals from Rare Earth Metal-Iron Alloy Waste

[0028] The present disclosure describes methods of extracting rare earth metals from waste. In particular, the methods can be used to extract rare earth metals from waste that contains rare earth metal-iron alloys. The methods utilize a combination of mechanical processes and chemical processes to separate rare earth metals from iron in an efficient and environmentally friendly way. In some examples, mechanical processes can include forming particles of rare earth metal-iron alloy-containing waste with a particle size that increases the reaction rates of chemical reactions involved in the methods. Other mechanical processes that play a role in these methods include filtering using filters with appropriate particle retention sizes to remove undissolved solids at particular points during the method. The methods also involve chemical reactions such as leaching, chelation, precipitation, flocculation, oxidization, and others. The methods described herein have been found to be surprisingly effective for separating rare earth metals from waste that contains rare earth metal-iron alloys.

[0029] In one example, a method of extracting rare earth metals from a rare earth metal- iron alloy waste can include providing a particulate rare earth metal-iron alloy-containing waste. The particulate waste can be mixed with an extraction solution to solubilize metals in the particulate waste to form a solubilized metal solution. The extraction solution can include an acid, a chelator having a coordination number of at least 2, and a volatile salt. The method can further include precipitating an iron compound from the solubilized metal solution to form an iron precipitate in a rare earth metal solution. The iron precipitate can be separated from the rare earth metal solution.

[0030] FIG. 1 is a flowchart illustrating one example method 100 in accordance with the present disclosure. This method includes steps of providing a particulate rare earth metal- iron alloy-containing waste 110; mixing the waste with an extraction solution to solubilize metals 120; precipitating an iron compound 130; and separating the iron compound from the solution 140. The extraction solution used in this method can include any of the ingredients described herein. Another, more detailed example method is illustrated in FIG. 2. This figure shows a flowchart of an example method 200 that includes the input of a particulate waste 210 and an extraction solution 212, which are mixed 220 to solubilize metals using acid and a chelator in the extraction solution. This solution is then filtered 250 to remove undissolved solids 252. An oxidizing agent 232 is added to cause iron to precipitate 230 as an iron precipitate. A flocculator 262 is added to flocculate 260 the iron precipitate. The solution is then filtered 240 to remove the flocculated and precipitated iron. The remaining solution is heated to dry the dissolved rare earth metals and to form rare earth metal oxides 270.

[0031] Another example method of separating a rare earth metal from a particulate rare earth metal-iron alloy-containing waste can include the following steps: dissolving metals from a particulate rare earth metal-iron alloy-containing waste using an acid; chelating iron from the particulate rare earth metal-iron alloy-containing waste using a chelator; filtering out undissolved solids; converting the iron to an iron precipitate; flocculating the iron precipitate; filtering out the flocculated iron precipitate; drying remaining dissolved metals to form a dried rare earth metal-containing solid; and heating the dried solid to vaporize organic material and to form a rare earth metal oxide.

[0032] FIG. 3 is a flowchart illustrating another example method 300 of extracting rare earth metals from a rare earth metal-iron alloy waste. This method includes: dissolving metals from a particulate rare earth metal-iron alloy-containing waste using an acid 310; chelating iron using a chelator 320; filtering out undissolved solids 330; converting iron to an iron precipitate 340; flocculating the iron precipitate 350; filtering out the flocculated iron precipitate 360; drying remaining dissolved metals to form a solid 370; and heating the dried solid to vaporize organic material and form a rare earth metal oxide.

[0033] It is noted that the figures described above are merely examples of the methods encompassed by the present disclosure. Methods according to the present disclosure can include any combination of the steps, processes, and limitations of any of the above examples or any of the more detailed examples described below.

[0034] The methods can be used for a variety of waste materials that include rare earth metal alloys. The methods can be particularly useful for waste materials that include a rare earth metal-iron alloy. Examples of products that may include rare earth metal-iron alloys include neodymium magnets, electric motors, smartphones, automobile parts, medical devices, lasers, speakers, and many others. Neodymium magnets can vary in their content of various metals. Many neodymium magnets include the elements neodymium, iron, and boron. For example, these elements can be present as the alloy NdzFeuB. Other elements may also be included in neodymium magnets, such as terbium, dysprosium, presidium, cobalt, gallium, nickel, aluminum, titanium, molybdenum, vanadium, and others. In some examples, multiple rare earth metals can be recovered by processing waste materials using he methods described here.

[0035] The waste material can be prepared by converting the waste to a particulate form. Any suitable method can be used to form the particulate waste, such as by grinding larger pieces of waste material. Neodymium magnets can be brittle, and therefore can be conveniently ground into a powder. The particle size can influence the rate of reaction when dissolving metals from the particulate waste. Reducing the particles to a smaller size can increase the reaction rate. In some examples, an average particle size of the particulate waste can be less than about 3 mm. Using particle sizes over 3 mm may result in long reaction times. In further examples, the average particle size can be less than about 2 mm, less than about 1 mm, from about 0.1 mm to about 1 mm, from about 0.1 mm to about 0.7 mm, from about 0.1 mm to about 0.5 mm, or from about 0. 1 mm to about 0.3 mm.

[0036] The amount of waste added to the extraction solution can be from about 1 kg of waste per 10 L of extraction solution to about 1 kg of waste per about 1 L of extraction solution. In further examples, the amount can be from about 1 kg of waste per 5 L of extraction solution to about 1 kg of waste per 1 L of extraction solution, or from about 1 kg of waste per 2 L of extraction solution to about 1 kg of waste per 1 L of extraction solution. In further examples, a weight ratio of the particulate waste to the extraction solution can be from about 1:5 to about 1:1, or from about 1:2 to about 1:1.

[0037] Particulate waste can be mixed with the extraction solution using an agitator to increase contact between the waste particles and the liquid solution. In some examples, the agitator can be sufficient to prevent clumping of the waste particles. A stir bar can be used in certain examples. The stir bar can stir the mixture at a speed of about 1,000 rpm or greater, or about 2,000 rpm or greater, or from about 1,000 rpm to about 2,000 rpm, or from about 1,000 rpm to about 3,000 rpm, or from about 1,000 rpm to about 4,000 rpm, or from about 1,000 rpm to about 5,000 rpm, in some examples.

