Process for the recovery of rare earths from FeNdB-containing magnets

Abstract

Process for the recovery of rare earths from FeNdB-containing magnets with the following process steps: a) Crushing the FeNdB-containing magnets under a protective gas atmosphere to a grain size in the range of 100 to 200 µm to produce crushed rare earth-containing compositions, b) Addition of solid ammonium chloride in a 1.0 to 1.5 times stoichiometric amount, based on the amount of chlorinable metals, to the crushed FeNdB magnets, c) Chlorination of the chlorinable metals to metal chlorides in a rotary kiln or a sublimation plant at a temperature in the range of 250-350°C for a period of 1 to 5 hours, d) adding an acidic solution to the metal chlorides to a pH in the range of 1 to 4.5, with solid components suspended, e) separation of the solution from the solid components, f) adding a precipitant to the separated solution, whereby a rare earth-containing precipitate precipitates, g) Separation of the rare earth-containing precipitate.

Description

The present invention relates to a method for recovering rare earths from FeNdB-containing magnets as rare earth fluorides or rare earth oxalates by means of solid chlorination.Rare earths, including rare earth or rare earth metals, include the chemical elements scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu). These are used in numerous key technologies such as, for example, in mobile telephones, electric cars, wind power turbines, motors of hybrid installations, LEDs or PC hard disks.More than 95% of the rare earths are currently supplying china for the world market. Large amounts of toxic residues are produced during the decomposition of the rare earths, which means a severe load on the environment and, in the case of an accident, immense damage. In order to contain this risk, but also in order to become the abundance of rare earth-containing scrap Mr, intensive research is being carried out on the recycling of these metals. In addition to old electrical appliances, mobile telephones, fluorescent lamps, etc., waste is also produced during the production of FeNdB permanent magnets.Previous methods for recovering rare earths are limited to the greatest possible extent to pyrometallurgical and wet chemical methods. Pyrometallurgical methods are described in the following documents.U.S. Pat. No. 6,960,240 B2 discloses a method in which a magnetic metal without rare earth metals is melted in a melting furnace and a rare earth-containing magnetic waste, such as slag, for example, and an alkali metal, alkaline earth metal or a rare earth metal halide are then added. An alloy is obtained from the melt, and the valuable elements can be recycled.JP2002060855 A discloses a method for recycling Nd-based rare earth metal magnetic scrap by means of a melt electrolysis bath.WO 0039514 A1 discloses a method for melting rare earth metals.Xu et al. (Xu, Y, Chumbley, L.S.; Laabs, F.C., J. Matter. Res. 2000, 15, 2296-2304) discloses liquid metal extraction of neodymium from NdFeB magnetic waste using liquid magnesium.Studies by Uda et al. (T. Uda, Mater. Trans., JIM 2002, 43(1), 55-62) propose a reaction of FeCl 2 with Nd to form NdCl 3 and Fe. The chlorination of neodymium takes place in an FeCl 2- melt at 800° C. for 12 h, whereby 78% of the rare earths can be chlorinated.In pyrometallurgical workup processes, the magnets are melted at temperatures up to 1550°C or extracted by hot salt melting. Disadvantages are the high energy input and the low selectivity, which often requires further hydrometallurgical process steps. The refining of the individual metal fractions takes place predominantly by vacuum distillation, which is very demanding from a process standpoint.Disadvantages of known hydrometallurgical leaching processes are on the one hand the high leaching agent-solids ratio and on the other hand the lack of recovery of the unused or excess digestion medium.Another method for obtaining rare earths is gas phase extraction, which is described by Adachi et al. (G. Adachi, K. Shiozaki, Y. Hirashima, K. Machida, J. Less-Common Met. 1991, 169, L1-L4) and Murase et al. (K. Murase, K. Machida, G. Adachi, J. Alloys Compd. 1995, 217, 218-225). A disadvantage of this method is that the chlorination is carried out at relatively high temperatures up to 1000° C. In addition, large amounts of chlorine gas, nitrogen and corresponding circulation systems are required, which place a burden on the economics of the process. AlCl 3 formed must be recovered, which must take place with greater effort and with complete exclusion of water because of the corrosive action.Magnetic recycling can also be carried out wet-chemically. Niinae et al. (Niinae et al. Proceedings of the International Mineral Processing Congress, 19th, San Francisco, 1995, Vol. 2, 227-231) describe the hydrometallurgical workup of NdFeB magnetic wastes and SmCo alloys. First, the starting materials are oxidized and subjected to an acid treatment. Subsequently, a liquid extraction takes place.WO / 1994 / 0266665 A1 discloses a process in which the grinding of the magnets is carried out with a NaOH solution in order to oxidize the rare earths to the oxides. The Fe is partly oxidized to Fe 2 O 3 in this case. The NaOH is not consumed because the oxidation reaction takes place between the H 2 O of the alkali and the metals. Unreacted