JP2020055719A - Calcined product containing calcium oxide - Google Patents

Abstract

To provide a calcined product having a high calcium oxide content, and provide a calcined product that can be easily pulverized to fine powders.SOLUTION: A method of producing a calcined product containing calcium oxide from a calcium carbonate and/or calcium hydroxide-containing starting material, comprises a primary firing step in which the starting material is fired at 1000°C or higher for 4 hours or more to obtain a primary fired product; a pulverization step of finely pulverizing the primary fired product; a secondary firing step in which the primary fired product is fired at 600°C or higher for 1 hour or more to obtain a secondary fired product; and a secondary cooling step in which the secondary fired product is cooled to ambient temperature under a vacuum atmosphere or an inert gas atmosphere.SELECTED DRAWING: None

Description

  The present invention relates to a calcined product containing calcium oxide, a method for producing the same, and the like. In particular, the present invention relates to a burned material of biological material containing calcium oxide obtained from a biological material containing calcium carbonate, a method for producing the same, and the like.

  In recent years, research on these burned products has been conducted as a method of utilizing waste such as shells, eggshells, and sea urchin shells. The main component of these wastes is calcium carbonate, and it is said that calcium oxide generated by liberation of carbon dioxide from calcium carbonate by high-temperature firing is the main component of the fired product.

  Conventional calcium oxide (quick lime) produced by calcining limestone, when it comes in contact with 5 times the mass of water, instantaneously comes into contact with the water, which generates a high heat exceeding 100 ° C. No exothermic hydration reaction is observed. It is considered that one of the factors is that calcium oxide was reduced by reacting with water vapor and carbon dioxide in the air during various processes.

  Conventional calcium hydroxide derived from limestone (slaked lime) has extremely high toxicity, whereas calcium hydroxide derived from burned materials of biological materials such as shells is a highly safe food additive with weak skin irritation. Approved as. On the other hand, it has been reported that calcium hydroxide derived from calcined products of biological materials such as shells has an organic poisoning substance adsorption effect, a bactericidal effect, a virus inactivating effect, and the like (for example, Patent Documents 1 to 4). As described above, calcium hydroxide derived from calcined products such as shells, eggshells and sea urchin shells has already been reported and marketed as a material for dealing with sanitary environments.

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

  Conventionally, calcium hydroxide is intended to be used for calcined products such as shells, and it has been possible to obtain fine powder of calcined products containing a large amount of calcium hydroxide. On the other hand, a calcined product mainly composed of calcium oxide can be expected to have novel properties such as oxidation, reduction, and radical reactions in addition to strong alkaline properties. However, such a calcined product mainly composed of calcium oxide has not been actually produced.

  The present invention has been made based on the above background. A first object is to provide a calcined product having a high calcium oxide content. A second object is to provide the fired product which can be easily pulverized into fine powder.

  The present inventors have made intensive studies and completed the present invention.

According to a first aspect of the present invention, there is provided a method for producing a calcined product containing calcium oxide from a starting material containing calcium carbonate and / or calcium hydroxide,
A primary firing step of firing the starting material at 1000 ° C. or higher for 4 hours or more to obtain a primary fired product;
A fine grinding step of finely grinding the primary fired product,
A secondary firing step of firing the primary fired product at 600 ° C. or higher for 1 hour or more to obtain a secondary fired product;
A secondary cooling step of cooling the secondary fired product to an outside temperature under a vacuum atmosphere or an inert gas atmosphere,
Are provided.

  The method may not include a step of pulverizing the fired product after the secondary cooling step.

  Some or all of the starting material may be a shell. Some or all of the shells may be scallop shells.

According to a second aspect of the present invention, there is provided a fired product produced by the above method. The average particle size of the fired product may be 2 μm or less. The weight loss ratio of this calcined product at 30 to 1000 ° C. measured by differential thermogravimetric analysis may be 1% or less. The BET specific surface area of the fired product may be 0.5 m ² / g or more and 3.0 m ² / g or less.

