Method for reducing cobalt content in cyanocobalt complex-containing aqueous solution

Abstract

Provided is a method for reducing a cobalt content in a cyanocobalt complex-containing aqueous solution, the method being capable of reducing a cobalt content in an aqueous solution even under conditions other than high-temperature and high-pressure conditions.　This method involves: generating a first precipitate in a cobalt-containing acidic aqueous solution by adding a copper compound and a dithiocarbamate polymer to a cyanocobalt complex-containing aqueous solution in a state where the pH is less than 5.0, and adjusting the pH of the cobalt-containing acidic aqueous solution to 8.0 or more after the first precipitate is generated to generate a second precipitate in the cobalt-containing basic aqueous solution, wherein at least part of the first precipitate and at least part of the second precipitate generated by the above method are removed.

Description

Method for reducing the cobalt content in an aqueous solution containing a cyanocobalt complex

[0001] The present invention relates to a method for reducing the cobalt content in an aqueous solution containing a cyanocobalt complex.

[0002] Cured products of compositions containing polyoxyalkylene polymers modified with hydrolyzable silyl groups have excellent properties such as durability, heat and cold resistance, and economy. For this reason, compositions containing polyoxyalkylene polymers modified with hydrolyzable silyl groups are used in a variety of applications, such as sealants. A known method for producing polyoxyalkylene polymers modified with hydrolyzable silyl groups involves introducing an unsaturated bond into the terminal of a polyoxyalkylene polymer and then adding a hydrosilane compound to the terminal unsaturated bond via a hydrosilylation reaction. Polyoxyalkylene polymers can be produced by ring-opening polymerization of an alkylene oxide in the presence of a composite metal cyanide complex catalyst (DMC catalyst). In the above production method, the DMC catalyst is removed from the polyoxyalkylene polymer when the unsaturated bond-introduced polyoxyalkylene polymer is purified with water. Therefore, when a zinc hexacyanocobaltate complex is used as the DMC catalyst, the aqueous solution discharged by purifying the polymer with water contains a cyanocobalt complex.

[0003] Many countries have set standards for the cobalt content in wastewater. In particular, in Europe, some regions plan to set stricter wastewater standards for cobalt content in the future, gradually lowering the standard value and ultimately restricting it to 50 μg / L or less. Therefore, in order to make the cobalt content in wastewater conform to the wastewater standards, it is necessary to reduce the cobalt content in the aqueous solution containing a cyanocobalt complex as much as possible. It is not necessary to reduce the cobalt content to below the wastewater standard value in a single treatment. If the cobalt content can be reduced to a certain extent in a single treatment, the dilution ratio can be reduced when diluting the wastewater to make the cobalt content conform to the wastewater standard value. Furthermore, even if the wastewater is repeatedly treated to reduce the cobalt content in the wastewater to below the wastewater standard value, the cobalt content in the wastewater can be reduced to below the wastewater standard value with a small number of treatments.

[0004] As a means for solving such problems, a method of subjecting wastewater containing heavy metal species such as cobalt to wet oxidation treatment has been proposed (see Patent Document 1). Specifically, in the method described in Patent Document 1, when wet oxidation is performed, the content of water-soluble or water-miscible iron compounds in the wastewater is adjusted to a specific amount, and then the wastewater is subjected to wet oxidation treatment under high temperature and high pressure to produce a precipitate containing the heavy metal elements, and the precipitate is removed from the wastewater, thereby removing the heavy metals from the wastewater.

[0005] Japanese Patent Application Publication No. 6-182364

[0006] However, the wet oxidation treatment in Patent Document 1 is carried out under high temperature and high pressure. To carry out the treatment under high temperature and high pressure, an expensive pressure-resistant device is required. Furthermore, the treatment under high temperature and high pressure requires sufficient care to ensure operational safety.

[0007] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a method for reducing the cobalt content in an aqueous solution containing a cyanocobalt complex, which method can reduce the cobalt content in the aqueous solution without using high-temperature and high-pressure conditions.

[0008] The present inventors have discovered that the above-mentioned problems can be solved by a method comprising the steps of adding a copper compound and a dithiocarbamate polymer to an aqueous solution containing a cyanocobalt complex at a pH of less than 5.0 to produce a first precipitate in the cobalt-containing acidic aqueous solution, and, after the first precipitate has been produced, adjusting the pH of the cobalt-containing acidic aqueous solution to 8.0 or higher to produce a second precipitate in the cobalt-containing basic aqueous solution, and removing at least a portion of the first precipitate and at least a portion of the second precipitate produced by the above-mentioned method, and have completed the present invention.

[0009] More specifically, the present invention provides the following (1) to (4): (1) A method for reducing the cobalt content in an aqueous solution containing a cyanocobalt complex, comprising: mixing an aqueous solution containing a cyanocobalt complex having a pH of less than 5.0 with a copper compound and a dithiocarbamate polymer, or mixing an aqueous solution containing a cyanocobalt complex having a pH of 5.0 or more with an acid, a copper compound and a dithiocarbamate polymer, thereby producing a first precipitate in a cobalt-containing acidic aqueous solution having a pH of less than 5.0; adjusting the pH of the cobalt-containing acidic aqueous solution after the production of the first precipitate to 8.0 or more, thereby producing a second precipitate in a cobalt-containing basic aqueous solution; and removing at least a portion of the first precipitate and at least a portion of the second precipitate from the cobalt-containing basic aqueous solution containing the first precipitate and the second precipitate. (2) A method for reducing the cobalt content in an aqueous solution containing a cyanocobalt complex, the method comprising: mixing a cyanocobalt complex-containing aqueous solution having a pH of less than 5.0 with a copper compound and a dithiocarbamate polymer, or mixing a cyanocobalt complex-containing aqueous solution having a pH of 5.0 or more with an acid, a copper compound and a dithiocarbamate polymer, thereby producing a first precipitate in the cobalt-containing acidic aqueous solution having a pH of less than 5.0, thereby obtaining a cobalt-containing acidic aqueous solution containing the first precipitate; removing at least a portion of the first precipitate from the cobalt-containing acidic aqueous solution containing the first precipitate; adjusting the pH of the cobalt-containing acidic aqueous solution from which at least a portion of the first precipitate has been removed to 8.0 or more, thereby producing a second precipitate; and removing at least a portion of the second precipitate from a cobalt-containing basic aqueous solution containing the second precipitate. (3) The method according to (1) or (2), wherein the copper compound is copper(II) sulfate. (4) The method according to any one of (1) to (3), wherein the cyanocobalt complex is a zinc hexacyanocobaltate complex. (5) The method according to (4), wherein the aqueous solution containing the cyanocobalt complex is a liquid produced in a method for producing a polyoxyalkylene polymer, which comprises polymerizing an alkylene oxide using a zinc hexacyanocobaltate complex as a catalyst. (6) The method according to any one of (1) to (5), wherein the aqueous solution containing the cyanocobalt complex contains sodium chloride.

