JPS60231420A - Separation of cobalt from aqueous solution containing cobalt and nickel - Google Patents

Abstract

PURPOSE:To extract effectively Co from an aqueous soln. contg. Co and Ni by mixing an extracting soln. contg. a monoalkyl alkylphosphonate with the aqueous soln. contg. Co and Ni. CONSTITUTION:An extracting solvent contg. the monoalkyl alkylphosphonate represented by formula I as an extracting reagent is mixed with an aqueous soln. contg. Co and Ni to separate Co from the aqueous soln. In the formula, each of R<1> and R<2> is 3-8C alkyl or alpha-branched alkyl or either of R<1>, R<2> is alpha-branched alkyl and the other is branched alkyl represented by formula II (where each of R<3> and R<4> is alkyl). Monol-methylheptyl 1-methylheptylphosphonate is especially suitable for use as the monoalkyl alkylphosphonate. High purity Co can be selectively extracted and separated from the aqueous soln. in a high yield by properly selecting the extracting reagent.

Description

TECHNICAL FIELD The present invention relates to a method for separating cobalt from a water bath solution containing cobalt and nickel using an extraction solvent containing a specific organic phosphorus compound.

BACKGROUND OF THE INVENTION An aqueous solution containing cobalt and nickel is generated during the wet smelting of various volatile ores and during the wet recovery of useful metals from industrial waste such as scrap and slag catalyst. A solvent extraction method is often used to separate cobalt and nickel from such an aqueous solution.

One such method is to use di-2-ethylhexyl phosphoric acid (abbreviated as D2EHPA) as an extractant. A water bath solution containing cobalt ions and nickel ions is brought into liquid-liquid contact with an organic solvent containing the extractant to extract cobalt in the aqueous solution into an organic phase.

This is a method in which nickel remains in the raffinate aqueous phase.

However, under extraction conditions that effectively recover cobalt into the organic phase, a large amount of nickel is also extracted into the organic phase, so performing the extraction operation once is extremely insufficient to separate cobalt and nickel. Therefore, in actual extraction operation, multi-stage extraction 4! Countercurrent contact takes place at the same position. A further washing step is installed to remove the nickel extracted along with the cobalt in the organic phase. The organic phase is washed with a diluted inorganic acid or the like, and at this time, a large amount of cobalt is also washed with nickel into the washing aqueous phase. Therefore, there is a drawback that a large amount of cobalt contained in the washing aqueous phase must be recovered by re-extraction. This is due to the insufficient ability of the extractant di-2-ethylhexyl phosphoric acid to separate and extract cobalt and nickel.

In view of the above, the present inventors have previously prepared an alkylphosphonic acid monoalkyl ester (abbreviated as APNA) in which the alkyl group is a branched alkyl group, such as 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester. Yes g9
Extract cobalt by solvent extraction method using a solvent,
Invention of method for separating cobalt and nickel
-141176) was completed.

2 shown as a representative example of the extractant in the method of the above invention.
-The method using mono-2-ethyl ethyl ester (BPNB) significantly improved the separation rate of cobalt and nickel compared to the method using D2EHPA as an extractant. However, there is still a need for a method that uses an extractant that has an excellent ability to separate and extract cobalt and nickel.

OBJECTS OF THE INVENTION An object of the present invention is to provide a method for effectively separating and extracting cobalt from an aqueous solution containing cobalt and nickel. Another object of the invention is.

A further object of the present invention is to provide a method for effectively separating cobalt from an aqueous solution containing calcium.

Summary of the Invention The present inventors have discovered that there are considerable differences in the ability of the extractant to separate and extract cobalt and nickel depending on the type of alkyl group in the extractant, alkylphosphonic acid monoalkyl ester (APNA). The present invention was completed by discovering a specific alkylphosphonic acid monoalkyl ester that has superior ability to separate and extract cobalt and nickel than APNA such as APNA.

Accordingly, one aspect of the present invention is to mix and contact an extraction solvent containing an alkylphosphonic acid monoalkyl ester represented by the following general formula as an extractant with an aqueous solution containing cobalt ions and nickel ions.

Cobalt is separated from the aqueous solution, thereby achieving the above objective.

RIOO)I Here, R1 and fLz each have 3 to 1 carbon atoms
8 and 8 R4-CH-(I ('' and R' are alkyl groups) σ-branched alkyl group or one of R1 and R1 is an α-branched alkyl group and the other is a branched alkyl group , especially a branched alkyl group having a branch on a carbon other than the alpha carbon.