  According to a third aspect of the present invention, there is provided a suspension in which the calcined product is suspended in an aqueous medium.

  According to a fourth aspect of the present invention, there is provided a method of storing the fired product under a vacuum atmosphere or an inert gas atmosphere.

  The calcined product of the present invention has a very high calcium oxide content. This fired product is a fine powder having a small average particle size. When this fired product was actually used, it was possible to obtain an effect superior to the conventional product.

The test result of the adsorption removal effect evaluation for lubricating oil is shown. The test result of the adsorption removal effect evaluation for odors is shown. The test result of a bactericidal effect evaluation is shown.

  Hereinafter, the present invention will be described in detail.

<< Definition of terms >>

  In the present invention, the term “outside air temperature” means the temperature of the surrounding environment in which an apparatus for firing (a firing furnace) is placed. Although not uniformly defined, a temperature of less than 100 ° C, less than 80 ° C, less than 60 ° C or less than 50 ° C may be interpreted.

  In the present invention, the term “inert gas” means a gas that does not react with calcium oxide at a temperature of 100 ° C. or less. In addition to nitrogen gas, noble gases such as helium and argon, oxygen is also included.

  In the present invention, the term “acid region” means a region having a pH of 6 or less. The term "neutral region" means a region where the pH is greater than 6 and less than 8. The “alkaline region” means a region having a pH of 8 or more. A region having a pH of 10 or more is sometimes referred to as a “strongly alkaline region”, and a region having a pH of 8 or more and less than 10 is sometimes referred to as a “weakly alkaline region”. In the present invention, the pH is a value measured at 25 ° C.

<<< Starting material >>>
In the method of the invention, a material comprising calcium carbonate and / or calcium hydroxide is used as starting material. Calcium carbonate and calcium hydroxide change into calcium oxide when heated.

  In the present invention, in particular, a biological material containing calcium carbonate is used as starting material. Such biological starting materials include, for example, shells, eggshells, sea urchin shells, corals, crustaceans. Shells, eggshells and shells are preferred from the viewpoints of availability, operability and processability, and shells are particularly preferred.

  A shell refers to the shell of a shell containing calcium carbonate. Shellfish are generally categorized into single clams, bivalves, and snails. Bivalve shells are preferred because of their simple structure and easy cleaning. Abalones and the like can be mentioned as single shellfish. Bivalves include scallops, oysters, clams, clams, clams and the like. Conch shells include turban shells. Among the shells, scallop shells and oyster shells are particularly preferred, and scallop shells are most preferred.

  Eggshell refers to the outer shell of an egg containing calcium carbonate. It is a material produced by egg organisms such as birds. Chicken and quail eggshells are preferred from the viewpoint of availability.

  Crustacean refers to the crustacean shell containing calcium carbonate. Crustaceans include shrimp, crabs and barnacles. Crab shells are preferred because they are easy to clean.

<< method >>
According to a first aspect of the present invention, there is provided a method described below.

(Primary firing step)
The method of the present invention includes a primary firing step of firing the above-described starting material in a firing furnace.

  The atmosphere in the firing furnace is arbitrary, but an oxygen-containing atmosphere is preferred. The oxygen-containing atmosphere may be an atmosphere containing oxygen in an amount of 1% by volume or more, 3% by volume or more, 5% by volume or more, 10% by volume or more, and 20% by volume or more. Usually, it is air (atmospheric atmosphere). In order to improve the combustion removal efficiency, an atmosphere containing 30% by volume or more, 40% by volume or more, 50% by volume or more, 60% by volume or more, 70% by volume or more, 80% by volume or more, 90% by volume or more may be used. An oxygen gas atmosphere (that is, an atmosphere having an oxygen content of 100%) may be used.

