KR100857587B1 - Compositions for artificial aggregates for orchid culture and its manufacturing method - Google Patents

Abstract

An artificial aggregate composition and a preparation method thereof are provided to control the microstructure, porosity, draining velocity and absorption velocity of the artificial aggregate by using industrial waste and clay. A preparation method of artificial aggregate composition comprises steps of: a) preparing a mixture body by mixing at least one industrial waste selected from spent bleaching clay, steelmaking dust and stone sludge with clay; b) forming an article having a shape after drying the mixture by filter pressing; and c) preparing an artificial aggregate by calcining the article in rotary kiln of a temperature, and the surface of the artificial aggregate has shell which is denser than the core. The core of the artificial aggregate has porous structure generated by the inhibition of the release of the gas which is generated in the calcination process, which results in expansion of the gas. The preparation method of artificial aggregate composition optionally comprises a step of: d) grinding the artificial aggregate, and modifying the surface of the dense surface of the aggregate by a secondary calcination. The mixture body of the step a) consists of: 60wt% of clay and at least one selected from a waste group consisting of 5-10wt% of spent bleaching clay, 5wt% of steelmaking dust and 25wt% of stone sludge. Further, the step of c) is performed by calcining the article in rotary kiln at a 1100 to 1150°C of temperature for 10 minutes.

Description

COMPOSITIONS FOR ARTIFICIAL AGGREGATES FOR ORCHID CULTURE AND ITS MANUFACTURING METHOD}

Figure 1 shows a flow chart of a method of manufacturing artificial turbulence according to an embodiment of the present invention.

FIG. 2 is a SEM observation of the microstructures of specimens 1 and 2, which are artificial turbulences, and natural eggs, according to an embodiment of the present invention.

FIG. 3 illustrates a shell surface and a cross section of specimen 1 of an artificial turbulence according to an embodiment of the present invention.

Figure 4 shows the measurement of the pore distribution of the specimen and the natural ovary artificial artificial dolmen according to an embodiment of the present invention measured.

Figure 5 shows the results of analyzing the micropore distribution using the pore analysis measuring apparatus according to an embodiment of the present invention.

Figure 6 shows the measured absorption, filling density, and unit volume weight of the specimens of the artificial turbulence according to an embodiment of the present invention.

FIG. 7 illustrates a measurement of water loss rate with time in a 25 ° C. atmosphere for a catcher specimen according to an embodiment of the present invention.

The present invention relates to a lightweight aggregate manufactured using various industrial wastes, and more particularly, to a composition for artificial stool for producing artificial calcite by using various industrial wastes mixed with clay, and a manufacturing method thereof.

Due to the rapid development of the industry, the types of industrial by-products and wastes are diversified, and the amount of their production is increasing rapidly. Accordingly, researches that recycle wastes and use them as useful alternative resources are being actively promoted due to environmental conservation and economic effects.

Electrification Arc Furnace (EAF) dust containing a large amount of harmful heavy metals among many wastes is a designated waste, and the treatment problem is seriously raised, and as a treatment method, valuable metals recovered in the electric steel making dust are recovered. And various methods such as treatment by solidification of cement have been studied.

However, in the case of recovery of valuable metals mainly used in developed countries, it is uneconomical due to expensive equipment cost and operation cost, and the treatment by cement solidification has not yet been verified for the long-term dissolution of harmful components. Therefore, a method of mixing and vitrifying steelmaking dust with clay has been studied at home and abroad.

However, methods that can be utilized as a useful and harmless alternative resource by using various industrial wastes including electric furnace steel dust have not been developed yet.

Accordingly, a first object of the present invention is to artificially manufacture artificial turbulence using a combination of various industrial wastes including clay furnace dust or waste clay together with clay, and to control microstructure, porosity and porosity, drainage rate, absorption rate, and the like. It is to provide a composition for ovary.

It is a second object of the present invention to provide a method for producing an artificial egg stone, which can produce an artificial egg stone made of the above composition for artificial eggs.

Composition for the artificial turbulence for achieving the first object of the present invention described above is 5 to 10 parts by weight (wt%) of waste clay, 5 parts by weight (wt%) of furnace steel dust, and 25 to 30 parts by weight (wt. 60 parts by weight (wt%) of clay is added to at least one waste selected from the waste group consisting of%).

