JP7233046B2 - baked shell - Google Patents

Description

TECHNICAL FIELD The present invention relates to a baked product obtained by baking shells and an article using the same.

In recent years, as a method of utilizing shell waste, research has been conducted on a calcined product obtained by calcining it. The main component of these shells is calcium carbonate. Carbon dioxide is liberated from calcium carbonate by high-temperature calcination to form calcium oxide, which reacts with water in the air to form calcium hydroxide. Therefore, the main component of baked shells is calcium hydroxide.

On the other hand, in addition to strong alkaline properties, there are still insufficient properties and applied research on calcined products mainly composed of calcium oxide, which can be expected to have new properties such as oxidation, reduction, and active radical reactions, and many things remain unexplained. is.

Patent Document 1 discloses the bactericidal effect of a sintered body of about 1 to 70 μm obtained by sintering scallop shell powder and other inorganic substances at 900° C. to 1100° C. for 15 to 90 minutes. However, the concentration and purity of calcium oxide in the sintered body, chemical properties, and the mechanism of bactericidal activity have not been clarified at all.

In Patent Document 2, roughly crushed scallop shells are baked at 1000 ° C. to 1100 ° C. for 2 to 4 hours, and an expensive crushing device such as a wet bead mill crusher is used to finely bake to an average particle size of 0.5 to 3 μm. An antiviral effect of the grind is disclosed. However, nothing has been clarified about the purity, content and chemical properties of calcium oxide produced by baking scallop shells.

Patent Document 3 discloses the application of the supernatant of a mixture of calcined nanopowder of 100 to 500 nm obtained by calcining washed scallop shells at 1100° C. for 2 hours as an antiviral agent. However, the production examples of calcined shell powder have poor reproducibility, and nothing has been clarified about the production method of calcined shell powder, the purity of calcium oxide, the content, and the chemical characteristics.

Patent Document 4 discloses a mixture of calcium oxide and calcium carbonate of 40 μm or less obtained by low temperature firing at 500 to 600° C., further intermediate firing at 500 to 900° C. and pulverization (calcium oxide/calcium carbonate = 1.05-1.25), and its sustained antibacterial activity are disclosed. However, nothing has been clarified about the purity, content and chemical properties of calcium oxide produced by baking scallop shells.

Japanese Patent Application Laid-Open No. 2001-233720 JP 2008-179555 A JP 2012-062257 A Japanese Patent No. 5019123

Conventionally, a water-dispersed suspension obtained by mixing a fired shell product mainly composed of calcium hydroxide with water is used. However, the solubility of this calcined product is low, and even if a fine powder is used, only about 0.1 part by mass dissolves in 100 parts by mass of water. The use of only the supernatant necessitated a step of removing the precipitate, which was disadvantageous in terms of production, such as a large loss of the precipitated baked product and an increase in cost. Furthermore, it was impossible to increase the concentration of the fired product in order to obtain a higher effect. In addition, the use of a high-concentration suspension that causes sedimentation is highly likely to cause clogging of the atomizer.

For the purpose of enhancing the dispersibility in water and the sterilization effect of baked shell products, improvements have been made to prepare fine powder with a smaller average particle size or to make the baked products porous (Patent Document 4). It is known that this increases the BET specific surface area and enhances hydrophilicity, dispersibility in water, and bactericidal/adsorptive activity. On the other hand, research on the physical properties of burned shells, which are mainly composed of calcium oxide, has been inadequate because they can be expected to have oxidation, reduction, and radical activity.

The problem to be solved by the present invention is to provide a baked shell product having a specific activity.

As a result of intensive research on shell calcined products, the present inventors have produced and stored shell calcined products made of high-purity calcium oxide, and have refined their material properties.

That is, according to the present invention, a baked product obtained by baking shells,
The calcium oxide content measured by differential thermal thermogravimetric analysis (TG-DTA) is 95% by weight or more, and the calcium hydroxide content is 5% by weight or less,
The calcium element content measured by X-ray fluorescence spectroscopy (XRF) is 95 atom% or more,
Calcium oxide content measured by X-ray diffraction analysis (XRD) is 95% by mass or more,
The average particle size is 20 μm or less,
A fired product having a BET specific surface area of 0.5 m 2 /g or more and 3.0 m 2 /g or less is provided.

