JPH03207825A - Method for separating and recovering rare earth elements from raw material containing rare earth elements and iron - Google Patents

Abstract

PURPOSE:To easily separate rare earth elements from a raw material contg. rare earth elements and iron at a high yield by dissolving the raw material into the aqueous soln. of sulfuric acid with nitric acid, adding alcohol to the soln. and selectively crystallizing out the sulfate of rare earth elements. CONSTITUTION:At the time of separating Nd, e.g. from Nd-Fe-B magnetic alloy powder, the powder is dissolved into the aqueous soln. of sulfuric acid and is thereafter admixed with the aqueous soln. of nitric acid while heating is executed to about 100 to 120 deg.C to convert Fe<2+> into Fe<3+>. Next, the soln. is admixed with alcohol (having a relatively low b.p. such as ethanol and methanol) by 25 to 40wt.% of the weight of the soln. to crystallize out the sulfate of Nd in the temp. range of about 20 to 60 deg.C, which is then separated and recovered. In this way, rare earth elements can surely be separated and recovered with good operability by using an inexpensive reagent.

Description

[Detailed Description of the Invention] [Industrial Application Field 1] The present invention is applicable to raw materials containing rare earth elements (hereinafter referred to simply as rare earths), such as scraps of ferrous alloy materials, rare earth smelting scraps, etc. This invention relates to a method for separating and recovering rare earths from.

[Conventional technology]

Hereinafter, neodymium (Nd) will be explained as an example of rare earth.

In recent years, rare-earth iron-boron magnet alloys, represented by Nd-Fe-B, have been developed, attracting attention from various quarters as permanent magnets with the highest magnetic performance at present, and their industrial production is rapidly progressing. .

Since such magnets contain about 30% by weight of rare and expensive rare earth elements, the supply of rare earth raw materials has become an important issue.

In particular, with the rapid increase in magnet production, the price of neodymium has been on the rise, and supply trends are expected to have a major impact on the magnet market.

On the other hand, during the manufacturing process of magnets, processing waste is generated that accounts for approximately 20 to 40% of the weight of the final product, and it is fully expected that the magnet products will become scrap due to a decline in performance or disassembly of the equipment during the use period. be done.

Generally, the content of rare earth elements in such scrap is much higher than that of ore raw materials, and separating and recovering rare earth elements from scrap for reuse is extremely important from the viewpoint of resource conservation and energy conservation.

Conventional methods for separating rare earths and other elements, such as iron, are the so-called fluoride precipitation method, which utilizes the low solubility of rare earth fluoride and rare earth cerate, and the l/X characteristic, and oxalate precipitation. well known. However, when these methods are applied to the treatment of scrap as described above, the fluoride precipitation method uses a concentrated fluorine ion-containing solution, which limits the equipment material, and also poses a major problem in the treatment of harmful wastewater. In addition, the separation of rare earth elements and iron is incomplete in the precipitation of ferric acid, and furthermore, the ferric acid used industrially is expensive.

On the other hand, solvent extraction may be considered as another separation method, but D2EHPAtDi, which is a known excellent extractant for rare earths,
-2-Et. hyl Phosphoric Acid
When using l, separation is not necessarily easy because it is extracted under almost the same conditions as rare earths and iron. Even if an extractant with good separation properties were developed, the scrubbing would contain a large amount of iron, so the use of an extractant would increase processing costs.

As described above, an economical and rational method for industrially separating and recovering rare earths from raw materials containing rare earths and iron has not yet been established. Development of processing methods that solve these problems and efficiently and economically recover rare earths from raw materials containing rare earths and iron. In other words, we aim to recover rare earths using inexpensive reagents and an easy-to-operate process. The purpose is to provide a method for efficiently separating and recovering substances with a purity that allows reuse.

[Means for Solving the Problems] In order to solve the above problems, the present invention dissolves raw materials containing rare earth elements and iron in an aqueous solution of sulfuric acid and nitric acid, and then adds alcohol to the resulting solution. Rare earth elements @
The present invention provides a method for separating and recovering rare earth elements, which is characterized by selectively crystallizing an acid salt and separating the crystallized product from the solution.

[Operation] In the present invention, raw materials such as Nd-Fe-B magnet slabs are first dissolved in an aqueous sulfuric acid solution. The amount of sulfuric acid used may be 1.0 to 1.5 times the stoichiometric amount required for rare earth and iron in the sample to form sulfate. Sulfuric acid concentration is 4~
Approximately 6 regulations are appropriate. If an aqueous sulfuric acid solution with a concentration higher than this is used, there is a risk that the sulfuric acid will interact with the ethanol that will be added later to produce a sulfuric acid ester. Sulfuric acid esters are nonvolatile oily liquids that adhere to crystallized substances and make their filtering and drying difficult.

