JPH1143324A - Formation of resource from shell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for converting shell collected from waterintake facilities into a resource recyclable as a cement raw material, etc. SOLUTION: This method for forming a resource from a shell comprises a grinding process 1 for crushing shell into shell powder, a decomposition process 3 for immersing the shell powder in water containing an acid and decomposing an organic substance contained in the shell powder, a separation process for separating the decomposed organic substance from the shell powder and obtaining powder comprising calcium carbonate as a main component and a purification process 5 for immersing the powder comprising calcium carbonate as a main component in hot water, eluting metals and halogens in the hot from the powder to obtain purified calcium carbonate powder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recycling shells, and more particularly, to a calcium carbonate material that can be effectively used by using shells attached to water intake facilities of a power plant or shells discharged as waste. The present invention relates to a method for recycling shells for producing coconut.

[0002]

2. Description of the Related Art In a facility having a portion in contact with water, such as a thermal power plant, a hydropower plant, or a water intake facility of a nuclear power plant, shellfish adheres to a portion in contact with water, and adverse effects such as a decrease in water intake capacity due to the attached shellfish. Affects equipment. For this reason, in a facility having a water intake facility and the like, the work of removing the attached shellfish is performed, and 12,300 tons of shellfish are generated as waste annually. Leaving shellfish, which is a waste product, causes problems such as the generation of bad odors due to the decay of shellfish, and most of them are landfilled at facility premises.

[0003]

However, since the amount of shellfish is large, it is difficult to secure disposal sites year by year. Shellfish that cannot be landfilled are necessarily incinerated at present. However, incineration treatment is economically disadvantageous because it requires only a large amount of cost to install an incineration facility and cannot be obtained. For this reason, there is a demand for the development of some shellfish treatment methods on the premise of recycling.

[0004] It is an object of the present invention to solve the above-mentioned problems and to provide a resource recycling method capable of effectively recycling shellfish as waste.

[0005]

According to the present invention, there is provided a method of recycling a shell according to the present invention, comprising the steps of: crushing a shell into shell powder; and immersing the shell powder in water containing an acid to decompose organic substances in the shell powder. A decomposition step; and a separation step of separating the decomposed organic matter from the shell powder to obtain a powder mainly composed of calcium carbonate.

The method for recycling a shell according to the present invention further comprises the step of immersing the powder containing calcium carbonate as a main component in heating water to elute metals and halogens from the powder into the heating water to obtain a purified calcium carbonate powder. Having a process.

[0007] The resource recycling method may further comprise, prior to the decomposing step, a first powder containing mainly conchiolin from the shell powder.
And the remaining shell powder from which the first shell powder has been removed is supplied to the decomposition step.

Alternatively, prior to the decomposing step, the above-mentioned shell powder is first shell powder mainly containing conchiolin, second shell powder mainly containing calcite, and third shell powder mainly containing aragonite. There is a separation step of separating the shell powder from the shell powder, and the second shell powder and the third shell powder are supplied to the decomposition step.
Only calcium-based powder obtained from the second shell powder through a decomposition step is supplied to the purification step.

In the above-mentioned pulverizing step, the shell is desirably pulverized into shell powder of 300 mesh or less.

Acetic acid is preferred as the acid,
It is desirable that water be contained at a ratio of 1 to 0.05% by weight.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

Since shells of shellfish contain calcium carbonate as a main component, shells obtained by removing shellfish from shellfish collected at water intake facilities and the like may be used as desulfurizing agents, fluorine removing agents, and cement raw materials. You. However, in the case of a cement raw material, for example, in order to prevent softening and elution of concrete, the provision that the content of alkali components such as sodium, potassium, etc., which cause these factors, is set to 0.75% or less is 19
It was established in 1986. The content of chloride ions is set to 0.02% or less in order to prevent the reinforcing steel in the concrete from rusting. Desulfurizing agents, fluorine removing agents and the like are not strictly limited as much as cement raw materials, but cannot be used favorably while containing impurities such as organic substances constituting shells. Therefore, it is necessary to extract calcium carbonate with less impurities from the shell.

Most mussels such as blue mussels are collected from water intake channels of power plants. Such bivalve shells include an inner pearl (aragonite) layer containing calcium carbonate as a main component. It has two outer prism (calcite) layers. Further, the outer surface of the prism layer is covered with a shell layer made of conchiolin, a kind of protein. The shells of other types of shellfish generally have a similar structure.

