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 with an acid to form a solution comp

Description

Sheet' MAGNET RECYCLING PROCESS 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 such as yttrium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium 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 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 etal, 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 4-5% 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 with an acid to form an acidic solution comprising one or more rare earth metal salts and one or more iron salts; (b) contacting the acidic solution formed in step (a) with one or more of (i) a water soluble bicarbonate salt or a solution thereof to form a precipitate comprising one or more rare earth metal carbonate salts; (ii) a water soluble carbonate salt or a solution thereof to form a precipitate comprising one or more rare earth metal carbonate salts; (iii) oxalic acid or a solution thereof to form a precipitate comprising one or more rare earth metal oxalate salts; and (iv) a water soluble oxalate salt or a solution thereof to form a precipitate comprising one or more rare earth metal oxalate salts; (c) separating the precipitate formed in step (b) from the solution to form a separated precipitate; (d) contacting the separated precipitate from step (c) with hydrochloric acid, nitric acid, or a combination thereof to form an acidic solution comprising one or more rare earth metal salts; (e) contacting the solution formed in step (d) with one or more oxidants to provide an oxidant-treated solution; (f) contacting the oxidant-treated solution formed in step (e) with one or more water soluble hydroxide salts to form a precipitate; (g) separating the precipitate formed in step (f) from the solution to provide a separated precipitate and a separated aqueous solution; and (h) contacting the separated aqueous solution formed in step (g) with one or more of (i) a water soluble bicarbonate salt or a solution thereof to form a precipitate comprising one or more rare earth metal carbonate salts; (ii) a water soluble carbonate salt or a solution thereof to form a precipitate comprising one or more rare earth metal carbonate salts; (iii) oxalic acid or a solution thereof to form a precipitate comprising one or more rare earth metal oxalate salts; and (iv) a water soluble oxalate salt or a solution thereof to form a precipitate comprising one or more rare earth metal oxalate salts. The process of the invention relies in parton a synergistic combination of separation steps. In an initial separation, a rare earth metal-containing composition is leached with acid to form an acidic solution comprising dissolved rare earth metal salts and dissolved impurities such as iron salts. The acidic solution is then contacted with oxalate, carbonate or bicarbonate to form a precipitate comprising rare earth metal salts. Surprisingly, it has been found that substantially all of the rare earth metals are recovered from the solution in the precipitate as salts whilst leaving around 90% of the iron impurities present in the acidic solution allowing separation of the rare earth metals therefrom. In a second separation, the rare earth metal salt-containing precipitate is dissolved in acid to form an acidic solution which is then treated with an oxidant before a second separation comprising a hydroxide precipitation is carried out. This step removes the 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, and the prior treatment of the solution with an oxidant. The present invention thus involves the synergistic combination of separation steps. A first separation is used to separate the rare earth metals from the bulk of impurities present. This step allows the provision of a low impurity concentration rare earth metal solution which can then be further purified in a separation using 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, Praseodymium (Pr) and Terbium (Tb). 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 or an ionic adsorption clay. 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) Step (a) comprises contacting the rare earth metal-containing composition with an acid to form an acidic solution comprising one or more rare earth metal salts and one or more iron salts. The purpose of acid treatment in step (a) is an acid leaching step to dissolve all rare earth elements present in the magnet and form a solution comprising the rare earth elements. Many impurities from the magnet such as iron and aluminium are also dissolved in this process and enter the acidic leachate solution. This acid leaching step can effectively dissolve almost all of the rare earth elements present in the original composition. The acid used in step (a) of the process may be any suitable acid. Typically, the acid used in step (a) comprises sulphuric acid, nitric acid, or a combination thereof. Preferably, the acid used in step (a) comprises sulphuric acid. Sulphuric acid is preferred over the use of other mineral acids due to corrosion and safety issues. Increased corrosion causes more impurities to be present in the subsequent solution 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 sulphuric acid is used. Where sulphuric acid is used, this has also surprisingly been found to minimise undesirable precipitation of iron along with rare earth metal salts in subsequent precipitation step (b) when compared to other mineral acids. Typically, the acid used in step (a) is an aqueous acid and the acidic solution formed in step (a) is an aqueous acidic solution. After acid treatment step (a), some solid material that does not contain the rare earth metals may remain. This material may be separated from the acidic solution by any suitable means such as filtration prior to carrying out step (b) of the process. The acid used in step (a) preferably has a pH of less than 1; and more preferably less than 0.5. It is desired for the acid to have this low pH in order to effectively digest and dissolve all rare earth metals present in the rare earth metal-containing composition so that they enter the acidic solution formed after step (a) as rare earth metal ions. Preferably, the acid used in step (a) has a molarity of from 1 M to 4 M; more preferably from 1.5 M to 3 M; and most preferably from 1.5 M to 2.5 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 1 M to 4 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 1.5 M to 3 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. More preferably, the acid used in step (a) has a molarity of from 1.5 M to 2.5 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. The acidic solution formed in step (a) will comprise rare earth metal ions and counterions depending on what acid was used in step (a). Typically the counter ions present in the solution are sulphate ions since sulphuric acid treatment is preferred. The solution of course comprises nitrate counterions in the case