[0010] According to the present invention, it is possible to provide a method for reducing the cobalt content in an aqueous solution containing a cyanocobalt complex, which method can reduce the cobalt content in the aqueous solution without using high-temperature and high-pressure conditions.

[0011] <<First Method>> Hereinafter, a method for reducing the cobalt content in an aqueous solution containing a cyanocobalt complex, the method comprising: mixing a cyanocobalt complex-containing aqueous solution having a pH of less than 5.0 with a copper compound and a dithiocarbamate polymer, or mixing a cyanocobalt complex-containing aqueous solution having a pH of 5.0 or more with an acid, a copper compound and a dithiocarbamate polymer, thereby producing a first precipitate in a cobalt-containing acidic aqueous solution having a pH of less than 5.0; adjusting the pH of the cobalt-containing acidic aqueous solution after the first precipitate has been produced to 8.0 or more, thereby producing a second precipitate in a cobalt-containing basic aqueous solution; and removing at least a portion of the first precipitate and at least a portion of the second precipitate from the cobalt-containing basic aqueous solution containing the first precipitate and the second precipitate. is referred to as the first method.

[0012] In the first method, first, a first precipitate is produced in a cobalt-containing acidic aqueous solution having a pH of less than 5.0 by mixing an aqueous solution containing a cyanocobalt complex having a pH of less than 5.0 with a copper compound and a dithiocarbamate polymer, or by mixing an aqueous solution containing a cyanocobalt complex having a pH of 5.0 or more with an acid, a copper compound and a dithiocarbamate polymer.

[0013] (Aqueous solution containing a cyanocobalt complex) The cyanocobalt complex contained in the aqueous solution containing a cyanocobalt complex is not particularly limited. Typical examples of cyanocobalt complexes include compounds used as catalysts for polymerizing alkylene oxides in the production method of polyoxyalkylene polymers described below. The cyanocobalt complex is preferably a zinc hexacyanocobaltate complex. The aqueous solution containing a cyanocobalt complex may contain, in addition to the cyanocobalt complex, a water-soluble cobalt compound other than the cyanocobalt complex.

[0014] The cobalt content in the aqueous solution containing a cyanocobalt complex is not particularly limited. The cobalt content in 1 L of the aqueous solution containing a cyanocobalt complex is, for example, preferably 500 μg or more and 10,000 μg or less, and more preferably 1,000 μg or more and 5,000 μg or less. The cobalt content in 1 L of the aqueous solution containing a cyanocobalt complex can be measured using an inductively coupled plasma mass spectrometry (ICP-MS) device.

[0015] The aqueous solution containing a cyanocobalt complex may contain organic matter as long as the desired effect is not impaired. Although it depends on the amount of organic matter contained in the aqueous solution containing a cyanocobalt complex, it is preferable that the aqueous solution containing the cyanocobalt complex containing the organic matter be subjected to a treatment for removing the organic matter in an activated sludge tank or the like after removing cobalt by the first method.

[0016] As mentioned above, a cyanocobalt complex is typically a catalyst for polymerizing alkylene oxide in a method for producing a polyoxyalkylene polymer. A typical example of an aqueous solution containing a cyanocobalt complex is an aqueous solution produced in a purification step in the process of producing a polyoxyalkylene polymer modified with a hydrolyzable silyl group. Hereinafter, the production of an aqueous solution containing a cyanocobalt complex in a purification step in the process of producing a polyoxyalkylene polymer modified with a hydrolyzable silyl group will be described.

[0017] The method for producing a polyoxyalkylene polymer modified with a hydrolyzable silyl group includes: obtaining a polyoxyalkylene polymer by ring-opening polymerization of alkylene oxide in the presence of a composite metal cyanide complex catalyst (DMC catalyst); reacting a terminal hydroxyl group of the polyoxyalkylene polymer with a metal alkoxide to convert the terminal of the polyoxyalkylene polymer into a metal alkoxide; reacting the alkoxidized terminal of the polyoxyalkylene polymer with an unsaturated group-containing halide to introduce an unsaturated bond into the terminal of the polyoxyalkylene polymer; purifying the polyoxyalkylene polymer having an unsaturated bond at its terminal so as to remove the alkali metal halide by-produced by the reaction of the alkoxidized terminal with the unsaturated group-containing halide compound from the polyoxyalkylene polymer having an unsaturated bond at its terminal; Examples of such methods include a method comprising introducing a hydrolyzable silyl group into the terminal of a polyoxyalkylene polymer by a hydrosilylation reaction between an unsaturated bond at the terminal of the polyoxyalkylene polymer and a hydrosilane that provides a hydrolyzable silyl group.

[0018] The DMC catalyst is not particularly limited as long as it has catalytic activity for promoting the ring-opening polymerization of alkylene oxide. A zinc hexacyanocobaltate complex is preferred as the DMC catalyst. The zinc hexacyanocobaltate complex may have an alcohol and / or an ether coordinated as an organic ligand.

[0019] The alkylene oxide is not particularly limited as long as it is a compound capable of undergoing ring-opening polymerization. Examples of the alkylene oxide include alkylene oxides such as ethylene oxide, propylene oxide, α-butylene oxide, β-butylene oxide, hexene oxide, cyclohexene oxide, styrene oxide, and α-methylstyrene oxide; and substituted or unsubstituted glycidyl ethers having 2 to 12 carbon atoms such as methyl glycidyl ether, ethyl glycidyl ether, isopropyl glycidyl ether, butyl glycidyl ether, allyl glycidyl ether, and phenyl glycidyl ether.