[0038] The particulate waste and extraction solution can be agitated for a time period sufficient to dissolve or leach metals in the particulate waste. In some examples, the dissolving time can be from about 30 minutes to about 12 hours, or from about 1 hour to about 12 hours, or from about 2 hours to about 12 hours, or from about 2 hours to about 8 hours, or from about 1 hour to about 8 hours.

[0039] The temperature of the particular waste and the extraction solution can also affect the dissolution rate of the metals. In some examples, the mixture of particulate waste and extraction solution can be at a temperature from about 100 °C to about 350 °C, or from about 100 °C to about 300 °C, or from about 100 °C to about 250 °C, or from about 100 °C to about 200 °C, or from about 150 °C to about 350 °C, or from about 150 °C to about 300 °C, or from about 150 °C to about 250 °C, or from about 150 °C to about 200 °C. In other examples, the mixture of particulate waste and extraction solution can be at a temperature below about 100 °C. In some embodiments, the temperature can be from about 5 °C to about 100 °C. In other embodiments, the temperature can be below about 75 °C, 50 °C, or 25 °C. In another embodiment, the temperature can be from about 5 °C to about 25 °C. The temperature can be held at a single temperature or fluctuated among various temperatures in these ranges during the agitation period to help the metals dissolve.

[0040] In the extraction solution, an acid can be included to dissolve the metals in the particulate waste. Without being bound to a specific mechanism, in some examples the acid can react with rare earth metals and iron to convert the metals into ions that can be soluble in the extraction solution. In some examples, the acid can supply protons that receive an electron from a metal atom in the particulate waste, raising the oxidation state of the metal and converting the proton to hydrogen. Accordingly, hydrogen gas may be formed during this process. The hydrogen gas can be recovered, if desired, and may be an additional valuable product produced by the process.

[0041] In certain examples, the particulate waste can include the alloy Nd2Fei4B. An acid can provide protons to react with this alloy according to the following reaction [1]:

[0042] Nd2Fei4B(s) + 37 H+(aq) 2 Nd3+(aq) + 14 Fe2+(aq) + B3+(aq) + 18 i H2(g) [1]

[0043] In some examples, the acid used can be acetic acid. The acetate anion can remain in the solution after the acetic acid reacts with the metal in the particulate waste. Thus, some of the neodymium can be in the form of neodymium acetate. The iron can also be in the form of iron(II) acetate after dissolving with acetic acid. In further examples, the extraction solution can also include ammonium acetate, which can also supply acetate anions in the solution.

[0044] The amount of acid in the extraction solution can be from about 5 wt% to about 25 wt%, or from about 10 wt% to about 20 wt%, or from about 15 wt% to about 20 wt%, or from about 15 wt% to about 25 wt%. In certain examples, the amount of acid can be sufficient to provide a pH from about 3 to about 7, or from about 4 to about 7, or from about 4 to about 6, or from about 4 to about 5. Additionally, the pKa of the acid can be from about 4 to about 7 in some examples, or from about 4 to about 6, or from about 4 to about 5. In addition to acetic acid, other acids that can be used include monocarboxylic acids and inorganic acids. Specific examples can include propionic acid, butyric acid, valeric acid, and others.

[0045] In some examples, the pH of the extraction solution can change throughout the processes described herein. For example, the pH can increase, decrease, or both during the dissolution of the metals from the particulate waste. In some examples, the extraction solution can have an initial pH from about 3 to about 7, and then the pH can increase during the dissolution process to a maximum pH from about 7 to about 11. In further examples, the pH can increase temporarily during the dissolution process and then decrease again.

[0046] During the dissolution process, the acid can react with rare earth metals to form rare earth metal oxides, rare earth metal salts, or a combination thereof. As an example, acetic acid can react with neodymium to from neodymium oxide, neodymium acetate (salt), or a combination of both. If rare earth metal salts, such as neodymium acetate, form during this process, then these salts can be converted to rare earth metal oxide during the baking step described in more detail below.

[0047] The extraction solution can also include a chelator. The chelator can be a molecule capable of coordinating with a metal ion at least two coordination sites. Thus, the chelator can have two coordination sites in some examples, while in other examples the chelator can have three coordination sites, four coordination sites, five coordination sites, six coordination sites, or another number of coordination sites greater than two. In one example, the chelator can have a minimum of four coordination sites. Without being bound to a specific mechanism, in some examples the chelator can coordinate with rare earth metal in the particulate waste, or with iron, or with other metals in the particulate waste, or a combination thereof. In certain examples, multiple chelators can be included and different chelators can be adapted to coordinate with different metals in the particulate waste. In certain examples, the extraction solution can include a chelator with two coordination sites and a chelator with six coordination sites. In other examples, the extraction solution can include a chelator with three coordination sites and a chelator with six coordination sites.

[0048] Some examples of chelators that can be used include citric acid, oxalic acid, malonic acid, 2-hydroxymalonic acid, methyl malonic acid, fumaric acid, succinic acid, 1,2- dimethyl succinic acid, maleic acid, itaconic acid, citraconic acid, glutaric acid, adipic acid, malic acid, pimelic acid, carboxy succinic acid, tricarballylic acid, 2-methyl tricarballylic acid, aconitic acid, 1,2,4-butane tricarboxylic acid, and combinations thereof.

[0049] The chelator can be included in the extraction solution in a relatively small amount. In some examples, the amount of chelator can be from about 0.5 wt% to about 2 wt% with respect to the total liquid weight of the extraction solution. In further examples, the amount of chelator can be from about 0.5 wt% to about 1.5 wt%, or from about 0.5 wt% to about 1 wt%, or from about 1 wt% to about 2 wt%. When multiple chelators are included, these amounts can be the individual amounts of each individual chelator, or these amounts can be the total amount of all chelators combined.

[0050] The extraction solution can also include a volatile salt. The volatile salt can be a salt that can vaporize at the temperatures encountered in the methods described herein. For example, the volatile salt can be vaporized during the drying or the baking steps of the methods described herein. The volatile salt can act as a buffer in the extraction solution and they can provide anions that can form salts with metal ions originating from the particulate waste. The volatile salt can include an anion that is the conjugate base of the acid that is used in the extraction solution. In some examples, ammonium acetate can be included as the volatile salt. In other examples, the volatile salt can include ammonium carbonate, ammonium bicarbonate, ammonium formate, pyridinium acetate, pyridinium formate, or others. In some examples, the amount of volatile salt in the extraction solution can be from about 3 wt% to about 15 wt%, or from about 5 wt% to about 15 wt%, or from about 10 wt% to about 15 wt%, or from about 8 wt% to about 12 wt%, with respect to the liquid weight of the extraction solution.