Since the waste clay contributes to foaming, the amount of artificial turbulence may be controlled to have a multi-pore structure and to improve absorption.

Method for producing an artificial turbulence for achieving the second object of the present invention described above comprises the steps of: a) adding clay to at least one of waste clay, electric furnace steel dust, and stone dust sludge to form a mixture; b) wet-drying the mixture by filter pressing and then molding the mixture into a shaped body; And c) first sintering the molded body in a rotary kiln at a predetermined temperature for a predetermined time to produce an artificial egg stone.

The method of manufacturing an artificial egg stone further includes d) changing the dense structure of the surface of the artificial egg stone by sintering or second sintering after the artificial egg stone is crushed.

In step c), since a shell having a structure in which the surface of the artificial turbulence is denser than a core exists, the gas generated during the sintering process is suppressed by the cell and is expanded, thereby expanding the artificial turbulence. It can be made to be a porous structure inside.

By forming or removing the cell through step d), the micropores having a predetermined size or less present in the cell site and the ability to inhibit water release may be controlled.

In the step a), the mixture is at least 5 to 10 parts by weight (wt%) of waste clay, 5 parts by weight (wt%) of electric furnace steel dust, and 25 to 30 parts by weight (wt%) of sludge dust. It can be done by adding 60 parts by weight (wt%) of clay to one or more wastes.

B) ball milling and filter pressing the mixture; And wet drying the ball milled and filter pressed mixture for about 2 hours. In the step b), the wet-dried mixture may be formed into a cylindrical shape having a predetermined diameter and height, and then, the spherical forming process may be performed to form the molded body.

Step c) may be manufactured by sintering for about 10 minutes in a rotary kiln of 1100 ~ 1150 ℃ to produce the artificial turbulence.

On the other hand, the ovary is a material for fixing the eggs and supplying water and nutrients to the roots to make the plants grow comfortably, breathable and water-retaining, should be able to slowly release the repaired water. The egg roots can decay if they are too moist, so airflow is required for smooth air flow, which is related to the porosity when filling the ovaries, and must contain as much water and nutrients as possible in the pores of the ovaries when water and nutrients are supplied. This is related to porosity. In addition, when water and nutrients are not supplied for a long time, drainage rate is required to gradually release the moisture and nutrients filled in the pores of the pores to maintain egg growth, which may be related to pore distribution.

Therefore, in one embodiment of the present invention, by controlling the foaming of artificial turbulence using the composition and manufacturing process of artificial turbulence, the process of controlling the microstructure, absorption rate, drainage rate, etc., and obtaining the optimal physical properties required for the turbulence Conditions can be given.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Figure 1 shows a flow chart of a method of manufacturing artificial turbulence according to an embodiment of the present invention.

Referring to FIG. 1, in the method of manufacturing artificial turbulence according to an embodiment of the present invention, clay and water are added to at least one or more wastes among waste white clay, furnace steel dust, and stone dust sludge to form a mixture. Reference)

Table 1 below shows the chemical composition of various raw materials used in one embodiment of the present invention. In other words, clay is used to make general clay bricks, and waste white clay is used as oil adsorbent and then discarded. Its main components are SiO ₂ and Al ₂ O ₃ , but the ignition loss is 48.4%. In the electric furnace steel dust, Fe ₂ O ₃ and ZnO are the main components, and in stone sludge, SiO ₂ and Al ₂ O ₃ are the main components and the content is similar to clay.

ingredient SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ CaO MgO Na ₂ O K ₂ O TiO ₂ P ₂ O ₅ Cr ₂ O ₃ MnO ZnO PbO SO ₃ I. loss Clay 64.8 17.7 7.2 0.2 0.7 0.2 1.8 1.0 0.1 - - - - - 6.3 Waste White Clay 41.9 5.4 1.7 0.3 0.7 0.3 0.6 0.7 0.1 - - - - - 48.4 EAF Dust 5.5 2.7 42.7 4.2 1.0 3.3 2.3 0.7 0.2 0.4 2.3 10.0 1.2 1.1 22.4 Stone Sludge 66.7 14.9 2.3 2.0 1.1 3.8 5.2 0.3 0.1 - - - - - 3.6

In addition, the mixture is at least one waste selected from the waste group consisting of 5 to 10 parts by weight (wt%) of waste clay, 5 parts by weight (wt%) of furnace steel dust, and 25 to 30 parts by weight (wt%) of sludge dust. It is made by adding 60 parts by weight (wt%) of clay and water.

