JPH078729B2 - Separation method of europium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for separating europium, and more specifically, to europium from a divalent europium and a rare earth mixture containing a trivalent rare earth other than europium. The present invention relates to an efficient separation method.

[Conventional technology]

The demand for europium as a fluorescent material for color televisions and high color rendering lamps has been increasing in recent years, and europium used for these applications needs to have high purity.

As a method for obtaining europium, an acidic aqueous solution of a rare earth mixture obtained from an ore such as monazite or bastnasite is treated with zinc or a zinc alloy to reduce europium to divalent, and then an acidic phosphate ester or the like. There is known a method of extracting trivalent rare earths with a cation-exchange solution and separating europium by leaving divalent europium on the aqueous phase side (for example, JP-A-55-122836). See the bulletin).

[Problems to be solved by the invention]

At the time of the extraction, in order to efficiently separate europium and other rare earths, alkali metal hydroxide, alkali such as ammonia is added at the time of extraction or added to the acidic aqueous solution or cation exchange solution of the rare earth mixture. It is often done. With the addition of this alkali, trivalent rare earths other than europium are extracted into the cation exchange liquid at a high rate, and the europium purity in the aqueous phase improves, but if the amount of alkali used is too large, divalent europium also There is a problem that the yield of europium is reduced due to extraction with a cation exchange liquid.

Therefore, there has been a demand for a method capable of efficiently and stably separating europium from other rare earths.

[Means for solving problems]

On the other hand, when the present inventors have used zinc or a zinc alloy as a reducing agent for europium, the inventors of the present invention, on the other hand, divalent zinc ions along with the following reduction reaction 2Eu ³⁺ + Zn → 2Eu ²⁺ + Zn ^2+. Is inevitably mixed in the solution, but intentional addition of divalent zinc was avoided because it had to be separated in the end, but surprisingly much more than was previously contained. It is known that the presence of a large amount of zinc ions in the aqueous solution increases the yield of europium remaining on the aqueous phase side and improves its purity, and that fluctuations in the extraction rate and other factors also decrease due to fluctuations in the amount of alkali added. did.

When zinc ions are added to the rare earth aqueous solution, (a) the rare earth aqueous solution is made strongly acidic and zinc, zinc chloride,
There is a method of dissolving zinc oxide, etc., and (b) a method of adding an aqueous solution in which zinc, zinc chloride, zinc oxide, etc. are dissolved to a rare earth aqueous solution, but in the case of (a) above, a free acid of zinc equivalent or more is required. Yes, since zinc and other substances are usually dissolved after adding a shortage of acid to the rare earth aqueous solution, the initial rare earth aqueous solution concentration and pH change, and it is necessary to re-analyze and re-prepare the liquid when performing subsequent extraction operations. Also, in the case of (b), there is a problem that the initial concentration of the rare earth aqueous solution also changes.

Therefore, as a result of various investigations by the present inventors to obtain a method for separating europium in which these problems have been solved, it is possible to stably separate europium with high purity and high yield by combining specific steps, and to obtain a rare earth element. The inventors arrived at the present invention by knowing that the aqueous solution of the mixture can be supplied to the extraction as it is, and at the same time, zinc ions can be easily recovered after the extraction, and the zinc ions can be easily reused.

That is, the gist of the present invention is to separate europium from an inorganic acid aqueous solution containing divalent europium and a trivalent rare earth other than europium, in which (a) a cation exchange liquid is used from an aqueous solution containing zinc. Zinc extraction step for extracting zinc, (b) divalent europium and 3 other than europium
Separation step of contacting an aqueous solution of an inorganic acid containing a valent rare earth and a cation exchange solution extracted with zinc to separate an aqueous phase rich in europium and a cation exchange solution rich in rare earth other than europium, ) Oxidation step of oxidizing the europium-rich aqueous phase to make europium trivalent, and (d) contacting the obtained trivalent europium-rich aqueous phase with a cation exchange liquid to exchange europium-rich cation. A method for separating europium is characterized by comprising each step of a zinc separation step of separating a liquid and an aqueous phase rich in zinc.

Hereinafter, the present invention will be described in detail. In the present invention, the rare earth element refers to a group including elements with atomic numbers 57 to 71 and yttrium.