The method of the present invention also uses an extraction solvent containing an alkylphosphonic acid monoalkyl ester represented by the general formula F as an extractant.

Cobalt is separated from the aqueous solution by mixing and contacting it with an aqueous solution containing nickel and calcium, thereby achieving the above purpose.

＼ノ1(+／＼RIOO)(Here, 几1 and W are α-branched alkyl groups each having 3 to 18 carbon atoms and represented by R4-CH- (R" and R4 are alkyl groups), Alternatively, one of R1 and gl is an α-branched alkyl group and the other is a branched alkyl group, particularly a branched alkyl group having a branch at a carbon other than the α carbon.

The alkylphosphonic acid monoalkyl ester has 12 to 36 carbon atoms, preferably 14 to 24 carbon atoms. If the carbon number is less than this, the proportion dissolved in the aqueous phase will increase, and if it is larger, the cobalt loading will decrease. α-branched alkyl groups include inpropyl group, 1-methylpropyl group,
Examples include 1-ethylpropyl group, 1-methylbutyl group, 1-methylpentyl group, 1-methylbequinyl group, 1-7'tylpentyl group, and 1-methylheptyl group. Branch alkyl group 1 is 2-ethylhexyl group, inoctyl group,
isodecyl group, isotridecyl group, instearyl group,
Examples include 2-ethylbutyl group. Among these, 1-methylhebutylphosphonic acid-7-methylheptyl ester C (hereinafter referred to as MHPNMH), 1-methylhebutylphosphonic acid-2-ethylhexyl ester (hereinafter referred to as MHPNMH),
NB).

2-Ethylhexylphosphonic acid mono-1-methylheptyl ester (hereinafter referred to as BPNMH) etc. are industrially available in Tateri #! It can be crushed.

When such an alkylphosphonic acid monoalkyl ester is used as an extractant, the amount of concomitant extraction of itemocalcium is lower than that of conventional alkylphosphonoic acid extractants. 2 is much smaller than, for example, 2-ethylhexylphosphonic acid-mono-2-ethylhexyl ester (referred to as BPNB).

When the amount of calcium extracted is large, when the organic solvent is purified or back-extracted with sulfuric acid or a water bath solution containing β salt after the extraction operation, the amount of I-cocalcium in the aqueous phase can be removed. Precipitation occurs. Among the alkylphosphonic acid monoalkyl esters, 1-methylhebutylphosphonic acid heptanyl-methylheptyl ester, 2-ethylhexylphosphonic acid mono-1-methylheptyl ester, etc. are sometimes preferable, and by selecting these, an aqueous solution can be obtained. It is possible to selectively extract and separate cobalt with high charge yield and high purity.

The basic method of separating cobalt by solvent extraction using this extractant is as follows.

(2) Extraction step: Cobalt is selectively extracted into the extraction bath W (organic phase) by bringing an aqueous solution containing at least cobalt ions and nickel ions into contact with an extraction solvent containing the above extractant (liquid-a). Since the extraction of cobalt is carried out by ion exchange between the extractant and cobalt ions, an appropriate pH exists for the extraction, and an alkaline substance is usually added to adjust the pH to this extraction pH. The organic phase is 1
It is then separated from the aqueous phase.

(2) Reverse Extraction Cobalt is back extracted into the aqueous phase by bringing the organic phase containing cobalt into liquid-liquid contact with a mineral acid-containing water bath solution. After back extraction, the living phase is separated from the aqueous phase and recycled to the single extraction step for fresh extraction.

In the present invention, an organic solvent that dissolves the extractant is used.

This solvent must dissolve the extractant so that two phases, an organic phase and an aqueous phase, are formed in a static state after liquid-liquid contact, and it must be insoluble in water and remove gold from the aqueous raw material solution. There are no particular limitations as long as it does not interfere with the extraction of the extractant during extraction. Effective solvents include high flash point paraffinic hydrocarbons, naphthenic hydrocarbons, aromatic hydrocarbons, and petroleum fractions such as kerosene or naphtha.

The extractant concentration in this extraction bath medium is determined in relation to the cobalt ion concentration in the shallow water bath (III liquid) and the phase ratio of the organic phase to the aqueous phase, but it is generally of extractant: 3.~70 volumes, preferably 5~406
It's mediocre.