Waste clay containing a lot of volatile components in the composition of artificial turbulence can directly affect foaming during sintering, so that specimen 1 contains 10 parts by weight of waste clay, and specimen 2 contains 5 parts by weight of waste clay.

Waste White Clay D dust Stone sludge Clay  Psalm 1 10 5 25 60  Psalm 2 5 5 30 60

The mixture is wet-dried for about 2 hours after ball milling and filter pressing (see S2, S3, and S4), and formed into a cylindrical shaped body having a predetermined diameter and height using an extruder. Afterwards, it is subjected to a spheronization process.

The molded body is first sintered for 10 minutes in a rotary kiln at 1100 to 1150 ° C. to be manufactured into artificial turbulence (see S6). Organization may change (see S7 and S8).

    I. D Processing  Psalm 3 crushed specimen1 to 1/2 ~ 1/3 of the ariginal size  Psalm 4 sintered specimen 1 at 1100 ℃ / 1hr

As shown in Table 3, the crushed artificial turbulence of Specimen 1 into 1/2 to 1/3 of its original size is called Specimen 3, and the refired Specimen 3 at 1100 ° C / 1hr is referred to as Specimen 4.

The physical properties of the artificial turbulence, such as unit weight, porosity, drainage rate, pore distribution, and surface microstructure, are evaluated by measuring the physical properties of the specimens 1, 2, 3, and 4 prepared above. See S9)

In the above description, the unit weight refers to the weight of the specimen per unit volume when the specimen is filled in a volume of the container, and the void content refers to the remaining portion of the specimen filled space except for the space occupied by the specimen. It is calculated as a percentage.

In addition, the drainage rate is calculated by measuring the mass loss over time after filling the artificial turbulence in a 250 ml container and put it in a thermostat, using a scanning electron microscope (SEM) to observe the microstructure of the artificial turbulence.

Pore distribution is measured using an image analyzer software and a porosimeter. Observation of the microstructure with an optical microscope and analysis by image analysis software are easy for macropore analysis, but it is thought that there will be a lot of error in micropore analysis of 30 ~ 40 ㎛ or less. Use additionally a measuring device.

Hereinafter, with reference to Figures 2 to 7 look at the characteristics of artificial turbulence centering on the microstructure, physical characteristics, drainage rate of artificial turbulence prepared by the composition for artificial turbulence according to an embodiment of the present invention and its manufacturing method As follows.

1) Microstructure

FIG. 2 is a SEM observation of the microstructures of specimens 1 and 2, which are artificial turbulences, and natural eggs, according to an embodiment of the present invention.

As shown in FIG. 2, the natural ovate has many pores and is connected to each other, and the microstructure is relatively uniform as compared to the artificial ovate. Specimen 1 of artificial turbulence has more pores than specimen 2 due to the difference in the amount of waste clay added.

That is, organic matter present in the waste clay produces gas in the sintering process and contributes to the foaming of specimens 1 and 2. Therefore, Specimen 1 to which 10 wt% of waste clay is added is more foamed than Specimen 2 to which 5 wt% is added.

FIG. 3 illustrates a shell surface and a cross section of specimen 1 of an artificial turbulence according to an embodiment of the present invention.

As shown in FIG. 3, in the sintering process of specimens 1 and 2, the surface generally reaches a high temperature for the first time, so that a liquid phase is rapidly formed on the surface, and thus the surface has a more dense structure than the core. Name it).

If the gas generated in the specimen is not released by the cell during the sintering process, it expands and the inside of the specimen becomes a porous structure, so the presence of the cell plays an important role in foaming. Specimen 1 is surrounded by a cell of dense structure throughout the surface, so there are few open pores and through pores, and many closed pores. On the other hand, specimen 3 is a crushing of the specimen 1 to a size of 1/2 to 1/3, the inner core of the specimen is exposed during the grinding process, most of the pores are composed of open pores.

Figure 4 shows the measurement of the pore distribution of the specimen and the natural ovary artificial artificial dolmen according to an embodiment of the present invention measured.