A nitric acid aqueous solution is added while heating the sample after adding sulfuric acid to a temperature of 100 to 120°C. Nitric acid has a commercially available concentration of 60%.
You may use it as is. Note that nitric acid may be mixed with an aqueous nitric acid solution. Nitric acid improves the solubility of the sample and at the same time serves as an oxidizing agent to oxidize Fe2+ to Fe3+. The reason why it is necessary to oxidize ferrous sulfate to ferric sulfate is due to the amount of ethanol added (wt%) to the solution obtained by the above method and the amount of Fe2
(SO4) 3, FeSO4, Nd2 (S04
) 3 (g/100m4 solution), as shown in Figure 1, the solubility of ferric sulfate is much higher than the solubility of ferrous sulfate in a solution containing alcohol; This is because crystallization separation from sulfate proceeds easily. The amount of nitric acid used is approximately 1.0 to 1.2 times the stoichiometric amount required for oxidizing ferrous iron. The presence of excess nitric acid increases the solubility of rare earth nitrate, making crystallization with alcohol difficult.

Ethanol and methanol were added to the solution obtained by the method described above. An alcohol with a relatively low boiling point, such as butanol, is added to precipitate the rare earth sulfate.

According to experimental results, the amount of alcohol added is 2 of the weight of the solution.
5 to 40% by weight is suitable. If less alcohol is added, precipitation of rare earth sulfate is insufficient. Furthermore, if a larger amount of alcohol is added, the crystal grains of the rare earth sulfate produced will become larger, and iron will be mixed in, reducing the purity of the crystallized product. Incidentally, the crystallization temperature may be within a temperature range of 20 to 60°C, which can be easily carried out.

Crystallization of rare earth sulfate due to the addition of alcohol proceeds extremely rapidly; for example, if the container is placed in a constant temperature water bath and shaken for several hours, a crystalline precipitate with good filterability will settle out. After complete precipitation, the crystallized product is separated. Separation can be easily carried out by filtration using a vacuum filter using filter paper, for example. The solubility of ferric sulfate in alcoholic solutions is extremely high, and the iron remains in the solution when removed. In addition, boron is dissolved as boric acid (83BO3) in the dissolution process, but
The solubility of boric acid in alcohol solution is high (25°C
It dissolves in ethanol at a rate of 1,8 g/l 00 g), hardly any boron is mixed into the crystallized product, and it is easily separated. The filtered crystallized product may be removed by cleaning the adhesion solution containing Fe and the like.

The obtained crystallized product is calcined in air at about 1400°C to obtain neodymium oxide. This neodymium oxide can be used as a raw material for neodymium metal, or directly as a raw material for manufacturing Nd-Fe-B magnets by a ring element diffusion method.

The alcohol used for crystallization separation is an inexpensive industrial raw material and has a low boiling point, so it can be easily recovered by the well-known distillation separation method, and processing costs can be reduced by reusing the recovered alcohol. is possible.

[Practical example] Nd-Fe-Bfa stone alloy powder 30 with the composition shown in Table 1
g was added little by little to a glass Erlenmeyer flask containing 390 ml of 5N @ acid aqueous solution, and dissolved by stirring. Then, the concentration was 61% while heating at 100 to 120°C.
20 mβ of nitric acid aqueous solution was added. The sample was completely dissolved in about 1 hour. The obtained solution was made into a constant volume of 450 mI2, and this old solution contained 22 g of neodymium/I2 and 45 g of iron.
/ I2, p} was about 11.

Add to this solution 99.5% ethanol 360rr + 125
It was shaken for a time to crystallize. After filtering the precipitated crystallized product from the mother liquor, it was directly placed in an electric Matsufuru furnace and fired at 1400° C. for 30 minutes in an air atmosphere.

The weight of the neodymium oxide obtained was lO. The chemical analysis value is shown in Table 1. The recovery rate of neodymium is 94
．． 1%, the grade as neodymium oxide is 97.2%,
We were able to separate and recover neodymium as a high-quality oxide with a high recovery rate.

[Effects of the Invention] According to the present invention, not only is it possible to separate and recover rare earths from raw materials containing rare earths and iron in good yield and high purity, but also it is possible to separate and recover rare earths from raw materials containing rare earths and iron. It uses innovatively inexpensive reagents, is therefore economical, has short steps, and can be carried out reliably and easily with simple equipment.

It goes without saying that the present invention is not limited to magnetic alloys, but can be applied to any raw material containing rare earth elements and iron. In addition to the exemplified neodymium, other rare earths can also be used.

[Brief explanation of drawings]

FIG. 1 is a graph showing an example of the relationship between the solubility of neodymium sulfate, ferrous sulfate, and ferric sulfate and the amount of ethanol added. Applicant Hitachi Powder Metallurgy Co., Ltd.

Claims (1)

[Claims] 1. A raw material containing a rare earth element and iron is dissolved in an aqueous solution of sulfuric acid and nitric acid, and then alcohol is added to the resulting solution to selectively crystallize the sulfate of the rare earth element, and the crystallized product is A method for separating and recovering rare earth elements, characterized by separating them from a solution.