JPH0134933B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for separating rare earth elements.
Specifically, the present invention relates to an industrially advantageous method for separating rare earths from an aqueous solution containing rare earths by a liquid-liquid extraction method. As a method for separating rare earths from an aqueous solution containing rare earths by a liquid-liquid extraction method, a multistage countercurrent extraction device in which multiple extraction separation units consisting of a stirring tank and a static separation tank are connected in series is used. The extraction agent is supplied to the first stage of the device, the acidic scrubbing liquid is supplied to the final stage, and the rare earth-containing raw material aqueous solution is supplied to the intermediate stage between the first stage and the final stage, and an alkali is added to the extraction system. The extractant selectively extracts specific rare earths from the raw material aqueous solution while adjusting the pH using
The extractant containing the specific rare earth is introduced from the final stage, and the aqueous phase containing the remaining rare earth is introduced from the first stage.
Methods for extracting each are known (for example,
(Refer to Japanese Patent Application Laid-open No. 122836/1983). The addition of alkali is to neutralize the acid liberated by the contact between the extraction agent and the rare earth aqueous solution and adjust the pH of the extraction system to a value corresponding to the rare earth to be separated. In this method, the entire required amount of alkali is added to the first stage along with the extraction agent. The extractant used in this extraction method is known to be an extractant containing di-2-ethylhexyl phosphoric acid as an active ingredient, and the alkali is aqueous ammonia, and the scrubbing liquid is an extractant containing rare earth elements. It is known to use a dilute mineral acid aqueous solution for cleaning and removing rare earths other than the target rare earths contained in the mineral. In the above extraction method, when using an extractant containing di-2-ethylhexyl phosphate as an active ingredient,
Rare earths can be separated efficiently, and even if there are slight fluctuations in the flow rate or concentration of the rare earth-containing raw material aqueous solution, extractant, alkali, or scrubbing liquid, the yield and purity of the target rare earths will not be affected. This allows for stable operation. However, when using an extractant containing di-2-ethylhexyl phosphate as an active ingredient, rare earths are removed from the extractant containing rare earths by back extraction.
It is necessary to use a highly concentrated aqueous acid solution. To obtain rare earths from the back oil solution containing rare earths obtained by back extraction, the rare earths are precipitated as hydroxides by neutralization, but when this method is used, the acid concentration of the back extraction solution is high. The disadvantage is that there is a large loss of acid. As an extractant that can perform back extraction by using an acid aqueous solution with a relatively low concentration, an alkylphosphonic acid monoalkyl ester such as 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester is used as an active ingredient. Extraction agent or di-[7,7-dimethyl-2-(3',3'-dimethyl-
Extractants containing higher dialkyl phosphates such as 1'-methylbutyl)-5-methyloctyl phosphoric acid as an active ingredient are known. However, when these extractants are used in the above extraction method, the extraction efficiency of these extractants is easily affected by pH, so it is necessary to strictly control the pH of the extraction system, that is, the amount of alkali added. However, in industrial equipment, this control is generally extremely difficult because the quantitative performance of the liquid pump is insufficient. In addition, the extraction efficiency of these extractants depends on the supply amount of extractants and scrubbing liquid, as well as fluctuations in the rare earth composition in the rare earth-containing aqueous solution (variations are generally unavoidable when natural materials are used as raw materials). Due to their susceptibility, combined with the alkali problem mentioned above, the industrial use of these extractants has been problematic, despite the fact that they are easy to back-extract. As a result of extensive research in order to avoid the above-mentioned disadvantages, the present inventors have developed a method for separating rare earths by using specific extractants that are easy to back-extract, and by adding a pH adjustment device to the extraction system. When adding alkali in portions, it is possible to greatly reduce the influence of fluctuations in the amount of alkali on the separation of rare earths, and it is also possible to reduce the influence of fluctuations in the rare earth-containing raw material aqueous solution, scrubbing liquid, extraction agent, etc. Furthermore, the present invention was completed based on the knowledge that this enables an extremely industrially advantageous rare earth separation process that takes advantage of the characteristics of the extractant. That is, the present invention aims to perform industrially advantageous separation of rare earth elements, and this purpose is a multi-stage system in which three or more extraction separation units consisting of a stirring tank and a static tank are connected in series. Using a flow extraction device, an oil agent is supplied to the first stage of the device, a scrubbing liquid is supplied to the final stage, and a rare earth-containing raw material aqueous solution is supplied to the intermediate stage between the first stage and the final stage, and
While adjusting the pH by adding alkali to the extraction system, specific rare earths are selectively transferred from the raw material aqueous solution to the extractant, and the extractant containing the specific rare earths is transferred from the final stage to the extractant from the first stage. In a rare earth separation method in which the aqueous phase containing the remaining rare earths is extracted from each stage, the general formula (In the formula, R ¹ and R ² represent a straight chain or side chain alkyl group having 6 to 20 carbon atoms, and these may be the same or different.) Alkylphosphonic acid monoalkyl ester or general formula (In the formula, R ³ and R ⁴ represent a straight chain or branched alkyl group having 12 to 30 carbon atoms, and these may be the same or different.) Using an extractant containing a higher alkyl phosphate ester as an active ingredient, an alkali for pH adjustment is added in portions to at least two stages from the first stage of the multistage countercurrent extraction device to the middle stage that supplies the aqueous solution of rare earth-containing raw materials. This is achieved by doing. The present invention will be explained in detail below. The rare earth-containing aqueous solution in the present invention is an aqueous solution containing two or more rare earths such as yttrium and lanthanide, or these and other metals,
Examples include aqueous solutions obtained by dissolving naturally occurring ores such as monazite and xenotime, or concentrated rare earths extracted and concentrated from these, in mineral acids such as nitric acid, hydrochloric acid, and sulfuric acid.
