Method for recovering rare earth elements

Abstract

The invention relates to methods for recovering rare earth elements from neodymium magnet material The method comprises leaching the neodymium magnet, separating iron, separating rare earth elements by adsorbing into an exchange material, and recovering rare earth elements from the ion exchange material.

Description

[0001] Method for recovering rare earth elements

[0002] Technical field

[0003] The invention relates to methods for recovering rare earth elements from neodymium magnet material. The method comprises leaching the neodymium magnet, separating iron, separating rare earth elements by adsorbing into an exchange material, and recovering rare earth elements from the ion exchange material.

[0004] Background

[0005] Neodymium magnets, also known as NdFeB, NIB or Neo magnets, are permanent magnets made from an alloy comprising 60-70 wt-% of Fe, 20-30 wt-% of Nd, and 0.3-1 wt-% of B, as well as 0.5-7 wt-% of Pr (as weight percentages of the total weight of the alloy) to form a Nd2FeuB tetragonal crystalline structure. Small amounts of other metals such as Al, Ga, Co, Cu, Dy and Tb are added to NdFeB magnets to adjust their properties. For example, Dy and Tb are typically added to increase the coercivity of a magnet at high temperatures. The addition of up to 5 wt-% of Co increases the Curie temperature of the magnet, a temperature in which the magnet retains its permanent magnetic properties, whereas Ga and Al improve the thermal stability of the magnet. Therefore, the used NdFeB magnets are not only a potential secondary source for rare earth elements but also for other critical elements such as Co, Al, or Ga. Neodymium magnets are often coated to prevent corrosion. Nickel, nickel-copper-nickel and zinc coatings are commonly used. Coating with other metals, or polymer and lacquer protective coatings, may also be used.

[0006] Rare earth elements, often abbreviated as REEs, are a set of lustrous silvery- white soft heavy metals. REEs are often difficult to isolate from ores and from each other. REEs are considered to include lanthanoids along with scandium and yttrium. Thus, REEs include 17 elements altogether: Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. REEs typically found in neodymium magnets include neodymium Nd, praseodymium Pr, dysprosium Dy, terbium Tb, samarium Sm, and holmium Ho. As mentioned above, neodymium magnets may be used as a secondary source for REEs through recycling of magnets at the end of their lifespan. Larger-sized wind turbine and electric car magnets can be recycled as they are, but smaller magnets from, e.g., electric appliances and hard disk drives (HDDs) must be separated from the other components including plastic or metal parts either by manual or automatic dismantling. After the separation, demagnetisation and grinding of magnets into small particles are typically required before the elements can be separated into their own fractions either by pyrometallurgy or hydro- / solvometallurgy. Pyrometallurgical recycling can yield rather pure fractions of REEs. However, it requires high temperatures making it an energy-intensive process, although waste heat can be recycled. In hydrometallurgy and solvometallurgy, the elements are typically leached from NdFeB magnets using acidic aqueous solutions or non-aqueous solvents and are then commonly separated from each other by precipitation, liquidliquid extraction, and / or ion-exchange. So far, the focus in literature has been on the separation of the main components of magnets, i.e. Fe, Nd, and Dy, from simulated NdFeB solutions and / or binary solutions containing only the most abundant elements (Fe / Nd or Nd / Dy). Using precipitation, 100% pure Nd fraction has been obtained from Nd / Fe and Nd / Dy binary systems, and Nd and Co have been successfully separated from the multicomponent solutions containing either Nd, Fe, Co, and Ni, or Co, Nd, and Dy, respectively. It has been shown that Nd / Pr mixture can be separated from heavier REEs by precipitation and afterwards Dy, Gd, and Ho can be recovered by solvent extraction. Fe separation from the magnet leachate with ionic liquids has been shown, followed by precipitation of REEs and Co with oxalic acid. Co was further separated from REEs by adding ammonia to form soluble Co ammonia complexes resulting in a 99.9% pure REE fraction.

[0007] The known methods rely on leaching the neodymium magnet material using strong acids, including also oxidative mineral acids. However, handling oxidative mineral acids, especially in high concentrations, is associated with an explosion risk. Therefore, more safe methods for REE recovery from neodymium magnets are needed.

[0008] Most of previously reported studies rely on simulated neodymium magnet leachate, whereby the leachate systems are rather simple. However, when recycling genuine end-of-life neodymium magnets, leachates comprising essentially all elements originally contained in the neodymium magnet are produced. Such leachates are much more complex than simulated leachate systems typically including, e.g., 2-4 elements. Methods for recovering REEs from genuine neodymium magnet waste, producing complex leachate solutions, are thus needed.

[0009] Summary

[0010] An object of the invention is to diminish or even eliminate the drawbacks found in the prior art.

[0011] Particularly, an object of the invention is to provide a more safe method for recovering REEs from neodymium magnet material.

[0012] A further object of the invention is to provide a more efficient method for recovering REEs from neodymium magnet material, even from complex neodymium magnet leachates comprising essentially all elements originally contained in the neodymium magnet material.

[0013] The invention is defined by what is stated in the independent claim. Advantageous embodiments and examples of the invention are presented in the dependent claims.

[0014] Any embodiments or examples of the invention presented herein that are specified with the open term “comprise” may be further limited with a closed term “consisting of’.

[0015] All embodiments or examples of the invention are mutually freely combinable, unless otherwise indicated. The presented embodiments and examples of the invention are applicable to all aspects of the invention.

