Method for producing Zn-Al layered double oxide

Abstract

To provide a method for producing a Zn-Al layered double oxide that can be used as an anion adsorbent, using zinc contained in waste water as a raw material.SOLUTION: A method for producing a Zn-Al layered double oxide (LDO) includes: a precipitation step in which an aluminum source and a carbonate ion source are added to zinc drainage containing zinc ions to precipitate a Zn-Al layered double hydroxide (LDH); and a sintering step in which the Zn-Al layered double hydroxide (LDH) are sintered.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a Zn-Al based layered double oxide. [Background technology]

[0002] BACKGROUND ART In recent years, from the viewpoint of environmental conservation and effective utilization of resources, efforts have been made to recycle and reuse waste that has been disposed of.

[0003] Metal-containing wastewater discharged from plating factories and metal refineries is generally treated within the factory, but this wastewater treatment process generates a large amount of metal sludge. This metal sludge is made by adding chemicals to the wastewater to turn the metals into insoluble solids, and is usually metal hydroxides or sulfides.

[0004] For sludge containing expensive metals such as precious metals and nickel, methods have been developed to recycle these metals by increasing the purity of the metals (for example, Patent Document 1).On the other hand, most sludge containing inexpensive metals such as zinc is landfilled without being recycled. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6616845 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in recent years, disposal costs have risen sharply due to a shortage of landfill sites for sludge. Furthermore, landfilling metal sludge may lead to metal contamination of the soil, and from the perspective of protecting the global environment, it is undesirable to continue landfilling.

[0007] From this perspective, there is a need for a method to convert the zinc contained in wastewater discharged from factories into useful substances and recycle or reuse it.

[0008] An object of the present invention is to provide a method for producing a Zn-Al layered double oxide that can be used as an anion adsorbent, using zinc contained in wastewater as a raw material. [Means for solving the problem]

[0009] The gist of the present invention is as follows. [1] A method for producing a Zn-Al-based layered double hydroxide (LDO), comprising: a precipitation step of adding an aluminum source and a carbonate ion source to zinc wastewater containing zinc ions to precipitate a Zn-Al-based layered double hydroxide (LDH); and a calcination step of calcining the Zn-Al-based layered double hydroxide (LDH). [2] The manufacturing method described in [1], characterized in that the step of adding the aluminum source and the carbonate ion source to the zinc wastewater comprises a first addition step of adding the aluminum source to the zinc wastewater, and a second addition step of adding the carbonate ion source to the zinc wastewater to which the aluminum source has been added. [3] The method according to [1] or [2], wherein the carbonate ion source is an alkali metal carbonate and / or carbon dioxide gas. [4] The method according to any one of [1] to [3], wherein the aluminum source is one or more compounds selected from the group consisting of aluminum nitrate, aluminum chloride, polyaluminum chloride, and aluminum sulfate. [5] The manufacturing method according to any one of [1] to [4], characterized in that the molar ratio of carbonate ions to sulfate ions in the zinc wastewater to which the aluminum source and the carbonate ion source have been added is 20 or more. [6] The method according to any one of [1] to [5], wherein the molar ratio of zinc contained in the Zn-Al-based layered double oxide (LDO) to aluminum contained in the Zn-Al-based layered double oxide (LDO) is 1.9 or more and 2.5 or less. [7] The method according to any one of [1] to [6], wherein the content of sulfate ions in the Zn-Al-based layered double oxide (LDO) is 2 mass % or less. [8] The method according to any one of [1] to [7], wherein the Zn-Al-based layered double oxide (LDO) is an anion adsorbent. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a method for producing a Zn—Al-based layered double oxide that can be used as an anion adsorbent, using zinc contained in wastewater as a raw material. [Brief explanation of the drawings]

[0011] [Figure 1] 2 is a flowchart of a manufacturing method according to the present embodiment. [Figure 2] 4 is a flowchart of a manufacturing method according to the present embodiment (modification). [Figure 3] FIG. 1 is a diagram showing an XRD pattern of the Zn—Al-based layered double oxide obtained in Example 1. [Figure 4] FIG. 1 shows XRD patterns of the Zn—Al-based layered double hydroxide and the Zn—Al-based layered double oxide obtained in Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0012] An embodiment of the present invention will be described below.

[0013] This embodiment relates to a method for producing a Zn-Al-based layered double oxide (LDO). As shown in Fig. 1, the method for producing a Zn-Al-based layered double oxide of this embodiment includes a precipitation step S101 and a calcination step S102.

[0014] The precipitation step S101 is a step in which an aluminum source and a carbonate ion source are added to zinc wastewater containing zinc ions to precipitate Zn—Al-based layered double hydroxides (LDHs).

[0015] In the precipitation step S101, the zinc wastewater to which the aluminum source and carbonate ion source are added is wastewater containing at least zinc ions, and may be, for example, zinc wastewater discharged from a plating factory, a metal refinery, or a zinc mine. The source of the zinc ions contained in the zinc wastewater is not particularly limited, but examples include zinc ions generated by dissolving water-soluble zinc salts such as ZnCl, ZnSO, and Zn(NO) in water (wastewater).

[0016] The zinc wastewater used in the precipitation step S101 may contain, in addition to zinc ions, substances other than zinc ions. The substances other than zinc ions vary depending on the source of the wastewater, but examples include metal ions other than zinc ions (hereinafter also referred to as "other metal ions"), non-metal ions, organic substances, and the like. Examples of other metal ions include iron ions, manganese ions, sodium ions, potassium ions, chromate ions, magnesium ions, and calcium ions. Examples of non-metal ions include ammonium ions, cyanide ions, and sulfate ions. Examples of organic substances include citric acid, succinic acid, aldehydes, benzalacetone, and PEG.

