JP2765740B2 - Separation and recovery of rare earth elements from raw materials containing rare earth elements and iron - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a raw material containing a rare earth and iron, such as a scrap of a rare earth element (hereinafter, simply referred to as a rare earth) -iron alloy material and a rare earth-iron smelting waste. And a method for separating and recovering rare earth from water.

[Related Art] Hereinafter, neodymium (Nd) will be described as an example of a rare earth.

In recent years, rare-earth-iron-boron-based magnet alloys represented by Nd-Fe-B have been developed, and are now attracting attention in various fields as permanent magnets having the highest magnetic performance, and this industrial production is rapidly advancing. .

Since such a magnet contains rare and expensive rare earth elements of about 30% by weight, supply of rare earth material is an important issue.

In particular, the price of neodymium has tended to soar in recent years with the rapid increase in magnet production, and its supply trend is expected to have a significant impact on the magnet market.

On the other hand, in the manufacturing process of magnets, it is expected that about 20 to 40% by weight of the final product weight will be generated, and that the magnet product will be scrapped due to performance degradation or dismantling of the equipment during use. Is done.

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

For the conventional separation of rare earths from other elements, for example, iron, the so-called fluoride precipitation method and oxalate precipitation method utilizing the low solubility of rare earth fluoride and rare earth oxalate are well known. However, when these methods are applied to the scrap treatment as described above, the fluoride precipitation method uses a solution containing concentrated fluoride ions, so the material of the apparatus is limited, and the treatment of harmful wastewater is also a major problem. Becomes In the oxalate precipitation method, separation of rare earth and iron is incomplete, and oxalic acid used industrially is expensive.

On the other hand, a solvent extraction method can be considered as another separation method,
D2EHPA (Di-2-), a known excellent rare earth extractant
When using Ethyl Phosphoric Acid), separation is not always easy because it is extracted under almost the same conditions as rare earth and iron. Even if an extractant having good separability is developed, a large amount of iron is contained in the scrap, so that the use of the extractant is considered to increase the processing cost.

Thus, an economical and rational method for industrially separating and recovering rare earths from a raw material containing rare earths and iron has not been established yet.

[Problems to be solved by the invention]

The present invention solves the above-mentioned problems of the prior art and develops a processing method for efficiently and economically recovering rare earth from a raw material containing rare earth and iron, that is, good operability using an inexpensive reagent. It is an object of the present invention to provide a method for separating and recovering rare earths with a high yield and a reusable purity by a simple process.

[Means for solving the problem]

In order to solve the above-mentioned problem, the present invention dissolves a raw material containing a rare earth element and iron in an aqueous sulfuric acid solution and adds nitric acid or an aqueous nitric acid solution to the dissolved solution, or adds nitric acid to an aqueous sulfuric acid solution of the raw material. The rare earth element sulfate by adding alcohol to the resulting solution to selectively crystallize the sulfate of the rare earth element, and separating the crystallized product from the solution. It provides a collection method.

[Action]

In the present invention, a raw material such as Nd-Fe-B magnet scrap is first dissolved in a sulfuric acid aqueous solution. The amount of sulfuric acid used should be the stoichiometric amount required for the rare earth and iron in the sample to form sulfate.
1.0 to 1.5 times is good. An appropriate sulfuric acid concentration is about 4 to 6 normal. If a sulfuric acid aqueous solution having a higher concentration is used, sulfuric acid may react with ethanol to be added later to form a sulfate ester. Sulfate esters are non-volatile oily liquids that adhere to the crystallization and make it difficult to filter and dry.

The aqueous solution of sulfuric acid is added while heating the sample after adding sulfuric acid to a temperature of 100 to 120 ° C. As nitric acid, a commercially available nitric acid having a concentration of about 60% may be used as it is. Note that nitric acid may be mixed with a sulfuric acid aqueous solution. Nitric acid improves the solubility of the sample and simultaneously oxidizes Fe ²⁺ to Fe ³⁺ as an oxidizing agent. The reason why it is necessary to oxidize ferrous sulfate to ferric sulfate is that the amount of ethanol added (% by weight) to the solution obtained by the above method and the amount of Fe ₂ (SO ₄ ) ₃ , FeSO ₄ , Nd ₂ (S
As shown in FIG. 1 as an example of the solubility of O ₄ ) ₃ (g / 100 ml solution), in the solution to which alcohol was added, the solubility of ferric sulfate was much higher than that of ferrous sulfate. This is because the crystallization separation from the rare earth sulfate easily proceeds.
The amount of nitric acid used is suitably about 1.0 to 1.2 times the stoichiometric amount required for the oxidation of ferrous iron. If there is an excess of nitric acid, the solubility as a rare earth nitrate increases, so that crystallization with alcohol becomes difficult.

