JPS6158533B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for selectively separating and recovering rare earth metals, particularly samarium, europium and cadrinium.

Up until now, so-called light rare earth metals such as lanthanum and cerium have been widely used as optical glass raw materials and abrasives, whereas so-called heavy rare earth metals such as samarium, europium, and cadrinium have rarely been used. As a result, there has been little research into methods for separating and purifying it. However, recently,
With the rapid development of the electronics industry, the development of applications for these heavy rare earth metals in semiconductors, phosphors, rare earth magnets, etc. has become active, and the demand for efficient separation methods and high purity products has increased. has been increasing.

Traditionally, common methods for separating rare earth metals include fractional crystallization, fractional precipitation, solvent extraction, and ion exchange, but these require special equipment and are difficult to operate. It is complicated and takes a long time, so it is not suitable as an industrial method.

Moreover, as is clear from the fact that the separation coefficient between cadrinium and europium is 1.02, and that between europium and samarium is 1.4,
Separation of samarium, europium, and gadolinium is particularly difficult, and until now no method for efficiently separating these metals has been known.

The present inventors have conducted extensive research in order to develop a method to efficiently separate heavy rare earth metals such as samarium, europium, and cadrinium, which are difficult to separate using conventional methods, and to obtain high-purity products. As a result, the objective can be achieved by first selectively separating only europium from these mixtures by reduction using zinc amalgam, and then separating the remaining samarium and gadolinium using cationic ion exchange fibers. Based on this finding, we have accomplished the present invention.

That is, in selectively separating each metal from a solution containing salts of samarium, europium, and gadolinium, the present invention first selectively reduces and precipitates only europium with zinc amalgam, and then separates the cationic metals. The present invention provides a method for selectively separating rare earth metals, which is characterized in that samarium and cadrinium are adsorbed using ion exchange fibers, and then fractionally eluted with an aqueous solution of a chelating agent.

As described above, the present invention removes europium, which is adjacent to samarium and gadolinium and is difficult to separate due to a small separation coefficient between them, by a zinc amalgam reduction method, and as a result, the separation coefficient between them is reduced. Since grown samarium and gadolinium are separated using cationic ion exchange fibers, highly pure rare earth metals can be obtained in a short time with simple operations.

The raw material used in the method of the present invention is a solution containing samarium, europium, and gadolinium in the form of salts, but in addition to these three, other metals such as neodymium may be added to the extent that they do not interfere with the separation. etc. may be included.

As such a raw material, an acid solution remaining after light rare earths are extracted from naturally occurring rare earth-containing minerals, such as bastnasite, or an acid solution of Mitsushimetal's electrolysis residue, etc., are used.

The first step of reduction with zinc amalgam in the method of the present invention is carried out by bringing the raw acid solution into contact with zinc amalgam, which is an alloy of zinc and mercury. This treatment is usually advantageously carried out by passing the raw liquid through a packed bed of zinc amalgam several times, for example from 1 to 5 times. When concentrated sulfuric acid in an amount 2 to 3 times the amount equivalent to europium is added to the raw material solution treated in this way, only europium precipitates.
This precipitate is filtered, dissolved by adding nitric acid and hydrogen peroxide, and then converted to oxalate by adding oxalic acid, which is then calcined to obtain europium as an oxide.

Next, in the second step of the method of the present invention, barium chloride is added to the filtrate after europium has been removed as described above to remove sulfuric acid, and the resulting solution is treated with a cationic ion exchange fiber. In this case, the solution usually has a rare earth metal concentration of 10 to 100 g/, pH
It is used by adjusting it to 0.5-3.0.

The cationic ion exchange fibers used in this second step include, for example, cationic ion exchange fibers made of a polymer having a sulfonic acid group as a strong cation exchange group and a carboxyl group as a weak cation exchange group. The ion exchange capacity of the strong cation exchange group and weak cation exchange group in this cationic ion exchange fiber is 1.0 meq/
g or more, and the molar ratio of the strong cation exchange group to the weak cation exchange group is preferably 5:1 to 1:1.

Such a cationic ion exchange fiber can be produced, for example, as follows.

That is, after spinning polyvinyl alcohol with an average degree of polymerization of 1,000 to 3,000, it is heat treated at 150 to 230°C for several hours in air or in an atmosphere of inert gas, and then placed in concentrated sulfuric acid and heated to 50 x 100°C for several hours. When treated for a period of time, polyethylenization occurs due to the dehydration reaction of polyvinyl alcohol, carboxyl group generation and sulfonation occur through oxidation of alkyl groups, and the desired cationic ion exchange fiber is obtained. By appropriately changing the heat treatment conditions in air or zero inert gas atmosphere and sulfuric acid treatment conditions, the cationic ion exchange capacity of the ion exchange fibers and the strong cationic exchange groups and weak cationic The molar ratio of exchange groups can be adjusted.

This cationic ion exchange fiber may be used as it is by being filled into a suitable column, or may be knitted and woven by a conventional method and then filled into a container for use.

Next, in the method of the present invention, known chelating agents such as ethylenediaminetetraacetic acid and nitrile triacetic acid can be mentioned as chelating agents used to elute the rare earth metals adsorbed on the above-mentioned cationic ion exchange fibers. I can do it. These are used in the form of salts as aqueous solutions, but ammonium salts are particularly preferred for convenience when regenerating and repeatedly using cationic ion exchange fibers. The chelating agent is advantageously used as an aqueous solution with a concentration of 0.05-3% and a pH of 7-9.

