Method and systems for recovering rare earth elements from waste magnets

Abstract

Methods and systems for the reclamation of rare earth elements from magnets by crushing a feed stock of waste magnets, immersing the magnet feed stock in water containing a catalyst, heating the immersed magnet feed stock to a predetermined temperature and pressure inside a reaction vessel, and maintaining the predetermined temperature and / or pressure inside the reaction vessel for a predetermined reaction time. In some examples the pressure inside the reaction vessel is maintained in part by bleeding off hydrogen produced by the reaction of rare earth elements inside the vessel and the temperature is maintained in part by combusting the bled off hydrogen in a furnace in thermal communication with the reaction vessel.

Description

70345-02 METHODS AND SYSTEMS FOR RECOVERING RARE EARTH ELEMENTS FROM WASTE MAGNETS CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is related and claims priority to US Provisional Patent Application No.63 / 581,632 filed on September 8, 2023, which is incorporated herein by reference. FIELD

[0002] The disclosed technology relates generally to recovery of materials from waste products and more particularly to recovery of rare earth elements (REEs) from waste magnets. BACKGROUND

[0003] Rare earth elements play a central role in modern technology, enabling the function of a wide range of products, including motors, electronic devices, renewable energy systems, and others. However, the procurement of these vital elements has presented environmental and geopolitical challenges. At the intersection of sustainable resource management, the importance of recycling waste magnets for rare earth recovery takes center stage. This research addresses the critical role that recycling of waste magnets plays in mitigating the scarcity of rare earths and provides a sustainable path for future technological advances.

[0004] Rare earths are not as rare as their name suggests. However, they are often present at low concentrations (ppm levels), making their extraction and purification to produce70345-02 99.5% purity individual REEs environmentally damaging and economically challenging. In addition, the extraction and purification processes, including the separations of REEs from radioactive uranium and thorium, can produce harmful wastes that contribute to environmental pollution. Therefore, reliance on conventional mining methods for these elements can exacerbate environmental degradation and geopolitical tensions. Waste magnets derived from end-of-life electronics, motors, medical equipment, and other products represent a latent reservoir of rare earths awaiting an environmentally friendly recovery process.

[0005] Recycling scrap magnets is not only a remedy for the impending shortage of rare earths, but also circumvents the environmental impacts associated with conventional mining. In this recycling process, discarded electronic products or motors are disassembled and processed to extract the REEs. In this way, the need for producing REEs from mineral ores is reduced. The burden of pollution on our ecosystems and the energy consumption and greenhouse gas emissions related to mining are also reduced. This recycling approach aligns with the principles of the circular economy, where materials remain in use as long as possible to minimize waste and maximize resource efficiency.

[0006] The environmental benefits of recycling waste magnets go beyond the recovery of rare earths. By keeping electronic waste out of landfills, we reduce the leaching of hazardous materials into soil and water, which curbs pollution and protects ecosystems. In addition, recycling reduces the need for new materials, saves energy, and reduces the carbon footprint associated with mining and manufacturing processes. This interplay of70345-02 resource conservation, pollution reduction, and energy efficiency underscores the multiple environmental benefits of recycling of waste magnets.

[0007] Moreover, the economic and technological implications of this practice are profound. As demand for REEs continues to grow, recycling waste magnets provides a cost-effective alternative to using only virgin sources. The recovery of REEs from waste magnets can be more energy efficient and economically viable compared to traditional mining methods. In addition, as recycling technologies advance, the potential for job creation in the recycling and recovery industry becomes apparent, strengthening local economies and providing sustainable employment opportunities. SUMMARY

[0008] In one aspect, A method of recovering rare earth elements from waste magnets where waste magnets are crushed to yield a magnet feedstock portion; the feedstock portion is then immersed in water to yield a hydrothermal portion; a catalyst is introduced into the hydrothermal portion at a predetermined catalyst concentration to yield a catalyzed hydrothermal portion; the catalyzed hydrothermal portion is heated to a predetermined temperature under a predetermine pressure; the catalyzed hydrothermal portion is then allowed to react for a predetermined amount of time; hydrogen gas and rare earth compounds are then harvested. In one example the catalyst is one or more of potassium chloride, potassium sulfide, and potassium sulfate. The predeterminedtemperature may be 250^C to 350^C. Further, the predetermined pressure andtemperature are maintained for a predetermined reaction time. The predetermined temperature and pressure may be maintained by harvesting hydrogen from the reaction.70345-02 Optionally, harvested hydrogen may be stored for later use or combusted in a hydrogen furnace in thermal communication with the reaction to maintain the predetermined temperature. The harvested rare earth compounds are powdered hydroxides of rare earth elements.