[0014] Conchiolin is also contained in the nacre and the prismatic layer, in which it acts as a bridge to bond the calcium carbonate grains together. The prismatic layer and the nacre contain alkali metals such as sodium and potassium and alkaline earth metals such as strontium, barium and magnesium, and the nacre contains halogens such as chlorine.

In view of the above, it can be seen that in order to remove calcium carbonate with less impurities from the shell, it is sufficient to efficiently remove organic substances (mainly proteins such as conchiolin), metal salts or metal ions, and halogens from the shell.

First, in order to remove organic substances, it is effective to use water containing an acid as a decomposing solution, soak the shell in the decomposition liquid, and decompose the organic substances in the shell. By soaking in an aqueous solution of an acid, the protein is decomposed into amino acids and the like and eluted in water. Therefore, if the shell is separated from the decomposition solution after the decomposition treatment and washed with water as necessary, the decomposition product is removed from the shell, and a shell with reduced organic mass is obtained.

The acids used for the decomposition of organic substances include nitric acid,
Hydrochloric acid, perchloric acid, mineral acids such as sulfuric acid, and acetic acid, citric acid, lactic acid, tartaric acid, organic acids such as ascorbic acid and the like,
Among them, acetic acid has the highest resolution, and it is preferable to use an aqueous solution of acetic acid as a decomposition solution. If the concentration of the acid and the treatment temperature are high, the decomposition rate of the organic matter is increased, so the decomposition treatment time is as follows:
It is set appropriately according to the type of acid used, the concentration of the acid, and the processing temperature. However, if the concentration of the acid in the decomposition solution is too high, the calcium itself of the shell is also eluted. In order to suppress the elution of calcium, for example, when using an aqueous acetic acid solution, the content of acetic acid is 0.001 to 0.1 wt%. %, Preferably 0.0
Set to 1 to 0.05 wt%. In order to prevent the shells from being contaminated by the decomposition solution during the organic decomposition treatment, care must be taken to ensure that the decomposition solution used does not contain a high concentration of impurities.

As described above, since the organic matter in the shell is dispersed between the calcium carbonate particles, the organic matter in the shell is subjected to a decomposition treatment of the organic matter so that the acid sufficiently acts on the shell and the decomposed matter is easily eluted. It is preferable to grind the shell beforehand. On the other hand, a certain size is necessary in consideration of handling in the collection process and the like. For this reason, shells are
Preferably 50-300 mesh, more preferably 10
The powder is pulverized to 0 to 200 mesh and subjected to a decomposition treatment. In order to sufficiently decompose the conchiolin between the calcium carbonate particles in the shell powder crushed to an appropriate size as described above, the shell powder is immersed in the decomposition solution at room temperature for about 7 days or more, preferably about 10 days or more. I do. When the decomposition solution is heated, the decomposition of the organic matter is promoted. Therefore, when the decomposition solution is heated to about 50 ° C., the immersion is preferably performed for about 5 days or more, preferably about 7 days or more.

Since the shell layer of the shell is mainly formed of conchiolin and contains almost no calcium carbonate, the shell layer of the shell is unnecessary in obtaining calcium carbonate. Therefore, in order to efficiently use the decomposition solution for decomposing organic substances, it is desirable to separate and remove the shell layer in advance and to subject only the prism layer and the pearl layer to decomposing organic substances. The shells can be separated by specific gravity separation utilizing a difference in specific gravity. Since the specific gravity of the shell layer is the smallest and the nacre layer is the largest, the ground shell is put into heavy liquid to remove the light shell layer, and the prism layer and the nacre layer are taken out and subjected to a decomposition treatment. As the heavy liquid used in this case, a bromoform / ethanol mixture liquid closest to the specific gravity of calcium carbonate is suitable, but not limited thereto. When performing heavy gravity separation, heavy liquids are easily contaminated by substances contained in shells, so when using heavy liquids repeatedly, it is necessary to pay attention to the purity of the heavy liquids so as not to contaminate the shells. . Therefore, it is preferable that the heavy liquid has the highest possible purity, and it is desirable that sodium is 10 ppb or less, potassium is 5 ppb or less, and chlorine is 10 ppb or less.

As described above, the shell powder from which the shell layer having a low content of calcium carbonate has been removed by the separation treatment is immersed in an aqueous acid solution and heated to decompose organic matter.
Because it elutes, organic matter can be removed from the calcium carbonate of the shell.

