阅读说明：本技术 基于电解的用于从Nd-Fe-B磁体废料中选择性回收稀土元素的方法 (Electrolysis-based method for selective recovery of rare earth elements from Nd-Fe-B magnet scrap ) 是由 许轩 萨索·斯特鲁姆 克里斯蒂娜·祖泽克·罗兹曼 于 2020-09-17 设计创作，主要内容包括：本发明涉及基于电解的用于从Nd–Fe–B磁体废料中选择性回收稀土元素的方法。本发明涉及一种用于从Nd-Fe-B磁体废料中回收稀土元素的方法。在该方法中,Nd-Fe-B磁体废料(2)在电化学反应器(1)中被阳极氧化,该电化学反应器(1)至少包括由所述Nd-Fe-B磁体废料(2)形成的阳极、阴极和含水液体电解质(5)。含水液体电解质(5)被选择成使得在阳极氧化期间,所述Nd-Fe-B磁体废料(2)在电解质(5)中浸出,并且Fe金属(7)沉积在阴极上。在所述阳极氧化步骤之后,向电解质(5)中添加Na-2SO-4(12),以使稀土元素沉淀。然后过滤电解质(5),以回收呈(RE,Na)(SO-4)-2复盐(13)形式的沉淀的稀土元素。(The invention relates to an electrolysis-based method for the selective recovery of rare earth elements from Nd-Fe-B magnet scrap. The invention relates to a method for recovering rare earth elements from Nd-Fe-B magnet waste. In the method, Nd-Fe-B magnet waste (2) is anodized in an electrochemical reactor (1), which electrochemical reactor (1) comprises at least an anode formed by the Nd-Fe-B magnet waste (2), a cathode and an aqueous liquid electrolyte (5). The aqueous liquid electrolyte (5) is selected such that during anodisation, the Nd-Fe-B magnet is spentThe material (2) is leached in the electrolyte (5) and Fe metal (7) is deposited on the cathode. Adding Na to the electrolyte (5) after the anodizing step 2 SO 4 (12) To precipitate the rare earth element. The electrolyte (5) is then filtered to recover (RE, Na) (SO) as 4 ) 2 Precipitated rare earth elements in the form of double salts (13).)

1. A method for recovering rare earth elements from Nd-Fe-B magnet scrap, comprising at least the steps of:

a. anodically oxidizing the Nd-Fe-B magnet waste (2) in an electrochemical reactor (1), the electrochemical reactor (1) comprising at least an anode formed by the Nd-Fe-B magnet waste (2), a cathode and an aqueous liquid electrolyte (5),

wherein the aqueous liquid electrolyte (5) is selected such that during the anodising, the Nd-Fe-B magnet waste (2) leaches out in the electrolyte (5) and Fe metal (7) deposits on the cathode;

b. adding Na to the electrolyte (5) after the anodizing step₂SO₄(12) To precipitate the rare earth element; and

c. filtering the electrolyte (5) to recover the precipitated rare earth element in the form of a rare earth-sodium sulfate double salt (13).

2. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,

characterized in that an aqueous sulphate-citrate solution is selected as the aqueous liquid electrolyte (5).

3. The method of claim 2, wherein the first and second light sources are selected from the group consisting of,

characterized in that an aqueous solution consisting at least of iron sulphate, one or several complexing agents and optionally a pH buffer is selected as the aqueous liquid electrolyte (5).

4. The method of claim 3, wherein the first and second light sources are selected from the group consisting of,

characterized in that said one or several complexing agents are selected to prevent Fe during said anodization step²⁺/Fe³⁺With Fe (OH)₂/Fe(OH)₃Is precipitated at the cathode and prevents addition of the Na to the electrolyte (5)₂SO₄(12) Then Fe²⁺And Fe³⁺Co-precipitation of (1).

5. The method of claim 4, wherein the first and second light sources are selected from the group consisting of,

characterized in that at least one of ammonium sulfate and sodium citrate is used as the one or several complexing agents.