[0020] In the ring-opening polymerization reaction of alkylene oxide, an initiator is usually used. The initiator is not particularly limited as long as it can be used to produce a polyoxyalkylene polymer. Examples of the initiator include monohydric alcohols such as methanol, ethanol, 1-propanol, 2-propanol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 2-methyl-2-butanol, 3-methyl-2-butanol, and 2,2-dimethyl-1-propanol; polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, hexamethylene glycol, methallyl alcohol, hydrogenated bisphenol A, neopentyl glycol, polybutadiene diol, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, polypropylene triol, polypropylene tetraol, dipropylene glycol, glycerin, trimethylolmethane, trimethylolpropane, and pentaerythritol; and various polymers having a hydroxyl group.

[0021] The main chain structure of the polyoxyalkylene polymer is composed of oxyalkylene repeating units. The main chain structure of the polyoxyalkylene polymer may be branched or crosslinked. The polyoxyalkylene polymer may contain, in addition to the multiple oxyalkylene repeating units, a structure derived from the initiator used in polymerization.

[0022] The oxyalkylene repeating unit is —CH ２ CH ２ O-, -CH(CH ３ ) CH ２ O—, —CH(C ２ H ５ ) CH ２ O-, -C(CH ３ ) ２ CH ２ O- and -CH ２ CH ２ CH ２ CH２ O- and the like.

[0023] The oxyalkylene repeating unit may, for example, be an oxyalkylene unit having 1 to 10 carbon atoms.

[0024] The metal alkoxide is not particularly limited as long as it is a compound capable of substituting an alkali metal atom for a hydrogen atom in a terminal hydroxyl group (—OH) of a polyoxyalkylene polymer. The metal alkoxide is preferably an alkali metal alkoxide having 1 to 4 carbon atoms. Examples of the alkali metal alkoxide include sodium methoxide, potassium methoxide, sodium ethoxide, and potassium ethoxide. Two or more types of metal alkoxides can be used in combination, but it is preferable to use one type alone.

[0025] The unsaturated group-containing halide is not particularly limited as long as it is a compound having a non-aromatic unsaturated bond and a halogen atom. Examples of the unsaturated group-containing halide include compounds represented by the following formula (1): CH ２ =CHRX (1) (In the formula, R is a divalent organic group. The organic group may contain a heteroatom such as an oxygen atom, a nitrogen atom, a sulfur atom, a silicon atom, a phosphorus atom, or a halogen atom. X is a halogen atom.) Examples of unsaturated group-containing halides include allyl chloride and methallyl chloride (3-chloro-2-methyl-1-propene). Two or more types of unsaturated group-containing halides can be used in combination, but it is preferable to use one type alone.

[0026] The pH of the obtained crude unsaturated group-containing polyoxyalkylene polymer is preferably 9.0 or less. When the pH is 9.0 or less, alkaline components can be easily removed. When the alkaline components are well removed, the oil phase and the wash water can be easily separated. Therefore, when the pH of the crude unsaturated group-containing polyoxyalkylene polymer is 9.0 or less, metal impurities and salts can be efficiently removed when the crude unsaturated group-containing polyoxyalkylene polymer is purified.

[0027] The crude unsaturated group-containing polyoxyalkylene polymer obtained by the above-mentioned method contains metal impurities and salts as impurities. Examples of water-soluble compounds to be removed as impurities include alkali metal compounds and compounds derived from DMC catalysts. More specifically, water-soluble compounds include zinc salts, cobalt salts, cyanocobalt complex salts, and alkali metal salts. In particular, when the end of an alkoxidized polyoxyalkylene polymer is reacted with an unsaturated group-containing halide to introduce an unsaturated bond into the end of the polyoxyalkylene polymer, the by-product alkali metal halide is contained in the crude unsaturated group-containing polyoxyalkylene polymer.

[0028] Next, the polyoxyalkylene polymer having an unsaturated bond at its terminal is purified so as to remove the alkali metal halide by-product produced by the reaction of the alkoxidized terminal with the unsaturated group-containing halogen compound from the polyoxyalkylene polymer having an unsaturated bond at its terminal. Typically, the crude unsaturated group-containing polyoxyalkylene polymer containing impurities is washed with water to remove alkali metal salts such as alkali metal halides, as well as cobalt salts and compounds derived from the DMC catalyst, such as cyanocobalt complex salts, from the crude unsaturated group-containing polyoxyalkylene polymer. In other words, the wash water after washing contains alkali metal halides. In this way, the aqueous solution containing the cyanocobalt complex from which cobalt is removed may contain alkali metal halides. Examples of alkali metal halides include sodium chloride, potassium chloride, sodium bromide, and potassium bromide.

[0029] In the above purification method, the crude unsaturated group-containing polyoxyalkylene polymer may be washed with water, or the organic solvent solution of the crude unsaturated group-containing polyoxyalkylene polymer may be washed with water.

[0030] When a liquid crude polyoxyalkylene polymer having an unsaturated group is washed with water, an aqueous phase is separated from an oil phase mainly consisting of the liquid crude polyoxyalkylene polymer after washing with water, and water-soluble compounds as impurities are extracted into the aqueous phase.

[0031] When washing an organic solvent solution of a crude unsaturated group-containing polyoxyalkylene polymer with water, a hydrophobic organic solvent that can be separated from water is used as the organic solvent. After washing with water, an aqueous phase is separated from an oil phase consisting mainly of the organic solvent solution of the crude unsaturated group-containing polyoxyalkylene polymer. Water-soluble compounds as impurities are extracted into the aqueous phase.

[0032] The temperature for washing with water is not particularly limited as long as it is possible to remove a desired amount of impurities from the crude unsaturated group-containing polyoxyalkylene polymer. The temperature for washing with water is preferably 10 to 90°C, since water-soluble compounds as impurities can be easily extracted into the aqueous phase.

[0033] The number of times of washing with water is not particularly limited. Although it depends on the amount of washing water, it is preferable to wash with water two or more times in terms of purification effect.

