WO2014033004A1

WO2014033004A1 - Method for reclaiming neodymium oxide from a starting mixture

Info

Publication number: WO2014033004A1
Application number: PCT/EP2013/067264
Authority: WO
Inventors: Marcus TEGEL; Lars RÖNTZSCH; Thomas WEISSGÄRBER; Bernd Kieback
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2012-08-30
Filing date: 2013-08-20
Publication date: 2014-03-06
Also published as: DE102012017418A1; DE102012017418B4

Abstract

The invention relates to a method for reclaiming Nd₂O₃ from starting mixtures/scrap containing NdFeB. The aim of the invention is to specify possibilities for effectively reclaiming neodymium oxide in order to recover a high proportion from unsorted waste/scrap at reduced cost. In the method according to the invention, a hydrometallurgical breakdown process is performed, in which acid is added, while the volumetric flow rate of hydrogen released during the hydrometallurgical breakdown process or the entire released hydrogen volume is simultaneously determined. The volumetric flow rate of hydrogen released or the entire hydrogen volume is used as a controlled variable for the amount of added acid and/or to determine the end of the hydrometallurgical breakdown process.

Description

Process for the recovery of neodymium oxide from a

starting mixture

The invention relates to a process for the recovery of Nd ₂ 0 ₃ from starting mixtures / scrap, in which NdFeB is included (the term NdFeB covers all neodymium-iron-boron magnetic materials, including those that additionally praseodymium, terbium to change the physical properties or dysprosium).

Neodymium is currently the rare earth metal with the highest demand. Above all due to its diverse field of application in powerful NdFeB permanent magnets for hard disks, loudspeakers and efficient motors and generators, there is a great need. Furthermore, neodymium oxide (Nd ₂ 0 ₃ ) is used as a doping agent for glasses, laser crystals, capacitors and as a polymerization catalyst for Polybutadienkautschuk- production. Due to the increasing importance of electric drives and generators (electromobility, wind power), with simultaneous The shortage of neodymium as a raw material on the world market becomes an efficient, environmentally friendly and cost-effective method of recycling neodymium from scrap to an urgent task in the field of rare earth recycling.

For the recovery of neodymium from unmixed NdFeB material, mainly pure powder metallurgical processes such as hydrogen embrittlement (HD or HDDR processes) have been used in the production of NdFeB magnets (see McGuiness et al., J. Mater. 1986, 21, 4107 and McGuiness et al., J. Mater, 1989, 24, 2541). However, these processes require very high initial purities of the starting materials to be recycled, since otherwise the yield is insufficient and thus produced magnets achieve only inferior properties. In particular, there is a problem with partially corroded magnetic material, which requires extensive prior removal of oxide and hydroxide layers for recycling by hydrogen embrittlement. On sintered NdFeB magnets, moreover, a protective layer of tin, nickel, aluminum or a spray or dip is usually applied. This can mean very high process engineering requirements for recycling by means of hydrogen embrittlement and, in most cases, prevents a recycling process for magnetic material of different origin and composition. A further problem is bound magnets in which the unsintered NdFeB material is transformed into a plastic such as e.g. An epoxy resin is embedded, which also prevents an efficient recycling process due to the limited possibilities for separation by hydrogen embrittlement.

In addition to powder metallurgy, various hydrometallurgical recycling processes are also known, which by principle offer better possibilities of substance separation by wet-chemical procedures. According to the

Revelation of WO 94/26665 AI is carried out the digestion of the NdFeB material to be recycled, for example by surface oxidation of NdFeB using NaOH to Nd ₂ 0 ₃ , which is then dissolved in acetic acid, selectively crystallized by concentration as Neodymacetat, fluorinated and elemen in the last step - tarem neodymium is reduced. Among other things, this process involves the only superficial oxidation of NdFeB to Nd ₂ O ₃ , the resulting Very slow digestion speed and the need for continuous mechanical comminution during the digestion process with simultaneous magnetic separation of elemental iron disadvantageous.

