Magnet recycling process

Abstract

A process for the removal of iron impurities from a rare earth metal-containing composition, which comprises contacting the rare earth metal-containing composition comprising rare earth metals and ir

Description

FIELD OF THE INVENTION The invention relates to processes for the removal of iron impurities and optionally other impurities from rare earth metal-containing compositions such as rare earth metalcontaining compositions from magnets and ores. BACKGROUND OF THE INVENTION Rare earth metal elements are an essential component of many modern technologies, and in particular many technologies that are important for the green transition. There are seventeen rare earth elements. These are scandium, yttrium and the fifteen lanthanide elements. In many applications, rare earth metal elements are used in magnets such as Neodymium-lron-Boron (NdFeB) magnets. These magnets are very strong permanent magnets and overtime, in many applications, have come to replace inferior magnets that do not contain rare earth metals. Rare earth metal-containing magnets are a critical component in technologies such as electric vehicles, industrial motors, consumer electronics and wind turbines used for electricity generation. Rare earth elements are thus essential for a transition to green energy and electrification of transport. Traditionally, rare earth metals have been acquired from their naturally occurring ores which are mined in various countries of the world. China, Vietnam, Brazil, Russia, India, Australia and USA amongst others all have significant reserves of rare earth metals with China by some way having the greatest amount. The rare earth metals are conventionally obtained from their ores by acid leaching followed by extraction of the rare earth metals from the ore leachates. The demand for rare earth metal elements is expected to greatly increase over the coming decades as the rate of adoption of technologies that require their use increases. Currently, only around 1% of rare earth elements are recycled. In more recent years, increasing research has been undertaken into recycling of rare earth metal elements from e.g. used rare earth metal-containing magnets and other rare earth metal-containing components in order to mitigate the risk of potential future supply chain issues. Supply chain issues are especially a concern in countries that do not have their own natural reserves of rare earth elements. Rare-earth metal containing magnets such as NdFeB typically contain only 25% to 30% by weight of neodymium and other rare earth metal elements. The remainder of the magnet is typically made up of iron and other impurity metals such as aluminium. The separation of the rare earth metal elements from the other metals and impurities of the magnet is however challenging. Various recycling techniques for attempting to extract the rare earth elements from NdFeB magnets and other compositions are known in the art. These techniques can be broadly divided into hydrometallurgical techniques, pyrometallurgical techniques and hydrogen decrepitation. Hydrometallurgical techniques involve the use of aqueous (typically acidic) solutions to extract the rare earth metals from the magnets. Pyrometallurgical techniques involve thermal treatment of the magnets. A problem with pyrometallurgical techniques is that the thermal treatment is energy intensive and the product purity is often too low. Hydrogen decrepitation involves treating the magnets with hydrogen gas to break them down and render easier the recovery of the rare earth elements. Problems with hydrogen decrepitation include that its success is highly feedstock dependent, and that the recycled products produced often contain impurities and are generally of inferior quality to new magnets. Hydrometallurgical techniques have been receiving increasing interest due to their ability to provide individual high purity rare earth oxides. High purity rare earth oxides are essential for the manufacture of the high-performance magnets used in wind turbines and electric vehicles. The known hydrometallurgical techniques for rare earth metal separation can be divided into rough separation processes and purification separation processes. Rough separation processes are processes for extracting the rare earth metal elements from impurities present in the magnets and other compositions such as iron, aluminium and other elements such as thorium, phosphorus, titanium and manganese. Purification separation processes are subsequent downstream processes for removing microamount impurities from aqueous solutions of one or more rare earth metals or processes for separating a specific rare earth element from an aqueous solution of more than one rare earth element. An example of such a purification separation process is that disclosed in WO2019 / 239150 where an acidic solution of a mixture of rare earth metals is contacted with an ionic liquid to selectively extract one of the rare earth metals from the mixture of rare earth metals in solution. Similar processes involving the use of organophosphorus based extractants are also known. Purification separation processes require a high purity aqueous solution feedstream containing the rare earth metal(s). It is thus important for upstream rough separation processes to be provided that can effectively separate the rare earth metals from the large amount of other impurities present in the magnets and other rare-earth metal containing compositions in order to provide sufficiently pure feedstreams for purification processes such as those discussed above. A variety of rough separation techniques for extracting the rare earth metal elements from the magnets and other high impurity-containing solid compositions are known in the art. However, most of these have been found by the present inventors to be largely unsatisfactory in that they either do not effectively separate the rare earth elements from the impurities, or only produce purified rare earth elements with undesirably low process yield such as 95% or lower. Double sulphate salt precipitation is an example of one such known rough separation process. In this process, the magnets are treated with acid to form an acidic solution. The solution is then treated with a sulphate salt such as sodium, potassium or ammonium sulphate. A double salt is then precipitated that comprises sulphate anions and both rare earth element cations and the cation of the added salt (i.e. a sodium, potassium or ammonium cation). The rare earth elements can then be extracted from the double salts. A problem with the use of double salt precipitation is that it is less effective with heavy rare earth elements such as yttrium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium which often remain in the precipitation mother liquor together with ferric iron and other base metals. Additionally, it has also been found by the inventors that when using double salt precipitation to separate rare earth elements from NdFeB magnets, if the precipitation is driven to completion, a significant quantity of the iron impurities end up within the double salt precipitate, predominantly as iron sulphate, which is difficult to separate therefrom. It is also known to use oxalic acid, salts thereof, and various carbonate salts to precipitate rare earth metals from an acidic solution formed from acid treatment of the NdFeB magnets. In the process, rare earth metal oxalates or carbonates are precipitated. Rare earth metal oxides can then be derived from these salts. It has been found by the present inventors that a problem with the use of oxalate precipitation is that the precipitate contains significant amounts of impurities, such as iron (II) oxalate. Iron (II) oxalate is an insoluble salt and so precipitates along with the rare earth metal oxalates. It has also been found that with carbonate precipitation, the rare earth carbonate precipitates still comprise significant quantities of iron impurities e.g. iron (II) carbonate or iron (II) hydroxide. These processes are thus not sufficiently effective at separating rare earth elements from other impurities in magnet compositions such as iron. It is also known to try and separate rare earth metals from an acidic solution formed from acid treatment of the NdFeB magnets by addition of aqueous alkali such as sodium hydroxide to the solution. The addition of alkali causes formation of iron hydroxide species which precipitate from the solution. These can then be separated from the solution to provide a purified solution comprising the rare earth elements. It has been found by the present inventors that a problem with alkali precipitation is that the iron hydroxide precipitate species formed are very difficult to filter and form a slurry upon precipitation. Without being limited by theory, this is believed to be due to the specific particle sizes of precipitate formed. The difficulty of filtration means that this process is only effective at very low impurity concentrations. Where the solution contains high amounts of impurities such as iron impurities (as in the case of a leachate from an acid treated NdFeB magnet), filtration is so slow that the process becomes unviable, especially when carried out at large scale. Another problem is that precipitation of, for example the iron hydroxide species, from high impurity content solutions causes losses of around 10% of the rare earth metals into the precipitate which unacceptably lowers the process yield. Recycling of rare earth elements from NdFeB magnets via solid-state chlorination, Lorenz et al, Journal of Cleaner Production 215 (2019) 131 -143 discloses a process where NdFeB magnets are leached with hydrochloric acid to provide an acidic solution comprising rare earth metal ions and iron ions. The solution is then oxidised to convert any Fe2+ ions present to Fe3+ ions. The oxidised solution is then treated with alkali in an attempt to precipitate the Fe3+ ions as Goethite (FeO(OH) which is easier to separate than other iron hydroxide species. It has been found by the present inventors that a problem with this process is that, again, the high amounts of iron present in the alkali treated solution cause significant losses of rare earth metals from the solution into the iron hydroxide precipitate reducing the process yield. Additionally, iron (III) hydroxide, which is formed, is very difficult to filter. The large amount of precipitate formed in the process forms a slurry making effective filtration of the solution very difficult. Another problem with the process disclosed in the Lorenz document is that the hydrochloric acid used causes too much foaming and corrosion. This can lead to additional impurities being present in the leachate which are hard to separate from the rare earth metals. Thus, there remains a need in the art for effective, preferably high yield, processes for recycling rare earth metals from magnets and other compositions that contain high quantities of impurities. SUMMARY OF THE INVENTION The present invention is based on the surprising finding that certain processes can be used to effectively separate rare earth metals from compositions that comprise rare earth elements and high amounts of impurities such as iron and its salts thereof (for example NdFeB magnets). Surprisingly, using the process of the invention, the rare earth elements can be effectively separated from impurities present