[0034] Acidic water can also be used as the washing water. When the crude unsaturated group-containing polyoxyalkylene polymer is washed with acidic water, impurities can be easily removed efficiently.

[0035] When washing is performed one or more times, the pH of the washing water after the final washing is preferably 3.5 to 8, more preferably 4.0 to 6.5. Furthermore, when washing is performed one or more times, the pH of the washing water after each washing is preferably 3.5 to 8, more preferably 4.0 to 6.5. When the pH of the washing water is within the above range, the impurity removal effect is high.

[0036] In terms of the impurity removal effect, the acidic component added to the acidic water is preferably at least one selected from the group consisting of ascorbic acid, isoascorbic acid, ascorbic acid esters, isoascorbic acid esters, ether derivatives of ascorbic acid, ether derivatives of isoascorbic acid, citric acid, and sulfuric acid. Examples of the ester derivatives include fatty acid esters and phosphate esters. Examples of the ether derivatives include glucosides.

[0037] The mixing ratio of the crude unsaturated group-containing polyoxyalkylene polymer to water is not particularly limited as long as the unsaturated group-containing polyoxyalkylene polymer phase and the water phase can be separated. The amount of water is preferably 10 to 1,000 parts by weight, more preferably 20 to 500 parts by weight, per 100 parts by weight of the crude unsaturated group-containing polyether.

[0038] The number of times the water-soluble compound is extracted into the aqueous phase is not particularly limited. The number of times of extraction is appropriately determined taking into consideration the amount of the water-soluble compound removed by washing with water. The number of times of extraction is preferably 1 to 10 times, more preferably 2 to 6 times, and particularly preferably 2 or 3 times.

[0039] Other methods besides the above purification methods include the following. In this method, first, a crude unsaturated group-containing polyoxyalkylene polymer is dissolved in a solvent that can undergo liquid-liquid separation when mixed with water. The resulting solution is then mixed with water to extract alkaline components, metal impurities derived from the DMC catalyst, and salts into the aqueous phase. In this purification method, following extraction, an oil phase, which is a solution of the unsaturated group-containing polyoxyalkylene polymer, and an aqueous phase are separated.

[0040] Examples of solvents that can undergo liquid-liquid separation when mixed with water include linear aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, aromatic hydrocarbon solvents, hydrophobic alcohol solvents, ether solvents, and halides thereof. Specific examples of these solvents include linear aliphatic hydrocarbon solvents such as butane, pentane, hexane, heptane, octane, nonane, decane, and dodecane; alicyclic hydrocarbon solvents such as cyclohexane and cyclopentane; aromatic hydrocarbon solvents such as benzene, toluene, and xylene; hydrophobic alcohol solvents such as butanol and pentanol; ether solvents such as dimethyl ether, diethyl ether, and diisopropyl ether; halogenated aliphatic hydrocarbon solvents such as methylene chloride, methyl chloroform, carbon tetrachloride, dichlorodifluoromethane, and perchloroethylene; and halobenzene solvents. The solvent is not limited to the above specific examples. Halobenzene solvents include benzene substituted with one or more halogen atoms selected from chlorine, bromine, and iodine atoms. Specific examples of halobenzene solvents include chlorobenzene, dichlorobenzene, and bromobenzene.

[0041] The method for producing a polyoxyalkylene polymer modified with a hydrolyzable silyl group described above includes polymerizing an alkylene oxide using a DMC catalyst. Therefore, the aqueous solution containing a cyanocobalt complex obtained by the purification step in the process for producing a polyoxyalkylene polymer modified with a hydrolyzable silyl group can also be said to be a liquid produced in a method for producing a polyoxyalkylene polymer that includes polymerizing an alkylene oxide. It is preferred that the aqueous solution containing a cyanocobalt complex is a liquid produced in a method for producing a polyoxyalkylene polymer that includes polymerizing an alkylene oxide using a zinc hexacyanocobaltate complex as a catalyst.

[0042] (Copper Compound) The copper compound is not particularly limited as long as the desired effect is not impaired. Various copper compounds can be used as the copper compound. The copper compound may be a compound capable of generating monovalent copper ions or a compound capable of generating divalent copper ions. Typically, organic copper salts and inorganic copper salts can be used as the copper compound. Inorganic copper salts are preferred as the copper compound because they are easily available, inexpensive, and have an excellent cobalt removal effect. Particularly suitable copper compounds include, for example, copper(II) chloride, copper(I) chloride, copper(II) fluoride, copper(II) nitrate, and copper(II) sulfate. Among these, copper(II) sulfate is particularly preferred.

[0043] The amount of the copper compound used is not particularly limited. It is preferable to appropriately determine the amount of the copper compound used based on the type and concentration of the cyanocobalt complex contained in the cyanocobalt complex-containing aqueous solution. When the cyanocobalt complex is a zinc hexacyanocobaltate complex, it is preferable to use an amount of the copper compound that is 6 mol or more in terms of copper per mol of cobalt in the cyanocobalt complex-containing aqueous solution.

[0044] (Dithiocarbamate polymer) The dithiocarbamate polymer is not particularly limited as long as it is a polymer having a dithiocarbamate structure. Suitable examples of the dithiocarbamate polymer include a polymer having a structure represented by the following formula (2) and a polymer represented by the following formula (3).

[0045] (-(CH ２ CH ２ NR １ ) ａ -CH ２ CH ２ ) ２ -N-(CH ２ CH ２ NR １ ) ａ - (2) (In formula (2), R １ are each independently a hydrogen atom, a dithiocarboxylic acid group, or a group represented by the following formula (a): -CS-S － A ＋ (a) is a group represented by the formula:＋ is a monovalent cation. Each of the three a's is independently an integer of 0 or more. The sum of the three a's is 15 or more. １ At least one of the groups represented by formula (a) is a group represented by formula (a). In the structure represented by formula (2), two -(CH ２ CH ２ NR １ ) ａ -CH ２ CH ２ - and one -(CH ２ CH ２ NR １ ) ａ - and a group represented by - are bonded to the same nitrogen atom.