[0017] When zinc wastewater contains other metal ions, the molar amount of zinc ions is preferably 90% or more of the total molar amount (including zinc ions) of metal ions excluding alkali metal ions. When the molar amount of zinc ions is 90% or more of the total molar amount of metal ions excluding alkali metal ions, Zn-Al layered double hydroxide (LDH) is more easily precipitated than when the molar amount of zinc ions is less than 90%.

[0018] Substances other than zinc ions that may be contained in zinc wastewater may be dissolved in the zinc wastewater, or may exist as solids (insoluble matter) in the zinc wastewater. To facilitate precipitation of Zn-Al-based layered double hydroxides (LDHs), it is preferable to remove the solids by solid-liquid separation before adding the aluminum source and carbonate ion source. Furthermore, if the solids that may be contained in the zinc wastewater are zinc salts that can be dissolved in inorganic acids, such as zinc hydroxide or basic zinc carbonate, inorganic acid may be added to the zinc wastewater to dissolve the zinc salt, and then the aluminum source and carbonate ion source may be added.

[0019] The zinc ion concentration in zinc wastewater is not particularly limited and can be, for example, 500 gm / L or more, or 1000 mg / L or more. The upper limit of the zinc ion concentration in zinc wastewater is also not particularly limited and can be, for example, 10000 mg / L or less. The zinc ion concentration in zinc wastewater can be determined using an ICP optical emission spectrometer (e.g., Shimadzu Corporation's Shimadzu sequential high-frequency plasma optical emission spectrometer ICPS-7510).

[0020] Furthermore, the pH of the zinc wastewater to which the aluminum source and carbonate ion source are added (zinc wastewater before addition) is not particularly limited, but from the viewpoint of facilitating precipitation of a Zn-Al layered double hydroxide (LDH), it is preferably less than 7, and more preferably less than 4. When the pH of the zinc wastewater to which the aluminum source and carbonate ion source are added is 7 or higher, it may be used as is, but it is preferable to adjust the pH to less than 7 using an inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid. However, when the pH of the zinc wastewater is highly alkaline, that is, the zinc in the solid matter of the zinc wastewater is less than 5% (in terms of molar amount) of the zinc ions dissolved in the wastewater, whether it is used as is or the pH is adjusted to less than 7 does not have a significant effect on the ease of precipitation of a Zn-Al layered double hydroxide (LDH).

[0021] The aluminum source to be added to the zinc wastewater is a substance that can cause aluminum ions to be contained in the zinc wastewater after addition, and examples thereof include water-soluble aluminum salts such as aluminum nitrate, aluminum chloride, polyaluminum chloride, and aluminum sulfate (aluminum sulfate hydrate). From the viewpoint of facilitating the precipitation of Zn-Al-based layered double hydroxide (LDH), the aluminum source is preferably polyaluminum chloride. Note that polyaluminum chloride is a compound represented by the formula [Al(OH) n Cl 6-n 〕 m (where 1≦n≦5, m≦10).

[0022] The amount of aluminum source added to zinc wastewater is not particularly limited. For example, the molar ratio of zinc ions to aluminum ions (hereinafter referred to as "Zn 2 O 3 ") in zinc wastewater to which the aluminum source and carbonate ion source have been added (hereinafter referred to as "zinc wastewater after addition") is 2+ / Al 3+ From the viewpoint of improving the anion adsorption performance of the Zn-Al-based layered double oxide (LDO) obtained by the production method of this embodiment, the amount of Zn 2+ / Al 3+ The concentration of aluminum ions in zinc wastewater may be determined by an ICP optical emission spectrometer (for example, Shimadzu Corporation's Shimadzu sequential high-frequency plasma optical emission spectrometer ICPS-7510). 2+ / Al 3+ If the amount is such that it does not affect the zinc content, it may be calculated from the amount of aluminum in the aluminum source, taking into account the solubility of the aluminum source added to the zinc wastewater.

[0023] The aluminum source to be added to the zinc wastewater may be one that is added to the zinc wastewater in a state in which aluminum ions have not yet been generated, thereby generating aluminum ions in the zinc wastewater, or one that is first dissolved in a solvent (e.g., water) to generate aluminum ions, and then added to the zinc wastewater in a state in which the aluminum ions are present.

[0024] The carbonate ion source added to zinc wastewater is used to generate carbonate ions (CO3 2- ) are substances that can be contained in zinc wastewater, and examples thereof include alkali metal carbonates, carbon dioxide gas, ammonium carbonate, and ammonium hydrogen carbonate. From the viewpoint of easily adjusting the carbonate ion concentration contained in zinc wastewater, it is preferable to use alkali metal carbonates and / or carbon dioxide gas among these carbonate ion sources.

[0025] The amount of carbonate ion source added to the zinc wastewater is not particularly limited. However, from the viewpoint of improving the anion adsorption performance of the Zn-Al layered double oxide (LDO) obtained by the manufacturing method of this embodiment, the molar ratio of carbonate ions to zinc ions in the zinc wastewater after addition (hereinafter referred to as "CO3 2- / Zn 2+ The amount of zinc added is preferably such that the carbon dioxide concentration (CO₃) is 2.8 or more, more preferably such that the carbon dioxide concentration (CO₃) is 2.8 or more and 9 or less, and even more preferably such that the carbon dioxide concentration (CO₃) is 4.5 or more and 6.5 or less. The concentration of carbonate ions in zinc wastewater may be determined by titration according to the Warder method. However, if the zinc wastewater before addition does not contain carbonate ions or if the carbonate ions in the zinc wastewater before addition are CO₃, the amount of carbonate ions in the zinc wastewater before addition may be determined by titration according to the Warder method. 2- / Zn 2+ If the amount is such that it does not affect the above, it may be calculated from the amount of carbonate in the carbonate ion source, taking into account the solubility of the carbonate ion source added to the zinc wastewater.