iron is removed by a magnetic separator. The actual decomposition of the oxides takes place by means of acetic acid. The treatment of the rare earth fluorides with hydrofluoric acid is possible without the HF being liberated by the acetic acid having a pKs value of 4.75. The solution is filtered and concentrated, with a preliminary separation of the less soluble rare earth acetates taking place, which are subsequently reacted with hydrofluoric acid to form the corresponding rare earth fluorides. For the rare earths remaining in the solution, a post-precipitation takes place with oxalic acid. Iron acetate remains in the solution. Disadvantages of this process are the high number of process steps and the use of acetic acid, which is about 3 to 4 times as expensive as 35% hydrochloric acid. Also, the production of different iron species (Fe, Fe 2 O 3, Fe(CH 3 COO) 3) with different purity contents at different ends of the process is problematic for sale or disposal thereof.DE19617942C1 discloses a wet chemical digestion of phosphors containing Hg and PO 4- by means of hydrochloric acid and an oxidizing agent, wherein Hg and the main amount of the phosphor containing PO 4- are dissolved out. Halophosphates present and phosphors containing undissolved PO 4- such as LaPO 4: Ce,Tb, are dissolved out with an organic complexing acid. Residual Y 2 O 3: Eu, barium magnesium aluminate:Eu and cerium magnesium aluminate:Tb are washed with deionized water, dried, calcined at >1200 °C and blended with new phosphors in the lamp production.DE 1020060255945 A1 describes an extraction-based process without the use of NH 4 Cl. It discloses the work-up of halophosphates either by leaching with a cold acid (<30°C) or with acid between 60-90°C together with the more readily soluble phosphor components, or they are removed beforehand by means of gravity separation. In the second case, high Ca concentrations are reduced by addition of sulfate (gypsum precipitation). Subsequently, the readily soluble SE phosphors, in particular Y 2 O 3: Eu, are disintegrated and separated. The sparingly soluble SE phosphors (phosphates) are subsequently broken down into mineral acids of relatively high concentration or more (hydrochloric or sulfuric acid). The Tb,Gd-containing aluminates are dissolved in the last step, in which they are treated with hot, concentrated sulfuric acid or are broken down by means of basic soda / soot-pocket digestion and subsequent water / acid treatment. The rare earths in the respective filtrates of the various digests are precipitated with oxalic acid and / or ammonia and then calcined to the oxides.A disadvantage of the wet chemical workup is the high requirement for a soluble oxalate salt or oxalic acid for the removal of the rare earths, which cannot be recovered on account of the subsequent calcination step.A combination of wet chemical and pyrometallurgical workup is also already known. U.S. Pat. No. 5,728,355 A discloses the HP process (hydrogenation disproportionation) instead of a conventional grinding step. FeNdB magnets are used and the method is based on oxidation in air under heat in order to obtain rare earth oxides which are subsequently washed out acidic. Ammonium chloride is not used.For this purpose, the coarse-grained magnetic waste is reduced at 200 to 500° C. at a hydrogen partial pressure of 1 to 5 bar for 3 to 5 h to a grain size of 200-2000 μm, in which fine cracks are formed in the magnet as a result of the hydride formation and the associated volume increase of up to 25% by volume, which fine cracks lead to the reduction of the grain size as a result. Subsequently, degassing must be carried out in order to recover the hydrogen. The process can be repeated up to the desired grain size. The resulting powder is converted by calcination at 300 to 600° C. into the acid-soluble rare earth oxides and acid-sparingly soluble iron and nickel oxides, in order to achieve preliminary separation of these constituents. The oxides are broken down by adding a mineral acid to the slurried oxides in a pot-wise manner. The selective precipitation of the rare earths is carried out with oxalic acid, hydrofluoric acid or ammonium fluoride. In the case of fluoride precipitation, most of the excess acid must be neutralized. A further disadvantage of the process is the high consumption of acid and hydrogen, and the lack of the concept of utilization for the other constituents with the exception of neodymium. Apart from a plant of Hitachi which is under construction according to the press release of Hitachi of December 6, 2010, no methods for recycling used NdFeB magnets have been known up to now.The wet chemical treatment processes for recovering rare earths from FeNdB magnets are disadvantageous since these are associated with high costs. Because of the mostly strongly acidic leaching agent with pH values <1, a corresponding neutralization effort has to be applied. This also applies to the use of oxalic acid in the subsequent step. Added to this is the disposal of the waste liquor as waste water. In particular, the costs of the digestion acid, which is usually hydrochloric acid or sulfuric acid, and the lack of effective acid recovery make the treatment processes uneconomical. Oxalic acid is used in most processes for the precipitation of the rare earths, which is solely based on precipitating already in the strongly acidic pH range of the leaching agent. The use of oxalic acid is expensive, however, which is enhanced by the lack of recovery due to the irretrievable loss of oxalate from calcination of oxalates to rare earth oxides.Itoh et al. (M. Itoh, K. Miura, K.