At least a portion of the shell may be a scallop shell. The shell may contain scallop shell as a main component, or may consist of scallop shell only. In the following description, Examples 1 and 4 are read as Reference Examples A1 and A4, respectively.

ADVANTAGE OF THE INVENTION According to this invention, the baked shellfish material with a small average particle diameter is provided. The baked product and its suspension are superior to conventional products mainly composed of calcium hydroxide in terms of oxidation/reduction/radical activity, adsorption effect, and sterilization effect. We have come to propose a new industrial field that utilizes this dense baked shell product.

1 is a SEM photograph of baked shells of Examples 1 and 2 of the present invention. Fig. 2 shows SEM photographs of baked shell products of Examples 1 and 2 of the present invention immediately after opening and after 7 days in a steam saturated incubator. It is a comparison of hydration exothermic reaction temperatures of the baked shell products of Examples 1 and 2 of the present invention. It is a comparison of hydration exothermic reaction temperatures of the fired products of Example 3, Comparative Example 1, and Reference Examples 1 to 3 of the present invention. 1 is a comparison of the reducing and removing power for nitrogen oxides of the fired products of Examples 1 and 2, Comparative Example 1, and Reference Examples 1 and 3 of the present invention.

The present invention will be described in detail below.

(Baked product of the present invention)
The starting material for producing the calcined products of the present invention is seashells. Seashells refer to materials containing calcium carbonate that are formed as outer shells by organisms commonly referred to as shellfish and similar organisms (mostly belonging to the subphylum Stelura).

Shellfish are generally classified into monovalves, bivalves, and snails. Examples of monovalves include abalone and Tokobushi, examples of bivalves include scallops, oysters, clams, clams, short-necked clams, and examples of snails include turban shells, whelks, and snails. Although any mussel shell can be used as a starting material, bivalve shells are preferred due to their ease of cleaning and reduced risk of contamination. Among bivalve shells, scallop shells and oyster shells are more preferred, and scallop shells are particularly preferred.

The average particle size of the fired product of the present invention is 20.0 μm or less, 15.0 μm or less, 10.0 μm or less, 8.0 μm or less, 6.0 μm or less, 5.0 μm or less, or 2.0 μm or less.

The average particle size of the baked product of the present invention may be measured using a particle size distribution analyzer. An example of such a device is CILAS (Aisin Nano Technologies Co., Ltd.). Further, the shape and surface structure of the fired product of the present invention can be obtained from an SEM image at any magnification of 2000 to 10000 times.

The ratio of calcium element to the elements measurable by wavelength dispersive X-ray fluorescence analysis (XRF) of the fired product is 90 atom% or more, 91 atom% or more, 92 atom% or more, 93 atom% or more, 94 atom% or more, 95 atom% Above, it may be 96 atom % or more, 97 atom % or more, 98 atom % or more, or 99 atom % or more.

By X-ray fluorescence spectroscopy (XRF), in addition to calcium, trace amounts of contents such as potassium, sulfur, phosphorus, magnesium, sodium, aluminum, silicon, and strontium can also be measured. Carbon and oxygen are not measured by wavelength dispersive X-ray fluorescence spectroscopy (XRF).

RIX3100 (manufactured by Rigaku Denki Kogyo Co., Ltd.) is exemplified as an apparatus for wavelength dispersive X-ray fluorescence spectroscopy (XRF).

The content of calcium oxide, calcium hydroxide, and calcium carbonate in the fired product is estimated using a differential thermal calorimetric analyzer. By differential thermal calorimetric analysis, the water content is estimated from the weight change around 300°C, the calcium hydroxide content is estimated from the weight change around 350°C, and the calcium carbonate content is estimated from the weight change around 600°C. can.