[0026] The carbonate ion source to be added to the zinc wastewater may be one that is added to the zinc wastewater in a state in which no carbonate ions have been generated, thereby generating carbonate ions in the zinc wastewater, or one that is first dissolved in a solvent (e.g., water) to generate carbonate ions, and then added to the zinc wastewater in a state in which carbonate ions are present.

[0027] In the precipitation step S101, the order in which the aluminum source and carbonate ion source are added to the zinc wastewater is not particularly limited, and the aluminum source and carbonate ion source may be added in that order (in any order), or the aluminum source and carbonate ion source may be added simultaneously. From the viewpoint of facilitating the precipitation of Zn-Al-based layered double hydroxides (LDHs), it is preferable to add the aluminum source to the zinc wastewater and then the carbonate ion source to the zinc wastewater. In other words, it is preferable that the step of adding the aluminum source and carbonate ion source to the zinc wastewater comprises a first addition step of adding the aluminum source to the zinc wastewater and a second addition step of adding the carbonate ion source to the zinc wastewater to which the aluminum source has been added.

[0028] The pH of the zinc wastewater to which the aluminum source and carbonate ion source have been added (hereinafter also referred to as "zinc wastewater after addition") is not particularly limited and can be, for example, 6.5 or more and less than 10.5, or 7.0 or more and less than 8.7. From the viewpoint of improving the anion adsorption performance of the Zn-Al-based layered double oxide (LDO) obtained by the production method of this embodiment, the pH of the zinc wastewater after addition is preferably 7.0 or more and less than 8.0, and more preferably 7.0 or more and less than 7.3.

[0029] The pH of the zinc-added wastewater can be adjusted by changing the type and amount of carbonate ion source added to the zinc-added wastewater. For example, increasing the amount of carbon dioxide gas (carbonate ion source) can lower the pH, while increasing the amount of sodium carbonate (carbonate ion source) can raise the pH. The pH of the zinc-added wastewater can be adjusted by changing the type and amount of carbonate ion source added to the zinc-added wastewater, or by adding a pH adjuster to the zinc-added wastewater. Examples of pH adjusters that can be added to the zinc-added wastewater include inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, and hydroxides such as sodium hydroxide and potassium hydroxide. The order in which the pH adjuster is added to the zinc-added wastewater is not particularly limited. For example, the pH adjuster may be added between the first and second addition steps, or after the first and second addition steps.

[0030] In the precipitation step S101, an aluminum source and a carbonate ion source are added to the zinc wastewater, whereby aluminum ions and zinc ions co-precipitate in the presence of carbonate ions, and a Zn-Al-based layered double hydroxide (LDH) is precipitated.

[0031] Coprecipitation of aluminum ions and zinc ions proceeds by adding an aluminum source and a carbonate ion source to zinc wastewater. To facilitate the coprecipitation, the zinc wastewater may be stirred after the addition. The time for coprecipitation (stirring time) is not particularly limited, but may be, for example, 30 minutes or more. From the viewpoint of improving the anion adsorption performance of the Zn-Al-based layered double oxide (LDO) obtained by the production method of this embodiment, the stirring time for the zinc wastewater after the addition is preferably 10 hours or more, more preferably 20 hours or more, and particularly preferably 24 hours or more.

[0032] The temperature of the waste zinc water when aluminum and zinc are co-precipitated is not particularly limited, and can be, for example, room temperature (1 to 30° C.).

[0033] Here, the Zn—Al-based layered double hydroxide precipitated in the precipitation step S101 will be described.

[0034] Layered double hydroxides (LDHs) are crystalline (or microcrystalline) substances represented by the following general formula (1) (crystalline substances having the following general formula (1) as a repeating unit), and are formed by the reaction of metal hydroxides, M(OH) 2 M in 2+ Part of M 3+ It is known that the octahedral host layer is positively charged due to substitution with , and the guest layer is composed of anions and interlayer water that compensate for the positive charge of the host layer. [M 2+ 1-x M 3+ x (OH)2][(A n- ) x / n ·yH2O]···(1) (In the above chemical formula (1), M 2+ is a divalent metal ion, and M 3+ is a trivalent metal ion, and A n- is an n-valent anion, x is a value greater than 0 and less than 1, n is 1 to 3, and y is a value greater than 0. Preferably, x is 0.22 to 0.3.

[0035] In contrast, the Zn-Al-based layered double hydroxide precipitated in the precipitation step S101 of this embodiment is a Zn-Al-based layered double hydroxide having M in the above chemical formula (1). 2+ as zinc ions (Zn 2+ ), and M in the above chemical formula (1) 3+ as aluminum ions (Al 3+ ) is a substance containing

[0036] The Zn-Al-based layered double hydroxide precipitated in the precipitation step S101 of this embodiment is preferably a carbonate-type Zn-Al-based layered double hydroxide represented by the following general formula (2), more preferably ZnAl(OH) 16 It is a substance represented by the formula CO3·4H2O. [Zn 2+ 1-x Al 3+ x (OH)2][CO3 2- x / 2·yH2O]···(2) (In the above formula (2), x is a value greater than 0 and less than 1, and y is a value greater than 0. It is preferable that x is 0.22 to 0.3.)