  In the first firing step, all or a part of the calcium carbonate / calcium hydroxide contained in the starting material is thermally decomposed to change to calcium oxide. In the case of a biological material, it may contain an organic substance such as a protein. In this step, many elements derived from these organic substances are removed as gas by thermal decomposition or combustion.

  The firing temperature in the primary firing step is 1000 ° C or higher, 1050 ° C or higher, 1100 ° C or higher, 1150 ° C or higher, 1200 ° C or higher, 1250 ° C or higher, 1300 ° C or higher, 1350 ° C or higher, 1400 ° C or higher, 1450 ° C or higher. By firing at a temperature higher than these temperatures, organic substances can be sufficiently removed, and the purity of the fired product increases. The firing temperature in the primary firing step is about 2600 ° C. (the melting point of calcium oxide) or lower, preferably 2000 ° C. or lower, 1800 ° C. or lower, and 1600 ° C. or lower.

  The rate of temperature rise in the primary firing step is not particularly limited, but is preferably 1 to 20 ° C / minute, 3 to 18 ° C / minute, 5 to 16 ° C / minute, 7 to 14 ° C / minute, and 9 to 12 ° C / minute. .

  The firing time in the primary firing step is 4 hours or more, 4.5 hours or more, 5 hours or more, 5.5 hours or more, 6 hours or more. By firing for more than these times, organic substances can be sufficiently removed and the purity of the fired product can be increased. On the other hand, the upper limit of the firing time is not particularly limited, and is preferably 10 hours or less, 9 hours or less, and 8 hours or less.

  As a matter of course, the firing temperature may be constant or may be varied within the above firing temperature range. The firing time means the total time during which the temperature in the firing furnace is within the above-described firing temperature range.

(Primary cooling process)
The method of the present invention may include a primary cooling step of cooling the primary fired product obtained by the primary firing step described above.

  Although the cooling target temperature is arbitrary, the fired product is usually cooled to the outside temperature for the subsequent operation.

  The cooling rate can be set arbitrarily. It may be cooled rapidly using any cooling means, or may be naturally cooled by heat radiation.

  The primary cooling step may be performed under any atmosphere. It may be in the same atmosphere as the firing step or in a different atmosphere. For example, the treatment may be performed in an inert gas atmosphere or in an air atmosphere.

  The primary cooling step may be performed in a baking furnace, may be taken out of the baking furnace, or may be partially performed in the baking furnace and the remaining may be performed outside the baking furnace.

(Preliminary grinding step)
The method of the present invention may include a preliminary grinding step of grinding the primary fired product.

  The preliminary pulverization step is an optional step of pulverizing the primary fired product before finely pulverizing the primary fired product. In particular, the primary fired material is extremely fragile, since the organic matter contained in the case of a biological material has disappeared. Therefore, it can be easily crushed. Any equipment and means can be used for the pre-milling step. The preliminary grinding step is not an essential step, but by grinding the primary fired product in advance, the efficiency of the later-described fine grinding step is improved, leading to the stabilization of the quality of the final product and the fine powdering.

  The preliminary pulverization step may be performed under any atmosphere. It may be the same as or different from the atmosphere in the other steps.

(Purification process)
The method of the present invention may include a purification step of purifying the primary fired product.

  The purification step may be performed by passing the powder or fine powder of the primary fired product through one or more filters from an air filter, a micro mist filter, an activated carbon filter, or the like.

  The purification step may be performed under any atmosphere. It may be the same as or different from the atmosphere in the other steps.

(Pulverizing process)
The method of the present invention may include a pulverizing step of pulverizing the primary fired product.

  The fine pulverization step is a step of pulverizing the primary fired product to a fine powder state to obtain finely pulverized primary fired material. It is performed before the secondary firing described below, that is, between the primary firing and the secondary firing. By performing the process before the secondary firing, it was possible to make the average particle size of the fired product as the final product smaller than that after performing the secondary firing.