As shown in FIG. 4, the hatched bar graph on the right side of the pore distribution of each specimen can be regarded as the porosity as the sum of all the pores, and from this porosity, it can be seen that natural porosity has a higher porosity than artificial fossils. In addition, the pore distribution of natural ovary is different from the pore distribution of artificial ovary, and there is a large pore size of 160 ~ 210 ㎛ in natural ovary.

Figure 5 shows the results of analyzing the micropore distribution using the pore analysis measuring apparatus according to an embodiment of the present invention.

As shown in FIG. 5, the image analysis software is considered to have a large error in micropore analysis of 30 to 40 μm or less, and analyzes the micropore distribution using a porosimeter. Since the apparatus grinds and analyzes the specimen to a diameter of 1 to 2 mm, the pore distribution of the specimen 1 and the specimen 3 is the same, and thus is not shown in FIG. 5.

Comparing the pore distribution of natural and artificial turbulence, as shown in Fig. 5 (a), the pore size of the main peak is 10 µm in size, while artificial turbulence is shown in Fig. 5 (b to d). Silver pore size is 40 μm.

In addition, all artificial turbulence except specimen 4 has micropores of 10 μm or less, but micropores of 10 μm or less do not exist in the natural turbulence. These micro pores can be seen mainly in the cell site of the specimen through SEM analysis.

On the other hand, as shown in Figure 5 (c) there is no micropores in the specimen 4. This can be confirmed by the change in peak intensity of 10 to 30 μm, and fine pores are coalesced and grown to larger pores in the process of crushing specimen 1 and sintering second. That is, since the 10 ~ 30 ㎛ peak strength of the specimen 4 is increased than the specimen 1, it can be seen that the micropores of 10 µm or less that existed in the specimen 1 were coalesced in the secondary sintering process to grow into large pores.

From the analysis results of the porosimeter, it can be seen that micropores of 10 μm or less can be controlled by forming or removing cells in the process.

2) physical properties

Figure 6 shows the measured absorption, filling density, and unit volume weight of the specimens of the artificial turbulence according to an embodiment of the present invention.

As shown in Figure 6 (a), the absorption rate of the natural ovary is 118%, which is very high compared to the artificial ovary. In general, the absorption rate is proportional to the porosity, and the result of FIG. 6 coincides with the result analyzed by the image analyzer (hatched bar graph of FIG. 4).

Among artificial turbulences, the absorption rate of specimen 1 is 72%, which is higher than that of specimen 2, and since porosity of specimen 1 is higher than that of specimen 2, it is shown that the porosity of specimen 1 is higher than that of specimen 2. Greater than

Despite having the same composition, the absorption of specimen 4 is lower than that of specimen 1 or specimen 3. This is because in the second sintering process of Specimen 1, the micropores are partially filled by the material movement, thereby lowering the porosity. As shown in FIG. 4, the porosity of Specimen 4 is lower than that of Specimen 1.

Large void content of the aggregate improves air permeability, which has a good effect on root rot prevention during egg culture. As can be seen in Figure 6 (b) the porosity of all artificial turbulence is larger than the natural turbulence. As shown in Equation 1, the porosity of the aggregate is closely related to the filling rate.

              Porosity (%) = 100-Fill Rate (%)

The general filling rate is related to the shape distribution of aggregates, and filling is good when several sizes of aggregates are mixed rather than a certain size. Artificial turbulence is manufactured in a spherical shape and relatively constant in size and shape, whereas natural turbulence is indefinite and wide in size distribution, so it is considered to have low porosity.

 Among artificial turbulence, specimen 1, specimen 3 and specimen 4 have the same composition, but showed different porosity. While specimen 3 and specimen 4 had a porosity of 46%, specimen 1 had 48% of porosity compared to specimen 3 and specimen 4. Slightly higher. This is because the specimens 3 and 4 were pulverized specimen 1, and the porosity was reduced because the basic pore size proportional to the specimen size was reduced and the specimen size distribution was widened and the filling was good.

Unit volume weight is the weight per unit volume of a fully dried specimen filled in a volume and means the light weight of the ovary. In Fig. As shown in 6 (c) unit weight of natural nanseok is 320kg / m ^3, indicates a value lower than 390 ~ 450kg / m ³ of an artificial nanseok, actually nature nanseok is very light, so the court when the bone dry water Lose. When comparing the physical properties such as absorption rate, packing density, unit volume weight, etc., of natural and artificial eggs, natural absorption is superior to unity weight, and porosity is high.