Metals and halogens in shells can be eluted into water by bringing the shells into contact with water. Heating water increases the elution rate, and pressurizing the water further facilitates elution. However, since metal components such as sodium are incorporated into conchiolin in the shell, if elution treatment with water is performed without removing organic matter, metals near the shell surface will elute but those inside the shell will elute. Difficult to do. In other words, by decomposing and removing the organic matter inside the shell, the metal contained in the shell is easily extracted. In other words, when metals and halogens are eluted after the decomposition and elution of organic substances, the removal of metals and halogens proceeds to a high level, and the purity of the obtained calcium carbonate is remarkably improved.

The amount of water used to elute the shell metal and halogen with water is not particularly limited, but is preferably equal to or more than the amount of the shell in order to obtain a more sufficient elution effect. Heating the water to a temperature of at least 40 ° C., preferably at least 50 ° C., more preferably around 100 ° C., can shorten the treatment time. When heated and eluted under pressure, the concentration of chlorine and sodium can be reduced to 50 ppm or less, so to obtain high-purity calcium carbonate from the shell that satisfies the requirements of the cement raw material, under pressure,
Preferably, the pressure is about 1 to 5 at a gage pressure of about 2 to 5 atm.
The metal and halogen may be eluted by heating the water to about 100 ° C. for at least about an hour, preferably about 3 hours.

Halogen (Cl) is added to the nacre and shell layers by 3%.
Although it is contained in the order of 00 to 400 ppm, it is hardly contained in the prism layer, so that the prism layer is separated from the nacre and only the nacre is treated with hot water to improve the processing efficiency. It is efficient to separate the prism layer and the nacre layer together with the shell layer separation using specific gravity separation or the like described above.

After the elution treatment of the metal and the halogen, the shell powder separated from the water is optionally washed with water and dried to obtain a high-purity calcium carbonate powder. According to the above operation, calcium carbonate powder having a content ratio of sodium, potassium and chlorine of generally 100 ppm or less, 20 ppm or less, and 50 ppm or less is obtained.

During the above-mentioned organic decomposition treatment, some of the metals and halogens in the shell elute into the aqueous acid solution. In particular, metals are easily eluted. Therefore, when the organic decomposition treatment is performed under pressure, the elution of metal and halogen is promoted simultaneously with the decomposition of the organic substance. Therefore, decomposition of organic matter and elution of metal and halogen can be achieved in one operation. However, as for halogen, it is possible to reduce the halogen in the shell to a low concentration by using neutral water rather than acidic water, and when the acidic solution is heated under pressure, the load such as the durability of the apparatus is large. The process design may be appropriately modified according to the quality and the like required for the calcium carbonate material.

As another means capable of decomposing and eluting organic substances and eluting metals and halogens, there is a treatment using supercritical water. By bringing the shell powder into contact with supercritical water, hydrolysis and elution of organic substances progress, and along with that, metals and halogens elute.

FIG. 1 shows an example of a preferred embodiment of the method for recycling shells according to the present invention.

In FIG. 1, the shell S from which the shell meat has been removed is
Pulverize to a size of about 100 to 200 mesh (pulverization step 1), and according to specific gravity separation using a heavy solution of bromoform / ethanol, etc., the shell layer S1, the prism layer S2, and the pearl layer S3
(Separation step 2). Next, the separated prism layer S2
An acid aqueous solution A is added to the nacre S3 as a decomposing solution to decompose organic substances such as proteins containing conchiolin in the shell (decomposition step 3). The organic decomposition products containing amino acids and the like are eluted in the aqueous acid solution A, and the organic decomposition products are removed by separating the aqueous acid solution A ′ containing the decomposition products from the prismatic layer S2 and the nacre layer S3 (separation step 4). You. Thereafter, water W is added to the nacre S3 and heated to elute metals and halogens into water (elution step 5). The water W ′ containing metal and halogen is separated from the mother-of-pearl layer S3 (separation step 6), washed with water as needed together with the prismatic layer S2 (washing step 7), and then dried (drying step 8). Thus, a highly pure calcium carbonate powder C is obtained.

