US20170107595A1

US20170107595A1 - Solution for use in extraction of cobalt, cobalt solution, and method for collecting cobalt

Info

Publication number: US20170107595A1
Application number: US15/123,865
Authority: US
Inventors: Takeshi Itakura; Seiji Nakabayashi; Masaru Ikeda; Akihiko Ikegaya
Original assignee: ALMT Corp
Current assignee: ALMT Corp
Priority date: 2014-03-07
Filing date: 2015-02-27
Publication date: 2017-04-20
Also published as: JP2015168858A; JP5850966B2; WO2015133385A1

Abstract

The purpose of the present invention is to provide a solution for use in the extraction of cobalt, whereby it becomes possible to extract cobalt at lower cost and more safely compared with a case in which a conventional one is used. The solution for use in the extraction of cobalt according to the present invention comprises: an ionic liquid containing a quaternary ammonium group; and an organic solvent which exists in such a state that the organic solvent is mixed with the ionic liquid and which has a kauri-butanol value of 60 or more.

Description

TECHNICAL FIELD

This invention relates to a solution for use in extraction of cobalt, a cobalt solution, and a method of collecting cobalt.

BACKGROUND ART

A cemented carbide alloy, which contains tungsten carbide as a main component and cobalt, nickel, or the like as a binder metal and which has added thereto a carbide of titanium, tantalum, chromium, or the like for improving performance, has been widely used in tools for metal processing or the like by virtue of its excellent hardness and abrasion resistance.
In the tools using such cemented carbide alloy, a tool which cannot be used any more due to a defect, abrasion, or the like during use or a defective part thereof is discarded as scrap called hard scrap.
Further, part of cemented carbide alloy powder generated during manufacturing of a cemented carbide tool, ground dust generated during processing of the cemented carbide tool with a grinding stone, and the like are discarded as scrap called soft scrap.
In the following description, the “cemented carbide scrap” refers to used scrap of an alloy containing 50 wt % or more of tungsten carbide, and cobalt or nickel as a binder phase.
The hard scrap and soft scrap each contain a large amount of tungsten, which is a rare metal. 60% or more of tungsten resources have been used in the cemented carbide tools. Further, the prices of ammonium paratungstate (APT) and tungsten oxide serving as intermediate raw materials for a tungsten material have continued to rise in recent years, and there is a demand for establishment of a recycling technology for tungsten contained in the cemented carbide tools.
In view of the foregoing, a recycling method for a cemented carbide tool involving recycling tungsten carbide from a used cemented carbide tool or the like has been proposed, and specifically, a zinc method, a molten salt dissolution method, an oxidizing roasting-alkali dissolution method, or the like has been known ( Patent Documents 1 and 2, and Non Patent Document 1).
Meanwhile, a residue produced at the time of the collection of tungsten by the method contains a large amount of cobalt, and hence the collection of cobalt has also been desired. However, the residue contains iron, manganese, nickel, copper, chromium, tantalum, tungsten, vanadium, or the like in addition to cobalt, and hence a problem in terms of the purity of cobalt occurs when the residue is reused as a cemented carbide raw material or when a cobalt base metal is produced from the residue.
Accordingly, there has been desired a technology involving separating cobalt in the residue from which tungsten has been collected, followed by the purification and collection thereof.
A solvent extraction method (Cited Document 3) or a method of removing a precipitate with a sulfide (Patent Document 4) has been reported as a technology involving separating cobalt from iron and nickel.
However, the solvent extraction method has involved problems in terms of safety and cost because the method requires the use of a large amount of a combustible hazardous solvent and requires an explosion-proof facility. Meanwhile, the method of removing a precipitate with a sulfide has involved problems in terms of an environmental load and the maintenance of a working environment because the method requires the use of a harmful sulfide.
In view of the foregoing, a method of extracting cobalt with an ionic liquid has been reported as a method of coping with those problems. The term “ionic liquid” as used herein means a liquid that: is a salt that becomes liquid at 100° C. or less; and is formed only of ions.
The ionic liquid has a structure formed of a cation portion and an anion portion. The extraction method involving using the ionic liquid is specifically, for example, the following method (Non Patent Documents 2 and 3). An ionic liquid containing a quatemary phosphonium group in the cation portion (hereinafter referred to as “quatemary phosphonium-based ionic liquid”) or an ionic liquid having a quatemary ammonium group in the portion (hereinafter referred to as “quatemary ammonium-based ionic liquid) is used, and its viscosity is adjusted through mixing with an organic solvent as required. After that, only cobalt is extracted in the ionic liquid by bringing the ionic liquid, and a solution containing cobalt and nickel into contact with each other.

