KR100578712B1 - Recovery of Neodymium from NdFeB Oxidation-Roasted Scrap by Acetic Acid Leaching - Google Patents

Abstract

The present invention provides a method for selectively separating neodymium from NdFeB permanent magnet waste scrap.

In the present invention, the NdFeB permanent magnet waste scrap powder is subjected to high temperature oxidation, and then, weak acid leaching is carried out using acetic acid to selectively leach neodymium, to recover neodymium acetate by fractional crystallization from acetic acid leaching solution, and remain in the concentrated filtrate. The remaining neodymium is to provide a selective separation method of neodymium to recover the total amount by reacting with oxalic acid.

NdFeB magnet scrap, roasted oxide, acetic acid leaching, fractional crystallization, neodymium acetate

Description

Recovery of Neodymium from NdFeB Oxidation-Roasted Scrap by Acetic Acid Leaching}

Figure 1. Complete dissolution time of neodymium (99.9%, 60g) for acetic acid (500ml)

Figure 2. Recovery of neodymium according to the concentration of the roasting oxide scrap in acetic acid (500ml)

3. XRD diffraction analysis results of oxide-sintered sintered magnet scrap powder

4. XRD diffraction analysis of neodymium acetate obtained by evaporation

The present invention provides a method for selectively separating neodymium from NdFeB permanent magnet waste scrap.

In general, an acid leaching method is used to separate and recover neodymium from waste scrap containing neodymium. This method results in a large amount of acid consumption, because iron metal is more readily soluble in acid than iron oxide.

An alternative to this method is to perform sulfuric acid leaching after roasting the waste scrap. However, the leaching method after roasting should also involve the separation of neodymium and iron since a significant amount of iron is leached in sulfuric acid solution.

Therefore, the soybean method to reduce the leaching of iron is to oxidize neodymium by alkali and leaching with weak acid. That is, when the waste scrap is mixed with sodium hydroxide and then pulverized, the neodymium surface reacts with water to oxidize to neodymium oxide. The grinding process provides a surface of fresh neodymium, with subsequent oxidation occurring at the surface. After filtering the oxidized neodymium oxide-containing scrap and leaching it with a weak acid, the entire amount of neodymium is leached, and only part of the iron is leached to simplify the recovery process of separation of neodymium and iron. However, this method causes the bad conditions of the operation by using a strong alkali sodium hydroxide, has a number of problems, such as the complexity of the process and the choice of reactor material.

The present invention is to provide a new method for recovering neodymium economically without impurities from waste scrap containing neodymium in order to solve the disadvantages of the existing method described above.

The present invention provides a method for separating neodymium in a simpler process and easier to handle than a conventional process of oxidizing neodymium using strong alkali such as sodium hydroxide.                         

The present invention provides a method for selectively and efficiently recovering neodymium from NdFeB based permanent magnet scrap.

In order to achieve the above object, the present invention used a method of selectively separating neodymium by oxidizing waste scrap containing neodymium at high temperature, and performing weak acid leaching using acetic acid.

That is, the present invention is to convert the neodymium-containing waste scrap at 400 ~ 800 ℃, preferably 500 ~ 600 ℃ to convert neodymium to neodymium oxide form, the oxide-burned scrap converted to neodymium oxide form to acetic acid Leaching to convert to neodymium acetate, and fractionating and recovering neodymium acetate by evaporating and cooling the solution in which the neodymium acetate is dissolved.

Another form of the present invention is the process of converting neodymium to neodymium oxide by roasting neodymium-containing waste scrap at 400 to 800 ° C., preferably 500 to 600 ° C. Leaching in acetic acid to convert to neodymium acetate, the solution of the neodymium acetate is dissolved by evaporation and cooling by fractional crystallization and recovery of neodymium acetate, and after filtering the fractionated neodymium acetate oxalic acid was added to the remaining concentrate Converting the extra micronized neodymium to neodymium oxalate and precipitating it.

At this time, the iron component contained in the waste scrap is dissolved as part of it is converted to iron acetate, but iron acetate has a higher solubility compared to neodymium acetate, so it is dissolved in the concentrated solution when recovering neodymium acetate crystals, and thus The iron component can be separated.