[0009] In another aspect, a system for recovering rare earth elements from waste magnets is disclosed having a hydrothermal reaction vessel for containing water and waste magnet feedstock, a hydrogen furnace in thermal communication with the hydrothermal reaction vessel, a condenser in fluidic communication with the hydrothermal reaction vessel and the hydrogen furnace, and a hydrogen gas port in fluidic communication with the hydrothermal reaction vessel and the condenser where hydrogen gas produced in the hydrothermal reaction vessel by decomposition of the waste magnet feedstock is separated in the condenser and combusted in the hydrogen furnace. Optionally, a hydrogen gas storage vessel is in fluidic communication with the condenser where hydrogen gas produced in the hydrothermal reaction vessel by decomposition of the waste magnet feedstock separated in the condenser is stored in the hydrogen gas storage vessel. Optionally, the hydrogen gas storage vessel is an adsorption vessel.

[0010] In yet another aspect a method of recovering rare earth elements from waste magnets is disclosed where a feedstock of crushed rare earth magnets is added to a reaction vessel; the feedstock is immersed in water to yield a hydrothermal portion; a catalyst is introduced at a predetermined concentration into the hydrothermal portion to yield a catalyzed hydrothermal portion; the reaction vessel is heated to a predetermined temperature and pressure; and the catalyzed hydrothermal portion is reacted to produce rare earth compounds and hydrogen gas. Optionally, the reaction vessel is maintained at70345-02 the predetermined pressure and temperature for a predetermined amount of time. Optionally the pressure is maintained by removing hydrogen from the reaction vessel. Optionally the temperature is maintained by a hydrogen furnace in thermal communication with the reaction vessel powered in part by hydrogen gas removed from the reaction vessel. In another example, the hydrogen gas removed from the reaction vessel is stored for later use. The catalyst may be one or more of potassium chloride, potassium sulfide, and potassium sulfate. The rare earth compounds produced by the reaction are powdered hydroxides of rare earth elements. The predetermined temperatureis 250^C to 350^C in one example.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG.1 is a diagram of an isothermal REEs recycling process according to one example of the disclosed technology.

[0012] FIG.2 is a table comparing yield percentages using different catalysts according to the disclosed technology.

[0013] FIG.3 is a graph of variations in reaction pressure from hydrogen generation using different catalysts.

[0014] FIG.4 is a graph of variations in reaction pressure from hydrogen generation using K2SO4 as a catalyst over different reaction times.

[0015] FIG.5 is a diagram of an isobaric REEs recycling process according to one example of the disclosed technology.

[0016] FIG.6 is x-ray diffraction of recovered REE product from one example of the disclosed technology.70345-02

[0017] FIG.7 is a graph comparing yields of an isobaric process according to the disclosed technology to an isothermal process according to the disclosed technology. DESCRIPTION

[0018] For the purposes of promoting an understanding of the principles of the claimed technology and presenting its currently understood best mode of operation, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the claimed technology is thereby intended, with such alterations and further modifications in the illustrated device and such further applications of the principles of the claimed technology as illustrated therein being contemplated as would normally occur to one skilled in the art to which the claimed technology relates

[0019] Hydrothermal recovery of rare earths from waste magnets uses aqueous solutions at high temperatures and pressures to catalyze various chemical reactions or the formation of materials. A specific variation of this process, catalytic hydrothermal extraction, is emerging as a strategic approach to recover REEs from waste magnets. By incorporating a catalyst into the hydrothermal process, this technique is fine-tuned to extract metals from sources such as REE-containing alloys, concentrates, or other REE- containing raw materials. This method is environmentally friendly and the introduction of a catalyst increases the efficiency and selectivity of the metal extraction process.

