JPH0643620B2 - Solvent extraction method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention removes metal ions as impurities from an aqueous solution containing a plurality of types of metal salts to recover target metal ions, or is difficult to separate by ordinary methods. The present invention relates to a solvent extraction method performed for the purpose of separately collecting various metal ions.

[Conventional technology]

Organic acidic extractants are known and widely used as typical extractants for extracting metal ions into an organic solvent phase by a solvent extraction method. (Shin Metal Industry December 1975 Issue 2
(See Table 1 on page 1) The extraction reaction of metals with such organic acidic extractants is as shown by the general formula nHA + M ^{+ n} MAn + nH ⁺ ... (1) [where HA is an organic acidic extractant and M is a metal] At the same time, metal ions M ^{+ n} are extracted into the solvent phase, and at the same time hydrogen ions are generated. Therefore, as the extraction reaction of formula (1) proceeds, the hydrogen ion concentration gradually increases, and the extraction reaction stops halfway. Therefore, in order to proceed this reaction to the right side sufficiently, it is necessary to remove the generated hydrogen ions. Therefore, it is usual to add an alkali to the aqueous phase for neutralization, but the addition of alkali is excessive. In some cases, a hydroxide precipitate may be formed or an insoluble compound composed of a metal ion and an extractant may be formed, and these solid substances are the cause of clogging of the pipeline of the reactor.

When this solvent extraction method is performed using a multi-stage countercurrent device, even if PH is properly controlled at the stage where the solvent is newly injected, the alkali supplied only at that stage is consumed during the extraction reaction. As a result, the PH decreases after that. Therefore, in order to perform a good extraction reaction also in the second and subsequent extraction stages, it is necessary to measure the pH in each stage and add an appropriate amount of alkali to each stage.
When the number of extraction stages is large, it is necessary to have an alkali injection device, a PH measurement device, personnel for operating these devices, electric power, installation place, etc. corresponding to the number of extraction stages.

It is extremely difficult in practice to prevent the excess or deficiency of the addition of such an alkali. Therefore, as described in JP-B-55-49582, the organic extractant is previously treated with an alkaline aqueous solution. There is a method of performing extraction without using hydroxide precipitation and insoluble compound formation.

However, in this method, some of the alkaline salts of the organic acidic extractant are soluble in water, and in this case, the alkaline salt does not work effectively because it elutes to the water phase side during the alkaline treatment, and the alkaline salt is contained in the organic phase. However, if the amount is more than a certain amount, an insoluble compound may still be formed during extraction, which may result in substantially the same result as the method of controlling the pH by directly adding an alkali to the aqueous phase, It was not always the right method.

[Problems to be solved by the invention]

The present invention eliminates the above-mentioned drawbacks when performing solvent extraction of an aqueous solution containing a plurality of types of metal ions using an organic acidic extractant, and performs solvent extraction operation without complicated PH control and results in poor pH control. Another object of the present invention is to provide a solvent extraction method capable of performing a stable extraction operation by eliminating the formation of an insoluble compound that is generated.

[Means for solving problems]

To achieve this object, the present invention provides a solvent extraction method of extracting metal ions from an aqueous solution containing metal ions using an organic acidic extractant, wherein the organic acidic extractant and its diluent are dissolved in an organic phase. However, extraction is carried out in the presence of a poorly soluble amine in water, and then metal ions in the organic phase are back-extracted to regenerate the organic acidic extractant,
In this method, an alkali is added to the remaining organic phase of the amine salt to regenerate the amine salt into the amine.

[Action]

As a simple example of the reaction mechanism of the present invention, an aqueous solution of yttrium nitrate Y (NO ₃ ) ₃ as an aqueous solution containing a metal ion is used as an organic acid extractant HA and its diluent, and a tertiary amine R ₃ N as a coexisting amine. The case of extraction in a mixed organic phase with and will be described. The extraction of the aqueous solution containing Y (NO ₃ ) ₃ into the organic phase is performed according to the following formula (2).

_{Y (NO 3) 3 + 3HA} → A 3 Y + 3HNO 3 ‥‥ (2) This Yotsute Y but is extracted into the organic phase, although the concentration of HNO ₃ to produce simultaneously increases sequentially, the HNO ₃ tertiary Reacts with amines according to the following formula (3).