Acetic acid leaching experiment of the oxide deoxidized scrap was injected into the reactor with an appropriate amount of acetic acid, and after adjusting the temperature was put a certain amount of deoxidized scrap. The concentration of neodymium and iron in the supernatant obtained by filtering the leaching residue after acetic acid leaching was measured using ICP (Jobin-Yvon Model JY-38 Plus). From these results, the leaching rates of Fe and Nd for each experimental condition Could get Neodymium acetate crystals could be recovered from the acetate leaching solution.

In this step of the present invention, the reason for using a weak acid such as acetic acid in the leaching of calcined scrap is to dissolve only the neodymium oxide contained in the scrap and to leave most of the iron oxide undissolved, and thus to neodymium oxide from iron oxide. This is because it can be separated.

In the roasting oxidation step of the present invention, the temperature for oxidizing the neodymium-containing waste scrap is roasted at 400 ~ 800 ℃, more preferably at 500 ~ 600 ℃. By heating, neodymium is converted into the form of neodymium oxide as shown in the following formula.

Nd ³⁺ + ₃ O ₂ ―――――――――― → Nd ₂ O ₃ (1)

                           600 ℃

If the oxidation temperature is below 400 ℃, the oxidation rate is slow and thus neodymium oxide is not well formed. If the oxidation temperature is above 800 ℃, other components are also oxidized. It is good. Oxidation roasting time is determined according to the amount of waste scrap and the yield, so that it is appropriately adjusted and used, although there is no particular limitation, it is better to give sufficient time.

In the leaching step of the present invention, if the oxidized scrap is leached into acetic acid, it is converted into neodymium acetate as shown in Reaction (2) below and dissolved in the solution.

Nd ₂ O ₃ + 6H ₂ C ₂ H ₃ O ₂ ――――――――― → 2Nd (C ₂ H ₃ O ₂ ) ₃ + 3H ₂ O (2)

Therefore, since the oxidized scrap is immersed in acetic acid of pK 4.7 or so, neodymium oxide is dissolved and iron oxide is not dissolved. Therefore, when oxidized scrap is leached into acetic acid, iron oxide, neodymium acetate (Nd (C ₂ H ₃ O ₂ ) ₃ ) insoluble in the leaching solution, and iron acetate (Fe ₃ (CH ₃ COO) in which some iron components react with acetic acid ) ₆ (CH ₃ COO) ₃ ). The content of neodymium acetate and acetic acid dissolving the same according to the present invention typically uses acetic acid having a solubility or higher that can completely dissolve the neodymium acetate. In general, neodymium acetate has a solubility of 260 g / l at room temperature, so when the nitric oxide leaching of the roasting oxide scrap, such neodymium acetate solubility can be used to determine the appropriate leaching conditions can be appropriately selected by those skilled in the art. In addition, in order to promote solubility, the case of dissolution temperature can also be selected and used, but in general, 1 to 10 hours at 40 to 110 ° C, preferably 70 to 90 ° C is appropriate.

The leaching solution filtered after acetic acid leaching of the oxidized oxide scrap as described above is neodymium acetate (Nd (C ₂ H ₃ O ₂ ) ₃ ) and trace amount of iron acetate (Fe ₃ (CH ₃ COO) _{6 which} is higher in solubility than neodymium acetate. (CH ₃ COO) ₃ ). Neodymium acetate is a simple ionic salt, whereas iron acetate is a complex salt.The fundamental difference in this structure is a large solubility difference, so that the acetate solution can be recovered by evaporating acetic acid solution from the acetic acid leaching solution. Iron acetate complex salts are highly soluble and cannot be recovered as crystals.

On the other hand, after recovering by filtering and filtering neodymium acetate, some unrecovered neodymium present in the concentrated solution can be recovered using oxalic acid as shown in the following equation.

2Nd (C ₂ H ₃ O ₂ ) ₃ + 3H ₂ C ₂ O ₄ → Nd ₂ (C ₂ O ₄ ) ₃ + 6HC ₂ H ₃ O ₂ (3)

The acetic acid leaching solution was added to a rotary evaporator to evaporate the acetic acid solution at a high temperature of 80 to 120 ° C. under reduced pressure, and then the rotary evaporator was naturally cooled to obtain neodymium acetate crystals. Therefore, it is also important to crystallize in the appropriate filtrate volume during the recovery of neodymium acetate in accordance with the volume change of the concentrated filtrate in accordance with the evaporation of acetic acid solution in the rotary evaporator. In addition, after crystallizing the concentrated filtrate and recovering the crystals of neodymium acetate by filtration, the concentrated filtrate contains some neodymium, which can be recovered as neodymium oxalate by reacting with oxalic acid.