[0046] R ５ - (R ３ -Z(-CH ２ C(OH)HCH ２ NR ４ -R ３ -NR ４ -) ｘ -H) ｙ (3) In formula (3), R ３ are each independently an organic group or a group represented by the following formula (b): ６ -NR ４ -R ６ -) ｚ - (b) is a group represented by the formula: ４ are each independently a hydrogen atom, a dithiocarboxylic acid group, or a group represented by the following formula (a): -CS-S － A ＋ (a) is a group represented by the formula: ＋ is a monovalent cation. ５ is a nitrogen atom or an optionally substituted organic group. ６ are each independently an organic group. Z is —O—, —S—, or —NR ４ -. x is an integer of 10 or greater. y is an integer of 2 or greater. z is an integer of 1 to 5.

[0047] In formula (2), R １The ratio of the total number of moles of the dithiocarboxylic acid group and the group represented by formula (a) to the total number of moles of the dithiocarboxylic acid group to the total number of moles of the group represented by formula (a) is not particularly limited as long as the desired effect is obtained. The ratio is preferably 50 mol % or more, more preferably 80 mol % or more.

[0048] A in formula (a) in formula (2) ＋ is a monovalent cation. ＋ The monovalent cation as A may be an organic cation or an inorganic cation. ＋ The monovalent cation as is preferably a monovalent inorganic cation, more preferably a monovalent metal ion, further preferably an alkali metal ion, and particularly preferably a sodium ion.

[0049] In formula (2), the sum of the three a's is preferably 100 or more, and more preferably 500 or more.

[0050] The dithiocarbamate polymer represented by formula (2) can be produced by known methods, such as reacting polyethyleneimine (PEI) with carbon disulfide in the presence of a base.

[0051] In formula (3), R ３ is an organic group or a group represented by the above formula (b). ３ The organic group as R may be an aliphatic group, an aromatic group, or a combination of an aliphatic group and an aromatic group. ３ The organic group as is preferably an aliphatic group, more preferably an aliphatic hydrocarbon group. As the aliphatic hydrocarbon group, an alkylene group is preferred, more preferably an alkylene group having 1 to 4 carbon atoms, and particularly preferably an ethylene group.

[0052] In formula (3), x is preferably 25 or more.

[0053] In formula (3), y is preferably 2.

[0054] In formula (3), R ５ is preferably a nitrogen atom.

[0055] In formula (3), R ４The ratio of the total number of moles of the dithiocarboxylic acid group and the group represented by formula (a) to the total number of moles of the dithiocarboxylic acid group to the total number of moles of the group represented by formula (a) is not particularly limited as long as the desired effect is obtained. The ratio is preferably 50 mol % or more, more preferably 80 mol % or more.

[0056] The formula (a) in the formula (3) is the same as the formula (a) in the formula (2).

[0057] In formula (3), Z is —NR ４ Preferably, it is -.

[0058] The dithiocarbamate polymer represented by formula (3) can be produced by known methods, such as reacting a polyamine with carbon disulfide in an aqueous solution.

[0059] Preferably, the dithiocarbamate polymer represented by formula (3) can be produced by reacting a terpolymer of ethylenediamine (EDA), tris(2-aminoethyl)amine (TREN), and PEI with carbon disulfide.

[0060] The form of the dithiocarbamate used in preparing the cobalt-containing aqueous solution having a pH of less than 5.0 is not particularly limited. A solid dithiocarbamate polymer may be used, or a solution of the dithiocarbamate polymer may be used. The solution of the dithiocarbamate polymer is preferably an aqueous solution. The concentration of the dithiocarbamate solution is not particularly limited, as long as a desired amount of dithiocarbamate can be added to the cobalt-containing aqueous solution having a pH of less than 5.0.

[0061] The amount of the dithiocarbamate polymer used is not particularly limited as long as the desired effect is not impaired. Preferably, the amount of the dithiocarbamate polymer used is appropriately determined by previously measuring the type and concentration of the cyanocobalt complex contained in the cyanocobalt complex-containing aqueous solution. The amount of the dithiocarbamate polymer used is preferably, for example, 0.1 to 10,000 mg / L as a concentration in the cobalt-containing acidic aqueous solution having a pH of less than 5.0.

[0062] (Acid) When preparing a cobalt-containing acidic aqueous solution having a pH of less than 5.0 using a cyanocobalt complex-containing aqueous solution having a pH of 5.0 or more, an acid is used. A protonic acid is typically used as the acid. The protonic acid may be an organic acid or an inorganic acid. Examples of organic acids include acetic acid, formic acid, propionic acid, butyric acid, succinic acid, oxalic acid, fumaric acid, maleic acid, and lactic acid. Examples of inorganic acids include hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid. Among these acids, hydrochloric acid and sulfuric acid are preferred because they are easily available and inexpensive.

[0063] (Cobalt-Containing Acidic Aqueous Solution) The cobalt-containing acidic aqueous solution is a cobalt-containing aqueous solution having a pH of less than 5.0, which is obtained by mixing a cyanocobalt complex-containing aqueous solution having a pH of less than 5.0 with a copper compound and a dithiocarbamate polymer, or by mixing a cyanocobalt complex-containing aqueous solution having a pH of 5.0 or more with an acid, a copper compound and a dithiocarbamate polymer.

[0064] The method for mixing a cyanocobalt complex-containing aqueous solution having a pH of less than 5.0 with a copper compound and a dithiocarbamate polymer, and the method for mixing a cyanocobalt complex-containing aqueous solution having a pH of 5.0 or more with an acid, a copper compound and a dithiocarbamate polymer are not particularly limited, and various methods can be used. Examples of mixing methods include dynamic mixing using a rotating stirring blade and static mixing using a static mixer. These mixing methods may be combined. A preferred mixing method involves stirring the aqueous solution. The stirring time is not particularly limited, but is preferably 30 minutes or longer.

[0065] When mixing an aqueous solution containing a cyanocobalt complex having a pH of less than 5.0 with a copper compound and a dithiocarbamate polymer, or when mixing an aqueous solution containing a cyanocobalt complex having a pH of 5.0 or more with an acid, a copper compound and a dithiocarbamate polymer, a surfactant may be added to the aqueous solution containing a cyanocobalt complex within a range that does not impair the effects of the present invention.