[0051] A defoamer can also be added to the extraction solution. The defoamer can reduce foaming while the extraction solution is agitated during the dissolution of metals in the particulate waste. A variety of defoamers can be used, such as mineral oil-based defoamers, vegetable oil-based defoamers, polydimethylsiloxanes, and others. The defoamer can be added in a small amount, such as about 0.01 wt% to about 1 wt%, or from about 0.05 wt% to about 0.5 wt%.

[0052] After metals have been dissolved in the extraction solution, some undissolved solids may still be present in the extraction solution. These solids can include metals that were not dissolved by the acid, non-metal materials such as polymeric materials, and others. The solids can be removed by passing the extraction solution through a filter, such as a mesh filter, filter paper, or other type of filter. The filter can have a particle retention size smaller than the initial particle size of the particulate waste. In some examples, the filter can have a particle retention size from about 1 pm to about 5 pm, or from about 2 pm to about 5 pm, or from about 3 pm to about 5 pm.

[0053] The liquid filtrate can include dissolved rare earth metal and iron. In order to remove the iron from this solution, a precipitating reactant can be added that can precipitate the iron without precipitating the rare earth metal. In some examples, the precipitating reactant can be a oxidizing agent that can oxidize Fe2+to Fe3+. In certain examples, the precipitating reactant can be hydrogen peroxide. The hydrogen peroxide can oxidize Fe2+to Fe3+, and the Fe3+can react with other components present to form solid precipitate particles. In some examples, the precipitate particles can be iron oxide, iron acetate, or a combination thereof. The amount of the precipitating reactant added can be from about 0.5 wt% to about 2 wt%, or from about 0.5 wt% to about 1.5 wt%, or from about 0.5 wt% to about 1 wt%, or from about 1 wt% to about 2 wt%.

[0054] Other metals can also precipitate similar to iron. Aluminum, if present, can precipitate as aluminum oxide when an oxidizing agent is added. Nickel, if present, can precipitate as nickel hydroxide. Nickel hydroxide can form in the presence of ammonium ions. Other metals can also form insoluble precipitates at this stage of the method.

[0055] The iron precipitate and other precipitates may be removed at this point by filtering or another separation process. Alternatively, the precipitate can be flocculated to increase particle size of the solid particles. A variety of flocculating agents can be used, such as starches, electrolytes capable of neutralizing the charge of Fe3+, lyophilic polymers, carboxymethyl cellulose, bentonite, detergents, polyoxyethylated nonylphenols, and others. In certain examples, the flocculating agent can include a starch. In further examples, the starch can be treated with a base to convert side chains of the starch to salts. For example, com starch can be treated with a base such as sodium hydroxide or potassium hydroxide. A flocculating starch solution can be prepared by suspending corn starch in water and adding the base. The starch solution can also be blended at high shear and high speed using a blender to form small particles and reduce the viscosity of the starch solution. This blending can be at a speed from about 1,000 rpm to about 5,000 rpm, or from about 1,000 to about 4,000 rpm, or from about 2,000 rpm to about 4,000 rpm, in some examples. The blending can be performed for a period of a few minutes, such as about 5 minutes to about 15 minutes.

[0056] The amount of flocculating agent added to the solution with the iron precipitate can be relatively small. For example, the flocculating agent, such as starch or base-treated starch, can be added to the solution in an amount from about 0.001 wt% to about 0.1 wt%, or from about 0.002 wt% to about 0.01 wt%. The solution can also be agitated after adding the flocculating agent. This can be performed using a blender at high speed, such as from about 1,000 rpm to about 5,000 rpm or from about 1 ,000 to about 4,000 rpm, or from about 2,000 rpm to about 4,000 rpm, in some examples. Again, the blending can be performed for a period of a few minutes, such as about 5 minutes to about 15 minutes.

[0057] The flocculated precipitates can be removed by filtering or another separation process. Other separation processes for separating solids from the liquid can include centrifugation, settling, floating, and others. In one example, the flocculated precipitates can be filtered out by passing the mixture through a filter with a particle retention size from about 0.05 mm to about 1 mm, or from about 0.1 mm to about 1 mm, or from about 0.2 mm to about 1 mm, or from about 0.2 mm to about 0.5 mm. If solid particles remain in the liquid after filtering, the liquid can be filtered a second time with the same filter or with a different filter having a smaller particle retention size.

[0058] After removing precipitates, the solution can contain dissolved rare earth metals. This solution can then be dried to remove water, forming a rare earth metal-containing solid. Drying can be accomplished by air drying, hot air drying, using a drying oven, infrared lamps, or other drying processes. The mass of the mixture can decrease as water is lost by drying. Drying can be performed for a drying time from about 1 hour to about 7 days, or from about 1 hour to about 2 days, or from about 1 hour to about 24 hours, or from about 1 hour to about 12 hours, or from about 1 hour to about 8 hours. The dried solid can then be baked at a higher temperature to form a rare earth metal oxide. The baking process can remove any remaining water, and the temperature can be high enough to burn off or evaporate any organic solid material and other volatile material in the dried solid. Any temperatures sufficient to accomplish such objectives can be used in view of the particular materials involved. As an example, if the dried solid contains neodymium acetate, then the acetate can be vaporized during the baking process. The baking can be performed in the present of oxygen so that the rare earth metals can be oxidized, if they are not in form of oxides already. In some examples, the baking temperature can be above about 50 °C, 75 °C, 100 °C, 200 °C, 300 °C, or above about 400 °C, or above about 500 °C, or from about 400 °C to about 600 °C. In short, any suitable temperature between 50 °C and 500 °C can be used as needed in view of the particular solvent or other materials involved.

[0059] The final solid product, after baking, can include a substantial amount of rare earth metal oxides. In some examples, the final solid product can include at least 50 wt% rare earth metal oxides, or at least 60 wt% rare earth metal oxides, or at least 70 wt% rare earth metal oxides, or at least 80 wt% rare earth metal oxides, or at least 90 wt% rare earth metal oxides. This product can be used or sold as a rare earth metal-enriched solid material.

