Composite metal oxide

Abstract

The present disclosure provides a novel composite metal oxide that can be used as a highly practical adsorbent.　The present disclosure relates to a composite metal oxide represented by formula (1).　Formula (1): Mg2+ 1−xFe3+ xO(2+x) / 2. In formula (1), x is a number satisfying 0.10 < x < 0.60.　The composite metal oxide according to the present disclosure has, in a powder X-ray diffraction pattern, a first peak that is positioned in a diffraction angle 2θ range of 42-43°, and a second peak that is positioned in a diffraction angle 2θ range of 61-63°. The half-value width of the first peak is 0.30° or greater. The half-value width of the second peak is 0.45° or greater.

Description

Composite metal oxides

[0001] This invention relates to a composite metal oxide that can be used as an adsorbent.

[0002] Water treatment technologies are primarily developed for the purpose of treating drinking water, sewage, or wastewater. For example, pollutants contained in drinking water and industrial wastewater can be removed by adsorption, electrodialysis, reverse osmosis, evaporation, or ion exchange. Among these, adsorption methods, which can remove pollutants with relatively inexpensive equipment and treatment costs, are attracting attention.

[0003] Furthermore, examples of pollutants include anions. Another example of anions is fluoride ions (F － ), nitrate ion (NO ３ － ), nitrite ion (NO ２ － ), sulfate ions (SO ４ ２－ ) are some examples.

[0004] Various techniques have been investigated for adsorbing and removing anions contained in water. For example, Patent Documents 1 to 3 and Non-Patent Document 1 each disclose techniques for adsorbing and removing various anions contained in water using Mg-Al or Mg-Fe composite metal oxides.

[0005] Japanese Patent Publication No. 2023-171188, Japanese Patent Publication No. 2011-56394, Japanese Patent Publication No. 2002-66548

[0006] Moriyama, Saya; Sasaki, Keiko; and Hirashima, Tsuyoshi, "Adsorption of B and F- in aqueous solutions using Mg-Al and Mg-Fe composite oxides," Journal of MMIJ Vol. 127, pp. 708-713 (2011).

[0007] Mg-Al composite metal oxides have a high ability to adsorb anions in an aqueous solution and are useful as adsorbents. On the other hand, since aluminum (Al) is an amphoteric element that dissolves in both acids and alkalis, there is a risk of Al elution at the liquid pH of the composite metal oxide that becomes basic. The Al concentration defined by the World Health Organization as a water quality limit for drinking water is less than 0.2 ppm. Therefore, there is a demand for a highly practical adsorbent in which the elution of metal ions such as Al is more suppressed and the adsorptivity is also excellent.

[0008] Therefore, an object of the present invention is to provide a novel composite metal oxide that can be used as a highly practical adsorbent.

[0009] This disclosure includes the following aspects.

[0010] (First disclosure) The first disclosure is a composite metal oxide represented by the following formula (1). Mg ２＋ １－ｘ Fe ３＋ ｘ O （２＋ｘ）／２ ... (1) In formula (1), x is a number satisfying 0.10 < x < 0.60. The composite metal oxide of the present disclosure has a first peak located in the range of diffraction angle 2θ of 42° to 43° and a second peak located in the range of diffraction angle 2θ of 61° to 63° in the powder X-ray diffraction pattern. And the half-width of the first peak is 0.30° or more. The half-width of the second peak is 0.45° or more.

[0011] (Second disclosure) The second disclosure further has the following characteristics in the composite metal oxide of the first disclosure. In the powder X-ray diffraction pattern, the half-width of the first peak is 0.60° or more. The half-width of the second peak is 0.65° or more.

[0012] (Third disclosure) The third disclosure further has the following characteristics in the composite metal oxide of the first or second disclosure. The crystallite size calculated from the half-width of the first peak is less than 420 Å. The crystallite size calculated from the half-width of the second peak is less than 280 Å.