  Any means can be used as means for finely pulverizing the primary fired product. For example, a device (Nano-jet miser; NJ-300-D, manufactured by Aisin Nano Technologies Co., Ltd.) for accelerating high-pressure gas particles with a special compressor and finely pulverizing the target by particle collision is exemplified. Here, the high-pressure gas may be dry air, but is preferably an inert gas such as nitrogen, helium, or argon.

  The pulverization step may be performed under any atmosphere. It may be the same as or different from the atmosphere in the other steps.

  When performing the preliminary pulverization step, the fine pulverization step, and / or the purification step, the pre-pulverization step is performed after the primary firing step and before the secondary firing step described later.

(Secondary firing step)
The method of the present invention includes a secondary firing step of firing the primary fired product in a firing furnace.

  Calcium hydroxide or calcium carbonate remaining in the primary firing step or generated during each step after the primary firing is thermally decomposed into calcium oxide.

  Unless stated otherwise, the description of the primary firing step also applies to this step.

  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, 950 ° C or higher. Calcination at above these temperatures can sufficiently convert calcium carbonate and calcium hydroxide to calcium oxide. The firing temperature in the secondary firing step is about 2600 ° C. (the melting point of calcium oxide) or lower, and usually 1500 ° C. or lower, 1200 ° C. or lower, and 1000 ° C. or lower.

  The firing time in the secondary firing step is 1 hour or more, 1.5 hours or more, or 2 hours or more. Calcination at above these temperatures can sufficiently convert calcium carbonate and calcium hydroxide to calcium oxide. On the other hand, the upper limit of the firing time is not particularly limited. It is preferably 7 hours or less, 6 hours or less, 5 hours or less, 4 hours or less, 3 hours or less from the viewpoint of the load on the firing furnace and energy cost.

(Secondary cooling process)
The method of the present invention includes a secondary cooling step of cooling the secondary fired product obtained by the above-described secondary firing step under a vacuum atmosphere or an inert gas atmosphere.

  Unless stated otherwise, the description of the primary cooling step also applies to this step.

  In a vacuum atmosphere means that the pressure is sufficiently lower than the atmospheric pressure (about 100,000 Pa). Specifically, it means 1000 Pa or less, 100 Pa or less, 10 Pa or less, 1 Pa or less, 0.1 Pa or less, 0.01 Pa or less, 0.001 Pa or less, 0.0001 Pa or less.

  An inert gas atmosphere means an inert gas atmosphere as described above. The pressure is not limited, but may be, for example, 10,000 Pa to 200,000 Pa, 50,000 Pa to 150,000 Pa, or 80,000 Pa to 120,000 Pa or more.

  By cooling in a vacuum atmosphere or an inert gas atmosphere, calcium oxide generated by firing can be stored without reacting. In the case of a vacuum atmosphere, the free gas generated in the secondary firing step is removed by the vacuuming means, and the calcium oxide in the fired product is preserved. It was also found that the particle size of the fired product was particularly small. For this reason, a vacuum atmosphere is more preferable.

  It is preferable that another step (for example, a pulverizing step) is not included between the secondary cooling step and the sealing step described below. This is because calcium oxide in the fired product may be deteriorated while other processes are being performed.

(Sealing process)
The method of the present invention may include a step of sealing the obtained secondary fired product in a sealing container.

  Any container can be used as long as it can shut off the gas and seal the object. The secondary fired product is sealed in a sealing container under a vacuum atmosphere or an inert gas atmosphere. As a result, a package in which the secondary fired product is sealed inside the sealing container is completed.

<< fired product >>
According to a second aspect of the present invention, there is provided a fired product produced by the method of the first aspect.

  The average particle size of the fired product of the present invention is usually 2.0 μm or less, 1.9 μm or less, 1.8 μm or less.

  The average particle size of the fired product may be measured using a particle size distribution measuring device. As such an apparatus, for example, CILAS (available from Aisin Nano Technologies Co., Ltd.) can be mentioned.