in the composition with a very high process yield and only very minimal loss of the rare earth elements. The process of the invention alleviates or avoids the drawbacks discussed above associated with processes known in the art such as significant loss of rare earth metal yield during the separation process; contamination of separated rare earths with impurities; and filtration difficulties. Using the process of the invention, more than 99% of the impurity metals present can be separated from the rare earth metals with less than 1-2 % loss of the rare earth metals. This is a surprising finding and far exceeds the separation capabilities of prior art processes. According to a first aspect of the invention, there is provided a process for the removal of iron impurities and optionally one or more other non-rare earth metal impurities from a rare earth metal-containing composition, the process comprising the following steps: (a) contacting the rare earth metal-containing composition comprising one or more rare earth metals and iron impurities with phosphoric acid to form an acidic solution comprising one or more iron phosphate salts and a precipitate comprising one or more rare earth metal phosphate salts; (b) separating the precipitate formed in step (a) from the acidic solution to form a separated precipitate; (c) contacting the separated precipitate from step (b) with hydrochloric acid, nitric acid, or a combination thereof to form an acidic solution comprising one or more rare earth metal salts; (d) contacting the acidic solution formed in step (c) with (i) oxalic acid or a solution thereof to form a precipitate comprising one or more rare earth metal oxalate salts; or (ii) a water soluble oxalate salt or a solution thereof to form a precipitate comprising one or more rare earth metal oxalate salts; (e) separating the precipitate formed in step (d) from the solution to provide a separated precipitate and a separated solution; and (f) heating the separated precipitate from step (e) to degrade the one or more rare earth metal oxalate salts to provide one or more rare earth metal oxides; (g) contacting the one or more rare earth metal oxides formed in step (f) with hydrochloric acid or nitric acid to provide an acidic solution comprising one or more rare earth metal salts; (h) contacting the acidic solution formed in step (g) with one or more water soluble hydroxide salts to form a precipitate; and (i) separating the precipitate formed in step (h) from the solution to provide a separated precipitate and a separated solution, where the separated solution comprises one or more rare earth metal salts. The process of the invention relies in part on a synergistic combination of several separations. In an initial separation, a rare earth metal-containing composition is leached with phosphoric acid to form a precipitate comprising rare earth metal phosphates. Surprisingly, it has been found that substantially all of the rare earth metals are recovered in the precipitate whilst leaving around 90% of the iron impurities present in an acidic solution allowing separation of the rare earth metals therefrom. In a second separation, the rare earth metal phosphate-containing precipitate is dissolved in acid before an oxalate precipitation is carried out. It has surprisingly been found that this oxalate precipitation can recover substantially all of the rare earth elements from the solution in the form of a rare earth metal oxalate precipitate whilst leaving the majority of the remaining iron impurities present in solution, allowing separation of the rare earth metals therefrom. The oxalate precipitate can then be further processed into a low impurity content rare earth metal-containing solution which can be treated in a final separation using hydroxide precipitation. This removes remaining iron impurities and other impurities from the solution in the form of a hydroxide precipitate. Surprisingly, in contrast with prior art hydroxide precipitations, it has been found that only very minimal loss of rare earth metals from the solution to the hydroxide precipitate occurs and that the filtration problems encountered with prior art processes do not occur. Without being limited by theory, these advantages are believed to be due to the much lower concentration of impurities present in the solution used in the hydroxide precipitation step. The present invention thus involves the synergistic combination of several separations. Phosphoric acid leaching and oxalate precipitation are used to separate the rare earth metals from the bulk of impurities present. These steps allow the provision of a low impurity concentration rare earth metal solution which can then be further purified by hydroxide precipitation without the problems associated with prior art processes to provide a rare earth metal-containing solution of very high purity. The rare earth metal-containing composition may be any suitable rare earth metalcontaining composition. Whilst the present invention is described preferably with reference to rare earth metal-containing magnets, the process is not limited to the removal of impurities from magnets but may also be used to remove impurities from other rare earth metal-containing compositions such as naturally occurring rare earth metal ores. Preferably, the rare earth metal-containing composition comprises one or more magnets. Preferably, the rare earth metal-containing composition comprises one or more ground magnets, although it will be understood that the process of the invention may also be performed using intact rare earth metal-containing magnets that have not been subjected to grinding. Any suitable type of rare earth metal-containing magnet may be used in the process of the invention as the rare earth metal-containing composition. However, preferably, the rare earth metal-containing composition comprises a Neodymium-lron-Boron magnet (NdFeB magnet). The term magnet as used herein is used to refer to material that is actively magnetic and also to material that was previously magnetic but that has been demagnetized, for example by a demagnetization process. Such demagnetization processes are known in the art and include heating the magnet above its Curie temperature or applying a strong magnetic field to the magnet. It is common for rare earth magnets to be demagnetized prior to chemical processing such as recycling processes as described herein. Accordingly, preferably, the rare earth metal-containing composition comprises a demagnetized magnet and more preferably a demagnetized Neodymium-lron-Boron magnet (NdFeB magnet). Typically, the rare earth metal-containing composition comprises from 20% to 35% by weight of rare earth metals and from 55% to 75% by weight of iron; and preferably from 25% to 35% by weight of rare earth metals and from 60% to 70% by weight of iron. These are the typical percentages of rare earth metals and iron in rare earth metal magnets such as Neodymium-lron-Boron magnets (NdFeB magnets). Preferably, the rare earth metal-containing composition comprises one or more additional impurities in addition to iron. Typically, the rare earth metal-containing composition comprises the additional impurities aluminium, boron, gallium, copper, nickel, cobalt, silicon, titanium manganese, or any combination thereof. Preferably, the rare earth metal-containing composition further comprises aluminium and the process of the invention comprises removing aluminium from the rare earth metalcontaining composition. Where the rare earth metal-containing composition comprises aluminium, typically, the aluminium is present in an amount of from 0.2% to 2% by weight of the rare earth metal-containing composition. The rare earth metal-containing composition can comprise any one or more of the rare earth metal elements. For example, the rare earth metal-containing composition may comprise Lanthanum (La), Cerium (Ce), Praseodymium (Pr), Neodymium (Nd), Samarium (Sm), Europium (Eu), Gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er), Thulium (Tm), Ytterbium (Yb), Lutetium (Lu), Scandium (Sc), Yttrium (Y), or any combination thereof. Preferably, the rare earth metal-containing composition comprises Neodymium, Dysprosium, Praseodymium, Terbium, Gadolinium, Samarium, Cerium, or any combination thereof. More preferably, the rare earth metal-containing composition comprises Neodymium, Dysprosium, Terbium (Tb) and Praseodymium (Pr). These are the rare earth metal elements most commonly found in rare earth metal magnets such as Neodymium-lron-Boron magnets (NdFeB magnets). Preferably, the rare earth metal-containing composition comprises Neodymium in an amount of from 10% to 35% by weight; and preferably from 15% to 25% by weight. Preferably, the rare earth metal-containing composition comprises Dysprosium in an amount of from 0.1% to 8% by weight; and / or Praseodymium in an amount of from 0.1% to 10% by weight. Preferably, the rare earth metal-containing composition comprises Terbium in an amount of from 0.25% to 3% by weight. In alternative embodiments, Neodymium is the only rare earth metal present in the rare earth metal-containing composition. In these embodiments, the Neodymium is typically present in the preferred ranges specified above. In other instances of the invention, the rare earth metal-containing composition comprises a rare earth metal containing ore. It has also been found that the process of the invention can be used to extract rare earth elements from impurities present in their naturally occurring ores or ion adsorption clays. Examples of rare earth metal ores that may be used include apatite, bastnasite, monazite, xenotime, or any combination or mixture thereof. Step (a) The process of the invention comprises step (a) of contacting the rare earth metalcontaining composition comprising one or more rare earth metals and iron impurities with phosphoric acid to form an acidic solution comprising one or more iron phosphate salts and a precipitate comprising one or more rare earth metal phosphate salts. Step (a) comprises an initial acid leaching step with phosphoric acid. This step causes dissolution of iron impurities and other impurity metals present in the rare earth metalcontaining composition and formation of a precipitate comprising one or more rare earth metal phosphate salts. The phosphoric acid leaching step has surprisingly been found to effectively recover substantially all of the rare earth metal elements from the original rare earth metal-containing composition in the rare earth metal phosphate precipitate. It has also advantageously been found that whilst some iron ions are present in the precipitate along with the rare earth metals in the form of iron (III) phosphate, the majority (around 90% of the iron present) is dissolved by the acid to form aqueous Fe(H2PO4)2 with iron in the +2 oxidation state. This is highly advantageous as it means that upon subsequent separation step (b), around 90% of the iron is effectively separated in one step from nearly all of the rare earth metals present. Preferably, the phosphoric acid used in step (a) is aqueous phosphoric acid and the acidic solution formed is an aqueous acidic solution. The acid used in step (a) preferably has a pH of less than 1; more preferably less than 0; still more preferably less than 0.5. It is desired for the acid to have this low pH in order to effectively digest all rare earth metals present in the