First, in the present invention, in the zinc extraction step (a), zinc is extracted from an aqueous solution containing zinc into a cation exchange liquid.

If the cation exchange liquid can be used to separate divalent europium from other trivalent rare earths in the next separation step (b), the well-known ones used for the extraction of rare earths are Any of them can be used, specifically di-2-
Ethylhexyl phosphoric acid, di- [7,7-dimethyl-2-
(3 ', 3'-Dimethyl-1'-methylbutyl) -5-methyloctyl] phosphoric acid, alkyl phosphate having an alkyl group having 6 to 30 carbon atoms, 2-ethylhexylphosphonic acid mono-2- Alkylphosphonic acid alkyl ester having an alkyl group having 6 to 30 carbon atoms such as ethylhexyl ester, naphthenic acid 180, naphthenic acid 230
Examples include cation exchange liquids containing naphthenic acid such as VA, tertiary acid 911, versatile acid such as VERSATIC 10, and tertiary fatty acids typified by versatile acid, higher fatty acids such as isocaprylic acid, and the like.

Particularly, water-insoluble fatty acids used for back-extraction of rare earths, which may have a low acid concentration, particularly naphthenic acid, are preferable because the presence of zinc ions at the time of extraction significantly improves the extraction efficiency of europium.

Since the active ingredient as described above is a liquid with high viscosity,
In order to facilitate the extraction operation, it is usually diluted with an organic medium and used as an extraction solvent. Examples of the organic solvent include petroleum fractions such as kerosene, aliphatic hydrocarbons such as hexane, octane and decane, ethers such as dibutyl ether and diisopropyl ether, alcohols such as n-hexanol, benzene and toluene. , Aromatic hydrocarbons such as xylene and diethylbenzene,
The concentration of the cation exchange liquid as the active ingredient is 0.001 to 2 mol /
It is preferable to use it as a solution of 1, preferably 0.05 to 1.5 mol / l.

The aqueous solution containing zinc may be any aqueous solution containing divalent zinc ions. Usually, a soluble zinc compound such as zinc, zinc oxide, zinc chloride, zinc bromide, zinc iodide, zinc sulfate, zinc nitrate, etc., in particular, zinc, zinc oxide, zinc chloride dissolved in a strongly acidic aqueous solution is used. However, it is preferable to re-prepare and use an aqueous solution containing zinc recovered in the subsequent zinc separation step (d) and others, and the zinc concentration of the aqueous solution used is not particularly limited and can be appropriately determined. The amount of zinc extracted into the cation exchange liquid is such that when the europium-containing inorganic acid aqueous solution supplied in the next separation step (b) contains zinc, the amount of zinc extracted is the same as that of europium 1 in order to exert the effect of zinc. The amount is preferably 5 mol or less, more preferably 10 mol or more, and if it is too large, a large amount of acid is required for the separation of zinc and rare earth or europium.

Incidentally, for zinc extraction, it is preferable to add an alkali metal hydroxide or alkali such as ammonia in advance to the cation exchange liquid for pH adjustment depending on the type of the cation exchange liquid used, such as naphthenic acid. In the case of the fatty acid of, it is preferable to add an alkali equivalent to 2.7 to 3.6 mol times with respect to the total rare earth in the inorganic acid aqueous solution containing europium etc. to be supplied to the subsequent separation step (b). Zinc is extracted by the following equilibrium equation. However, in the following formula, the cation exchange liquid is represented by HX, the zinc-containing aqueous solution is an aqueous solution of zinc chloride, and ammonia is used as the alkali, and the compound with (O) is mainly distributed to the organic phase. Is.

H × (O) + NH ₄ ⁺ NH ₄ × (O) + H ⁺ 2NH ₄ × (O) + ZnCl ₂ ZnX ₂ (O) + 2NH ₄ Cl Next, in the separation step (b), divalent europium and 3 other than europium Aqueous inorganic acid containing divalent rare earth is brought into contact with the cation exchange liquid extracted with zinc in the zinc extraction step (a) to extract into an aqueous phase rich in europium and a cation exchange liquid rich in rare earths other than europium. To separate.