The weight retention ratio (also expressed as calcium oxide content ratio) at 30 to 1000 ° C. measured by differential thermal calorimetric analysis (TG-DTA) of the fired product of the present invention is 75.0% by weight or more and 80.0% by weight. % or more, 85.0 wt% or more, 90.0 wt% or more, 95.0 wt% or more, 99.0 wt% or more, 99.3 wt% or more, or 99.5 wt% or more. The weight retention rate is the percentage of the weight at 1000°C to the weight at 30°C.

An apparatus for differential thermal thermogravimetric analysis (TG-DTA) includes, for example, TGA851e (manufactured by Mettler Toledo). Differential thermal thermogravimetric analysis is performed by heating from 30° C. to 1000° C. at a rate of 10° C./min in a nitrogen stream of 100 mL/min.

The calcium oxide content measured by X-ray diffraction analysis (XRD) of the fired product of the present invention is 90.0% by mass or more, 92% by mass or more, 94% by mass or more, 96% by mass or more, 98% by mass or more. , 99% by mass or more, or 99.5% by mass or more.

Equipment for X-ray diffraction analysis (XRD) includes, for example, X'Pert-PRO (Philips).

The BET specific surface area of the fired product of the present invention is 0.2 m ² /g or more, 0.3 m ² /g or more, 0.4 m ² /g or more, 0.5 m ² /g or more, 0.6 m ² /g or more. , 0.7 m ² /g or greater, 0.8 m ² /g or greater, 0.9 m ² /g or greater, or 1.0 m ² /g or greater. On the other hand, 3.0 m ² /g or less, 2.8 m ² /g or less, 2.6 m ² /g or less, 2.4 m ² /g or less, 2.2 m ² /g or less, or 2.0 m ² /g or less is.

An example of an apparatus for analyzing the BET specific surface area is ChemBET3000 manufactured by Quantachrome. The method for measuring the BET specific surface area is not particularly limited, and the measurement may be carried out under commonly used conditions.

The baked shell product and its aqueous suspension of the present invention have effects such as adsorption, cleaning (skin/wound cleaning, gargling, etc.), removal, detoxification activity, bactericidal activity, and deodorant activity of toxic substances and organic substances. Better than Here, the solvent of the aqueous suspension is a solvent containing water (for example, pure water or an aqueous solution obtained by adding a water-soluble compound such as alcohol, sodium phosphate, or polyphosphoric acid to pure water).

When the calcined product of the present invention is subjected to a hydration reaction with water vapor or the like, the surface changes to micronize crystals due to the formation of calcium hydroxide, and changes occur in the surface structure due to the formation of cracks and pores, resulting in a characteristic change with improved hydrophilicity. occur. Actually, the calcium oxide content measured by X-ray diffraction analysis (XRD) is 99% or more, and the average particle size is 5 μm or less. Compared to baked shells with a content of 75 to 95%, a calcium hydroxide content of 5 to 20%, and an average particle size of 5 μm or less, hydrophilicity and water suspension properties are poor at the beginning of water addition, and more A large amount of precipitate is produced.

(Method for producing fired product of the present invention)
An example of a method for producing the fired product described above is described below. Naturally, the fired product described above may be produced by a method modified from the following method or by a completely different method.

In the manufacturing method, the following steps (1) to (6) are performed in the order described.
(1) Primary firing step of firing shells,
(2) a step of naturally cooling the fired primary fired product to the ambient temperature;
(3) Impurities are removed from the primary fired product through each filter (air filter, micromist filter, activated carbon filter), and the dry ultrafine pulverization system (nano jetmizer) and/or bag or cyclone dust collector is used as high-pressure gas. A step of uniform pulverization and dust collection while removing carbon dioxide and water vapor by replacing and removing carbon dioxide and water vapor by injecting nitrogen gas or argon gas, which is an inert gas, in addition to dried air;
(4) a secondary firing step of secondary firing the primary fired product;
(5) A step of naturally cooling the secondary fired product to the outside temperature under low pressure conditions of 10 ³ Pa or less and/or under inert gas atmosphere conditions;
(6) Carry out the cooled baked product in a nitrogen gas or argon gas atmosphere with the firing furnace opening/closing door (the outside of the firing furnace opening/closing door is also under an argon gas atmosphere), and fill with vacuum and/or nitrogen gas or argon gas. packaging process

Each step will be described below.