[0066] The pH of the cobalt-containing acidic aqueous solution is preferably 3.0 or more and less than 5.0, and more preferably 4.0 or more and less than 5.0. When the pH of the cobalt-containing acidic aqueous solution is within the above range, the cobalt removal effect is good.

[0067] (First Precipitate) The first precipitate is a precipitate produced in a cobalt-containing acidic aqueous solution having a pH of less than 5.0 by mixing a cyanocobalt complex-containing aqueous solution having a pH of less than 5.0 with a copper compound and a dithiocarbamate polymer, or by mixing a cyanocobalt complex-containing aqueous solution having a pH of 5.0 or more with an acid, a copper compound and a dithiocarbamate polymer. The cobalt-containing acidic aqueous solution may contain solids other than the first precipitate in addition to the first precipitate. The other solids are typically derived from the cyanocobalt complex-containing aqueous solution having a pH of less than 5.0 or a pH of 5.0 or more, the copper compound, the dithiocarbamate polymer, or the acid.

[0068] Next, after the first precipitate is formed, the pH of the cobalt-containing acidic aqueous solution is adjusted to 8.0 or higher to form a second precipitate in the cobalt-containing basic aqueous solution.

[0069] (Cobalt-Containing Basic Aqueous Solution) The cobalt-containing basic aqueous solution is a cobalt-containing aqueous solution obtained by adjusting the pH of the cobalt-containing acidic aqueous solution after the first precipitate has been produced to 8.0 or higher.

[0070] The method for adjusting the pH of the cobalt-containing acidic aqueous solution to 8.0 or higher is not particularly limited. Examples of the method for adjusting the pH of the cobalt-containing acidic aqueous solution to 8.0 or higher include adding a basic compound such as sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, potassium carbonate, or potassium bicarbonate.

[0071] The pH of the cobalt-containing basic aqueous solution is 8.0 or higher, preferably 8.0 to 11.0, and more preferably 9.5 to 11.0.

[0072] (Second Precipitate) The second precipitate is a precipitate formed in the cobalt-containing basic aqueous solution by adjusting the pH of the cobalt-containing acidic aqueous solution to 8.0 or higher. The cobalt-containing basic aqueous solution may contain, in addition to the first and second precipitates, other solids other than the first and second precipitates. The other solids are typically derived from the cyanocobalt complex-containing aqueous solution, copper compound, dithiocarbamate polymer, or acid, which has a pH of less than 5.0 or a pH of 5.0 or higher.

[0073] Then, at least a portion of the first precipitate and at least a portion of the second precipitate are removed from the cobalt-containing basic aqueous solution containing the first precipitate and the second precipitate.

[0074] (Method for Removing the First Precipitate and the Second Precipitate) The method for removing the first precipitate and the second precipitate is not particularly limited. The first precipitate and the second precipitate contain cobalt derived from the aqueous solution containing a cyanocobalt complex. Therefore, the amount of the first precipitate and the second precipitate removed is preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, even more preferably 90% by weight or more, and most preferably 100% by weight, based on the total amount of the first precipitate and the second precipitate. In other words, the amount of the first precipitate and the second precipitate removed is preferably 50% by weight to 100% by weight, more preferably 70% by weight to 100% by weight, even more preferably 80% by weight to 100% by weight, and even more preferably 90% by weight to 100% by weight, based on the total amount of the first precipitate and the second precipitate.

[0075] Examples of methods for removing the first precipitate and the second precipitate include a method of separating the first precipitate and the second precipitate by precipitation using a settling tank or the like, a method of separating the first precipitate and the second precipitate from a supernatant using a centrifuge, and a method of filtering the first precipitate and the second precipitate using a filter. A preferred method for removing the first precipitate and the second precipitate is to allow the cobalt-containing basic aqueous solution containing the first precipitate and the second precipitate to settle in a tank or container, and then obtain a supernatant. According to this method, the cobalt-containing basic aqueous solution containing the first precipitate and the second precipitate is continuously or intermittently supplied to a tank or container, while continuously or intermittently recovering the supernatant, and the cobalt-containing basic aqueous solution is allowed to remain in the tank or container for a sufficiently long time, thereby enabling continuous removal of the first precipitate and the second precipitate.

[0076] Typically, the cobalt-containing basic aqueous solution from which the first precipitate and the second precipitate have been removed is neutralized, or treated in an activated sludge tank or the like to reduce BOD or COD, and then treated as wastewater. Furthermore, the cobalt-containing basic aqueous solution from which the first precipitate and the second precipitate have been removed may be diluted with water, as necessary. Even when the cobalt-containing basic aqueous solution from which the first precipitate and the second precipitate have been removed is diluted to comply with the cobalt content standard for wastewater, the amount of water used for dilution and the workload for dilution are reduced because the cobalt content has been reduced in advance by the above-described method.

[0077] <<Second Method>> Hereinafter, a method for reducing the cobalt content in an aqueous solution containing a cyanocobalt complex, the method comprising: mixing a cyanocobalt complex-containing aqueous solution having a pH of less than 5.0 with a copper compound and a dithiocarbamate polymer, or mixing a cyanocobalt complex-containing aqueous solution having a pH of 5.0 or more with an acid, a copper compound and a dithiocarbamate polymer, thereby producing a first precipitate in the cobalt-containing acidic aqueous solution having a pH of less than 5.0, thereby obtaining a cobalt-containing acidic aqueous solution containing the first precipitate; removing at least a portion of the first precipitate from the cobalt-containing acidic aqueous solution containing the first precipitate; adjusting the pH of the cobalt-containing acidic aqueous solution from which at least a portion of the first precipitate has been removed to 8.0 or higher, thereby producing a second precipitate; and removing at least a portion of the second precipitate from the cobalt-containing basic aqueous solution containing the second precipitate, will be referred to as the second method.

[0078] The second method is similar to the first method, except that after the formation of the first precipitate and before the formation of the second precipitate, at least a portion of the first precipitate is removed from the cobalt-containing acidic aqueous solution containing the first precipitate; forming a second precipitate in the cobalt-containing acidic aqueous solution from which at least a portion of the first precipitate has been removed; and removing at least a portion of the second precipitate from the cobalt-containing basic aqueous solution containing the second precipitate.