-I. Machida, J. Alloys Compd. 2009, 477, 484-487) discloses solid chlorination by means of ammonium chloride, wherein operation was carried out at 350° C. with a 2-fold stoichiometric batch of ammonium chloride, based on the molar amount of the rare earths present, and 90% of the rare earths present have gone over into water-soluble chlorides. At the same time, only 1% of the iron was chlorinated. This was due to the difference between the standard formation enthalpies of NdCl 3 and FeCl 2 and the reaction of the intermediate FeCl 2 with Nd to Fe and NdCl 3. The chlorination of the Nd is complete from 250° C. as soon as neodymium(III) oxide and iron powder are present as pure substances in the starting mixture and not as an alloy. Disadvantageously, there is a strong disassociation of the individual metals in the magnets, which prevents a selective and at the same time almost complete digestion of all components. For complete chlorination of the individual constituents, accordingly, as much iron as possible must be reacted.Neodymium as well as dysprosium are critical raw materials in the future. In order to avoid potential supply bottle necks, new recycling methods are currently being intensively studied in addition to the discovery of new deposits. However, up to now only about 1% of the rare earths have been recovered from FeNdB magnets. This also relates almost exclusively to production waste.CN 1028389888 B discloses precipitation of yttrium and europium as oxalates from phosphor wastes. Potassium pyrophosphate and relatively large amounts of ammonium chloride have to be added disadvantageously in this process. In addition, an additional calcination step is necessary, which necessitates the use of high temperatures.WO2013037577A1 discloses the recycling of rare-earth-containing oxysulfides as a constituent of scintillator ceramics for radiation detectors or as a constituent of similar lighting bodies and materials. Such production wastes are first cleaned of metallic impurities by an acid treatment. For this purpose, the oxysulfides are annealed at 1300-1400° C. and converted into the respective oxides and SO 2. Residual sulfur in sulfatic form can be removed by washing with water. The mixture of the rare earth oxides can then be used again in the production process. Low contents of certain rare earths are compensated by adding appropriate amounts of rare earth oxides.CN 1237539 A deals with the recovery of rare earth carbonates from the mineral bastnasite. Bastnasite describes a mineral class of carbonates and nitrates. The mass ratios in Embodiment 1 to 3 show that the stoichiometric amount of the NH 4 Cl used (calculated in equivalents) should be at least 10 times. In addition to the NH 4 Cl, CaCl 2 is also used.CN 101817547 A shows the recovery of rare earths from FeNdB magnets by addition of carbon powder and treatment at 450-500° C. under Cl 2- gas.DE 697 01 155 T2 discloses a method for recovering valuable materials from scrap alloy containing rare earth and nickel. It relates to such alloys which are substantially free of iron and is therefore unsuitable for the purpose of the invention.In JP 6135715 A, rare earth halides are prepared from rare earth oxides (by means of a >2 times amount of NH 4 Cl). For an application with FeNdB magnets, it does not offer any aid.The object of the present invention is to provide a cost-effective, energy-friendly process for recovering rare earths from rare earth-containing compositions.The object is achieved by a process for recovering rare earths from FeNdB-containing magnets, comprising the following process steps a) comminution of the FeNdB-containing magnets under a protective gas atmosphere to a particle size in the range from 100 to 200 μm to comminuted rare earth-containing compositions, b) addition of solid ammonium chloride in a 1.0 to 1.5 times stoichiometric amount, based on the amount of chlorable metals, to the comminuted FeNdB magnets, c) chlorination of the chlorable metals to metal chlorides in a rotary kiln or a sublimation plant at a temperature in the range from 250-350° C. in a period of from 1 to 5 h, d) adding an acidic solution to the metal chlorides to a pH in the range of 1 to 4.5 with solid components suspended, e) separating the solution from the solid components, f) adding a precipitant to the separated solution to precipitate a rare earth-containing precipitate, g) separating the rare earth-containing precipitate.The method according to the invention for recovering rare earths from FeNdB-containing magnets enables acid-free, dry digestion at substantially lower temperatures than corresponding pyrometallurgical recycling methods.Recovery is understood by those skilled in the art to involve dissolving one or more components from a composite of components in the form of the pure component and / or in the form of a compound containing the component.According to the invention, rare earth-containing compositions refer to compositions which contain at least one rare earth metal. The rare earth metals can be present here both as individual metals and / or as metal alloy.According to