of nitric acid treatment. In step (a) a sufficient amount of acid is typically added to the rare earth metal-containing composition to effectively digest and dissolve all rare earth metals in the composition. This amount is typically a molar excess relative to the total amount of rare earth metals present in the rare earth metal-containing composition. Preferably, at least 1.5 moles of acid are added per mole of rare earth metals present in the rare earth metal-containing composition. More preferably, at least 2 moles of acid are added per mole of rare earth metals present in the rare earth metal-containing composition. Still more preferably, at least 2.5 moles of acid are added per mole of rare earth metals present in the rare earth metal-containing composition. Most preferably, at least 3 moles of acid are added per mole of rare earth metals present in the rare earth metal-containing composition. In some instances, at least 3.5, at least 4, at least 4.5 or at least 5 moles of acid are added per mole of rare earth metals present in the rare earth metal-containing composition. The amount of acid added will typically depend upon the nature of the acid used. Where sulphuric acid is used, typically, at least 1.5 moles of acid are added per mole of rare earth metals present in the rare earth metal-containing composition. Where nitric acid is used, typically, at least 3 moles of acid are added per mole of rare earth metals present in the rare earth metal-containing composition. Where sulphuric acid is used, preferably, an amount of sulphuric acid is added such that the amount of sulphate added is less than 2.5 moles of sulphate per total moles 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. At the end of step (a), the acidic solution provided comprises dissolved rare earth metal ions; dissolved impurity ions such as iron ions and aluminium ions; and dissolved 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. Step (b) Step (b) comprises contacting the acidic solution formed in step (a) with one or more of (i) a water soluble bicarbonate salt or a solution thereof to form a precipitate comprising one or more rare earth metal carbonate salts; (ii) a water soluble carbonate salt or a solution thereof to form a precipitate comprising one or more rare earth metal carbonate salts; (iii) oxalic acid or a solution thereof to form a precipitate comprising one or more rare earth metal oxalate salts; or (iv) a water soluble oxalate salt or a solution thereof to form a precipitate comprising one or more rare earth metal oxalate salts. Preferably, step (b) comprises contacting the acidic solution formed in step (a) with one or more of (i) a water-soluble bicarbonate salt or a solution thereof to form a precipitate comprising one or more rare earth metal carbonate salts; or (ii) a water soluble carbonate salt or a solution thereof to form a precipitate comprising one or more rare earth metal carbonate salts. More preferably, step (b) comprises contacting the acidic solution formed in step (a) with ammonium bicarbonate ora solution thereof, an alkali metal bicarbonate salt or a solution thereof, an alkali earth metal bicarbonate salt or a solution thereof, or a combination thereof. Still more preferably, step (b) comprises contacting the aqueous solution formed in step (a) with ammonium bicarbonate or a solution thereof, sodium bicarbonate or a solution thereof, magnesium bicarbonate or a solution thereof, calcium bicarbonate or a solution thereof, potassium bicarbonate or a solution thereof, or a combination thereof. Most preferably, step (b) comprises contacting the aqueous solution formed in step (a) with ammonium bicarbonate or a solution thereof. The use of carbonate or bicarbonate salts as precipitants is preferred over the use of oxalic acid or oxalate salts as precipitants. This is because iron (II) oxalate is insoluble and so this salt may precipitate at the end of step (b) along with rare earth metal oxalates when oxalic acid or a salt there of is used. This is undesirable as it is desired for as much iron as possible to remain in the solution after the carbonate / oxalate precipitation. Where a bicarbonate salt is added in step (b), the salt can be added to the acidic solution formed in step (a) in any suitable form. For example, solid powders of the salt may be added or aqueous solutions of the salt may be added. Preferably, step (b) comprises contacting the acidic solution formed in step (a) with an aqueous solution of a water-soluble bicarbonate salt Typically, during the contacting in step (b), the acidic solution is heated. Preferably, step (b) comprises heating the acidic solution to a temperature of from 25°C to 40°C; and more preferably from 30°C to 35°C during the contacting. These steps of adding the bicarbonate salt as a solution and of heating the solution in step (b) are preferred since they have been found by the inventors to provide a more easily filterable precipitate. Step (b) typically comprises contacting the acidic solution formed in step (a) with an amount of (i) a water soluble bicarbonate salt or a solution thereof; (ii) a water soluble carbonate salt or a solution thereof; (iii) oxalic acid or a solution thereof; or (iv) a water soluble oxalate salt or a solution thereof sufficient to increase the pH of the aqueous solution to at least 5.0; preferably from 5.5 to 7.0; and more preferably from 5.5 to 6.5. 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. It has been found by the inventors of the present invention that the abovementioned pH ranges are desirable for the process of the invention in order to effectively maximise precipitation of all (or nearly all) rare earth metals present in the solution as a carbonate or oxalate salt. At lower pH ranges, not all rare earth metals may effectively precipitate. At higher pH ranges, a fine solid comprising iron begins to precipitate. This is undesirable as it reduces the amount of iron effectively separated from the rare earth metals in this step. In step (b) it is desired that the rare earth metals precipitate with the impurities remaining in solution. Additionally, the formation of the fine iron-containing solid makes the precipitate hard to filter and separate from the solution. Use of the abovementioned pH ranges are thus particularly preferred. In step (b) a sufficient amount of (i) a water soluble bicarbonate salt or a solution thereof; (ii) a water soluble carbonate salt or a solution thereof; (iii) oxalic acid or a solution thereof; or (iv) a water soluble oxalate salt or a solution thereof is typically added to the acidic solution to effectively precipitate all rare earth metals from the acidic solution. As discussed above, this amount 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 metalcontaining composition. Preferably, at least 3 moles of the salts or acids defined in components (i) to (iv) listed above are added per mole of rare earth metals present in the rare earth