[0060] Methods of extracting rare earth metal from waste materials are described above. The present disclosure also describes systems for extracting rare earth metals from rare earth metal-iron alloy-containing waste. Such systems can include the equipment used to perform any of the methods described herein. In one example, a system for extracting rare metals from a rare earth metal-iron alloy waste can include a dissolution vessel containing a particulate rare earth metal-iron alloy-containing waste in an extraction solution. The extraction solution can include an acid to dissolve metals from the particulate waste, a chelator having a coordination number of at least 2 to chelate iron from the particulate waste, and a volatile salt. The system can also include an agitator to agitate the extraction solution in the dissolution vessel. A precipitating react can also be a part of the system. The precipitating reactant can be capable of precipitating iron when added to the extraction solution. The system can also include a filter having a particle retention size from about 1 pm to about 5 pm to filter out an iron precipitate from the extraction solution. A heater can also be included to heat the extraction solution, to dry dissolved rare earth metals, to vaporize organic material, to oxidize rare earth metals, or a combination thereof. FIG. 4 shows an example system 400. This system includes a dissolution vessel 402 filled with a mixture of particulate rare earth metal-iron alloy-containing waste 410 and an extraction solution 412. The system also include a magnetic stir bar 420 and stir base 422 that act as the agitator to agitate the extraction solution while the metals in the waste are dissolving. This example includes a hydrogen recovery unit 430 over the dissolution vessel, the hydrogen recovery unit can be configured to collect hydrogen that is produced by chemical reactions in the extraction solution. A precipitating reactant 440 is included, which can be added to the extraction solution to cause iron to precipitate. A blender 450 is also included, which can be used to prepare a starch solution for flocculation and also to blend the flocculated iron particles. The solution of dissolved metal can be placed in the blender after the iron has precipitated, as shown by the arrow in the figure. The system also includes a filter 460 with a particle retention size from about 1 pm to about 5 pm to filter out an iron precipitate from the extraction solution. The solution can be passed from the blender through the filter as shown by the arrow in the figure. The filtered liquid can then be dried in an oven 470, which can also be used to bake the dried solid to vaporize organic material and to oxidize rare earth metals.

[0061] It is noted that this figure shows merely one example of a system according to the present disclosure. In further examples, systems can include any of the equipment, compositions, and features described herein. Descriptions of methods can be applicable to the systems as the systems can include any equipment used to perform the methods.

[0062] Examples

[0063] Powdered magnetic waste (1 kg) was suspended in 5 liters of extraction solution. The extraction solution consisted of water and 15% acetic acid, 10% ammonium acetate, and 1% citric acid, with 1 mL of defoamer added. The pH of the extraction solution was about 4. This mixture was stirred at 1,000 rpms for 2 hours. The mixture was then filtered through filter paper having a particle retention size of 2.7 pm to remove any undissolved solids.

[0064] Hydrogen peroxide (H2O2) was added to the filtrate to adjust the filtrate to 1% H2O2 and the solution was allowed to stand for 2 hours. The hydrogen peroxide oxidized iron in the solution, causing the iron to precipitate out of solution as ferric acetate. The solution also contained neodymium acetate, which is soluble in water. Thus, the neodymium acetate remained in solution.

[0065] 0.5 gram of a starch solution was then added. The starch solution was prepared by mixing 40 grams / liter of corn starch in distilled water with an equal volume of 1 N sodium hydroxide. The sodium hydroxide converted side chains of the corn starch to salts. After the starch solution was added to the extraction solution, the extraction solution was blended in a blender at high speed (4,000 rpm) for 10 min. The corn starch solution acted as a flocculator to flocculate the iron precipitate. The flocculated iron precipitate was then removed by filtering with a filter having a particle retention size of 0.05 mm.

[0066] The remaining solution contained dissolved neodymium. The solution was then dried under infrared heat lamps, forming a dry solid. The solid was then baked at 500 °C for 2 hours to vaporize organic material in the solid. Any other volatile materials were also vaporized and removed during baking. The baking also oxidized the neodymium, forming neodymium oxide. If the original waste material included other rare earth metals such as terbium or dysprosium, these will also be present as oxides in the final solid. This solid can be used or sold as a rare earth metal-enriched composition.

[0067] Example Embodiments

[0068] The following examples pertain to specific invention embodiments and point out specific features, elements, or steps that can be used or otherwise combined in achieving such embodiments.

[0069] In Example 1 there is provided a method of extracting rare earth metals from a rare earth metal-iron alloy waste, comprising: providing a particulate rare earth metal-iron alloy-containing waste; mixing the particulate waste with an extraction solution to solubilize metals in the particulate waste to form a solubilized metal solution, wherein the extraction solution comprises an acid, a chelator having a coordination number of at least 2, and a volatile salt; precipitating an iron compound from the solubilized metal solution to form an iron precipitate in a rare earth metal solution; and separating the iron precipitate from the rare earth metal solution.

[0070] In Example 2, the method of Example 1 further comprises drying the rare earth metal solution to form a dried solid. In Example 3, the method of any of examples 1-2, further comprises baking the dried solid at a temperature above about 300 °C to form a rare earth metal oxide.

[0071] In Example 4, the particulate waste in any of examples 1-3 comprises magnet waste.

[0072] In Example 5, the rare earth metal-iron alloy in any of examples 1-4 comprises neodymium, iron, and boron.

[0073] In Example 6, the rare earth metal-iron alloy in any of examples 1-5 further comprises terbium, dysprosium, presidium, or a combination thereof.

[0074] In Example 7, the particulate waste in any of examples 1-6 has an average particle size less than about 3 mm.

[0075] In Example 8, the particulate waste in any of example 1-7 has an average particle size from about 0.1 mm to about 0.7 mm.

[0076] In Example 9, the mixing the particulate waste with the extraction solution in any of examples 1-8 comprises stirring the extraction solution.

[0077] In Example 10, the stirring in any of examples 1-9 is done using a stir bar at a speed of at least 1000 rotations per minute.

[0078] In Example 11, the stirring in any of examples 1-10 is performed for a time period from about 1 hour to about 8 hours.