_{HNO 3 + R 3 N → R} 3 HN + · NO 3 - ‥‥ (3) (3) 3 amine salt produced in formula R ₃ HN ⁺ · NO ₃ ^- in is soluble in the organic solvent phase into water phase Is insoluble. When the concentration of free acid in the initial aqueous solution of yttrium nitrate is high and acidic, this free acid is also extracted into the organic phase in a similar form.

Y in the organic phase is back-extracted with an acid such as HNO _{3 according} to the following equation (4).

A ₃ Y + 3HNO ₃ → 3HA + Y (NO ₃ ) ₃ (4) By this reaction, the organic acidic extractant is regenerated, and Y is transferred from the aqueous solution to be treated to another aqueous phase. Y is ZanTsuta tertiary amine salt in the organic phase after the back extraction R ₃ HN ⁺ · NO ₃ ^-
Is regenerated to the tertiary amine with an alkali such as aqueous ammonia according to the following formula (5).

R ₃ HN ⁺ · NO ₃ ^- regeneration reaction of _{+ NH 4 OH → R 3 N} + NH 4 NO 3 + H 2 O ‥ (5) the amine salts with alkali, and previously played in stripping of yttrium organic acidic extractant Since it is carried out prior to the reaction for forming the salt of (3), it is possible to preferentially carry out only (5) by adding an equivalent amount of alkali to the amine.

The organic acidic extractant HA regenerated by the formula (4) and the amine R ₃ N regenerated by the formula (5) can be reused as the extractant of the formula (2) and the additive of the formula (3). .

The organic acidic extractant used in the present invention is an extractant that extracts metal ions into the organic phase by virtue of the active H of the molecule carrying out ion exchange with the metal ions. Acid bis-2-ethylhexyl phosphate (D
2EHPA) and 2-ethylhexylphosphonate mono-2-ethylhexyl, etc. (R ₁ , R ₂ and R ₃ are alkyl groups and at least one is a methyl group) One or more tertiary saturated fatty acids having carbon chain lengths of 9, 10 and 11 (trade name: Versatik Acid, Shell) Typical examples are carboxylic acids such as those manufactured by Kagaku Co., Ltd., and hafthenic acid.

The amine used in the present invention is soluble in the organic acidic extractant and its diluent to be used, but it is necessary that it is sparingly soluble in water, for example, trinormal octylamine (THO).
Tertiary amines such as A) are suitable, and secondary amines such as triisooctylamine and di-2-ethylhexylamine can also be used. When the amine used is insoluble in the organic acidic extractant and the diluent but is soluble in water, the amine will elute in the aqueous phase, and the pH control ability of the organic solvent will be lost. Further, when this amine is soluble in the solvent phase and also in water, the organic solvent has a PH control ability to some extent, but since the amine is eluted in the aqueous phase, PH
The controllability is gradually lost and the object of the present invention is not achieved.

In order to carry out the present invention, a suitable amount of the above-mentioned amine is added to the organic acidic extractant, preferably in approximately equimolar amounts, and petroleum hydrocarbon oil such as kerosene and xylene is diluted as a diluent as needed. Then, the viscosity of the organic phase is reduced to bring the organic phase into contact with an aqueous solution containing metal ions to be treated.
At this time, the liquid to be treated contains a plurality of metal ions,
In the case of selective extraction and separation, (a) is the molar ratio of the amine to the organic acidic extractant in the organic solvent phase changed? (B) The molar ratio of the organic acidic extractant and the amine is constant Can change the distribution ratio of the metal element by changing the amount of the diluent and changing the concentration of the organic acidic extractant at about 1: 1. Further, even when it contains only a single metal ion, the distribution ratio can be increased by the method (a) or (b).

However, in the above method (a), when the amine concentration is too low, there is insufficient amine to capture the generated hydrogen ions exemplified in formula (3), and when the amine concentration is too high, the hydrogen ion capture In some cases, the pH control effect cannot be effectively exerted due to excessive progress, and the method (b) is more suitable.

Next, the distribution ratio of each metal, the change of the separation coefficient, etc., when the extraction conditions are variously changed for an aqueous solution containing a large number of metal ions by applying the method of the present invention, for example, an aqueous solution obtained by dissolving a rare earth-containing ore with nitric acid Will be described.