  The proportion of the calcium element in the element which can be measured by the wavelength dispersive X-ray fluorescence spectroscopy (XRF) of the calcined product of the present invention is usually 99.0 atom% or more, 99.1 atom% or more, and 99.2 atom%. Above, it is 99.3 atom% or more, 99.4 atom% or more, 99.5 atom% or more, 99.6 atom% or more, 99.7 atom% or more, 99.8 atom% or more, 99.9 atom% or more. Note that carbon and oxygen are not measured by the wavelength dispersive X-ray fluorescence spectroscopy (XRF).

  In addition to / besides this, the peak intensity of the element other than calcium element measured by X-ray fluorescence spectroscopy (XRF) of the calcined product of the present invention is 1/1000 or less of the peak intensity of calcium element, / 1500 or less, 1/2000 or less, 1/2500 or less, 1/3000 or less.

  As an apparatus for wavelength dispersive X-ray fluorescence spectroscopy (XRF), RIX3100 (manufactured by Rigaku Corporation) can be mentioned.

  The contents of calcium oxide, calcium hydroxide, and calcium carbonate in the calcined product are estimated using a differential calorimetric gravimetric analyzer. When the calcined product contains calcium hydroxide, a weight loss is observed at 200 ° C to 500 ° C. When the calcined product contains calcium carbonate, a weight loss is observed at 500 ° C to 1000 ° C. No pre-treatment is required before the differential thermogravimetric analysis.

  The weight maintenance ratio at 30 to 1000 ° C. of the calcined product of the present invention measured by differential thermogravimetry is usually 99.0% or more, 99.1% or more, 99.2% or more, and 99.3%. Above, it is 99.4% or more, 99.5% or more, 99.6% or more. The upper limit is usually 100% or less. The weight retention ratio is a percentage of the weight at the time of 1000 ° C. with respect to the weight at the time of 30 ° C.

  In other words, the weight reduction ratio of the calcined product of the present invention at 30 to 1000 ° C. measured by differential thermogravimetry is usually 1% or less, 0.9% or less, 0.8% or less, and 0.1% or less. 7% or less, 0.6% or less, 0.5% or less, 0.4% or less. The weight loss ratio is the percentage of weight loss from 30 ° C. to 1000 ° C. with respect to the weight at 30 ° C.

  An example of such an apparatus is TGA851e (manufactured by METTLER TOLEDO). The measurement by the differential thermogravimetric analysis is performed by increasing the temperature from 30 ° C. to 1000 ° C. at a rate of 10 ° C./min in a stream of nitrogen at 100 mL / min.

The BET specific surface area of the fired product of the present invention is usually 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 or more. / G or more, 0.7 m ² / g or more, 0.8 m ² / g or more, 0.9 m ² / g or more, 1.0 m ² / g or more, 1.1 m ² / g or more, 1.2 m ² / g It is 1.3 m ² / g or more, 1.5 m ² / g or more, 1.7 m ² / g or more, 1.9 m ² / g or more and 2.0 m ² / g or more. On the other hand, usually, 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, 2.1 m ² / g or less.

  As an apparatus for analyzing the BET specific surface area, for example, ChemBET3000 manufactured by Quantachrome Co., Ltd. may be mentioned. The method for measuring the BET specific surface area is not particularly limited, and the BET specific surface area may be measured under commonly used conditions.

  The calcined product of the present invention has excellent adsorption ability and can be used for adsorption of harmful substances.

  The fired product of the present invention can be used by suspending it in an aqueous medium.

(Aqueous medium)
90% by mass or more, 91% by mass or more, 92% by mass or more, 93% by mass or more, 94% by mass or more, 95% by mass or more, 96% by mass or more, 97% by mass or more, 98% by mass or more, 99% by mass of the aqueous medium More than% is water. Of course, 100% by weight of the aqueous medium may be water (ie, the aqueous medium may be pure water).