In the present invention, the "outside temperature" means the temperature of the ambient environment in which the firing device (firing furnace) is placed. The temperature of the surrounding environment fluctuates depending on the region and place where the kiln is arranged, as well as the time and season, and it cannot be defined uniformly, but it is less than 100°C, less than 80°C, less than 60°C, or less than 50°C. It may be interpreted as temperature.

Step (1) is a step of primary firing of the starting material. During this baking, carbon and hydrogen derived from proteins and the like contained in the starting material are released, and calcium carbonate, which is the main component, is transformed into calcium oxide.

The firing temperature is 1200° C. or higher, 1400° C. or higher, or 1600° C. or higher. By setting the temperature above these temperatures, the organic substances can be sufficiently removed and the purity of calcium oxide is increased. On the other hand, the upper limit of the firing temperature is not particularly limited as long as it is below the melting point of calcium oxide (approximately 2600°C). Alternatively, 1500° C. or less is preferable. Of course, throughout the firing process, the firing temperature may be constant or may vary, as long as it remains within the above ranges.

The firing time is 3 hours or longer, 4 hours or longer, or 5 hours or longer. On the other hand, the upper limit of the firing time is preferably 8 hours or less, 7.5 hours or less, 7 hours or less, or 6.5 hours or less.

Step (1) is carried out in an oxygen-containing atmosphere (usually in an air atmosphere) to remove organic matter. Carbon and hydrogen contained in proteins and the like react with oxygen to form carbon dioxide and water, which are liberated from the starting materials.

There are no particular restrictions on the rate at which the temperature is raised from the ambient temperature to the previous firing temperature, but it is usually 100 to 500°C/hour, 150 to 450°C/hour, 200 to 400°C/hour, or 250 to 350°C/hour. .

Step (2) is a step of cooling the primary fired product fired in step (1). Instead of actively cooling, the heating is stopped and heat is released to naturally cool to the outside temperature. The time required for step (2) is considered to depend on the temperature of the outside air and the starting material, but is generally 10 hours or more, 15 hours or more, or 20 hours or more.

Step (2) may be performed under any atmosphere. For example, an inert gas (helium, nitrogen gas, etc.) atmosphere or an air atmosphere may be used. Moreover, the atmosphere may be the same as or different from that in step (1). Cooling in a low-humidity environment is preferred to prevent hydration reactions.

It is understood that in the process of slow natural cooling, calcium oxide is cooled while maintaining high crystallinity.

In step (3), impurities are removed from the powdered calcined product through filters such as air filters, micromist filters, activated carbon filters, etc., and the particles are accelerated with high-pressure gas energy that has been extremely dried by a special compressor. It is pulverized using a device capable of achieving ultra-fine pulverization by collision (Nano Jet Mizer; NJ-300-D). As the high-pressure gas, it is possible to use nitrogen gas or argon gas, which is an inert gas, in addition to air obtained by drying the air.

Step (4) is a secondary firing step of further firing the fired product. After firing the primary fired product, it is thought that the proportion of calcium oxide decreases by reacting with water vapor in the atmosphere and carbon dioxide, which is a gas generated by firing. Therefore, in order to maintain and improve the purity of calcium oxide, re-firing is performed.

The firing temperature in the secondary firing step is 600° C. or higher, 700° C. or higher, 800° C. or higher, 850° C. or higher, 900° C. or higher, and 950° C. or higher. Firing at these temperatures or higher can sufficiently convert calcium carbonate and calcium hydroxide into calcium oxide. The firing temperature in the secondary firing step is about 2600° C. (melting point of calcium oxide) or less, and usually 1500° C. or less, 1200° C. or less, or 1000° C. or less.