6. Method according to one or several of claims 1 to 5,

characterized in that after the filtration step the filtered electrolyte (5) is recycled to the electrochemical reactor (1) for reuse in another anodization step.

7. Method according to one or several of claims 1 to 6,

characterized in that during the anodization step, the pH of the electrolyte (5) is maintained between 3.5 and 4.5 by continuously or repeatedly adding an acid (9) to the electrolyte (5).

8. Method according to one or several of claims 1 to 7,

characterized in that the Na is added₂SO₄(12) Thereafter, the electrolyte (5) is heated for one or several hours to support precipitation of the rare earth element.

9. Method according to one or several of claims 1 to 8,

characterized in that the total Fe ions (Fe) in the electrolyte (5) are brought to a value in the range of 71-75% by adjusting the current efficiency of Fe deposition on the cathode and the leaching efficiency of Nd-Fe-B magnet scrap (2) on the anode to be close to 100%²⁺And Fe³⁺) Is kept in equilibrium.

The invention belongs to the field of the following:

the invention relates to a method for recovering rare earth elements from Nd-Fe-B magnet waste.

Rare Earth Elements (REEs) have excellent electronic, optical, catalytic and magnetic properties, making them useful in a wide range of applications such as catalysts, phosphors and pigments, batteries, Permanent Magnets (PMs) and ceramics. In 2016, global REE consumption was estimated to be 119,650 metric tons in the form of Rare Earth Oxide (REO), with the catalyst being the largest fraction, followed by PM. By 2020, the annual growth rate of global REE demand is expected to increase by 5%. Among all REEs, neodymium (Nd) and dysprosium (Dy) are mainly used for neodymium-iron-boron (Nd-Fe-B) PM, which represent the major share of the REE market in terms of quantity and value. Typically, Nd-Fe-B PM contains between 60 wt.% and 70 wt.% iron (Fe), between 28 wt.% and 35 wt.% re (Pr, Nd, Tb and Dy), between 1 wt.% and 2 wt.% boron (B) and between 0 wt.% and 4 wt.% cobalt (Co). The benefit of adding Dy instead of Nd is that it improves coercivity (coercivity) and thus improves temperature resistance. Terbium (Tb) can function with similar functions, but is rarely used due to its high price. Praseodymium (Pr) can directly substitute for Nd to some extent without having a serious influence on magnetic properties. Co is typically added to improve corrosion resistance. The main applications of Nd-Fe-B PM are Electric Vehicles (EV), industrial motors, Wind Turbines (WT), Magnetic Resonance Imaging (MRI) and Hard Disk Drives (HDD). It is reported that Nd-Fe-B PM may have a high recovery potential due to the high number of applications and the expected high growth rate mainly driven by electric cars and wind turbines. There are two major sources of Nd-Fe-B PM to be recovered. One source is magnet scrap, including magnets that fail quality control during the manufacturing process and magnets from scrap products such as EV and WT. Another source is magnet swarf/slag, which is generated during magnet finishing processes such as shaping and polishing.

The prior art is as follows:

various methods for recovering Nd — Fe-B PM so far are currently under development, and these methods can be roughly classified into direct reuse, alloy reprocessing, and raw material recovery. Sintered Nd-Fe-B PM is a multiphase material: they have an REE-rich phase at the grain boundaries, which contains the majority of oxygen and represents about 10% -12% of the magnet, while the virtually oxygen-free matrix Nd₂Fe₁₄The B phase accounts for 85-87% of the whole magnet. Direct reuse of Nd-Fe-B PM, such as re-sintering and hydro-disproportionation and desorption and recombination (HDDR), is considered to be the best ecological and economical recycling route due to low energy input and no waste production. However, this process is only applicable to magnet scrap, and it leaves the REO phases formed in the grain boundaries during lifetime to remain in the grain boundaries without further separation of the REO phases, and therefore, it is often necessary to add additional REE material (e.g., 2-10 wt.% NdH)₂) To achieve a fully dense recovered magnet. Thus, with each recovery cycle, a large amount of non-ferromagnetic phase (REO and added NdH)₂) Resulting in poor magnetic properties. For the actual reprocessing of magnetic alloys from Nd-Fe-B PM, several processes are under investigation, such as remelting and electroslag refining. All these options allow feeding cleaned magnet scrap into an already established production chain of Nd-Fe-B magnets. However, these processes operate at 750-950 ℃, making them very energy consuming and the yield of the alloy has traditionally been a problem due to the loss of large amounts of material by evaporation at high temperatures. For raw material recovery, such as REE, e.g. Nd and Dy, various methods, such as glass slag extraction, gas phase extraction and hydrometallurgical methods have been developed in recent years. Hydrometallurgical processes may be considered the most promising approaches as they require relatively simple equipment to extract the REE at mild temperatures in continuous operation and are generally applicable to both magnet waste and magnet kerf/slag for high purity REE recovery. In a conventional hydrometallurgical process, Nd-Fe-B magnets are first treated with a mineral acid solution such as HCl or H₂SO₄Finish of solutionAnd (4) fully dissolving. A calcination pretreatment at 900 ℃ is usually applied to completely oxidize Fe to Fe₂O₃This would facilitate the Fe removal step after the complete acid-based leaching process of the magnet is completed. It should be noted that for completely dissolving 1,000kg of Nd-Fe-B magnet scrap, H is required₂SO₄The amount of (A) was 2,172kg, with 272kg for Nd and 1,900kg for Fe. Furthermore, the consumption of alkali for Fe removal and effluent neutralization was 1,600kg of NaOH or 1,100kg of CaO, respectively. These large amounts of acid, base and other precipitants cannot be recovered in the overall process and therefore generate large amounts of waste water (about 10 m)³1,000kg of Nd-Fe-B magnet). Nd-Fe-B magnets typically contain a mixture of Dy, Tb or Pr in addition to Nd, so that a mixture of REEs is obtained after recovery. The final product after the entire hydrometallurgical process is RE trifluoride (REF)₃) Or RE oxalate, which is obtained by adding HF or oxalic acid after the removal of Fe. However, in addition to being used for permanent magnets, REF₃And REO (obtained by calcining RE oxalate) were prepared for all RE-related applications.

In hydrometallurgical processes, acid leaching is the most important step, since it determines the extraction efficiency of valuable metals and their concentration in the leachate. To date, two different leaching routes are under investigation: a complete leaching route and a selective leaching route. For example, as a result of the formation of RE sulfate, a neodymium- (sodium or ammonium) sulfate double salt, H, then precipitates₂SO₄The solution was used to leach Nd-Fe-B magnet scrap. To treat 1kg of Nd-Fe-B magnet scrap, 10L of 2M H was required₂SO₄Solution (10% w/v solid-liquid (S: L) ratio) which completely dissolves magnet waste and keeps the pH low enough to prevent Fe (OH)₃Precipitation of (4). Then passing through NaOH, KOH or NH₄OH raises the pH to 1.5, at which a complex salt Nd, a neodymium- (sodium or ammonium) sulfate salt, is formed₂(SO₄)₃·M₂SO₄·6H₂O(M＝Na、K、NH₄). As long as the pH does not exceed 2.0, iron will remain in solution. The double sulfate salt can be converted into NdF by leaching in HF solution₃Or is orIs converted to an Nd oxalate by the addition of an aqueous oxalic acid solution. Other REEs such as Dy, Pr and Tb present in magnet scrap may also be recovered as RE sulfate double salts and converted to RE fluorides or RE oxalates. The RE oxalate can then be calcined to form RE₂O₃。REF₃And RE₂O₃Both can be reduced to the corresponding RE metals by calthermic reduction or molten salt electrolysis. After removal of the RE sulfate double salt, bubbling oxygen or addition of H₂O₂Solution to completely oxidize ferrous iron to ferric iron as yellow jarosite (jarosite) NaFe₃(SO₄)₂(OH)₆Precipitation, which is greater than Fe (OH)₃Easier to filter.