The amount is preferably about 0.005 to 2 g atoms/, preferably 0.05 to 1.5 g atoms/. The extraction agent used in the present invention is an extraction agent containing an alkylphosphonic acid monoalkyl ester represented by the general formula [] or a higher dialkyl phosphate ester represented by the general formula [] as an active ingredient, R ¹ and R ² in the general formula [] shown above
Examples include 2-ethylhexyl group, octyl group, dodecyl group, octadecyl group, 7,7-dimethyl-2-(3',3'-dimethyl-1'-methylbutyl)-5-methyloctyl group, etc. , R ¹
and R ² may be of the same type or of different types. In addition, in the general formula [] shown above,
R ³ and R ⁴ include a 2-heptylundecyl group, 7,7-dimethyl-2-(3',3'-dimethyl-1'-methylbutyl)-5-methyloctyl group,
2-octyldodecyl group, 2-nonyltridecyl group, 2-decyltetradecyl group, 2-undecyltetradecyl group, 2-undecylpentadecyl group, 2-dodecylhexadecyl group, 2-tridecylpentadecyl group, 2 -tridecylheptadecyl group, etc., and R ³ and R ⁴ may be the same or different. These alkyl sulfonic acid monoalkyl esters or higher dialkyl phosphate esters are liquids with high viscosity, and therefore are usually used after being diluted with an organic solvent in order to facilitate the extraction operation. Examples of organic solvents 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, etc., and the concentration of the alkylphosphonic acid monoalkyl ester or higher dialkyl phosphoric acid ester is 0.001 to 2.
It is preferable to use it as a solution at a concentration of about 0.05 to 1.5 mol/mol/, preferably about 0.05 to 1.5 mol/mol. The amount of extractant used is usually selected from a range of about 0.1 to 10 times the volume of the rare earth-containing raw material aqueous solution. As a scrubbing liquid, a 0.01-2N aqueous solution of a mineral acid such as nitric acid, hydrochloric acid, or sulfuric acid, preferably 0.05-1N
An aqueous solution of about 0.1
~1 times the capacity is used. In addition, examples of alkali include sodium hydroxide,
an aqueous solution of a caustic alkali, such as potassium hydroxide,
Examples include ammonia water. The amount of alkali used is
Although it varies depending on the composition of the extraction agent and scrubbing liquid, the type of rare earth to be separated, etc., the optimum pH is usually determined by using an amount equivalent to the rare earth to be extracted and the acid in the scrubbing liquid. be selected. When the rare earth-containing raw material aqueous solution contains a free acid, a neutralizing alkali is required in addition to the above-mentioned amount of alkali in order to neutralize the free acid. Alkali for neutralizing free acids may be introduced into the extraction device together with the rare earth-containing raw material aqueous solution, but industrially, the rare earth-containing raw material aqueous solution is neutralized in advance with an alkali to bring the pH to 2-2. It is best to adjust the temperature to about 6 and supply this to the extraction device. The multistage countercurrent extraction device used in the present invention is an extraction separation unit consisting of a stirring tank and a static separation tank, such as a mixer-settler or a device in which such devices are connected in series. ,
Mc Grow Hill Book Company (Mc
Published by Grow-Hill Book Company, Chemical Engineer's Hand Book (Chemical
Engineers' Hand Book), pp. 21-21, Figure 21.