Used divalent europium and 3 other than europium
The inorganic acid aqueous solution containing divalent rare earth is an inorganic acid salt such as chloride, sulfate or perchlorate of a raw material rare earth mixture containing divalent europium and other trivalent rare earth, particularly inorganic chloride. It can be obtained by a method such as reducing an aqueous acid solution to reduce europium to a divalent state.

Specifically, ores such as monazite and bastnaesite,
Or, other rare earths, especially light rare earths, can be obtained by conventional solvent extraction or ion exchange method using a raw material having a europium content of 1% or less, which is obtained from a residue obtained by obtaining a cerium group mixed rare earth metal from these ores. Isolate the soil (lanthanum, cerium) and increase the concentration of europium in the rare earth as much as possible. In the conventional method such as solvent extraction, samarium,
Since separation from gadolinium is difficult, industrially a rare earth mixture of europium, samarium and gadolinium is used as an aqueous solution of an inorganic acid in which each rare earth is trivalent. The concentration of this trivalent rare earth mixture in the inorganic acid aqueous solution is
If it is too low, a large apparatus is required for the following operations, which is not industrially advantageous. Therefore, the europium concentration (as oxide) should be 0.01 g / l or more, preferably 0.1 g / l or more. .

The aqueous solution of the raw material rare earth mixture containing trivalent europium is reduced to make europium in a divalent state. The reduction method may be a method using a reducing agent, an electrolytic reduction method or the like, but since the present invention uses zinc during the subsequent separation, zinc or zinc alloy such as zinc amalgam, particularly zinc powder,
It is preferable to use a fixed bed or the like.

The inorganic acid aqueous solution of the rare earth mixture containing trivalent europium supplied to the reduction reaction has a pH of 0.5 to 6, preferably 0.8 to 3.
It is good to adjust to. If the pH is too low, the zinc reduction efficiency will decrease, and if it is too high, the rare earth components will precipitate as hydroxides, which is not preferable.

The reduction reaction is usually carried out in a state where oxygen is eliminated by bubbling an inorganic acid aqueous solution of a rare earth mixture with an inert gas such as nitrogen and sealing the atmosphere with an inert gas.For example, when using zinc powder, an aqueous solution is used. It is advisable to add zinc powder in an amount of 3 to 20 times equivalent to that of europium under stirring, and mix for 3 minutes or more, preferably 10 minutes or more.

The resulting inorganic acid aqueous solution containing divalent europium and other trivalent rare earths is removed as it is, or when solid zinc remains, it is removed separately, and then the zinc extraction step (a) Contact with a cation exchange liquid containing zinc obtained from.

The amount of the cation exchange liquid used is selected such that the amount of the active ingredient in the extraction solvent diluted with the organic solvent is 6 times or more, preferably 8 to 80 times the molar amount of the rare earth other than europium. Is good. If the amount of the active ingredient is too small, the separation of europium and rare earth other than europium will be insufficient. On the contrary, even if it is used excessively, no special effect can be expected, and a large device is required, which is not a good idea.

This cation exchange liquid can be supplied to the separation step (b) as it is or when an alkali such as an alkali metal hydroxide or ammonia is added in the zinc extraction step (a) or by adding an alkali. Even in the case where no alkali is added in the zinc extraction step (a), alkali can be added before the contact in the separation step (b) to improve the purity of europium transferred to the aqueous phase.

In the extraction / separation operation of the present invention, it is desirable to exclude oxygen in order to avoid the oxidation of divalent europium during the operation, and an inert gas such as nitrogen is added to the aqueous solution of the rare earth mixture and the cation exchanger. It is advisable to introduce and deoxidize it before use, and to introduce an inert gas such as nitrogen into the separator to deoxidize it.

From the above separation operation, an aqueous phase mainly containing divalent europium and divalent zinc and a cation exchange liquid mainly containing trivalent rare earth other than europium are obtained.

Since the divalent europium in the obtained aqueous phase is easily oxidized, oxygen, oxygen-containing gas such as air, europium such as hydrogen peroxide can be oxidized in the aqueous solution in the oxidation step (c), and zinc is Using a compound which cannot be oxidized, europium is trivalently oxidized by a known method such as stirring.

Subsequently, in the zinc separation step (d), this aqueous solution is brought into contact with a cation exchange liquid to extract trivalent europium into a cation exchange liquid to obtain a cation exchange liquid rich in europium, and leave zinc in the aqueous solution. The zinc-rich aqueous phase is separated off, which makes it easy to obtain europium.