the invention, the rare earth-containing composition is an FeNdB-containing magnet. According to the invention, FeNdB-containing magnet denotes a magnet which, among other things, contains the constituents iron (Fe), neodymium (Nd) and boron (B), which are preferably present in the form of an alloy. It is known to the person skilled in the art that a magnet is a body which has a magnetically attracting and / or magnetically repulsive effect due to the natural phenomenon of magnetism. FeNdB-containing magnets are among the strongest permanent magnets. Permanent magnet refers according to the invention to a magnet that permanently retains its static magnetic field. An additional current flow, such as in electromagnets for generating the magnetic field, is not necessary.The FeNdB-containing magnet preferably contains, measured in terms of the total composition, a proportion of iron in the range from 50 to 80 wt %, a proportion of neodymium in the range from 15 to 45 wt %, a proportion of dysprosium in the range from 1 to 9 wt %, a proportion of boron in the range from 0.5 to 3 wt % and other constituents with a proportion of less than 1 wt %, particularly preferably a proportion of iron in the range from 60 to 70 wt %, a proportion of neodymium in the range from 25 to 35 wt %, a proportion of dysprosium in the range from 2 to 6 wt %, a proportion of boron in the range from 0.5 to 2 wt % and further constituents with a proportion of less than 0.5 wt %.The further constituents of the FeNdB-containing magnets are preferably selected from nickel, cobalt, praseodymium, terbium, samarium and / or gadolinium.In a preferred embodiment of the invention, FeNdB-containing magnets are processed with a composition of 65% by weight iron, 30% by weight neodymium, 4% by weight dysprosium and 1% by weight boron.Various types of comminution of metals, metal alloys and metal-containing workpieces are known to the person skilled in the art. Preferably, the comminution of the FeNdB-containing magnets is effected mechanically, particularly preferably with the aid of a ball mill and / or a planetary mill.Comminution is effected under a protective gas atmosphere. According to the invention, a protective gas atmosphere describes the use of an inert gas. The inert gas is preferably selected from nitrogen or argon.Advantageously, comminution under a protective gas atmosphere prevents the metals contained in the FeNdB-containing magnets from oxidizing to metal oxides which are difficult to dissolve. Advantageously, the metals remain in their original form.According to the invention, the FeNdB-containing magnets are comminuted to a grain size in the range from 100 to 200 μm.Advantageously, a larger surface is obtained in the case of the FeNdB-containing magnets.Preferably, the comminuted rare earth FeNdB-containing magnets are sieved. Advantageously, they can thereby be separated according to the preferred grain size. If the grain sizes are too large, they can be comminuted again.In a preferred embodiment of the invention, the FeNdB-containing magnets are already present as comminuted FeNdB-containing magnets.According to the invention, ammonium chloride is added to the comminuted FeNdB-containing magnets in a 1.0 to 1.5 mass ratio, based on the amount of chloratable metals.Advantageously, the required mass of ammonium chloride for the same stoichiometric batch is only about half as large as it would be for a decomposition of the rare earth-containing compositions by means of 35% hydrochloric acid known from the prior art. Thus, advantageously, the use of NH 4 Cl chemicals and costs are saved.According to the present invention, ammonium chloride is added in a stoichiometric amount based on the amount of chloratable metals to crushed FeNdB-containing magnets in a 1.0 to 1.5 times stoichiometric amount, more preferably in a 1.4 times stoichiometric amount.Preferably, the comminuted rare earth-containing compositions and the ammonium chloride are mixed in a reaction vessel. According to the invention, the reaction vessel is a rotary kiln or a sublimation apparatus.According to the invention, a rotary kiln denotes a kiln for heating a bulk material within a rotating pipe, wherein the heating is effected, for example, by a hot gas stream and / or via combustion or resistance heating. Advantageously, the use of a rotary kiln enables continuous operation.According to the invention, sublimation plant denotes an apparatus which makes possible a separation of substances by evaporating a solid within a heating zone and depositing the same solid on a cooling device such as, for example, a cooling finger.The skilled person is familiar with various methods for mixing substances. Preferably, the mixing is carried out manually with the aid of an auxiliary suitable for mixing. An aid suitable for mixing is known to the skilled person and is, for example, a spatula and / or a spoon. However, the mixing can also be carried out automatically using, for example, a magnetic stirrer.Advantageously, the comminuted FeNdB-containing magnets and the ammonium chloride can be mixed homogeneously with one another by comminution of the FeNdB-containing magnets in process step a.Homogeneously mixed means according to the invention the uniform mixing of a plurality of components to form a mixture, so that the components are uniformly distributed and no regions of