The firing time of the secondary firing step is 1 hour or longer, 1.5 hours or longer, or 2 hours or longer. On the other hand, it is preferably 7 hours or less, 6 hours or less, 5 hours or less, 4 hours or less, or 3 hours or less from the viewpoint of the load on the firing furnace and the energy cost.

Step (5) is a cooling step after secondary firing. In order to maintain the content of calcium oxide in the secondary fired product, natural cooling is performed under low pressure conditions of 10 ³ Pa or less and/or under inert gas conditions.

In step (6), an inert gas is injected into the firing furnace, and the firing furnace door is opened and closed. In this case, it is preferable to use a sliding door instead of a double door. It is easy to cover the inner state under an inert gas atmosphere. Furthermore, the fired product is vacuum-packaged under this inert gas atmosphere.

The inert gas in the present invention is not particularly limited as long as it is not reactive with calcium oxide, and examples thereof include helium gas, argon gas, nitrogen gas and oxygen gas.

In addition, what was mentioned above is only an example, and for example, step (5) may be executed instead of step (2). Step (5) may be omitted and step (3) and step (6) may be performed successively.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples.

(Example 1)
The scallop shells were baked at 1450° C. for 6 hours and allowed to cool naturally to ambient temperature.

(Example 2)
The sample of Example 1 was passed through an air filter, a micromist filter and an activated carbon filter to remove impurities, and pulverized with a dry ultra-pulverization system (Nano Jet Mizer). After that, it was baked at 950° C. for 2 hours. This secondary fired product was naturally cooled to the outside temperature under low pressure conditions (10 ⁻⁴ Pa or less).

(Example 3)
Impurities are removed from the sample of Example 1 through an air filter, a micromist filter, and an activated carbon filter, and an inert gas such as nitrogen gas or argon gas is injected using a dry ultrafine pulverization system (nanojetmizer) to remove carbon dioxide and water vapor. It was pulverized with displacement removal.

(Example 4)
The scallop shells were baked at 1250° C. for 5 hours and allowed to cool naturally to ambient temperature. This primary fired product was pulverized using IMP-400 manufactured by Seishin Enterprise Co., Ltd.

All steps were carried out under an atmospheric atmosphere and atmospheric pressure unless otherwise specified.

(Comparative example 1)
The scallop shells were baked at 1100° C. for 4 hours and allowed to cool naturally to ambient temperature.

(Comparative example 2)
As Comparative Example 2, reagent limestone-derived calcium oxide (99.9%; Wako Pure Chemical Industries, Ltd.) immediately after opening was tested.

(Reference example 1)
As Reference Example 1, a reagent limestone-derived calcium hydroxide (99.9%; Wako Pure Chemical Industries, Ltd.) immediately after opening was tested.

(Reference example 2)
As Reference Example 2, a commercially available baked scallop shell immediately after opening was tested.

(Reference example 3)
As Reference Example 3, another commercially available baked scallop shell immediately after opening was tested.

(Average particle size)
The average particle size of each powder was measured using a particle size distribution analyzer (CILAS; Aisin Nano Technologies Co., Ltd.).

(Calcium element content ratio)
The calcium element content of each powder was measured using a fluorescent X-ray analyzer (RIX3100; manufactured by Rigaku Denki Co., Ltd.).

(Calcium oxide content ratio)
The calcium oxide content and calcium hydroxide content of each powder were measured using a differential thermal calorimetric analyzer (TGA851e; Mettler Toledo) and an X-ray diffractometer (X'Pert-PRO; Philips).

(BET specific surface area)
The BET specific surface areas of Examples 1-4, Comparative Examples 1-2, and Reference Examples 1-3 were measured using ChemBET3000 manufactured by Quantachrome.

(Electron microscope observation)
The baked products according to the examples and comparative examples were coated with osmium metal using a neo-osmium coater (Neoc-STB; Meiwaforsys Co., Ltd., Tokyo), and then subjected to field emission scanning electron microscope (JSM-6340F; JEOL Ltd., Tokyo). ) was used to analyze the surface shape of the dry powder state based on SEM images of 3000 times and 10000 times.