PRIOR ART DOCUMENTS

Patent Document

Patent Document 1: JP-A-H11-505801
Patent Document 2: WO 2010/104009 A1
Patent Document 3: JP-A-2013-194269
Patent Document 4: JP-A-2012-211375

Non Patent Document

Non Patent Document 1: Yasuhiko Tenmaya, Development Project for Highly Efficient Recovery System for Rare Metal etc. “Recovery of Tungsten etc. from Discarded Cemented Carbide Tools,” Mineral Resources Report, Japan Oil, Gas and Metals National Corporation, Vol. 38, No. 4, November, 2008, pp. 407-413
Non Patent Document 2: Sil Wellens, Ben Thijs, Koen Binnemans. “An environmentally friendlier approach to hydrometallurgy: highly selective separation of cobalt from nickel by solvent extraction with undiluted phosphonium ionic liquids” Green Chemistry, 2012, 14, 1657
Non Patent Document 3: Patrycja Rybka et. al., Separation Science and Technology, 47, 1296-1302, 2012

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

However, the technology described in Non Patent Document 2 or 3 has involved such problems as described below.
First, the quatemary phosphonium-based ionic liquid is much more expensive than the quatemary ammonium-based ionic liquid, and hence the quatemary phosphonium-based ionic liquid has involved a problem in terms of cost when used for collecting cobalt from a used cemented carbide tool or the like.
In addition, the quatemary ammonium-based ionic liquid is less expensive than the phosphonium-based ionic liquid, but has solubility in water higher than that of the quatemary phosphonium-based ionic liquid.
Accordingly, when the quatemary ammonium-based ionic liquid is used in the extraction of cobalt from an aqueous solution containing cobalt, the following problem occurs. The ionic liquid dissolves in the aqueous solution and hence it becomes difficult to separate cobalt.
As described above, each of the related-art cobalt collection technologies has involved a problem, and under the present circumstances, no technology that brings together low cost and high collection efficiency has been available.
This invention has been made in view of the problems, and an object of this invention is to provide a solution for use in extraction of cobalt with which cobalt can be extracted at lower cost and more efficiently than ever before.

Means to Solve the Problem

To solve the problems, the inventors of this invention have made investigations on the composition of an ionic liquid with which cobalt can be extracted at lower cost and more efficiently than ever before, and which is less expensive than a phosphonium-based ionic liquid.
In particular, the inventors of this invention have made investigations on whether or not the solubility of a quatemary ammonium-based ionic liquid in water can be reduced.
As a result, the inventors have found that mingling the quatemary ammonium-based ionic liquid with a certain kind of organic solvent can significantly reduce the solubility in water, and hence enables the extraction of an ion from an aqueous solution containing cobalt. Thus, the inventors have completed this invention.
Specifically, a first aspect of this invention is a solution for use in extraction of cobalt comprising an ionic liquid containing a quatemary ammonium group and an organic solvent that is present in a state of being mingled with the ionic liquid and has a kauri-butanol value of 60 or more.
A second aspect of this invention is a cobalt solution comprising the solution for use in extraction of cobalt of the first aspect and an aqueous solution of cobalt and an acid containing chlorine, the aqueous solution being dissolved in the solution for use in extraction of cobalt, wherein cobalt is dissolved in the solution for use in extraction of cobalt.
A third aspect of this invention is a method of collecting cobalt comprising dissolving an aqueous solution of cobalt and an acid containing chlorine in a solution for use in extraction of cobalt, the solution including an ionic liquid containing a quatemary ammonium group, and an organic solvent that is present in a state of being mingled with the ionic liquid and has a kauri-butanol value of 60 or more, to dissolve cobalt in the solution for use in extraction of cobalt to separate and collect cobalt.

Effect of the Invention

According to this invention, the solution for use in extraction of cobalt with which cobalt can be extracted at lower cost and more efficiently than ever before can be provided.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a flow chart for illustrating an example of a cobalt extraction method of an embodiment of this invention.

FIG. 2 is a graph for showing a relationship between a mingling ratio between TOMAC (tri-octhyl-methyl-ammnoiumu-chloride) and an organic solvent, and a viscosity.

FIG. 3 is a graph for showing a relationship between the mingling ratio between TOMAC and the organic solvent, and a Co extraction ability or a Co—Ni separation ability.

