Hydrotalcite and production method therefor

Abstract

The present disclosure provides a novel hydrotalcite that can be used as a highly practical adsorbent.　The present disclosure is a Mg-Fe-based Cl-type hydrotalcite that is represented by formula (1).　Formula (1): Mg(1–x)FexCly(An–)(x–y) / n(OH)2∙mH2O　In formula (1), x is a number satisfying 0.10<x≤0.60, y is a number satisfying 0.04≤y≤0.60, x≥y, An– is an n-valent anion, and m is a number satisfying m>0.　The half-value width of the diffraction peak of the (003) plane in a powder X-ray diffraction pattern of this hydrotalcite is 0.60° or less.

Description

Hydrotalcite and method for producing the same

[0001] The present invention relates to a hydrotalcite that can be used as an adsorbent.

[0002] Water treatment technologies have been mainly developed for the purpose of treating raw water, sewage, or wastewater. For example, pollutants contained in drinking water or industrial wastewater can be removed by an adsorption method, an electrodialysis method, a reverse osmosis method, an evaporation method, or an ion exchange method. Among them, the adsorption method, which can remove pollutants at relatively low equipment and treatment costs, has attracted attention.

[0003] Examples of pollutants include anions. Further examples of anions include fluoride ions (F － ), nitrate ions (NO ３ － ), nitrite ions (NO ２ － ), and sulfate ions (SO ４ ２－ ).

[0004] Technologies for adsorbing and removing anions contained in water have been variously studied. For example, each of Patent Documents 1 to 3 and Non-Patent Document 1 discloses a technique for adsorbing and removing various anions contained in water using a Mg—Al-based or Mg—Fe-based hydrotalcite.

[0005] International Publication No. 2018 / 124190 JP-A-2009-137801 JP-A-2009-45523

[0006] Kenichi Honda et al., "Synthesis and Anion Exchange Characteristics of Fe-Mg-Based and Al-Mg-Based Hydrotalcite-Like Compounds," Journal of Ion Exchange Vol. 16 No. 1 (2005), p41-47

[0007] Mg-Al-based hydrotalcite has a high ability to adsorb anions in an aqueous solution and is useful as an adsorbent. 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 basic hydrotalcite. 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 that more effectively suppresses the elution of metal ions such as Al and also has excellent adsorption properties.

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

[0009] The present disclosure includes the following aspects.

[0010] (First Disclosure) The first disclosure is a Mg-Fe-based Cl-type hydrotalcite represented by the following formula (1). The hydrotalcite of the first disclosure has a half-width of the diffraction peak of the (003) plane in the powder X-ray diffraction pattern of 0.60° or less. Mg （１－ｘ） Fe ｘ Cl <( ｙ (A ｎ－ ) （ｘ－ｙ）／ｎ (OH) ２ ・mH ２ O ・・・(1) In formula (1), x is a number satisfying 0.10 < x ≤ 0.60, y is a number satisfying 0.04 ≤ y ≤ 0.60, x ≥ y, A ｎ－ is an n-valent anion, and m is a number satisfying m > 0.

[0011] (Second Disclosure) The second disclosure is that in the hydrotalcite of the first disclosure, the half-width is 0.25° or more.

[0012] (Third Disclosure) The third disclosure is that in the hydrotalcite of the first disclosure or the second disclosure, the BET specific surface area is in the range of 10 m ２ / g to 60 m ２ / g.

[0013] (Fourth Disclosure) The fourth disclosure is a method for producing hydrotalcite. The production method of the fourth disclosure includes the following generation step and maturation step. The generation step involves mixing Mg raw material and Fe raw material in an Mg / Fe ratio. ２ The process involves reacting an acidic mixed solution containing 2.0 to 9.0 molar ratios with an alkaline substance to produce Mg-Fe-Cl type hydrotalcite represented by the following formula (1). The maturation process involves maturing the Mg-Fe-Cl type hydrotalcite at a temperature of 100°C to 170°C for 2 to 5 hours. （１－ｘ） Fe ｘ Cl ｙ (A ｎ－ ) （ｘ－ｙ）／ｎ (OH) ２ ・mH ２ O ... (1) In equation (1), x is a number satisfying 0.10 < x ≤ 0.60, y is a number satisfying 0.04 ≤ y ≤ 0.60, x ≥ y, A ｎ－ is an n-valent anion, and m is a number satisfying m > 0.