Adjustment of the pH is usually carried out by using in advance an appropriate proportion of the acidic groups of the extractant in the organic solvent as an alkali salt. Moreover, even if this alkali is a nickel salt, it can be used. Furthermore, the pH ttr+q can also be determined by adding and mixing an alkali or an aqueous solution thereof to the organic phase or aqueous phase introduced into the apparatus as required. Effective alkalis include ammonium ions and alkali metal ions, such as ammonia, caustic soda, and soda carbonate. The pH during extraction is set to 3.5 to 7.0 when performing multi-stage extraction, but for example, when performing single-stage extraction, it is preferably set to pH 5.0 to 7.0.
is adjusted to

It is also possible to add a reforming agent to the extraction solvent to prevent it from forming an emulsion and promote phase separation, or to increase the solubility of the extracted metal complexes in the organic phase. be. Examples of retrieval agents include neutral phosphorus compounds such as tributyl phosphate and higher alcohols such as isodecanol.
Contained at a rate of 5 volumes.

During extraction, the temperature at which liquid-liquid contact and phase separation are carried out is preferably higher in order to reduce the viscosity of the organic phase and promote phase separation, but it is not critical. Its temperature is usually related to the flash point of the diluted organic solvent and the need for heating energy.

Maintained at 20-70°C.

The method of bringing the organic solvent used in the present invention into contact with the raw material aqueous solution for extraction may be any known procedure used in solvent extraction methods. Not only continuous multi-stage contact method,
Batch, continuous batch and batch circulation methods are also effective.

When performing countercurrent multi-stage extraction, column-type equipment such as a packed column, pulse column, or disk tower is preferably used, but the present invention can use any commonly used equipment for solvent extraction. It is possible. According to the method of the present invention, the separation effect of cobalt and nickel is excellent, so the mixer is used.

It is also possible to use settlers in stages 1-a.

During extraction, the mixing ratio of the organic phase and the aqueous phase with which contact is carried out is not particularly limited. The most effective ratio depends on the degree of extraction agent in the organic solvent and the concentration of the metal ions to be extracted in the aqueous feedstock solution and the method of contacting the organic and aqueous phases, such as the type of equipment. Generally, the ratio of the organic phase to the aqueous phase is adjusted to minimize the retention of cobalt in the raffinate and to allow virtually all of the cobalt to be incorporated into the organic phase. It is possible to load up to 1 gram equivalent of cobalt per mole of extractant. Usually, adjustment is made so that 0.5 to 0.8 gram equivalent of cobalt is loaded.

After the cobalt is extracted into the organic phase and the aqueous and organic phases are separated, the organic phase is transferred to a back-extraction circuit and contacted with one current of thermal acid to remove and recover the cobalt. This back-extraction circuit can be carried out using any liquid-liquid contact device.9 For example, by using a mixer or settler in one or two stages, it is possible to actually remove and recover the entire amount of cobalt from the organic phase.

The beak volume ratio of the organic phase to the inorganic acid is related to the cobalt concentration in the organic phase and the concentration of the inorganic acid, and can be set within a fairly wide range for the desired concentration of cobalt salt in the removed and recovered aqueous phase. . As the inorganic acid, 0.25 to 5N sulfuric acid, nitric acid, hydrochloric acid, etc. are used. The type of inorganic acid is selected depending on the cobalt salt.

The inorganic acid may also contain cobalt, such as a cobalt electrolyte tailing solution. The organic phase from which cobalt has been removed is circulated to an extraction circuit.

Removes trace amounts of nickel contained in the organic phase.

In order to improve the purity of cobalt, it is also possible to provide a cleaning circuit between the extraction circuit and the back extraction circuit. In the washing process, the organic phase is obtained by using Kasen's solvent extraction contact device and applying the liquid-liquid extraction method described above to obtain an aqueous solution containing an inorganic acid, an aqueous solution containing cobalt, and a back extraction circuit. part of the aqueous phase.

Or contacted with a portion of the cobalt electrolyte Mffl liquid.

The metal salts obtained in the aqueous phase after washing are recycled to the extraction process or recovered separately. The g rectangle (0/A) of the contact between the organic phase and the aqueous phase at this time can be set over a wide range, but industrially it is usually selected from 0.2 to 2.0. contact p
The pH of H is selected so that the metal ions to be cleaned are sufficiently transferred to the aqueous phase, and at the same time, the cobalt is not transferred as much as possible.