FIG. 4 is a flow chart of a cobalt extraction method of Examples.

MODE FOR EMBODYING THE INVENTION

A preferred embodiment of this invention is described in detail below with reference to the drawings.

Principle of This Embodiment

First, the principle of cobalt extraction of this embodiment is briefly described.
In this embodiment, an ionic liquid is used for separating cobalt from an aqueous solution containing nickel and cobalt.
Specifically, first, an aqueous solution containing nickel, cobalt, and chlorine is prepared.
Specifically, a reaction represented by Equation 1 is caused by dissolving a compound containing nickel and cobalt in an acid containing chlorine, such as hydrochloric acid.
CoO+2HCl→CoCl₂+H₂O Equation 1
A cobalt aqueous solution can be obtained because cobalt chloride to be produced is water-soluble.
Next, the aqueous solution containing nickel, cobalt, and chlorine, and an ionic liquid having a chloride ion as an anion portion are brought into contact with each other.
At this time, cobalt in the aqueous solution is bonded to chlorine, and is extracted as a chloride complex into the ionic liquid.
Meanwhile, nickel does not form any chloride complex, and hence remains in the aqueous solution and is separated from cobalt. The foregoing is the principle of the cobalt extraction of this embodiment.
The reactions in which cobalt is thus extracted into the ionic liquid are shown below.
Co²⁺+4Cl⁻→CoCl₄ ²⁻ Equation 2
2I.L.-Cl+CoCl₄ ²⁻→(I.L.)₂-CoCl₄+Cl⁻(I.L.: cation portion of ionic liquid) Equation 3
In addition, an extraction ability and a separation ability for cobalt are defined as follows.
Extraction ability: amount of cobalt (g/dm³=kg/m³) that can be extracted into ionic liquid per unit volume
Separation ability: quotient (g/g) obtained by dividing amount of cobalt extracted into ionic liquid per unit volume by extraction amount of nickel