[0016] A method for recovering rare earth elements, i.e., REEs, from neodymium magnet material is provided. The method comprises

[0017] 1 ) leaching the neodymium magnet material using methanesulfonic acid, thus providing a leachate; 2) separating iron from the metal salt solution, thus providing an iron- depleted leachate;

[0018] 3) separating rare earth elements from the iron-depleted leachate by adsorbing the rare earth elements into a first ion exchange material, thus providing REE-enriched ion exchange material and a REE-depleted leachate, whereby the REE-depleted leachate comprises any remaining elements originally contained in the neodymium magnet material, one or more of aluminium, cobalt, copper, nickel, and boron;

[0019] 4) recovering rare earth elements from the REE-enriched ion exchange material by eluding the REE-enriched ion exchange material using an acid, thus providing a fraction of rare earth elements.

[0020] Neodymium magnet material should be understood as material originating from neodymium magnets, such as neodymium magnet waste. The neodymium magnet waste may originate from, e.g., magnets in electric apparatuses such as hard disk drives, in a recycling process at the end of the lifespan of these apparatuses. The neodymium magnet material used in the presented invention may be separated from other parts of the electric apparatuses, demagnetized and ground into small particles. Grain size of the ground neodymium magnet material may be, e.g., smaller than 250 pm, meaning that the ground neodymium magnet material may be sieved through a 250 pm sieve without losses. The neodymium magnet material comprises all elements originally contained in the neodymium magnet to be recycled.

[0021] In the course of this specification, rare earth elements, i.e., REEs, are understood to include at least neodymium Nd, praseodymium Pr, dysprosium Dy, terbium Tb, samarium Sm, and holmium Ho.

[0022] Using methanesulfonic acid, i.e., MSA, at 1 ) to leach the neodymium magnet material has several advantages over other acids, such as mineral acids, e.g., sulfuric acid, hydrochloric acid, or nitric acid. Firstly, methanesulfonic acid is not an oxidative acid. Therefore, the risk of explosion when handling is reduced, thus improving the working safety of the method. Secondly, methanesulfonic acid may dissolve several metals in higher concentrations compared to mineral acids. Thirdly, methanesulfonic has a smaller environmental footprint compared to mineral acids, whereby the method is more environmentally friendly than conventional methods. The leaching by MSA may yield a leachate containing up to over 80 % of each of an individual rare earth element originally contained in the neodymium magnet material, the percentage defined as the weight percentage of the an individual rare earth element in the leachate of the weight of the same individual rare earth element originally contained in the neodymium magnet material. For some REEs, the leaching efficiency can reach even 90 or 100%.

[0023] Separating iron at 2) prior to the separation of the REEs improves the separation efficiency and purity of the REE fraction.

[0024] Adsorbing the rare earth elements at 3) may be performed by adsorbing the REEs from the iron-depleted leachate into a first ion exchange material. Various ion exchange materials may be used, provided that the adsorption process specifically separates the rare earth elements from any other elements contained in the iron-depleted leachate. Adsorption is a simple and efficient method to separate the REEs from the iron-depleted leachate.

[0025] Recovering the rare earth elements at 4) is most conveniently performed by eluding the REE-enriched ion exchange material using an acid. The obtained REE fractions may be obtained in a very high purity of up to 99.4 ± 0.4 wt-%, the purity as weight percentage defined as the dry weight of the desired REEs in the REE fraction compared to the total dry weight of the REE fraction.

[0026] The adsorption at 3) and the elution at 4) provide a very efficient method for recovering REEs from the iron-depleted leachate. Adsorption efficiency of the first ion exchange material at 3) may be in the range of 90-100%, defined as the weight of the adsorbed REEs compared to the original weight of the REEs in the iron-depleted leachate. The elution, or in other words, desorption, at 4) is essentially quantitative, i.e., in the range of 95-100 wt-% of the REEs adsorbed in the first ion exchange material at 3) may be desorbed at 4).

[0027] All in all, the presented method provides a very efficient method for recovering REEs from neodymium magnet material. With a leaching efficiency exceeding 80%, combined with an adsorption efficiency exceeding 90% at 3) and a quantitative elution efficiency at 4), the overall recovery efficiency of the method may exceed 70 %, defined as the dry weight of the recovered REE fraction compared to the dry weight of the REEs originally contained in the neodymium magnet material. The overall recovery efficiency may be even further enhanced to exceed 80% or even 90%, defined as the dry weight of the recovered REE fraction compared to the dry weight of the REEs originally contained in the neodymium magnet material, by repeating the adsorption and desorption steps on the REE-depleted leachate.

[0028] Brief description of the drawings

[0029] Figure 1 presents a schematical process flow of methods according to the invention.

[0030] Figure 2 presents adsorption efficiencies of the elements comprised in the neodymium magnets at different pH values. The adsorption efficiencies are determined using 3D-printed PA12-filters with aminomethylphosphonic acid additive (LEWATIT® MonoPlus TP 260) as ion exchange material.

[0031] Figure 3 presents leaching efficiencies of the elements comprised in the neodymium magnets as a function of concentration of the methanesulfonic acid solution.

[0032] Figure 4 presents total amounts of adsorbed and desorbed REEs during an adsorption-desorption cycle study.