metal-containing composition or present in the acidic solution formed in step (a). More preferably, at least 5 moles of the salts or acids defined in components (i) to (iv) listed above are added per mole of rare earth metals present in the rare earth metalcontaining composition or present in the acidic solution formed in step (a). Still more preferably, at least 8 moles of the salts or acids defined in components (i) to (iv) listed above are added per mole of rare earth metals present in the rare earth metal-containing composition or present in the acidic solution formed in step (a). Most preferably, from 8 to 12 moles of the salts or acids defined in components (i) to (iv) listed above are added per mole of rare earth metals present in the rare earth metal-containing composition or acidic solution formed in step (a). In some instances, from 8 to 10 moles of the salts or acids defined in components (i) to (iv) listed above are added per mole of rare earth metals present in the rare earth metal-containing composition or acidic solution formed in step (a). Step (c) Step (c) of the process comprises separating the precipitate formed in step (b) from the solution to form a separated precipitate. Step (c) of the process typically comprises separating the precipitate formed in step (b) by filtering the solution formed in step (b), although other separation methods known in the art may also be used. For example, centrifugation and similar techniques may also be used. Step (c) typically comprises separating the precipitate formed in step (b) to form a separated precipitate and a separated solution. The separated precipitate typically comprises rare earth metal carbonates or rare earth metal oxalates, and preferably rare earth metal carbonates. The separated solution typically comprises iron (II) oxalate or iron (II) hydroxide and preferably iron (II) hydroxide. The separated solution formed in step (c) may be disposed of after the separation step (c). Advantageously, the separated solution comprises the majority of the iron present in the initial rare earth metal-containing composition, typically in the form of dissolved iron (II) hydroxide. The separated precipitate formed in step (c) comprises substantially all of the rare earth metal elements from the original rare earth metal-containing composition. The process comprises step (d) of contacting the separated precipitate from step (c) 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 salt 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. Step (d) The process comprises step (d) of contacting the separated precipitate from step (c) 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 salt 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. Step (d) involves the use of hydrochloric or nitric acid. Sulphuric acid cannot be used for this step due to subsequent precipitation step (f) 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 (d) comprises contacting the separated precipitate from step (c) with an aqueous acid to form an aqueous acidic solution. Typically, step (d) comprises contacting the separated precipitate from step (c) 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. Typically, the acid used in step (d) has a pH of less than 0.5; and more preferably less than 0.25. These pH ranges are preferred in order to effectively redissolve all of the solid rare earth metal carbonate / oxalate. Where hydrochloric acid is used, preferably, hydrochloric acid with a molarity of from 2 M to 3 M is used. In step (d) a sufficient amount of acid is typically added to the separated precipitate formed in step (c) to effectively dissolve all of the precipitate. This amount is typically a molar excess relative to the total amount of rare earth metals present in the rare earth metalcontaining composition or present in the precipitate formed in step (c). Preferably, at least 2 moles of acid are added per mole of rare earth metals present in the rare earth metalcontaining composition or present in the precipitate formed in step (c). 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 (c). 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 (c). 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 (c). 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 (c). Step (e) Step (e) of the process comprises contacting the solution formed in step (d) with one or more oxidants to provide an oxidant-treated solution. The purpose of step (e) is to oxidise any Fe2+ ions remaining in solution to Fe3+ ions prior to step (f) of the hydroxide precipitation. It has been found by the inventors that Fe (III) hydroxide has a lower precipitation pH than Fe (II) hydroxide meaning precipitation of remaining iron impurities in hydroxide precipitation step (f) is easier and more effective where the solution to be treated comprises Fe3+ ions instead of Fe2+ ions. It has also been found that loss of rare earth metals in the precipitate formed in step (f) is less when the precipitate comprises iron (III) hydroxide rather than iron (II) hydroxide. The one or more oxidants used in step (e) may comprise any suitable oxidant for oxidising a solution containing Fe2+ ions to Fe3+ ions. Preferably, the one or more oxidants used in step (e) comprise oxygen, hydrogen peroxide, ozone, nitric acid, a nitrate salt, peroxydisulphuric acid, peroxymonosulphuric acid, a hypochlorite salt, a chlorite salt, a chlorate salt, a perchlorate salt, a perhalide salt, a permanganate salt, a chromium compound, ora combination thereof. More preferably, the one or more oxidants comprise hydrogen peroxide. Typically, the one or more oxidants are added to the acidic solution formed in step (f) in any amount suitable for oxidising the Fe2+ ions present in the solution to Fe3+ ions. Preferably, the one or more oxidants are added to the acidic solution formed in step (d) in a molar ratio of from 1 to 2 moles of oxidant to 1 mole of iron present in the rare earth metal-containing composition used in step (a); and preferably from 1.5 to 2 moles of oxidant to 1 mole of iron present in the rare earth metal-containing composition used in step (a). Step (f) The process comprises step (f) of contacting the oxidant-treated solution formed in step (e) with one or more water soluble hydroxide salts to form a precipitate. The purpose of this step is to precipitate any iron and aluminium present in the oxidant-treated 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 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 slurry 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 oxidant-treated 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 (f) comprises an alkali metal hydroxide salt; and preferably sodium hydroxide. Typically, the alkali metal hydroxide salt is added to the oxidant-treated 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 5M to 7M. Preferably, the one or more water soluble hydroxide salts are added in step (f) 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 oxidant-treated 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 (f), the one or more water soluble hydroxide salts are added to the oxidant-treated solution to effectively precipitate all iron and other impurities from the oxidant-treated 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. Typically, the precipitate formed in step (f) comprises iron hydroxide. Preferably, the precipitate formed in step (f) comprises iron (III) hydroxide. Where the rare earth metalcontaining composition comprises aluminium, typically the precipitate formed in step (f) also comprises aluminium hydroxide. Preferably, in step (f), the process further comprises the addition of an adsorbent to the oxidant-treated solution formed in step (e). 