Construction of This Embodiment

Next, the construction of a solution for use in extraction of cobalt to be used in the cobalt extraction in this embodiment is described.
As described in the foregoing, the solution for use in extraction of cobalt of this embodiment is configured to separate cobalt by being brought into contact with an aqueous solution containing cobalt and chlorine, and includes: an ionic liquid containing a quaternary ammonium group; and an organic solvent that is present in a state of being mingled with the ionic liquid and has a kauri-butanol value (hereinafter described as “KB value”) of 60 or more.
The term “KB value” as used herein refers to the number of milliliters of a sample when a certain amount of a solution of a kauri resin in butanol is loaded into an Erlenmeyer flask, the flask is placed on standard printing type paper, the sample is added to the flask, and a printing type becomes unreadable owing to the occurrence of turbidity.
(Ionic Liquid)
The ionic liquid is a liquid configured to extract cobalt by being brought into contact with an aqueous solution containing cobalt and chlorine, and in this embodiment, an ionic liquid containing a quatemary ammonium-based ionic liquid having a chloride ion as an anion portion is used.
This is because the quatemary ammonium-based ionic liquid is an ionic liquid much less expensive than other ionic liquids, such as a quatemary phosphonium-based ionic liquid.
Examples of the quatemary ammonium-based ionic liquid include, but not necessarily limited to, tri-octyl-methyl-ammonium-chloride (tri-octhyl-methyl-ammnoiumu-chloride, TOMAC) or di-octadecyl-di-methyl-ammonium-chloride (di-octadethyl-di-methyl-ammoniumu-chloride).
(Organic Solvent)
The organic solvent of this embodiment is configured to reduce the solubility of the ionic liquid containing a quatemary ammonium group in water, and to adjust its physical properties, such as a viscosity, and an organic solvent having a KB value of 60 or more is used.
Now, the reason why the organic solvent having a KB value of 60 or more is used is described.
As described above, a quatemary ammonium-based ionic liquid having a chloride ion as an anion portion is an ionic liquid much less expensive than other ionic liquids.
However, in an investigation on the extraction of a metal ion, a quatemary phosphonium-based ionic liquid much more expensive than the quatemary ammonium-based ionic liquid has been mainly used.
This is because the phosphonium-based ionic liquid does not dissolve in water and has a low viscosity.
In contrast, the inexpensive ammonium-based ionic liquid involves a problem in that the liquid mixes at a volume ratio of about 10% with water, and a problem in that its viscosity is high. Particularly when cobalt is extracted, the viscosity becomes so high that the separability of the liquid from water becomes poor. Accordingly, the liquid cannot be passed through, for example, a continuous extraction column. Accordingly, despite the fact that the ionic liquid having high extraction efficiency is used, a treatment can be performed only by a batch system poor in efficiency. The dissolution of the ionic liquid in water leads to the discharge of the ionic liquid serving as an expensive extractant to the outside of a system, and hence collection and decomposition treatments for the ionic liquid need to be performed. In addition, the liquid involves a problem in that its ability to separate cobalt and nickel from each other is lower than that of the phosphonium-based ionic liquid.
To cope with the problems, the inventors of this invention have discovered that the organic solvent having a KB value of 60 or more mingles with the quatemary ammonium-based ionic liquid, and in the mingled state, the solubility of the liquid in water reduces and its viscosity also reduces. Thus, the inventors have decided to use the organic solvent having a KB value of 60 or more.
Examples of the organic solvent having a KB value of 60 or more include an alkylbenzene derivative and toluene. For example, when an alkylbenzene derivative having a KB value of 80 (trade name: Solvesso 150) is added at a volume ratio of about 10% to a quatemary ammonium-based ionic liquid, the viscosity of the solvent can be reduced to 1/10 or less. In addition, the separability of the quatemary ammonium-based ionic liquid from water is improved, and hence a phenomenon in which the liquid dissolves in water does not occur (the quatemary ammonium-based ionic liquid dissolves at a ratio of about 3% in terms of wt % in water before its mingling with the organic solvent, but the ratio is reduced to 0.01% or less after the mingling). Thus, the loss of the quatemary ammonium-based ionic liquid (dissolution in water) in an extraction treatment can be suppressed. An upper limit for the KB value is not particularly limited, but it is difficult to produce an organic solvent that can be industrially utilized, the solvent having a KB value of more than 110.
A possible reason why mixing the organic solvent and the quatemary ammonium-based ionic liquid to mingle the solvent and the liquid with each other can suppress the dissolution of the liquid in water is that the quatemary ammonium-based ionic liquid preferentially dissolves in the hydrophobic organic solvent and hence its dissolution in water does not occur.
In addition, the quatemary ammonium-based ionic liquid dissolves in water, and the water similarly dissolves in the quatemary ammonium-based ionic liquid. Nickel in the water cannot be separated by an extraction treatment, and the ionic liquid needs to be washed after the extraction. However, when the quatemary ammonium-based ionic liquid is mixed with the organic solvent to be mingled therewith, the amount of the water dissolving in the quatemary ammonium-based ionic liquid reduces. Accordingly, the amount of nickel to be included also reduces, and hence the ability of the solution for use in extraction of cobalt to separate cobalt and nickel from each other can be improved.
The foregoing is the description of the reason why the organic solvent having a KB value of 60 or more is used.
The solution for use in extraction of cobalt desirably contains the organic solvent at a volume ratio of 2% or more and 50% or less, and more desirably contains the solvent at a volume ratio of 5% or more and 15% or less. This is because of the following reasons: when the content of the organic solvent is less than 2%, an effect of incorporating the organic solvent is not obtained; and when the content is more than 50%, the Co extraction ability of the solution reduces because the organic solvent is not involved in the extraction of Co.
In addition, the solution for use in extraction of cobalt desirably contains the organic solvent so that its viscosity may be 0.02 Pa·s or more and 0.5 Pa·s or less. This is because of the following reasons: a large amount of the organic solvent needs to be incorporated for producing a solution having a viscosity of less than 0.02 Pa·s, and hence the Co extraction ability reduces; and when the viscosity is more than 0.5 Pa·s, it becomes difficult to perform a treatment with a continuous extractor at the time of Co extraction. The viscosity of the solution for use in extraction of cobalt reduces as the content of the organic solvent therein increases. As described above, however, when the content is excessively large, the Co extraction ability reduces, and hence the content of the organic solvent needs to be set in consideration of both the viscosity and the extraction ability.
<Cobalt Extraction Method>
Next, a cobalt extraction method involving using the solution for use in extraction of cobalt according to this embodiment is described with reference to FIG. 1.
The following method is given as an example herein. A cemented carbide scrap containing tungsten, cobalt, nickel, and iron is subjected to oxidizing roasting and an alkali extraction treatment or a molten salt dissolution treatment, and an aqueous solution of sodium tungstate thus produced is filtered to produce a tungsten extraction residue, followed by the collection of a cobalt aqueous solution from the residue.