[0033] Detailed description

[0034] Referring to Figure 1 , the presented method may comprise, at 1 ), leaching the neodymium magnet material using methanesulfonic acid (MSA). Thus, a leachate is provided. The method may further comprise a filtering step after the MSA leaching to remove any undissolved solids. The filter may be selected from ultrafiltration membranes, filter papers, filter presses, and the like. The average pore size of the filter may be in the range of 0.01-100 pm, such as in the range of 0.01-0.1 pm for ultrafiltration membranes, or in the range of I Q- 50 pm for filter papers. Therefore, the leachate as presented herein is a homogeneous solution comprising dissolved material originally contained in the neodymium magnet material.

[0035] The neodymium magnet material may originate from, e.g., neodymium magnet waste. The neodymium magnet material, such as magnet waste, may be demagnetized and ground to an average particle size of 250 pm or less prior to the leaching. The average particle size of 250 pm or less should be understood such that the ground neodymium magnet material may be sieved through a sieve having a pore size of 250 pm without losses.

[0036] The methanesulfonic acid used for the leaching at 1 ) may be pure methanesulfonic acid or an aqueous methanesulfonic acid solution. The methanesulfonic acid may be an aqueous methanesulfonic acid solution having a methanesulfonic acid concentration in the range of 10-100 vol-% of the total volume of the methanesulfonic acid solution (vol / vol). Pure methanesulfonic acid may be expressed as a solution having a methanesulfonic acid concentration of 100 vol-%. Preferably, the methanesulfonic acid is an aqueous methanesulfonic acid solution having a methanesulfonic acid concentration in the range of 10-60 vol-% or in the range of 90-100 vol-% of the total volume of the methanesulfonic acid solution (vol / vol). Extensive research has shown that the leaching efficiency at MSA concentrations in the range of 10-60 vol-% and 90-100 vol-% may exceed 80%, or even 90%, but that there is a decrease in the leaching efficiency at MSA concentrations in the range of ca. 65-85 vol-%, the leaching efficiency defined as the percentage of dissolved material compared to the original weight of the neodymium magnet material. Without being bound to any theory, the decrease in leaching efficiency may be explained by decreased solubility of metal salts as the MSA concentration increases. In part, the decreased solubility may be explained by the formation of instable, insoluble complexes at the 65-85 vol-% concentration region, whereas in the higher concentration range of 90-100 vol-%, more soluble methanesulfonate salts are formed.

[0037] The leaching at 1 ) may be performed at a temperature selected in the range of 40-100°C, preferably 50-70°C. The use of elevated temperatures as defined herein for the leaching may provide a higher leaching efficiency compared to temperatures below 40°C. On the other hand, temperatures above 100°C are not practical, especially when the MSA is used as an aqueous solution, due to the rapid evaporation of water due to temperatures above its boiling point. Furthermore, leaching at temperatures below 100°C is less energy-consuming than leaching at higher temperatures. The leaching at 1 ) may be performed for 0.5-40 h to ensure a good leaching efficiency. Leaching times shorter than 0.5 h may not dissolve the neodymium magnet material completely, whereas leaching times longer than 40 h do not provide any further advantages. The leaching efficiency does not substantially improve even when continuing the leaching for longer than 40 h. The leaching process may further comprise a leach-enhancing treatment by using, e.g., microwave radiation or ultrasound treatment. The advantage of such treatment may be a more efficient leaching, leading to decreased leaching times. In such cases, the leaching time may be decreased to even tens of minutes. Thus, in leaching processes comprising such a leach-enhancing treatment, the leaching may preferably be carried out for 0.5-10 h, such as 0.5-2 h. For leaching processes without a leach-enhancing treatment, the leaching is preferably carried out for 10-30 h.

[0038] The leaching at 1 ) may be performed using a solid / liquid ratio (S / L ratio) in the range of 1-10 g / L. The solid / liquid ratio is determined as the ratio of the mass of the neodymium magnet material to the total volume of the methanesulfonic acid used for the leaching. If methanesulfonic acid is used as an aqueous solution, the solid / liquid ratio is defined as the ratio of the mass of the neodymium magnet material to the total volume of the methanesulfonic acid solution used for the leaching. Preferably, the solid / liquid ratio is in the range of 3-6 g / L. Research has shown that solid / liquid ratios as specified herein ensure an adequate leaching efficiency while keeping the acid usage at a moderate level. Solid / liquid ratios higher than specified herein, i.e., larger amount of neodymium magnet material compared to the acid amount, may not be enough to dissolve the neodymium magnet material. On the other hand, solid / liquid ratios lower than specified herein, i.e., larger amount of acid compared to the amount of the neodymium magnet material, may lead to excessive acid usage, which aggravates the working safety and health concerns always associated with handling chemicals, and incurs unnecessary cost.

[0039] Still referring to Figure 1 , the method may comprise separating iron from the metal salt solution at 2). Thus, an iron-depleted leachate is provided. Removal of iron, being the most abundant element in alloys making up neodymium magnets, is crucial for the separation of REEs from the leachate to be efficient, as REEs are present in the leachate in concentrations far smaller than iron. Research has shown that no clear iron precipitation occurs during the leaching at concentration regions of 10-60 vol-% and 90-100 vol-%. This might be due to the fact that iron is not fully oxidized to the +3 state during the leaching process. Thus, in the leachate, iron is mostly found in the Fe(ll) oxidation state.