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 (g). 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........(g) The process comprises step (g) 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 (g) of separating the precipitate formed in step (f) comprises filtering the solution formed in step (f), although other separation methods known in the art may also be used. For example, centrifugation and similar techniques may also be used. Step (h) The process of the invention comprises step (h) of precipitating the rare earth metals from the separated aqueous solution formed in step (g). The separated aqueous solution formed in step (g) is of a high purity due to the prior impurity removal steps of the process. The purpose of step (h) is to recover the rare earth metals from the separated aqueous solution formed in step (g) in pure form. Preferably, step (h) comprises contacting the separated solution formed in step (g) with ammonium bicarbonate ora solution thereof, an alkali metal bicarbonate salt or a solution thereof, an alkali earth metal bicarbonate salt or a solution thereof, or a combination thereof; preferably, wherein step (h) comprises contacting the solution formed in step (g) with ammonium bicarbonate or a solution thereof, sodium bicarbonate or a solution thereof, magnesium bicarbonate or a solution thereof, calcium bicarbonate or a solution thereof, potassium bicarbonate or a solution thereof, or a combination thereof. It is preferred to use these salts over the use of oxalic acid or an oxalate salt as a precipitant. Preferably, step (h) comprises contacting the solution formed in step (g) with ammonium bicarbonate or a solution thereof. More preferably, step (h) comprises contacting the solution formed in step (g) with an aqueous solution of a water-soluble bicarbonate salt. Where a bicarbonate salt is added in step (h), the salt can be added to the separated solution formed in step (g) in any suitable form. For example, solid powders of the salt may be added or aqueous solutions of the salt may be added. Preferably, step (g) comprises contacting the separated solution formed in step (g) with an aqueous solution of a water-soluble bicarbonate salt. Typically, during the contacting in step (h), the solution is heated. Preferably, step (g) comprises heating the solution to a temperature of from 25°C to 40°C; and more preferably from 30°C to 35°C during the contacting. These steps of adding the bicarbonate salt as a solution and of heating the solution in step (g) are preferred since they have been found by the inventors to provide a more easily filterable precipitate. Step (h) typically comprises contacting the separated solution formed in step (g) with an amount of (i) a water soluble bicarbonate salt or a solution thereof; or (ii) a water soluble carbonate salt or a solution thereof; (iii) oxalic acid or a solution thereof; and (iv) a water soluble oxalate salt or a solution thereof sufficient to increase the pH of the aqueous solution to at least 5.0; preferably at least 5.5; more preferably from 5.5 to 7.0; and most preferably from 5.5 to 6.5. 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. It has been found by the inventors of the present invention that the abovementioned pH ranges are desirable for the process of the invention in order to effectively maximise precipitation of all (or nearly all) rare earth metals present in the solution as a carbonate or oxalate salt. At lower pH ranges, not all rare earth metals may effectively precipitate. In step (h) a sufficient amount of (i) a water soluble bicarbonate salt or a solution thereof; (ii) a water soluble carbonate salt or a solution thereof; (iii) oxalic acid or a solution thereof; or (iv) a water soluble oxalate salt or a solution thereof is typically added to the separated solution formed in step (g) to effectively precipitate all rare earth metals from the solution. As discussed above, this amount 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 metalcontaining composition. Preferably, at least 1.5 moles of the salts or acids defined in components (i) to (iv) listed above are added per mole of rare earth metals present in the rare earth metal-containing composition or present in the solution formed in step (g). More preferably, at least 2 moles of the salts or acids defined in components (i) to (iv) listed above are added per mole of rare earth metals present in the rare earth metal-containing composition or present in the solution formed in step (g). Still more preferably, at least 2.5 moles of the salts or acids defined in components (i) to (iv) listed above are added per mole of rare earth metals present in the rare earth metal-containing composition or present in the solution formed in step (g). Most preferably, at least 3 moles of the salts or acids defined in components (i) to (iv) listed above are added per mole of rare earth metals present in the rare earth metal-containing composition or solution formed in step (g). In some instances, at least 3.5, at least 4, at least 4.5 or at least 5 moles of the salts or acids defined in components (i) to (iv) listed above are added per mole of rare earth metals present in the rare earth metal-containing composition or solution formed in step (g). As a result of step (g) of the process, the rare earth metals from the rare earth metalcontaining composition are present as substantially pure rare earth metal carbonate or oxalate salts, and preferably rare earth metal carbonate salts. The precipitate formed in step (g) typically comprises at least 95% by weight of one or more rare earth metal carbonates or oxalates; preferably at least 97% by weight of one or more rare earth metal carbonates or oxalates; more preferably at least 98% by weight of one or more rare earth metal carbonates or oxalates; and most preferably at least 99% by weight of one or more rare earth metal carbonates or oxalates. The rare earth metal carbonate or oxalate salts formed are substantially pure and are 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. 