rare earth metal-containing composition and form the rare earth metal phosphates. Preferably, the acid used in step (a) has a molarity of from 4 M to 6 M. Preferably, in step (a), a liquid to solid ratio (i.e. acid to rare earth metal-containing composition ratio) of from 5:1 to 15:1 is used; and more preferably from 8:1 to 12:1. Accordingly, typically, the acid used in step (a) has a molarity of from 4 M to 6 M and a liquid to solid ratio (i.e. acid to rare earth metal-containing composition ratio) of from 5:1 to 15:1 is used. Preferably, the acid used in step (a) has a molarity of from 4 M to 6 M and a liquid to solid ratio (i.e. acid to rare earth metal-containing composition ratio) of from 8:1 to 12:1 is used. In step (a) a sufficient amount of acid is typically added to the rare earth metal-containing composition to effectively digest all rare earth metals in the composition. Preferably, step (a) comprises adding a molar excess of phosphoric acid relative to the total amount of rare earth metals in the rare earth metal-containing composition. Typically, from 1 to 5 moles of phosphoric acid is added per mole of all metals present in the rare earth metalcontaining composition. Preferably, from 2.5 to 4 moles of phosphoric acid is added per mole of all metals present in the rare earth metal-containing composition.. Typically, the amount of acid used in step (a) is sufficient to provide an aqueous solution with a pH of 2.5 or less; preferably 2.2 or less; and more preferably 2.0 or less. Suitable steps of determining the pH of a solution are known in the art and will be apparent given the benefit of the present disclosure. Such steps include testing with e.g. universal indicator paper. Preferably, the acid used in step (a) has a temperature of from 20 °C to 90 °C; more preferably from 40 °C to 80°C; and most preferably from 50 °C to 70 °C. It has surprisingly been found that a more effective precipitation of rare earth phosphate salts is achieved within these temperature ranges. At the end of step (a), the acidic solution provided comprises dissolved impurity ions such as iron ions and aluminium ions; and dissolved phosphate anions as discussed above. The majority of dissolved iron ions present are in the form of Fe2+ although some Fe3+ ions may also be present. An advantage of the use of phosphoric acid in step (a) is that any iron that remains in the rare earth metal phosphate-containing precipitate is in the form of iron (III) phosphate. The iron in the precipitate does not comprise Fe2+ ions which remain in the acidic solution. This is very useful since further processing of the rare earth metal phosphate-containing precipitate into acidic solutions in subsequent steps of the process means that no Fe2+ ions are present in the subsequently formed acidic solutions (only Fe3+ ions). This is advantageous for the subsequent oxalate and hydroxide precipitation steps as described in further detail below. Another advantage of using phosphoric acid instead of hydrochloric acid as used in the prior art (e.g. Lorenz et al.) is that it has been found that hydrochloric acid undesirably causes increased corrosion and foaming during acid treatment of the magnet. Increased corrosion causes more impurities to be present in the subsequent solution and precipitates formed from acid leaching which have to be separated from the rare earth elements. Surprisingly, this has been found not to be a problem where phosphoric acid is used. Step (b) The process comprises step (b) of separating the precipitate formed in step (a) from the acidic solution to form a separated precipitate. Step (b) of the process typically comprises separating the precipitate formed in step (a) by filtering the solution formed in step (a), although other separation methods known in the art may also be used. For example, centrifugation and similar techniques may also be used. Step (b) typically comprises separating the precipitate formed in step (a) to form a separated precipitate and a separated solution. The separated precipitate comprises rare earth metal phosphates. The separated solution typically comprises the iron salt, for example Fe(H2PO4)2. The separated solution formed in step (b) may be disposed of after the separation step (b). Advantageously, the separated solution comprises the majority of the iron present in the initial rare earth metal-containing composition. The separated precipitate formed in step (b) comprises substantially all of the rare earth metal elements from the original rare earth metal-containing composition. Step (c) The process comprises step (c) of contacting the separated precipitate from step (b) with hydrochloric acid, nitric acid, ora combination thereof to form an acidic solution comprising one or more rare earth metal salts. The purpose of this step is to redissolve the rare earth metal phosphate precipitate to form a solution that comprises substantially all rare earth metal elements from the original rare earth metal-containing composition but with far less impurities. Typically, step (c) comprises contacting the separated precipitate from step (b) with hydrochloric acid to form an acidic solution comprising (i) one or more rare earth metal chloride salts and (ii) one or more iron salts. Preferably, the acid used in step (c) is an aqueous acid and the acidic solution formed is an aqueous acidic solution. Typically, the acid used in step (c) has a pH of less than 0.5; and preferably less than 0.25. These pH ranges are preferred in order to effectively redissolve all of the solid rare earth metal phosphate. In step (c) a sufficient amount of acid is typically added to the separated precipitate formed in step (b) to effectively dissolve all of the precipitate. Preferably, step (c) comprises contacting the separated precipitate from step (b) with a molar excess of acid relative to the total amount of rare earth metals in the initial rare earth metal-containing composition. Preferably, at least 2 moles of acid are added per mole of rare earth metals present in the rare earth metal-containing composition or present in the precipitate formed in step (b). More preferably, at least 3 moles of acid are added per mole of rare earth metals present in the rare earth metal-containing composition or present in the precipitate formed in step (b). Still more preferably, at least 3.5 moles of acid are added per mole of rare earth metals present in the rare earth metal-containing composition or present in the precipitate formed in step (b). Most preferably, at least 4 moles of acid are added per mole of rare earth metals present in the rare earth metal-containing composition or present in the precipitate formed in step (b). In some instances, at least 4.5, at least 5, at least 5.5 or at least 6 moles of acid are added per mole of rare earth metals present in the rare earth metal-containing composition or present in the precipitate formed in step (b). Preferably, the acid used in step (c) has a molarity of from 2 M to 7 M, and more preferably a molarity of 4 M to 5 M. Preferably, in step (c), a liquid to solid ratio (i.e. acid to precipitate ratio) of from 5:1 to 15:1 is used; and preferably from 8:1 to 12:1. Preferably, the acid used in step (c) has a molarity of from 2 M to 7 M and the liquid to solid ratio (i.e. acid to precipitate ratio) used is from 5:1 to 15:1. More preferably, the acid used in step (c) has a molarity of from 4 M to 5 M and a liquid to solid ratio (i.e. acid to precipitate ratio) of from 8:1 to 12:1. Preferably, the acid and precipitate in step (c) are contacted at a temperature of from 60°C to 90°C; and preferably from 75°C to 85°C. Step (d) Step (d) comprises contacting the acidic solution formed in step (c) with one or more of (i) oxalic acid or a solution thereof to form a precipitate comprising one or more rare earth metal oxalate salts; or (ii) a water soluble oxalate salt or solution thereof to form a precipitate comprising one or more rare earth metal oxalate salts. More preferably, step (d) comprises contacting the acidic solution formed in step (c) with oxalic acid or a solution thereof to form a precipitate comprising one or more rare earth metal oxalate compounds. Surprisingly, it has been found that addition of oxalic acid or its salts causes precipitation of rare earth metal oxalates whilst leaving most of the Fe3+ ions remaining in solution. Without being limited by theory, this is believed by the present inventors to be due to formation of the highly water-soluble complex Fe2(C2O4)3 which forms by association of oxalate anions with the Fe3+ ions present in the acidic solution. Since the acidic solution comprises Fe3+ and not Fe2+, nearly all of the iron remains in solution as the water-soluble complex Fe2(C2O4)3 instead of precipitating as iron (II) oxalate. Additionally, it has also surprisingly been found that substantially all rare earth metals present in the acidic solution can be effectively precipitated in oxalate precipitation. Accordingly, in subsequent separation step (e), more iron is effectively isolated from the rare earth metals. The one or more of (i) oxalic acid or a solution thereof; or (ii) a water-soluble oxalate salt or solution thereof are added in step (d) in any suitable amount to effectively precipitate rare earth metals from the acidic solution formed in step (c) as oxalate salts. Preferably, step (d) comprises adding a molar excess of oxalic acid or a water-soluble oxalate salt to the acidic solution relative to the total amount of rare earth metals in the rare earth metalcontaining composition. This is preferred in order to effectively remove as many rare earth metals as possible from the mother liquor solution by precipitation in order to maximise yield and recovery of the rare earth elements. More preferably, a molar ratio of from 1 to 5 moles of oxalic acid ora water-soluble oxalate salt per total moles of metals present in the acidic solution formed in step (c) are added; and more preferably from 1 to 2 moles of oxalic acid or a water-soluble oxalate salt per total moles of metals present in the acidic solution formed in step (c) are added. Step (e~) Step (e) of the process typically comprises separating the precipitate formed in step (d) by filtering the solution formed in step (d), although other separation methods known in the art may also be used. For example, centrifugation and similar techniques may also be used. Step (f) Step (f) of the process involves heating the separated precipitate formed in step (e) of the process. The purpose of step (f) is to degrade the oxalate anion to release carbon dioxide and carbon monoxide and provide a rare earth metal oxide solid. Typically, step (f) of the process comprises calcination of the rare earth metal oxalate. Suitable process conditions and apparatus for the calcination of the rare earth metal salts will be apparent given the benefit of the present disclosure. Preferably, step (f) of heating the separated precipitate from step (e) comprises heating the precipitate to a temperature of at least 700°C; and preferably at least 800°C. More preferably, step (f) of heating the separated precipitate from step (e) comprises heating the precipitate to a temperature of from 750°C to 850°C such as from 800°C to 850°C. Preferably, step (f) of heating the separated precipitate from step (e) comprises heating the precipitate fora time period of from 1 hours to 4 hours; and more preferably from 1.5 