[0040] Separating the iron at 2) may be performed by oxidising iron as Fe(ll) into Fe(lll). The oxidation may be followed by precipitating the iron as Fe(lll) from the leachate. In the precipitation process, it is beneficial to first oxidize the iron into Fe(lll), since precipitation of iron as Fe(ll) would require a pH as high as 9.5. At such high pH, co-precipitation of other elements such as the REEs would be undesirably high. Thus, to be able to precipitate iron as Fe(lll) at a pH where the co-precipitation of the valuable REEs is minimal, pH of the leachate at the iron separation at 2) should be in the range of 3-5. The pH of the leachate obtained at the leaching at 1 ) is typically lower than 3. Thus, the pH may be adjusted to a value in the range of 3-5 by adding a base and / or an acid, preferably a base. Preferably, the base is a hydroxide selected from the group comprising ammonium hydroxide, potassium hydroxide, sodium hydroxide, and any combination thereof, more preferably ammonium hydroxide. Ammonium hydroxide has advantages in process economy: ammonium salts are used in other phases of the method. Thus, it is preferable to use the same cations for the pH adjustment purposes to avoid contamination and to simplify recycling of the process liquids. If the pH is accidentally increased too much, adjusting the pH may comprise adding an acid. The acid may be selected from the group comprising methanesulfonic acid, sulfuric acid, hydrochloric acid, nitric acid, and any combination thereof. Preferably, the acid is methanesulfonic acid, providing the advantages of simplifying the chemical system, eliminating the need to separate different acid anions, and recyclability of the process liquids.

[0041] Oxidation of Fe(ll) may be performed with any suitable oxidant, such as hydrogen peroxide, preferably used as an aqueous solution, or an oxygen-rich gas. In an example, the oxidation of Fe(ll) may be performed by adding an aqueous hydrogen peroxide solution, having a concentration in the range of 10-50 vol-% (vol / vol), defined as the volume percentage of hydrogen peroxide in the total volume of the hydrogen peroxide solution, to the leachate. In another example, the oxidation of Fe(ll) may be performed by bubbling an oxygen-containing gas, such as air, an oxygen-enriched gas, or oxygen, through the leachate. As the iron oxidises into Fe(lll), it precipitates and may conveniently be removed from the leachate, for example by filtering. The separation step may be very selective towards iron, since the REEs, typically present in the leachate in their +3 oxidation state, remain dissolved upon addition of the oxidant.

[0042] Referring to Figure 1 , the method may comprise separating rare earth elements from the iron-depleted leachate at 3) by adsorbing the rare earth elements into a first ion exchange material. Thus, REE-enriched ion exchange material and a REE-depleted leachate are provided. The REE-depleted leachate comprises any remaining elements originally contained in the neodymium magnet material. Preferably, the REE-depleted leachate comprises at least one or more of aluminium, cobalt, copper, nickel, and boron. The REE-enriched ion exchange material comprises at least a majority of the rare earth elements originally contained in the neodymium magnet material. As noted above, the adsorption efficiency may be as high as 90-100%, defined as the weight of the adsorbed REEs compared to the original weight of the REEs in the iron-depleted leachate. In other words, the REE-enriched ion exchange material may comprise 90-100 wt-% of the REEs originally contained in the iron-depleted leachate.

[0043] The adsorbing at 3) may be performed at a pH in the range of 0-0.5. Preferably, the adsorbing is performed at a pH in the range of 0-0.3, more preferably in the range of 0.1-0.2. Extensive research has shown that the adsorption process is highly selective towards the REEs at pH values as specified herein. As presented in Figure 2, 90-100 % adsorption efficiencies for all separated REEs may be obtained at these low pH values.

[0044] Alternatively or in addition, the adsorbing at 3) may comprise adjusting the pH using an acid selected from the group comprising methanesulfonic acid, sulfuric acid, hydrochloric acid, nitric acid, and any combination thereof. Preferably, the adsorption at 3) comprises adjusting the pH using methanesulfonic acid. Using methanesulfonic acid, i.e. , the same acid than at the leaching at 1 ), provides the advantage of simplifying the chemical system at the end of the process. No additional ions are introduced into the process, which reduces the risk of contamination in the used equipment and eliminates the need to separate different acid anions from each other. With only methanesulfonates in the system, the process liquids, i.e. , the methanesulfonic acid solutions, may be recycled and used repeatedly. This mono-acid system makes the method compatible with the concept of circular economy.

[0045] Referring to Figure 1 , the method may further comprise separating one or more of aluminium, cobalt, copper, nickel, and boron from the REE-depleted leachate at 3.a). The separation at 3. a) may be comprised in the method after the adsorption step 3). The REE-depleted leachate is a rather complex system, as it comprises any remaining elements originally contained in the neodymium magnet material. Preferably, the REE-depleted leachate comprises at least one or more of aluminium, cobalt, copper, nickel, and boron. It is beneficial to be able to separate the REE-depleted leachate into simpler fractions comprising a majority of Al, B, Cu, and Co for further separation.

[0046] The separating at 3. a) may comprise separating aluminium and copper from the REE-depleted leachate at 3.a.1 ) by adsorbing the aluminium and copper and possibly co-adsorbing cobalt into a second ion exchange material. Thus, an aluminium-and-copper-enriched ion exchange material and a cobalt-boron fraction are provided. At this step, aluminium and copper may be adsorbed essentially quantitatively in the second ion exchange material, whereas boron passes through into the solution (i.e., into the cobalt-boron fraction). Cobalt may be partly adsorbed, i.e., co-adsorbed, and partly passed through in the solution. Thus, the separating at 3.a.1 ) may provide a quantitative separation of aluminium and copper from boron. The cobalt-boron fraction may comprise 55-65 wt-% of B and 35-45 wt-% of Co, of the total dry weight of the cobalt- boron fraction.