[0020] Given the nature of batch systems hydrothermal recovery of REEs from waste magnets, in which hydrogen is generated during the process, there are significant70345-02 uncertainties about the efficiency and safety of its application on a large scale. The disclosed technology involves an innovative and scalable catalytic hydrothermal recycling process tailored to address these issues, and at the same time with more efficient catalysts. By incorporating specific operating conditions and catalysts, the disclosed technology not only ensures the efficiency of the recycling process, but also to improves its safety in larger scale applications. Recognizing the limitations of the proposed batch system, the disclosed technology seeks to overcome these limitations by employing a catalytic hydrothermal recycling process. This method takes advantage of controlled reactions in a semi-batch system, mitigating potential hazards associated with hydrogen accumulation and achieving a more consistent and controllable process.

[0021] A diagrammatic view of an isothermal REEs recycling process 10 according to one example of the disclosed technology is shown in FIG.1. In this particular example, the recovery process is isothermal. Waste magnets 12 are arranged in a semi-batch reactor vessel 14. A volume of deionized water 16 is added along with the catalyst (for example, K2SO4). The precise amount of catalyst is determined based on the desired concentration and the weight of the waste magnets. Typically catalyst concentrations of 1-20 millimolar (mM) is used. More typically, catalyst concentrations of 1-10 mM is used. To reach the required temperature and pressure, a hydrogen furnace system 18 heats the reactor 14 to the desired temperature and pressure. The heating process is closely monitored to ensure safety and optimal efficiency using one or more temperature 20 and pressure 22 sensors or monitoring devices.

[0022] During the startup, the temperature in the reactor 14 increases until it reaches the desired set point. Once the temperature reaches the desired level, the reaction begins,70345-02 causing the production of hydrogen gas as a byproduct of the reaction between rare earths and iron with water. As the hydrogen gas 24 accumulates, the pressure inside the reactor 14 rises. To maintain a stable and controlled pressure level, a backpressure valve 26 is employed to regulate the reactor's pressure. When the pressure reaches a preset threshold, the excess pressure is relieved through purging. To separate hydrogen from water vapor, the resulting outlet gases 28 are passed through a condenser 30. As the outlet gas cools to room temperature, the water vapor condenses to liquid water 32 and is separated from hydrogen 34.

[0023] The hydrogen byproduct of the recovery reaction may be recycled and returned to the hydrogen furnace thereby increasing the efficiency of the disclosed recovery methods and reducing the need for additional energy input. Excess generated hydrogen may be stored, such as in a high-pressure storage tank 36 or an adsorbent column 38, for later use in recovery reactions, for use in other processes, and / or for sale. The disclosed methods also produce REE hydroxides in a powdered form thereby eliminating the need for additional processing such as grinding or milling of the end product further reducing the required energy input as compared to existing methods of REE recovery from waste magnets. Optionally, the resulting REE hydroxides can be dissolved in a weak acid and purified in a chromatography process to produce high-purity individual REEs.

[0024] A diagrammatic view of an isobaric REEs recycling process 40 according to one example of the disclosed technology is shown in FIG.5. In this particular example, a condenser 42 is operationally connected to a reaction vessel 44 and to a pressure regulator 46. As with the previous example, shredded waste magnet material 48 is loaded into the reaction vessel 44 and immersed in water 50 containing a catalyst (typically a70345-02 potassium salt). Hydrogen gas is evolved during the reaction, fed through the condenser 42, and bled off by the pressure regulator 46 so as to maintain a desired pressure within the reaction vessel 44. As with the previous example, the removed hydrogen can then be stored for later use or sale.

[0025] In one example of the disclosed methods, discarded magnets from hard disk drives were collected and crushed. The resulting magnet fragments were introduced into a reactor chamber. A selected catalyst consisting of a series of potassium salts such as potassium chloride, potassium sulfate, and potassium sulfite were dissolved in purified water. The resulting solution was introduced into the reactor. The heating element of the reactor was set to an initial temperature of 275 ^ C. Initial residence time for the reaction was determined to be 8-36 hours and the reaction monitored for 36 hours. Once the reaction began there was a gradual generation of hydrogen, REE hydroxides, and iron oxides which gradually changed the pressure of the batch system. This led to a noticeable increase in reactor pressure over time.

[0026] Two primary reactions are expected to occur in the reactor. Iron reacts with ionized water to form Fe3O4 and hydrogen gas, Equation (1). REEs react with ionized water to form REE hydroxides and hydrogen gas, Equation (2). Understanding the interplay between these two reactions is important in optimizing the reactor conditions to achieve maximum rare earth element recovery rates. To estimate the yield of the reactions, two methods for quantification may be used. The first method involves accurate measurements of the solid mass before and after the70345-02 reactions. The ratio between the two measurements provides an estimate of the conversion or yield Ys, (Equation 3). The actual weight of the products was measured after a careful washing and drying process; the theoretical weight of the products was calculated from the stoichiometry of reactions 1 and 2.