First, an acidic aqueous solution is prepared by bringing an acid, such as hydrochloric acid or sulfuric acid, into contact with the tungsten extraction residue to leach out cobalt as cobalt chloride or cobalt sulfate into the aqueous solution (S1 of FIG. 1). The kind of the acid is preferably hydrochloric acid in consideration of a subsequent treatment. However, when chlorine is supplied by using, for example, sodium chloride later, the kind of the acid is not necessarily limited to hydrochloric acid as long as the acid is a strong acid, and sulfuric acid or the like is also permitted.
In addition, the concentration of the acid is desirably 1 N or more and 10 N or less, more desirably 2 N or more and 5 N or less.
This is because of the following reasons: when the concentration of the acid is more than 10 N, the ratio at which manganese or copper is removed at the time of an ion exchange treatment to be described later reduces; and when the concentration of the acid is less than 1 N, a cobalt concentration in a leachate (aqueous solution into which cobalt has been leached out) reduces to cause a reduction in treatment efficiency or an increase in cost.
Next, hydrogen peroxide is added to the aqueous solution. The addition is intended for such oxidation of iron in the residue that iron may be trivalent. A specific addition amount thereof is about 0.5-fold mol or more and about 3-fold mol or less of iron. When the addition amount is 0.5-fold mol of iron, the amount is equal to that of iron and hence all iron can be oxidized.
The case where the addition amount of hydrogen peroxide is more than 3-fold mol of iron is not desirable because excess hydrogen peroxide decomposes to produce oxygen and oxygen is responsible for the entry of air bubbles into a resin pipe at the time of the ion exchange to be described later. Meanwhile, the case where the addition amount of hydrogen peroxide is less than 0.5-fold mol of iron is not desirable because unoxidized iron remains in the solution. Iron is oxidized immediately after the hydrogen peroxide addition.
Next, iron is precipitated by adjusting the pH of the aqueous solution to 1 or more and 6 or less with an alkali, such as sodium hydroxide or calcium hydroxide, and the precipitated iron is removed by filtration or the like (S2 of FIG. 1).
A specific alkali is preferably a hydroxide formed of a monovalent cation, and is preferably sodium hydroxide in consideration of cost. This is because of the following reason: when the finally extracted Co is used as a raw material for a cemented carbide tool, Co needs to be precipitated by adding oxalic acid to the Co aqueous solution, but when a hydroxide formed of a divalent cation is used in the S2, the hydroxide is precipitated together with cobalt at the time of the production of the oxalic acid precipitate, and is liable to be included as an impurity. However, when Co is directly reduced, there is no need to limit the alkali to the hydroxide formed of a monovalent cation, and calcium hydroxide, magnesium hydroxide, potassium hydroxide, strontium hydroxide, cobalt hydroxide, or the like can be used. However, a carbonate, such as sodium carbonate, is not desirable because cobalt carbonate is produced, and ammonia is not desirable because a cobalt-ammine complex is produced and hence cobalt cannot be extracted into an ionic liquid.
The precipitated iron is removed by filtration. In addition, the case where the pH is more than 6 is not desirable because cobalt is precipitated as a hydroxide and hence the ratio at which cobalt is collected reduces. In addition, the case where the pH is less than 1 is not desirable because the precipitation of iron does not completely progress, and hence the ratio at which iron is removed reduces, and the ratios at which manganese and copper are removed by the subsequent ion exchange also reduce.
Next, a chloride is added to the aqueous solution to set its chloride ion concentration to 2-fold mol or more of cobalt. The addition is intended for efficient extraction of cobalt into the ionic liquid.
When hydrochloric acid is used in the cobalt leaching treatment (treatment corresponding to the S1 of FIG. 1), the addition of the chloride here is not essential.
Next, manganese and copper are removed by bringing the aqueous solution into contact with an ion exchange resin (S3 of FIG. 1).
Specifically, it is desirable that a chelate-type anion exchange resin having a volume equal to or more than 1/100 of the volume of the aqueous solution be immersed in the aqueous solution for 10 minutes or more, or the aqueous solution be passed after the ion exchange resin has been filled into a column.
The case where the volume of the resin is less than 1/100 of the volume of the aqueous solution is not desirable because the ratios at which manganese and copper are removed reduce.
In addition, the case where the time period for which the resin is immersed is less than 10 minutes is not desirable because the ratios at which manganese and copper are removed reduce.
In addition, when the aqueous solution is passed after the filling into the column, the solution is passed at a space velocity (SV) of 0.1 or more and 10 or less.
The case where the space velocity at the time of the filling into the column is less than 0.1 is not desirable because the removal treatment takes time and such time-consuming treatment is not realistic.
In addition, the case where the space velocity at the time of the filling into the column is more than 10 is not desirable because the breakthrough of manganese and copper quickens, and hence the frequency at which the ion exchange resin is reproduced increases.
Next, the ionic liquid mingled with an organic solvent in advance is brought into contact with the aqueous solution so that Co may be extracted and dissolved in the ionic liquid, and may be separated from nickel (S4 of FIG. 1). A method for the contact may be a batch-type method or may be a continuous method as in a general solvent extraction treatment. Nickel remains in the aqueous solution and is hence collected.
In addition, a chlorine concentration at the time of the contact between the ionic liquid and the aqueous solution is desirably 2-fold molar concentration or more and 10-fold molar concentration or less of the cobalt concentration.
This is because of the following reason: when the chlorine concentration is more than 10-fold molar concentration of the cobalt concentration, the concentration becomes close to the upper limit at which a general chloride, such as sodium chloride or calcium chloride, dissolves in water, and hence the dissolution takes much time, and when the concentration is further increased, a precipitate remains, and hence it becomes difficult to separate the quaternary ammonium-based ionic liquid and the precipitate from each other.
This is also because when the chlorine concentration is less than 2-fold molar concentration of the cobalt concentration, a chloride complex of cobalt is hardly produced and hence an extraction ability reduces.
Finally, the solution into which cobalt has been extracted (hereinafter referred to as “cobalt solution”) is brought into contact with water, such as pure water (S5 of FIG. 1).
The pure water is free of any chloride ion, and hence the chloride complex of cobalt decomposes and cobalt is subjected to back extraction into the pure water. As the temperature of the pure water becomes lower, cobalt can be extracted more efficiently.
The foregoing is the cobalt extraction method of this embodiment.
As described above, the solution for use in extraction of cobalt of this embodiment includes: an ionic liquid containing a quaternary ammonium group; and an organic solvent that is present in a state of being mingled with the ionic liquid and has a kauri-butanol value of 60 or more.
Accordingly, cobalt can be extracted at lower cost and more efficiently than ever before.