3) drainage speed

FIG. 7 illustrates a measurement of water loss rate with time in a 25 ° C. atmosphere for a catcher specimen according to an embodiment of the present invention.

As shown in FIG. 7, the rate of water release, that is, the rate of drainage, of the specimen of the artificial turbulence is affected by the pore distribution. All specimens have a moisture loss rate of less than 50% even after one week, and after three weeks, The water loss rate is over 70%.

For most specimens, the slope of the water loss graph remains straight up to three days after the start of the experiment (initial stage). The first water released from the specimen was adsorbed or thinly wetted on the surface of the artificial turbulence, and is believed to be released through the void between the aggregate and the aggregate.

Looking at the initial stages of water release of the specimens, the drainage rate of all artificial turbulence (moisture loss with time), that is, the slope is larger than the natural one in the graph of Figure 7, the moisture loss rate of specimen 4 is the largest appear.

In the initial stage of water release, the effect of the porosity of the specimen is greater than that of the specimen itself, so the initial drainage speed of the artificial turbulence having a low porosity (see FIG. 6 (b)) is low. After moisture adsorbed or wetted onto the surface of the artificial turbulence is released through the pores, the moisture in the specimen pores begins to escape.

When the water filled in the specimen pores is released, the rate of drainage is affected by the pore size. The rate of water exiting the capillary is calculated by Equation 2 below.

= 물과 수증기 간 계면장력,

= 물과 모세관 간의 접촉각,

= 물의 점도, L = 모세관의 길이, Rc = 모세관 반경이다. here,

= Interfacial tension between water and water vapor,

= Contact angle between water and capillary,

= Viscosity of water, L = length of capillary, Rc = capillary radius.

In Equation 2, assuming that the capillary is the pores in the aggregate specimen, the rate of moisture coming out of the pores is proportional to the radius of the pores. Therefore, the release of water is thought to start from the macropores first and exit in the order of micropores.

After 6 days, the amount of water released from the natural turbulence is greater than that of the specimen 1 of the artificial turbulence (see part A of FIG. 7), and after 14 days, the water is larger than all the artificial turbulences (part B of FIG. 7).

Comparing the water loss rate of each specimen on the 25th day of the drainage experiment, as shown in Figure 7, the natural ovary is 91%, both the specimen 3 and 4 of the artificial ovary 87%, 83% of the specimen 1 appears. It is believed that the presence of macropores causes the most loss of moisture in long-term drainage experiments.

That is, the large pore of 160 ~ 210 ㎛ present in the natural turbulence (see Fig. 4) serves as a path to easily release the moisture, but compared to the time it takes to lose 80% of moisture, in the case of specimen 1 It is 23 days and natural ovulation is 19 days, and it can be seen that the ability to suppress water release of artificial ovaries is superior to natural ovaries.

Specimen 1 has a relatively low water release even after prolonged exposure to natural or other artificial eggs, because of the presence of cells. The cells are dense tissues containing large amounts of glassy phase, which slow down the release of moisture in the specimen. Therefore, artificial turbulence, in particular, specimen 1 having a cell structure, has been shown to release moisture more slowly than natural turbulence, that is, excellent sustained release (徐 放 性).

However, even with artificial turbulence of the same composition, specimens 3 and 4 have a lower moisture release capacity than specimens 1. Specimen 3 is crushed specimen 1 to 1/2 to 1/3 size and specimen 4 is sintered to 1100 ℃ / 1h after crushing specimen 1 to 1/2 to 1/3 size It is a psalm. Therefore, in specimen 3, the cell tissue was destroyed, and in specimen 4, the cell tissue was not regenerated.

As a result, when analyzing the relationship between drainage rate, drainage rate and microstructure, the initial drainage rate within 3 days is affected by the filling rate, and then from the middle to the last stage, the drainage is 160 ~ 210 ㎛ macropore and cell structure. The degree of sustained release varies depending on the presence of.

As described above, the composition for artificial turbulence according to an embodiment of the present invention and a method for manufacturing the same are manufactured by using wet waste mixed with clay such as waste clay, electric furnace steel dust, stone flour sludge, etc. in a clay mixture to dry and produce lightweight aggregate. As a result of evaluating the characteristics of artificial turbulence, waste clay is a waste having a ignition loss of 48%, which contributes to the increase of porosity and absorption rate by generating gas in the specimen during sintering.