That is, neodymium, which is not recovered by neodymium acetate crystallization and remains in the concentrated solution, is recovered as neodymium oxalate by reacting with oxalic acid. Since oxalic acid has excellent selectivity with rare earths, it can be recovered by converting unrecovered neodymium to neodymium oxalate and precipitating by adding an aqueous solution of oxalic acid to the concentrated solution.

Hereinafter, the present invention will be described in more detail with reference to Examples, and it is well known to those skilled in the art that the present invention is not limited only to the following Examples. In the present invention,% is% by weight unless otherwise specified.

In the present invention, NdFeB-based permanent magnet waste scrap powder was used as the starting material. The NdFeB-based permanent magnet scrap powder was analyzed by ICP (Jobin-Yvon Model JY-38 Plus) as a result of the analysis of Fe 73.39%, Nd 25.48% and B as shown in Table 1 is composed of about 0.86% have.

Table 1. Chemical Composition of Permanent Magnet Scrap Powder

Experimental Example 1

Experiment for confirming leaching condition of neodymium oxide

Into the 500 ml of acetic acid, a purity of 99.9% neodymium oxide (65 g) was added to conduct a test for a completely soluble reaction temperature and leaching time. The 65 g of neodymium oxide is used in an amount corresponding to about 95% of the neodymium content for 260 g / l of the solubility of neodymium acetate in acetic acid. The results are shown in FIG. As a result, it was found that in order to effectively dissolve neodymium oxide completely within the solubility range and to be economical, it is possible to dissolve completely within about 3 hours when the reaction temperature is 80 ° C or higher.

Experimental Example 2

Leaching Rate of Neodymium According to Mineral Concentration of Scrap

The leaching rate of neodymium according to the mineral concentration of the scrap was tested. In 500 ml of acetic acid, the amount of calcined oxide powder obtained by oxidizing and roasting the permanent magnet scrap powder of Table 1 at 600 ° C for 2 hours was changed to 15 to 45% of the weight of acetic acid, and leached at 80 ° C for 3 hours. The leaching rate of neodymium according to the concentration was investigated and listed in FIG. 2.

It can be seen that the leaching rate of neodymium decreases as the concentration of mineral solution increases. The concentration of 45% of mineral solution to 500 ml of acetic acid is 46.7g of neodymium in the roasted oxide powder (see Table 2), which is 104g in terms of neodymium acetate. Since this value is 208g per liter of acetic acid and less than 260g / l of neodymium acetate solubility in acetic acid, the total amount of neodymium in the scrap should be leached in acetic acid, but according to the result of FIG. . Figure 3 shows the results of XRD diffraction analysis of the oxidized sintered magnet scrap powder, it can be seen that the oxidized scrap has a crystal structure of Fe ₂ O ₃ and FeNdO ₃ . Therefore, the leaching rate of 74.4% suggests that the leaching behavior of pure Nd ₂ O ₃ is different from that of acetic acid.

EXAMPLE

The NdFeB-based permanent magnet scrap powder having the composition shown in Table 1 was oxidized and roasted at 600 ° C. for 2 hours in a muffle furnace using a 30 cm (H) × 30 cm (W) × 30 cm (L) siliconit heating element as a heat source. The results of ICP analysis of the roasted permanent magnet powder components are listed in Table 2.

Table 2. Chemical Composition of Scrap Powders Oxidized and Baked at 600 ℃ for 2 Hours

Oxidized roasted scrap was leached at 80 ° C. for 3 hours at a concentration of 35 wt% in 500 ml of acetic acid in a reactor equipped with a Pyrex jaket having an inner diameter of φ 85 mm, an outer diameter of φ 90 mm, and a height of 100 mm. The reaction temperature was controlled using a water bath. A condenser was attached to the reactor to prevent evaporation of the solution at high temperature leaching. After filtering the leached solution, the composition of the supernatant (500 mL, d = 1.1203) was analyzed in ICP. From this result, the neodymium in the leaching solution is 33.6g, which shows a leaching rate of about 92.6% compared to the 36.3g of the neodymium content in the roasted oxide oxide powder. Also, Fe is 3.42 g, which shows a leaching rate of about 3.6% with respect to the iron content of 94.3 g of iron oxide scrap scrap, which is initially added. Therefore, when leaching acetic acid oxide, the selective leaching of neodymium by weak acid is well performed. It can be seen that.