Aqueous PH1-6 nitrate solutions containing the components shown in Table 1.
50 ml of a structural formula of 15% by volume in a diluent (trade name: Cielsol A, manufactured by Ciel Chemical Co., Ltd.) consisting of a hydrocarbon oil mainly containing trimethylbenzene as an organic phase. "R ₁ , R ₂ and R ₃ are alkyl groups and at least one is a methyl group. 90% by weight of a tertiary saturated fatty acid having a carbon chain length of 10%, the balance being an organic acidic extractant (secondary saturated fatty acid) Ciel Chemical Co., trade name Versatik 10, hereinafter referred to as "VA-10") "and a solvent containing 35% by volume of trinormal octylamine (hereinafter referred to as" TNOA ") (corresponding to approximately the same moles as VA-10). Shake 50 ml with 10 min in a separatory funnel at room temperature,
The pH of the aqueous phase after liquid separation was measured. The relationship between the pH of the undiluted solution and the pH after extraction is shown in FIG.

As is clear from FIG. 1, the PH after extraction shows a substantially constant value regardless of the level of PH before extraction. This is because the acid generated in the reaction as illustrated in formula (2) reacts with an amine to form an amine salt as illustrated in formula (3), and hydrogen ions that already exist in the undiluted solution have the same form as the organic phase. Therefore, it becomes unnecessary to add an alkali for neutralizing the acid at the time of extraction.

As described above, in the extraction of the method of the present invention, if the extraction conditions are constant, the PH after the extraction reaction is constant regardless of changes in the pH of the stock solution, so that the distribution ratio and the separation coefficient are also constant.

Fig. 2 shows the relationship between the PH of the stock solution and the distribution ratio of each metal obtained by measuring the concentration of each metal in the aqueous phase and the organic phase after extraction. Fig. 2 shows the relationship between the PH of the stock solution and the separation coefficient between the metals. It is shown in FIG.
As is clear from FIGS. 2 and 3, the distribution ratio for each metal is almost constant regardless of the pH of the stock solution, so the separation coefficient between the metals shown in FIG. 3 is also almost constant.

Then, the molar ratio of VA-10 as an organic acidic extractant and TNOA as an amine was kept at 1: 1 and the concentration of VA-10 was 10-3.
The relationship between the concentration of the organic acidic extractant and the distribution ratio of each metal when extracted with an equal volume of the stock solution in Table 1 and the relationship between the pH of the aqueous phase after extraction were changed to 0% by volume. FIG. 4 shows the relationship between the concentration of the organic acid extractant and the separation coefficient between metals, and FIG. As can be seen from Fig. 4, even if the concentration of the extractant changes or the pH of the stock solution changes, there is no great difference around PH6, but the distribution ratio changes greatly and the concentration of the extractant is higher. The distribution ratio becomes large. However, as shown in FIG. 5, the separation coefficient is almost constant regardless of the concentration of the extractant.

On the other hand, even if the concentration of the extractant in the organic phase and the concentration of the amine are constant, the distribution ratio can be changed by changing the concentration in the stock solution for treatment. Total amount of rare earth elements in undiluted solution shown in Table 1 20.6
Based on 6 g /, this is diluted with water to change the concentration to 1/5, and VA-10 and TNOA are mixed as an organic solvent at an equimolar ratio, and the concentration of VA-10 is set to 15% by volume. FIG. 6 shows the relationship between the dilution ratio of the stock solution and the distribution ratio when the same amount of the aqueous phase and the solvent phase was shaken, and FIG. 7 shows the relationship with the separation coefficient. In this case, an ordinary extraction reaction has a characteristic that the distribution ratio is higher when the concentration of the stock solution is lower, whereas the distribution ratio is higher when the concentration of the stock solution is higher, as shown in FIG. However, as shown in FIG. 7, the separation coefficient is not so different due to the change in the concentration of the stock solution.

To regenerate the organic solvent after extracting the metal ions, back extraction is carried out with an acid by a known means. The acid used may be one that is stronger in acidity than the organic acid extractant, and the concentration of acid and the mixing ratio with the organic phase differ depending on the type of acid.
Use the same volume of normal nitric acid as the organic phase.