[0014] According to the present invention, a novel hydrotalcite can be provided that can be used as a highly practical adsorbent.

[0015] Figure 1 is a graph showing the powder X-ray diffraction patterns of hydrotalcite for Examples 1 to 3 and Comparative Examples 1 to 3. Figure 2 is a graph showing the powder X-ray diffraction patterns of hydrotalcite for Comparative Examples 4 and 5.

[0016] Preferred embodiments of the hydrotalcite 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.

[0017] The inventors of the present invention conducted diligent research to achieve the above objective and discovered that by aging Mg-Fe-based Cl-type hydrotalcite under specific conditions, it is possible to obtain Mg-Fe-based hydrotalcite that is less prone to metal ion elution and has excellent adsorption properties.

[0018] The present invention has been completed based on the above findings. The present invention includes the following embodiments.

[0019] <Hydrotalcite> Hydrotalcite according to one embodiment of the present invention is Mg-Fe-based Cl-type hydrotalcite represented by the following formula (1). Mg （１－ｘ） Fe ｘ Cl ｙ (A ｎ－ ) （ｘ－ｙ）／ｎ (OH) ２ ・mH ２ O ... (1) In equation (1), x is a number satisfying 0.10 < x ≤ 0.60, y is a number satisfying 0.04 ≤ y ≤ 0.60, x ≥ y, A ｎ－ is an n-valent anion, and m is a number satisfying m > 0.

[0020] The hydrotalcite of this embodiment is a Mg-Fe-based Cl-type hydrotalcite and does not contain metal ions such as Al that would leach out at the basic pH of hydrotalcite. Furthermore, Fe is less likely to leach out at the basic pH of hydrotalcite. Therefore, the hydrotalcite of this embodiment is less likely to release metal ions in aqueous solution.

[0021] Furthermore, the hydrotalcite of this embodiment has a unique characteristic in that, in the powder X-ray diffraction pattern obtained by powder X-ray diffraction (XRD), the full width at half maximum of the diffraction peak of the (003) plane is 0.60° or less. The diffraction peak of the (003) plane of hydrotalcite is detected at a diffraction angle 2θ of 10.0 to 11.0°. The sharper the diffraction peak of this (003) plane, the larger the crystallite size and the more the crystal structure is growing. When the layered crystal structure of hydrotalcite has grown beyond a certain point, the layered crystal structure becomes stable and can incorporate more anions between its layers.

[0022] The hydrotalcite of this embodiment has a diffraction peak with a half-width of 0.60° or less on the (003) plane, and the diffraction peak on the (003) plane is a very sharp peak. In other words, because the hydrotalcite of this embodiment is a hydrotalcite with very high crystallinity, it can incorporate more anions between its layers. Therefore, the hydrotalcite of this embodiment can exhibit excellent adsorption performance for various anions.

[0023] As described above, the hydrotalcite of this embodiment is less prone to metal ion elution and has excellent adsorption properties, making it a highly practical adsorbent. Furthermore, as a result, the hydrotalcite of this embodiment can significantly contribute to water purification, thus having the advantage of contributing to the achievement of the SDGs (Sustainable Development Goals) adopted at the UN Summit.

[0024] The lower limit of the full width at half maximum (FWHM) of the diffraction peak of the (003) plane is not particularly limited, and any FWHM greater than 0° is acceptable. While a smaller FWHM of the diffraction peak of the (003) plane is preferable, attempting to make the FWHM excessively small may lead to a decrease in productivity. Therefore, it is preferable that the FWHM of the diffraction peak of the (003) plane be 0.25° or greater.

[0025] The powder X-ray diffraction pattern of hydrotalcite and the full width at half maximum of the diffraction peak of the (003) plane can be obtained by the following powder X-ray diffraction method.