The natural ovary shows a fine structure with better through pores than the artificial ovary. The porosity of the natural ovary is higher than that of the artificial ovary and the absorption rate is 118%, which is 1.6 times that of the artificial ovary.

The porosity of artificial turbulence with a constant size and shape of specimens varies in size and shows higher porosity compared to natural fillers with good filling. Pore distribution and porosity of turbulence affect drainage rate and drainage rate. The section with a straight time ratio is within 3 to 7 days, depending on the specimen, and the drainage (moisture loss) during that period is 30 to 40%.

Since the initial water release occurs between the pores, the initial stage drainage rate of the natural porosity with low porosity is lower than that of the artificial one, but the large pore size of 120 ~ 180 ㎛ existing only in the natural follicle acts as a water release path after the initial stage. However, it can be seen that the amount of natural turbulence is larger than that of artificial turbulence.

It can be seen that artificial turbulence has a superior ability to inhibit water release than natural turbulence. Particularly, in case of specimen 1, the time taken to lose 80% of moisture is 24 days, and the water discharge is slower than the 19 days of natural ovary. This is due to the presence of cells with dense surface tissue. It seems to be slow.

However, it can be seen that the specimen 3 which pulverized the specimen 1 or the specimen 4 which pulverized and secondary sintered the specimen 1 lost the cell on the surface, and thus the ability to inhibit moisture release was lowered compared to the specimen 1.

According to such a composition for artificial turbulence and a method for manufacturing the same, various industrial wastes are mixed with clay, wet mixed and dried to prepare artificial turbulence, and thus industrial wastes can be recycled and used as useful alternative resources. There is an effect that can be activated in economic terms.

In addition, according to the composition for the artificial ovary and its manufacturing method, by controlling the foaming of the artificial ovate with the composition and the process as a variable, it is possible to adjust the cell, micropores, absorption rate and drainage rate, etc. There is an effect that can get the characteristics.

In the detailed description of the present invention described above with reference to a preferred embodiment of the present invention, those skilled in the art or those skilled in the art having ordinary knowledge in the scope of the invention described in the claims to be described later It will be understood that various modifications and variations can be made in the present invention without departing from the scope of the present invention.

Claims (11)

delete delete a) adding clay to at least one of the waste clay, the furnace steel dust, and the sewage sludge to form a mixture; b) wet-drying the mixture by filter pressing and then molding the mixture into a shaped body; And c) first sintering the molded body in a rotary kiln at a predetermined temperature for a predetermined time to produce an artificial egg stone; and In step c), since a shell having a structure in which the surface of the artificial turbulence is denser than a core exists, the gas generated during the sintering process is suppressed by the cell and is expanded, thereby expanding the artificial turbulence. Method for producing artificial turbulence, characterized in that the inside is a porous structure. The method of claim 3, d) pulverizing or artificial sintering after crushing the artificial turbulence further comprises the step of changing the dense structure of the surface of the artificial dolmen. delete The method of claim 4, wherein Forming or removing the cell through the step d), the method of manufacturing artificial turbulence, characterized in that it is possible to control the generation of fine pores of a predetermined size or less, and the ability to inhibit water release. The method of claim 3, In the step a), the mixture is at least 5 to 10 parts by weight (wt%) of waste clay, 5 parts by weight (wt%) of electric furnace steel dust, and 25 to 30 parts by weight (wt%) of sludge dust. A method for producing artificial turbulence, characterized in that by adding 60 parts by weight (wt%) of clay to one or more wastes. The method of claim 7, wherein Since the waste clay contributes to foaming, the artificial turbulence has a multi-porous structure and the composition for artificial turbulence can be adjusted so that the absorption rate is improved. The method of claim 3, B) ball milling and filter pressing the mixture; And wet-drying the ball milled and filter pressed mixture for about 2 hours. The method of claim 3, The step b) is the manufacturing method of the artificial turbulence, characterized in that for forming the molded body through a spherical process after molding the wet-dried mixture in a cylindrical shape having a predetermined diameter and height. The method of claim 3, The step c) is a method for producing artificial dolmens, characterized in that the artificial sintered by sintering for about 10 minutes in a rotary kiln of 1100 ~ 1150 ℃.

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