[0013] (Fourth Disclosure) The fourth disclosure further features the composite metal oxides of any of the first to third disclosures: The composite metal oxides of this disclosure do not have a third peak in the powder X-ray diffraction pattern where the diffraction angle 2θ is in the range of 35° to 36°. Alternatively, the composite metal oxides of this disclosure have a third peak, and the full width at half maximum of the third peak is 0.30° or more.

[0014] (Fifth Disclosure) The fifth disclosure further features the composite metal oxide of the fourth disclosure above: Peak intensity I of the first peak １ and the peak intensity of the third peak I ３ Ratio I ３ / I １ However, it is less than 0.80.

[0015] (Sixth Disclosure) The sixth disclosure further features the composite metal oxide of the fourth or fifth disclosure described above: The crystallite size calculated from the full width at half maximum of the third peak is less than 360 Å.

[0016] (Disclosure No. 7) Disclosure No. 7 further features the composite metal oxide of any of the disclosures No. 1 to No. 6 above. The composite metal oxide of this disclosure has a BET specific surface area of ​​20 m². ２ / g ~ 170m ２ It is within the range of / g.

[0017] (Disclosure No. 8) Disclosure No. 8 is a method for producing a composite metal oxide. The method for producing the composite metal oxide of Disclosure No. 8 includes the following calcination step and cooling step. The calcination step is a step of heating a composite metal hydroxide represented by the following formula (2) at a temperature of 300°C to 750°C for a predetermined time. [Mg ２＋ １－ｘ Fe ３＋ ｘ (OH) ２ ] ｘ＋ (A ｎ－ ) ｘ／ｎ ・mH ２ O...(2) In equation (2), A ｎ－ CO ３ ２－ and OH －This indicates an anion selected from the group consisting of the following. n represents 1 or 2. x is a number satisfying 0.10 < x < 0.60. m is a number satisfying 0 ≤ m < 1. The cooling step is a step of cooling the calcined composite metal hydroxide produced by the calcination step from the above temperature to 25°C at a rate of 2°C / min to 15°C / min.

[0018] According to the present invention, it is possible to provide a novel composite metal oxide that can be used as a highly practical adsorbent.

[0019] Figure 1 is a graph showing the powder X-ray diffraction patterns of each composite metal oxide in Examples 1 and 2 and Comparative Example 1. Figure 2 is a graph showing the powder X-ray diffraction patterns of each composite metal oxide in Examples 3 to 5 and Comparative Examples 2 to 4.

[0020] Preferred embodiments of the composite metal oxide of the present invention will be described in detail below. In this specification, unless otherwise specified, various numerical ranges refer to the range including their upper and lower limits.

[0021] The inventors conducted diligent research to achieve the above objective and discovered that by calcining and cooling an Mg-Fe composite metal hydroxide under specific conditions, an Mg-Fe composite metal oxide with few crystalline impurities can be obtained. Furthermore, the inventors discovered that such an Mg-Fe composite metal oxide with few crystalline impurities is less prone to metal ion elution and exhibits excellent adsorption properties.

[0022] The present invention has been completed based on the above findings. The present invention includes the following embodiments.

[0023] <Composite Metal Oxide> The composite metal oxide according to one embodiment of the present invention is a composite metal oxide represented by the following formula (1): Mg ２＋ １－ｘ Fe ３＋ ｘ O （２＋ｘ）／２ ... (1) In equation (1), x is a number that satisfies 0.10 < x < 0.60.

[0024] In other words, the composite metal oxide of this embodiment is a Mg-Fe composite metal oxide. The Mg-Fe composite metal oxide does not contain metal ions such as Al that dissolve at the basic pH of the composite metal oxide solution. Furthermore, Fe is difficult to dissolve at the basic pH of the composite metal oxide solution. Therefore, metal ions are difficult to dissolve from the composite metal oxide of this embodiment in aqueous solution.

[0025] Furthermore, the composite metal oxide of this embodiment has a first peak located in the range of 42° to 43° with a diffraction angle 2θ of 42° to 43° in the powder X-ray diffraction pattern obtained by powder X-ray diffraction (XRD), and a second peak located in the range of 61° to 63° with a diffraction angle 2θ of 61° to 63°.