Alternatively, a calcination pretreatment at 900 ℃ may be applied to fully oxidize Fe to Fe prior to the acid leaching step₂O₃This facilitates the Fe removal step after the complete leaching process.

For complete leaching of Nd-Fe-B magnet scrap, the HCl acid is H₂SO₄An alternative to acids. For example, 3M-6M HCl solution has been applied to completely dissolve magnet scrap. However, iron as Fe²⁺Leaching into solution, Fe²⁺Are stable substances at pH up to 6 and cannot be selectively precipitated. Thus, a calcination pretreatment at 900 ℃ may be applied prior to the acid leaching step to fully oxidize Fe to Fe₂O₃Or by adding H in general₂O₂Using the solution as an oxidant to react with Fe²⁺Is oxidized into Fe^{3 +}. After oxidation, the separation of Fe from the other elements as precipitates (. alpha. -FeO (OH) or/and. beta. -FeO (OH)) can be achieved at pH 2-4. The solution obtained after Fe removal is reacted with oxalic acid to form a precipitate containing REE. The calcined precipitate in the form of rare earth oxide can then be returned to the original manufacturing process of Nd-Fe-B magnets or any other re-related application.

Selective leaching of REE would be practically desirable compared to complete leaching of Nd-Fe-B magnet scrap, as it would greatly reduce the consumption of inorganic acids and bases. Because Fe occupies the magnetMore than 60 wt.% of waste material. The rationale for selective leaching of REE relies on pH-dependent dissolution of calcined materials, which is called the potential-pH diagram. Theoretically Fe in the pH range of 1-7₂O₃And Nd³⁺Can be used to dissolve Nd³⁺Iron as Fe₂O₃Leaving behind in the residue. Koyama, K. et al, "Selective learning of random-earth elements from an Nd-Fe-B magnet"; kidorui,2009.54: pages 36-37 reported that after oxidizing the calcined magnet scrap at 900 ℃ for 6h, selective leaching of REE was achieved by using 0.02M HCl in an autoclave at 180 ℃ for 2 h. More than 99% REE recovery has been achieved with less than 5% Fe extraction. In contrast, although more than 99% of the REE is extracted, more than 50% of the Fe is leached without roasting. Selective leaching of the fired magnet at lower temperatures is also possible by increasing the initial acid concentration with extended etching duration.

US 5,362,459A describes that complete leaching of magnet sludge (Nd-Fe-B magnet sludge filled in an electroplating tank as an anode) and simultaneous Fe refining (cathodic deposition) can be performed at 50A dm^-2In the case of applied current densities, in the sulfamic acid bath. Obtaining a leachate containing Nd and Fe after electrolysis, followed by addition of hydrofluoric acid to treat Nd as NdF₃And precipitating. The remaining solution is returned to the electrolytic cell for further electrorefining. However, because of Fe³⁺And Fe²⁺Low solubility of (3), Fe³⁺And Fe²⁺Both can be made to act as FeF by adding HF₃And FeF₂Precipitate thus, NdF₃Can be used as NdF₃、FeF₃And FeF₂Without being selectively precipitated. There is no description in the patent of how to further purify NdF from fluoride mixtures₃。

Therefore, selective precipitation of Nd from leachate containing Nd and Fe still requires further investigation. Furthermore, the critical parameters of the leaching efficiency of the magnet sludge on the anode and of the galvanic efficiency of the iron deposition on the cathode are not described in this patent. Since these two parameters are used to evaluate REEAnd (4) selective leaching. If the Fe leached from the anode cannot be balanced by the Fe consumption (Fe deposition) on the cathode, the total dissolved Fe (including Fe) in the electrolyte³⁺And Fe²⁺) Will continue to increase with electrolysis time and will therefore further complicate selective Nd precipitation and purification. In addition, more acid will need to be added to maintain the pH of the electrolyte due to the hydrogen evolution reaction at the cathode.