one-sided concentration of one of the components are present in the mixture.According to the invention, chlorination of the chloratable metals means that the metals present in the comminuted rare earth-containing compositions are converted into the metal chlorides by oxidation of the metals with the aid of a suitable chlorination agent.The chlorination is carried out at a temperature in the range from 250 to 350°C.The solid chlorination is advantageously carried out without vacuum and at substantially lower temperatures than the conventional pyrometallurgical processes. Furthermore, advantageously, no liquid leaching agent is added during the solid chlorination, the recovery of which is generally complicated, complicated and expensive.Advantageously, at the temperatures specified for the chlorination, the ammonium chloride used is decomposed to gaseous ammonia (NH 3) and gaseous hydrogen chloride (hydrochloric acid, HCl).Preferably, the gaseous ammonia is removed from the reaction vessel.In a particular embodiment of the invention, the ammonia is passed into a scrubber filled with water and absorbed in the water.In another aspect of the invention, the ammonia will be removed by freezing the gas stream at temperatures in the range of -30 to -50°C.Advantageously, the ammonia removed represents a further usable, saleable by-product.The HCl formed preferably reacts with the chloratable metals to form the metal chlorides and hydrogen.The rare earths are preferably converted into the rare earth chlorides. Advantageously, more efficient chlorination is achieved by comminution of the FeNdB-containing magnets in process step a.According to the invention, the chlorination takes place in a period of time in the range from 1 to 5 h, particularly preferably in the range from 1 to 4 h, very particularly preferably in the range from 1 to 3 h.Preference is given to solid chlorination under a protective gas atmosphere. The protective gas is preferably passed through the reaction vessel in a continuous gas stream.Advantageously, iron is converted under these reaction conditions and with the exclusion of oxygen to the nonvolatile FeCl 2 and not to the volatile FeCl 3.The chlorinatable metals are preferably present in solid form (aggregate state) during their chlorination. For this reason, chlorination can also be referred to as solid chlorination. The metal chlorides are also advantageously obtained as solids and all further by-products formed in the solid chlorination can be removed directly via the gas stream. By-products are, for example, ammonia, excess unreacted HCl and hydrogen.Advantageously, excess unreacted HCl can also react again with the excess ammonia to form ammonium chloride by cooling below the decomposition temperature and is thus available again for solid chlorination. Advantageously, the ammonium chloride separates in the reaction vessel on cooler components. The deposition is preferably carried out on a cooling finger. According to the invention, a cooling finger is a component in a reaction vessel which is cooled with a coolant such as water and thus has a lower temperature than the temperature in the reaction vessel. Various designs of cooling fingers are known to the person skilled in the art.In a particular embodiment of the invention, the comminuted FeNdB-containing magnets are moved during chlorination. Preferably, the comminuted FeNdB-containing magnets are stirred.Solid particles discharged with the gas stream, such as, for example, ammonium chloride, metal chlorides and / or comminuted rare earth-containing composition, can be separated from gas stream with the aid of a centrifugal separator.In a particular embodiment of the invention, the comminuted FeNdB-containing magnets contain mercury. Advantageously, the mercury is evaporated and is deposited with the ammonium chloride as a mercury-ammonium chloride mixture on the cooling finger. Preferably, the mercury is removed from the mercury-ammonium chloride mixture by vacuum distillation or by dissolving the ammonium chloride-mercury mixture in water and subsequent phase separation. The skilled worker is familiar with methods for phase separation, for example by means of separating funnels.Mercury can also be discharged from the reaction vessel together with the gas stream. Advantageously, the mercury can be removed from the gas stream by cooling.In a particular embodiment of the invention, the comminuted FeNdB-containing magnets contain Y 2 O 3: Eu and Gd and / or Tb, wherein Gd is present in the form of the borate (Gd,Ce,Tb)MgB 5 O 10 and Tb is present in the form of the aluminate (Ce,Tb)MgAl 11 O 19. Advantageously, the borate (Gd,Ce,Tb)MgB 5 O 10 and the aluminate (Ce,Tb)MgAl 11 O 19 are not chlorinated, while the rare earths Y and Eu are chlorinated. This advantageously achieves a pre-separation of the rare earths Y and Eu of Gd and Tb. The Gd-containing borate and the Tb-containing aluminate remain unchanged as a solid in the crushed FeNdB-containing magnets.According to the invention, acidic solution denotes a solution whose pH is so low that, when it is added to the metal chlorides, a solution whose pH is in the range from 1 to 4.5 is formed.According to the invention, the metal chlorides are leached at a pH in the range from 1 to 4.5, particularly preferably at a pH in the range from 2 to 4. The metal chlorides as metal cation and