JPH07109015B2 - Method of separating europium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for separating europium,
More specifically, it relates to a method for separating europium from a rare earth mixture containing divalent europium and trivalent rare earth other than europium.

[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 of the above 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]

In the above 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 liquid 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]

The present inventors have made various studies in view of the problems in the separation of divalent europium, and as a result, when zinc or a zinc alloy was conventionally used as a reducing agent for europium, the following reduction reaction 2E _u ³⁺ + Z Divalent zinc ions are inevitably mixed in the solution along with _n → 2E _u ²⁺ + Z _n ²⁺ , but divalent zinc is intentionally added because it must be separated in the end. That was avoided, surprisingly, the presence of a much larger amount of divalent zinc than was previously contained, yields a large amount of europium separated by the cation exchanger, and improves the purity, Further, the inventors have reached the present invention by knowing that the fluctuation of the extraction rate due to the fluctuation of the amount of alkali added becomes small.

That is, the gist of the present invention is a method for separating europium by bringing an aqueous solution of an inorganic acid containing divalent europium and a trivalent rare earth other than europium into contact with a cation exchanger to separate europium from 1 mol of europium. The method for separating europium is characterized in that it is carried out in the presence of 5 mol or more of divalent zinc ions.

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.

The inorganic acid aqueous solution containing divalent europium and trivalent rare earths other than europium used in the present invention is a chloride, sulfate or peroxide of a raw material rare earth mixture containing trivalent europium and other trivalent rare earths. It can be obtained by a method of reducing an inorganic acid salt such as a chlorate, especially an inorganic acid aqueous solution of chloride to reduce europium to a divalent state.

Specifically, ores such as monazite and bastnaesite,
Or other rare earths, especially light ones, can be obtained by conventional solvent extraction or ion exchange method using a raw material having a europium content of 1% or less obtained from a residue obtained from a cerium group mixed rare earth metal from these ores. The rare earth (lanthanum, cerium) is separated to increase the europium concentration in the rare earth as much as possible. Since it is difficult to separate samarium and gadolinium by a conventional method such as solvent extraction, 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. If the concentration of the inorganic acid aqueous solution of this trivalent rare earth mixture is too low, a large apparatus is required for the following operation, which is not industrially advantageous, so the concentration of europium (oxide conversion) is 0.01 g / or more, Preferably 0.1 g /
The above is preferable.

Then, 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 in the subsequent separation, zinc or zinc alloy such as zinc amalgam, particularly zinc powder, fixed bed, etc. Is preferably used.

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 obtained inorganic acid aqueous solution containing divalent europium and other trivalent rare earths is removed as it is, or when solid zinc or the like remains, it is removed as a cation exchanger. The europium is separated by bringing them into contact with each other to collect the trivalent rare earth in the cation exchanger and leaving the divalent europium in the aqueous solution.

The present invention is characterized in that this separation is carried out in the presence of a specific amount of divalent zinc ions.

The divalent zinc ion may be contained in either one or both of the cation exchanger and the aqueous solution containing the divalent europim, etc., if it exists during the separation. They may be mixed during the operation of contacting the cation exchanger with the above aqueous solution. Examples of the zinc ion source include zinc, zinc oxide, zinc chloride, zinc bromide, zinc iodide, zinc sulfate, zinc nitrate, etc., but other impurities are not introduced into the system, and divalent europium is used. Zinc, zinc oxide, zinc chloride and the like are preferable because they do not oxidize. These mixing methods are a method in which a cation exchanger is used to extract zinc in advance,
A method in which an aqueous solution containing a rare earth is made strongly acidic and zinc chloride, zinc oxide, zinc, etc. are dissolved, and an aqueous solution in which zinc chloride, zinc oxide, zinc, etc. are dissolved are added at any stage until the separation operation, etc. However, the present invention is not limited to these.

In the conventional method for reducing europium with zinc or a zinc alloy, divalent zinc ions were eluted up to about 3 to 4 mol per mol of divalent europium. In order to play, 5 mol or more per 1 mol of europium, including the elution amount associated with the reduction,
In particular, it is necessary to contain 10 mol or more. If it is too large, a large amount of acid is required to separate zinc from rare earth or europium. Therefore, it is preferably 100 mol or less.

As the cation exchanger used for the separation of divalent europium and other trivalent rare earths, any of the well-known ones used for extracting rare earths can be used. Specifically, di-2-ethylhexyl phosphate can be used. , 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 alkyl group having 6 to 30 carbon atoms such as ethylhexyl ester, naphthenic acid 180, naphthenic acid 230
Liquid cation exchangers such as tertiary fatty acids typified by versatiic acid such as naphthenic acid, versatile acid 911, versatile acid 10 and higher fatty acids such as isocaprylic acid, and particularly used for back extraction of rare earths. Preference is given to using water-soluble fatty acids, which may be low in acid, especially naphthenic acid. The effect of the present invention is particularly remarkable when this fatty acid is used.

Since the cation exchanger as described above is a liquid with high viscosity, it is usually diluted with an organic solvent and used as an extraction solvent in order to facilitate the extraction operation. 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. , Xylene,
Aromatic hydrocarbons such as diethylbenzene are listed, and the concentration of the cation exchanger as an active ingredient is 0.001 ~
It is preferable to use it as a 2 mol / solution, preferably 0.05 to 1.5 mol / solution.

The amount of the extraction solvent used is preferably selected so that the amount of the active ingredient in the extraction solvent is 6 times or more, and preferably about 8 to 80 times the mole of the rare earth other than europium. 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.

The method for separating europium and other rare earths by a cation exchanger is not limited to the liquid-liquid extraction with the above-mentioned extraction solvent, and the liquid cation exchanger is impregnated into the porous polymer to obtain the polymer. Can also be carried out by contacting with an aqueous solution containing a rare earth element such as europium, or by using an ion exchange resin having the same functional group as the cation exchanger.