[0079] The method for removing at least a portion of the first precipitate from the cobalt-containing acidic aqueous solution containing the first precipitate is the same as the method for removing the first precipitate and the second precipitate from the cobalt-containing basic aqueous solution in the first method. The amount of the first precipitate removed is preferably 50 wt% or more, more preferably 70 wt% or more, even more preferably 80 wt% or more, even more preferably 90 wt% or more, and most preferably 100 wt% based on the total amount of the first precipitate. That is, the amount of the first precipitate removed is preferably 50 wt% to 100 wt%, more preferably 70 wt% to 100 wt%, even more preferably 80 wt% to 100 wt%, and even more preferably 90 wt% to 100 wt% based on the total amount of the first precipitate.

[0080] The method for producing a second precipitate in a cobalt-containing acidic aqueous solution from which at least a portion of the first precipitate has been removed is similar to the method in the first method in which the pH of the cobalt-containing acidic aqueous solution after the first precipitate has been produced is adjusted to 8.0 or higher to produce a second precipitate in a cobalt-containing basic aqueous solution, except that at least a portion of the first precipitate has been removed from the cobalt-containing acidic aqueous solution.

[0081] The method for removing at least a portion of the second precipitate from a cobalt-containing basic aqueous solution containing the second precipitate is the same as the method for removing the first precipitate and the second precipitate from a cobalt-containing basic aqueous solution in the first method, except that at least a portion of the first precipitate is removed from the cobalt-containing basic aqueous solution. The amount of the second precipitate removed is preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, even more preferably 90% by weight or more, and most preferably 100% by weight, based on the total amount of the second precipitate. That is, the amount of the second precipitate removed is preferably 50% by weight to 100% by weight, more preferably 70% by weight to 100% by weight, even more preferably 80% by weight to 100% by weight, and even more preferably 90% by weight to 100% by weight, based on the total amount of the second precipitate.

[0082] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0083] (Number Average Molecular Weight) The number average molecular weight was measured using a gel permeation chromatograph (GPC) ("HLC-8220" manufactured by Tosoh Corporation) and a column (TSKgel Super H series manufactured by Tosoh Corporation). In the GPC measurement, the measurement temperature was set to 40°C, and tetrahydrofuran (THF) was used as the mobile phase. The number average molecular weight (Mn) was calculated from the GPC measurement chart obtained by the GPC measurement. The number average molecular weight (Mn) is a relative value converted into polystyrene.

[0084] (Cobalt Concentration) The cobalt concentration was measured by a high-frequency inductively coupled plasma mass spectrometry (ICP-MS) device.

[0085] Synthesis Example 1: Using polyoxypropylene glycol with a number-average molecular weight of approximately 4,500 as an initiator, propylene oxide was polymerized in the presence of a zinc hexacyanocobaltate glyme complex catalyst to obtain polyoxypropylene having hydroxyl groups at both ends. 1.2 molar equivalents of sodium methoxide relative to the hydroxyl groups of the resulting hydroxyl-terminated polyoxypropylene was added as a 28 wt% methanol solution. The methanol was then distilled off by vacuum devolatilization. Next, 1.5 molar equivalents of allyl chloride relative to the hydroxyl groups were added to convert the terminal hydroxyl groups to allyl groups. Unreacted allyl chloride was removed by vacuum devolatilization to obtain crude allyl-terminated polyoxypropylene. To 100 parts by weight of the resulting crude allyl-terminated polyoxypropylene, 150 parts by weight of n-hexane, 200 parts by weight of water, and 1.6 parts by weight of a 37.5 wt% aqueous sulfuric acid solution were added and stirred. The aqueous solution and the hexane solution containing the allyl-terminated polyoxypropylene were then centrifuged to obtain an aqueous solution containing a cyanocobalt complex, which had a cobalt concentration of 2600 μg / L, a pH of 4.5, and a sodium chloride concentration of 0.7 wt %.

[0086] Example 1 1,000 parts by weight of the cyanocobalt complex-containing aqueous solution obtained in Synthesis Example 1 was placed in a beaker. 0.6 parts by weight of copper (II) sulfate pentahydrate was added to the cyanocobalt complex-containing aqueous solution. Thereafter, using a mechanical stirrer, the cyanocobalt complex-containing aqueous solution in the beaker was stirred at 300 rpm for 30 minutes. Next, 0.3 parts by weight of a dithiocarbamate polymer (MetClear MR2405 (manufactured by Suez)) was added to the cyanocobalt complex-containing aqueous solution. The cyanocobalt complex-containing aqueous solution was then further stirred at 300 rpm for 30 minutes to obtain a cobalt-containing acidic aqueous solution. After stirring, the cobalt-containing acidic aqueous solution was allowed to stand for 60 minutes to allow a first precipitate to settle. After allowing the first precipitate to settle, the supernatant (cobalt-containing acidic aqueous solution) was sampled, and the cobalt concentration of the supernatant was measured. The results are shown in Table 1.

[0087] The cobalt-containing acidic aqueous solution obtained by the above method was placed in another beaker. While stirring the cobalt-containing acidic aqueous solution at 300 rpm, 0.1 M sodium hydroxide aqueous solution (manufactured by Merck) was added to the cobalt-containing acidic aqueous solution until the pH of the aqueous solution reached 9.5, thereby obtaining a cobalt-containing basic aqueous solution. Next, the cobalt-containing basic aqueous solution was stirred for 30 minutes. Thereafter, the cobalt-containing basic aqueous solution was allowed to stand for 60 minutes, allowing the second precipitate to settle. The supernatant (cobalt-containing basic aqueous solution) was sampled, and the cobalt concentration of the supernatant was measured. The results are shown in Table 1.

[0088] Example 2 A cobalt removal treatment was carried out in the same manner as in Example 1, except that a cyanocobalt complex-containing aqueous solution obtained by performing the same operation as in Synthesis Example 1 was used, and that the dithiocarbamate polymer (MetClear MR2405 (manufactured by Suez)) was replaced with a dithiocarbamate polymer (MetClear MR2435 (manufactured by Suez)). The cyanocobalt complex-containing aqueous solution had a cobalt concentration of 2800 μg / L, a pH of 4.5, and a sodium chloride concentration of 0.7 wt %.