The cation exchange liquid supplied to the zinc separation step (d) can be the same cation exchange liquid as that used in the zinc extraction step (a) and the separation step (b). 6 times or more, preferably 8 to 80 times by mole, preferably in the presence of alkali metal hydroxide, ammonia or the like, and more preferably 2.7 times with respect to europium.
Contact is performed in the presence of ~ 3.6 mol times alkali.

The obtained zinc-rich aqueous phase can be used as it is, preferably by adjusting the zinc concentration, as an aqueous solution containing zinc in the zinc extraction step (a). Moreover, the cation exchange liquid rich in rare earths other than europium obtained in the separation step (b) usually elutes divalent zinc contained to some extent by a dilute acid such as dilute hydrochloric acid having a concentration of 0.001 to 0.01 mol / l. After removal, the residual rare earth can be extracted and separated with a high concentration of acid, and the aqueous solution containing zinc obtained at this time is also circulated as part of the aqueous phase of the zinc extraction step (a) or separation step (b). Can be made.

Each of the steps (a), (b), (d), etc. of the method of the present invention described above can be carried out by any apparatus used for ordinary liquid-liquid extraction, and single or multistage extraction is also possible, for example, mixer settler. It is possible to use a combination of a stirring tank typified by 1 and a stationary separation tank.

〔The invention's effect〕

According to the method of the present invention, the separation efficiency between divalent europium and other trivalent rare earths can be significantly improved by intentionally allowing zinc ions to be present, and the separation efficiency can be improved even when the separation conditions such as the addition of alkali change. Change is small, a stable separation operation can be easily performed, and an aqueous solution of a rare earth mixture as a raw material can be directly supplied to an extraction step, which facilitates recovery and reuse of zinc ions. It is industrially excellent as a method for separating europium, which is desired to be converted into.

〔Example〕

 Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1 A europium separation experiment was continuously conducted based on a system diagram showing one example of the method of the present invention shown in FIG.

A 13N-ammonia solution (12) was added to a sorbetso (lower alkylbenzene mixture manufactured by Etsuso Co.) solution (11) containing naphthenic acid at a concentration of 1 mol / l as a cation exchange solution.
Zinc introduced from (13) 0.23 by supplying 4l / hr to the zinc extractor (1) by mixing the mixture of 0.018 l / hr
6 l / hr of water containing mol / hr was countercurrently contacted with a zinc extractor (1) consisting of a three-stage countercurrent mixer / settler to bring the aqueous phase into (1
From 4), a cation exchange liquid containing 0.12 mol / hr of zinc was extracted from (15) and degassed with nitrogen gas.

Trivalent europium 0.0069 mol / l Trivalent samarium 0.
After degassing an aqueous solution containing 025 mol / l with nitrogen, it is reduced with zinc powder to obtain an inorganic acid aqueous solution containing divalent europium, trivalent amarium and 0.015 mol / l divalent zinc. Obtained. The cation exchange liquid extracted from the above (15) was used in the first stage of the separator (2) consisting of a seven-stage mixer-settler, and in the seventh stage, from the above inorganic acid aqueous solution and (17) from the above (16). The aqueous phase obtained from the zinc recovery unit (3) described below is introduced, the europium-rich aqueous phase (18) is extracted from the first stage, and the samarium-rich cation exchange liquid (19) is extracted from the seventh stage. It was

The cation exchange liquid (19) was contacted with 0.9 N / hydrochloric acid (20) 0.9 l / hr deaerated with nitrogen in the zinc recovery unit (3) to remove zinc, and then from (21). It was introduced into the samarium back extractor (4) and countercurrently contacted with 2H-hydrochloric acid (22) 0.9l / hr to extract the aqueous phase containing samarium etc. from (23),
The extracted cation exchange liquid was circulated again from (11) to the zinc extractor (1).

In addition, the water phase extracted from (23) contained samarium 0.04
It contained 9 mol / hr, europium 0.0005 mol / hr and zinc 0.03 mol / hr.