hours to 2.5 hours. Step (q) Step (g) of the process comprises contacting the one or more rare earth metal oxides formed in step (f) with one or more of hydrochloric acid or nitric acid to provide an acidic solution comprising one or more rare earth metal salts. The purpose of step (g) is to provide a solution of the rare earth metal elements and remaining impurities such as iron and aluminium that can then be treated in neutralization step (h). Sulphuric acid cannot be used for this step due to subsequent precipitation step (h) where a water-soluble hydroxide salt is added to the solution. Sulphuric acid treatment would form sulphate anions in solution. On subsequent addition of water-soluble hydroxide, rare earth metals would undesirably precipitate as a double salt (for example a double salt comprising rare earth metal and sodium cations and sulphate anions if sodium hydroxide was added). This is undesirable since it would decrease the yield of rare earth metals in the process as they would be lost in the hydroxide precipitate along with any remaining impurities. Typically, step (g) comprises contacting the one or more rare earth metal oxides formed in step (f) with aqueous hydrochloric acid or aqueous nitric acid to provide an aqueous acidic solution comprising one or more rare earth metal chloride salts or one or more rare earth metal nitrate salts. Typically step (g) comprises adding a molar excess of hydrochloric acid or nitric acid. This is preferred in order to effectively dissolve all rare earth metal oxides present in order to maximise yield and recovery of the rare earth metals. Preferably the aqueous hydrochloric acid or nitric acid has a pH of 0.5 or less. Step (h) The process comprises step (h) of contacting the acidic solution formed in step (g) with one or more water soluble hydroxide salts to form a precipitate. The purpose of this step is to precipitate any remaining iron and aluminium present in the acidic solution as iron (III) hydroxide or aluminium (III) hydroxide. Where this process step has been carried out in prior art processes, much greater amounts of iron impurities have been present in the treated solution. This means that a great deal more iron hydroxide has been precipitated from the solution in prior art processes. The result of this is that a portion of rare earth metals from the solution are also precipitated from the solution. In processes known in the art, typically around 10% of rare earth metals have been lost from the solution along with impurities in the hydroxide precipitation step. However, surprisingly, using the process of the invention, it has been found that only very low amounts of rare earth metal are lost to the precipitate. Without being limited by theory this is believed to be due to the much lower levels of iron present in the treated solution. Additionally, iron hydroxide is a difficult material to filter and often forms a fine precipitate in water which is hard to filter. In prior art processes, where large amounts of iron hydroxide are precipitated from the solution, the resultant fine precipitate is very hard to filter often making hydroxide precipitation of impurities technically unfeasible as a rare earth metal separation process step. However, in the process of the invention, the lower amounts of iron present in the acidic solution mean that less iron hydroxide is precipitated so that filtration is far easier and more effective. Typically, the one or more water soluble hydroxide salts used in step (h) comprises an alkali metal hydroxide salt or ammonium hydroxide; and preferably sodium hydroxide. Typically, the alkali metal hydroxide salt is added to the acidic aqueous solution in the form of an aqueous solution. Preferably, the molarity of the aqueous solution is from 4 M to 8 M; and more preferably from 5 M to 7 M. Preferably, the one or more water soluble hydroxide salts are added in step (h) in an amount sufficient to increase the pH of the aqueous solution to from 4.0 to 6.0; preferably to from 4.0 to 5.0; and more preferably from 4.2 to 5.0. These pH ranges are preferred since at lower pH ranges not all iron and aluminium is precipitated from the acidic solution. In contrast, at higher pH ranges, some of the rare earth metals may also begin to precipitate which is less desirable as process yield of rare earth metal recovery will decrease. Typically, in step (h), the one or more water soluble hydroxide salts are added to the acidic solution to effectively precipitate all iron and other impurities from the acidic solution as hydroxide salts. The amount of the one or more water soluble hydroxide salts added is typically a molar excess relative to the total amount of rare earth metals present in the acidic solution or present in the original rare earth metal-containing composition. This is so as to effectively remove as many remaining iron and aluminium impurities as possible from the mother liquor solution. Typically, the precipitate formed in step (h) comprises iron hydroxide. Preferably, the precipitate formed in step (h) comprises iron (III) hydroxide. Where the rare earth metalcontaining composition comprises aluminium, typically the precipitate formed in step (h) also comprises aluminium hydroxide. As discussed above, an advantage of the use of phosphoric acid in acid digestion step (a) is that iron present in the rare earth metalcontaining composition is oxidised to both Fe2+ ions and Fe3+ ions. The Fe2+ ions remain in the solution formed in step (a) and can thus be effectively separated from the rare earth metals and Fe3+ ions which are precipitated as insoluble phosphate salts. This is advantageous for later stages of the process such as the oxalate precipitation discussed above and alkali precipitation step (h). It has been found by the inventors that Fe (III) hydroxide is less soluble than Fe (II) hydroxide at the pH ranges used meaning precipitation of remaining iron impurities in hydroxide precipitation step (h) is easier and more effective where the solution to be treated comprises Fe3+ ions instead of Fe2+ ions. It has also been found by the inventors that precipitated iron (III) hydroxide settles well after precipitation meaning that removal from the remaining mother liquor solution is easier than with iron (II) hydroxide which is more prone to forming a slurry which is far harder to filter and effectively perform solid-liquid separation on. It has also been found that loss of rare earth metals in the precipitate formed in step (h) is less when the precipitate comprises more iron (III) hydroxide to iron (II) hydroxide as a result of the lower precipitation pH of iron (III) hydroxide. Preferably, in step (h), the process further comprises the addition of an adsorbent to the acidic solution formed in step (g). Preferably, the adsorbent comprises activated carbon such as activated carbon powder or pellets. It has been found by the present inventors that the iron (III) hydroxide precipitate formed adsorbs well to the adsorbent making it much easier to remove in subsequent separation step (i). The use of the adsorbent increases the extent of iron removal and also eliminates the need to allow the iron (III) hydroxide precipitate to settle prior to filtering, thereby increasing process efficiency. Step.......(i) The process comprises step (i) of separating the precipitate formed in step (h) from the solution to provide a separated precipitate and a separated solution, where the separated solution comprises one or more rare earth metal salts. Preferably, step (i) of separating the precipitate formed in step (g) comprises filtering the solution formed in step (g), although other separation methods known in the art may also be used. For example, centrifugation and similar techniques may also be used. The separated solution formed in step (i) is a substantially pure solution of dissolved rare earth metal chloride or nitrate salts. The separated solution formed in step (i) is thus suitable for use as a feedstream in rare earth metal purification separation processes as discussed above. Purification processes are typically for removing microamount impurities from aqueous solutions of one or more rare earth metals or processes for separating a specific rare earth element from an aqueous solution of more than one rare earth element. In such processes, the feedstream is preferably an aqueous feed stream and more preferably an acidic feedstream such as an aqueous acidic feedstream that is substantially pure. The separated solution formed in step (i) may be used directly as a feedstream in a purification process. Alternatively, the separated solution formed in step (i) may be further processed before use as a feedstream in a purification process. For example, the pH of the solution may be adjusted. Alternatively, the rare earth metals may be precipitated from the solution (e.g. by the use of a bicarbonate or oxalate salt) and redissolved in another aqueous solution such as an aqueous acid before use in a rare earth metal purification / separation process. Accordingly, the process of the invention may further comprise a step of providing an acidic or aqueous feedstream for use in a rare earth metal purification separation process. The process of the invention can thus be considered a pre-treatment process for the preparation of substantially pure rare earth metal-containing feedstreams for use in subsequent rare earth metal separation and purification processes. Extracting a rare earth metal from a mixture of rare earth metals Accordingly, the process of the invention may further comprise process steps for extracting a rare earth metal from a mixture of rare earth metals, which process steps comprise: processing the separated solution formed in step (i) into an acidic solution comprising a mixture of rare earth metals; and contacting an acidic solution of the rare earth metals with a composition which comprises an extractant to form an aqueous phase and a non-aqueous phase into which the rare earth metal has been selectively extracted. Any such suitable process steps known in the art may be used. For example, the process of the invention may comprise any of the process steps discussed in WO2019 / 239150 and similar process steps known in the art. The extractant used in the process can be any suitable extractant known to be suitable for use in extracting a rare earth metal from a mixture of rare earth metals. Typically, the extractant used in the process comprises an ionic liquid extractant, or an organophosphorus based extractant. Any suitable organophosphorus based extractant known in the art may be used and suitable extractants will be apparent given the benefit of the present disclosure. Examples of organophosphorus based extractants that may be used include a phosphoric acid compound or hydrocarbyl ester thereof; a phosphonic acid compound or hydrocarbyl ester thereof; a phosphinic acid compound or hydrocarbyl ester thereof; a tertiary phosphine oxide of the formula RR1R2P=O where R, R1 and R2 are independently selected from hydrocarbyl moieties; a dithiophosphinic acid compound or hydrocarbyl ester thereof; an a-aminophosphonate compound; or any combination thereof. Specific examples of such extractants include tributyl phosphate and di(2-ethylhexyl)phosphoric acid (D2EHPA). Preferably, the extractant comprises an ionic liquid. Any suitable ionic liquid extractant known for use in processes such as those discussed