[0027] The second method for estimating the reaction yield is to monitor the pressure of the reactor and examine the amount of hydrogen gas produced throughout the conversion process. This method is based on hydrogen gas generated and it provides an independent measure of the reaction yield, YH in addition to the first method, YS, which is based on weight change of the solid before and after the conversion. This second method relies on two calculations: (1) the actual moles of hydrogen generated, (2) the theoretical moles of hydrogen generated, as explained in more detail below.

[0028] To determine the actual moles of hydrogen produced, the reactor pressure is monitored during the reaction and after the reactor is cooled to room temperature. The equation of state is used to convert hydrogen pressure into moles of hydrogen generated. The calculated moles of hydrogen are taken to be the actual moles of hydrogen produced in the reaction.

[0029] Theoretical Hydrogen Moles are based on the reaction stoichiometry. If the conversion is complete, the theoretical moles of hydrogen generated can be calculated from the weight of magnets and Equations (1) and (2). The ratio of the actual moles of hydrogen produced, which are estimated from hydrogen pressure, and the Theoretical70345-02 Hydrogen Moles gives the yield estimated from hydrogen pressure YH, as shown in Equation 4. Using bothreaction yields. Furthermore, it enables a holistic assessment of the reaction conditions (type of catalyst, water loading, reaction temperature, and reaction time) on yields.

[0030] To determine the potential of the waste magnets as a secondary REE source, a series of total dissolution experiments were conducted and inductively-coupled-plasma optical emission spectroscopy (ICP-OES) techniques employed to analyze their elemental composition. Results show that the starting material contains the following weight percentages: 68% iron (Fe), 22.2% neodymium (Nd), 6.5% praseodymium (Pr), 0.9% dysprosium (Dy), 0.7% aluminum (Al), 0.8% cobalt (Co), and 1% boron (B). These results provide a comprehensive understanding of the elemental composition of magnetic samples obtained from hard disk drives.

[0031] To compare the performances of various catalysts, experiments were conducted using a starting material of 20 grams of waste magnets under uniform conditions and introduced 400 mL of water into a batch reactor with a total volume of 0.5 liters, operating at an elevated temperature of 275°C. A constant catalyst concentration of 5 millimolar (mM) was used for all experiments to ensure consistency and aid comparisons of catalysts. Catalyst concentration is a factor in assessing the catalytic activities and efficiency of the catalysts studied. The results of one set of experiments assessing the catalytic performance of various catalysts and reaction times is shown in FIG.2. The table also includes important performance parameters such as "YS" and "YH", further70345-02 indicating the efficiency of the catalysts studied. The data show that potassium sulfate achieved the highest yield of 94.4%, outperforming other catalysts like potassium chloride, and potassium sulfite.

[0032] The x-ray diffraction (XRD) pattern as seen in FIG.6 of the final solid product shows most of the characteristic peaks of magnetite (Fe₃O₄). The most significant peaks for Fe₃O₄ and their corresponding planes are found at the following 2θ: 18.3° (111), 30.1° (220), 35.5° (311), 37.1° (222), 43.1° (400), 53.5° (422), 57.0° (511), and 62.6° (440). These planes are part of the cubic crystal structure of Fe₃O₄, producing its characteristic XRD peaks. Some of these XRD peaks in the figures can also be related to Fe₂O₃: 35.6° (110), 40.9° (113), 49.5° (024), 57.6° (018), 62.5° (214), and 72° (1010) planes. However, due to the better match of the Fe₃O₄ peaks with the XRD pattern, only the Fe₃O₄ peaks are shown and attributed in the patterns. Fig.4(b) also shows the presence of neodymium hydroxide (Nd(OH)₃) and, to a lesser extent, praseodymium hydroxide (Pr(OH)₃). However, some of the characteristic peaks of these materials overlap with the peaks of the iron oxides. The more distinct peaks are highlighted in the figures. For Nd(OH)₃, the prominent peaks are observed at about 17.6° (100), 28.2° (101), 30.4° (110), 43.7° (201) and 49.5° (210). For Pr(OH)₃, the notable peaks are at 30.4° (002), 34.9° (201), 40.5° (210) and 53.5° (220).