[0047] The separating at 3.a.1 ) may be performed at a pH in the range of 1-4, preferably in the range of 1-2. The separating at 3.a.1 ) may comprise adjusting the pH with a base and / or an acid. The REE-depleted leachate obtained at 3) may have a pH in the range of 0-0.5. Thus, adjusting the pH may comprise increasing the pH of the REE-depleted leachate prior to the separation at 3.a.1 ). The pH may be adjusted with a base. Preferably, the base is a hydroxide selected from the group comprising ammonium hydroxide, potassium hydroxide, sodium hydroxide, and any combination thereof, more preferably ammonium hydroxide. Ammonium hydroxide has advantages in process economy: ammonium salts are used in other phases of the method. Thus, it is preferable to use the same cations for the pH adjustment purposes to avoid contamination and to simplify recycling of the process liquids. If the pH is accidentally increased too much, adjusting the pH may comprise adding an acid. The acid may be selected from the group comprising methanesulfonic acid, sulfuric acid, hydrochloric acid, nitric acid, and any combination thereof. Preferably, the acid is methanesulfonic acid, providing the advantages of simplifying the chemical system, eliminating the need to separate different acid anions, and recyclability of the process liquids, as already discussed above.

[0048] Alternatively or in addition, the separating may comprise eluding the aluminium-and-copper-enriched ion exchange material 3. a.2) using an ammonium salt. Preferably, the ammonium salt is selected from the group comprising ammonium chloride, ammonium nitrate, ammonium sulfate, and any combination thereof, more preferably ammonium chloride. Preferably, the ammonium salt is used as an aqueous solution. The elution at 3.a.1 ) may separate at least part of the adsorbed copper and the co-adsorbed cobalt from the aluminium-and-copper-enriched ion exchange material (in other words, the second ion exchange material enriched in aluminium and copper). Thus, a cobalt-copper fraction is separated. The cobalt-copper fraction may comprise 80-90 wt-% Co and 10-20 wt-% Cu, of the total dry weight of the cobaltcopper fraction. Essentially all aluminium may be retained in the ion exchange material. Furthermore, some copper is also retained in the aluminium-and- copper-ion exchange material together with cobalt.

[0049] The separating at 3. a) may further comprise eluding the aluminium-and- copper-enriched ion exchange material for a second time 3. a.3) using an oxalate. The oxalate may be potassium oxalate. The oxalate is preferably provided in the form of an aqueous solution. Thus, an aluminium-enriched fraction is provided.

[0050] Alternatively to the subsequent elutions at 3. a.1 ) and 3. a.2), the separating at 3. a) may comprise separating boron by adsorbing the one or more of aluminium, cobalt, copper and nickel into a third ion exchange material at a pH in the range of 3-5, preferably in the range of 3.5-4.5, thus providing ion exchange material enriched in the one or more of aluminium, cobalt, copper and nickel, and a boron fraction. In other words, boron may be passed through the third ion exchange material, while the one or more of aluminium, cobalt, copper and nickel are adsorbed into the third ion exchange material at an adsorption efficiency in the range of 90-100%. The one or more of aluminium, cobalt, copper and nickel may be subsequently released from the third ion exchange material.

[0051] Referring to Figure 1 , the method may further comprise, after 3), separating co-adsorbed copper from the REE-enriched ion exchange material at 3.b) by eluding the REE-enriched ion exchange material using an ammonium salt. Preferably, the ammonium salt is selected from the group comprising ammonium chloride, ammonium nitrate, ammonium sulfate, and any combination thereof. More preferably, the ammonium salt is ammonium chloride. The ammonium salt is preferably used as an aqueous solution. Concentration of the ammonium salt, particularly in the aqueous solution, is preferably in the range of 0.5-2 M, more preferably in the range of 1-1.5 M. Thus, a copper fraction is provided. Separating the copper at 3.b), prior to the REE recovery, may improve the purity of the REE fraction.

[0052] The process may further comprise recovering copper, e.g., as a solid copper salt from the solid fraction, e.g., by precipitation. The process may thus comprise providing copper as a profitable product.

[0053] Still referring to Figure 1 , the process may comprise recovering rare earth elements from the REE-enriched ion exchange material at 4) by eluding the REE-enriched ion exchange material using an acid. Thus, a fraction of rare earth elements is provided.

[0054] The eluding at 4) may be performed using an acid selected from the group comprising methanesulfonic acid, sulfuric acid, hydrochloric acid, nitric acid, and any combination thereof. Preferably, the acid is methanesulfonic acid. The acid at 4) may be an aqueous acid solution having a concentration in the range of 1-10 M, preferably 3-6 M. The acid elution ensures an efficient recovery of the rare earth elements from the REE-enriched ion exchange material. The selection of methanesulfonic acid as the acid provides the advantages of improved working safety and smaller environmental impact, as already discussed above regarding the use of MSA for the leaching. Furthermore, upon selecting methanesulfonic acid as the eluent at 4), the introduction of additional ions to the process system may be avoided. Thus, contamination of the process chemicals with foreign ions may be eliminated. This enables recycling the used process chemicals (e.g., the methanesulfonic acid) without the need for cumbersome purification from the foreign ions. Further, usage of the process chemicals such as MSA may be reduced. By enabling the recycling of the process chemicals, the process may be compatible with the concept of circular economy.