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, wherein the acidic or aqueous feedstream comprises the one or more rare earth carbonate or oxalate salts formed in step (h) of the process. The aqueous feedstreams may be formed in any suitable manner. For example, the precipitate formed in step (h) may be separated from the mother liquor solution from which it was precipitated and contacted with water or acid to form an aqueous or acidic feedstream comprising a dissolved rare earth metal carbonate salt or oxalate salt. Accordingly, the process may further comprise contacting the one or more rare earth metal carbonate salts or oxalate salts with hydrochloric acid or nitric acid to form an acidic solution of one or more rare earth metal chloride salts or rare earth metal nitrate salts. This step is typically carried out after the precipitate formed in step (h) is separated from its mother liquor solution. 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 one or more rare earth carbonate salts or one or more rare earth oxalate salts formed in step (h) 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: / [Y+] I’ l2 l2 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 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. 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-io 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 -(CHzjq- 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 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 -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 or C1-6 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: where: R1 and R2 are independently selected from optionally substituted C3-20, preferably C4-15, and more preferably Ce-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. 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 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. Figure 2 depicts a graph showing percentage metal loss at various stages of the process of the invention. Figure 3 shows a process flow chart for the process of the invention integrated as a pretreatment process before a known rare metal separation and purification process. DETAILED DESCRIPTION OF THE INVENTION The following examples are for illustrative purposes only, and are not intended to limit the scope of the invention in any way. Example 1 1. A Neodymium iron boron magnet was digested using 2 M sulphuric acid. All metals present in the magnet were dissolved by the acid, oxidised, and converted to water soluble sulphate salts present in solution. The pH of the solution after acid treatment was pH 2. 2. Ammonium bicarbonate was added to adjust the pH of the solution from pH 2 to pH 6.5, forming insoluble rare earth carbonates and a small amount of insoluble impurity carbonates (Fe, Al, Ni, Co etc) as a precipitate. 3. The bulk of Fe and Co formed soluble carbonates and remain in solution. The solution was separated from the precipitate in a filtration step. 4. The precipitate from step 3 containing solid rare earth carbonates was dissolved in 3 M hydrochloric acid to form an acidic solution. 5. The acidic solution formed in step 4 was treated with hydrogen peroxide to convert any Fe2+ present to Fe3+ and form an oxidant treated solution. 6. The oxidant treated solution from step 5 was contacted with 6 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. 7. The solution formed in step 6 was then further treated with ammonium bicarbonate to increase the pH of the solution to >7. Rare earth carbonates were then precipitated from the solution in pure form (>99.8%). A flow chart of the process is shown in Figure 1. Figure 2 shows a graph of percentage metal loss at each stage of the process. The data that the graph is based on is shown below in Table 1. Mass balance Total Rare earth metals Nd Dy Pr Fe Al Other impurities Dissolution -sulphuric acid (g) 34.48 22.81 3.28 6.19 70.42 0.64 2.04 Metal carbonate precipitation (g) 34.69 23.60 3.08 6.02 6.84 0.60 0.13 Sodium hydroxide neutralisation (g) 33.21 22.43 2.82 6.02 0.00 0.01 0.11 Rare earth carbonate precipitation (g) 33.33 22.56 2.84 6.07 0.00 0.01 0.05 Final recovery (%) 97% 98% 86% 98% 0% 1% 2% As can be seen in Table 1 and Figure 2, the total amount of rare earth metals is not reduced at all in the step of sulphuric acid digestion and the step of ammonium carbonate precipitation. All rare earth metals from the original magnet are effectively digested and recovered in the carbonate precipitation. In the subsequent sodium hydroxide neutralisation and rare earth carbonate precipitation steps, there is only a very small reduction in the total amount of rare earth metals recovered. This indicates that only a very small amount of rare earth metals are lost in the neutralisation step along with iron and aluminium hydroxides. The loss of rare earth metals was mainly down to dysprosium being lost in the iron hydroxide and aluminium hydroxide precipitates. It can also be seen that the majority of the iron was separated from the rare earth metals in the first ammonium carbonate precipitation step where most iron remained in the mother liquor solution as soluble iron (II) carbonate. The remaining iron was then effectively separated along with the small amount of aluminium present in the sodium hydroxide neutralization step. The data thus shows that the process of the invention is an effective process for recovering the rare earth metals in very high yield from neodymium-iron-boron magnets with only minimal impurity contamination. Figure 3 shows a process flow chart for integrating the process of the invention as a pretreatment separation process for forming a pure rare earth metal-containing feedstream for use in a rare earth metal purification separation process, such as the process disclosed in WO2019 / 239150. The process of the invention is shown in the top right of the figure and is encircled. Magnets are initially demagnetised and then crushed. The crushed magnets are then fed to a tank for sulphuric acid treatment to digest the magnet. The digestate is then filtered to remove any solid material present. The digestate is then diluted with water in a separate tank before being transferred to a further tank for ammonium bicarbonate precipitation to be carried out. The precipitate is then separated from the solution by filtration before being treated with hydrochloric acid to dissolve the precipitate in further tank. The acidic solution is then transferred to a further tank for contact with hydrogen peroxide and subsequent neutralisation with sodium hydroxide to precipitate the remaining impurities. The precipitate is then separated from the solution by filtration before being transferred to a subsequent tank for a second ammonium bicarbonate precipitation to precipitate the rare earth metals as rare earth metal carbonates. The rare earth metal carbonates can then be further processed (such as by HCI treatment) into aqueous acidic feedstreams for use in downstream purification processes where individual rare earth metal elements can be extracted from solutions containing mixtures of rare earth metal elements.