[0037] The fact that the precipitate deposited in the precipitation step S101 is a Zn-Al-based layered double hydroxide can be identified by comparing the XRD pattern of the precipitate deposited in the zinc wastewater (hereinafter also referred to as the "XRD pattern of the precipitate") with the XRD pattern of a known Zn-Al-based layered double hydroxide (hereinafter also referred to as the "XRD pattern of a known LDH"). For example, when the XRD pattern of the precipitate is compared with the XRD pattern of a known LDH, if the FOM (Figure of Merit) is 10 or less, the precipitate can be determined to be the Zn-Al-based layered double hydroxide. Furthermore, for example, if three peaks with the highest intensities are selected from the peaks contained in the XRD pattern of the precipitate (the three peaks are selected in descending order of intensity), and the peak top positions (diffraction angles) and intensities are similar to three peaks contained in the XRD pattern of a known LDH, and if the FOM when comparing the XRD pattern of the known LDH with the XRD pattern of the precipitate is 10 or less, the precipitate can be determined to be the Zn-Al-based layered double hydroxide. The FOM is a value that quantitatively indicates the difference between the XRD patterns being compared, and the smaller the FOM, the higher the degree of match.

[0038] The conditions for measuring the XRD pattern of the precipitates can be, for example, the following conditions: Furthermore, the XRD pattern of a known LDH, which can be used for comparison with the XRD pattern of the precipitates, is, for example, Zn6Al2(OH) 16 CO3·4H2O can be used. [XRD measurement conditions] Radiation source: CuKα radiation Voltage: 40kV Current value: 30mA Measurement range: 2θ=5°~90°

[0039] Next, the calcination step S102 will be described. The calcination step S102 is a step of calcining the Zn—Al-based layered double hydroxide (LDH).

[0040] In the calcination step S102 of this embodiment, the conditions for calcining the Zn-Al-based layered double hydroxide can be any known calcination conditions used to obtain a layered double oxide (LDO) from a layered double hydroxide (LDH), and are not particularly limited.

[0041] For example, the temperature for calcining the Zn-Al-based layered double hydroxide can be 300° C. or higher and lower than 600° C. Preferably, the calcination temperature is 380° C. or higher and lower than 520° C., and more preferably, the calcination temperature is 420° C. or higher and lower than 510° C.

[0042] Furthermore, for example, the atmosphere in which the Zn—Al-based layered double hydroxide (LDH) is calcined can be an air atmosphere or a nitrogen atmosphere, with a nitrogen atmosphere being preferred.

[0043] For example, the calcination time for the Zn-Al-based layered double hydroxide (LDH) can be 1 hour or more. Preferably, the calcination time is 2 hours or more, and more preferably, 3 hours or more. The upper limit of the calcination time is not particularly limited, but can be, for example, 8 hours or less.

[0044] In the calcination step S102 of this embodiment, the Zn-Al-based layered double hydroxide (LDH) is calcined to obtain A in the above formula (1). n- The n-valent anions represented by the formula (1) are removed to produce Zn-Al layered double oxide (LDO).

[0045] Here, the Zn-Al-based layered double oxide produced by the production method of this embodiment will be described.

[0046] Layered double oxides (LDOs) are crystalline (or microcrystalline) substances represented by the following chemical formula (3), and are known to have a structure in which the guest layer in layered double hydroxides (LDHs) has been removed. M 2+ 2(1-x) / (2+x) M 3+ 2x / (2+x) O···(3) (In the above chemical formula (3), M 2+ is a divalent metal ion, and M 3+ is a trivalent metal ion, and x is a value greater than 0 and less than 1. Preferably, x is 0.2 to 0.35.

[0047] The Zn-Al-based layered double oxide produced by the production method of this embodiment is a Zn-Al-based layered double oxide having M in the above chemical formula (3). 2+ as zinc ions (Zn 2+ ), and M in the above chemical formula (3) 3+ as aluminum ions (Al 3+ ) is a substance containing

[0048] The Zn-Al-based layered double oxide produced by the production method of this embodiment is preferably a compound represented by the following chemical formula (4): Specific examples of the Zn-Al-based layered double oxide represented by the following chemical formula (4) include ZnAlO. Zn 2+ 2(1-x) / (2+x) Al 3+ 2x / (2+x) O···(4) (In the above formula (4), x is a value greater than 0 and less than 1. It is preferable that x is 0.2 to 0.35.)

[0049] The substance produced by the production method of this embodiment can be identified as a Zn-Al-based layered double oxide by comparing the XRD pattern of the produced substance (hereinafter also referred to as the "XRD pattern of the product") with the XRD pattern of a known Zn-Al-based layered double oxide (hereinafter also referred to as the "XRD pattern of a known LDO"). Specifically, for example, when the XRD pattern of the product is compared with the XRD pattern of the known LDO, if the FOM is 10 or less, the product can be determined to be the Zn-Al-based layered double oxide. Alternatively, for example, if three peaks with the highest intensities are selected from the XRD pattern of the product (selecting the three peaks in descending order of intensity), and the peak top positions (diffraction angles) and intensities are similar to the three peaks in the XRD pattern of the known LDO, and if the FOM is 10 or less when the XRD pattern of the known LDO is compared with the XRD pattern of the product, the product can be determined to be the Zn-Al-based layered double oxide.

[0050] The conditions for measuring the XRD pattern of the product are the same as those for measuring the XRD pattern of the precipitates described above, and therefore, the explanation will be omitted. As the XRD pattern of a known LDO to be compared with the XRD pattern of the product, for example, Zn6Al2O9 disclosed as DB card number 00-051-0037 of the ICDD (International Centre for Diffraction Data) can be used.