[0026] Furthermore, the composite metal oxide of this embodiment has a unique characteristic in its powder X-ray diffraction pattern, where the full width at half maximum (FWHM) of the first peak is 0.30° or more, and the FWHM of the second peak is 0.45° or more. This means that both the first and second peaks are broad diffraction peaks, which in turn means that there are few crystalline impurities.

[0027] Generally, composite metal oxides absorb ions and moisture from the atmosphere to form layered composite metal hydroxides such as hydrotalcite. Furthermore, because composite metal oxides are positively charged, they readily adsorb anions. When composite metal oxides absorb moisture from the atmosphere and transform into hydroxides, they can intercalate, meaning they can incorporate anions between their layers.

[0028] However, if a large amount of crystalline impurities are formed in the composite metal oxide, the composite metal oxide becomes less likely to absorb moisture from the atmosphere and change into hydroxide, and it becomes less likely to incorporate anions between its layers. In other words, the adsorption performance is significantly reduced. Furthermore, when a large amount of crystalline impurities are formed in the composite metal oxide, the half-width of the diffraction peaks in the powder X-ray diffraction pattern described above is small, resulting in sharp diffraction peaks.

[0029] As described above, the composite metal oxide of this embodiment has broad diffraction peaks for both the first and second peaks, and contains few crystalline impurities. Therefore, when it absorbs moisture from the atmosphere and changes into a hydroxide, it readily incorporates anions between its layers. In other words, it can exhibit high adsorption performance for anions.

[0030] As described above, the composite metal oxide of this embodiment is less prone to metal ion elution and also exhibits excellent adsorption properties, making it suitable for use as a highly practical adsorbent. Furthermore, as a result, the composite metal oxide of this embodiment can significantly contribute to water purification, thus offering the advantage of contributing to the achievement of the SDGs (Sustainable Development Goals) adopted at the UN Summit.

[0031] In this embodiment, the composite metal oxide preferably has a first peak with a full width at half maximum of 0.60° or more and a second peak with a full width at half maximum of 0.65° or more in its powder X-ray diffraction pattern. When the first and second peaks are broader diffraction peaks, there are fewer crystalline impurities, and the high adsorption performance for the anions mentioned above can be more reliably achieved.

[0032] The powder X-ray diffraction patterns and the full width at half maximum of each peak of a composite metal oxide can be obtained by the following powder X-ray diffraction method.

[0033] (Powder X-ray Diffraction Method) First, the sample is loaded into the sample holder of the powder sample molding machine (PX-700). Then, an X-ray diffraction pattern is obtained by measuring under the following conditions using an X-ray diffractometer (RIGAKU Ultima IV): Measurement angle: 5.0–70.0° Sampling width: 0.0100 Scan speed: 0.5° / min Tube voltage: 45kV Tube current: 40mA

[0034] Then, the powder X-ray diffraction patterns measured under the above conditions are processed using X-ray analysis software (HighScore Plus, Malvern Panalogical), and the full width at half maximum (FWHM) of each peak is determined.

[0035] Furthermore, in this embodiment, it is preferable that the composite metal oxide has a crystallite size of less than 420 Å calculated from the full width at half maximum of the first peak, and a crystallite size of less than 280 Å calculated from the full width at half maximum of the second peak. When the size of crystalline impurities is small in this way, the high adsorption performance to the anions mentioned above can be more reliably achieved.

[0036] Furthermore, it is more preferable that the composite metal oxide has a crystallite size of less than 160 Å calculated from the full width at half maximum of the first peak, and a crystallite size of less than 160 Å calculated from the full width at half maximum of the second peak.

[0037] (Method for calculating crystallite size) The crystallite size can be calculated using the full width at half maximum (FWHM) of each peak using the following Scherrer equation: D = Kλ / βcosθ. Here, D represents the crystallite size (nm). K represents the Scherrer constant. λ represents the wavelength of the X-ray (nm). β represents the broadening of the diffraction line width, i.e., the FWHM (°). And θ represents the Bragg angle (°).