above may be used. Suitable ionic liquids that may be used as extractants will be apparent given the benefit of the present disclosure. For example, any of the ionic liquid extractants used in WO2019 / 239150 may be used. Preferably, the ionic liquid has the formula: [Cat+][X-] in which: [Cat*] represents a cationic species having the structure: L2 I                              I EDG EDG where: [Y+] comprises a group selected from ammonium, benzimidazolium, benzofuranium, benzothiophenium, benzotriazolium, borolium, cinnolinium, diazabicyclodecenium, diazabicyclononenium, 1,4-diazabicyclo[2.2.2]octanium, diazabicyclo-undecenium, dithiazolium, furanium, guanidinium, imidazolium, indazolium, indolinium, indolium, morpholinium, oxaborolium, oxaphospholium, oxazinium, oxazolium, iso-oxazolium, oxothiazolium, phospholium, phosphonium, phthalazinium, piperazinium, piperidinium, pyranium, pyrazinium, pyrazolium, pyridazinium, pyridinium, pyrimidinium, pyrrolidinium, pyrrolium, quinazolinium, quinolinium, iso-quinolinium, quinoxalinium, quinuclidinium, selenazolium, sulfonium, tetrazolium, thiadiazolium, iso-thiadiazolium, thiazinium, thiazolium, iso-thiazolium, thiophenium, thiuronium, triazinium, triazolium, iso-triazolium and uranium groups; each EDG represents an electron donating group; and Li represents a linking group selected from Ci-w alkanediyl, C2-10 alkenediyl, C1-10 dialkanylether and C1-10 dialkanylketone groups; each L2 represents a linking group independently selected from C1-2 alkanediyl, C2 alkenediyl, C1-2 dialkanylether and C1-2 dialkanylketone groups; and [X’] represents a phosphinate anion, a phosphate anion, or a phosphonate anion. Typically, when the nitrogen linking Li to each L2 and one of the EDG both coordinate to a metal, the ring formed by the nitrogen, L2, the EDG and the metal is a 5 or 6 membered ring, and preferably a 5 membered ring. Preferably, the ionic liquid is as further defined as in any one or more of features (a) to (f) defined as follows: (a) wherein [Y+] represents: an acyclic cation selected from: [-N(Ra)(Rb)(Rc)]+, [-P(Ra)(Rb)(Rc)]+ and [-S(Ra)(Rb)]+, where: Ra, Rb and Rc are each independently selected from optionally substituted C1-30 alkyl, C3-8 cycloalkyl and Ce-w aryl groups; or a cyclic cation selected from: where: Ra, Rb, Rc, Rd, Re and Rf are each independently selected from: hydrogen and optionally substituted C1.30 alkyl, C3-8 cycloalkyl and C6-10 aryl groups, or any two of Ra, Rb, Rc, Rd and Re attached to adjacent carbon atoms form an optionally substituted methylene chain -(CHajq- where q is from 3 to 6; or a saturated heterocyclic cation having the formula: where: Ra, Rb, Rc, Rd, Re and Rf are each independently selected from: hydrogen and optionally substituted C1.30 alkyl, C3-8 cycloalkyl and C6-10 aryl groups, or any two of Ra, Rb, Rc, Rd and Re attached to adjacent carbon atoms form an optionally substituted methylene chain -(CH2)q- where q is from 3 to 6; preferably, wherein [Y+] represents a cyclic cation selected from: and and more preferably represents the cyclic cation: wherein preferably Rf is a substituted C1-5 alkyl group, and the remainder of Ra, Rb, Rc, Rd, Re and Rf are independently selected from H and unsubstituted C1-5 alkyl groups; (b) wherein Li represents: a linking group selected from C1-10 alkanediyl and C1-10 alkenediyl groups; preferably a linking group selected from C1-5 alkanediyl and C2-5 alkenediyl groups; more preferably a linking group selected from C1-5 alkanediyl groups; and still more preferably a linking group selected from -CH2-, -C2H4- and -C3H6. (c) wherein each L2 represents: a linking group independently selected from C1-2 alkanediyl and C2 alkenediyl groups; preferably a linking group independently selected from C1-2 alkanediyl groups; and more preferably a linking group independently selected from -CH2- and -C2H4-. (d) wherein each EDG represents: an electron donating group independently selected from -CO2RX, -OC(O)RX, -CS. 2Rx, -SC(S)Rx,-S(O)ORx, -OS(O)Rx, -NRxC(O)NRyRz, -NRxC(O)ORy, -OC(O)NRyRz, -NRxC(S)ORy, -OC(S)NRyRz, -NRxC(S)SRy, -SC(S)NRyRz, - NRxC(S)NRyRz, -C(O)NRyRz, -C(S)NRyRz, wherein Rx, Ry and Rz are independently selected from H orCi-6 alkyl; and preferably an electron donating group independently selected from -CO2RX and -C(O)NRyRz, wherein Rx, Ry and Rz are each independently selected from C3-6 alkyl; preferably, wherein each -L2-EDG represents an electron donating group independently selected from: wherein Ry = Rz, and wherein Rx, Ry and Rz are each selected from C3-6 alkyl, preferably C4 alkyl, for example / -Bu; (e) wherein [Cat+] represents one or more ionic species having the structure: where: [Z+] represents a group selected from ammonium, benzimidazolium, benzofuranium, benzothiophenium, benzotriazolium, borolium, cinnolinium, diazabicyclodecenium, diazabicyclononenium, 1,4-diazabicyclo[2.2.2]octanium, diazabicyclo-undecenium, dithiazolium, furanium, guanidinium, imidazolium, indazolium, indolinium, indolium, morpholinium, oxaborolium, oxaphospholium, oxazinium, oxazolium, iso-oxazolium, oxothiazolium, phospholium, phosphonium, phthalazinium, piperazinium, piperidinium, pyranium, pyrazinium, pyrazolium, pyridazinium, pyridinium, pyrimidinium, pyrrolidinium, pyrrolium, quinazolinium, quinolinium, iso-quinolinium, quinoxalinium, quinuclidinium, selenazolium, sulfonium, tetrazolium, thiadiazolium, iso-thiadiazolium, thiazinium, thiazolium, iso-thiazolium, thiophenium, thiuronium, triazinium, triazolium, iso-triazolium and uranium groups; (f) wherein [X’] represents a phosphinate anion having the structure: R2 R1 I / ° II 0 where: R1 and R2 are independently selected from optionally substituted C3-20, preferably C4-15, and more preferably C6-10, hydrocarbyl groups in which up to 3 carbon atoms may be replaced with a heteroatom; preferably, wherein R1 and R2 are independently selected from alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkyl-cycloalkyl, cycloalkyl-alkyl, aryl, alkyl-aryl and aryl-alkyl groups; preferably from alkyl groups; and more preferably from branched alkyl groups. In the above-described processes, typically, the process comprises recovering the rare earth metal from the non-aqueous phase, for instance by stripping with an acidic stripping solution, e.g. an aqueous hydrochloric acid or nitric acid solution, preferably having a pH of 1 or lower and preferably a pH of 0 or higher. Preferably, the acidic solution comprising a mixture of rare earth metals in the above described processes comprises a first and a second rare earth metal, and the method comprises: (a) preferentially partitioning the first rare earth metal into the non-aqueous phase. Preferably, the process further comprises, in step (a), separating the non-aqueous phase from the acidic solution; and (b) contacting the acidic solution depleted of the first rare earth metal with the composition which comprises an ionic liquid, and optionally recovering the second rare earth metal therefrom; and preferably the first rare earth metal is recovered from the non-aqueous phase in step (a), and said non-aqueous phase is recycled and used as the composition in step (b); In these process steps, preferably, the acidic solution has a pH of less than 3.5 in step (a), and the acidic solution has a pH of greater than 3.5 in step (b). Preferably, in the processes described above, the first rare earth metal is dysprosium, and the second rare earth metal is neodymium; or the first rare earth metal is europium, and the second rare earth metal is lanthanum. More preferably, the first rare earth metal is dysprosium, and the second rare earth metal is neodymium. Preferably, the acidic solution from which the rare earth metal is extracted has a pH of from 2 to 4. Preferably, the composition is added to the acidic solution in a volume ratio of from 0.5 : 1 to 2 : 1, more preferably 0.7 : 1 to 1.5 : 1, and most preferably 0.8 : 1 to 1.2 : 1. For example 1 : 1. Preferably, prior to contacting the composition with the acidic solution of the rare earth metal the composition is equilibrated with an acidic solution having the same pH as the acidic solution of the rare earth metal. Preferably, the acidic solution is contacted with the composition for from 1 to 40 minutes, and more preferably from 5 to 30 minutes. Preferably, the process comprises contacting and physically mixing the acidic solution of the rare earth metal and the composition. Typically, the composition further comprises a lower viscosity ionic liquid and / or one or more organic solvents. The cations and anions of the ionic liquid can be included in the abovementioned compositions in any suitable amount. Typically, the cation of the ionic liquid is present in the composition in a concentration of at least 0.001 M, preferably from 0.005 M to 0.01 M, for example 0.0075 M. Typically, the anion of the ionic liquid is present in the composition in a concentration of at least 0.001 M, preferably from 0.005 M to 0.01 M, for example 0.0075 M. Further details of the processes and extractants described above are as described in WO2019 / 239150. DESCRIPTION OF THE DRAWINGS Figure 1 depicts a process flow chart for the process of the invention. DETAILED DESCRIPTION OF THE INVENTION Example 1 1. A Neodymium iron boron magnet was digested using 6M phosphoric acid at 60 °C. All metals present in the magnet were dissolved by the acid and oxidised. The acid treatment caused formation of an acidic solution and precipitation of rare earth metal phosphates. The pH of the solution after acid treatment was pH 2. The acidic solution was found to comprise 94.95% of the iron present in the original Neodymium iron boron magnet; 0.10% of the neodymium present in the original Neodymium iron boron magnet; 0.04% of the praseodymium present in the original Neodymium iron boron magnet; and 0.41% of the dysprosium present in the original Neodymium iron boron magnet. 2. The acidic solution was separated from the precipitate in a filtration step. It was found that the precipitate comprised over 95% of rare earth metal phosphate salts with a small quantity of iron (III) phosphate. 3. The precipitate from step 2 containing solid rare earth metal phosphates was dissolved in 5 M hydrochloric acid at 80 °C to form an acidic solution. It was found that complete dissolution of the rare earth metals and iron present in the precipitate occurred. 4. The acidic solution formed in step 3 was treated with oxalic acid in a molar ratio of 1.5 moles of oxalic acid to moles of metal present in the acidic solution to form a rare earth metal oxalate precipitate. Over 95% of rare earth metals present in the acidic solution were recovered in the oxalate precipitate whereas around only 2% of iron from the acidic solution was precipitated with the rare earth oxalate precipitate. 5. The rare earth metal oxalate precipitate formed in step 6 was separated from the solution by filtration and then heated to 800°C for two hours in the absence of oxygen to form rare earth metal oxides. 6. The rare earth metal oxides formed in step 5 were contacted with a molar excess of 3M hydrochloric acid to dissolve the rare earth metal oxide salts and form a solution. 7. The solution from step 6 was contacted with 8 M NaOH to increase its pH to 4.5 and form insoluble Al &Fe impurity hydroxides as a precipitate which were then removed from the solution via filtration. A flow chart of the process is shown in Figure 1.

