JPH0734151A - Extraction agent for rare earth metal and method for separating and refining rare earth metal - Google Patents

Abstract

PURPOSE:To provide a method for separating and refining rare earth metals, in which the separation factor of every adjacent rare earth elements from each other is large and the rare earth metals can be back-extracted with a dilute mineral acid and no gelation occurs even when the amount to be extracted is large, by specifying an acid phosphate compound used for extracting rare earth metals with the solvent exraction from an aqueous solution contg. them. CONSTITUTION:An extractant contg. an acid phosphoric ester represented by the general formula as the extraction agent is brought into liquid-liquid contact with an aqueous solution contg. rare earth metals and the pH of the aqueous solution is appropriately adjusted to separate desired one or several of the rare earth metals from the other rare earth metals. Then the extracted rare earth metals in the extractant are back-extracted by allowing the extractant contg. the extracted rare earth metals to contact with another aqueous solution having a lower pH than that of the aqueous solution used at the time of extracting the rare earth metals. The above acid phosphoric ester is generally used as a 5 to 70vol.% solution obtained by diluting it with an organic diluent. As the effective diluent, an aliphatic or aromatic hydrocarbon having a high flash point, etc., can be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an extractant for efficiently solvent-extracting one or several kinds of target rare earth metals from an aqueous solution containing rare earth metals, and a method for separating and purifying rare earth metals.

[0002]

2. Description of the Related Art Conventionally, a solvent extraction method has been widely used as a method for obtaining a rare earth metal, and many reagents have been developed as an extracting agent therefor. Among them, di (2-ethylhexyl) phosphoric acid ( D2EHPA) and 2
Acidic phosphorus compounds such as -ethylhexylphosphonic acid mono-2-ethylhexyl ester (MEHPNA) have been widely used. However, even if these extractants are used, the separation coefficient between rare earth metals is not very satisfactory, and it is quite difficult to separate neodymium / praseodymium, samarium / gadolinium / europium, and erbium / yttrium / holmium. It was accompanied by. Moreover, these extractants have relatively low extraction p
Since it occurs in the H region, a large amount of mineral acid was required to back-extract and recover the extracted rare earth metal, and a large amount of alkali was required to neutralize this free acid. Further, with these extractants, when the amount of metal extracted becomes large, polymerization of the extracted metal complex occurs, and a gel insoluble in an organic solvent is generated, which makes it difficult to operate smoothly in a mixer-settler. was there. Therefore, for the separation and purification of rare earth metals, 1) the mutual separation coefficient of adjacent elements is large, 2) the back extraction can be performed with a mineral acid having a high pH and a relatively low concentration for the extraction, and 3 ) It has been desired to develop an extractant that does not cause gelation even when the amount of extracted metal increases.

The present invention provides an extractant for extracting a target rare earth metal from an aqueous solution containing a rare earth metal and a method for separating and purifying a rare earth metal using the extractant capable of achieving the above object. To aim.

[0004]

[Means for Solving the Problems] That is, according to the present invention, an extractant used for solvent extraction of a target rare earth metal from an aqueous solution containing the rare earth metal, comprising:

An extractant for a rare earth metal represented by the general formula of Formula 1 is provided,

[Formula 1] Also,

By bringing an extraction solvent containing an acidic phosphoric acid ester represented by the general formula represented by the formula 1 as an extractant into liquid-liquid contact with an aqueous solution containing a rare earth metal, and appropriately adjusting the pH of the aqueous solution, A method for extracting a rare earth metal for separating one or several kinds of desired rare earth metals from other rare earth metals, and an aqueous solution containing the rare earth metal

By subjecting an extraction solvent containing an acidic phosphoric acid ester represented by the general formula represented by [Formula 1] as an extractant to liquid-liquid contact and appropriately adjusting the pH of the aqueous solution, one or several kinds of the objective The rare earth metal is separated from other rare earth metals, and an extraction solvent containing the rare earth metal is brought into contact with an aqueous solution having a pH lower than that at the time of extraction to separate and purify the rare earth metal. The above-mentioned object is achieved by the above-mentioned provision.

In the present invention, the extractant represented by the above general formula is generally diluted to 5 to 70% by volume and used. Effective diluents include high flash point aliphatic or aromatic hydrocarbons, but may also be halogenated hydrocarbons, higher alcohols, ethers, esters, or mixtures thereof. Good.

In the extraction, the selection of the conditions is particularly important for the pH during the extraction and the back extraction. That is, in order to extract one or only a desired metal from an aqueous solution, or to extract a desired metal from a metal once extracted.
PH of aqueous solution to back-extract species or only a few species
Need to be adjusted. As a method of adjusting the pH at the time of extraction, it can be performed by adding a mineral acid or an alkaline agent to the aqueous solution in advance. Alternatively, it may be carried out by previously preparing an alkaline salt in an appropriate ratio as the extractant. As the alkaline agent, ammonium ion,
Alkali metal ion hydroxides and carbonates can be used.
As the mineral acid, hydrochloric acid, sulfuric acid, nitric acid or the like can be used.

The acidic phosphoric acid ester represented by the above general formula used in the present invention undergoes extraction at a pH as high as 1 to 3 as compared with the conventionally used D2EHPA and MEHPNA, and therefore pH at which back extraction occurs. Since it is higher than the conventional one, it has a feature that the amount of mineral acid required for back extraction can be kept low.

[0008]

EXAMPLE 1 Examples of the present invention are shown below, but these examples do not limit the present invention. In addition, this Example shows a synthesis example of bis (4-cyclohexylcyclohexyl) phosphoric acid which is an extractant according to the present invention.
The extraction agent bis (4-cyclohexylcyclohexyl) phosphoric acid is

[Formula 2] as well as

[Formula 3] Was synthesized according to the reaction formula of. Note that R is

[Formula 4] Is shown in.