[0038] Furthermore, it is preferable that the composite metal oxide of this embodiment does not have a third peak in the powder X-ray diffraction pattern where the diffraction angle 2θ is in the range of 35° to 36°. Alternatively, even if a third peak is present, it is preferable that the full width at half maximum of the third peak is 0.30° or more, and more preferably 0.70° or more. If there are no crystalline impurities related to the above-mentioned third peak, or if there are only a few, then high adsorption performance for anions can be more reliably achieved even with a short contact time with treated water. In other words, high adsorption performance for anions can be achieved earlier and more reliably.

[0039] Since such effects can be obtained more reliably, the composite metal oxide of this embodiment has a peak intensity of the first peak I １ and the peak intensity of the third peak I ３ Ratio I ３ / I １ However, it is less than 0.80, and preferably less than 0.60.

[0040] Furthermore, for similar reasons, the composite metal oxide of this embodiment preferably has a crystallite size of less than 360 Å, and less than 130 Å, calculated from the full width at half maximum of the third peak.

[0041] The composite metal oxide of this embodiment is a composite metal oxide represented by the above formula (1) and has few crystalline impurities; other than this, its configuration is not particularly limited.

[0042] For example, the composite metal oxide of this embodiment has a BET specific surface area of ​​20 m². ２ / g ~ 170m ２ It is preferable that the BET specific surface area is within the range of / g. When the BET specific surface area is within this range, high adsorption performance for multiple types of anions can be more reliably achieved.

[0043] In this specification, BET specific surface area refers to the specific surface area of ​​particulate composite metal oxides obtained by the BET method. The BET specific surface area is determined using the "Belsolp-MR6" manufactured by Microtrac-Bell Co., Ltd., with a mixed gas (N ２ Measurement can be performed using a multi-point method with 30% + He 70%).

[0044] The BET specific surface area of ​​the composite metal oxide is 60 m². ２ More preferably 70 m ２ More preferably 80m / g or more. ２ A value of 1 / g or more is particularly preferred.

[0045] Next, preferred embodiments of the method for producing the composite metal oxide of the present invention will be described in detail.

[0046] <Manufacturing Method> The manufacturing method of the composite metal oxide of this embodiment includes at least the following firing step and cooling step. The firing step is a step of heating the composite metal hydroxide represented by the following formula (2) at a temperature of 300°C to 750°C for a predetermined time. [Mg ２＋ １－ｘ Fe ３＋ ｘ (OH) ２ ] ｘ＋ (A ｎ－ ) ｘ／ｎ ・mH ２ O...(2) In the above equation (2), Aｎ－ CO ３ ２－ and OH － This represents an anion selected from the group consisting of the following, where n is 1 or 2, x is a number satisfying 0.10 < x < 0.60, and m is a number satisfying 0 ≤ m < 1.

[0047] The cooling process involves cooling the calcined composite metal hydroxide produced by the calcination process from the above temperature to 25°C at a rate of 2°C / min to 15°C / min.

[0048] The manufacturing method of this embodiment may include a production step that generates a composite metal hydroxide represented by formula (2) above, prior to the firing step. The steps in the manufacturing method of this embodiment will be described below.

[0049] (Production Process) In the manufacturing method of this embodiment, the production process is a process of producing the composite metal hydroxide represented by the above formula (2) before the calcination process. However, if the composite metal hydroxide represented by the above formula (2) is available without production, such a production process may be omitted.

[0050] The composite metal hydroxide represented by formula (2) above can be produced, for example, as follows: First, the Mg raw material and the Fe raw material are prepared as Mg / Fe ２ A mixed solution containing 4.5 to 8.0 molar ratios is reacted with an alkaline substance to obtain a slurry. Subsequently, the slurry is subjected to dehydration, water washing, sodium carbonate washing, water washing, and drying to obtain the composite metal hydroxide represented by formula (2) above.