It is usually in the range of 3 to 6, but preferably in the range of pi-1a, s to 55.

The contact method can be not only one-stage but also multi-stage gauze processing, and preferably a multi-stage extraction device is used to bring the organic phase and the aqueous phase into countercurrent contact. The contact temperature is preferably 20 to 70C as in the case of the extraction step.

At this time, the aqueous solution containing an inorganic acid and cobalt used for cleaning may also contain nickel. In this case, the nickel concentration has an influence on the cleaning effect, and naturally the lower the nickel concentration, the better the result, but if the nickel concentration is 5 g/
Considerable effects can be expected even when using a water bath solution containing in the range of 1 to 60 g/liter. Therefore, an aqueous raw material solution containing cobalt and nickel to be separated can be used, which is industrially advantageous.

When the raw material aqueous solution contains impurities such as iron, salivary lead, @, arsenic, etc., these metal ions are extracted with priority over cobalt, and the purity of cobalt in the organic phase deteriorates. Therefore, it is desirable that these metal ions be removed in advance. However, even if such ions are contained, cobalt can be selectively extracted first by extracting them into the organic phase and then recovering them at the same time as cobalt back-extraction, or by selecting the contact pH during back-extraction. It can also be removed from the organic phase by back extraction followed by refecal extraction.

Therefore, the presence of these metals in the raw material aqueous solution does not particularly restrict the present invention.

In addition, the present invention extracts each metal from a water bath solution containing metal salts other than cobalt and nickel salts, such as 'e, Cr, Zn, Mn, Cu, etc., and adjusts the pH conditions for extracting the four metals. By setting an excessive number of stages during extraction, these metals can be extracted and separated from each other.

In addition, cobalt, nickel, calcium,
All metals such as iron contain cobalt (II) and nickel (II).
), calcium (■), and iron (mouth or ■).

Example The present invention will be described below with reference to Examples.

Example 1 In order to demonstrate that the method of the present invention is superior as a method for separating cobalt and nickel, cobalt and nickel were separated using 1-methylhebutylphosphonic acid-1-methylheptyl ester (MHPNMH) as an extractant. An experiment was conducted to demonstrate the separation and extraction ability of nickel.

An extraction bath (organic phase) was prepared in which the extractant was diluted and dissolved in kerosene to a concentration of 0.59 m/f (approximately 20 volume fraction). This was brought into contact with an aqueous solution (aqueous phase) containing cobalt sulfate and nickel sulfate. Contact was carried out using a constant temperature shaking aqueous phase at 25° C. and shaking for 10 minutes. The volume ratio of organic to aqueous phase (0/A) is 1:1. The initial amounts of cobalt and nickel were each 10 g/no in the aqueous solution. The pH during extraction was adjusted by neutralizing a portion of the extractant components in the organic phase with aqueous ammonia in advance.

The amount of cobalt and nickel contained in the organic phase and aqueous phase of the extract was determined, respectively, and the extraction rate was calculated.

The results are shown in Table 1.

The extraction is shown in Equation I below.

The relationship between the pH of the contact during extraction and the extraction rate of cobalt and nickel in Table 1 is shown in FIG.

Table 1 Comparative Example 1 Example except that 2-ethylhexylbosphonic acid mono 2-ethylhexyl ester (BPNB) was used as the extractant in order to compare the separation and extraction properties of cobalt and nickel with the conventional extractant. It is the same as 1.

From the experimental results of Example 1 and Comparison Column 1, extraction of cobalt
Table 2 shows the relationship between extraction of nickel and nickel.

Table 2゜From the results in Table 2, it can be seen that the separation performance of cobalt and nickel is greatly affected by simply changing the alkyl group from 2-ethylhexyl group to 1-methylheptyl group in the alkylphosphonic acid monoalkylnisder having the same number of carbon atoms. It can be seen that the extractant of the present invention has excellent separation performance for cobalt and nickel.

Example 2 An experiment was conducted to confirm the effectiveness of extraction of cobalt from a nickel-containing IJVt aqueous solution. 0.3 of 1-methylhebutylphosphonic acid-7-methylheptyl ester (MHPNMH) as an extractant.
Dissolved in kerosene to a concentration of malt/no,
This was brought into contact with an aqueous solution containing cobalt and nickel oxalates. Contact was carried out at a temperature of 50° C. with shaking for 10 minutes. The volume ratio of organic to aqueous phase (0/A) is 1:1.
The initial concentration of the aqueous solution containing cobalt and nickel was set to 4.91 cobalt/106171 nickel. The pH was adjusted with aqueous ammonia in the same manner as in Example 1.