[0026] (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

[0027] Then, the powder X-ray diffraction patterns measured under the above conditions are processed using X-ray analysis software (HighScore Plus, manufactured by Malvern Panalogical), and the full width at half maximum of the diffraction peak of the (003) plane is determined.

[0028] The hydrotalcite of this embodiment is not particularly limited in its configuration other than being an Mg-Fe-based Cl-type hydrotalcite represented by the above formula (1) and having high crystallinity.

[0029] For example, the hydrotalcite of this embodiment has a BET specific surface area of ​​10 m². ２ / g ~ 60m 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.

[0030] In this specification, BET specific surface area refers to the specific surface area of ​​particulate hydrotalcite measured by the BET method. The BET specific surface area is measured 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%).

[0031] The BET specific surface area of ​​hydrotalcite is 15 m². ２ More preferably 20 m ２ A value of 1 / g or more is even more preferable. The BET specific surface area is 45 m². ２ It may be less than / g.

[0032] Next, preferred embodiments of the hydrotalcite manufacturing method of the present invention will be described in detail.

[0033] <Manufacturing Method> The manufacturing method of hydrotalcite according to this embodiment includes at least the following production step and maturation step. The production step involves mixing Mg raw material and Fe raw material in an Mg / Fe ratio. ２ This process involves reacting an acidic mixed solution containing Mg in a molar ratio of 2.0 to 9.0 with an alkaline substance to produce Mg-Fe-based Cl-type hydrotalcite represented by the following formula (1). （１－ｘ） Fe ｘ Cl ｙ (A ｎ－ ) （ｘ－ｙ）／ｎ (OH) ２ ・mH ２O ... (1) In equation (1), x is a number satisfying 0.10 < x ≤ 0.60, y is a number satisfying 0.04 ≤ y ≤ 0.60, x ≥ y, A ｎ－ is an n-valent anion, and m is a number satisfying m > 0.

[0034] The maturation process involves aging the Mg-Fe-based Cl-type hydrotalcite at a temperature of 100°C to 170°C for 2 to 5 hours.

[0035] Furthermore, the manufacturing method of this embodiment may include optional post-processing steps after the maturation step, such as a cooling step, a dehydration step, a washing step, and a drying step.

[0036] The following describes each step in the manufacturing method of this embodiment.

[0037] (Production Process) As described above, the production process involves combining Mg raw material and Fe raw material in an Mg / Fe ratio. ２ This process involves reacting an acidic mixed solution containing a substance in a molar ratio of 2.0 to 9.0 with an alkaline substance to produce Mg-Fe-based Cl-type hydrotalcite represented by the above formula (1).

[0038] In the production process, Mg raw material and Fe raw material are used in Mg / Fe ２ = By mixing an acidic mixed solution containing 2.0 to 9.0 molar ratios with an alkaline substance and reacting them, a slurry containing Mg-Fe-based Cl-type hydrotalcite represented by the above formula (1) is produced.

[0039] 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. Furthermore, examples of acids included in the acidic mixed solution include hydrochloric acid and nitric acid.

[0040] Molar ratio of Mg raw material and Fe raw material Mg / Fe ２ The molar ratio Mg / Fe is preferably 3.0 or higher, more preferably 4.0 or higher, and even more preferably 4.5 or higher. ２ Preferably, it is 8.5 or less, and more preferably 8.0 or less.

[0041] Examples of alkaline substances include sodium hydroxide, potassium hydroxide, sodium carbonate, and ammonia.

[0042] The reaction between the acidic mixed solution and the alkaline substance can be carried out, for example, by stirring for 10 to 60 minutes. The pH during the reaction is, for example, 10.0 to 10.5. The reaction can be carried out in a sealed container. After the reaction, stirring is stopped and the slurry containing the hydrotalcite produced is allowed to mature.

[0043] (Aging Process) As described above, the aging process involves aging the Mg-Fe-based Cl-type hydrotalcite at a temperature of 100°C to 170°C for 2 to 5 hours. More specifically, it involves aging a slurry containing Mg-Fe-based Cl-type hydrotalcite at a temperature of 100°C to 170°C for 2 to 5 hours.