[0079] In Example 12, the extraction solution in any preceding example has a temperature below about 100 °C during the stirring.

[0080] In Example 13, the extraction solution of any preceding example has a pH from about 4 to about 11.

[0081] In Example 14, a weight ratio of the particulate waste to the extraction solution of any preceding example is from about 1:5 to about 1: 1.

[0082] In Example 15, the acid of any preceding example comprises a monocarboxylic acid or an inorganic acid.

[0083] In Example 16, the acid of any preceding example comprises acetic acid, butyric acid, or a combination thereof.

[0084] In Example 17, the chelator of any preceding example comprises citric acid, oxalic acid, malonic acid, 2-hydroxymalonic acid, methyl malonic acid, fumaric acid, succinic acid, 1,2-dimethyl succinic acid, maleic acid, itaconic acid, citraconic acid, glutaric acid, adipic acid, malic acid, pimelic acid, carboxy succinic acid, tricarballylic acid, 2-methyl tricarballylic acid, aconitic acid, 1 ,2,4-butane tricarboxylic acid, or a combination thereof.

[0085] In Example 18, the volatile salt of any preceding example comprises an anion that is a conjugate base of the acid.

[0086] In Example 19, the volatile salt of any preceding example comprises ammonium acetate.

[0087] In Example 20, the extraction solution of any preceding example comprises the acid in an amount from about 5 wt% to about 20 wt%, the chelator in an amount from about 0.5 wt% to about 2 wt%, and the volatile salt in an amount from about 3 wt% to about 15 wt%.

[0088] In Example 21, the extraction solution of any preceding example further comprises a defoamer.

[0089] In Example 22, the extraction solution of any preceding example further comprises a second chelator having a coordination number of 6.

[0090] In Example 23, the method of any preceding example further comprising filtering the solubilized metal solution to remove solids.

[0091] In Example 24, the filtering of any preceding example is performed using a filter with a particle retention size from about 1 pm to about 5 pm.

[0092] In Example 25, precipitating the iron compound in any preceding example comprises adding hydrogen peroxide to the solubilized metal solution.

[0093] In Example 26, the hydrogen peroxide is added in any preceding example in amount of about 0.5 wt% to about 2 wt% with respect to a liquid weight of the solubilized metal solution.

[0094] In Example 27, the method of any preceding example further comprises flocculating the iron precipitate before separating the iron precipitate from the rare earth metal solution.

[0095] In Example 28, the flocculating the iron precipitate of any preceding example comprises adding a starch solution to the rare earth metal solution. In Example 29, the starch solution of any preceding example comprises corn starch and a base selected from the group consisting of sodium hydroxide, potassium hydroxide, and combinations thereof.

[0096] In Example 30, flocculating the iron precipitate in any preceding example further comprises blending the rare earth metal solution.

[0097] In Example 31, separating the iron precipitate in any preceding example comprises filtering the rare earth metal solution.

[0098] In Example 32, the filtering of any preceding example is performed using a filter with a particle retention size from about 0.05 mm to about 1 mm.

[0099] In Example 33, the method of any preceding example further comprises precipitating aluminum from the solubilized metal solution.

[0100] In Example 34, the method of any preceding example further comprises removing nickel rom the solubilized metal solution.

[0101] In Example 35, the method of any preceding example further comprises recovering hydrogen gas from the solubilized metal solution.

[0102] In Example 36, there is provided a method of separating a rare earth metal from a particulate rare earth metal-iron alloy-containing waste, comprising: dissolving metals from a particulate rare earth metal-iron alloy-containing waste using an acid; chelating iron from the particulate rare earth metal-iron alloy-containing waste using a chelator; filtering out undissolved solids; converting the iron to an iron precipitate; flocculating the iron precipitate; filtering out the flocculated iron precipitate; drying remaining dissolved metals to form a dried rare earth metal-containing solid; and heating the dried solid to vaporize organic material and to form a rare earth metal oxide.

[0103] In Example 37, heating the dried solid of example 36 comprises baking the dried solid at a temperature above about 300 °C.

[0104] In Example 38, the particulate waste in either of examples 36-37 comprises magnet waste.

[0105] In Example 39, the rare earth metal-iron alloy of any of examples 36-38 comprises neodymium, iron, and boron.

[0106] In Example 40, the rare earth metal-iron alloy of any of examples 36-39 further comprises terbium, dysprosium, presidium, or a combination thereof. In Example 41, the particulate waste of any of examples 36-40, has an average particle size less than about 3 mm.

[0107] In Example 42, the particulate waste any of examples 36-41has an average particle size from about 0.1 mm to about 0.7 mm.

[0108] In Example 43, the dissolving metals from the particulate rare earth metal-iron alloy-containing waste in any of examples 36-42 comprises stirring the particulate waste in an extraction solution that includes the acid.

[0109] In Example 44, the stirring of any of examples 36-43 is done using a stir bar at a speed of at least 1000 rotations per minute.

[0110] In Example 45, the stirring of any of examples 36-44 is performed for a time period from about 1 hour to about 8 hours

[0111] In Example 46, the extraction solution of any of examples 36-45 has a temperature below about 100 °C during the stirring.

[0112] In Example 47, the extraction solution of any of examples 36-46, has a pH from about 4 to about 11.

[0113] In Example 48, a weight ratio of the particulate waste to the extraction solution of any of examples 36-47 is from about 1:5 to about 1: 1.

[0114] In Example 49, the acid of any of examples 36-48 comprises a monocarboxylic acid or an inorganic acid.

[0115] In Example 50, the acid of any of examples 36-49 comprises acetic acid, butyric acid, or a combination thereof.

[0116] In Example 51, the chelator of any of examples 36-50 comprises citric acid, oxalic acid, malonic acid, 2-hydroxymalonic acid, methyl malonic acid, fumaric acid, succinic acid, 1 ,2-dimethyl succinic acid, maleic acid, itaconic acid, citraconic acid, glutaric acid, adipic acid, malic acid, pimelic acid, carboxy succinic acid, tricarballylic acid, 2-methyl tricarballylic acid, aconitic acid, 1,2,4-butane tricarboxylic acid, or a combination thereof.