chloride ion dissolve. An undissolved residue remains. The undissolved residue preferably consists of nonchlorinated, unreacted metals.It is preferred to suspend with stirring in a period in the range from 0.5 to 5 h, particularly preferably in the range from 1 to 3.5 h, particularly preferably in the range from 1.5 to 3 h.The removal of the solid constituents from the solution is preferably carried out by means of filtration, centrifugation and / or decantation.The solid constituents preferably consist of metals and / or boron which have not reacted to form metal chlorides. Boron accumulates in the solid constituents and reaches a correspondingly high concentration after several cycles. Once the correspondingly high concentration has been reached, the solid constituents are fed to a separate workup and / or disposed of.The solid constituents which contain the rare earths Gd and / or Tb are preferably treated with an acid at a pH of less than 1.The acid is preferably selected from mineral acids, particularly preferably nitric acid.Preferably, the acid is a concentrated nitric acid.The concentrated nitric acid is preferably used at a mass of 2 to 3 times the mass of Tb and / or Gd.The rare earths Tb and Gd preferably pass as metal cations into solution and solid constituents remain suspended in solution.The solid constituents are preferably separated from the solution. Preferably, the solid separated components are supplied to the disposal. The separated solution is preferably adjusted to a pH in the range from 1 to 4.5 and treated after process steps f and g.Methods for adjusting the pH are known to the skilled person.Preferably, an alkali solution is added to adjust the pH.The alkali is preferably selected from a basic inorganic salt, particularly preferably sodium hydroxide.A precipitant is preferably added to the separated solution, so that a rare earth-containing precipitate precipitates.In a preferred embodiment of the invention, the rare earths are precipitated from the separated solution as rare earth fluorides (also metal fluorides).Hydrofluoric acid is preferably added to the solution in order to precipitate the metal cations as metal fluorides.The hydrofluoric acid preferably has a concentration of 20 to 60% by volume, very particularly preferably of 30 to 50% by volume, very particularly preferably 25 to 45% by volume, even more preferably 40% by volume.In a preferred embodiment of the invention, sodium fluoride is added to the solution in order to precipitate the metal cations as metal fluorides. Advantageously, the solid sodium fluoride is more manageable and less toxic than hydrofluoric acid.Advantageously, in the case of metal fluoride precipitation, the rare earths are precipitated selectively as poorly soluble fluoride complexes, while the metals iron, nickel and cobalt do not form fluoride complexes, and thus do not remain precipitated and in solution. The metals iron, nickel and cobalt remain as metal cations in the solution. This selective precipitation is possible by the pH value fixedly adjusted in process step d. Advantageously, only the rare earths are precipitated as fluorides.In a particular embodiment of the invention, the rare earths are precipitated from the separated solution as rare earth oxalates (also metal oxalates). The rare earths are preferably precipitated as rare earth oxalates if the solution contains calcium ions. Calcium ions in the solution would precipitate as poorly soluble CaF 2 upon precipitation with hydrofluoric acid. Precipitation with oxalic acid advantageously prevents the contamination of the rare earth precipitates with CaF 2.Preferably, oxalic acid dihydrate is added to the separated solution to precipitate the metal cations as metal oxalates.Preferably, the oxalic acid dihydrate is added as a solid. The skilled person is aware that the amount of oxalic acid dihydrate used is limited by its solubility product. Only as much oxalic acid dihydrate as is soluble in the solution can be used to avoid contamination of the rare earth precipitate with oxalic acid dihydrate.In a preferred embodiment of the invention, an oxalic acid dihydrate solution is prepared by dissolving oxalic acid dihydrate in distilled water.Oxalic acid dihydrate is preferably used in a stoichiometric amount, based on the amount of the precipitated rare earths, in a 1.0 to 2.5 times stoichiometric amount, particularly preferably in a 1.0 to 2.0 times stoichiometric amount, very particularly preferably in a 1.0 to 1.2 times stoichiometric amount.Advantageously, the rare earths are precipitated selectively as poorly soluble oxalate complexes in the case of metal oxalate precipitation, while the metals iron, nickel, cobalt, aluminum, strontium and barium do not form oxalate complexes and are therefore not precipitated. The metals iron, nickel and cobalt remain as metal cations in the solution. This selective precipitation is possible by the pH value fixedly adjusted in process step d. Advantageously, only the rare earths are precipitated as oxalates.Advantageously, when precipitating the metal cations as metal fluorides or metal oxalates at a pH in the range from 1 to 4.5, the metal cations are prevented from being precipitated prematurely as their hydroxides.The rare earth-containing precipitates are preferably separated from the solution by filtration.The rare earth-containing precipitates