Next, the organic solvent from which the metal ions have been removed is subjected to a regeneration treatment by adding an alkaline aqueous solution. The alkali used has a stronger basicity than the amine present in the solvent, and the amount of the alkali needs to be equimolar to the amine. For example
A concentration of 30 to regenerate the organic phase 1 containing 1 mol / TNOA
Requires about 63 ml of% NH ₄ OH. At this time, an aqueous salt solution having a desired concentration can be obtained by using an alkaline aqueous solution having a predetermined concentration. For example, when the amine salt to be regenerated is a nitrate of amine, ammonium nitrate crystals can be easily recovered from the aqueous solution after the reaction and taken out of the system by using a concentrated aqueous ammonia solution for regeneration.

In this way, the metal ions extracted from the organic solvent are back-extracted and removed, and the amine salt is regenerated to the amine, so that the organic acidic extractant and the amine generally coexist in the diluent. As such, it can be recycled as the organic phase used in the present invention.

The aqueous solution containing various kinds of rare earth ions as described in the application example of the present invention can be separated into two or more kinds of metals having a separation coefficient of more than 1 by applying the solvent extraction method in multiple stages. You can For example, the separation coefficient for Sm and Nd is about 2.3, but they can be separated efficiently.

〔Example〕

Example 1 Solvent extraction was performed on an aqueous solution containing Ni and Co. P containing Ni 41.0 g / and Co 17.2 g / as undiluted solution
An aqueous solution of H3 in nitric acid is used as a solvent, and as a solvent, di-2-ethylhexyl phosphite hydrate (PC-
88A) 33.4% by volume (containing 1 mol in solvent 1), TNOA
The solvent containing 35.4% by volume (1 mol / solvent) and the balance consisting of Sielsol A was placed in a separating funnel for 50 ml, shaken for 10 minutes and allowed to stand, and the Ni and Co contents in the aqueous phase and the organic phase were analyzed. . At this time, the value in the organic phase was determined by shaking the organic phase with an equal volume of 4N nitric acid in a separating funnel for 10 minutes and analyzing the obtained back extract. This organic phase was back-extracted again in the same manner, but the content of residual metal ions after one back-extraction was 0.1 g / Ni or less for both Ni and Co. Table 2 also shows the results of the same treatment when the pH of the first stock solution was set to 4 and 5.

From the results of Table 2, the extraction results obtained were almost the same regardless of the pH of the undiluted solution, and the PH of the obtained aqueous phase was 6.1,
The distribution ratio is Ni 0.013, Co 8.56, and the separation coefficient Co / Ni = 6.6 × 10 ²
It was.

50 ml of the organic phase that had been back-extracted (containing 0.05 mol of TNOA nitrate) was 2.8 g of ammonia water with a concentration of 30% by weight (≈3.3 ml,
(0.05 mol) and shaken for 10 minutes. As a result, the amine in the organic phase was regenerated and an aqueous ammonium nitrate solution containing NH ₄ NO ₃ crystals was obtained as the aqueous phase. Ammonia water for regeneration could be regenerated by using 33 ml of a 10-fold diluted aqueous solution, but in that case, no NH ₄ NO ₃ crystals were precipitated in the aqueous phase.

The solvent regenerated as described above was shaken again with the stock solution and an extraction test was conducted, but after the extraction, the distribution ratios of PH, Ni, Co, and the separation coefficient were the same as those obtained when a new solvent was used. .

Example 2 When the method of the present invention is applied to a multistage countercurrent solvent extraction method, the magnitude of its effect can be clearly confirmed. In this embodiment, a multi-stage countercurrent solvent extraction apparatus having three extraction stages and three scraping stages is used as an ER tracer.
(RETREY BAL) by Liquid Extraction, page 370 9.
6 A batch simulation test was carried out according to the present invention when the present invention was applied. In this case, as the liquid to be treated,
The rare earth salt-containing aqueous solution shown in Table 1 was used to analyze the target elements so that Sm was separated from Nd as much as possible and recovered. The specific method is shown in FIG. 8 and the relationship between the concentrations of Sm and Nd, the concentration ratio, etc. is shown in FIG.