[0051] One form of Zn-Al-based layered double oxide (LDO) includes a divalent metal oxide containing at least zinc oxide (ZnO) in which a trivalent metal (metal capable of forming a trivalent metal ion) containing at least aluminum is dissolved (hereinafter referred to as the "solid solution form"). When this solid solution form is present, the XRD pattern of the product may not show a peak due to aluminum. In such cases, the property of Zn-Al-based layered double oxide (LDO) that it transforms (reconstructs) into Zn-Al-based layered double hydroxide (LDH) in an aqueous solution containing anions, such as a borate solution (borate ion), a fluoride solution (fluoride ion), or a phosphate solution (phosphate ion), can be utilized to determine whether the product is a Zn-Al-based layered double oxide (LDO). Specifically, when the XRD pattern of the product and the XRD pattern of a known divalent metal oxide containing at least zinc oxide (ZnO) (hereinafter referred to as the "XRD pattern of the known divalent metal oxide") show a similar agreement when compared with the XRD pattern of the known LDH described above, and when the XRD pattern of a substance obtained by immersing the product in an aqueous solution containing anions shows a similar agreement when compared with the XRD pattern of the known LDH described above, the product can be determined to be a Zn-Al-based layered double oxide (specifically, a Zn-Al-based layered double oxide in solid solution form).

[0052] As an XRD pattern of a known divalent metal oxide to be compared with the XRD pattern of the product, for example, ZnO disclosed as DB card number 00-005-0664 in the ICDD (International Centre for Diffraction Data, PDF-2 Release 2020 RDB) can be used. The XRD patterns of known LDHs have been described above, so a detailed description will be omitted.

[0053] As can be seen from the above formulas (3) and (4), layered double oxides (LDOs) are positively charged and typically contain counter anions that compensate for this positive charge. In the Zn-Al-based layered double oxides produced by the production method of this embodiment, the counter anions that compensate for the positive charge are not particularly limited, and examples include sulfate ions, chloride ions, and phosphate ions. However, when sulfate ions are included as counter anions, the sulfate ion content is preferably 2% by mass or less relative to 100% by mass of the Zn-Al-based layered double oxide. Because sulfate ions are divalent anions, they have a high charge density and are strongly bound between layers. Therefore, when the Zn-Al-based layered double oxide produced by the production method of this embodiment is used as an anion adsorbent, they are difficult to exchange with other anions, which can reduce the anion adsorption capacity. For this reason, the sulfate ion content in the Zn-Al-based layered double oxide is preferably 2% by mass or less. The sulfate ion content in the Zn-Al-based layered double oxide can be determined using an ICP optical emission spectrometer (for example, Shimadzu Sequential High-Frequency Plasma Optical Emission Spectrometer ICPS-7510 manufactured by Shimadzu Corporation). In this specification, a sulfate ion content of 0 mass% means that no sulfate ions are contained.

[0054] The content of sulfate ions in the Zn-Al layered double oxide varies depending on the type and content of anions (excluding metal ions) contained in the zinc wastewater after addition. For example, the molar ratio of carbonate ions to sulfate ions in the zinc wastewater after addition (hereinafter referred to as CO3 2- / SO4 2- This can be adjusted by changing the CO3 2- / SO4 2-is not particularly limited, but from the viewpoint of further reducing the sulfate ion content in the Zn-Al-based layered double oxide, it is preferably 20 or more, more preferably 22 or more, and particularly preferably 22 to 50. The sulfate ion content in the zinc wastewater after addition can be determined using an ICP optical emission spectrometer (e.g., Shimadzu Corporation's Shimadzu sequential high-frequency plasma optical emission spectrometer ICPS-7510). Note that the zinc wastewater and the aluminum source may not contain sulfate ions, in which case the total amount of sulfate ions in the zinc wastewater and the aluminum source will be 0.

[0055] The content of sulfate ions in the Zn-Al based layered double oxide is 2- / Zn 2+ It can also be adjusted by changing the molar ratio of carbonate ions to zinc ions in the wastewater after adding CO3 2- / Zn 2+ is not particularly limited, but is preferably 2.8 or more from the viewpoint of further reducing the content of sulfate ions contained in the Zn-Al based layered double oxide.

[0056] In the Zn-Al-based layered double oxide produced by the production method of this embodiment, the molar ratio of zinc contained in the Zn-Al-based layered double oxide to aluminum contained in the Zn-Al-based layered double oxide (hereinafter also referred to as "Zn / Al") is not particularly limited and can be, for example, 1.9 to 3.5. From the viewpoint of improving the anion adsorption performance of the Zn-Al-based layered double oxide, Zn / Al is preferably 1.9 to 2.5, and more preferably 1.9 to 2.2. The aluminum and zinc contents in the Zn-Al-based layered double oxide can be determined using an ICP optical emission spectrometer (for example, Shimadzu Sequential High-Frequency Plasma Optical Emission Spectrometer ICPS-7510, manufactured by Shimadzu Corporation).

[0057] According to the production method of this embodiment, which includes the above-mentioned steps S101 and S102, a Zn-Al-based layered double oxide can be produced using zinc contained in wastewater as a raw material. Furthermore, the Zn-Al-based layered double oxide produced by the production method of this embodiment can be used as an anion adsorbent that adsorbs anions.

[0058] The method for adsorbing anions by the Zn-Al-based layered double oxide according to this embodiment is not particularly limited, but for example, anions can be adsorbed by contacting a fluid containing anions with the Zn-Al-based layered double oxide. The fluid containing anions may be a liquid (e.g., water) or a gas (e.g., air). Examples of anions adsorbed by the Zn-Al-based layered double oxide include borate ions, phosphate ions, nitrate ions, and sulfate ions.