are preferably washed with an aqueous solution.The aqueous solution preferably has a pH in the range from 2 to 5, more preferably in the range from 2 to 4, very preferably of 3.The chloratable metals are preferably selected from iron, scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium, nickel, magnesium, calcium, strontium, barium, aluminum and / or cobalt.Preferably, the acidic solution in method step d is an acid and / or a buffer solution.Preferably, the pH ≤4.5 is adjusted by addition of an acid.The skilled worker is familiar with acids for adjusting the pH. Preferably, the acid is selected from hydrochloric acid, nitric acid and / or sulfuric acid. It is well known to those skilled in the art that no acids can be used to adjust the pH which would lead to premature precipitation of the metals. Acids which would lead to premature precipitation of the metals are, for example, oxalic acid and hydrofluoric acid.A dilute acid is preferably used. Advantageously, the use of small amounts of dilute acid to establish a pH results in less acidic wastewaters.In a particular embodiment of the invention, the pH is adjusted with a buffer. Buffer refers according to the invention to a substance mixture whose pH does not change significantly even when an acid and / or an alkali is added. The skilled person is familiar with buffer substances for adjusting a pH. For example, a sodium acetate / acetic acid buffer may be used to adjust the pH to 3.9.Preferably, the solid constituents separated from the solution, unreacted metals and / or boron, are fed back to process step b.Preferably, the precipitant is hydrofluoric acid or oxalic acid dihydrate. In the case of precipitation with hydrofluoric acid, rare earth fluorides are precipitated, and in the case of precipitation with oxalic acid dihydrate, rare earth oxalates are precipitated.The rare earths are preferably precipitated as rare earth fluorides in the processing of NdFeB-containing magnets.The hydrofluoric acid is preferably added in a 1.0 to 2 times stoichiometric amount, very particularly in a 1.0 to 1.1 times stoichiometric amount, based on the amount of precipitated rare earths.Precipitation of the rare earth fluorides or rare earth oxalates is preferably effected in a period in the range from 0.5 to 20 h, very particularly preferably in a period in the range from 2 to 5 h.The rare earth oxalates are preferably calcined at a temperature in the range from 500 to 1200° C., particularly preferably in a range from 600 to 900° C., very particularly preferably in the range from 700 to 850° C.Calcination, according to the invention, describes heating a substance in order to dry or decompose it.The rare earth oxalates are preferably calcined over a period in the range from 0.5 to 5 h, very particularly preferably in the range from 1 to 4 h, even more preferably in the range from 2 to 3 h.After the removal of the rare earth fluorides, CaCl 2 is preferably added to a filtrate in order to precipitate excess unused fluoride ions as CaF 2.The invention is explained in more detail on the basis of the exemplary embodiments listed, without being restricted to these.Exemplary EmbodimentsReference Example 1 - Magnetic powderThe reference example was carried out with used FeNdB magnets and production wastes from magnet production. For standardization, these were ground with a ball mill under a nitrogen atmosphere to a particle size <100 μm. The composition of the magnetic powder was determined by hydrochloric acid digestion and liquid phase analysis by atomic emission spectroscopy (ICP OES), whereby contents of 65.6 wt % of Fe, 29.3 wt % of Nd and 4.7 wt % of Dy were determined. The remaining 0.4 wt% was boron as the insoluble residue.5.05 g of magnetic powder were mixed with 10.87 g (1.40-fold stoichiometric mixture) of NH 4 Cl and introduced into a sublimation plant. To exclude atmospheric oxygen, the apparatus was rendered inert for 10 min with 6 l / h of nitrogen. The reaction mixture was then maintained at 350°C for 240 minutes. The stream of nitrogen stream was 6 l / h and serves as a carrier gas for the ammonia formed. Unused ammonium chloride separated out as a white solid on the cooling finger during the reaction. Subsequently, a sodium acetate / acetic acid buffer was added to the solid residue in the reactor to adjust the pH to 3.9. The metal chlorides were leached for 2.5 hours. The solid constituents were separated off by applying vacuum by means of pressure filtration at 2 bar gauge pressure.In addition, to the filtrate containing FeCl 2, NdCl 3 and DyCl 3 was added 1.47 g of solid NaF to precipitate the rare earth fluorides. This corresponds to the stoichiometrically required amount of fluoride ions, based on the rare earths contained in the magnet. Since the rare earth digestion was not complete in the chlorination, the amount of NaF used corresponded to about 1.1 times the stoichiometric batch.The precipitated fluorides were again separated by vacuum filtration. In the filtrate, Nd or Dy could not be measured any longer (detection limit of ICP-OES for Nd, Dy: 0.01 mg / I). Prior to fluoride precipitation, 90.8% by weight of the Fe was in solution. After precipitation, it was 90.2 wt%. The deviation is thus within the range of measurement imprecision. The purity determination of the washed rare earth fluorides gave a purity of 99.65% based on the