In US 5,129,945 Bl it is described that the digestion of process waste of the rare earth magnet production can be done with 2M H ₂ S0 ₄ . From the solution, the addition of NaOH or NH ₄ OH selectively the double salt

NaNd (S0 ₄ ) ₂ -H ₂ 0 or NH ₄ Nd (S0 ₄ ) ₂ -H ₂ 0 like. For the separation of magnetic scrap of different composition, this method points to the possibility that, due to the different solubility product of the double salts, ceric earths (La, Ce, Pr, Nd, Sm, Eu, Gd) and ytera earth (Tb, Dy, Ho, Er, Tm, Yb, Lu) can be separated from each other with little effort.

In US Pat. No. 5,129,945 B1, the double salt is fluorinated by the addition of hydrofluoric acid to NdF ₃ , which, after thorough drying, is then reduced calciothermally to elemental Nd. However, this approach is problematic due to the use and release of hydrogen fluoride (HF). It is therefore desirable to develop a simpler and more environmentally friendly processing of the precipitation products to a required raw material. In US 5,129,945 Bl is also the reaction of the double salt with a

Oxalic acid to Neodytnoxalat described, which can be decomposed by thermal treatment at 900 ° C to Nd ₂ 0 ₃ , C0 ₂ and H ₂ 0. Another problematic salt-metathesis step in connection with the loss of the oxalic acid used is problematic.

One of the main obstacles to the effective recycling of neodymium from waste magnetic materials by hydrometallurgical processes, however, is a lack of or insufficient control of the digestion of magnetically rich materials of varying origin with varying texture and composition. Thus, the time required for digestion, depending on the composition and nature of the material to be recycled, is very long (eg, by passivation and agglomeration, but also not otherwise separable inert foreign materials) and both the digestion itself and the subsequent precipitation require unnecessary HO use of chemicals.

Furthermore, it is problematic that NdFeB-containing scrap / waste from different sources can contain very different impurities that do not occur in unmixed process waste during magnet production - including, for example, other rare earth magnets such as SmCo. According to the prior art, in this case, for example, only the precipitation of a mixed double salt such as NaNdi- _x Sm _x (S0 ₄ ) 2-H ₂ 0 is carried out with subsequent solvent extraction or ion exchange for the separation of the rare earths. However, this procedure is very complicated and prevents a simple recycling process. Other separation paths during digestion, such as by hydrogen flotation process (US 5,238,489 Bl), are not or hardly realizable in actually occurring waste materials due to other impurities (eg by plastics).

None of the known recycling processes can efficiently recycle mixed, non-grade magnetic materials that are subject to variations in composition and texture.

It is therefore an object of the invention to provide opportunities for effective recovery of neodymium oxide in order to recover from unsorted waste / scrap a high proportion with reduced effort.

According to the invention, this object is achieved by a method having the features of the claim. Advantageous embodiments and further developments of the invention can be achieved with features described in the subordinate claims.

The present invention solves the recycling problem of non-grade NdFeB magnetic materials of variable composition and nature by a combination of various process steps, which are described in detail below.

First of all, pre-comminution of the material mixture to be recycled, in which NdFeB is contained, can take place. In the process according to the invention, a starting mixture in which NdFeB is present is subjected to a hydrometallurgical digestion with addition of an acid, such as in particular sulfuric acid. At the same time, the determination of the released during the hydrometallurgical digestion of hydrogen volume flow or of the total released

Hydrogen volume carried out, wherein the released hydrogen volume flow or the total volume of hydrogen is used as a controlled variable for the amount of acid to be added and / or used to determine the course and in particular the termination of the hydrometallurgical digestion ses.

Thus, the increase of the released hydrogen volume flow can be determined and, if this increase has dropped to a predefinable threshold, can be reacted accordingly.

If the hydrogen volume flow falls below a predeterminable threshold value, the hydrometallurgical digestion can be ended, since at least the major part of a chemical reaction in which Nd ^{3+ can be} converted into a chemical compound in which neodymium is present has been reacted.