  The medium other than water is not particularly limited as long as it is a liquid soluble in water. Typically, alcohols such as methanol, ethanol, propanol, butyl alcohol and the like can be mentioned.

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

(Starting material)
Scallop shells were used as starting material.

(Example)
The starting material was first fired at 1450 ° C. for 6 hours. The primary fired product after firing was left to cool naturally to the outside temperature. The primary fired material cooled to the outside temperature was pre-ground and stirred to be homogenized. The primary fired product was passed through an air filter, a micro mist filter, and an activated carbon filter, and then finely pulverized by a dry ultrafine pulverizing system (nano jet miser). Thereafter, the fired product was secondarily fired at 950 ° C. for 2 hours. After the completion of the firing, the secondary fired product was allowed to cool naturally to the outside temperature by leaving it in a vacuum atmosphere (10 ⁻⁴ Pa or less) using a vacuuming means. Thus, a powdered fired product of the example was obtained.

(Comparative Example 1)
The starting material was first fired at 1450 ° C. for 6 hours. The primary fired product after firing was left to cool naturally to the outside temperature. The primary fired material cooled to the outside temperature was pre-ground and stirred to be homogenized. The fired product was secondarily fired at 1450 ° C. for 4 hours. This secondary fired product was left to cool naturally to the outside temperature. After secondary cooling, it was pulverized in the same manner as in the example. Thus, a powdered fired product of Comparative Example 1 was obtained.

(Comparative Example 2)
The starting material was first fired at 1450 ° C. for 6 hours. The primary fired product after firing was left to cool naturally to the outside temperature. The primary fired material cooled to the outside temperature was pre-ground and stirred to be homogenized. Thus, a powdered fired product of Comparative Example 2 was obtained.

(Comparative Example 3)
The starting material was first fired at 1100 ° C. for 4 hours. The primary fired product after firing was left to cool naturally to the outside temperature. The primary fired material cooled to the outside temperature was pre-ground and stirred to be homogenized. Thus, a powdered fired product of Comparative Example 3 was obtained.

  Unless otherwise specified, all the steps were performed in an air atmosphere and an atmospheric pressure. The rate of temperature rise in the firing step was set at 10 ° C./min.

(Comparative Example 4)
As the powder of Comparative Example 4, a commercially available fired scallop shell was used.

<< Powder evaluation >>
The powders of Examples and Comparative Examples were measured by the measurement method described below.

(Particle size)
The average particle size of each powder was measured using a particle size distribution analyzer (CILAS). Table 1 shows the measurement results.

(Calcium oxide content)
The calcium oxide content of each powder was measured using a differential calorimetric gravimetric analyzer (TGA851e) (analysis temperature was 30 ° C. to 1000 ° C.). The weight loss (%) from 200 to 500 ° C was defined as calcium hydroxide content (%), and the weight (%) maintained at 30 to 1000 ° C was defined as calcium oxide content (%). Table 1 shows the measurement results.

(Measurement of BET specific surface area)
The BET specific surface area of each powder was measured using ChemBET3000 manufactured by Quantachrome. Table 1 shows the measurement results.

  The purity of the powders of the examples is extremely high. Moreover, the average particle diameter of the fired product of the example was significantly smaller than that of the fired product of the comparative example. Therefore, a fine powder having extremely high calcium oxide purity could be obtained by the method of the present invention.

  Further, each powder was evaluated by the evaluation method described below.

(Adsorption performance: lubricating oil)
Lubricating oil was added to pure water so as to have a concentration of 1% by volume, and stirred to prepare a lubricating oil suspension (the lubricating oil suspension was pale yellow). To 100 parts by mass of the lubricating oil suspension, 0.04 parts by mass, 0.2 parts by mass, and 1 part by mass of each powder were added and suspended. Thereafter, the powder was precipitated by centrifugation at 3000 rpm for 10 minutes, and the turbidity of the supernatant was measured using a turbidimeter (Turbidimeter, TR-55, manufactured by Kasagi Rika Kogyo Co., Ltd.). Smaller turbidity means that the lubricating oil has been removed. The results are shown in FIG. 1A. As is clear from the figure, the powder of the example was found to be the most excellent.