In Examples 1 to 4, a dense cocoon-like surface structure was observed, and the BET specific area was observed to have an inversely proportional relationship with the average particle size of the powder. Reference Examples 1 to 3 are calcined products mainly composed of calcium hydroxide, and the BET specific area was high at 5 m ² /g or more. In addition, both Comparative Example 1 containing 20% or more calcium hydroxide with an average particle size of 50 μm or more and Comparative Example 2 containing calcium hydroxide calcined from reagent limestone showed a high BET specific area of 5 m ² /g or more. .

In Examples 1 and 2, in which scallop shells were baked at 1450 ° C. for 6 hours, adjacent particles were firmly fused, dense cocoon-like crystals and particles grew, and the reaction interface area was reduced due to clogging of pores. A decrease was observed (Fig. 1; Example 1 and Example 2). On the other hand, in the reagent limestone-derived calcium oxide fine powder (99.9%; Wako Pure Chemical Industries, Ltd.) of Comparative Example 2, a lattice-like porous surface structure was observed, and reactivity such as hydration reaction was observed. was expected to be higher. A similar lattice-like porous surface structure was observed in Reference Example 1, reagent limestone-derived calcium hydroxide fine powder (99.9%; Wako Pure Chemical Industries, Ltd.) (Fig. 1).

In Examples 1 and 2, as described above, cocoon-like dense crystals and particles with closed pores were observed immediately after opening (Fig. 2). When placed in a water vapor saturated incubator at 37° C. for 7 days, the surface of the fine powder became porous and the dispersibility in water suspension was remarkably improved. In Examples 3 and 4, although there was a difference in particle size, a change from a dense cocoon-like surface structure with closed pores to a porous surface structure was observed immediately after opening and after incubation for 7 days. was done. This is because when the calcined calcium oxide fine powder undergoes a hydration reaction with steam or the like, the crystals become finer due to the formation of a portion of calcium hydroxide from the surface, and the surface structure changes due to the formation of cracks and pores, resulting in an improvement in hydrophilicity. From this, it is inferred that the water suspension dispersibility was remarkably improved.

(hydration exothermic)
For 5% by weight of Example 1 and Example 2, the water temperature increased to a maximum of 40° C. 5-30 minutes and 15-40 minutes after water addition, respectively (FIG. 3). In addition, 10% by weight of Examples 1 and 2, 5 to 30 minutes and 15 to 40 minutes, respectively, the water temperature is up to 50 ° C., and further 20% by weight of Examples 1 and 2, respectively, The water temperature rose to a maximum of 60° C. at 10 min and 15-40 min (data not shown).

The hydration reaction of calcium oxide to calcium hydroxide is an exothermic reaction, and most of the calcium oxide in the commercially available baked scallop shells, which is said to be heat-free, is dissolved in water during the cooling, wet pulverization, and storage processes after baking. It is inferred that it changed to calcium oxide. As an example, when Example 1 and Example 2 were incubated at 37° C. for 7 days under water vapor saturation conditions, the water temperature of 5% by mass of Example 1 and Example 2 decreased to about 30° C. after 5 to 10 minutes (Fig. 3). Although data are not shown, a similar decrease in calorific value due to incubation for 7 days at 37° C. under steam-saturated conditions was also observed for Examples 3 and 4 (data not shown).

On the other hand, 20% by mass of reagent limestone-derived calcium oxide (99.9%; Wako Pure Chemical Industries, Ltd.) exhibited an exotherm with a maximum water temperature exceeding 100° C. within 2 to 6 minutes after addition of water (FIG. 4). On the other hand, in Examples 1 to 4 containing 20% by mass, the maximum water temperature remained at 60° C. 6 to 30 minutes after the addition of water (data not shown).