-30 or of the form described as Figure 21-31. The number of stages in the extraction and separation unit may be three or more, but the present invention can achieve great effects when using a multistage countercurrent extraction device with a large number of stages, such as five or more stages. In the present invention, a multi-stage countercurrent extraction apparatus as described above is used, the extraction agent is supplied to the first stage of the apparatus, the scrubbing liquid is supplied to the final stage, and the rare earth is supplied to the intermediate stage between the first stage and the final stage. The extraction operation is carried out while supplying the raw material aqueous solutions containing the raw materials, respectively, and adding alkali for pH adjustment in portions to at least two stages from the first stage to the intermediate stage to which the rare earth-containing raw material aqueous solutions are supplied. The optimum stage for adding alkali exists depending on conditions such as the type of rare earth to be separated and the composition of each feed solution, so it is best to determine it through experiment.
Usually, this purpose is often achieved by adding alkali in portions to the first stage, which supplies the extraction agent, and the intermediate stage, which supplies the rare earth-containing raw material aqueous solution. Any stage between the first stage and the intermediate stage, any stage between the first stage and the intermediate stage and the intermediate stage,
Alternatively, it can be added dividedly to any two stages between the first stage to the intermediate stage, or it can be added dividedly to any three or more stages within the above range. For example, when selectively extracting samarium from a raw material aqueous solution containing a large amount of gadolinium and small amounts of europium and samarium, any stage and intermediate stage between the first stage and the middle stage, or the first stage and Good results can be obtained by adding the alkali in portions to any two stages between the intermediate stages. The amount of alkali added to one stage of alkali addition is 2 to 98% of the total amount of alkali added to the extraction system.
It is best to select from a range of 5 to 95% by weight, preferably about 5 to 95% by weight. The optimum dividing ratio when adding alkali in parts depends on the type of rare earth to be separated, the composition of each supply liquid supplied to the extraction device, and other conditions, and it is difficult to decide uniformly, but for example, 10 To selectively extract gadolinium from a raw material aqueous solution containing about the same amount of gadolinium and samarium by using an extraction device with ~15 stages and adding alkali in portions to the first stage and the middle stage, the first stage It is best to add about 30 to 50% by weight of the total alkali amount to the alkali, and about 70 to 50% by weight to the intermediate stage. In order to separate the alkali, it is preferable to add about 10 to 30% by weight of the total alkali amount to the first stage and about 90 to 70% by weight to the intermediate stage. Addition of alkali may be carried out by providing separate piping to each alkali addition stage, or when adding to the first stage that supplies the extraction agent or the intermediate stage that supplies the rare earth-containing raw material aqueous solution, An alkali may be added in advance to the agent or rare earth-containing raw material aqueous solution. After the extraction operation is performed in this way, the extractant containing the specific rare earth is extracted from the final stage of the multistage countercurrent extraction device, and the remaining aqueous phase containing the rare earth is extracted from the first stage of the same device. . From extractants containing specific rare earth elements, specific rare earth elements can be extracted by back extraction using an aqueous mineral acid solution such as nitric acid, hydrochloric acid, or sulfuric acid with a concentration of 1N or more, preferably about 1.5 to 1.5N. of rare earths as a mineral salt aqueous solution. According to the method of the present invention, when extraction is performed while adding alkali for pH adjustment in portions, compared to a method in which the alkali for pH adjustment is supplied together with the extraction agent to the first stage of a multistage countercurrent extraction device, rare earth-containing raw material Even if there is a fluctuation in the flow rate or concentration of aqueous solution, alkali, extractant or scrubbing liquid, the effect on the separation of rare earths is extremely small, operation management is easy, and rare earths can be separated stably over a long period of time. Moreover, since the amount of alkali used can be reduced, it is extremely advantageous industrially. EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to the following Examples unless the gist of the invention is exceeded. Examples 1 to 5 Using a multistage countercurrent extraction device in which 15 stages of extraction separation units consisting of mixers and settlers were connected in series,
In the first stage, 1.6/hr of an extractant consisting of 1 mol of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester/Solbetsuso 150 (manufactured by Etsuso Chemical Co., Ltd., lower alkylbenzene mixture) solution was added in the 15th stage.
0.1N nitric acid aqueous solution 0.3/hr as scrubbing liquid
In addition, in the seventh stage, a rare earth-containing raw material aqueous solution of PH4 containing 0.00977 mole of samarium nitrate/0.0504 mole of gadolinium nitrate/0.00455 mole of terbium nitrate/0.0217 mole of dysprosium nitrate/and 0.016 mole of yttrium nitrate/1/hr.
At the same time, a 7.98N aqueous sodium hydroxide solution was added to the first stage and the seventh stage at a rate of 0.0154
/hr and 0.0414/hr while dividing supply.