To suitably carry out this second step, fill the specified cationic ion exchange fiber, condition it with dilute hydrochloric acid solution and dilute ammonium chloride aqueous solution, and then inject rare earth metal-containing aqueous solution adjusted to pH 1.5. Then, the rare earth metal is adsorbed onto the cationic ion exchange fiber. Next, the adsorbed column is washed with water, and then an aqueous ammonium ethylenediaminetetraacetate solution having a concentration of 0.1 to 2.0% and a pH of approximately 7 to 9 is passed through the column at an elution rate of 1.0 to 5.0 for elution. A fixed volume of the flowing liquid is collected, and the rare earth metals contained therein are traced using a fluorescent X-ray method, and each fraction of the same metal is collected.

By adding oxalic acid to the solution of each metal thus obtained and recovering each metal as an oxalate, and then firing this, samarium and gadolinium can be obtained as highly pure oxides. .

According to the method of the present invention, by utilizing the chemical properties of samarium, europium, and gadolinium, only europium is first separated by pretreatment, and then fractions of each metal are obtained in a short time using cationic ion exchange fibers. These metals can be separated and recovered in high purity.

Next, the present invention will be explained in more detail with reference to Examples.

Reference example A stock solution of fully saponified polyvinyl alcohol with an average degree of polymerization of 1200 and 5% ammonium polyphosphate per weight was dry-spun to
A polyvinyl alcohol fiber of 150d/50f was obtained.

When this fiber was treated in nitrogen gas at 220°C for 3 hours, its weight decreased by 23% and it became a blackish brown partially polyenated fiber. Next, this polyenated fiber was treated in 98% sulfuric acid at 60° C. for 3 hours, and then thoroughly washed in boiling water to obtain a cationic ion exchange fiber.

Example samarium oxide 64.1% by weight, europium oxide
40 g of mixed rare earth consisting of 8.8% by weight and 13.7% by weight of gadolinium oxide is dissolved in 200ml of 4N hydrochloric acid to prepare a raw material solution. Next, after diluting this solution with 300 ml of water, zinc amalgam (particle size approximately 1 mm) was added.
Column packed with 500g (diameter 20mm, length 300mm)
I passed it three times. Next, approximately 3 ml of concentrated sulfuric acid was added to the thus treated solution and mixed, and the precipitate formed was filtered off. To this precipitate, 10 ml of 6N nitric acid and 1 ml of hydrogen peroxide were added to dissolve it, and 10 ml of oxalic acid was added to form an oxalate salt.
3.46 g of 99.5% E〓 ₂ O ₃ (yield 99%) was obtained.

Add 1N to the filtrate after removing the europium precipitate.
- Add and mix 100 ml of barium chloride aqueous solution, and filter off the white precipitate formed.

1700ml of cationic ion exchange fiber obtained in reference example
Fill a column (diameter 50 mm, length 1000 mm), connect three columns in series, condition three times each with 1N hydrochloric acid and 1N ammonium chloride aqueous solution, and then pass the filtrate through. , adsorbed, and washed with water.

Then, elution was performed using a 0.5% ammonium salt aqueous solution of ethylenediaminetetraacetate (PH8.5).
200 ml of this eluent was taken, oxalic acid was added to convert the rare earth metals into oxalates, and the oxides were then calcined. did.

In this way, 89% purity _{Sm2O3 and} 92% purity
Gd ₂ O ₃ were obtained in 98% and 99% yield, respectively.

In addition, the purity was 99.6% using the same procedure except passing it through the cationic ion exchange fiber column twice.
25.12g of Sm ₂ O ₃ (98% yield), purity 99.8%
5.42 g (yield 99%) of Gd ₂ O ₃ was obtained.

Comparative example: A column with an inner diameter of 7.6 mm and a length of 300 mm was filled with a cationic ion exchange resin (Rohm & Haas,
Product name "Amberlite IR-120B") and anionic ion exchange resin (same as "Amberlite IRA")
-400'') at a weight ratio of 2:1, and 8.6 ml of the mixture was filled.

Next, a mixed oxide of samarium-europium-gadolinium (weight ratio Sm:Eu:Gd=64.1:
A sample prepared by dissolving 8.8:13.7) in nitric acid and adjusting the concentration to 2 × 10 ^-3 mol was injected from the top of the column and adsorbed.
2.8) was eluted at a rate of 120 ml/hr, and each fraction was collected every 2 minutes.

For each fraction obtained in this way,
High-frequency plasma emission spectroscopy was performed to determine the amounts of samarium, europium, and gadolinium in the sample. The results are shown in the drawing as a graph.

As is clear from this graph, these three components, especially europium, are hardly separated.

[Brief explanation of the drawing]

The figure is a graph showing the state of separation between Sm, Eu and Gd according to the conventional method.

Claims (1)

[Claims] 1. In selectively separating each metal from a solution containing salts of samarium, europium, and gadolinium, first, only europium is selectively reduced with zinc amalgam to precipitate and separate. 1. A method for selectively separating rare earth metals, which comprises adsorbing samarium and gadolinium using ion-exchange fibers and then performing fractional elution with an aqueous solution of a chelating agent. 2. The method according to claim 1, wherein the cationic ion exchange fiber has a strong cation exchange group and a weak cation exchange group. 3. The method according to claim 1, wherein the aqueous chelating agent solution is an aqueous solution of an ammonium salt of ethylenediaminetetraacetic acid or nitriletriacetic acid.