[0033] Pressure in the reactor may be monitored to track the generation of hydrogen gas during the reaction. Figures 3-4 show the pressure changes over time. The pressure data indicate that the initial pressure change is due to water evaporation, regardless of the experimental scenario. In one example, a reaction temperature of 275 ℃ and 400 mL water were used to generate a water vapor pressure about 850 psig to initiate the70345-02 reactions. However, as the reaction progressed, a decline in the rate of hydrogen generation was observed. This trend indicates that the rate of conversion decreased over time. Overall, these findings provide valuable insights into the reaction kinetics and the potential for developing strategies to maintain high levels of reaction rates throughout the process.

[0034] In another example, the isothermal process previously described was compared to the isobaric process previously described. In this particular example, the isobaric hydrothermal process produced higher yields in shorter times than the isothermal process. Figure 7 shows 10% higher yield after 8 h, 35% higher yield at 12 h, and 97% yield at 24 h for the isobaric process when compared to the isothermal process.

[0035] Under certain conditions the methods described herein can produce sufficient hydrogen gas such that no additional energy input is required to start and / or maintain the process. For example, starting with waste neodymium magnets, which are typically an alloy of primarily iron (Fe) and neodymium (Nd), the energy required to start and maintain a hydrothermal recycling process such as those disclosed herein consists of two parts: 1) raising the temperature of the waste magnets and water to operating temperature, and 2) evaporating water in the reaction vessel as the reaction proceeds. Using an operating temperature of 275^C and an ambient temperature of 25^C results in a temperature change (ΔT) of 250^C. The heat required to raise the temperature of each material may be calculated using the equation: Q = mc ΔT (5) where Q is the amount of heat in Joules (J), m is the mass of the substance in grams (g), c is the specific heat of the substance, and ΔT is the temperature difference between room70345-02 temperature and the reaction temperature. Using equation (5) to calculate the heat required to raise the temperature of iron and neodymium by 250^C yields: Complete reaction of iron and neodymium requires at least 4 / 3 moles of water for every mole of iron and 3 moles of water for every mole of neodymium. Using equation (5) to calculate the amount of water for complete reaction of iron plus the amount of water for complete reaction of neodymium yields: resulting in the energy required to heat this water to be: TheThe total energy required to start and maintain this example reaction until completion would be the sum of the individual heat requirements:Using the one methods 20 g of waste magnet and 7.8g of water would require 0.0276 MJ of energy and generate an amount of hydrogen capable of producing 0.101 MJ of energy. In another example, 1 kg of waste magnet and 0.39 kg of water would require 1.38 MJ of energy and generate an amount of hydrogen capable of producing 5 MJ of energy. In yet another example, 1 kg of waste70345-02 magnet and 1.17 kg of water would require 4 MJ of energy and generate an amount of hydrogen capable of producing 5 MJ of energy. These examples assume 100% efficiency of extracting energy from hydrogen. Even at a lower efficiency such as 80%, the first two examples would still produce an excess of energy in the form of hydrogen and third example would break even.

[0036] The efficiency and effectiveness of the REE recycling processes through hydrothermal methods are significantly influenced by various operating conditions. These conditions play a role in determining the yield, purity, and overall sustainability of the recycling process. The following operating parameters have notable effects on the REE recycling process from waste magnets using hydrothermal methods.

[0037] Temperature. Given these complicated dynamics, finding the optimal temperature range is advantageous. The goal is to find a balance between maximizing REE yield and ensuring energy efficiency while maintaining the integrity of the catalyst. In the specific context of hydrothermal conversion of waste magnets to REE hydroxide and iron oxide, a carefully selected minimum temperature is helpful. In this case, a temperature threshold of 250 °C was used, as significant water ionization requires at least 250 °C.

[0038] However, the system provides some latitude for temperature adjustment. Taking into account the factors discussed previously, the upper limit of the temperature range can be extended up to 350 °C. Within this range, the trade-offs between improved REE recovery and associated energy consumption and catalyst stability can be weighed and evaluated in more detail. Careful calibration of this parameter within the prescribed range of 250 °C to 350 °C allows for a complex balance that enables optimal REE yield while considering energy aspects and catalyst longevity.70345-02

[0039] Pressure. Pressure exerts a significant influence on the solubility of hydrogen gas in the reaction medium. This influence on solubility, in turn, has a number of implications for the rare earth elements recycling process. The efficient conversion in the hydrothermal process largely depends on the reaction rates shown in Equations (1) and (2). Rapid generation of hydrogen gas causes pulverization of the waste magnets into fine particles and facilitates the conversion of REEs to REE hydroxides. This phenomenon is attributed to the enhanced molecular interactions between the super-heated steam and the magnet metals favored by the increased pressure.