Claims

1. A process for the removal of iron impurities and optionally one or more other non-rare earth metal impurities from a rare earth metal-containing composition, wherein the process comprises the following steps:(a) contacting the rare earth metal-containing composition comprising one or more rare earth metals and iron impurities with phosphoric acid to form an acidic solution comprising one or more iron phosphate salts and a precipitate comprising one or more rare earth metal phosphate salts;(b) separating the precipitate formed in step (a) from the acidic solution to form a separated precipitate;(c) contacting the separated precipitate from step (b) with hydrochloric acid, nitric acid, or a combination thereof to form an acidic solution comprising one or more rare earth metal salts;(d) contacting the acidic solution formed in step (c) with (i) oxalic acid or a solution thereof to form a precipitate comprising one or more rare earth metal oxalate salts; or (ii) a water soluble oxalate salt or a solution thereof to form a precipitate comprising one or more rare earth metal oxalate salts;(e) separating the precipitate formed in step (d) from the solution to provide a separated precipitate and a separated solution; and(f) heating the separated precipitate from step (e) to degrade the one or more rare earth metal oxalate salts to provide one or more rare earth metal oxides;(g) contacting the one or more rare earth metal oxides formed in step (f) with hydrochloric acid or nitric acid to provide an acidic solution comprising one or more rare earth metal salts;(h) contacting the acidic solution formed in step (g) with one or more water soluble hydroxide salts to form a precipitate; and(i) separating the precipitate formed in step (h) from the solution to provide a separated precipitate and a separated solution, where the separated solution comprises one or more rare earth metal salts.