Table 31 shows the extraction rates of cobalt and nickel at each pH. In addition, the separation and extraction effect of cobalt and nickel is expressed by the separation coefficient 1, and the separation coefficient for the cobalt extraction plan is shown in Figure 2. The cobalt-nickel separation coefficient is expressed by the following formula.

Cobalt-nickel separation factor=-! 2-c? ! -i Tata LNI Example 3 2-ethylhexylphosphonic acid-mono 1 as extractant
- Same as Example 2 except that methylheptyl ester (BPNMH) was used. The results are shown in Table 3 and FIG.

Comparative Example 2 2-ethylhequinylphosphonic acid-nanano2 as extractant
-Ethylhexyl ester (BPNB) was used. The results are shown in Table 3 and FIG.

Table 3 As is clear from Table 3 and FIG. 2, the extractants 1v1 HPNMH and BPNMH in the method of the present invention are 1 Kyoto aqueous sD containing a large amount of nickel. It is clear that the separation performance of cobalt and nickel is better than that of the conventional method.

That is, by slightly replacing either one of the branched alkyl groups of the alkylphosphonic acid monoalkyl ester with an α-branched alkyl group (an alkyl group having a branched alkyl group on the carbon bonded to P or 0).

Results were obtained in which the effects of cobalt and nickel in the extractant were enhanced.

Example 4 Separate extraction of cobalt and nickel in a case where calcium is contained together with cobalt and nickel in the water bath solution - JJ fruit and calcium extraction young fruit were tested.

0.6 mo I! using MHPNMH as an extractant. /
12 (7) The kerosene was heated to 9 degrees and brought into contact with a water bath containing sulfate groups of cobalt (1), nickel (Ill), and calcium (Ill).

The contact was carried out by shaking for 10 minutes at a temperature of 50°C, and the pH during extraction was adjusted in the same manner as in Example 1. The volume ratio of organic to aqueous phase (0/A) is 1:1. The initial concentrations of metals in water 7@Sokari were set to be 11.31/1 for cobalt, 11.0171° for nickel, and 0.341/l for calcium. Figure 3 shows the relationship between the extraction rate of cobalt, nickel, and calcium and the pH at the time of extraction.

Further, FIG. 7 shows the change in the separation coefficient between cobalt and nickel with respect to the extraction rate of cobalt, and FIG. 8 shows the change in the separation coefficient between cobalt and calcium.

Example 5 Same as Example 4 except that MHPNB was used as the extractant. FIG. 4 shows the relationship between the extraction rate of cobalt, nickel, and calcium and the pH at the time of extraction.

Example 6 Same as Example 4 except that BPNMH was used as the extractant. The relationship between the extracted amounts of cobalt, nickel, and calcium and the pH at the time of extraction is shown in Figure g45.

Comparative Example 3 Same as Example 4 except that BPNB was used as the extractant. FIG. 6 shows the relationship between the extraction rate of cobalt, nickel, and calcium and the pH at the time of extraction.

31st section 1 to 31 showing the results of Examples 4 to 6 and Comparative Example 3
As is clear from FIG. 7, when cobalt calcium coexists in an aqueous solution containing cobalt and nickel, the extractant used in the method of the present invention is the conventional extractant BPN.
It can be seen that the separation of cobalt and nickel is better than in B. Among the extractants in the present invention, BPNMH,
That is, an alkylphosphonic acid monoalkyl ester in which R1 of the structural formula R'O of the extractant is a branched alkyl group having carbon I/branches excluding the α-position, and R3 is an α-branched anolyl group. When used, cobalt and nickel can be effectively separated.

Also, as shown in Figure 8, BPNMH, an extractant in which R1 is a branched alkyl group other than the α-position, and R'' is an α-branched alkyl group, has good firmness in the separation of cobalt and calcium. First, it can be seen that an extractant in which both R1 and R2 are α-branched alkyl groups is good, and Fl. Therefore, when cobalt is back-extracted from the organic phase using dilute sulfuric acid or the like, calcium does not exceed the saturation concentration and precipitate.