[0051] Examples of Mg raw materials include magnesium chloride, magnesium nitrate, and magnesium sulfate. Examples of Fe raw materials include iron chloride, iron nitrate, and iron sulfate. Examples of alkaline substances include sodium hydroxide, potassium hydroxide, sodium carbonate, and ammonia.

[0052] The composite metal hydroxide represented by formula (2) above, produced in the manner described above, is subjected to the next calcination step.

[0053] (Firing process) The firing process is a process of heating the composite metal hydroxide represented by the above formula (2) at a temperature of 300°C to 750°C for a predetermined time.

[0054] In the firing process, the composite metal hydroxide represented by formula (2) is fired under the specific heating conditions described above, causing the carbonate ions present between the layers of the composite metal hydroxide, as well as the hydroxyl groups bonded to the crystal water and metal ions, to detach. As a result, the composite metal oxide represented by formula (1) is produced. In the firing process, performing the firing under the specific heating conditions described above makes it difficult for crystalline impurities to form.

[0055] The heating conditions in the firing process, i.e., the firing conditions, are not particularly limited as long as the firing temperature is within the range of 300°C to 750°C as described above. Note that the firing temperature refers to the highest temperature reached during the firing process. The composite metal hydroxide is fired by being held at this highest temperature for a predetermined time, and becomes a composite metal oxide.

[0056] The firing temperature is preferably in the range of 460°C to 620°C, more preferably in the range of 480°C to 600°C, and particularly preferably in the range of 480°C to 550°C.

[0057] Furthermore, in the firing process, the time required to raise the composite metal hydroxide to the firing temperature, i.e., the heating time, is, for example, 0.5 hours to 8 hours. The heating time is preferably 0.5 hours to 6 hours, and more preferably 1 hour to 4 hours.

[0058] In the firing process, the time the composite metal hydroxide is held at the firing temperature, i.e., the holding time, is, for example, 0.5 hours to 8 hours, preferably 0.5 hours to 6 hours, and more preferably 1 hour to 4 hours.

[0059] The calcined composite metal hydroxide, i.e., the composite metal oxide produced by the calcination process, is then subjected to the next cooling process.

[0060] (Cooling Process) The cooling process involves cooling the composite metal oxide produced by the firing process from the firing temperature (maximum temperature reached) to 25°C at a rate of 2°C / min to 15°C / min. By cooling the composite metal oxide after firing at this rate, it becomes possible to control the size of crystalline impurities to a certain size or smaller.

[0061] Furthermore, the cooling rate when cooling from the firing temperature to 25°C is preferably 3°C / min to 10°C / min, and more preferably 4°C / min to 8°C / min.

[0062] The composite metal oxide obtained by the above manufacturing method is an Mg-Fe-based composite metal oxide represented by formula (1) above, and is a composite metal oxide with few crystalline impurities. In other words, it is a composite metal oxide that can be used as a highly practical adsorbent because it is less prone to metal ion elution and has excellent adsorption properties.

[0063] (Application Examples) The composite metal oxide of the present invention can be suitably used, for example, as an adsorbent for removing anions contained in drinking water or industrial wastewater. In particular, because the composite metal oxide of the present invention does not easily cause the elution of metal ions, it can be especially suitably used as an adsorbent for removing anions contained in drinking water. For example, the composite metal oxide of the present invention can be suitably used in various products such as purification materials, water purifiers, filtration devices, and packed columns.

[0064] Furthermore, the composite metal oxide of the present invention is also useful as a gas adsorbent. Examples of gases to be adsorbed include combustion exhaust gases generated in thermal power generation and waste incineration. These combustion exhaust gases contain several types of harmful acidic substances, such as hydrogen chloride, sulfur oxides, and nitrogen oxides, but the composite metal oxide of the present invention can remove these simultaneously.