[0117] In Example 52, dissolving metals from the particulate rare earth metal-iron alloycontaining waste of any of examples 36-51 comprises mixing the particulate waste with an extraction solution comprising the acid, the chelator, and a volatile salt.

[0118] In Example 53, the volatile salt of any of examples 36-52 comprises an anion that is a conjugate base of the acid. In Example 54, volatile salt of any of examples 36-53, comprises ammonium acetate.

[0119] In Example 55, the extraction solution of any of examples 36-54 comprises the acid in an amount from about 5 wt% to about 20 wt%, the chelator in an amount from about 0.5 wt% to about 2 wt%, and the volatile salt in an amount from about 3 wt% to about 15 wt%.

[0120] In Example 56, the extraction solution of any of examples 36-55 further comprises a defoamer.

[0121] In Example 57, the extraction solution of any of examples 36-56 further comprises a second chelator having a coordination number of 6.

[0122] In Example 58, the undissolved solids of any of examples 36-57 are filtered out using a filter with a particle retention size from about 1 pm to about 5 pm.

[0123] In Example 59, converting the iron to the iron precipitate of any of examples 36- 58 comprises adding hydrogen peroxide to oxidize the iron.

[0124] In Example 60, the hydrogen peroxide of any of examples 36-59 is added in amount of about 0.5 wt% to about 2 wt% with respect to a total weight of liquid present.

[0125] In Example 61, flocculating the iron precipitate of any of examples 36-60 comprises adding a starch solution to the rare earth metal solution.

[0126] In Example 62, the starch solution of any of examples 36-61comprises com starch and a base selected from the group consisting of sodium hydroxide, potassium hydroxide, and combinations thereof.

[0127] In Example 63, flocculating the iron precipitate of any of examples 36-62 further comprises blending.

[0128] In Example 64, filtering out the flocculated iron precipitate of any of examples 36- 63 is performed using a filter with a particle retention size from about 0.05 mm to about 1 mm.

[0129] In Example 65, the method of any of examples 36-64, further comprises precipitating aluminum.

[0130] In Example 66, the method of any of examples 36-65, further comprising removing nickel.

[0131] In Example 67, the method of any of examples 36-66, further comprises recovering hydrogen gas. In Example 68, there is provided a system for extracting rare earth metals from a rare earth metal-iron alloy waste, comprising: a dissolution vessel containing a particulate rare earth metal-iron alloy-containing waste in an extraction solution, wherein the extraction solution comprises an acid to dissolve metals from the particulate waste, a chelator having a coordination number of at least 2 to chelate iron from the particulate waste, and a volatile salt; an agitator to agitate the extraction solution in the dissolution vessel; a precipitating reactant to precipitate iron when added to the extraction solution; a filter having a particle retention size from about 0.05 mm to about 1 mm to filter out an iron precipitate from the extraction solution; a heater to heat the extraction solution, to dry dissolved rare earth metals, to vaporize organic material, to oxidize rare earth metals, or a combination thereof.

[0132] In Example 69, the particulate waste of example 68 comprises magnet waste.

[0133] In Example 70, the rare earth metal-iron alloy of any of examples 68-69 comprises neodymium, iron, and boron.

[0134] In Example 71, the rare earth metal-iron alloy of any of examples 68-70 further comprises terbium, dysprosium, presidium, or a combination thereof.

[0135] In Example 72, the particulate waste of any of examples 68-7 lhas an average particle size less than about 3 mm.

[0136] In Example 73, the particulate waste of any of examples 68-72 has an average particle size from about 0.1 mm to about 0.7 mm.

[0137] In Example 74, the extraction solution of any of examples 68-73 has a pH from about 4 to about 11.

[0138] In Example 75, the acid of any of examples 68-74 comprises a monocarboxylic acid or an inorganic acid.

[0139] In Example 76, the acid of any of examples 68-75 comprises acetic acid, butyric acid, or a combination thereof.

[0140] In Example 77, the chelator of any of examples 68-76 comprises citric acid, oxalic acid, malonic acid, 2-hydroxymalonic acid, methyl malonic acid, fumaric acid, succinic acid, 1,2-dimethyl succinic acid, maleic acid, itaconic acid, citraconic acid, glutaric acid, adipic acid, malic acid, pimelic acid, carboxy succinic acid, tricarballylic acid, 2-methyl tricarballylic acid, aconitic acid, 1,2,4-butane tricarboxylic acid, or a combination thereof. In Example 78, the volatile salt of any of examples 68-77 comprises an anion that is a conjugate base of the acid.

[0141] In Example 79, volatile salt of any of examples 68-78 comprises ammonium acetate.

[0142] In Example 80, the extraction solution of any of examples 68-79 comprises the acid in an amount from about 5 wt% to about 20 wt%, the chelator in an amount from about 0.5 wt% to about 2 wt%, and the volatile salt in an amount from about 3 wt% to about 15 wt%.

[0143] In Example 81, the extraction solution of any of examples 68-80 further comprises a defoamer.

[0144] In Example 82, the extraction solution of any of examples 68-81 further comprises a second chelator having a coordination number of 6.

[0145] In Example 83, the system of any of examples 68-82, further comprises a filter with a particle retention size from about 1 pm to about 5 pm to filter out undissolved solids from the extraction solution before adding the precipitating reactant.

[0146] In Example 84, the precipitating reactant of any of examples 68-83 comprises hydrogen peroxide.

[0147] In Example 85, the system of any of examples 68-84, further comprises a flocculator to flocculate the precipitated iron.

[0148] In Example 86, the flocculator of any of examples 68-85 comprises a starch solution.

[0149] In Example 87, the starch solution of any of examples 68-86 comprises com starch and a base selected from the group consisting of sodium hydroxide, potassium hydroxide, and combinations thereof.

[0150] In Example 88, tThe system of any of examples 68-87, further comprises a blender to blend the flocculated iron.

[0151] In Example 89, the system of any of examples 68-88, further comprises a hydrogen recovery unit to recover hydrogen gas from the dissolution vessel.

[0152] It is to be understood that the above-referenced arrangements are illustrative of the application for the principles of the present invention. Thus, while the present invention has been described above in connection with the exemplary embodiments, it will be apparent to those of ordinary skill in the art that numerous modifications and alternative arrangements can be made without departing from the principles and concepts of the invention as set forth in the claims.