Example 7 A cobalt back extraction recovery experiment was conducted from the organic phase from which cobalt was extracted.

Cobalt 9.711/min and nickel 0.411/t obtained when adjusting I) R5,6 in Example 1
This was brought into contact with 0.5N sulfuric acid at room temperature (25°C) to recover cobalt contained in the organic phase by back extraction into the aqueous phase. At this time, each time a new 0
．． Contact and liquid separation were performed a total of three times using 5N sulfuric acid. The contact time for each round was 5 minutes, and the organic to aqueous phase ratio (0/A) was 2.

The experimental results are shown in Table 4.

Table 4 The concentration of cobalt contained in the organic phase after back extraction is o, op
7i, indicating that cobalt can be easily removed and recovered from the organic phase with low concentration sulfuric acid.

It can also be seen that by using less nitric acid than the total equivalents of cobalt and nickel in the organic phase, nickel in the organic phase can be removed in preference to cobalt.

Similar results were obtained using hydrochloric acid or nitric acid instead of sulfuric acid.

Effects of the Invention According to the method of the present invention, since a specific alkylphosphonic acid monoalkyl ester is selected as an extractant, cobalt and nickel can be separated and recovered with high purity and high recovery rate from an aqueous solution in which cobalt and nickel coexist. Furthermore, even when calcium is mixed at the same time, cobalt is extracted in a pure manner without being affected by other metal ions, using a high-recovery process.

It is possible to separate. Additionally, the required number of stages of liquid-liquid contacting equipment used in the extraction and washing steps is significantly reduced compared to when using the conventional extractant di-2-ethylhexyl phosphoric acid.

When the fc cleaning process is employed, the amount of cobalt that migrates together with the nickel in the cleaning aqueous phase is also significantly reduced. This makes it possible to downsize the device.

It is possible to reduce the amount of organic extraction bath medium required and also reduce the amount of alkali used for the extraction side. Therefore, there are great advantages in that the amount of investment can be reduced, the operating cost of the device during operation can be reduced, and the operation control can be simplified.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the pH during extraction and the extraction height of cobalt and di-ethyl in Example 1; Figure 2 is a graph showing the relationship between the cobalt extraction rate and the cobalt-nickel separation constant in Examples 2 to 4. Graphs shown; Figures 3 to 6 are graphs showing the relationship between the pH during extraction and the extraction rate of cobalt, nickel, and calcium in Example 5.6.7 and Comparative Example 3, respectively; Figure 7 is the graph of the example Graph I FIG. 8 showing the relationship between the cobalt extraction rate and the cobalt-nickel separation constant in Example 5.5.6.7 and Comparison column 3.
7 is a graph showing the relationship between the cobalt extraction rate and the cobalt-calcium separation coefficient in 6°7 and Comparative Example 3. l Yuno superior agent patent attorney Hide Yamamoto Strategy 1st figure jI! Hour/l pH Figure 2) So+1-1- /I Ship 7pm mt〆) Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1. An extraction solvent containing an alkylphosphonic acid monoalkyl ester represented by the following general formula as an extractant is brought into contact with an aqueous solution containing at least cobalt and nickel, and cobalt is separated from the aqueous solution. how to. Here) 11 and 几2 each have 3 to 18 carbon atoms.
and 8 B'-C)(-(R' and R6 are α-branched alkyl groups represented by an alkyl group or l(, one of l and W is an α-branched alkyl group and the other is a branched alkyl group) It is an alkyl group. 2. The method according to claim 1, wherein the substituents R1 and 1 (1 is a 1-methylhebutyl group). 3. Any one of the substituents R1 and W The method according to claim 1, wherein one is a 1-methylheptyl group and the other is a 2-ethylhexyl group. 4. Contains an alkylphosphonic acid monoalkyl ester represented by the following general formula as an extractant. A method for separating cobalt from a water bath solution by mixing and contacting an extraction solvent containing at least cobalt, nickel and calcium with an aqueous solution containing at least cobalt, nickel and calcium. 9) tl and R3 each have 3 to 18 carbon atoms
3 α-branched alkyl group represented by R'-CI (-()pi and R4 are alkyl groups), or one of R1 and )41 is an α-branched alkyl group and the other is a branched alkyl group It is the basis.゛5, the substituent R1 is 1-methylheptyl group or 2
-ethylhexyl group, and R'' is 1-methylhebutyl group.