[0059] Although the above-described manufacturing method of this embodiment is described as a manufacturing method including only the precipitation step S101 and the calcination step S102, the manufacturing method of this embodiment may include other steps in addition to the precipitation step S101 and the calcination step S102. For example, the manufacturing method of this embodiment may include a filtration step S103 and a drying step S104 between the precipitation step S101 and the calcination step S102, as shown in FIG.

[0060] The filtration step S103 is a step of filtering the Zn-Al-based layered double hydroxide (LDH) precipitated in the precipitation step S101 from the zinc wastewater. The filtration treatment in the filtration step S103 can be performed by a conventionally known method, and is not particularly limited, but can be performed using a membrane filter, for example.

[0061] The drying step S104 is a step of drying the Zn—Al-based layered double hydroxide precipitated in the precipitating step S101 (or the Zn—Al-based layered double hydroxide filtered in the filtration step S103). The drying conditions in the drying step S104 can be conventionally known drying conditions and are not particularly limited, but can be, for example, in an air atmosphere at 1 to 60° C. for 1 to 24 hours. [Example]

[0062] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0063] Calcined bodies were obtained using the manufacturing methods shown in Examples 1 to 9, which will be described later, and evaluations 1 to 4, which will be described later, were performed. In the manufacturing methods shown in Examples 1 to 9, actual wastewater 1 was wastewater from zinc plating using an ammonium chloride bath, and it was confirmed that the zinc concentration (zinc ion concentration) was 1200 mg / L, the pH was 2.2, the ammonium chloride concentration was approximately 500 mg / L as nitrogen, the sulfate ion was 250 mg / L, and the heavy metals iron and manganese were each less than 10 mg / L. Furthermore, actual wastewater 2 was wastewater from zinc plating using an ammonium chloride bath, and it was confirmed that the zinc concentration (zinc ion concentration) was 1000 mg / L, the pH was 4.4, the sulfate ion was 110 mg / L, and the heavy metals iron and manganese were each less than 10 mg / L. It was confirmed that actual wastewater 1 and actual wastewater 2 contained almost no aluminum ions or carbonate ions.

[0064] The content of each component in Actual Wastewater 1 and Actual Wastewater 2 was measured using an ICP optical emission spectrometer (Shimadzu Corporation, Shimadzu sequential type high frequency plasma optical emission spectrometer ICPS-7510) and a total nitrogen analyzer (Analytik Jena AG TOC / TN analyzer multi N / C 3100), etc.

[0065] [Example 1] 200 mL of actual wastewater 1 was placed in a beaker, and 0.312 g of polyaluminum chloride (Kishida Chemical Co., Ltd., aluminum oxide 30.0% or more, solubility: 71 g / 100 mL) was added thereto. Then, 11 mL of aqueous sodium carbonate solution (100 g / L, Kanto Chemical Co., Ltd., special grade, solubility: 17.4 g / 100 mL) was added dropwise to adjust the pH to 7.1. After stirring for 24 hours at room temperature (23°C) using a magnetic stirrer, the white precipitate obtained by suction filtration was dried in a drying oven at 60°C. The calcined product was then calcined for 4 hours at 450°C in a nitrogen atmosphere (flow rate: 1 L / min) using an electric furnace to obtain the calcined product of Example 1.

[0066] [Example 2] 200 mL of actual wastewater 2 was placed in a beaker, and 0.266 g of polyaluminum chloride (Kishida Chemical Co., Ltd., aluminum oxide 30.0% or more, solubility: 71 g / 100 mL) was added. Hydrochloric acid (Kanto Chemical Special Grade) was then added to adjust the pH to 1.9. 11 mL of sodium carbonate aqueous solution (100 g / L, Kanto Chemical Co., Ltd., Special Grade, solubility: 17.4 g / 100 mL) was added dropwise to adjust the pH to 7.1. After stirring for 24 hours at room temperature (23°C) using a magnetic stirrer, the white precipitate obtained by suction filtration was dried in a drying oven at 60°C. The calcined product was then calcined for 4 hours at 450°C in a nitrogen atmosphere (flow rate: 1 L / min) using an electric furnace to obtain the calcined product of Example 2.

[0067] [Example 3] The calcined body of Example 3 was obtained under the same conditions as in Example 1, except that an aqueous sodium hydroxide solution (200 g / L, Kanto Chemical Co., Inc., special grade) was further added to the actual wastewater, the pH of which had been adjusted to 7.1 in Example 1, to adjust the pH to 8.0.

[0068] [Example 4] The calcined body of Example 4 was obtained under the same conditions as in Example 1, except that an aqueous sodium hydroxide solution (200 g / L, Kanto Chemical Co., Inc., special grade) was further added to the actual wastewater, the pH of which had been adjusted to 7.1 in Example 1, to adjust the pH to 9.0.

[0069] [Example 5] The calcined body of Example 5 was obtained under the same conditions as in Example 1, except that an aqueous sodium hydroxide solution (200 g / L, Kanto Chemical Co., Inc., special grade) was further added to the actual wastewater, the pH of which had been adjusted to 7.1 in Example 1, to adjust the pH to 10.0.

[0070] [Example 6] 200 mL of actual wastewater 1 was placed in a beaker, and 0.312 g of polyaluminum chloride (Kishida Chemical Co., Ltd., 30.0% or more aluminum oxide, solubility: 71 g / 100 mL) was added. Then, hydrochloric acid (Kanto Chemical Special Grade) was added to adjust the pH to 1.4. 20 mL of aqueous sodium carbonate solution (100 g / L, Kanto Chemical Co., Ltd., Special Grade, solubility: 17.4 g / 100 mL) was added dropwise to adjust the pH to 7.1. After stirring for 24 hours at room temperature (23°C) using a magnetic stirrer, the white precipitate obtained by suction filtration was dried in a drying oven at 60°C. The calcined body of Example 6 was then obtained by calcining for 4 hours at 450°C in a nitrogen atmosphere (flow rate: 1 L / min) using an electric furnace.