It is advantageously possible to control the amount of acid to be added by means of the increase in the volume flow of the released hydrogen and / or its integral.

The solution containing neodymium containing a obtained in the hydrometallurgical digestion neodymium-containing solution can be subsequently converted into neodymium oxide, and possibilities will be discussed below.

For enrichment of the neodymium concentration of a neodymium-containing fraction, prior to carrying out the hydrometallurgical digestion, a classification of parts of the starting mixture can be carried out. It can be classified according to different size criteria. These may in particular be average fragment or particle sizes and / or form factors. Almost isotropic parts of parts can be classified separately those which have a greater extent in one axis than is the case in at least one other axis.

Such a classification allows, for example, the separation of smaller, relatively isotropic NdFeB fragments of larger, often anisotropic parts such as back plates or chipboard, which may occur in the starting mixture. It can be realized, for example, by sieving.

In the invention, at least one magnetic separation can be performed. All ferro- and ferrimagnetic materials such as NdFeB are separated from a starting mixture / scrap.

Alternatively, a separation of all magnetized (remanent) materials in the scrap can take place. For separation can be used magnetic separation technique, which is preferably not selective for all ferromagnetic materials, but only for magnetized (remanent) ferro- and

ferrimagnetic materials, in particular NdFeB or SmCo magnets. Subsequent to this magnetic separation or, if appropriate, subsequent to a further magnetic separation, fine comminution and homogenization of the enriched and demagnetized and NdFeB-containing part of the starting mixture / scrap can be carried out with the subsequent hydrometallurgical digestion.

This reverse magnetic separation can be realized, for example, by a technically comparatively simple adaptation of conventional magnetic separators by substitution of the separator magnets or coils by soft-magnetic ferromagnetic separators (eg of iron). This pre-sorting of the metal-containing scrap also allows the separation of all unbound super-para-, para- and diamagnetic foreign matter from the magnets, such as plastics. With reverse magnetic separation, remanent ferromagnetic materials can also be separated from non-remanent ferromagnetic materials from the starting mixture. The advantage of this process step is therefore a strong accumulation of NdFeB, which considerably reduces the required amounts of chemicals for the subsequent hydrometallurgical digestion and considerably reduces its susceptibility to possibly interfering foreign materials. ed. In addition, the time required for digestion is greatly reduced because less foreign matter and foreign matter must be digested with.

After heating the separated magnetized material over the

Curie temperature of NdFeB (583 K) can optionally be followed by another magnetic separation analogous to the first process step to separate materials with higher Curie temperature (eg SmCo, AlNiCo) from demagnetized NdFeB and thus the NdFeB content in the starting material mixture (scrap) on to enrich. Any buildup of NdFeB on magnetized materials will not interfere with this process, since such materials are usually minority constituents of the starting material mixture / scrap. This physical separation of, in particular, SmCo, even before the hydrometallurgical digestion, is technically much easier to implement than a complex chemical separation of the various rare earths by means of solvent extraction or ion exchange after the digestion process. If no other rare earth magnets are present in the starting mixture / scrap apart from NdFeB, the demagnetization can also take place by means of an electromagnetic alternating field instead of by heating above the Curie temperature. Degaussing should, however, be performed for subsequent mechanical comminution and hydrometallurgical digestion to prevent coalescence of the milled particles.

In the next step, the fine comminution and homogenization of the enriched and demagnetized scrap can take place. In many experiments, the particle size distribution of the milled scrap was investigated for optimized digestion. Average particle sizes in the range from 100 μm to 250 μm have proved favorable for the hydrometallurgical digestion with regard to a short grinding time, a high digestion rate and an optimum yield.

A corresponding fine comminution is possible instead of mechanical processes and by embrittlement of enriched by magnetic separation NdFeB-containing scrap with hydrogen (in this case, eliminates the need for a prior demagnetization of still remanentem material). In a chemical reaction of NdFeB with Hydrogen are formed a neodymium-containing metal hydride. Hydrogen released during hydrometallurgical venting can be used both for embrittlement and for the formation of neodymium-containing metal hydride.