An alcohol having a relatively low boiling point, such as ethanol, methanol, or butanol, is added to the solution obtained by the above-described method to precipitate a rare earth sulfate as a precipitate. According to the experimental results, the amount of alcohol to be added is suitably 25 to 40% by weight of the solution weight. Thus, the addition of a small amount of alcohol causes insufficient precipitation of the rare earth sulfate. Further, when an alcohol in a larger amount is added, the crystal grains of the generated rare earth sulfate become large, and iron is mixed in, thereby lowering the purity of the crystallized product. The crystallization temperature may be in the range of 20 to 60 ° C., which can be easily implemented.

Crystallization of the rare earth sulfate by the addition of alcohol proceeds very quickly. For example, when a container is placed in a thermostatic water bath and shaken for several hours, a crystalline precipitate having good filterability precipitates. After complete settling, the crystallization is separated. Separation can be easily performed by filtration with a vacuum filter using, for example, filter paper.

The solubility of ferric sulfate in the alcohol solution is extremely high, and the iron remains in the solution and is removed. Boron is dissolved as boric acid (H ₃ BO ₃ ) in the dissolving step, but boric acid has a high solubility in an alcohol solution (dissolves in ethanol at 25 ° C at a rate of 11.8 g / 100 g). Hardly contains boron and is easily separated. The crystallized substance separated by filtration may be removed by washing the adhesion solution containing Fe or 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 producing Nd-Fe-B-based magnets by a reduction diffusion method.

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

[Example] 30 g of Nd-Fe-B magnet alloy powder having the composition shown in Table 1 was used.
The mixture was added little by little to a glass Erlenmeyer flask containing 390 ml of a 5N aqueous sulfuric acid solution, and stirred to dissolve.
While heating to 120120 ° C., 20 ml of a 61% aqueous nitric acid solution was added. The sample dissolved completely in about 1 hour. The resulting solution was made up to a constant volume of 450 ml, this solution was neodymium 22 g /,
The iron content was about 45 g / pH1.

360 ml of 99.5% ethanol (35% of solution weight)
%), And the mixture was shaken at 50 ° C. for 5 hours for crystallization. After the sedimented crystallized product is separated from the mother liquor by filtration, it is put into an electric muffle furnace as it is, and 1400 ° C. in an air atmosphere.
For 30 minutes.

The weight of the obtained neodymium oxide was 10.71 g, and its chemical analysis values are shown in Table 1. The recovery rate of neodymium is 94.1%,
The grade of neodymium oxide was 97.2%, and neodymium could be separated and recovered as a high-quality oxide at a high recovery rate.

[Effects of the Invention] According to the present invention, not only can rare earths be separated and recovered with good yield and high purity from raw materials containing rare earths and iron, but they are not known at all in comparison with conventional treatment methods. Inexpensive reagents are used, which is economical, and the process is short, and can be carried out reliably and easily with a simple apparatus.

It is needless to say that the present invention can be applied not only to the magnet alloy but also to any raw material containing a rare earth element and iron, and can be applied not only to neodymium as exemplified but also to other rare earth elements.

[Brief description of the 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.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C22B 59/00 C22B 3/00-3/46

Claims (1)

(57) [Claims] A raw material containing a rare earth element and iron is dissolved in an aqueous sulfuric acid solution, and a nitric acid or nitric acid aqueous solution is added to the dissolved solution, or the raw material is dissolved in an aqueous solution obtained by adding nitric acid to an aqueous sulfuric acid solution. Then, alcohol was added to the resulting solution to selectively crystallize rare earth sulfates,
A method for separating and recovering a rare earth element, wherein the crystallized product is separated from the solution.