EXAMPLES

This invention is specifically described below with reference to Examples.

Example 1

A quatemary ammonium-based ionic liquid was brought into contact with various organic solvents, whether or not the liquid was able to mingle with each of the solvents was judged, and as a change in physical property when the liquid was able to mingle with a solvent, the viscosity of a solution obtained by the mingling was measured.
Specifically, first, TOMAC was prepared as the quatemary ammonium-based ionic liquid.
Next, organic solvents each having a KB value of from 30 to 100 were prepared as the organic solvents, and TOMAC and each of the organic solvents were brought into contact with each other. A relationship between a used organic solvent and its KB value is as described below.
Organic solvent having KB value of 30: Isopar C (isoparaffin-based solvent manufactured by Exxon Mobil Corporation), organic solvent having KB value of 40: Exxsol DSP 80 (naphthene-based solvent manufactured by Exxon Mobil Corporation), organic solvent having KB value of 60: cyclohexane, organic solvent having KB value of 80: Solvesso 150 (aromatic solvent manufactured by Exxon Mobil Corporation), and organic solvent having KB value of 100: toluene. The results are shown in Table 1.

	TABLE 1

	KB value

	30	40	60	80	100

Whether or not	Impossible	Impossible	Possible	Possible	Possible
quaternary
ammonium-based
ionic liquid can
mingle with organic
solvent

As apparent from Table 1, an organic solvent having a KB value of less than 60 did not mingle with TOMAC, and the solvent and TOMAC were separated into two phases. Meanwhile, a solvent having a KB value of 60 or more was confirmed to mingle with TOMAC.
Next, Solvesso 150 was prepared as a solvent having a KB value of 60 or more out of the organic solvents. The Solvesso 150 was mingled at various ratios with TOMAC, and an influence of a mingling ratio on the viscosity of a solution obtained by the mingling was measured. The results are shown in FIG. 2.
As shown in FIG. 2, it was able to be confirmed that when the mingling ratio of the organic solvent was increased, the viscosity of the solution obtained by the mingling reduced in a substantially linear manner. Accordingly, the addition of the organic solvent to TOMAC was found to affect its physical properties.