However, since the brittleness or hydrogenability of the NdFeB in the starting mixture / scrap is very different from the brittleness of existing foreign materials (e.g., Ni), the refining

Hydrogen embrittlement parameters for optimized perfusion can be individually adapted to the composition of the starting mixture / scrap. In the present invention, the grinding parameters (eg rotational speed, throughput, grinding time) or hydrogen spraying parameters (for example hydrogen pressure, hydrogen mass flow, temperature, reaction time) can be optimized for the respective current scrap composition for the first time in the ongoing process. In this case, the control unit used may be the released hydrogen volume flow or the hydrogen volume flow (V _H2 ) integrated over a certain period of time from the hydrometallurgical pulping process described below. Particularly advantageous is a possible real-time reaction control of the acidic hydrometallurgical digestion. Depending on the chemical composition of the starting mixture or finely comminuted scrap (various proportions of NdFeB and optionally Fe, Ni, NdH ₃ , plastics, etc.) appropriate amounts of a strong acid are required for an optimized Aüfschluss, and depending on Ausgangsgemisch- / scrap quality (Particle sizes, agglomeration behavior, etc.) but also environmental conditions (eg acid temperature) requires the hydrometallurgical Aüfschluss different lengths of time. Although both the initial mixture / scrap composition and nature can vary greatly, a measure has been found that surprisingly permits reliable and reproducible control of many important process parameters. By continuously measuring the hydrogen volume flow (d \ _H2 / di), the hydrogen released during the hydrometallurgical digestion, and comparing this variable with its time course, the respective amount and concentration of the acid required for the extraction can be precisely controlled. In this way, not only the amount of acid used can be greatly reduced, but The time required for the hydrometallurgical digestion can be significantly reduced, since the reaction end of the digestion reaction can be determined. The performance of this process step is shown, for example, in direct comparison with the digestion process described in US 5,129,945 B1. There, the complete digestion according to the embodiments requires 24 hours, whereas in the present invention the total duration of mechanical pretreatment and digestion takes only a few minutes. The chemical background for the reaction control, the different reaction kinetics for the oxidation of the various components occurring in the starting mixture / scrap constituents by acid

Hydrogen release, for example:

Nd ₂ Fei ₄ B + 34 H ⁺ > 2 Nd ³⁺ + 14 Fe ²⁺ + B + 17 H ₂ (very fast)

Ni + 2 H ⁺ ► Ni ²⁺ + H ₂ (very slow) In the case of hydrometallurgical digestion, H ₂ S0 ₄ in particular can be added as the acid.

After the end of the reaction of the hydrometallurgical digestion, in the next step analogous to the prior art, undissolved constituents can be separated off from the reaction mixture and a double salt, for example the

Composition NaNd (S0) ₂ -H ₂ 0, by addition of a neutral sodium-containing salt solution and / or a sodium-containing salt, in particular saturated Na ₂ S0 ₄ solution, can be precipitated in excess and / or by addition of NaOH. The so-separated double salt can be annealed in a heat treatment until Nd ₂ 0 ₃ has been obtained.

This double salt can also be converted to elemental neodymium by halogenation with HF or HCl followed by metallothermal, electrolytic or other reduction of the neodymium halide.

In general terms insbesonde- re saturated ₂ S0 ₄ solution {A = Na, K, [NH _4] can be said that contains by addition of a salt solution with alkali metal cations and / or ammonium ions or a salt, which alkali metal cations and / or ammonium ions, ) in excess and / or by

Addition of AOH (A = Na, K, [NH ₄ ]), the formed sparingly soluble Neodymium-containing double salt y4Nd (S0 ₄ ) ₂ -H ₂ O [A = Na, K, [NH ₄ ]) can be precipitated and separated after hydrometallurgical digestion.