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 with an acid to form an acidic solution comprising one or more rare earth metal salts and one or more iron salts;(b) contacting the acidic solution formed in step (a) with one or more of (i) a water soluble bicarbonate salt or a solution thereof to form a precipitate comprising one or more rare earth metal carbonate salts; (ii) a water soluble carbonate salt or a solution thereof to form a precipitate comprising one or more rare earth metal carbonate salts; (iii) oxalic acid or a solution thereof to form a precipitate comprising one or more rare earth metal oxalate salts; or (iv) a water soluble oxalate salt or a solution thereof to form a precipitate comprising one or more rare earth metal oxalate salts;(c) separating the precipitate formed in step (b) from the solution to form a separated precipitate;(d) contacting the separated precipitate from step (c) with hydrochloric acid, nitric acid, or a combination thereof to form an acidic solution comprising one or more rare earth metal salts;(e) contacting the solution formed in step (d) with one or more oxidants to provide an oxidant-treated solution;(f) contacting the oxidant-treated solution formed in step (e) with one or more water soluble hydroxide salts to form a precipitate;(g) separating the precipitate formed in step (f) from the solution to provide a separated precipitate and a separated aqueous solution; and(h) contacting the separated aqueous solution formed in step (g) with one or more of (i) a water soluble bicarbonate salt or a solution thereof to form a precipitate comprising one or more rare earth metal carbonate salts; (ii) a water soluble carbonate salt or a solution thereof to form a precipitate comprising one or more rare earth metal carbonate salts; (iii) oxalic acid or a solution thereof to form a precipitate comprising one or more rare earth metal oxalate salts; or (iv) a water soluble oxalate salt or a solution thereof to form a precipitate comprising one or more rare earth metal oxalate salts.