Recently, Prakash Venkatesan et al, "Selective Extraction of ray-Earth Elements from NdFeB magnetics by a Room-Temperature electronics Prestream Step", ACS Sustainable Chemistry&Engineering,2018.6(7) pages 9375-9382 describe an electrochemical recovery process for selective extraction of REE from Nd-Fe-B magnet scrap at room temperature. The magnet waste is used as an anode to convert the elements present in the magnet waste into the corresponding hydroxides. More than 97% of the REE is leached into solution by HCl, leaving iron in the residue. The REE is then selectively precipitated as a rare earth oxalate using oxalic acid and regenerated HCl, resulting in a closed-loop process. Calcination of rare earth oxalates produces high purity (99.2%) rare earth oxides. The electrochemical process completely dissolves (anodizes) the Nd-Fe-B magnet scrap and precipitates more than 90% of the Fe in the form of tetrafineite (Akaganeite) (FeOOH). Is required for mixing Fe²⁺Conversion to Fe³⁺The power consumption of (2). Furthermore, the resulting leachate cannot be recovered as waste water.

In summary, hydrometallurgical processes based on strong mineral acid leaching are indispensable, since they can treat all types of Nd-Fe-B magnets with different compositions and oxidation states, including magnet scrap and magnet swarf. Electrochemical leaching (anodization) is an alternative to mineral acid leaching of magnet waste/magnet swarf. However, the selective recovery of REEs that leave Fe still requires further investigation to reduce chemical consumption and wastewater production.

Summary of The Invention

In view of the problems associated with hydrometallurgical recovery of Nd-Fe-B magnet scrap, it is an object of the present invention to provide a method for recovering REE from Nd-Fe-B magnet scrap, which method allows selective leaching and recovery of REE with high efficiency and in a more environmentally friendly and cost-effective manner.

This object is achieved by a method according to claim 1. Advantageous embodiments of the method are subject matter of the dependent claims or will become apparent from the detailed description and the examples set forth below in connection with the drawings.

It has been found according to the invention that by means of electrochemical anodization, Nd-Fe-B magnet scrap can be completely dissolved in a suitably selected aqueous solution, in particular a sulphate-citrate-aqueous solution, while metallic iron (Fe) is obtained on the cathode by electrodeposition. However, it has been found in accordance with the present invention that REE metals such as neodymium (Nd) cannot be electrodeposited from aqueous solutions. For electrolytic processes in electrochemical reactors, in particular in electrochemical cells, Nd-Fe-B magnet scrap-preferably attracted by external magnets-is used as anode and conductive materials such as Fe, Cu are used as cathode, both immersed in an aqueous electrolyte, so that Nd-Fe-B magnet scrap is anodically oxidized into solution and iron (Fe) is deposited on the cathode.

The pH in the electrolyte increases as operation proceeds due to hydrogen evolution reactions at the cathode which react OH^-Released into the electrolyte. Therefore, the pH should be periodically (or continuously) adjusted downward to maintain a stable electrolysis process. Preferably, the pH is maintained between 3.5 and 4.5 by continuously or repeatedly adding acid to the electrolyte during the electrolysis process.

According to the invention, rare earth-sodium double salts, e.g. neodymium-sodium-sulphate double salts (Nd, Na) (SO)₄)₂By adding Na to the electrolyte after the electrolysis process₂SO₄But selectively precipitates, which effectively separates the REE from the electrolyte. The REE is then recovered by filtering the electrolyte.

After this filtration, the electrolyte can also be reused for the next batch of electrolysis.

Using the proposed method, the REE can be selectively leached and recovered from Nd-Fe-B magnet scrap with high REE recovery efficiency of over 90% and lowest production cost. The process does not require any calcination pretreatment and can be carried out at room temperature. The electrochemical solution allows a minimum of chemical input and does not produce an output of chemical waste, in particular does not produce any waste water. The method also allows recovery of pure metallic iron (Fe) deposited on the cathode.