[0065] Furthermore, the composite metal oxide of the present invention exhibits excellent adsorption performance even after regeneration. For example, to regenerate the adsorbent after the above-mentioned removal treatment, it is common to contact it with an alkali such as a carbonated aqueous solution. In this case, with adsorbents containing amphoteric elements such as Al in their structure, such as Mg-Al layered double hydroxides and Mg-Al composite metal oxides, these elements may dissolve upon contact with alkali, potentially impairing the stability of the composition and structure. As a result, there is a risk that the adsorption performance after regeneration will be significantly reduced. On the other hand, the composite metal oxide of the present invention does not contain amphoteric elements such as Al in its structure. Therefore, the composition and structure of the composite metal oxide of the present invention remain stable even during recycling using alkali, and as a result, the adsorption performance is less likely to deteriorate.

[0066] The composite metal oxide of the present invention may be used in particulate form such as powder, granules, or molded products, or it may be used in the form of a mixture by mixing it with other components. Furthermore, when used in the form of a mixture, a liquid such as water may be added to the mixture to make it a paste, or it may be dried and solidified into a predetermined shape to be used in the form of a molded product.

[0067] Furthermore, the composite metal oxide of the present invention can be granulated by known methods, from the viewpoint of its usage and ease of handling. In addition, the composite metal oxide of the present invention can be formed into pellet-like or spherical particles using a foaming agent or binder.

[0068] When molding using a binder, the moldability can be improved. Examples of binders include silicate binders. Among these, sodium metasilicate is preferred as the binder from the viewpoint of reactivity with magnesium contained in the composite metal oxide.

[0069] When using a foaming agent during molding, the porosity of the granulated material can be controlled. Examples of foaming agents include perlite or obsidian.

[0070] The granules or molded bodies obtained in the manner described above can be used by packing them into a column or the like.

[0071] Furthermore, another removal method according to yet another embodiment of the present invention involves contacting the above-mentioned adsorbent, granules, or molded body with a gas containing an acidic substance. This removal method can also be used in combination with a composite metal oxide composed of metal elements other than Mg and Fe, which has adsorption properties for acidic substances.

[0072] Furthermore, the present invention is not limited to the embodiments described above or the examples described later, and can be appropriately combined, substituted, or modified without departing from the purpose and spirit of the present invention.

[0073] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0074] (Example 1) A mixed solution containing 0.69 mol / L magnesium chloride and 0.23 mol / L iron(III) chloride hexahydrate (Mg / Fe ２ A solution of 6.0 mol / L NaOH and a 3.3 mol / L NaOH solution were prepared. These two solutions were poured into a 1 L volume reaction vessel being stirred at 1000 rpm, and the reaction was carried out continuously while adjusting the flow rate to maintain a reaction pH of 10.0 to 10.5.

[0075] Next, the recovered reaction slurry was dehydrated and washed with 30 times the amount of water relative to the solid product. Furthermore, the product was divided into two parts: CO2 and Fe. ３ The molar ratio of CO ３ / Fe ２ 0.18 mol / L Na so that the ratio becomes 2.0 ２ CO ３ After washing with a solution, the product was washed again with 30 times its volume of water. The product after washing was then dried overnight at a temperature of 105°C to obtain the composite metal hydroxide represented by formula (2) above.

[0076] The obtained composite metal hydroxide was fired under firing conditions of heating time of 2 hours, firing temperature of 500°C, and holding time of 2 hours. After the 2-hour holding time, the fired product was cooled at a rate of 5°C / min until it reached 25°C to obtain the composite metal oxide of Example 1.

[0077] (Example 2) The composite metal oxide of Example 2 was obtained in the same manner as in Example 1, except that the firing temperature was set to 600°C.

[0078] (Example 3) The molar ratio of Mg to Fe is Mg / Fe ２ The composite metal oxide of Example 3 was obtained in the same manner as in Example 1, except that the ratio was set to 8.0.

[0079] (Example 4) The molar ratio of Mg to Fe is Mg / Fe ２ The composite metal oxide of Example 4 was obtained in the same manner as in Example 1, except that the ratio was set to 8.0 and the firing temperature was set to 600°C.