An extraction operation is performed to separate dysprosium and terbium by extracting an extractant containing dysprosium and yttrium from the 15th stage and an aqueous phase containing terbium, gadolinium, and samarium from the 1st stage. Ivy. The residual rate of dysprosium in the resulting aqueous phase and the rate of terbium mixed into the extractant were as shown in Table 1 below. Further, the results when the amount of the aqueous sodium hydroxide solution was changed only in the first stage and when only the seventh stage was changed were as shown in Examples 2 to 9 in Table 1 below.

[Table] However, the residual rate of dysprosium in the aqueous phase and the mixing rate of terbium in the extractant are percentages of dysprosium and terbium in the raw materials, respectively. Comparative Examples 1 to 3 In the extraction operation in Example 1, instead of supplying the 7.98N aqueous sodium hydroxide solution in portions, the extraction operation was performed by supplying it only to the first stage. In order to make the residual rate of dysprosium in the aqueous phase 6.1%, a 7.98N aqueous sodium hydroxide solution is
0.0789/hr was required. The residual rate of dysprosium in the resulting aqueous phase and the rate of terbium mixed into the extractant were as shown in Table 2 below. Further, the results when the amount of the sodium hydroxide aqueous solution was changed were as shown in Table 2 below.

[Table] Examples 6 to 10 Using a multi-stage countercurrent extraction device in which 10 stages of extraction separation units consisting of mixers and settlers are connected in series,
In the first stage, di-[7,7-dimethyl-2-(3',
3′-dimethyl-1′-methylbutyl)-5-methyloctyl phosphoric acid at 1.6/hr as an extractant consisting of 1 mol/Solbetsuso 150 solution, 0.5N nitric acid 0.3/hr as a scrubbing liquid in the 10th stage, and , in the fifth stage, a rare earth-containing raw material aqueous solution of PH2 containing terbium nitrate 0.02 mol/dysprosium nitrate 0.022 mol/and yttrium nitrate 0.116 mol/hr/hr
At the same time, 7.98N sodium hydroxide aqueous solution was added to the first stage and third stage at a rate of 0.025% each.
The extraction operation was performed while dividing the supply at 0.03/hr and 0.03/hr, and the extractant containing dysprosium and yttrium was extracted from the 10th stage, and the aqueous phase containing terbium was extracted from the 1st stage. and separated terbium. The residual rate of dysprosium in the resulting aqueous phase and the rate of terbium mixed into the extractant were as shown in Table 3 below. Further, the results were as shown in Examples 7 to 10 in Table 3 below when the amount of the sodium hydroxide aqueous solution was changed only in the first stage and when only the third stage was changed.

[Table] Comparative Examples 4 to 6 In the extraction operation in Example 6, instead of supplying the 7.98N aqueous sodium hydroxide solution in portions, the extraction operation was performed by supplying it only to the first stage. In order to make the residual rate of dysprosium in the aqueous phase 5.8%, 7.98N sodium hydroxide aqueous solution is
0.062/hr was required. The residual rate of dysprosium in the resulting aqueous phase and the rate of terbium mixed into the extractant were as shown in Table 4 below. Further, the results when the amount of the sodium hydroxide aqueous solution was changed were as shown in Table 4 below.

【table】

Claims (1)

[Claims] 1. A multistage countercurrent extraction device in which three or more stages of extraction separation units consisting of a stirring tank and a static separation tank are connected in series is used, and the extraction agent is applied to the first stage of the equipment and the scrubbing agent is applied to the final stage of the equipment. In addition, a rare earth-containing raw material aqueous solution is supplied to the intermediate stage between the first stage and the final stage, and the pH is adjusted by adding alkali to the extraction system.
A specific rare earth element is selectively transferred from the raw material aqueous solution to the extractant while adjusting the amount, and the extractant containing the specific rare earth element is extracted from the final stage, and the aqueous phase containing the remaining rare earth element is extracted from the first stage. In rare earth separation methods, the general formula (In the formula, R ¹ and R ² represent a straight chain or branched alkyl group having 6 to 20 carbon atoms, and these may be the same or different.) Alkylphosphonic acid monoalkyl ester or general formula (In the formula, R ³ and R ⁴ represent a straight chain or branched alkyl group having 12 to 30 carbon atoms, and these may be the same or different.) Using an extraction agent containing a higher dialkyl phosphate ester as an active ingredient, an alkali for pH adjustment is added in portions to at least two stages from the first stage of the multistage countercurrent extraction device to the middle stage that supplies the rare earth-containing raw material aqueous solution. A method for separating rare earth elements. 2. The rare earth separation method according to claim 1, wherein the amount of alkali added to one stage of adding the alkali for pH adjustment is 2 to 98% by weight of the total amount of alkali added to the extraction system.