Brief description of the drawings:

the proposed method will be described below by way of example with reference to the accompanying drawings, which show:

FIG. 1 is a schematic diagram of an embodiment of the proposed method for selective recovery of REE from sintered Nd-Fe-B magnet scrap based on electrolytic technology;

FIG. 2A shows (RE, Na) (SO)₄)₂Back-scattered electron images of the recovered REEs in double salt form; and

figure 2B X-ray diffraction pattern of the recovered REE of figure 2A.

Embodiments of the invention:

based on the illustration in fig. 1, the process steps of an exemplary embodiment of the proposed method for recovering REE from Nd-Fe-B magnet scrap are described below:

1. the electrolytic process is achieved by using an electrochemical cell 1, which electrochemical cell 1 comprises Nd-Fe-B magnet scrap 2 held by an external magnet 3. The Nd-Fe-B magnet scrap 2 serves as an anode, and the conductive material 4 such as a Cu sheet serves as a cathode. With a mixture containing iron (II) sulfate heptahydrate (FeSO)₄·7H₂O), ammonium sulfate ((NH)₄)₂SO₄) Sodium citrate dihydrate (Na)₃C₆H₅O₇·2H₂O) and boric acid (H)₃BO₃) The electrolyte bath 5 of (a) fills the cell. The anode and cathode are connected to a power source 6 so that Nd-Fe-B magnet scrap is anodized into a solution while simultaneously depositing metallic iron (Fe)7 on the cathode with stirring by a stirrer 8.

2. During electrolysis, concentrated sulfuric acid 9 is added to maintain the pH of the electrolyte between 3.5 and 4.5.

3. After electrolysis, a pump 10 was used to transfer the electrolyte to a precipitation tank 11, followed by addition of sodium sulfate (Na)₂SO₄) Salt 12 and the solution is heated for 2 hours to precipitate the REE as a rare earth-sodium double salt 13.

4. The rare earth-sodium double salt is separated using filter 14 and the electrolyte bath is recycled back to step 1 so that it can be reused.

Examples

Referring to fig. 1, the recovery of REE and Fe metals from Nd-Fe-B magnet scrap according to the present invention basically includes three steps. The whole process can be repeated until the rare earth-sodium double salt is precipitated and recovered.

Step 1: electrolysis

The first step consists in carrying out the electrolytic process by using an electrochemical cell comprising a sintered Nd-Fe-B magnet (model material for Nd-Fe-B magnet scrap) acting as anode and a Cu sheet acting as cathode. With a catalyst containing 0.8mol of L^-1Iron (II) sulfate heptahydrate (FeSO)₄·7H₂O)、0.4mol L^-1Ammonium sulfate ((NH)₄)₂SO₄)、0.175mol L^-1Sodium citrate dihydrate (Na)₃C₆H₅O₇·2H₂O) and 0.4mol L^-1Boric acid (H)₃BO₃) The electrolyte bath of (a) fills the cell. Complex reagent of ammonium sulfate and sodium citrate (complexing reagent) is used to prevent Fe²⁺/Fe³⁺With Fe (OH)₂/Fe(OH)₃Is precipitated at the cathode surface, which favors Fe deposition. The anode and cathode were connected to a potentiostat and an applied current of 0.2A was maintained, i.e. 2.5A m on the anode^-2And 1.25A m on the cathode^-2So that the Nd-Fe-B magnet is anodized into solution while metallic Fe is simultaneously deposited in the cathode. Every 10min during electrolysis, concentrated sulfuric acid was added to maintain the pH of the electrolyte between 3.5-4.5. The chemical half-reaction equation for this step is as follows:

Nd₂Fe₁₄B-37e^-→2Nd³⁺+14Fe²⁺+B³⁺(1) anodic reaction

Neodymium (Nd) accumulates in the electrolyte bath. When Fe is dissolved at the anode, it is deposited on the cathode:

Fe²⁺+2e^-→ Fe (2) cathode reaction

Fe in electrolyte bath²⁺Concentration of (Fe)²⁺Net consumption) depends on its leaching rate at the anode and deposition rate at the cathode. Due to hydrogen evolution reaction and consumption of H⁺Occurs together with the deposition of Fe, so that H must be added₂SO₄The solution is used for keeping the pH value of the electrolyte within the range of 3.5-4.5.