Example 2

A solution (solution for use in extraction of cobalt) in which a quatemary ammonium-based ionic liquid and an organic solvent mingled with each other was brought into contact with an aqueous solution of Co and Ni, and was evaluated for its extraction ability and separation ability for Co. Specific procedures are as described below.
First, TOMAC was prepared as the quatemary ammonium-based ionic liquid and Solvesso 150 was prepared as the organic solvent. The solution for use in extraction of cobalt was produced by mingling TOMAC and the organic solvent with each other at a mingling ratio of from 0 vol % to 60 vol %.
Next, the aqueous solution of Co and Ni (Co: 43 g/dm³, Ni: 1.0 g/dm³) was produced by dissolving Co and Ni in a 4 mol/L hydrochloric acid. The unit “g/dm³” is equal to the unit “kg/m³” (the same holds true for the following).
Next, the aqueous solution of Co and Ni, and the solution for use in extraction of cobalt were loaded into a separating funnel, and were brought into contact with each other by shaking the funnel for 10 minutes so that Co was caused to migrate toward the solution for use in extraction of cobalt. Thus, Co was extracted and Ni was caused to remain in the aqueous solution.
Next, the Co and Ni concentrations of the aqueous solution before and after the extraction were determined and analyzed by ICP-AES, and a Co extraction ability and a Co—Ni separation ability were calculated from a difference between the concentrations of each element before and after the extraction. The results are shown in FIG. 3.
As shown in FIG. 3, as the volume ratio of the Solvesso 150 increased, the Co extraction ability reduced. This is probably because the Solvesso 150 in the solvent is not involved in the extraction of Co.
Meanwhile, as the volume ratio of the Solvesso 150 increased, the Co—Ni separation ability was improved. This is probably because as the ratio of the Solvesso 150 increased, the hydrophobicity of the solution for use in extraction of cobalt was improved and hence the dissolution of the aqueous solution containing Ni in the solution for use in extraction of cobalt was suppressed.

Example 3

An attempt was made to extract Co from a compound (cobalt residue) containing cobalt, copper, chromium, manganese, iron, and nickel by the Co extraction method according to this embodiment in accordance with procedures illustrated in FIG. 4. Specific procedures are as described below.
First, an acid leachate was obtained by dissolving 130 g of the cobalt residue in 1,000 ml of hydrochloric acid (concentration: 2 mol/l) as an acid (S11 of Fig.). The concentrations (mg/dm³) of the metal components in the acid leachate are as follows: Cu: 1, Cr 150, Mn: 27, Fe: 1,460, Ni: 500.
Next, iron was precipitated by adding 2 ml of a hydrogen peroxide solution (concentration: 0.59 mol/l) and sodium hydroxide (concentration: 8 mol/l) to the acid leachate to set its pH to 3, followed by the collection of iron (S12 of Fig.).
Next, Mn and Cu were removed from the acid leachate from which iron had been removed by bringing the acid leachate into contact with an ion exchange resin (50 ml) to cause the ion exchange resin to adsorb Mn and Cu (S13 of Fig.).
Next, the acid leachate from which Mn and Cu had been removed was brought into contact with a solution for use in extraction of cobalt obtained by mingling TOMAC serving as an ionic liquid and Solvesso 150 serving as an organic solvent with each other (mingling ratio: 10:1). Thus, cobalt was extracted into the ionic liquid in the solution for use in extraction of cobalt (S14 of Fig.).
Finally, cobalt was subjected to back extraction into pure water by bringing the solution for use in extraction of cobalt into contact with the pure water (S15 of Fig.).
The results of the quantitative analysis of the metal concentrations in the aqueous solution in the respective procedures by ICP-AES are shown in Table 2.

TABLE 2

		After
		precipi-
	After acid	tation	After ion	After	After back
Treatment	leaching	treatment	exchange	extraction	extraction
stage	(after S11)	(after S12)	(after S13)	(after S14)	(after S15)

Cu mg/dm ³	1	1	<1	<1	<1
Cr mg/dm ³	150	8	3	<1	1
Mn mg/dm³	27	9	2	<1	3
Fe mg/dm³	1,460	<2	<2	<2	<2
Ni mg/dm ³	500	490	280	89	<2

As apparent from Table 2, the metals were sequentially removed in the respective procedures, and Co was finally purified.