The difference in exothermic reaction rate between the fired scallop shells and reagent limestone-derived calcium oxide in Examples 1 to 4 can be presumed to be due to the surface structure of each fine powder of calcium oxide. That is, in the baked scallop shell, the adjacent particles are firmly fused together, dense cocoon-like crystals and particles grow, and the BET specific surface area, which is the reaction interface area, decreases due to the clogging of pores. On the other hand, the reagent limestone-derived calcium oxide has a lattice-like porous surface structure, which is considered to increase the BET specific surface area and hydration reactivity.

In contrast to this calcined product, 20% by mass of reagent limestone-derived calcium hydroxide (99.9%; Wako Pure Chemical Industries, Ltd.) as Reference Example 1, commercial scallop shells as Reference Examples 2 and 3 No increase in water temperature was observed after adding water to the fired product.

(Reducing Ability of Nitrogen Oxide)
In the course of this study, the calcium oxide aqueous suspension reduced NO ₂ and NO ₃ and caused the denitrification reaction by NO ₃ -> NO ₂ -> N ₂ O -> N ₂ , i.e. the denitrification ability was found. rice field. Calcium hydroxide has no reducing power for this nitrogen oxide, which is characteristic of calcium oxide. In this study, the denitrification ability of each calcined material was evaluated.

In this experiment, each baked product was added directly to water containing NO ₃ (30 ppm) and NO ₂ (1.8 ppm) so that the concentration was 0.2% by mass, and after stirring well, Residual NO ₃ and NO ₂ were measured at (Fig. 5A).

Examples 1-2 and Comparative Example 2 at 0.15% by weight completely lost NO ₃ (30 ppm) and NO ₂ (1.8 ppm) in water within 15 minutes after mixing. Similarly, in Examples 3 and 4, NO ₃ (30 ppm) and NO ₂ (1.8 ppm) in water disappeared completely within 15 minutes after mixing (data not shown).
On the other hand, Reference Examples 2 and 3 did not reduce NO ₃ (30 ppm) and NO ₂ (1.8 ppm) in water at all. Similarly, Reference Example 1 did not reduce NO ₃ (30 ppm) and NO ₂ (1.8 ppm) in water at all (data not shown).
Examples 1-2, steam-saturated incubated at 37° C. for 7 days, mildly reduced NO ₃ (30 ppm) and NO ₂ (1.8 ppm) in water within 15 minutes after mixing.

Furthermore, water was added to each fired product and hydrated for a predetermined time, and then mixed with water containing NO ₃ (30 ppm) and NO ₂ (1.8 ppm). After 1 hour, residual NO ₃ and NO ₂ was measured.

In Examples 1 to 3 and Comparative Example 2, it was found that the denitrification capacity decreased as the hydration reaction time increased. In particular, in Comparative Example 2, the denitrification capacity decreased to less than half after 1 hour of hydration reaction. In contrast, Examples 1-3 lose half their denitrification capacity over 3 hours after mixing with water (FIG. 5B). Similarly, in Example 4 and Comparative Example 1, the denitrification ability was halved 3 hours or more after mixing with water (data not shown). On the other hand, no denitrification ability was observed in Reference Examples 1-3. It was speculated that the main denitrifying ability was calcium oxide, and the hydration reaction caused by the addition of water changed calcium oxide to calcium hydroxide, and the denitrifying ability decreased as the calcium oxide content decreased.

From the above results, the aqueous suspensions of Examples 1 to 4 can be expected to have sufficient effects as calcium oxide.

Claims (2)

A baked product obtained by baking shells,
The calcium oxide content measured by differential thermal thermogravimetric analysis (TG-DTA) is 95% by weight or more, and the calcium hydroxide content is 5% by weight or less,
The calcium element content measured by X-ray fluorescence spectroscopy (XRF) is 95 atom% or more,
Calcium oxide content measured by X-ray diffraction analysis (XRD) is 95% by mass or more,
The average particle size is 20 μm or less,
A fired product having a BET specific surface area of more than 1 m ² /g and not more than 3.0 m ² /g. 2. The baked product according to claim 1, wherein part or all of the shell is scallop shell.

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