In Fig. 8 (a), "1" is TNO of equimolar to VA-10 15% by volume.
50 ml of a solvent containing A and the balance Sielsol A, "2"
Is a stock solution of the composition shown in Table 1 adjusted to pH 5.76, 25 ml, "3"
Means to inject 25 ml of nitric acid aqueous solution with a concentration of 0.1 N each, and each circle means to shake for 10 minutes at room temperature in a separating funnel, and the numbers in the circle mean the pH of the aqueous phase after shaking. ,
"→" is the injection of the aqueous phase, Indicates the injection of the organic phase.

The numbers I, II, III, I ', II', and III '(the number of stages in the multistage countercurrent solvent extraction method) in Fig. 8 (b) indicate I and II described below Fig. 8 (a). , III, etc.

From the values in FIG. 8 (a), it can be seen that the PH of the extraction stage is controlled to around 5.8 and the PH of the scrubbing stage is controlled to an average value of about 5.3. In addition, in the aqueous phase and organic phase obtained from each stage
The concentrations of Sm and Nd and the Sm / Nd ratio are shown in FIGS. 9 (a) and 9 (b). S
Even with a stock solution of m / Nd = 16 g / 2.5 g / = 6.4, it was purified with Sm up to Sm / Nd≈80 in only 6 steps.

No formation of insoluble compounds was observed in any of the above examples. Also, when a phosphoric acid ester-based extractant was used as the organic acidic extractant, the same separation effect was obtained, and no formation of an insoluble compound was observed.

〔The invention's effect〕

As described in detail above, according to the present invention, pH adjustment by alkali addition during the extraction reaction, which is indispensable for extraction of metal ions using a conventional acidic extractant, is completely unnecessary, and many problems occur in the extraction operation. It is possible to eliminate the formation of an insoluble compound that gives rise to a multistage solvent extraction efficiently and stably.

Therefore, PH control is automatically performed not only for the mutual separation and purification of ordinary base metals but also for the mutual separation and purification of rare earth elements, which requires the use of a multi-stage countercurrent solvent extraction method, and PH measurement and control equipment are all unnecessary. Therefore, operating cost and space are not required, operation stoppage due to these failures can be avoided, and the number of required stages can be reduced because each extraction stage works more effectively than when the PH control is incomplete. In addition, rare earth elements that require high purity can be stably produced, and their industrial value is great.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the PH of the stock solution after shaking by changing the PH of the stock solution in Table 1 to 1 to 6 and the PH of the stock solution, and FIG. 2 is the PH of the stock solution. Fig. 3 shows the relationship between the distribution ratio of each element and each element, Fig. 3 shows the relationship between the PH of the undiluted solution and the separation coefficient, and Fig. 4 shows the distribution ratio after shaking against the VA-10 concentration and water. Figure 5 shows the relationship between the phase and PH. Figure 5 shows VA-1.
Fig. 6 shows the relationship between the 0 concentration and the separation coefficient, Fig. 6 shows the relationship between the distribution ratio with respect to the dilution rate of the stock solution, and PH of the aqueous phase, and Fig. 7 shows the separation coefficient with respect to the dilution rate of the stock solution. FIG. 8 (a) is a diagram showing the relationship, and FIG. 8 (a) is a diagram showing a pH of the aqueous phase and an operation method of the batch milling test similar to the six-stage countercurrent solvent extraction method of three-stage extraction and three-stage scrubbing stage. , Fig. 8 (b)
Is a diagram showing a six-stage countercurrent solvent extraction method corresponding to Fig. 9 (a), and Fig. 9 (a) is the rare earth concentration and Sm / in the aqueous phase at each stage in Fig. 8.
FIG. 9 (b) is a diagram showing the Nd ratio, and FIG. 9 (b) is a diagram showing the rare earth concentration in the organic phase and the Sm / Nd ratio in each stage of FIG.

Claims (2)

[Claims] 1. A solvent extraction method for extracting metal ions from an aqueous solution containing metal ions using an organic acidic extractant, which is soluble in the organic acidic extractant and its diluent in the organic phase, but in water. After extracting the metal ions in the coexistence of a poorly soluble amine and then back-extracting the metal ions in the organic phase to regenerate the organic acidic extractant, an alkali is added to the organic phase in which the amine salt remains to add the amine salt. A method for extracting a solvent, which comprises regenerating the compound into an amine. 2. The organic acidic extractant is an acidic phosphoric acid ester or a carboxylic acid.
The solvent extraction method as described in the item.