rare earth elements.Comparative Example 2 - Fluorescent Lamp Wastes10.11 g of NH 4 Cl was mixed with 5.01 g of a ground powdered phosphor from end-of-life fluorescent lamp waste. The waste fluorescent lamp contained 5.36% by weight of Y, 0.34% by weight of Eu, 0.21% by weight of Gd, 0.30% by weight of Tb and 18.59% by weight of SiO 2( glass component of the lamp) and had a grain size of less than 100 μm. The phosphor is also contaminated with small amounts of mercury. The temperature for solid chlorination was 300°C.In the filtrate of the leaching with 104.01 g of sodium acetate / acetic acid buffer solution (pH=3.88), 99.76% of Y, 96.03% of Eu, 1.11% of Gd and 0.67% of Tb were detected by means of ICP-OES. Overall, the yield based on the 4 mentioned rare earths was 93.16%. With the solid chlorination, it was accordingly possible to achieve a pre-separation between Y-Eu (in the filtrate) and Gd-Tb (in the solid).In the unused NH 4 Cl, which separated from the gas phase by reaction of NH 3(g) and HCl (g) at the cooling finger of the sublimation plant, it was possible to detect qualitatively mercury by means of ICP-MS.Comparative Example 3 - Phosphor wastesThe procedure of Example 2 was repeated except that 5.10 g of a dried, powdered phosphor from production waste of the fluorescent lamp production, which contained 15.73 wt % Y, 1.28 wt % Eu, 0.58 wt % Gd and 0.99 wt % Tb, was used instead of the end-of-life phosphor. The SiO 2- content was 8.08 wt % lower than the end-of-life phosphor wastes. The phosphor from the production wastes contains no mercury. The phosphor was present as an aqueous suspension and had to be dried at 120° C. for 6 h before use. In the filtrate of the leaching with the sodium acetate / acetic acid buffer, it was detected by means of ICP-OES 91.24% Y, 78.98% Eu, 3.47% Gd and 0.20% of Tb. Overall, the yield based on the 4 mentioned rare earths was 82.84%. It was also possible to achieve a pre-separation between Y-Eu (in the filtrate) and Gd-Tb (in the solid) by means of solid chlorination with the phosphors from the production wastes.

Claims

A process for recovering rare earths from FeNdB-containing magnets, comprising the following process steps: a) comminution of the FeNdB-containing magnets under a protective gas atmosphere to a particle size in the range from 100 to 200 μm to comminuted rare earth-containing compositions, b) addition of solid ammonium chloride in a 1.0 to 1.5 times stoichiometric amount, based on the amount of chloratable metals, to the comminuted FeNdB magnets, c) chlorination of the chloratable metals to metal chlorides in a rotary kiln or a sublimation plant at a temperature in the range from 250-350°C in a period of from 1 to 5h, d) adding an acidic solution to the metal chlorides to a pH in the range of 1 to 4.5 with solid components suspended, e) separating the solution from the solid components, f) adding a precipitant to the separated solution to precipitate a rare earth-containing precipitate, g) separating the rare earth-containing precipitate.Method according to claim 1, characterized in that the chloratable metals are selected from iron, scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium, nickel, magnesium, calcium, strontium, barium, aluminum and / or cobalt.Method according to claim 1 or 2, characterized in that the acidic solution is an acid and / or a buffer solution.Process according to one of Claims 1 to 3, characterized in that the solid constituents, unconverted metals and / or boron, separated from the solution are fed back to process step b.Method according to one of Claims 1 to 4, characterized in that the solid constituents, gadolinium and / or terbium in the form of their borates and / or aluminates, separated from the solution are treated with a mineral acid at a pH of less than 1, solid constituents being suspended and gadolinium and / or terbium as metal cation going into solution and the solution being separated from the suspended constituents.Process according to Claim 5, characterized in that the solution separated off is adjusted to a pH in the range from 1 to 4.5 and treated after process steps f and g.Method according to one of Claims 1 to 6, characterized in that the precipitant is hydrofluoric acid or oxalic acid dihydrate, with rare earth fluorides or rare earth oxalates precipitating out.Process according to Claim 7, characterized in that the hydrofluoric acid is added in a 1.0 to 2 times stoichiometric amount, based on the amount of precipitated rare earths.Process according to Claim 7, characterized in that the oxalic acid dihydrate is used in a 1.0 to 2.5 times stoichiometric amount based on the amount of the precipitateable rare earths.Method according to claim 7, characterised in that precipitation of the rare earth fluorides or rare earth oxalates takes place in a period in the range from 0.5 to 20 h.Process according to any of Claims 7 and 9 to 10, characterized in that the rare earth oxalates are calcined at a temperature in the range from 500 to 1200°C.The method according to claim 11, characterized in that the rare earth oxalates are calcined for a period in the range of 0.5 to 5 hours.Process according to one of Claims 7 to 8 and 10, characterized in that, after the rare-earth fluorides have been separated off, CaCl 2 is added to the filtrate in order to precipitate excess, unused fluoride ions as CaF 2.