In this case, a neodymium-containing double salt> 4Nd (S0) ₂ -H ₂ 0 (A = Na, K, [NH ₄ ]) can also be dissolved in a mineral acid, preferably nitric acid or hydrochloric acid in the concentration range 0.1-8 mol / L, and a salt metathesis by precipitating a neodymium-containing oxalate Nd ₂ (C ₂ O ₄ ) ₃ ^■ n H ₂ O (0 <n <18) by means of an oxalic acid solution and / or solid oxalic acid and / or a water-soluble oxalate.

Formed neodymium-containing double salt \ Nd (S0 ₄ ) ₂ -H ₂ O (A = Na, K, [NH ₄ ]) and / or a formed neodymium-containing oxalate Nd ₂ (C ₂ O ₄ ) ₃ · n H ₂ 0 (0 < n <18) can be subjected to a heat treatment, preferably in the temperature range between 700 ° C and 1400 ° C, at which a neodymium-containing oxide, in particular Nd ₂ 0 ₃ , is obtained.

As has been shown in many experiments, in contrast to the prior art in the present invention, a problematic measurement and targeted adjustment of the pH for the precipitation reaction of the double salt is no longer necessary because the acid concentration by the previous in s / tu optimization the hydrometallurgical digestion is already in the optimum range with regard to product purity and yield. Furthermore, the required amount of precipitating reagents (and acid concentration) can be calculated from the total volume of hydrogen measured at digestion, resulting in a further reduction in the amount of chemicals needed for the process. The quantitative precipitation can also be achieved at very low pH values.

Following the precipitation of the double salt this is separated. It can be washed and recrystallized for further purification depending on the required product purity.

In the last step, the prior art double salt can either be reduced to elemental neodymium by the multi-step work-ups described above or annealed to neodymium oxide after saline metathesis, but this implies the problems already described. On the other hand, the direct thermal decomposition of NaNd (S0 ₄ ) 2 * H ₂ O to Nd ₂ 0 ₃ and Na ₂ 0, S0 ₃ and H ₂ 0 is much easier to implement, although the additional salt metathesis step with oxalic acid is also without loss of quality can do without the product. The greatly differing melting or sublimation temperatures of Nd ₂ O ₃ (melting point 3043 K), Na ₂ O (sublimation temperature 1548 K) and S0 ₃ (decomposition a-S0 ₃ : 323 K) not only allow separation of the decomposition by-products of Nd ₂ 0 ₃ during the thermal decomposition, but also through the targeted resublimation of Na ₂ 0 as well as by introducing S0 ₃ in water can be recovered for the process required NaOH and H ₂ S0 ₄ , which makes the present recycling process even more efficient and environmentally friendly ,

Through a combination of magnetic separation and final thermal magnetization stages in conjunction with real-time control of the fine comminution (grinding or hydrogen embrittlement) of the enriched feedstock / scrap and the hydrometallurgical digestion process and precipitation process (reaction times, chemical levels, concentrations), with in situ measurement The hydrogen volume flow of the hydrogen generated in the digestion can be used particularly advantageously, a significant improvement over the prior art can be achieved. The effort can be reduced and the yield and product purity can be significantly increased.

The invention will be explained in more detail by way of example in the following. Individual features can be combined independently of each other. Characteristics are not necessarily bound to the respective example.

Showing:

Figure 1: An example of a lifting magnetic separation for the separation of SmCo magnets from a mixture of different magnetic starting materials; FIG. 2: Left-measured integrated hydrogen volume flow for the hydrometallurgical digestion of the enriched and demagnetized starting mixture / scrap after different grinding times. Right - the measured integrated hydrogen volume flow taking into account the grinding time to optimize the overall process time and

FIG. 3: Left-the measured integrated hydrogen volume flow for the digestion of the enriched and demagnetized starting mixture / scrap for different amounts of acid. Right - the time course of the hydrogen volume flow during the hydrometallurgical digestion with the marking of possible control-technical threshold values for a further acid addition and for the determination of the end of the reaction.