2H⁺+2e^-→H₂↓ (3) cathode reaction

Step 1 takes place in an electrolytic cell. When 50 g/l of Nd-Fe-B magnet scrap was leached (dissolved), electrolysis was interrupted as one batch. The leaching efficiency was 99.9%. Since the transition metal (mainly Fe) accounts for 70.9% -75.7% of the Nd-Fe-B magnet scrap, about 70.9% -75.7% of the current contributes to the leaching of Fe from the anode. The current efficiency results for Fe deposition on the cathode were in the range 71% -75%. Thus, the Fe leaching from the anode is balanced by the Fe deposition on the cathode.

Thus, the net consumption of Fe is generally about zero, which enables a relatively stable composition of the electrolyte. The pure iron deposited on the cathode can be collected for use in manufacturing.

Step 2: selective precipitation of REE by addition of sodium sulfate

The second step involved adding 8.14 grams/liter of sodium sulfate (Na) to the electrolyte bath₂SO₄) To produce a rare earth-sodium sulfate double salt ((RE, Na) (SO) after (optionally) adjusting the pH of the solution/electrolyte to 3.5₄)₂). The reason for adjusting the pH of the electrolyte prior to REE precipitation is to maintain the pH of the solution within the range of 3.5 to 4.5, whereby the electrolyte can be reused in the next batch of electrolysis. The compound reagent of sodium citrate and ammonium sulfate in the embodiment prevents Fe²⁺And Fe³⁺And REE³⁺Plays a key role in co-precipitation.

This step takes place in a precipitation tank. (RE, Na) (SO)₄)₂The double salt is precipitated by: the solution was heated to 70 ℃ for 2 hours or naturally at room temperature for 3 days without stirringStir and allow it to settle.

And step 3: filtration

The third step involves the separation of (RE, Na) (SO)₄)₂Double salt and recycle the electrolyte bath back to step 1 so that it can be reused.

This step is carried out by means of a filter in which (RE, Na) (SO) is retained₄)₂Precipitate of double salt, as shown in FIG. 2A. X-ray diffraction (XRD) analysis (fig. 2B) shows that the diffraction peaks indicate well (Nd, Na) (SO)₄)₂·H₂O (PDF # 01-076-. The filtrate is recycled back to the electrolytic cell.

The process of the present invention for recovering REE (and optionally Fe metal) from Nd-Fe-B magnet scrap has a number of advantageous features. It achieves very high REE recovery efficiency: in the above example, 92.5% of the REE in the magnet was recovered at a high purity of 99.4%. It also brings minimal chemical and energy costs: the whole process achieves "selective" leaching of the REE, per kilogram of magnet waste and sodium sulfate (Na)₂SO₄) Consuming only 0.34kg of sulfuric acid (H)₂SO₄). High temperature firing pretreatment of the magnet is avoided. The calculated energy consumption per kg of Nd-Fe-B magnet was 1.36kWh kg^-1. It has also been demonstrated with high environmental standards: recyclable electrolyte, no hazardous waste, and minimal workplace hazards. Finally, it also produces pure iron metal, which can be used in manufacturing.

Although specific embodiments of the invention have been described with reference to the accompanying drawings, it is to be understood that such embodiments are by way of example only and merely illustrative of but a few of the many possible specific embodiments which can represent applications of the principles of the invention. Many variations and modifications are within the scope of the invention as defined in the claims.