[0040] The pursuit of elevated pressure is not without its associated difficulties. The application of elevated pressure requires specialized equipment to withstand the additional mechanical stresses. In addition, operational safety considerations play an important role, as managing high-pressure conditions requires strict protocols and safety precautions to minimize potential hazards. This interplay between enhanced extraction REE and the requirement for advanced equipment and safety measures underscores the multi-faceted role of pressure.

[0041] In an effort to optimize the REE recycling process, determining the pressure conditions is of central importance. This key task involves balancing two compelling objectives: maximizing REE recovery and ensuring operational safety. Finding this balance is important to ensure both the efficiency and costs of the process. Specifically, a pressure of about 800 psig is needed for accelerating the reaction cascade.

[0042] The process pressure over time curve indicated high hydrogen generation rates in the 900 to 1400 psig range. Within this range, the reaction kinetics exhibit remarkable acceleration, providing high REE conversion rates. Given this kinetic advantage,70345-02 maintaining the reactor pressure within this window can significantly increase the overall efficiency of the recycling process.

[0043] Pressure in the hydrothermal process plays a key role in the energy efficiency, REE conversion rates, and operating and capital costs. Pulverizing dynamics due to pressure has a direct impact on the efficiency of REE conversion and extraction from the waste magnets. The hydrothermal process can reduce or eliminate multiple size reduction processes for producing powder materials before REE oxidation and acid leaching in conventional REE recycling. The hydrothermal process also eliminates the energy- intensive oxidation step for converting REE metals to REE oxides before acid leaching, which is required for producing soluble REE salts prior to chromatography purification. Furthermore, conversion of REEs to REE hydroxides is achieved simultaneously as the size reduction step prior to acid leaching. The hydrogen generated can also be used for providing the energy needed for the reactions. The combined size reduction steps with the REE conversion step help streamline the recycling process and reduce material waste, making it a more sustainable and cost-effective option for REE production.

[0044] The optimization of the hydrothermal process for particle size reduction, REE conversion, equipment requirements, energy efficiency, and safety considerations requires a holistic approach. Prudent selection of reaction temperature and pressure, encompassing both initiation and kinetic optimization, can increase REE recovery yields while achieving process safety and efficiency.

[0045] Water loading. The amount of water used in the hydrothermal process plays a role in the reaction environment and generating the initial pressure. Water loading has far- reaching implications for REE conversion, material and energy efficiency, waste water70345-02 recycling, costs, and sustainability. Adding more water is proven to be an effective strategy for creating a favorable reaction environment. This dynamic stems from the ability of water to create an environment conducive to efficient heat and mass transfer rates. A higher water content provides a robust aqueous medium in which the reactions of the magnetic materials can occur optimally. This increased heat and mass transfer rates promote the reactions in the magnets, increase the conversions of REEs to REE hydroxides and iron to iron oxides, and thus increase the overall yields of the REE recycling process.

[0046] The pursuit of higher water volumes should be weighed carefully, as excess water leads to potential trade-offs. While excess water promotes efficient mass transfer, it can lead to increased material and energy consumption in the subsequent waste water treatment steps. This additional energy demand could counteract the benefits derived from improved heat and mass transfer efficiency, highlighting the need for optimization of water loading.

[0047] The role of water in this hydrothermal process goes beyond its function as a reaction medium. It also assumes the role of a key reactant, participating in the chemical reactions and contributing to the formation of reaction products. At the same time, the vapor pressure of water at elevated temperatures triggers a cascade of effects ranging from creating the necessary vapor pressure for reaction initiation to influencing the reactor pressure in a batch reactor.

[0048] When the amount of water used in the hydrothermal process exceeds a certain threshold in a vessel with a fixed volume, it can lead to a high pressure within the reactor at a high temperature. High pressure levels can pose risks to both the process and70345-02 personnel safety, underscoring the importance of careful choice of water loading to ensure optimal process efficiency and safety in REE recycling.