[0044] In the maturation process, the slurry containing the hydrotalcite generated in a sealed container is heated at a temperature of 100°C to 170°C, thereby pressurizing it at a constant pressure. By maturing the hydrotalcite under these specific heating and pressurizing conditions, the full width at half maximum of the diffraction peak of the (003) plane in the powder X-ray diffraction pattern of the hydrotalcite can be controlled to 0.60° or less. That is, the layered crystalline structure of the hydrotalcite grows beyond a certain point, and the layered crystalline structure can be stabilized. As a result, the hydrotalcite obtained by the manufacturing method of this embodiment can incorporate more anions between its layers. Furthermore, by maturing the hydrotalcite at a temperature of 170°C or less, the formation of iron oxide as an impurity can be suppressed. This makes it less likely for Fe to dissolve as a metal ion.

[0045] The heating conditions during the maturation process, i.e., the maturation temperature, are not particularly limited as long as they are within the range of 100°C to 170°C as described above. Note that the maturation temperature refers to the highest temperature reached during the maturation process. Hydrotalcite is matured by being held at this highest temperature for 2 to 5 hours, resulting in hydrotalcite with high crystallinity and few impurities as described above.

[0046] The aging temperature is preferably in the range of 110°C to 170°C, more preferably in the range of 120°C to 150°C, and particularly preferably in the range of 125°C to 145°C.

[0047] In the maturation process, the time for which the hydrotalcite is held at the above-mentioned maturation temperature, i.e., the maturation time, is not particularly limited as long as it is within the range of 2 to 5 hours. However, a maturation time within the range of 3 to 5 hours is preferred, and a time within the range of 3.5 to 4.5 hours is more preferred.

[0048] The hydrotalcite obtained through the above maturation process may be subjected to any post-processing step. Examples of post-processing steps include cooling, dehydration, washing, and drying.

[0049] (Post-processing step) The manufacturing method of this embodiment may include a cooling step in which the slurry containing hydrotalcite produced by the aging step is cooled from the aging temperature (maximum temperature reached) to 25°C at a rate of 0.2°C / min to 2.0°C / min. By cooling the hydrotalcite after aging at such a rate, it is possible to control the layered crystalline structure of the hydrotalcite and the size of the crystals of crystalline impurities.

[0050] Furthermore, the cooling rate when cooling from the maturation temperature to 25°C is preferably 0.3°C / min to 1.6°C / min, and more preferably 0.5°C / min to 1.5°C / min.

[0051] After the cooling process, the slurry containing the matured hydrotalcite may be subjected to a dehydration process. In the dehydration process, water is removed from the slurry containing the matured hydrotalcite using drainage means such as a suction pump or separation means such as suction filtration. This allows for obtaining solid, unrefined hydrotalcite.

[0052] After the dehydration process, the solid, unrefined hydrotalcite may be subjected to a washing process. In the washing process, impurities are removed by washing the solid, unrefined hydrotalcite with, for example, 10 to 50 times its volume of water.

[0053] After the washing step, the washed hydrotalcite may be subjected to a drying step. In the drying step, the washed hydrotalcite is dried by heating it at a temperature of, for example, 80°C to 120°C for a predetermined time. The drying step may be carried out under reduced pressure or under an inert gas atmosphere. Purified solid hydrotalcite can be obtained through the drying step.

[0054] The hydrotalcite obtained by the above manufacturing method is an Mg-Fe-based Cl-type hydrotalcite represented by formula (1) above, and is a highly crystalline hydrotalcite in which the full width at half maximum of the diffraction peak of the (003) plane in the powder X-ray diffraction pattern is 0.60° or less. In other words, it is a hydrotalcite that can be used as a highly practical adsorbent because it is less prone to metal ion elution and has excellent adsorption properties.

[0055] (Application Examples) The hydrotalcite 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 hydrotalcite 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 hydrotalcite of the present invention can be suitably used in various products such as purification materials, water purifiers, filtration devices, and packed columns.