Production of calcium carbonate material using shells is as follows.
A crusher for crushing the shell according to the method described above,
A separation tank for separating shell powder into shell layers, prism layers, and nacre layers, a decomposition tank for decomposing organic matter in shell powder, and an elution tank for eluting metals and halogens from shell powder. And a drying device for drying the shell powder. The decomposition tank is provided with a decomposition liquid container for storing the decomposition liquid used for decomposition and a separation device for separating the shell powder and the decomposition liquid after the decomposition treatment, and the elution tank is provided with a container for storing water. The washing treatment of the shell powder, which is performed as necessary, can be performed using a decomposition tank and an elution tank.

In order to avoid the above-mentioned processing apparatus from becoming a new source of contamination of the shell, each tank, storage vessel, separation apparatus and the like were manufactured or coated with a material from which impurities such as Teflon and synthetic quartz do not elute. It is desirable to use one and care must be taken to contaminate the processing environment.

In the present invention, the shellfish to be treated is not limited to any kind, and the above-mentioned method can be applied and modified as appropriate to apply to the recycling of shellfish.

[0032]

The present invention will be further described below with reference to examples.

(Preparation of Sample) The mussel collected in the intake channel of the power plant was separated into shells and shell meat, and
Crushed to 200 mesh.

When the concentration of Na in the shell powder was measured by a flame atomic absorption spectrometer and the concentration of Cl using an ion chromatograph, Na: 3200 ppm, C
l: 470 ppm. The shell powder was put into a platinum crucible and incinerated at 700 ° C., and the organic content P ₀ in the shell powder was calculated from the weight change before and after the incineration.
It was 0 wt%.

(Example 1a) 5 kg of the shell powder obtained in the sample preparation was placed in a Teflon container, and 10 kg of a 0.05 wt% acetic acid aqueous solution was charged and heated to 50 ° C. for 7 days. afterwards,
The acetic acid aqueous solution was removed from the shell powder using a Teflon filter, washed with pure water, and dried at 50 ° C. for 2 days to obtain 3.9 kg of shell powder. When the concentrations of Na and Cl in the obtained shell powder were measured using a flame atomic absorption spectrometer and an ion chromatograph, Na: 25 ppm, Cl: 1.
It was greatly reduced to 50 ppm. Further, the shell powder after the treatment is put into a platinum crucible and incinerated at 700 ° C., the residual organic content P of the shell powder is calculated from the weight change before and after the incineration, and the organic matter removal rate [%]: 100 × (P ₀ −P) / P ₀
Is shown in Table 1.

(Example 1b) The concentration of acetic acid aqueous solution was adjusted to 0.0
The same processing operation as in Example 1a was repeated except that the amount was changed to 01% by weight, to obtain 4.5 kg of shell powder after the processing. Table 1 shows the results of similarly measuring the concentrations of Na and Cl in the shell powder and the organic matter removal rate.

(Example 1c) The heating time of the acetic acid aqueous solution was 1
The same procedure as in Example 1a was repeated, except that the period was changed to days, to obtain 4.8 kg of shell powder after the treatment. Table 1 shows the results of similarly measuring the concentrations of Na and Cl in the shell powder and the organic matter removal rate.

(Example 1d) The heating time of the acetic acid aqueous solution was 1
The same treatment operation as in Example 1a was repeated except that the period was changed to days, to obtain 4.5 kg of shell powder after the treatment. Table 1 shows the results of similarly measuring the concentrations of Na and Cl in the shell powder and the organic matter removal rate.

Example 1e The same treatment as in Example 1a was repeated except that the temperature of the acetic acid aqueous solution was kept at 20 ° C. for 7 days to obtain 4.6 kg of shell powder after the treatment. Table 1 shows the results of similarly measuring the concentrations of Na and Cl in the shell powder and the organic matter removal rate.

(Example 1f) 5 kg of the shell powder obtained in the sample preparation was placed in a Teflon container, and 10 kg of a 0.05 wt% acetic acid aqueous solution was charged and heated to 50 ° C. for 7 days. afterwards,
The acetic acid aqueous solution was removed from the shell powder using a Teflon filter, and 1 liter of pure water was added to the shell powder, followed by heating at 100 ° C. for 3 hours in an autoclave (gauge pressure: 4.7 atm). Thereafter, the shell powder was separated from water, washed with pure water and dried at 50 ° C. for 2 days to obtain 4.2 kg of shell powder. When the concentrations of Na and Cl in the obtained shell powder were measured using a flame atomic absorption spectrometer and an ion chromatograph, it was found to be greatly reduced to 120 ppm Na and 45 ppm Cl. Further, the shell powder after the treatment was put into a platinum crucible, incinerated at 700 ° C., and the result of calculating the organic matter removal rate in the same manner is shown in Table 1.