When separating with a cation exchanger, the pH of the extraction is controlled, the extraction rate is improved, and the separation of europium and other rare earths is efficiently performed. It is also possible to add it to the aqueous inorganic acid solution or the extraction solvent of the rare earth mixture at any time. The amount of this alkali metal hydroxide or ammonia used can increase the purity of europium if it is too much, but europium also migrates to the cation exchanger side, taking into consideration that the yield of europium decreases. To decide. In particular, it is preferable to appropriately determine the amount depending on the cation exchanger used.

In the 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 introduced into the aqueous solution of the rare earth mixture and the cation exchanger. Then, it is preferable to deoxidize by using an inert gas such as nitrogen also in the separator.

The aqueous solution obtained by the above separation operation contains divalent europium and divalent zinc, and the divalent europium is easily oxidized. Therefore, oxygen, oxygen-containing gas such as air, and peroxide are contained in the aqueous solution. Europium, such as hydrogen oxide, which can oxidize europium but not zinc, is trivalently oxidized by a known method such as stirring, and the aqueous solution is brought into contact with a cation exchanger to form trivalent europium. Europium can be easily obtained by collecting the cation in a cation exchanger and leaving zinc in the aqueous solution.

Further, the cation exchanger containing a rare earth element other than europium, which is obtained from the separation operation, usually has a concentration of 0.001 to 0.01 mol.
The divalent zinc contained to some extent can be eluted with a dilute acid such as / dilute hydrochloric acid, and then the remaining rare earth can be extracted with a high concentration of acid.

〔The invention's effect〕

According to the method of the present invention, by mixing a specific amount of a specific metal ion, the separation efficiency between divalent europium and other trivalent rare earths can be significantly improved, and the separation conditions such as pH change can also be changed. Since the change in separation efficiency is small and a stable separation operation can be easily performed, the present invention provides an industrially excellent method for separating europium for which high purification is desired.

〔Example〕

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

Examples 1 to 3 and Comparative Example 1 300 ml of a hydrochloric acid solution containing 0.0038 mol of europium and 0.15 mol of samarium and gadolinium in total as trivalent ions was prepared. In the acidic hydrochloric acid solution in which zinc chloride (ZnCl ₂ ) was dissolved, divalent zinc ion was 4.9 mol times (Example 1), 9.9 mol times (Example 2), and 19.7 mol times relative to Europium (implementation). Example 3) was added, the pH was adjusted to 1 with aqueous ammonia, and the mixture was stirred in the presence of zinc powder in the state of eliminating oxygen with nitrogen to divalently reduce europium and then remove zinc powder. did.

On the other hand, Solvesso (lower alkylbenzene mixture manufactured by Esso Co.) 1 containing naphthenic acid at a concentration of 1 mol /
A specific amount of aqueous ammonia was added, and each of the obtained organic solvents was brought into contact with the reduced aqueous solution under liquid-liquid stirring under nitrogen. Subsequently, the aqueous phase and the organic phase are separated, the organic phase is contacted with 200 ml of 0.01 mol / dilute acid under nitrogen,
The organic phase was washed.

The amount of europium extracted on the organic phase side was measured, and the europium loss rate obtained by the following formula is shown in FIG. The horizontal axis of FIG. 1 represents the amount of ammonia added to all rare earths (molar ratio) at the time of extraction, and the vertical axis (left side) represents the europium loss rate. The results of Examples 1 to 3 in the figure are shown by solid lines 1 to 3 Shown in each. In addition, as Comparative Example 1, a solid line 4 shows the result obtained in the same manner except that the aqueous solution containing divalent zinc ions was not added. In this comparative example, the amount of zinc ions eluted along with the reduction of europium was 2.6 mol per 1 mol of europium.

Further, the amounts of samarium and gadolinium extracted on the organic phase side in Example 2 were measured, and the samarium or gadolinium extraction ratios are shown in FIG. 1 by the following formulas as dotted lines 5 and 6, respectively.

The europium loss rate is preferably low, and the samarium extraction rate and gadolinium extraction rate are preferably high. From the graph, it can be seen that the example can more stably separate europium than the comparative example 1.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the relationship between the ammonia addition amount (horizontal axis) and the europium loss rate, samarium extraction rate, and gadolinium extraction rate (vertical axis) in Examples 1 to 3 and Comparative Example. is there.

Front page continuation (72) Inventor Toshiharu Shibata 2447, Fujita, Hachimansai-ku, Kitakyushu, Fukuoka Prefecture 1 447, Kurosaki Plant, Mitsubishi Chemical Industries (72) Keisuke Nishiyama 1447, Fujita, Hachimansai-ku, Kitakyushu, Fukuoka Kurosaki Plant, Mitsubishi Kasei Co., Ltd. (56) References Japanese Patent Publication No. S23-23460 (JP, B1)

Claims (3)

[Claims] 1. A method for separating europium by bringing an aqueous solution of an inorganic acid containing divalent europium and a trivalent rare earth other than europium into contact with a cation exchanger.
The above-mentioned separation is carried out with 5 mol or more of 2 per 1 mol of europium.
A method for separating europium, which is characterized in that it is carried out in the presence of divalent zinc ions. 2. An inorganic acid aqueous solution containing divalent europium and a trivalent rare earth other than europium is a solution of an inorganic acid aqueous solution containing trivalent europium and a trivalent rare earth other than europium by zinc or a zinc alloy. The method for separating europium according to claim 1, wherein the method is a reduction treatment. 3. The cation exchanger is a water-insoluble fatty acid,
The method for separating europium according to claim 1 or 2, which is an acidic phosphoric acid ester or a phosphonic acid ester.