Table 3. Chemical Composition of Leaching Solution by Acetic Acid

500 ml of the acetic acid leaching solution was added to a rotary evaporator, and the acetic acid aqueous solution was evaporated while maintaining the temperature at 100 to 105 ° C. under reduced pressure (−750 mm Hg). After evaporation of certain acetic acid solution, the rotary evaporator is naturally cooled to form neodymium acetate crystals. When the acetic acid aqueous solution was evaporated and the content of the remaining concentrate was adjusted to 250, 150, 100, and 50 ml, after filtering and recovering the neodymium acetate crystallized according to the volume change, the composition of the filtrate was analyzed by ICP and the results are shown in Table 4. .

Table 4. Chemical composition of the concentrate after evaporation of acetic acid leachate and recovery of neodymium acetate crystals

From the above results, it is possible to calculate the neodymium content in the concentrate from the volume and specific gravity of the concentrate, and after evaporation, the neodymium content of the filtrate is about 109 g / l, regardless of the volume of the concentrate, and converted to neodymium acetate as about 243 g / l. It can be seen that the neodymium acetate solubility value is close to. It can be seen that iron is present in an amount almost equal to the amount of iron (3.42 g) (3.34 g) contained in the starting materials. However, when the concentrated filtrate is 50 ml, the iron content (2.35 g) is drastically reduced. This is because, when concentrated to 50 ml, the filtrate has a very increased viscosity, and thus, when filtered to recover neodymium acetate crystals. This may be due to poor filtration and the precipitation of some iron acetate. Therefore, in order to precipitate neodymium acetate crystals from the leaching solution and recover them through filtration, it was appropriate to concentrate about 1/5 (100 ml) of the initial leaching solution volume at a temperature of 100 ° C. or higher under reduced pressure. Under these conditions, the neodymium content in the concentrate was 10.9 g from Table 4, so the recovery rate of neodymium recovered as neodymium acetate was 67.5% compared to the starting solution (neodymium content 33.6g, see Table 3).

Neodymium unrecovered by neodymium acetate crystallization and remaining in the concentrated solution is recovered as neodymium oxalate by reacting with oxalic acid. Since oxalic acid has excellent selectivity with rare earths, it can be recovered by converting unrecovered neodymium to neodymium oxalate and precipitating by adding an aqueous solution of oxalic acid to the concentrated solution.

According to the present invention, the neodymium contained in the waste scrap of the permanent magnet can be separated with high efficiency with high selectivity, and can be separated more easily and conveniently than with the conventional strong alkali method. It can provide a way to.

Claims (6)

In the method for separating and recovering neodymium from waste scrap containing neodymium, Oxidizing waste scrap powder; Treating the oxidized waste scrap powder with acetic acid to leach it with neodymium acetate; Concentrating and cooling the leached leaching solution to fractionally crystallize neodymium acetate; Method for selectively separating neodymium from waste scrap comprising a. The method of claim 1, The method of selectively separating neodymium from waste scrap, characterized by further comprising the step of condensation cooling the leached leaching solution to crystallize neodymium acetate. The method of claim 2, Reacting the filtrate with oxalic acid after filtration to precipitate and separate unrecovered neodymium remaining in the filtrate with neodymium oxalate, the method for selectively separating neodymium from waste scrap. The method according to any one of claims 1 to 3, The process for selectively separating neodymium from waste scrap, characterized in that the roasting is carried out in a furnace of 500 ~ 600 ℃. The method according to any one of claims 1 to 3, A method for selectively separating neodymium from waste scrap, characterized in that the soaking by acetic acid is carried out for 1 to 10 hours at 40 ~ 110 ℃. The method according to any one of claims 1 to 3, The step of concentrated crystallization, the method for selectively separating neodymium from waste scrap, characterized in that carried out at 100 ~ 110 ℃ under reduced pressure.

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