Example 1g 5 kg of the shell powder obtained in the sample preparation was placed in a Teflon container, and 10 kg of a 0.05 wt% acetic acid aqueous solution was charged and heated to 50 ° C. for 7 days. afterwards,
Remove the acetic acid aqueous solution from the shell powder using a Teflon filter, add 1 liter of pure water to the shell powder, and add
The mixture was heated to reflux at 0 ° C. for 3 hours. Thereafter, the shell powder was separated from water, washed with pure water, and dried at 50 ° C. for 2 days to obtain 4.6 kg of shell powder. When the concentrations of Na and Cl in the obtained shell powder were measured using a flame atomic absorption spectrometer and an ion chromatograph, Na: 180 ppm, C
l: 100 ppm. Further, the shell powder after the treatment was put into a platinum crucible, incinerated at 700 ° C., and the result of calculating the organic matter removal rate in the same manner is shown in Table 1.

Example 1h 5 kg of the shell powder obtained in the sample preparation was placed in a Teflon container, 10 kg of a 0.05 wt% acetic acid aqueous solution was charged, and heated at 50 ° C. for 7 days. afterwards,
The acetic acid aqueous solution is removed from the shell powder using a Teflon filter, and 1 liter of pure water is added to the shell powder and the pressure is reduced to 50 at atmospheric pressure.
Heated to 3 ° C for 3 hours. After this, the shell powder is separated from the water,
3. Wash with pure water and dry at 50 ° C. for 2 days;
7 kg were obtained. When the concentrations of Na and Cl in the obtained shell powder were measured using a flame atomic absorption spectrometer and an ion chromatograph, Na: 200 ppm, Cl: 12
It was 0 ppm. Further, the shell powder after the treatment was put into a platinum crucible, incinerated at 700 ° C., and the result of calculating the organic matter removal rate in the same manner is shown in Table 1.

(Example 2a) 5 kg of the shell powder obtained in the sample preparation was placed in a Teflon container, and 10 kg of a 0.05 wt% nitric acid aqueous solution was charged and heated to 50 ° C. for 7 days. afterwards,
The nitric acid aqueous solution was removed from the shell powder using a Teflon filter, washed with pure water, and dried at 50 ° C. for 2 days to obtain 4.6 kg of shell powder. When the concentrations of Na and Cl in the obtained shell powder were measured using a flame atomic absorption spectrometer and an ion chromatograph, Na: 300 ppm, Cl:
It was 350 ppm. In addition, the shell powder after the treatment was put into a platinum crucible, incinerated at 700 ° C., the residual organic matter content of the shell powder was calculated from the weight change before and after the incineration processing, and the result of calculating the organic matter removal rate was shown. It is shown in FIG.

(Example 2b) The concentration of the aqueous nitric acid solution was set to 0.0
The same treatment operation as in Example 1a was repeated except that the amount was changed to 01% by weight, and 4.8 kg of shell powder after the treatment was obtained. Table 1 shows the results of similarly measuring the concentrations of Na and Cl in the shell powder and the organic matter removal rate.

Example 2c The heating time of the aqueous nitric acid solution was 1
The same procedure as in Example 1a was repeated, except that the period was changed to days, to obtain 4.8 kg of shell powder after the treatment. Table 1 shows the results of similarly measuring the concentrations of Na and Cl in the shell powder and the organic matter removal rate.

Example 2d The heating time of the aqueous nitric acid solution was 1
The same treatment operation as in Example 1a was repeated, except that the number of days was changed to days, to obtain 4.9 kg of treated shell powder. Table 1 shows the results of similarly measuring the concentrations of Na and Cl in the shell powder and the organic matter removal rate.

(Example 2e) The same treatment as in Example 1a was repeated except that the temperature of the aqueous nitric acid solution was kept at 20 ° C. for 7 days to obtain 4.7 kg of shell powder after the treatment. Table 1 shows the results of similarly measuring the concentrations of Na and Cl in the shell powder and the organic matter removal rate.