[0056] Furthermore, the hydrotalcite 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 hydrotalcite of the present invention can remove these simultaneously.

[0057] Furthermore, the hydrotalcite 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 that contain amphoteric elements such as Al in their structure, such as Mg-Al layered double hydroxides and Mg-Al hydrotalcite, these elements may leach out 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 hydrotalcite of the present invention does not contain amphoteric elements such as Al in its structure. Therefore, the composition and structure of the hydrotalcite of the present invention remain stable even when recycled using alkali, and as a result, the adsorption performance is less likely to deteriorate.

[0058] The hydrotalcite 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.

[0059] Furthermore, the hydrotalcite of the present invention can be granulated by known methods, from the viewpoint of its usage and ease of handling. In addition, the hydrotalcite of the present invention can be molded into pellet-like or spherical particles using a foaming agent or binder.

[0060] 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 hydrotalcite.

[0061] When using a foaming agent during molding, the porosity of the granulated material can be controlled. Examples of foaming agents include perlite or obsidian.

[0062] The granules or molded bodies obtained in the manner described above can be used by packing them into a column or the like.

[0063] 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 hydrotalcite or the like, which is composed of metal elements other than Mg and Fe and has adsorption properties for acidic substances.

[0064] 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.

[0065] 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.

[0066] (Example 1) A mixed solution containing 0.80 mol / L magnesium chloride and 0.20 mol / L iron(III) chloride hexahydrate (Mg / Fe ２ A solution of 8.0 (= ) and a 3.3 mol / L NaOH solution were prepared. These two solutions were poured into a 1 L 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.

[0067] Next, stirring was stopped, and the slurry containing hydrotalcite generated in the reaction vessel was aged in an autoclave at 140°C for 4 hours (aging step). Furthermore, the aged slurry was dewatered to obtain solid, unrefined hydrotalcite. Impurities were removed from this solid, unrefined hydrotalcite by washing it with 30 times its volume of water. Then, the hydrotalcite after washing was heated at 105°C for a predetermined time to dry it. This yielded the purified hydrotalcite of Example 1.

[0068] (Example 2) The molar ratio of Mg to Fe is Mg / Fe ２ The ratio was set to 6.0. Otherwise, hydrotalcite for Example 2 was obtained in the same manner as in Example 1.

[0069] (Comparative Example 1) Hydrotalcite of Comparative Example 1 was obtained in the same manner as in Example 1, except that the maturation process was omitted.

[0070] (Comparative Example 2) The molar ratio of Mg to Fe is Mg / Fe ２ The ratio was set to 6.0. Furthermore, the maturation process was omitted. Otherwise, the hydrotalcite of Comparative Example 2 was obtained in the same manner as in Example 1.

[0071] (Example 3) The molar ratio of Mg to Fe is Mg / Fe ２ The ratio was set to 4.5. Furthermore, the maturation conditions were set to 170°C for 2 hours. Otherwise, hydrotalcite for Example 3 was obtained in the same manner as in Example 1.

[0072] (Comparative Example 3) The molar ratio of Mg to Fe is Mg / Fe ２ The ratio was set to 4.5. Furthermore, the maturation process was omitted. Otherwise, the hydrotalcite of Comparative Example 3 was obtained in the same manner as in Example 1.

[0073] (Comparative Example 4) FeCl ３ Al ２ (SO ４ ) ３ Using this method, the molar ratio of Mg to Al is Mg / Al ２ The ratio was set to 8.0. Furthermore, the maturation conditions were set to 150°C for 8 hours. Otherwise, the hydrotalcite of Comparative Example 4 was obtained in the same manner as in Example 1.

[0074] (Comparative Example 5) FeCl ３ Al ２ (SO ４ ) ３ The molar ratio of Mg to Al was set to Mg / Al. ２ The ratio was set to 6.0. Furthermore, the maturation conditions were set to 170°C for 2 hours. Otherwise, the hydrotalcite of Comparative Example 5 was obtained in the same manner as in Example 1.

[0075] The hydrotalcite obtained in Examples 1 to 3 and Comparative Examples 1 to 5 were analyzed for their respective compositions. The results are shown in Table 1 below.