[0055] Alternatively or in addition to the separating one or more of aluminium, cobalt, copper, and boron from the REE-depleted leachate at 3. a, the method may comprise repeating the separation of the REEs by adsorption at 3) and the elution of the REEs by elution at 4). Thereby, the overall recovery efficiency of the REEs may be enhanced to exceed 80% or even 90%, the overall recovery efficiency defined as the dry weight of the recovered REE fraction compared to the dry weight of the REEs originally contained in the neodymium magnet material. Repetition of the adsorption at 3) and the elution at 4) may be carried out using the same ion exchange material. In other words, the same ion exchange system may be used repeatedly for multiple adsorption-desorption cycles. Figure 4 presents the performance of a single ion exchange system used for as many as 50 cycles (see Example 4).

[0056] The rare earth element fraction obtained at 4) may be utilized as a REE source as is. The REE fraction may be used as a solution, or the rare earth elements may be recovered from the solution into a solid REE mixture by, e.g., precipitation or crystallization as phosphonates, sulfates, fluorides, or oxalates that may be further converted to oxides.

[0057] Alternatively, the method may further comprise separating one or more individual rare earth elements from the REE fraction obtained at 4). Separating one or more individual REEs may comprise, e.g., ion exchange, extraction, precipitation or crystallization as phosphonates, sulfates, fluorides, or oxalates that may be further converted to oxides.

[0058] Alternatively or in addition, it is also possible to separate the REE fraction to produce less complex systems, such as bicomponent mixtures. Thus, it is possible to separate, e.g., a mixture of neodymium and praseodymium, also known as didymium, from the remaining REE fraction. Any of the ion exchange materials, i.e., the first ion exchange material, the second ion exchange material, and / or the third ion exchange material, may individually comprise a polymer matrix. The polymer matrix preferably comprises a polymer selected from polyamides, polypropene, polystyrene, and any combination thereof, more preferably polyamide 12. The polymer matrix may be a cross-linked polymer matrix, comprising a cross-linker such as divinylbenzene (DVB).

[0059] Any of the ion exchange materials, i.e., the first ion exchange material, the second ion exchange material, and / or the third ion exchange material, may individually further comprise an additive. Preferably, the additive is selected from the group comprising phosphonic acids, sulfonic acids, phosphates, and any combinations thereof. More preferably, the additive is selected from aminophosphonic acids, such as aminomethylphosphonic acids, aminobisphosphonic acids, or any combinations thereof. The additive may improve the selectivity of the ion exchange resin towards specific elements to be adsorbed.

[0060] Any of the ion exchange materials, i.e., the first ion exchange material, the second ion exchange material, and / or the third ion exchange material may individually be arranged as one or more filters, as spherical beads, or as one or more membranes.

[0061] The ion exchange materials may be arranged as one or more filters. A filter should be understood a porous structure through which liquid may flow. A filter should have, however, fixed outer dimensions. In the case of more than one filter, such as two, three, four, or five filters, the filters may conveniently be placed in contact with each other, in other words, superimposed on each other. Filter-like ion exchange materials may be obtained by, e.g., additive manufacturing methods, also known as 3D printing methods. Suitable methods include, but are not limited to, selective laser sintering (SLS), direct ink writing (DIW), and digital light processing (DLP).

[0062] 3D printed adsorption materials have become increasingly common over the past decade, a trend influenced by the development of 3D printers as well as the ease of manufacturing 3D printed filters with different sizes, shapes, and adsorbents. Typically, an additive is mixed with a polymer matrix, which serves as a framework where the additive can either attach or become encapsulated within the pores of the matrix.

[0063] Porous structures can be obtained using various 3D printing techniques. Selective laser sintering (SLS) may be a preferred method for preparing the ion exchange materials for the presented method. SLS is shown to offer distinct advantages. SLS can utilize commercial polymer powders for essentially any printable additive. In comparison, DIW and DLP require more careful tailoring of the composition of the ink or resin. Furthermore, objects printed by SLS techniques require no further curing, unlike the ones manufactured with DIW or DLP. When considering metal recovery, the polymer matrix used in SLS printing have also been demonstrated to be relatively inert and capable of withstanding strongly acidic metal containing solutions which are commonly used in industrial applications. As presented in Figure 4, 3D printed filters used as the first ion exchange material in the presented method may withstand several tens of adsorption-desorption cycles without being damaged by the iron-depleted leachate at the REE separation at 3) or the acid at the REE recovery at 4).

[0064] Examples

[0065] Example 1. Magnet composition

[0066] Leaching of the NdFeB magnet. The elemental composition of ground NdFeB magnets was determined by total acid digestion with aqua regia and S / L ratio of 5 g / l. The total dissolution time for the magnet was 3 h in 60 °C and no residues were detected after filtration. Any undissolved material was filtered, and the solution was diluted to 100 ml with ultrapure water. The amount of leached elements was determined using inductively coupled plasma-optical emission spectroscopy (ICP-OES, Perkin Elmer ICP-OES Optima 8300 spectrometer). The elemental composition of the studied magnets is presented in Table 1 . The main components were Fe (63 wt%) and Nd (21 wt%) followed by Pr (6 wt%), Dy (3 wt%) and B (1 wt%). The magnet also contained small amounts of Al, Co, Cu, Sm, Tb, and Ho (<1 wt%).