(Example 2f) 5 kg of the shell powder obtained in the sample preparation was placed in a Teflon container, 10 kg of a 0.05 wt% aqueous nitric acid solution was charged, and heated to 50 ° C. for 7 days. afterwards,
The nitric acid aqueous solution was removed from the shell powder using a Teflon filter, 1 liter of pure water was added to the shell powder, and the shell powder was heated to 100 ° C. for 3 hours in an autoclave (gauge pressure: 4.7 atm). Thereafter, the shell powder was separated from water, further washed with pure water, and dried at 50 ° C. for 2 days to obtain 4.4 kg of shell powder. When the concentrations of Na and Cl in the obtained shell powder were measured using a flame atomic absorption spectrometer and an ion chromatograph, it was found to be greatly reduced to 220 ppm for Na and 120 ppm for Cl. Further, the shell powder after the treatment was put into a platinum crucible, incinerated at 700 ° C., and the result of calculating the organic matter removal rate in the same manner is shown in Table 1.

(Example 3a) 5 kg of the shell powder obtained in the sample preparation was placed in a Teflon container, 10 kg of pure water was charged, and the mixture was heated and refluxed at 100 ° C. under atmospheric pressure for 7 days. Then, it is further put in an autoclave (gauge pressure 4.7 atm) for 100
Heated to 3 ° C for 3 hours. After this, the shell powder is separated from the water,
3. Wash with pure water and dry at 50 ° C. for 2 days;
9 kg were obtained. When the concentrations of Na and Cl in the obtained shell powder were measured using a flame atomic absorption spectrometer and an ion chromatograph, Na: 1300 ppm, Cl: 1
It was 00 ppm. Further, the shell powder after the treatment was put into a platinum crucible, incinerated at 700 ° C., and the result of calculating the organic matter removal rate in the same manner is shown in Table 1.

(Example 3b) 5 kg of the shell powder obtained in the sample preparation was placed in a Teflon container, 10 kg of pure water was charged, and the water temperature was maintained at 20 ° C. under atmospheric pressure for 7 days. Thereafter, the shell powder was separated from water, washed with pure water, and dried at 50 ° C. for 2 days to obtain 4.9 kg of shell powder. When the concentrations of Na and Cl in the obtained shell powder were measured using a flame atomic absorption spectrometer and an ion chromatograph, Na: 2 was obtained.
400 ppm, Cl: 120 ppm. Also, the shell powder after the treatment is put into a platinum crucible and incinerated at 700 ° C.
Table 1 shows the results of calculating the organic matter removal rate in the same manner.

Example 3c Example 3a except that the period of heating to reflux at 100 ° C. under atmospheric pressure was changed to 3 days.
The same operation as described above was repeated to obtain 4.9 kg of the treated shell powder. Table 1 shows the results of similarly measuring the concentrations of Na and Cl in the shell powder and the organic matter removal rate.

Example 3d Example 3a except that the period of heating to reflux at 100 ° C. under atmospheric pressure was changed to one day.
The same operation as described above was repeated to obtain 4.9 kg of the treated shell powder. Table 1 shows the results of similarly measuring the concentrations of Na and Cl in the shell powder and the organic matter removal rate.

(Example 3e) The same operation as in Example 3b was repeated except that the period during which the temperature of the water in which the shell powder was soaked was maintained at 20 was changed to one day, and the shell powder after the treatment was 4.9.
kg gained. Table 1 shows the results of similarly measuring the concentrations of Na and Cl in the shell powder and the organic matter removal rate. (Example 3f) 5 kg of the shell powder obtained in the sample preparation was placed in a Teflon container, and 10 kg of pure water was added thereto.
The mixture was heated to reflux at 00 ° C. for 7 days. Thereafter, the shell powder was separated from water, further washed with pure water, and dried at 50 ° C. for 2 days to obtain 4.8 kg of shell powder. Na and Cl in the obtained shell powder
Was measured using a flame atomic absorption apparatus and an ion chromatograph apparatus.
Cl: 100 ppm. Further, the shell powder after the treatment was put into a platinum crucible, incinerated at 700 ° C., and the result of calculating the organic matter removal rate in the same manner is shown in Table 1.