Claims

CLAIMSWhat is claimed is:

1. A method of extracting rare earth metals from a rare earth metal-iron alloy waste, comprising: providing a particulate rare earth metal-iron alloy-containing waste; mixing the particulate waste with an extraction solution to solubilize metals in the particulate waste to form a solubilized metal solution, wherein the extraction solution comprises an acid, a chelator having a coordination number of at least 2, and a volatile salt; precipitating an iron compound from the solubilized metal solution to form an iron precipitate in a rare earth metal solution; and separating the iron precipitate from the rare earth metal solution.

2. The method of claim 1, further comprising drying the rare earth metal solution to form a dried solid.

3. The method of claim 2, further comprising baking the dried solid at a temperature above about 300 °C to form a rare earth metal oxide.

4. The method of claim 1, wherein the particulate waste comprises magnet waste.

5. The method of claim 1, wherein the rare earth metal-iron alloy comprises neodymium, iron, and boron.

6. The method of claim 5, wherein the rare earth metal-iron alloy further comprises terbium, dysprosium, presidium, or a combination thereof.

7. The method of claim 1, wherein the particulate waste has an average particle size less than about 3 mm.

8. The method of claim 7, wherein the particulate waste has an average particle size from about 0.1 mm to about 0.7 mm.

9. The method of claim 1, wherein the mixing the particulate waste with the extraction solution comprises stirring the extraction solution.

10. The method of claim 9, wherein the stirring is done using a stir bar at a speed of at least 1000 rotations per minute.

11. The method of claim 9, wherein the stirring is performed for a time period from about 1 hour to about 8 hours.

12. The method of claim 9, wherein the extraction solution has a temperature below about 100 °C during the stirring.

13. The method of claim 9, wherein the extraction solution has a pH from about 4 to about 11.

14. The method of claim 1, wherein a weight ratio of the particulate waste to the extraction solution is from about 1:5 to about 1:1.

15. The method of claim 1, wherein the acid comprises a monocarboxylic acid or an inorganic acid.

16. The method of claim 15, wherein the acid comprises acetic acid, butyric acid, or a combination thereof.

17. The method of claim 1, wherein the chelator comprises citric acid, oxalic acid, malonic acid, 2-hydroxymalonic acid, methyl malonic acid, fumaric acid, succinic acid, 1,2-dimethyl succinic acid, maleic acid, itaconic acid, citraconic acid, glutaric acid, adipic acid, malic acid, pimelic acid, carboxy succinic acid, tricarballylic acid, 2-methyl tricarballylic acid, aconitic acid, 1,2,4-butane tricarboxylic acid, or a combination thereof.

18. The method of claim 1, wherein the volatile salt comprises an anion that is a conjugate base of the acid.

19. The method of claim 1, wherein the volatile salt comprises ammonium acetate.

20. The method of claim 1, wherein the extraction solution comprises the acid in an amount from about 5 wt% to about 20 wt%, the chelator in an amount from about 0.5 wt% to about 2 wt%, and the volatile salt in an amount from about 3 wt% to about 15 wt%.

21. The method of claim 1, wherein the extraction solution further comprises a defoamer.

22. The method of claim 1, wherein the extraction solution further comprises a second chelator having a coordination number of 6.

23. The method of claim 1, further comprising filtering the solubilized metal solution to remove solids.

24. The method of claim 23, wherein the filtering is performed using a filter with a particle retention size from about 1 pm to about 5 pm.

25. The method of claim 1, wherein precipitating the iron compound comprises adding hydrogen peroxide to the solubilized metal solution.

26. The method of claim 25, wherein the hydrogen peroxide is added in amount of about 0.5 wt% to about 2 wt% with respect to a liquid weight of the solubilized metal solution.

27. The method of claim 1, further comprising flocculating the iron precipitate before separating the iron precipitate from the rare earth metal solution.

28. The method of claim 27, wherein flocculating the iron precipitate comprises adding a starch solution to the rare earth metal solution.

29. The method of claim 28, wherein the starch solution comprises com starch and a base selected from the group consisting of sodium hydroxide, potassium hydroxide, and combinations thereof.

30. The method of claim 28, wherein flocculating the iron precipitate further comprises blending the rare earth metal solution.

31. The method of claim 1 , wherein separating the iron precipitate comprises filtering the rare earth metal solution.

32. The method of claim 31, wherein the filtering is performed using a filter with a particle retention size from about 0.05 mm to about 1 mm.

33. The method of claim 1, further comprising precipitating aluminum from the solubilized metal solution.

34. The method of claim 1, further comprising removing nickel rom the solubilized metal solution.

35. The method of claim 1, further comprising recovering hydrogen gas from the solubilized metal solution.

36. A method of separating a rare earth metal from a particulate rare earth metal-iron alloy-containing waste, comprising: dissolving metals from a particulate rare earth metal-iron alloy-containing waste using an acid; chelating iron from the particulate rare earth metal-iron alloy-containing waste using a chelator; filtering out undissolved solids;converting the iron to an iron precipitate; flocculating the iron precipitate; filtering out the flocculated iron precipitate; drying remaining dissolved metals to form a dried rare earth metal-containing solid; and heating the dried solid to vaporize organic material and to form a rare earth metal oxide.

37. The method of claim 36, wherein heating the dried solid comprises baking the dried solid at a temperature above about 300 °C.

38. The method of claim 36, wherein the particulate waste comprises magnet waste.

39. The method of claim 36, wherein the rare earth metal-iron alloy comprises neodymium, iron, and boron.

40. The method of claim 36, wherein the rare earth metal-iron alloy further comprises terbium, dysprosium, presidium, or a combination thereof.

41. The method of claim 36, wherein the particulate waste has an average particle size less than about 3 mm.

42. The method of claim 36, wherein the particulate waste has an average particle size from about 0.1 mm to about 0.7 mm.

43. The method of claim 36, wherein the dissolving metals from the particulate rare earth metal-iron alloy-containing waste comprising stirring the particulate waste in an extraction solution that includes the acid.

44. The method of claim 43, wherein the stirring is done using a stir bar at a speed of at least 1000 rotations per minute.