[0067] Table 1. Elemental composition of NdFeB magnets.

[0068] Example 2. Magnet leaching

[0069] MSA was used for leaching ground NdFeB magnets with 10-100 vol% MSA solutions. The temperature was kept at 60 °C for 24 hours and S / L ratio of 5 g / l was used by weighing 25 mg of the magnet to 5 ml of the acid. Any undissolved material was filtered, and the solution was diluted to 100 ml with ultrapure water and adjusted with MSA to obtain 5% MSA (vol / vol). The concentrations of each metal were measured with ICP-OES (Perkin Elmer ICP-OES Optima 8300 spectrometer). The leaching results were compared with the results of the total dissolution (Example 1 ) and presented in Figure 3.

[0070] Example 3. Iron precipitation

[0071] Iron was removed from the magnet leachate by oxidizing Fe(ll) to Fe(lll) with an excess of H2O2 and setting the pH to 4 with 25% NH4OH. During the oxidation process, a brown precipitate formed, which was removed by filtration. The absence of Fe in the filtrate was confirmed by ICP-OES measurement (Perkin Elmer ICP-OES Optima 8300 spectrometer). Only traces of Fe were detected in the filtrate, and the obtained precipitation percentage for Fe was 99.9 wt-%, indicating complete removal of Fe from the magnet leachate. Only Al (27 ± 3 wt-%) and Cu (12 ± 7 wt-%) co-precipitated clearly with Fe during the oxidation process, whereas the precipitation of other elements was less than 5 wt-%. The weight percentages are expressed as weight percentages of each element in the iron precipitate of the total weight of said element originally contained in the neodymium magnet material.

[0072] Table 2. Precipitation efficiency of iron and co-precipitated other elements as weight-%. The weight percentages are expressed as weight percentages of each element in the iron precipitate of the total weight of said element originally contained in the neodymium magnet material.

[0073] Example 4. Adsorption-desorption cycles.

[0074] A 9 ml sample of the simulated NdFeB solution containing 22 mg / l of Nd, 3,5 mg / l of Dy, 8 mg / l of Pr, 2 mg / l of Al, 1 ,5 mg / l of B and <1 mg / l of Co, Sm, Tb, Ho, and Cu was injected to one 3D-printed filter at pH 0.15 with a flowrate of 90 ml / h. The elements were desorbed from the filter with a 20 ml of 5M MSA, except for the first five cycles where 3M MSA was used, using the flow rate of 15 ml / h. Elemental concentrations were measured using ICP-OES (Perkin Elmer ICP-OES Optima 8300 spectrometer). The structural changes in the filter during 50 adsorption-desorption cycles were investigated with X-ray tomography. The adsorbed and desorbed total amounts of the REEs after every 5 cycles are presented in Figure 4, indicating very efficient adsorption and desorption of the REE fraction as well as robustness and prolonged performance of the filters. Previously reported methods typically show a decrease in the adsorption efficiency after, e.g., five cycles.

[0075] Example 5. Separation process

[0076] The process may be started with the leaching step 1 ) (Example 2), after which Fe is removed from the leachate as described above at 2) (Example 3). All the concentrations from the initial solutions and filtrates were determined using ICP-OES (Perkin Elmer ICP-OES Optima 8300 spectrometer).

[0077] For the recovery, a 10 ml portion of the NdFeB leachate was first passed through three stacked 3D-printed PA12-filters with aminomethylphosphonic acid additive (LEWATIT® MonoPlus TP 260) at pH 0.15 using 5% MSA (vol / vol), using the flowrate of 90 ml / h. Rare earth elements were completely adsorbed into the stack of three filters at 3), while most of Al, Cu, Co, and B passed through the filters. The filters containing REEs, and possibly a small amount of Co, Cu, and Al, was eluted with 1 M NH4CI with a flowrate of 15 ml / h to desorb Cu from the filter at 3.b). This step was followed by the elution of the filter with a 30 ml of 5 M MSA, to recover REEs almost completely (>96 wt-%) from the filter into their own fraction with a purity of 99.4% at 4). The pH of the filtrate, containing B, Al, Co, and Cu at 3. a), is adjusted to 1.5 using 25% NH4OH at 3.a.1 ). The resulting solution is injected into a new set of filters to adsorb 100 wt-% of Al, 80 wt-% of Cu, and 50 wt-% of Co, whereas B remains in the solution resulting in the filtrate containing 62 wt-% of B and 38 wt-% of Co at 3.a.1 ). The percentages are expressed as weight-% of each element of the total weight of the respective fraction. The amount of Cu in the Co + B fraction was minimal. The filters containing Al, Cu and Co is then eluted first with a 30 ml of 1 M NH4CI at 3. a.2) followed by a 30 ml of 0.4 M potassium oxalate elution at 3.a.3) to obtain Co-rich (3. a.2) and Al-rich (3. a.3) fractions, respectively.

Claims

Claims:

1. A method for recovering rare earth elements, i.e., REEs, from neodymium magnet material, the method comprising1 ) leaching the neodymium magnet material using methanesulfonic acid, thus providing a leachate;2) separating iron from the metal salt solution, thus providing an iron- depleted leachate;3) separating rare earth elements from the iron-depleted leachate by adsorbing the rare earth elements into a first ion exchange material, thus providing REE-enriched ion exchange material and a REE-depleted leachate, whereby the REE-depleted leachate comprises any remaining elements originally contained in the neodymium magnet material, preferably at least one or more of aluminium, cobalt, copper, nickel, and boron;4) recovering rare earth elements from the REE-enriched ion exchange material by eluding the REE-enriched ion exchange material using an acid, thus providing a fraction of rare earth elements.