  The same test was performed on the supernatant obtained by mixing 0.04 parts by mass, 0.2 parts by mass, and 1 part by mass of each powder with respect to 100 parts by mass of pure water. The results are shown in FIG. 1B. As is clear from the figure, it was found that the supernatant of the powder of the example was the best.

(Adsorption performance: odor 1)
10 g of ground pork is sealed with 5 mL of supernatant obtained by mixing 0.04 parts by mass, 0.2 parts by mass, and 1 part by mass of each powder with respect to 100 parts by mass of pure water, and left at 37 ° C. for 3 days. did. The odor after 3 days was measured using an odor meter (Handheld Odor Meter, OMX-SR, manufactured by Shinei Technology Co., Ltd.). The results are shown in FIG. 2A. As is clear from the figure, it was found that the supernatant of the powder of the example was the best.

(Adsorption performance: odor 2)
Sawdust that had been reared and used in rats was prepared as an object for deodorization. 0.04 g, 0.2 g, and 1 g of each powder were mixed well with 10 g of the sawdust and allowed to stand for 30 minutes. The odor after 30 minutes was measured using the odor meter. The results are shown in FIG. 2B. As is clear from the figure, the powder of the example was found to be the most excellent.

(Sterilization performance)
Pure water suspensions in which the mass concentration of each powder was 1600 ppm, 800 ppm, 400 ppm, 200 ppm, and 100 ppm were prepared. The sterilization performance of this suspension was evaluated.

A 2% DMEM medium (D5796, Sigma Life Science, Sigma-Aldrich Japan, Tokyo) was added to the turbid water in the pond, and the mixture was allowed to stand at room temperature for 18 hours to culture the general live bacteria and Escherichia coli to be sterilized. The number of bacteria in the general live bacteria group and the number of bacteria in the Escherichia coli group were 4.6 and 4.2 (Log ₁₀ CFU / mL), respectively.

100 parts by volume of the aqueous suspension was added to 100 parts by volume of the liquid containing the general viable bacteria and coliforms, and the mixture was stirred well, and then left at room temperature for 30 minutes. The number of general viable bacteria and the number of coliforms were measured using a medium kit for measuring the number of general viable bacteria and colon colony (compact dry “Nissui” TC and CF, respectively, manufactured by Nissui Pharmaceutical Co., Ltd.). The results of the number of general viable bacteria are shown in FIG. 3A, and the results of the number of coliforms are shown in FIG. 3B (the horizontal axis is the final concentration of the powder). As is clear from the figure, the suspension of the powder of the example was found to be the best.

Claims (7)

A method for producing a calcined product containing calcium oxide from a starting material containing calcium carbonate and / or calcium hydroxide,
A primary firing step of firing the starting material at 1000 ° C. or higher for 4 hours or more to obtain a primary fired product;
A fine grinding step of finely grinding the primary fired product,
A secondary firing step of firing the primary fired product at 600 ° C. or higher for 1 hour or more to obtain a secondary fired product;
A secondary cooling step of cooling the secondary fired product to an outside temperature under a vacuum atmosphere or an inert gas atmosphere,
A method that includes   The method according to claim 1, wherein the method does not include a step of pulverizing the fired product after the secondary cooling step.   3. The method according to any one of claims 1 to 2, wherein part or all of the starting material is a shell.   4. The method according to claim 3, wherein part or all of the shell is a scallop shell.   A fired product produced by the method according to claim 1.   A suspension in which the calcined product according to claim 5 is suspended in an aqueous medium. A method for storing the fired product according to claim 5 in a vacuum atmosphere or an inert gas atmosphere.

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