[0049] Within these multi-faceted requirements, a carefully selected water loading, i.e. the amount of water in a given reactor volume, is needed. Water is a key reactant in the conversion reactions. A minimum water load may be calculated using Equations (1) and (2) above. Furthermore, additional water is needed to maintain an operating pressure above 800 psig for fast reactions. A pressure range from 800 to 1,400 psig reflects a balance between efficient heat and mass transfer, conversion rates, energy consumption, process safety, and the costs for equipment and subsequent water recycling. Therefore, optimization of water loading, temperature, and pressure will require a comprehensive understanding of the interdependence of the various parameters in hydrothermal processing.

[0050] Catalyst type and concentration. The choice of catalyst significantly impacts reaction kinetics and product selectivity. Catalyst type and concentration determine the reaction rates and detailed reaction pathways. The choice of optimal catalyst requires careful consideration of catalyst cost, effective recovery of REE hydroxide, iron oxide, and the catalyst, and the environmental footprints.

[0051] In the context of hydrothermal conversion of waste magnets to REE hydroxide and iron oxide, a strategic set of catalysts is important. A combination of three potassium salts - consisting of potassium chloride, potassium sulfide, and potassium sulfate – are one example. This selection is underpinned by their central role in the water ionization process, a key aspect of the reaction cascade. Potassium salts are also readily available and cost-effective, making them a practical option for large-scale operations.70345-02 Additionally, they have a relatively low environmental impact compared to other potential catalysts, as they do not introduce toxic elements into the reaction mixture. Overall, the use of potassium salts represents a strategic and effective choice for catalyzing the hydrothermal conversion process. One particular property of the chosen catalysts is their propensity to dissolve readily in water. This property is important for their use in the hydrothermal process. Their easy dissolution into the liquid phase sets the stage for their far-reaching catalytic capabilities throughout the reaction medium.

[0052] Catalyst concentration is also important. A catalyst concentration of 5 mM is used in one example of the disclosed methods. This concentration represents a balance between triggering the reaction pathways and avoiding the potential pitfalls associated with excessive catalyst use. It was observed in one example that less than 5% of water was consumed in the reaction and the rest of the water was recovered. The amount of catalyst remained the same after the reaction. The results indicated that the process water containing catalyst can be recovered and reused with consistent effectiveness. This phenomenon not only underscores the catalyst's resilience, but also its cost effectiveness and small environmental footprints.

[0053] Magnet Loading. The conversion of waste magnets into iron oxide and REE hydroxides in the hydrothermal processes also results in the generation of significant amount of hydrogen gas (Equations (1) and (2)). Increasing magnet loading in a given reactor volume is an effective strategy for increasing productivity. However, increasing magnet loading corresponds to a proportional increase in operating pressure, which raises safety concerns and must be considered. It is crucial to find a balance between increasing magnet loading for high productivity and mitigating the associated increase in operating70345-02 pressure. This balance requires the conditions that allow for high hydrogen production while keeping the resulting pressure within the safe limits. One must carefully consider the tradeoffs between magnet loading, productivity, and safety. To achieve the goals of both profitability and operational safety, the conditions that satisfy both requirements must be carefully selected. A comprehensive understanding of the interplay between magnet loading and pressure is needed to find the optimal conditions for a productive and safe hydrothermal conversion process. Typically, greater magnet loading will result in a more efficient process but may be limited by reaction vessel size and construction.

[0054] Reaction Time. The duration of the hydrothermal reaction impacts the extent of REE conversion. The longer the reaction time, the greater the potential for higher yields. However, there is a threshold above which the benefits diminish. Determining the optimal reaction time requires a comprehensive analysis that strikes a balance between kinetics, energy consumption, and the desired yield of the process. In one example nearly 60% of the conversion occurred within the first 6 hours of reaction initiation, after which the conversion rate gradually decreased. This observation prompts the development of methods to achieve significant conversion within shorter reaction times. This approach is important because of its economic implications, as it aims to maximize conversion while minimizing time. On the other hand, working under more severe operating conditions may also play a role in shortening the required time.

[0055] The drive to increase conversion rates within a shortened reaction time is a key aspect of the disclosed invention. By deciphering the mechanisms that drive the initial rapid conversion and finding innovative ways to extend this highly efficient phase, the disclosed invention is able to increase both economic efficiency and REE recovery70345-02 efficiency over the prior art. In one example, an isobaric reaction setup such aspreviously described maintained at a pressure of 1,000 psig and a temperature of 275^Cwill achieve nearly complete conversion of REE to REE hydroxides in approximately 24 hours.