[0080] (Example 5) The molar ratio of Mg to Fe is Mg / Fe ２ The composite metal oxide of Example 5 was obtained in the same manner as in Example 1, except that the ratio was set to 4.5 and the firing temperature was set to 500°C.

[0081] (Comparative Example 1) The molar ratio of Mg to Fe is Mg / Fe ２ A composite metal oxide of Comparative Example 1 was obtained in the same manner as in Example 1, except that the ratio was set to 6.0 and the firing temperature was set to 800°C.

[0082] (Comparative Example 2) The molar ratio of Mg to Fe is Mg / Fe ２ A composite metal oxide of Comparative Example 2 was obtained in the same manner as in Example 1, except that the ratio was set to 4.5 and the firing temperature was set to 800°C.

[0083] (Comparative Example 3) A composite metal oxide of Comparative Example 3 was obtained in the same manner as in Example 1, except that the firing temperature was set to 250°C.

[0084] (Comparative Example 4) FeCl ３ Al ２ (SO ４ ) ３ Using this method, the molar ratio of Mg to Al is Mg / Al ２ A composite metal oxide of Comparative Example 4 was obtained in the same manner as in Example 1, except that the ratio was set to 4.5 and the firing temperature was set to 600°C.

[0085] The compositions of the composite metal oxides obtained in Example 1, Example 2, and Comparative Example 1 as described above were analyzed, and the chemical formula was found to be Mg in all cases. ０．７５ Fe ０．２５ O１．１２５ It was. Also, the chemical formulas of the composite metal hydroxides before firing were all Mg ０．７５ Fe ０．２５ (OH) ２ (CO ３ ) ０．１２５ ·0.50H ２ O. Similarly, the chemical formula of the composite metal oxide of Comparative Example 4 was Mg ０．４５ Al ０．２０ O ０．７５ . In addition, the compositions of the composite metal oxides of Examples 3 to 5 and Comparative Example 2 all satisfied Formula (1). Also, the composition of the composite metal oxide of Comparative Example 3 contained a carbonate group (CO ３ ) and a hydroxyl group (OH) and did not satisfy Formula (1).

[0086] For each of the composite metal oxides of Examples 1 to 5 and Comparative Examples 1 to 4, powder X-ray diffraction analysis was performed, and the half-value widths, crystallite sizes, and ratios I ３ / I １ of the peak intensities of the first to third peaks were measured. Furthermore, the BET specific surface areas of each of the composite metal oxides were measured.

[0087] Then, for each of the composite metal oxides of Examples 1 to 5 and Comparative Examples 1 to 4, the following adsorption test was carried out, and the adsorption rates (%) of various anions and the elution concentrations (ppm) of metal ions were measured. These results are shown in Tables 1-1 and 1-2 below. Also, the powder X-ray diffraction patterns of each of the composite metal oxides of each Example and Comparative Example are shown in FIGS. 1 and 2. In FIGS. 1 and 2, P1 indicates the first peak. P2 indicates the second peak. P3 indicates the third peak.

[0088] <Adsorption test method> 0.03 g of a sample of the composite metal oxide is placed in a centrifuge tube with a volume of 50 mL, and 30 mL of an aqueous solution of various anions is added. The types of anions are fluoride ion (F － ), chromate ion (CrO ４ ２－ ), nitrate ion (NO ３ － ), nitrite ion (NO ２ － ), borate ion (B(OH) ４ －) Note that the concentrations of various elements D ０ This solution contains 2.5 ppm of boron (B), and the other elements are fluorine (F), chromium (Cr), and nitrate nitrogen (NOx). ３ -N), nitrite nitrogen (NO ２ -N) is 10 ppm.

[0089] Next, the centrifuge tube is placed in the shaker and shaken at room temperature at a shaking speed of 160 rpm for 24 hours.

[0090] Place the shaken centrifuge tube in a centrifuge and centrifuge at 10,000 g for 5 minutes. Filter the supernatant after centrifugation through a membrane filter with a pore size of 0.2 μm.