[0009]

[Formula 2]

[0010]

[Formula 3]

[0011]

[Formula 4]

12.5 g of phosphorus trichloride was prepared by dissolving 51.6 g of commercially available 4-cyclohexylcyclohexanol and 18.5 g of triethylamine in 200 ml of anhydrous benzene.
Was dissolved in 200 ml of anhydrous benzene at room temperature for 5
After dropping over a period of time, the mixture was heated under reflux in a nitrogen atmosphere for 16 hours. After completion of the reaction, the mixture was shaken with 1N sulfuric acid and then with water, the organic phase was taken out, dehydrated with anhydrous sodium sulfate and filtered, and then benzene and by-product cyclohexylcyclohexyl chloride were distilled off under reduced pressure to give an intermediate. Bis (4-cyclohexylcyclohexyl) phosphite was obtained. The intermediate phosphite was dissolved in a mixture of potassium permanganate and 250 ml of a supersaturated aqueous solution of acetone, and the mixture was heated under reflux in an oil bath for 48 hours. After the reaction was completed, ethanol was added, suction filtration was performed, and acetone and ethanol were distilled off under reduced pressure. The remaining residue was dissolved in 300 ml of benzene, and the mixture was shaken in the order of water, a mixed solution of 1N sulfuric acid and hydrogen peroxide solution, and water. The organic phase was taken out and dehydrated with anhydrous sodium sulfate, benzene was distilled off under reduced pressure, and the residue was recrystallized twice in ethyl acetate to give the final product bis (4-).
Cyclohexylcyclohexyl) phosphoric acid was obtained. The final product is a white powder having a melting point of 193-200 ° C. and a purity of 93.
%Met. The yield was 47%.

[0013]

[Embodiment 2] This embodiment shows an example of extracting rare earth metals. Using a toluene solution containing bis (4-cyclohexylcyclohexyl) phosphoric acid synthesized in the above example at a concentration of 0.01 ml, several kinds of sodium nitrate having a concentration of about 1 mol / l and an initial concentration of 0.00014 mol / l were prepared. O / A with an aqueous solution containing a rare earth metal at 30 ° C.
Extraction was performed by shaking at a ratio of 1: 1. The relationship between the partition coefficient at that time and the pH after extraction

[Table 1] as well as

FIG. 1 shows. Here, the partition coefficient is the ratio between the metal concentration of the organic phase after extraction and the metal concentration remaining in the aqueous phase.

[0014]

[Table 1]

The separation coefficient between several kinds of rare earth metals when extraction was carried out with bis (4-cyclohexylcyclohexyl) phosphoric acid used in the present invention, was calculated using the existing extractant D2EHPA (TBPierce and PFPeck, Analyst,
88, 217 (1963)) and bis (4-ethylcyclohexyl) phosphoric acid, which is a novel extractant previously proposed by the present inventors (JP-A-4-131331 and JP-A-4-13408).
It is shown in Table 2 in comparison with 7). Here, the separation coefficient is a ratio of the distribution coefficients of two kinds of metals under the same conditions, and is a value that is an index of difficulty when the two kinds of metals are separated from each other by solvent extraction.

[0016]

[Table 2]

Compared with D2EHPA, the separation coefficient between yttrium and ytterbium in heavy rare earth is slightly smaller,
Also heavy rare earth yttrium / holmium, medium rare earth gadolinium / samarium, and light rare earth praseodymium /
Separation coefficients between cerium are almost the same, but holmium / gadolinium, samarium / neodymium, cerium /
The separation factor of lanthanum is significantly higher. Also,
It can be seen that the separation coefficient between neodymium and praseodymium, which is said to be the most difficult to separate among the rare earth metals, is improved by about 10%.

[0018]

Industrial Applicability According to the present invention as described above, an extractant capable of efficiently separating and purifying a target rare earth metal can be obtained, and a separating, purifying method and a back-extracting method using the extractant can be obtained. In addition, since the separation coefficient between rare earth metals can be made large and the extraction takes place in a relatively high pH region, it is possible to back-extract with a relatively low-concentration mineral acid, and even if the amount of extracted metal increases This has the effect that no change occurs.

[Brief description of drawings]

FIG. 1 is a relationship diagram showing an influence of a pH of an aqueous phase on a distribution ratio D in an example of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Norio Nakaji Ebisu Building, 2-chome, Nakamachi, Omuta City, Fukuoka 406 (72) Inventor Takashi Hashida 210 Shirokanemachi, Omuta City, Fukuoka Prefecture 202 Shirokane Heights No. 202 (72) Inventor Koki Domoto 247-6 Miike, Omuta City, Fukuoka Prefecture

Claims (3)

[Claims] 1. An extractant used for solvent extraction of a target rare earth metal from an aqueous solution containing the rare earth metal, comprising: An extractant for rare earth metals represented by the general formula: [Formula 1] 2. An aqueous solution containing a rare earth metal is brought into liquid-liquid contact with an extraction solvent containing an acidic phosphoric acid ester represented by the general formula represented by the formula as an extractant, and the pH of the aqueous solution is appropriately adjusted. A method for extracting a rare earth metal, in which one or several kinds of target rare earth metals are separated from other rare earth metals by adjusting. 3. An aqueous solution containing a rare earth metal is brought into liquid-liquid contact with an extraction solvent containing an acidic phosphoric acid ester represented by the general formula represented by the formula as an extractant, and the pH of the aqueous solution is adjusted appropriately. By adjusting, one or several kinds of the target rare earth metal is separated from the other rare earth metal, and the rare earth metal-containing extraction solvent is contacted with an aqueous solution having a pH lower than that at the time of extraction to obtain the rare earth metal. Method for separating and purifying rare earth metals by back-extracting.