INDUSTRIAL APPLICABILITY

While this invention has been described above with reference to the embodiment and Examples, this invention is not limited to the above-mentioned embodiment.
It should be understood that a person skilled in the art could arrive at various modification examples and improvement examples within the scope of this invention, and that those modification examples and improvement examples are encompassed in the scope of this invention.

Claims

1. A solution for use in extraction of cobalt, comprising:

an ionic liquid containing a quaternary ammonium group; and

an organic solvent that is present in a state of being mingled with the ionic liquid and has a kauri-butanol value of 60 or more.

2. A solution for use in extraction of cobalt according to claim 1, wherein the solution comprises the organic solvent at a volume ratio of 2% or more and 50% or less.

3. A solution for use in extraction of cobalt according to claim 1, wherein the solution comprises the organic solvent at a volume ratio of 5% or more and 15% or less.

4. A solution for use in extraction of cobalt according to claim 1, wherein the organic solvent comprises an alkylbenzene derivative or toluene.

5. A solution for use in extraction of cobalt according to claim 1, wherein the ionic liquid comprises tri-octyl-methyl-ammonium-chloride (TOMAC) or di-octadecyl-di-methyl-ammonium-chloride.

6. A solution for use in extraction of cobalt according to claim 1, wherein the solution has a viscosity of 0.02 Pa·s or more and 0.5 Pa·s or less.

7. A solution for use in extraction of cobalt according to claim 1, wherein the solution has a solubility in water of 0.01% or less.

8. A cobalt solution, comprising:

the solution for use in extraction of cobalt of claim 1; and

an aqueous solution of cobalt and an acid containing chlorine, the aqueous solution being dissolved in the solution for use in extraction of cobalt,

wherein cobalt is dissolved in the solution for use in extraction of cobalt.

9. A method of collecting cobalt, comprising dissolving an aqueous solution of cobalt and an acid containing chlorine in a solution for use in extraction of cobalt, the solution including an ionic liquid containing a quaternary ammonium group, and an organic solvent that is present in a state of being mingled with the ionic liquid and has a kauri-butanol value of 60 or more, to dissolve cobalt in the solution for use in extraction of cobalt to separate and collect cobalt.

10. A method of collecting cobalt according to claim 9, wherein the method comprises:

(a) dissolving a compound containing cobalt in an acid to prepare an acidic aqueous solution;

(b) dissolving the acid in the solution for use in extraction of cobalt to extract cobalt into the solution for use in extraction of cobalt; and

(c) bringing the solution for use in extraction of cobalt into contact with water to perform back extraction of cobalt into the water, followed by collection thereof.

11. A method of collecting cobalt according to claim 9, wherein the solution for use in extraction of cobalt contains the organic solvent at a volume ratio of 2% or more and 50% or less.

12. A method of collecting cobalt according to claim 9, wherein the solution for use in extraction of cobalt contains the organic solvent at a volume ratio of 5% or more and 15% or less.

13. A method of collecting cobalt according to claim 9, wherein the organic solvent comprises an alkylbenzene derivative or toluene.

14. A method of collecting cobalt according to any claim 9, wherein the ionic liquid comprises tri-octyl-methyl-ammonium-chloride (TOMAC) or di-octadecyl-di-methyl-ammonium-chloride.

15. A method of collecting cobalt according to claim 10, wherein:

the compound contains nickel; and

the (b) comprises dissolving the acidic aqueous solution in the solution for use in extraction of cobalt to extract cobalt into the solution for use in extraction of cobalt, and to collect nickel remaining in the acidic aqueous solution.

16. A method of collecting cobalt according to claim 10, wherein:

the compound contains at least one of manganese and copper; and

the method further comprises (d) bringing the acidic aqueous solution into contact with a chelate resin to separate at least one of manganese and copper from the acidic aqueous solution.

17. A method of collecting cobalt according to claim 10, wherein:

the compound contains iron; and

the method further comprises (e) removing iron from the acidic aqueous solution.

18. A method of collecting cobalt according to claim 17, wherein the (e) comprises:

adding hydrogen peroxide to the acidic aqueous solution to oxidize iron;

adjusting a pH of the acidic aqueous solution to 1 or more and 6 or less to precipitate iron; and

removing the precipitated iron by filtration.

19. A method of collecting cobalt according to claim 10, wherein the (a) comprises adding a chloride to the acidic aqueous solution.

20. A method of collecting cobalt according to claim 10, wherein the compound contains a residue after collection of tungsten from a cemented carbide scrap containing tungsten and cobalt.