2. A process according to Claim 1, wherein the acids used in any one or more of steps (a) and (d) are aqueous acids and / or wherein the acidic solutions formed in any one or more of steps (a) and (d) are aqueous acidic solutions; preferably wherein the acids used in all of steps (a) and (d) are aqueous acids and / or wherein the acidic solutions formed in all of steps (a) and (d) 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) and (d) 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) and (d) 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 (b), (f) 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 (b), (f) 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 Claim 11, wherein the rare earth metal-containing 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 acid used in step (a) comprises sulphuric acid, nitric acid, ora combination thereof.

17. A process according to any preceding claim, wherein the acid used in step (a) comprises sulphuric acid.

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

19. A process according to any preceding claim, wherein 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.

20. A process according to any preceding claim, wherein step (b) comprises contacting the acidic solution formed in step (a) with ammonium bicarbonate or a solution thereof, an alkali metal bicarbonate salt or a solution thereof, an alkali earth metal bicarbonate salt or a solution thereof, or a combination thereof; preferably, wherein step (b) comprises contacting the aqueous solution formed in step (a) with ammonium bicarbonate or a solution thereof, sodium bicarbonate or a solution thereof, magnesium bicarbonate or asolution thereof, calcium bicarbonate or a solution thereof, potassium bicarbonate or a solution thereof, or a combination thereof.

21. A process according to Claim 20, wherein step (b) comprises contacting the aqueous solution formed in step (a) with ammonium bicarbonate or a solution thereof.

22. A process according to any preceding claim, wherein step (b) comprises contacting the acidic solution formed in step (a) with an aqueous solution of a water soluble bicarbonate salt.

23. A process according to any preceding claim, wherein step (b) comprises heating the acidic solution to a temperature of from 30°C to 45°C; and preferably from 40°C to 45°C during the contacting.

24. A process according to any preceding claim, wherein step (b) comprises contacting the acidic solution formed in step (a) with an amount of (i) a water soluble bicarbonate salt or a solution thereof; (ii) a water soluble carbonate salt or a solution thereof; (iii) oxalic acid or a solution thereof; and (iv) a water soluble oxalate salt or a solution thereof sufficient to increase the pH of the aqueous solution to at least 5.0; preferably from 5.5 to 7.0; and more preferably from 5.5 to 6.5.