[0071] [Example 7] The calcined body of Example 7 was obtained under the same conditions as in Example 1, except that the amount of sodium carbonate aqueous solution (100 g / L) added to actual wastewater 1 was 12 mL and the stirring time for actual wastewater 1 to which polyaluminum chloride and sodium carbonate had been added was 30 minutes.

[0072] [Example 8] 200 mL of actual wastewater 1 was placed in a beaker, and 0.312 g of polyaluminum chloride (Kishida Chemical Co., Ltd., 30.0% or more aluminum oxide, solubility: 71 g / 100 mL) was added. Then, 5 mL of aqueous sodium carbonate solution (100 g / L, Kanto Chemical Co., Ltd., special grade, solubility: 17.4 g / 100 mL) was added dropwise, followed by the dropwise addition of aqueous sodium hydroxide solution (200 g / L, Kanto Chemical Co., Ltd., special grade) to adjust the pH to 7.1. After stirring for 24 hours at room temperature (23 °C) using a magnetic stirrer, the white precipitate obtained by suction filtration was dried in a drying oven at 60 °C. The calcined product of Example 8 was then obtained by calcining for 4 hours at 450 °C in a nitrogen atmosphere (flow rate: 1 L / min) using an electric furnace.

[0073] [Example 9] 200 mL of actual wastewater 2 was placed in a beaker, and 0.266 g of polyaluminum chloride (Kishida Chemical Co., Ltd., aluminum oxide 30.0% or more, solubility: 71 g / 100 mL) was added. Then, 5 mL of aqueous sodium carbonate solution (100 g / L, Kanto Chemical Special Grade, solubility: 17.4 g / 100 mL) was added dropwise to adjust the pH to 7.0. After stirring for 24 hours at room temperature (23 °C) using a magnetic stirrer, the white precipitate obtained by suction filtration was dried in a drying oven at 60 °C. The calcined body of Example 9 was then obtained by calcining for 4 hours at 450 °C in a nitrogen atmosphere (flow rate: 1 L / min) using an electric furnace.

[0074] Table 1 below shows the physical properties of the zinc wastewater used in Examples 1 to 9. The zinc wastewater after addition shown in Table 1 below refers to the zinc wastewater after addition of an aluminum source (polyaluminum chloride), a carbonate ion source (sodium carbonate), and a pH adjuster (hydrochloric acid or sodium hydroxide) that was added as needed.

[0075] [Table 1]

[0076] The calcined bodies obtained in Examples 1 to 9 were subjected to the following evaluations 1 to 4.

[0077] <Evaluation 1: Identification of crystalline phase> Using a powder X-ray diffractometer (Smart Lab, manufactured by Rigaku Corporation), XRD patterns of the white precipitates (deposits) and calcined bodies of Examples 1 to 9 were obtained under the following measurement conditions. [XRD measurement conditions] Radiation source: CuKα radiation Voltage: 40kV Current value: 30mA Measurement range: 2θ=5°~90°

[0078] The XRD pattern of the obtained white precipitate (deposit) was determined to be Zn6Al2(OH) as disclosed in the ICDD (International Centre for Diffraction Data) DB card number 00-038-0486. 16 When compared with the XRD patterns of CO3 4H2O, the FOMs were all less than 2. From the agreement of the XRD patterns, it was determined that the white precipitates (precipitates) obtained in Examples 1 to 9 were Zn-Al-based layered double hydroxides (more specifically, Zn6Al2(OH) 16 CO3·4H2O).

[0079] Furthermore, when the XRD patterns of the obtained calcined bodies were compared with the XRD pattern of ZnO disclosed as DB card number 00-005-0664 in ICDD (PDF-2 Release 2020 RDB), the FOMs were all 2 or less.

[0080] In addition, 50 mL of a boric acid aqueous solution (boron concentration: 43.1 mg / L) prepared by diluting a borate pH standard solution (type 2) pH 9.18 (Kanto Chemical Co., Inc.) 10 times was taken, and 100 mg of each of the calcined bodies obtained in Examples 1 to 9 was added thereto and shaken (200 times / min) at room temperature for 16 hours. After shaking, the mixture was filtered through a membrane filter with a pore size of 0.45 μm to obtain a residue (hereinafter also referred to as "calcined body after treatment with boric acid aqueous solution"). The calcined bodies of Examples 1 to 9 after treatment with boric acid aqueous solution were dried, and the XRD patterns of the calcined bodies were obtained under the measurement conditions described above.

[0081] The XRD pattern of the calcined body obtained after the boric acid aqueous solution treatment was compared with that of Zn6Al2(OH) disclosed in ICDD DB card number 00-038-0486. 16 When compared with the XRD pattern of CO3·4H2O, the FOMs were all less than 10. Note that the boric acid aqueous solution in which the calcined bodies of Examples 1 to 9 were immersed did not contain carbonate ions, and therefore, immersion of the calcined bodies of Examples 1 to 9 in the boric acid aqueous solution did not produce Zn6Al2(OH) 16 Although it cannot become a carbonate type Zn-Al layered double hydroxide (LDH) such as CO3·4H2O, the carbonate in the Zn-Al layered double hydroxide (LDH) does not appear in its XRD pattern, so in this evaluation, it is assumed that Zn6Al2(OH) 16 The XRD pattern of CO3·4H2O was used for comparison.