2. A process according to Claim 1, wherein the acids used in any one or more of steps (a), (c) and (g) are aqueous acids and / or wherein the acidic solutions formed in any one or more of steps (a), (c) and (g) are aqueous acidic solutions; preferably wherein the acids used in all of steps (a), (c) and (g) are aqueous acids and / or wherein the acidic solutions formed in all of steps (a), (c) and (g) are aqueous acidic solutions.

3. A process according to Claim 1 or Claim 2, wherein the process comprises adding a molar excess of acid in any one or more of steps (a), (c) and (g) relative to the total amount of rare earth metals in the rare earth metal-containing composition; preferably wherein the process comprises adding a molar excess of acid in all of steps (a), (c) and (g) relative to the total amount of rare earth metals in the rare earth metal-containing composition.

4. A process according to any preceding claim, wherein the process comprises adding a molar excess of the salts in any one or more of steps (d) and (h) to the solution relative to the total amount of rare earth metals in the rare earth metal-containing composition; preferably wherein the process comprises adding a molar excess of the salts in all of (d) and (h) to the solution relative to the total amount of rare earth metals in the rare earth metal-containing composition.

5. A process according to any preceding claim, wherein the rare earth metalcontaining composition comprises one or more magnets.

6. A process according to any preceding claim, wherein the rare earth metalcontaining composition comprises ground magnets.

7. A process according to any preceding claim, wherein the rare earth metalcontaining composition comprises a Neodymium-lron-Boron magnet (NdFeB magnet).

8. A process according to any preceding claim, wherein the rare earth metalcontaining composition comprises a demagnetized magnet.

9. A process according to any preceding claim, wherein the rare earth metalcontaining composition comprises a rare earth metal ore.

10. A process according to any preceding claim, wherein the rare earth metalcontaining composition comprises from 20% to 35% by weight of rare earth metals and from 55% to 75% by weight of iron; and preferably from 25% to 35% by weight of rare earth metals and from 60% to 70% by weight of iron.

11. A process according to any preceding claim, wherein the one or more other non-rare earth metal impurities comprise aluminium and wherein the rare earth metalcontaining composition further comprises aluminium.

12. A process according to any preceding claim, wherein the rare earth metalcontaining composition comprises from 0.2% to 2% by weight of aluminium; and preferably from 0.5% to 1% by weight of aluminium.

13. A process according to any preceding claim, wherein the rare earth metalcontaining composition comprises Neodymium, Dysprosium, Praseodymium, Terbium, Gadolinium, Samarium, Cerium, or any combination thereof.

14. A process according to any preceding claim, wherein the rare earth metalcontaining composition comprises Neodymium in an amount of from 10% to 35% by weight; and preferably from 15% to 25% by weight.

15. A process according to any preceding claim, wherein the rare earth metalcontaining composition comprises Dysprosium in an amount of from 0.1% to 8% by weight; and / or Praseodymium in an amount of from 0.1% to 10% by weight.

16. A process according to any preceding claim, wherein the one or more iron phosphate salts present in the solution formed in step (a) comprise one or more salts of the formula Fe(H2PO4)2.

17. A process according to any preceding claim, wherein the phosphoric acid used in step (a) has a pH of less than 1; and preferably less than 0.5.

18. A process according to any preceding claim, wherein the amount of phosphoric acid used in step (a) is sufficient to provide solution with a pH of 2.5 or less.

19. A process according to any preceding claim, wherein step (b) of separating the precipitate formed in step (a) comprises filtering the solution formed in step (a).

20. A process according to any preceding claim, wherein step (c) comprises contacting the separated precipitate from step (b) with hydrochloric acid to form an acidic solution comprising (i) one or more rare earth metal chloride salts and (ii) one or more iron chloride salts.

21. A process according to any preceding claim, wherein the acid used in step (c) has a pH of less than 0.5; and preferably less than 0.25.

22. A process according to any preceding claim, wherein step (d) comprises contacting the solution formed in step (c) with oxalic acid or a solution thereof.

23. A process according to Claim 21, wherein the oxalic acid is added in a molar ratio of from 1 to 5 moles of oxalic acid per total moles of metals present in the acidic solution formed in step (c); and preferably from 1 to 2 moles of oxalic acid per total moles of metals present in the acidic solution formed in step (c).

24. A process according to any preceding claim, wherein step (e) of separating the precipitate formed in step (d) comprises filtering the solution.

25. A process according to any preceding claim, wherein step (f) of heating the separated precipitate from step (e) comprises heating the precipitate to a temperature of at least 700°C; and preferably at least 800°C.

26. A process according to any preceding claim, wherein step (f) of heating the separated precipitate from step (e) comprises heating the precipitate to a temperature of from 750°C to 850°C such as from 800°C to 850°C.

27. A process according to any preceding claim, wherein step (f) of heating the separated precipitate from step (e) comprises heating the precipitate for a time period of from 1 hours to 4 hours; and preferably from 1.5 hours to 2.5 hours.

28. A process according to any preceding claim, wherein step (g) comprises contacting the one or more rare earth metal oxides formed in step (f) with aqueous hydrochloric acid or aqueous nitric acid to provide an acidic solution comprising one or more rare earth metal chloride salts; preferably, wherein the aqueous hydrochloric acid has a pH of 0.5 or less.

29. A process according to any preceding claim, wherein the one or more water soluble hydroxide salts used in step (h) comprises an alkali metal hydroxide salt; preferably, wherein the one or more water soluble hydroxide salts used in step (h) comprises sodium hydroxide.

30. A process according to Claim 29, wherein the alkali metal hydroxide salt is added to the acidic solution in the form of an aqueous solution; preferably wherein the molarity of the solution is from 4 M to 8 M; and more preferably from 5M to 7M.

31. A process according to any preceding claim, wherein the one or more water soluble hydroxide salts are added in step (h) in an amount sufficient to increase the pH of thesolution to from 4.0 to 6.0; preferably to from 4.0 to 5.0; and more preferably to from 4.2 to 5.0.

32. A process according to any preceding claim, wherein step (i) of separating the precipitate formed in step (h) comprises filtering the solution formed in step (h).

33. A process according to any preceding claim, wherein the precipitate formed in step (h) comprises iron (III) hydroxide and optionally aluminium (III) hydroxide.

34. A process according to any preceding claim, wherein the process further comprises process steps for extracting a rare earth metal from a mixture of rare earth metals, which process steps comprise: processing the separated solution formed in step (i) into an acidic solution comprising a mixture of rare earth metals; and contacting the acidic solution of the rare earth metals with a composition which comprises an extractant to form an aqueous phase and a non-aqueous phase into which the rare earth metal has been selectively extracted.

35. A process according to Claim 34, wherein the extractant comprises an ionic liquid extractant, a phosphoric acid compound or hydrocarbyl ester thereof; a phosphonic acid compound or hydrocarbyl ester thereof; a phosphinic acid compound or hydrocarbyl ester thereof; a tertiary phosphine oxide of the formula RR1R2P=O where R, R1 and R2 are independently selected from hydrocarbyl moieties; a dithiophosphinic acid compound or hydrocarbyl ester thereof; an a-aminophosphonate compound; or any combination thereof.

36. A process according to Claim 34 or Claim 35, wherein the extractant comprises an ionic liquid.

37. A process according to Claim 36, wherein the ionic liquid has the formula:[Cat+][X-]in which:[Cat*] represents a cationic species having the structure:L2EDG EDGwhere: [Y+] comprises a group selected from ammonium, benzimidazolium,benzofuranium, benzothiophenium, benzotriazolium, borolium, cinnolinium, diazabicyclodecenium, diazabicyclononenium, 1,4-diazabicyclo[2.2.2]octanium, diazabicyclo-undecenium,dithiazolium, furanium, guanidinium, imidazolium, indazolium, indolinium, indolium, morpholinium, oxaborolium, oxaphospholium, oxazinium, oxazolium, iso-oxazolium, oxothiazolium, phospholium, phosphonium, phthalazinium, piperazinium, piperidinium, pyranium, pyrazinium, pyrazolium, pyridazinium, pyridinium, pyrimidinium, pyrrolidinium, pyrrolium, quinazolinium, quinolinium, iso-quinolinium, quinoxalinium, quinuclidinium, selenazolium, sulfonium, tetrazolium, thiadiazolium, iso-thiadiazolium, thiazinium, thiazolium, iso-thiazolium, thiophenium, thiuronium, triazinium, triazolium, iso-triazolium and uranium groups;each EDG represents an electron donating group; andLi represents a linking group selected from C1-10 alkanediyl, C2-10 alkenediyl, C1-10 dialkanylether and C1.10 dialkanylketone groups;each L2 represents a linking group independently selected from C1-2 alkanediyl, C2 alkenediyl, C1-2 dialkanylether and C1-2 dialkanylketone groups; and[X’] represents a phosphinate anion, a phosphate anion, ora phosphonate anion.