[0091] Fluoride ions, nitrate ions, and nitrite ions were measured using an ion chromatograph (model EcoIC, manufactured by Metrohm), and fluorine (F) and nitrate nitrogen (NO) in the solution were measured. ３ -N) and nitrite nitrogen (NO) ２ -N) The concentration D (ppm) was calculated.

[0092] The concentrations D (ppm) of chromium (Cr), boron (B), and metal ions (Fe and Al) were quantified using ICP emission spectroscopy with an emission spectrometer (model SPS3500DD, Hitachi). The adsorption rates of each element were calculated based on the following formula: Adsorption rate (%) = (D) ０ -D) / D ０ ×100

[0093]

[0094]

[0095] As shown in Tables 1-1 and 1-2, each of the composite metal oxides in Examples 1 to 5 of the present invention was found to have low levels of crystalline impurities and to be able to remove multiple types of anions with high adsorption rates. Furthermore, it was found that all of these composite metal oxides exhibited low levels of Fe and Al elution. Therefore, it has been demonstrated that each of the composite metal oxides in Examples 1 to 5 of the present invention can be used as a highly practical adsorbent.

[0096] On the other hand, both the composite metal oxides in Comparative Example 1 and Comparative Example 2 were found to have a large amount of crystalline impurities and poor adsorption capacity to multiple types of anions. Comparative Example 3 was found to have poor adsorption capacity due to the persistence of the composite hydroxide peak. Furthermore, the composite metal oxide in Comparative Example 4 was found to have a large amount of Al elution.

Claims

1. A composite metal oxide represented by the following formula (1), characterized in that, in a powder X-ray diffraction pattern, it has a first peak located in the range of 42° to 43° with a diffraction angle 2θ of 61° to 63°, the full width at half maximum of the first peak is 0.30° or more, and the full width at half maximum of the second peak is 0.45° or more. ２＋ １－ｘ Fe ３＋ ｘ O （２＋ｘ）／２ ... (1) In equation (1) above, x is a number that satisfies 0.10 < x < 0.

60.

2. The composite metal oxide according to claim 1, characterized in that, in the powder X-ray diffraction pattern, the full width at half maximum of the first peak is 0.60° or more, and the full width at half maximum of the second peak is 0.65° or more.

3. The composite metal oxide according to claim 1 or 2, characterized in that the crystallite size calculated from the full width at half maximum of the first peak is less than 420 Å, and the crystallite size calculated from the full width at half maximum of the second peak is less than 280 Å.

4. The composite metal oxide according to any one of claims 1 to 3, characterized in that the powder X-ray diffraction pattern does not have a third peak located in the range of 35° to 36° where the diffraction angle 2θ is, or has the third peak and the full width at half maximum of the third peak is 0.30° or more.

5. The peak intensity I of the first peak １ and the peak intensity I of the third peak ３ The ratio I ３ / I １ is less than 0.80, and the composite metal oxide according to claim 4 is characterized in that 6. The composite metal oxide according to claim 4 or 5, characterized in that the crystallite size calculated from the full width at half maximum of the third peak is less than 360 Å.

7. BET specific surface area is 20 m² ２ / g ~ 170m ２ A composite metal oxide according to any one of claims 1 to 6, characterized in that it is within the range of / g.

8. A method for producing a composite metal oxide, comprising: a firing step of heating a composite metal hydroxide represented by the following formula (2) at a temperature of 300°C to 750°C for a predetermined time; and a cooling step of cooling the fired composite metal hydroxide produced by the firing step from the temperature to 25°C at a rate of 2°C / min to 15°C / min. [Mg ２＋ １－ｘ Fe ３＋ ｘ (OH) ２ ] ｘ＋ (A ｎ－ ) ｘ／ｎ mH ２ O...(2) In the above formula (2), A ｎ－ CO ３ ２－ and OH － This represents an anion selected from the group consisting of the following, where n is 1 or 2, x is a number satisfying 0.10 < x < 0.60, and m is a number satisfying 0 ≤ m < 1.

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