[0056] While the claimed technology has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character. It is understood that the embodiments have been shown and described in the foregoing specification in satisfaction of the best mode and enablement requirements. It is understood that one of ordinary skill in the art could readily make a nigh-infinite number of insubstantial changes and modifications to the above-described embodiments and that it would be impractical to attempt to describe all such embodiment variations in the present specification. Accordingly, it is understood that all changes and modifications that come within the spirit of the claimed technology are desired to be protected.

Claims

70345-02 CLAIMS What is claimed is:

1. A method of recovering rare earth elements from magnets, comprising: a) crushing magnets to yield a magnet feedstock portion; b) immersing the feedstock portion in water to yield a hydrothermal portion; c) introducing catalyst into the hydrothermal portion at a predetermined catalyst concentration to yield a catalyzed hydrothermal portion; d) heating the catalyzed hydrothermal portion to a predetermined temperature under a predetermine pressure; and e) harvesting hydrogen gas, iron oxides, and rare earth compounds.

2. The method of claim 1 wherein the catalyst is one or more of potassium chloride, potassium sulfide, and potassium sulfate.

3. The method of claim 1 wherein the predetermined temperature is 250^C to350^C.

4. The method of claim 1, further comprising: f) maintaining the predetermined pressure.

5. The method of claim 4, wherein the predetermined temperature is maintained by a hydrogen furnace powered in part by harvested hydrogen.70345-02 6. The method of claim 4, wherein the predetermined pressure is maintained in part by harvesting hydrogen.

7. The method of claim 1 wherein harvested hydrogen is stored for later use.

8. The method of claim 1 wherein harvested rare earth compounds are powdered hydroxides of rare earth elements.

9. A system for recovering rare earth elements from waste magnets, comprising: a hydrothermal reaction vessel for containing water and waste magnet feedstock; a hydrogen furnace in thermal communication with the hydrothermal reaction vessel; a condenser in fluidic communication with the hydrothermal reaction vessel and the hydrogen furnace; and a hydrogen gas port in fluidic communication with the hydrothermal reaction vessel and the condenser; wherein hydrogen gas produced in the hydrothermal reaction vessel by decomposition of the waste magnet feedstock is separated in the condenser and combusted in the hydrogen furnace.70345-02 10. The system for recovering rare earth elements from waste magnets of claim 9, further comprising a hydrogen gas storage vessel in fluidic communication with the condenser; wherein hydrogen gas produced in the hydrothermal reaction vessel by decomposition of the waste magnet feedstock separated in the condenser is stored in the hydrogen gas storage vessel.

11. The system for recovering rare earth elements from waste magnets of claim 10, wherein the hydrogen gas storage vessel is an adsorption vessel.

12. A method of recovering rare earth elements from waste magnets, comprising: a) adding a feedstock of crushed rare earth magnets to a reaction vessel; b) immersing the feedstock in water to yield a hydrothermal portion; c) introducing a catalyst at a predetermined concentration into the hydrothermal portion to yield a catalyzed hydrothermal portion; d) heating the reaction vessel to a predetermined temperature and pressure; and e) reacting the catalyzed hydrothermal portion to produce rare earth compounds and hydrogen gas.

13. The method of recovering rare earth elements from waste magnets of claim 12 further comprising:70345-02 f) maintaining the predetermined pressure.

14. The method of recovering rare earth elements from waste magnets of claim 13 wherein the pressure is maintained by removing hydrogen from the reaction vessel.

15. The method of recovering rare earth elements from waste magnets of claim 14 wherein the predetermined temperature is maintained by a hydrogen furnace in thermal communication with the reaction vessel powered in part by hydrogen gas removed from the reaction vessel.

16. The method of recovering rare earth elements from waste magnets of claim 14 wherein the hydrogen gas removed from the reaction vessel is stored for later use.

17. The method of recovering rare earth elements from waste magnets of claim 12 wherein the catalyst is one or more of potassium chloride, potassium sulfide, and potassium sulfate.

18. The method of claim 12 wherein the rare earth compounds are powdered hydroxides of rare earth elements.70345-0219. The method of claim 12 wherein the predetermined temperature is 250^C.

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