(Example 4a) 5 kg of shell powder was put into 10 kg of pure water in a decomposition reactor, the reaction temperature was set to 673 K, the reaction pressure was set to 30 MPa, and the reaction time was set to 30 minutes to adjust the water to a supercritical state. In this state, the treatment was performed for 30 minutes. Then, the shell powder is separated from the water, washed with pure water, and then heated to 50 ° C.
For 2 days to obtain 3.8 kg of shell powder. The concentrations of Na and Cl in the obtained shell powder were measured using a flame atomic absorption spectrometer and an ion chromatograph.
a: 230 ppm and Cl: 43 ppm. Further, the shell powder after the treatment was put into a platinum crucible, incinerated at 700 ° C., and the result of calculating the organic matter removal rate in the same manner is shown in Table 1.

Example 4b The same processing operation as in Example 4a was repeated except that the period of maintaining the supercritical state was changed to 3 days, to obtain 3.8 kg of shell powder after the processing. Table 1 shows the results of similarly measuring the concentrations of Na and Cl in the shell powder and the organic matter removal rate.

(Example 4c) The same processing operation as in Example 4a was repeated except that the period of maintaining the supercritical state was changed to one day, to obtain 3.8 kg of shell powder after the processing. Table 1 shows the results of similarly measuring the concentrations of Na and Cl in the shell powder and the organic matter removal rate.

[0057]

[Table 1]--------------------------------------------------------------- Concentration Time Temperature Temperature Pressure Medium concentration (ppm) Removal rate (wt%) (days) (° C) (° C) NaCl (%)--------------------- −−−−−−−−−−−−−−−− (before treatment) 3200 470-Example 1a Acetic acid 0.05 7 50--250 150 97 Example 1b Acetic acid 0.001 7 50--1500 320 31 Example 1c Acetic acid 0.05 1 50--2700 400 18 Example 1d acetic acid 0.05 3 50--1300 360 35 Example 1e acetic acid 0.05 7 20--1000 350 60 Example 1f acetic acid 0.05 7 50 100 Pressurized 120 45 98 Example 1g acetic acid 0.05 7 50 100 Normal pressure 180 100 81 Example 1h Acetic acid 0.05 7 50 20 Normal pressure 200 120 75 Example 2a Nitric acid 0.05 7 50--300 350 70 Example 2b Nitric acid 0.001 7 50--1700 370 32 Example 2c Nitric acid 0.05 1 50--3000 450 29 Actual Example 2d Nitric acid 0.05 3 50--1200 420 38 Example 2e Nitric acid 0.05 7 20--1100 380 58 Example 2f Nitric acid 0.05 7 50 100 Pressurized 220 120 78 Example 3a--7 100 100 Pressurized 1300 100 3 Example 3b--7 20--2400 120 3 Example 3c--3 100 100 Pressurization 2200 190 1 Example 3d--1 100 100 Pressurization 2800 360 1 Example 3e--1 20--3000 380 1 Example 3f--7 100--1800 100 2 Example 4a Supercritical water 7 400--230 43 98 Example 4b Supercritical water 3 400--240 50 97 Example 4c Supercritical water 1 400--300 55 89 −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− The removal rate of organic matter varies depending on the type, concentration, processing time, and processing temperature. For the elution of metals and halogens, the elution efficiency is improved by heating and pressurizing, but if organic matter is not removed, the elution of metals such as sodium is suppressed. For the elution of the halogen, the use of neutral water is suitable. The halogen is effectively removed from the shell powder by bringing the shell powder into contact with neutral water after the organic substance is decomposed by an aqueous acid solution.

[0058]

As described above, according to the method for recycling a shell according to the present invention, a high-purity calcium carbonate material that can be used as a cement raw material, a desulfurizing agent, or the like can be obtained using shellfish collected from a water intake facility or the like. Because it can be prepared, the need for landfill sites and disposal equipment by waste can be significantly reduced,
Its value in industrial and environmental protection is great because the effective use of waste is realized.

[Brief description of the drawings]

FIG. 1 is a flowchart showing one embodiment of a method for recycling a shell according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Crushing process 2 Separation process 3 Decomposition process 4 Separation process 5 Elution process 6 Separation process 7 Rinsing process 8 Drying process

Claims (2)

[Claims] 1. A crushing step of crushing shells into shell powder, a decomposition step of immersing the shell powder in water containing an acid to decompose organic substances in the shell powder, and separating the decomposed organic substances from the shell powder. And obtaining a powder containing calcium carbonate as a main component. 2. The method further comprises a step of immersing the powder containing calcium carbonate as a main component in heated water to elute metals and halogens from the powder into the heated water to obtain a purified calcium carbonate powder. A method for recycling shells according to claim 1.