[0076]

[0077] Powder X-ray diffraction analysis was performed on each hydrotalcite sample from Examples 1 to 3 and Comparative Examples 1 to 5, and the full width at half maximum of the diffraction peak of the (003) plane was measured. Furthermore, the BET specific surface area of ​​each hydrotalcite sample was measured.

[0078] Adsorption tests were then performed on each hydrotalcite sample from Examples 1 to 3 and Comparative Examples 1 to 5, and the adsorption rates (%) of various anions and the elution concentrations (ppm) of metal ions were measured. These results are shown in Table 1 below. Figure 1 shows the powder X-ray diffraction patterns of each hydrotalcite sample from Examples 1 to 3 and Comparative Examples 1 to 3. Figure 2 shows the powder X-ray diffraction patterns of each hydrotalcite sample from Comparative Examples 4 and 5.

[0079] <Adsorption Test Method> Place 0.03 g of hydrotalcite sample in a 50 mL centrifuge tube and add 30 mL of various anion aqueous solutions. The type of anion is 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) The anion concentration is 10 ppm.

[0080] Next, the centrifuge tube is placed in the shaker and shaken at room temperature at a shaking speed of 160 rpm for 24 hours. For fluorine, the shaking is performed for 0.5 to 24 hours.

[0081] 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.

[0082] 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.

[0083] 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

[0084]

[0085]

[0086] As shown in Tables 2-1, 2-2, and Figure 1, each of the hydrotalcite samples in Examples 1 to 3 of the present invention exhibited high crystallinity and low impurity levels, and was found to be capable of removing multiple types of anions with high adsorption rates. Furthermore, it was found that all of these hydrotalcite samples exhibited low elution of Fe and Al. Therefore, it has been demonstrated that each of the hydrotalcite samples in Examples 1 to 3 of the present invention can be used as a highly practical adsorbent.

[0087] On the other hand, as shown in Tables 2-1, 2-2, Figures 1 and 2, the hydrotalcite samples from Comparative Examples 1 to 5 were found to have poor adsorption capacity to multiple types of anions due to low crystallinity or high levels of impurities. Furthermore, the hydrotalcite samples from Comparative Examples 4 and 5 were found to have high levels of Al elution.

Claims

1. Hydrotalcite of the Mg-Fe-based Cl type represented by the following formula (1), characterized in that the half-width of the diffraction peak of the (003) plane in the powder X-ray diffraction pattern is 0.60° or less. Mg （１－ｘ） Fe ｘ Cl ｙ (A ｎ－ ) （ｘ－ｙ）／ｎ (OH) ２ mH ２ O ... (1) In equation (1) above, x is a number satisfying 0.10 < x ≤ 0.60, y is a number satisfying 0.04 ≤ y ≤ 0.60, x ≥ y, A ｎ－ is an n-valent anion, and m is a number satisfying m > 0.

2. The hydrotalcite according to claim 1, characterized in that the half-width is 0.25° or more.

3. The BET specific surface area is within the range of 10 m ２ / g to 60 m ２ / g, and the hydrotalcite according to claim 1 or 2 is characterized in that.

4. A method for producing hydrotalcite, wherein the Mg raw material and Fe raw material are Mg / Fe ２ A manufacturing method comprising: a production step of reacting an acidic mixed solution containing a substance in a molar ratio of 2.0 to 9.0 with an alkaline substance to produce Mg-Fe-Cl type hydrotalcite represented by the following formula (1); and a maturation step of maturing the Mg-Fe-Cl type hydrotalcite at a temperature of 100 to 170°C for 2 to 5 hours. （１－ｘ） Fe ｘ Cl ｙ (A ｎ－ ) （ｘ－ｙ）／ｎ (OH) ２ mH ２ O ... (1) In equation (1) above, x is a number satisfying 0.10 < x ≤ 0.60, y is a number satisfying 0.04 ≤ y ≤ 0.60, x ≥ y, A ｎ－ is an n-valent anion, and m is a number satisfying m > 0.

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