[0089] Comparative Example 1 Cobalt removal treatment was carried out in the same manner as in Example 1, except that copper (II) sulfate pentahydrate was changed to magnesium sulfate.

[0090] Comparative Example 2 Cobalt removal treatment was carried out in the same manner as in Example 1, except that copper (II) sulfate pentahydrate was replaced with zinc sulfate.

[0091] Comparative Example 3 Cobalt removal treatment was carried out in the same manner as in Example 1, except that the dithiocarbamate polymer was changed to an anionic acrylamide copolymer (KLARAID AB1501 (manufactured by Suez)).

[0092]

[0093] According to Examples 1 and 2, it can be seen that cobalt contained in the aqueous solution containing a cyanocobalt complex is effectively removed by adding a copper compound and a dithiocarbamate polymer to the aqueous solution containing a cyanocobalt complex to form a first precipitate in a cobalt-containing acidic aqueous solution having a pH of less than 5.0, adjusting the pH of the cobalt-containing acidic aqueous solution to fall within the aforementioned predetermined range to form a second precipitate in a cobalt-containing basic aqueous solution, and then removing the first and second precipitates. On the other hand, in Comparative Examples 1 to 3, in which a metal compound other than a copper compound or a polymer other than a dithiocarbamate polymer was added to the aqueous solution containing a cyanocobalt complex, the cobalt contained in the aqueous solution containing a cyanocobalt complex could not be effectively removed.

[0094] Example 3 A cobalt removal treatment was carried out in the same manner as in Example 1, except that a cyanocobalt complex-containing aqueous solution newly obtained by carrying out the same operation as in Synthesis Example 1 was used. The obtained cyanocobalt complex-containing aqueous solution had a cobalt concentration of 2400 μg / L, a pH of 4.5, and a sodium chloride concentration of 0.7 wt %.

[0095] Comparative Example 4 A cobalt removal treatment was carried out in the same manner as in Example 3, except that a 0.1 M aqueous solution of sodium hydroxide (manufactured by Merck) was added to the aqueous solution containing a cyanocobalt complex to adjust the pH to 6.5. In Table 2, the aqueous solution containing a cobalt complex whose pH was adjusted to 6.5 is referred to as a "cobalt-containing acidic aqueous solution" for convenience.

[0096] Comparative Example 5 Cobalt removal treatment was carried out in the same manner as in Example 3, except that a 0.1 M aqueous solution of sodium hydroxide (manufactured by Merck) was added to the cobalt-containing acidic aqueous solution until the pH of the aqueous solution reached 6.5. In Table 2, the cobalt-containing aqueous solution with a pH adjusted to 6.5 is conveniently referred to as a "cobalt-containing basic aqueous solution."

[0097]

[0098] According to Example 3, it can be seen that the cobalt contained in the cyanocobalt complex-containing aqueous solution can be effectively removed by adding a copper compound and a dithiocarbamate polymer to the cyanocobalt complex-containing aqueous solution to form a first precipitate in the cobalt-containing acidic aqueous solution having a pH of less than 5.0, adjusting the pH of the cobalt-containing acidic aqueous solution to fall within the aforementioned predetermined range to form a second precipitate in the cobalt-containing basic aqueous solution, and then removing the first and second precipitates. On the other hand, in Comparative Examples 4 and 5, in which the pH of the cobalt-containing acidic aqueous solution was 5.0 or higher or the pH of the cobalt-containing acidic aqueous solution was adjusted to less than 8.0 when forming the second precipitate, the cobalt contained in the cyanocobalt complex-containing aqueous solution could not be effectively removed.

Claims

1. A method for reducing a cobalt content in an aqueous solution containing a cyanocobalt complex, comprising: mixing an aqueous solution containing a cyanocobalt complex having a pH of less than 5.0 with a copper compound and a dithiocarbamate polymer, or mixing an aqueous solution containing a cyanocobalt complex having a pH of 5.0 or more with an acid, a copper compound and a dithiocarbamate polymer, thereby generating a first precipitate in a cobalt-containing acidic aqueous solution having a pH of less than 5.0; adjusting the pH of the cobalt-containing acidic aqueous solution after the generation of the first precipitate to 8.0 or more, thereby generating a second precipitate in a cobalt-containing basic aqueous solution; and removing at least a portion of the first precipitate and at least a portion of the second precipitate from the cobalt-containing basic aqueous solution containing the first precipitate and the second precipitate.

2. A method for reducing the cobalt content in a cyanocobalt complex-containing aqueous solution, comprising: mixing a cyanocobalt complex-containing aqueous solution having a pH of less than 5.0 with a copper compound and a dithiocarbamate polymer, or mixing a cyanocobalt complex-containing aqueous solution having a pH of 5.0 or more with an acid, a copper compound and a dithiocarbamate polymer, thereby generating a first precipitate in a cobalt-containing acidic aqueous solution having a pH of less than 5.0, thereby obtaining a cobalt-containing acidic aqueous solution containing the first precipitate; removing at least a portion of the first precipitate from the cobalt-containing acidic aqueous solution containing the first precipitate; adjusting the pH of the cobalt-containing acidic aqueous solution from which at least a portion of the first precipitate has been removed to 8.0 or more, thereby generating a second precipitate; and removing at least a portion of the second precipitate from the cobalt-containing basic aqueous solution containing the second precipitate.

3. The method according to claim 1 or 2, wherein the copper compound is copper(II) sulfate.

4. The method of claim 1 or 2, wherein the cyanocobalt complex is a zinc hexacyanocobaltate complex.

5. The method according to claim 4, wherein the aqueous solution containing a cyanocobalt complex is a liquid produced in a process for producing a polyoxyalkylene polymer, which comprises polymerizing an alkylene oxide using a zinc hexacyanocobaltate complex as a catalyst.

6. The method according to claim 1 or 2, wherein the aqueous solution containing a cyanocobalt complex contains sodium chloride.

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