[0082] From the consistency of the XRD patterns described above, it was understood that the calcined bodies obtained in Examples 1 to 9 were Zn-Al-based layered double oxides (more specifically, hexagonal cation-deficient solid solution form in which Al is solid-solved in ZnO).

[0083] The XRD pattern of the calcined body (LDO) obtained in Example 1 is shown in Figure 3. In Figure 3, representative (characteristic) intensities contained in the XRD pattern of ZnO are shown as a bar graph. Furthermore, the XRD patterns of the white precipitate (LDH) and calcined body (LDO) obtained in Example 5 are shown in Figure 4. In addition to the XRD patterns of the white precipitate (LDH) and calcined body (LDO), Figure 4 also shows the XRD pattern of the calcined body (LDO) after treatment with an aqueous boric acid solution.

[0084] <Evaluation 2: Zn / Al and sulfate ion contents of calcined body> Ten milligrams of the Zn-Al-based layered double oxides (calcined bodies) obtained in Examples 1 to 9 were each placed in a dilute aqueous nitric acid solution (Kanto Chemical Co., Inc., for measuring hazardous metals), and the total volume was adjusted to 50 mL with ultrapure water. This solution was appropriately diluted and introduced into a high-frequency plasma emission spectrometer (Shimadzu Sequential ICPS-7510, Shimadzu Corporation) to measure the concentrations of zinc, aluminum, and sulfur. From the measurement results, the Zn / Al and sulfate ion contents in the Zn-Al-based layered double oxides of Examples 1 to 9 were calculated. The results are shown in Table 2 below.

[0085] <Evaluation 3: Evaluation of anion adsorption performance> A 50 mL boric acid solution (boron concentration: 43.1 mg / L) was prepared by diluting a borate pH standard solution (type 2) pH 9.18 (Kanto Chemical Co., Inc.) 10 times, and 100 mg of each of the Zn-Al-based layered double oxides (calcined bodies) obtained in Examples 1 to 9 was added and shaken (200 rpm) at room temperature for 16 hours. After shaking, the Zn-Al-based layered double oxide (calcined body) was removed by filtration through a 0.45 μm pore membrane filter, and the boron and zinc concentrations in the resulting filtrate were measured using a high-frequency plasma emission spectrometer (Shimadzu Sequential Type ICPS-7510, Shimadzu Corporation).

[0086] The measurement results for boron concentration were compared with the boron concentration in the solution before the addition of the Zn-Al layered double oxide (calcined body), and the amount of boron adsorbed per gram of boron (hereinafter also referred to as "B adsorption amount") was determined. The measurement results for zinc concentration were taken as the amount of zinc eluted (hereinafter also referred to as "Zn elution amount"). The results are shown in Table 2 below. In Table 2, ND stands for not detected.

[0087] <Evaluation 4: Measurement of pH change before and after adsorption treatment> Before and after the adsorption treatment performed in Evaluation 3, the pH of the boric acid solution was measured using a glass electrode hydrogen ion concentration indicator (MM-43X, manufactured by DKK-TOA Corporation) and a pH combination electrode (GST-5841C, manufactured by DKK-TOA Corporation). From the measurement results, the change in pH of the boric acid solution before and after the adsorption treatment was determined. The results are shown in Table 2 below. In Table 2, (+) indicates that the pH after the adsorption treatment was higher than before the adsorption treatment, and (-) indicates that the pH after the adsorption treatment was lower than before the adsorption treatment.

[0088] [Table 2]

[0089] As is clear from the results of Evaluation 1, a Zn-Al-based layered double oxide could be produced using zinc contained in wastewater as a raw material according to the production methods of Examples 1 to 9. Furthermore, as is clear from the amount of B adsorption in Evaluation 3, the Zn-Al-based layered double oxide produced by the production methods of Examples 1 to 9 was able to adsorb borate ions in a boric acid solution.

[0090] Furthermore, even when the Zn-Al-based layered double oxides produced by the production methods of Examples 1 to 9 were subjected to adsorption treatment, zinc did not elute and the change in pH was limited to -1 to +1. From these results, it was understood that the Zn-Al-based layered double oxides produced by the production methods of Examples 1 to 9 are useful substances that do not easily cause environmental pollution even when used as adsorbents.

Claims

1. A method for producing a Zn-Al-based layered double oxide (LDO) which is an anion adsorbent, comprising: a precipitation step of adding an aluminum source and a carbonate ion source to zinc wastewater containing zinc ions to precipitate a Zn—Al-based layered double hydroxide (LDH); and a calcination step of calcining the Zn—Al-based layered double hydroxide (LDH), The zinc wastewater to which the aluminum source and the carbonate ion source have been added has a CO 3 2− / Zn 2+ ratio of 2.8 to 9.1 and a CO 3 2− / SO 4 2− ratio of 22 to 50.

2. The manufacturing method described in claim 1, characterized in that the process of adding the aluminum source and the carbonate ion source to the zinc wastewater comprises a first adding process of adding the aluminum source to the zinc wastewater, and a second adding process of adding the carbonate ion source to the zinc wastewater to which the aluminum source has been added.

3. 3. The method according to claim 1, wherein the carbonate ion source is an alkali metal carbonate and / or carbon dioxide gas.

4. 4. The method according to claim 1, wherein the aluminum source is polyaluminum chloride.

5. 5. The method according to claim 1, wherein a molar ratio of zinc contained in the Zn—Al-based layered double oxide (LDO) to aluminum contained in the Zn—Al-based layered double oxide (LDO) is 1.9 or more and 2.5 or less.

6. 6. The method according to claim 1, wherein the Zn-Al-based layered double oxide (LDO) has a sulfate ion content of 2 mass % or less.

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