Example 1 (Magnetic Separation): To separate Sm from a starting mixture of various rare earth magnetic materials, a pre-crushed mixture consisting of 14.8 g of uncoated SmCo sintered magnets and 144.8 g of nickel-plated, sintered NdFeB magnets under nitrogen atmosphere was grown to 375 ° C heated (heating rate 3 K / min, holding time 60 min). The still magnetized SmCo magnetic fragments were separated by a reverse magnetization separation using a 100x100x2.5 mm ³ iron sheet behind a lifting belt. There were obtained 86.6 g of unmixed NdFeB magnets and 73.0 g of SmCo magnets with NdFeB adhesions. 2nd example (recycling):

200 g of nickel-coated, sintered NdFeB magnets from disk servos were demagnetized by heating to 375 ° C. (heating rate 3 K / min, holding time 60 min) under a nitrogen atmosphere. Twenty-five grams of the demagnetized magnets were then ground in a disk vibratory mill under air for 60 seconds. 1000 mg of the milled magnets were then digested by adding 6 ml of 2 MH ₂ S0 ₄ at 24 ° C. while measuring the volume of hydrogen released. In each case when flattening the reaction (reduction of the released hydrogen volume flow to less than 20 ml / min) as long as 1 ml 2 MH ₂ S0 _{4 was} added until also was released after renewed acid addition less than 1 ml / minute of hydrogen

= 440 mL, Vge _S [H ₂ S0 ₄ ] = 8 mL_). The total time for milling and digestion was 5 min. The reaction mixture was filtered, and by addition of saturated Na ₂ S0 ₄ solution in excess (10 mL) at pH = 0.5, the sparingly soluble double salt NaNd (S0 ₄ ) ₂ -H ₂ 0 within

Crystallized quantitatively for 20 min. The double salt was filtered off, washed with water, predried at 80 ° C and then calcined at 1350 ° C for 10 hours in flowing air. 293 mg X-ray homogeneous Nd ₂ O _{3 were} obtained (yield 99% including 5 mass% nickel in the milled starting mixture). Ferrous impurities were less than 350 ppm.

Claims

claims

A process for recovering neodymium oxide from a starting mixture containing NdFeB, in which

a magnetic separation and a fine comminution are carried out and then a hydrometallurgical digestion with the addition of acid, while determining the released during the hydrometallurgical pulping hydrogen volume flow or the total volume of hydrogen released is carried out, wherein the released hydrogen volume flow or the total volume of hydrogen as a controlled variable for the amount to be added Acid used and / or used to determine the completion of the hydrometallurgical digestion.

A method according to claim 1, characterized in that the in-solution neodymium of a solution obtained by the hydrometallurgical digestion is converted into neodymium oxide.

A method according to claim 1 or 2, characterized in that the amount of acid to be added is controlled by means of the increase in the volume flow of the released hydrogen and / or its integral.

Method according to one of the preceding claims, characterized in that

in a magnetic separation demagnetized NdFeB is separated from a starting mixture / scrap and / or a magnetic separation only for magnetized (remanent) ferromagnetic and ferrimagnetic materials, in particular NdFeB or SmCo magnets are separated.

Method according to one of the preceding claims, characterized in that before demagnetization a demagnetization of the NdFeB with a warming up to above it

Curie temperature and / or the use of electromagnetic alternating fields is performed.

Method according to one of the preceding claims, characterized in that in a magnetic separation all unbound super-para, para- and diamagnetic foreign substances are separated from the magnets.

Method according to one of the preceding claims, characterized in that in a magnetic separation materials with higher Curie temperature of demagnetized NdFeB are separated.

Method according to one of the preceding claims, characterized in that a fine comminution and / or demagnetization of NdFeB by an embrittlement with hydrogen is carried out and / or that in a chemical reaction of NdFeB with hydrogen, a neodymium-containing metal hydride is formed.