45. The method of claim 43, wherein the stirring is performed for a time period from about 1 hour to about 8 hours.

46. The method of claim 43, wherein the extraction solution has a temperature below about 100 °C during the stirring.

47. The method of claim 43, wherein the extraction solution has a pH from about 4 to about 11.

48. The method of claim 43, wherein a weight ratio of the particulate waste to the extraction solution is from about 1:5 to about 1:1.

49. The method of claim 36, wherein the acid comprises a monocarboxylic acid or an inorganic acid.

50. The method of claim 49, wherein the acid comprises acetic acid, butyric acid, or a combination thereof.

51. The method of claim 36, wherein the chelator comprises citric acid, oxalic acid, malonic acid, 2-hydroxymalonic acid, methyl malonic acid, fumaric acid, succinic acid, 1,2-dimethyl succinic acid, maleic acid, itaconic acid, citraconic acid, glutaric acid, adipic acid, malic acid, pimelic acid, carboxy succinic acid, tricarballylic acid, 2-methyl tricarballylic acid, aconitic acid, 1,2,4-butane tricarboxylic acid, or a combination thereof.

52. The method of claim 36, wherein the dissolving metals from the particulate rare earth metal-iron alloy-containing waste comprising mixing the particulate waste with an extraction solution comprising the acid, the chelator, and a volatile salt.

53. The method of claim 52, wherein the volatile salt comprises an anion that is a conjugate base of the acid.

54. The method of claim 52, wherein the volatile salt comprises ammonium acetate.

55. The method of claim 52, wherein the extraction solution comprises the acid in an amount from about 5 wt% to about 20 wt%, the chelator in an amount from about 0.5 wt% to about 2 wt%, and the volatile salt in an amount from about 3 wt% to about 15 wt%.

56. The method of claim 52, wherein the extraction solution further comprises a defoamer.

57. The method of claim 52, wherein the extraction solution further comprises a second chelator having a coordination number of 6.

58. The method of claim 36, wherein the undissolved solids are filtered out using a filter with a particle retention size from about 1 pm to about 5 pm.

59. The method of claim 36, wherein converting the iron to the iron precipitate comprises adding hydrogen peroxide to oxidize the iron.

60. The method of claim 59, wherein the hydrogen peroxide is added in amount of about 0.5 wt% to about 2 wt% with respect to a total weight of liquid present.

61. The method of claim 36, wherein flocculating the iron precipitate comprises adding a starch solution to the rare earth metal solution.

62. The method of claim 61, wherein the starch solution comprises com starch and a base selected from the group consisting of sodium hydroxide, potassium hydroxide, and combinations thereof.

63. The method of claim 61, wherein flocculating the iron precipitate further comprises blending.

64. The method of claim 36, wherein filtering out the flocculated iron precipitate is performed using a filter with a particle retention size from about 0.05 mm to about 1 mm.

65. The method of claim 36, further comprising precipitating aluminum.

66. The method of claim 36, further comprising removing nickel.

67. The method of claim 36, further comprising recovering hydrogen gas.

68. A system for extracting rare earth metals from a rare earth metal-iron alloy waste, comprising: a dissolution vessel containing a particulate rare earth metal-iron alloy-containing waste in an extraction solution, wherein the extraction solution comprises an acid to dissolve metals from the particulate waste, a chelator having a coordination number of at least 2 to chelate iron from the particulate waste, and a volatile salt; an agitator to agitate the extraction solution in the dissolution vessel; a precipitating reactant to precipitate iron when added to the extraction solution; a filter having a particle retention size from about 0.05 mm to about 1 mm to filter out an iron precipitate from the extraction solution; a heater to heat the extraction solution, to dry dissolved rare earth metals, to vaporize organic material, to oxidize rare earth metals, or a combination thereof.

69. The system of claim 68, wherein the particulate waste comprises magnet waste.

70. The system of claim 68, wherein the rare earth metal-iron alloy comprises neodymium, iron, and boron.

71. The system of claim 70, wherein the rare earth metal-iron alloy further comprises terbium, dysprosium, presidium, or a combination thereof.

72. The system of claim 68, wherein the particulate waste has an average particle size less than about 3 mm.

73. The system of claim 72, wherein the particulate waste has an average particle size from about 0. 1 mm to about 0.7 mm.

74. The system of claim 68, wherein the extraction solution has a pH from about 4 to about 11.

75. The system of claim 68, wherein the acid comprises a monocarboxylic acid or an inorganic acid.

76. The system of claim 75, wherein the acid comprises acetic acid, butyric acid, or a combination thereof.

77. The system of claim 68, wherein the chelator comprises citric acid, oxalic acid, malonic acid, 2-hydroxymalonic acid, methyl malonic acid, fumaric acid, succinic acid,1 ,2-dimethyl succinic acid, maleic acid, itaconic acid, citraconic acid, glutaric acid, adipic acid, malic acid, pimelic acid, carboxy succinic acid, tricarballylic acid, 2-methyl tricarballylic acid, aconitic acid, 1,2,4-butane tricarboxylic acid, or a combination thereof.

78. The system of claim 68, wherein the volatile salt comprises an anion that is a conjugate base of the acid.

79. The system of claim 68, wherein the volatile salt comprises ammonium acetate.

80. The system of claim 68, wherein the extraction solution comprises the acid in an amount from about 5 wt% to about 20 wt%, the chelator in an amount from about 0.5 wt% to about 2 wt%, and the volatile salt in an amount from about 3 wt% to about 15 wt%.

81. The system of claim 68, wherein the extraction solution further comprises a defoamer.

82. The system of claim 68, wherein the extraction solution further comprises a second chelator having a coordination number of 6.

83. The system of claim 68, further comprising a filter with a particle retention size from about 1 pm to about 5 pm to filter out undissolved solids from the extraction solution before adding the precipitating reactant.

84. The system of claim 68, wherein the precipitating reactant comprises hydrogen peroxide.

85. The system of claim 68, further comprising a flocculator to flocculate the precipitated iron.

86. The system of claim 85, wherein the flocculator comprises a starch solution.

87. The system of claim 86, wherein the starch solution comprises com starch and a base selected from the group consisting of sodium hydroxide, potassium hydroxide, and combinations thereof.

88. The system of claim 86, further comprising a blender to blend the flocculated iron.

89. The system of claim 68, further comprising a hydrogen recovery unit to recover hydrogen gas from the dissolution vessel.

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