2. The method according to claim 1 , wherein separating iron at 2) is carried out by oxidising iron as Fe(ll) into Fe(lll), followed by precipitating the iron as Fe(lll) from the leachate.

3. The method according to claim 1 or 2, further comprising, after 3),3. a) separating one or more of aluminium, cobalt, copper, and boron from the REE-depleted leachate.

4. The method according to claim 3, wherein the separating 3. a) comprises one or more of the following:3.a.1 ) separating aluminium and copper from the REE-depleted leachate by adsorbing the aluminium and copper and possibly co-adsorbing cobalt into a second ion exchange material, thus providing an aluminium-and- copper-enriched ion exchange material and a cobalt-boron fraction;3. a.2) eluding the aluminium-and-copper-enriched ion exchange material using an ammonium salt, preferably an ammonium salt selected from the group comprising ammonium chloride, ammonium nitrate, ammonium sulfate, and any combination thereof, more preferably ammonium chloride,to separate at least part of the adsorbed copper and the co-adsorbed cobalt, thus separating a cobalt-copper fraction; and3. a.3) eluding the aluminium-and-copper-enriched ion exchange material for a second time using an oxalate, such as potassium oxalate, thus providing an aluminium-enriched fraction.

5. The method according to claim 4, wherein the adsorbing at 3.a.1 ) is performed at a pH in the range of 1-4, preferably in the range of 1-2; and / or wherein 3.a.1 ) comprises adjusting the pH with a base and / or an acid, preferably wherein the base is a hydroxide selected from the group comprising ammonium hydroxide, potassium hydroxide, sodium hydroxide, and any combination thereof; and / or wherein the acid is selected from the group comprising methanesulfonic acid, methanesulfonic acid, sulfuric acid, hydrochloric acid, nitric acid, and any combination thereof.

6. The method according to claim 3, wherein the separating 3. a) comprises separating boron by adsorbing the one or more of aluminium, cobalt, copper and nickel into a third ion exchange material at a pH in the range of 3-5, preferably in the range of 3.5-4.5, thus providing ion exchange material enriched in the one or more of aluminium, cobalt, copper and nickel, and a boron fraction.

7. The method according to any of the preceding claims, wherein the method further comprises, after 3),3.b) separating co-adsorbed copper from the REE-enriched ion exchange material by eluding the REE-enriched ion exchange material using an ammonium salt, preferably an ammonium salt selected from the group comprising ammonium chloride, ammonium nitrate, ammonium sulfate, and any combination thereof, more preferably ammonium chloride, thus providing copper fraction, preferably wherein the concentration of the ammonium salt is in the range of 0.5-2 M, more preferably in the range of 1-1.5 M.

8. The method according to any of the preceding claims, wherein the methanesulfonic acid used at 1 ) for the leaching is an aqueous methanesulfonic acid solution having a methanesulfonic acid concentration in the range of 10-100 vol-% of the total volume of the methanesulfonic acid solution.

9. The method according to any of the preceding claims, wherein the leaching at 1 ) is performed at a temperature selected in the range of 40-100°C, preferably 50-70°C; and / or wherein the leaching at 1 ) is performed for 0.5-40 h, preferably 10-30 h; and / or wherein the leaching at 1 ) is performed using a solid / liquid ratio in the range of 1-10 g / L, preferably in the range of 3-6 g / L, the solid / liquid ratio being determined as the ratio of the mass of the neodymium magnet material to the total volume of the methanesulfonic acid used for the leaching.

10. The method according to any of the preceding claims, wherein the adsorbing at 3) is performed at a pH in the range of 0-0.5, preferably in the range of 0-0.3, more preferably in the range of 0.1 -0.2; and / or wherein 3) comprises adjusting the pH using an acid selected from the group comprising methanesulfonic acid, sulfuric acid, hydrochloric acid, nitric acid, and any combination thereof, preferably wherein 3) comprises adjusting the pH using methanesulfonic acid.11 . The method according to any of the preceding claims, wherein the first ion exchange material, the second ion exchange material, and / or the third ion exchange material is individually arranged as one or more filters, as spherical beads, or as one or more membranes.

12. The method according to any of the preceding claims, wherein the first ion exchange material, the second ion exchange material, and / or the third ion exchange material individually comprises a polymer matrix, preferably wherein the polymer matrix comprises a polymer selected from polyamides, polypropene, polystyrene, and any combination thereof, more preferably polyamide 12.

13. The method according to claim 12, wherein the first ion exchange material, the second ion exchange material, and / or the third ion exchange material individually further comprises an additive, preferably an additive selected from the group comprising phosphonic acids, sulfonic acids, phosphates, and any combinations thereof, more preferably aminophosphonic acids, such as aminomethylphosphonic acids, aminobisphosphonic acids, or any combinations thereof.

14. The method according to any of the preceding claims, wherein the eluding at 4) is performed using an acid selected from the group comprising methanesulfonic acid, sulfuric acid, hydrochloric acid, nitric acid, and any combination thereof, preferably methanesulfonic acid; and / or wherein the acid at 4) is an aqueous acid solution having a concentration in the range of 1-10 M, preferably 3-6 M.

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