Method according to one of the preceding claims, characterized in that the liberated during hydrometallurgical pulping hydrogen for embrittlement of NdFeB and / or for the formation of a neodymium-containing metal hydride is used.

Method according to one of the preceding claims, characterized in that a fine comminution to a medium

Particle size in the range of 100 μιη to 250 μιη is performed.

Method according to one of the preceding claims, characterized in that an enrichment of the Nd concentration of a Nd-containing fraction before the hydrometallurgical digestion by a classification according to different size criteria, in particular for average fragment sizes and / or shape factors, is performed.

12. The method according to any one of the preceding claims, characterized in that by addition of a neutral sodium-containing salt solution and / or a sodium-containing salt, in particular saturated Na ₂ S0 ₄ solution, in excess and / or by addition of NaOH, the formed sparingly soluble double salt NaNd (S0 ₄ ) ₂ -H ₂ 0 precipitated after the hydrometallurgical digestion, separated and this double salt is annealed in a heat treatment until Nd ₂ 0 ₃ has been obtained.

13. The method according to any one of the preceding claims, characterized in that by addition of a neutral sodium-containing salt solution and / or a sodium-containing salt, in particular a saturated Na ₂ S0 ₄ solution in excess and / or by the addition of NaOH the formed sparingly soluble double salt NAND ( S0 ₄ ) ₂ -H ₂ 0 is precipitated after the hydrometallurgical digestion, separated and this double salt is converted to elemental neodymium by halogenation with HF or HCl and subsequent metallothermal, electrolytic or other reduction of the neodymium halide.

14. The method according to any one of the preceding claims, characterized in that by addition of a salt solution with alkali metal cations and / or ammonium ions or a salt containing alkali metal cations and / or ammonium ions, in particular saturated> 4 ₂ S0 ₄ solution [A = Na, K , [NH]), in excess and / or by adding AOH (A = Na, K, [NH ₄ ]), the formed sparingly soluble neodymium-containing double salt / 4Nd (S0 ₄ ) ₂ -H ₂ 0 (A = Na, K, [NH ₄ ]) is precipitated and separated after the hydrometallurgical digestion.

15. The method according to any one of the preceding claims, characterized in that a neodymium-containing double salt ANd (S0 ₄ ) ₂ -H ₂ 0 [A = Na, K, [NH]) in a mineral acid, preferably nitric acid or hydrochloric acid in the concentration range 0.1 - dissolved 8 mol / L and a salt metathesis by precipitating a neodymium oxalate Nd ₂ (C ₂ 0) ₃ · n H ₂ 0 (0 <n <18) by means of an oxalic acid solution and / or solid oxalic acid and / or a water-soluble oxalate and / or one

Oxalate solution is performed.

16. The method according to any one of the preceding claims, characterized in that formed neodymium-containing double salt

4Nd (SO ₄ ) ₂ -H ₂ O (A = Na, K, [NH ₄ ]) and / or a formed one

neodymium-containing oxalate Nd ₂ (C ₂ O ₄ ) ₃ · n H ₂ O (0 <n <18) is subjected to a heat treatment, preferably in the temperature range between 700 ° C and 1400 ° C, until a neodymium-containing oxide, in particular Nd ₂ 0 _{3 /} is received.

17. The method according to any one of the preceding claims, characterized in that by deliberate Resublimation of Na ₂ 0 and by introducing S0 ₃ in water for the hydrometallurgical digestion NaOH and H ₂ S0 _{4 are} recovered.

18. The method according to any one of the preceding claims, characterized in that the fine comminution, which is carried out prior to the hydrometallurgical digestion, is optimized on the basis of the released during hydrometallurgical pulping hydrogen volume flow in situ.

19. The method according to any one of the preceding claims, characterized in that still magnetized SmCo magnetic fragments are separated by a reverse Aushebemagnetscheid.

20. The method according to any one of the preceding claims, characterized in that remanent ferromagnetic materials are separated by a reverse magnetic separation of non-retentive ferromagnetic material.