Further, the europium-rich aqueous phase (18) is air-oxidized in the oxidation reactor (5), and from (24), a five-stage mixer
Introduced into a zinc separator (6) consisting of a settler, 2-ethylhexylphosphonic acid mono-2 as a cation exchange liquid.
-Solvetso solution (25) containing 1 mol / l of ethylhexyl ester was brought into countercurrent contact with 4 l / hr of 13N-ammonia water (26) combined with 0.004 l / hr, and a cation exchange liquid rich in europium from (27) And an aqueous phase rich in zinc (containing zinc at 0.112 mol / hr) was extracted from (28). The extracted cation exchange liquid was introduced into the europium back extractor (7) and brought into countercurrent contact with 2N-nitric acid supplied from (29) to convert europium or the like from (30) as an aqueous phase. The cation exchange liquid after extraction and back extraction was washed with water and then circulated again to the zinc separator (6). The aqueous phase extracted from (30) is europium 0.0133 mol / hr, samarium.
It contained 0.001 mol / hr and zinc 0.008 mol / hr.

Further, the zinc-rich aqueous phase extracted from (28) is supplied to the zinc preparation device (8), and the zinc concentration is adjusted together with the aqueous phase extracted from (14) above (13). The zinc-containing water was supplied to the zinc extractor (1).

From the above results, the europium yield based on the following formula is 96.2
%, The loss rate was 3.8%. Even when continuously operated, the europium yield could be stably separated within the range of 96 ± 2%.

Comparative Example 1 The procedure of Example 1 was repeated except that the zinc extractor (1), the oxidation reactor (5) and the subsequent steps were omitted, and the europium yield was 87.0%. The europium loss rate was 13.0%. In addition, continuous operation made it difficult to perform a stable separation operation, and the europium yield fluctuated within the range of 85 ± 10%.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of the method of the present invention. In the figure, (1) is a zinc extractor, (2) is a separator, (3) is a zinc collector, (4) is a samarium back extractor, (5) is an oxidation reactor, (6) is a zinc separator, (7) shows a europium back extractor and (8) shows a zinc preparation device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiharu Shibata 1 2447 Fujita, Hachimansai-ku, Kitakyushu, Fukuoka Prefecture 1 Kurosaki Plant, Mitsubishi Kasei Co., Ltd. (72) Keiko Nishiyama 2447 Fujita, Hachimansai-ku, Kitakyushu, Fukuoka No. 1 Mitsubishi Chemical Industries Kurosaki Plant (56) Reference JP 61-83624 (JP, A) JP 62-252317 (JP, A) JP 61-58533 (JP, B2)

Claims (6)

[Claims] 1. A method for separating europium from an aqueous solution of an inorganic acid containing divalent europium and trivalent rare earths other than europium, wherein (a) zinc is extracted from an aqueous solution containing zinc using a cation exchange liquid. Zinc extraction step, (b) divalent europium and 3 other than europium
Separation step of contacting an aqueous solution of an inorganic acid containing a valent rare earth and a cation exchange solution extracted with zinc to separate an aqueous phase rich in europium and a cation exchange solution rich in rare earth other than europium, ) Oxidation step of oxidizing the europium-rich aqueous phase to make europium trivalent, and (d) contacting the resulting trivalent europium-rich aqueous phase with a cation exchange solution to exchange europium-rich cation. A method for separating europium, which comprises each step of separating zinc into a liquid and a zinc-rich aqueous phase. 2. The zinc-rich aqueous phase obtained in the zinc separation step (d) is recycled as an aqueous solution containing zinc in the zinc extraction step (a).
Separation method of europium described in paragraph. 3. A cation exchange solution rich in rare earths other than europium obtained in the zinc step (b) is brought into contact with a dilute acid to extract zinc contained in the cation exchange solution into a dilute acid. The method for separating europium according to claim 1 or 2. 4. The cation exchange liquid is a water-insoluble fatty acid,
The method for separating europium according to any one of claims 1 to 3, which is an acidic phosphoric acid ester, a phosphonic acid ester, or a solution of these in an organic solvent. 5. The method for separating europium according to claim 4, wherein the cation exchange liquid is a water-insoluble fatty acid or a solution of the fatty acid in an organic solvent. 6. The separation in the separation step (b) is carried out in the presence of 5 mol or more of zinc ions per 1 mol of europium.
The method for separating europium according to any one of the items.