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

26. A process according to any preceding claim, wherein step (c) comprises separating the precipitate formed in step (b) to form a separated precipitate and a separated solution; wherein the separated solution comprises iron (II) carbonate; iron (II) oxalate, or a combination thereof; preferably wherein the precipitate comprises iron (II) carbonate.

27. A process according to any preceding claim, wherein step (d) comprises contacting the separated precipitate from step (c) 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.

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

29. A process according to any preceding claim, wherein the one or more oxidants used in step (e) comprises oxygen, hydrogen peroxide, ozone, nitric acid, a nitrate salt, peroxydisulphuric acid, peroxymonosulphuric acid, a hypochlorite salt, a chlorite salt, a chlorate salt, a perchlorate salt, a perhalide salt, a permanganate salt, a chromiumcompound, or a combination thereof; preferably wherein the one or more oxidants comprise hydrogen peroxide.

30. A process according to any preceding claim, wherein step (e) comprises adding the oxidant to the acidic solution formed in step (d) in a molar ratio of from 1 to 2 moles of oxidant to 1 mole of iron present in the material used in step (a); and preferably from 1.5 to 2 moles of oxidant to 1 mole of iron present in the material used in step (a).

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

32. A process according to Claim 31, wherein the alkali metal hydroxide salt is added to the oxidant-treated aqueous 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.

33. A process according to any preceding claim, wherein the one or more water soluble hydroxide salts are added in step (f) 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.

34. A process according to any preceding claim, wherein step (g) of separating the precipitate formed in step (f) comprises filtering the solution formed in step (g).

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

36. A process according to any preceding claim, wherein step (h) comprises contacting the separated solution formed in step (g) with ammonium bicarbonate or a solution thereof, an alkali metal bicarbonate salt ora solution thereof, an alkali earth metal bicarbonate salt or a solution thereof, or a combination thereof; preferably, wherein step (h) comprises contacting the solution formed in step (g) with ammonium bicarbonate or a solution thereof, sodium bicarbonate or a solution thereof, magnesium bicarbonate or a solution thereof, calcium bicarbonate or a solution thereof, potassium bicarbonate or a solution thereof, or a combination thereof.

37. A process according to Claim 36, wherein step (h) comprises contacting the solution formed in step (g) with ammonium bicarbonate or a solution thereof.

38. A process according to any preceding claim, wherein step (h) comprises contacting the solution formed in step (g) with an aqueous solution of a water soluble bicarbonate salt.

39. A process according to any preceding claim, wherein step (h) comprises heating the solution to a temperature of from 30°C to 45°C; and preferably from 40°C to 45°C during the contacting.

40. A process according to any preceding claim, wherein step (h) comprises contacting the solution formed in step (g) with an amount of (i) a water soluble bicarbonate salt ora solution thereof; or (ii) a water soluble carbonate salt or a solution thereof sufficient to increase the pH of the aqueous solution to at least 6.5; and preferably at least 7.

41. A process according to any preceding claim, wherein the process further comprises contacting the one or more rare earth metal carbonate salts with hydrochloric acid or nitric acid to form an acidic solution of one or more rare earth chloride salts or one or more rare earth nitrate salts.

42. 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 one or more rare earth carbonate salts or one or more rare earth oxalate salts formed in step (h) 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.

43. A process according to Claim 42, 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.

44. A process according to Claim 42 or Claim 43, wherein the extractant comprises an ionic liquid.

45. A process according to Claim 44, wherein the ionic liquid has the formula:[Cat+][X-]in which:[Cat+] represents a cationic species having the structure:-1L2 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[Xj represents a phosphinate anion, a phosphate anion, or a phosphonate anion.

46. The process of Claim 44 or Claim 45, 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.

47. The process of any one of Claims 44 to 46, 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.

48. The process of Claim 47, 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).

49. The process of Claim 47 or Claim 48, 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.

50. The process of any of Claims 45 to 49, 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.

51. The process according to any one of Claims 45 to 50, 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.

52. The process according to any one of Claims 45 to 51, 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-io 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 andCe-io 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;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 Ce-io 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 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 orC-i-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:where: R1 and R2 are independently selected from optionally substituted C3-20, preferably C4-15, and more preferably Ce-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.

53. The process of any one or more of Claims 44 to 52, 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.

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