38. The process of Claim 36 or Claim 37, wherein the process comprises recovering the rare earth metal from the non-aqueous phase, for instance by stripping with an acidic stripping solution, e.g. an aqueous hydrochloric acid or nitric acid solution, preferably having a pH of 1 or lower and preferably a pH of 0 or higher.

39. The process of any one of Claims 36 to 38, wherein the acidic solution comprises a first and a second rare earth metal, and the method comprises:(a) preferentially partitioning the first rare earth metal into the non-aqueous phase.

40. The process of Claim 39, wherein the process further comprises, in step (a), separating the non-aqueous phase from the acidic solution; and(b) contacting the acidic solution depleted of the first rare earth metal with the composition which comprises an ionic liquid, and optionally recovering the second rare earth metal therefrom;and preferably wherein:the first rare earth metal is recovered from the non-aqueous phase in step (a), and said non-aqueous phase is recycled and used as the composition in step (b); and / orthe acidic solution has a pH of less than 3.5 in step (a), and the acidic solution has a pH of greater than 3.5 in step (b).

41. The process of Claim 39 or Claim 40, wherein:the first rare earth metal is dysprosium, and the second rare earth metal is neodymium; orthe first rare earth metal is europium, and the second rare earth metal is lanthanum.

42. The process of any of Claims 37 to 41, wherein:the acidic solution from which the rare earth metal is extracted has a pH of from 2 to 4;the composition is added to the acidic solution in a volume ratio of from 0.5 : 1 to 2 : 1, preferably 0.7 : 1 to 1.5 : 1, more preferably 0.8 : 1 to 1.2 : 1, for example 1 : 1;prior to contacting the composition with the acidic solution of the rare earth metal the composition is equilibrated with an acidic solution having the same pH as the acidic solution of the rare earth metal;the acidic solution is contacted with the composition for from 1 to 40 minutes, preferably from 5 to 30 minutes; and / orthe process comprises contacting and physically mixing the acidic solution of the rare earth metal and the composition.

43. The process according to any one of Claims 37 to 42, wherein when the nitrogen linking Li to each L2 and one of the EDG both coordinate to a metal, the ring formed by the nitrogen, L2, the EDG and the metal is a 5 or 6 membered ring, preferably a 5 membered ring.

44. The process according to any one of Claims 37 to 43, wherein the ionic liquid is as further defined as in any one or more of features (a) to (f) defined as follows:(a) wherein [Y+] represents:an acyclic cation selected from:[-N(Ra)(Rb)(Rc)]+, [-P(Ra)(Rb)(Rc)]+ and [-S(Ra)(Rb)]+,where: Ra, Rb and Rc are each independently selected from optionally substituted C1.30 alkyl, C3-8 cycloalkyl and Ce-w aryl groups;or a cyclic cation selected from:where: Ra, Rb, Rc, Rd, Re and Rf are each independently selected from:hydrogen and optionally substituted C1-30 alkyl, C3-8 cycloalkyl andC6-10 aryl groups, or any two of Ra, Rb, Rc, Rd and Re attached toadjacent carbon atoms form an optionally substituted methylenechain -(CH2)q- where q is from 3 to 6;or a saturated heterocyclic cation having the formula:> andwhere: Ra, Rb, Rc, Rd, Re and Rf are each independently selected from: hydrogen and optionally substituted C1.30 alkyl, C3-8 cycloalkyl and C6-10 aryl groups, or any two of Ra, Rb, Rc, Rd and Re attached to adjacent carbon atoms form an optionally substituted methylene chain -(CHzjq- where q is from 3 to 6; preferably, wherein [Y+] represents a cyclic cation selected from:and more preferably represents the cyclic cation:v / WV*wherein preferably Rf is a substituted C1-5 alkyl group, and the remainder of Ra, Rb, Rc, Rd, Re and Rf are independently selected from H and unsubstituted C1-5 alkyl groups;(b) wherein Li represents:a linking group selected from C1-10 alkanediyl and C1-10 alkenediyl groups;preferably a linking group selected from C1-5 alkanediyl and C2-5 alkenediyl groups;more preferably a linking group selected from C1-5 alkanediyl groups;and still more preferably a linking group selected from -CH2-, -C2H4- and -C3H6.(c) wherein each L2 represents:a linking group independently selected from C1-2 alkanediyl and C2 alkenediyl groups;preferably a linking group independently selected from C1-2 alkanediyl groups;and more preferably a linking group independently selected from -CH2- and -C2H4-.(d) wherein each EDG represents:an electron donating group independently selected from -CCER’S -OC(O)RX, -CS. 2Rx, -SC(S)Rx,-S(O)ORx, -OS(O)Rx, -NRxC(O)NRyRz, -NRxC(O)ORy, -OC(O)NRyRz, -NRxC(S)ORy, -OC(S)NRyRz, -NRxC(S)SRy, -SC(S)NRyRz, -NRxC(S)NRyRz, -C(O)NRyRz, -C(S)NRyRz, wherein Rx, Ry and Rz are independently selected from H orCi-6 alkyl;and preferably an electron donating group independently selected from -CO2RX and -C(O)NRyRz, wherein Rx, Ry and Rz are each independently selected from C3-6 alkyl; preferably, wherein each -L2-EDG represents an electron donating group independently selected from:wherein Ry = Rz, and wherein Rx, RY and Rz are each selected from C3-6 alkyl, preferably C4 alkyl, for example / -Bu;(e) wherein [Cat+] represents one or more ionic species having the structure:EDGJ.L2 l2I                                       IEDG EDGwhere: [Z+] represents a group selected from ammonium, benzimidazolium,benzofuranium, benzothiophenium, benzotriazolium, borolium, cinnolinium, diazabicyclodecenium, diazabicyclononenium, 1,4-diazabicyclo[2.2.2]octanium, diazabicyclo-undecenium,dithiazolium, furanium, guanidinium, imidazolium, indazolium, indolinium, indolium, morpholinium, oxaborolium, oxaphospholium, oxazinium, oxazolium, iso-oxazolium, oxothiazolium, phospholium, phosphonium, phthalazinium, piperazinium, piperidinium, pyranium, pyrazinium, pyrazolium, pyridazinium, pyridinium, pyrimidinium, pyrrolidinium, pyrrolium, quinazolinium, quinolinium, iso-quinolinium, quinoxalinium, quinuclidinium, selenazolium, sulfonium, tetrazolium, thiadiazolium, iso-thiadiazolium, thiazinium, thiazolium, iso-thiazolium, thiophenium, thiuronium, triazinium, triazolium, iso-triazolium and uranium groups;(f) wherein [X-] represents a phosphinate anion having the structure:r2 " -R1 | ,0II 0where: R1 and R2 are independently selected from optionally substituted C3-20, preferably C4-15, and more preferably Cs-w, hydrocarbyl groups in which up to 3 carbon atoms may be replaced with a heteroatom; preferably, wherein R1 and R2 are independently selected from alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkyl-cycloalkyl, cycloalkyl-alkyl, aryl, alkyl-aryl and aryl-alkyl groups; preferably from alkyl groups; and more preferably from branched alkyl groups.

45. The process of any one or more of Claims 34 to 44, wherein the composition further comprises a lower viscosity ionic liquid and / or one or more organic solvents; optionally, wherein:the cation of the ionic liquid is present in the composition in a concentration of at least 0.001 M, preferably from 0.005 M to 0.01 M, for example 0.0075 M; and / orthe anion of the ionic liquid is present in the composition in a concentration of at least 0.001 M, preferably from 0.005 M to 0.01 M, for example 0.0075 M.40

Images