JP2018091768A - Bentonite pellet production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method capable of reducing a production cost of a high-density bentonite pellet.SOLUTION: A bentonite production method produces a bentonite pellet using a roll press machine capable of compression molding by allowing a processing object to pass between two rolls, and includes: a compression molding process S11 of producing a primary bentonite pellet by feeding a bentonite containing material into the roll press machine so as to be compression-molded; and a compression molding process S12 of producing a secondary bentonite pellet having a greater thickness than the primary bentonite pellet by feeding the primary bentonite pellet obtained by the compression molding process S11 into the roll press machine whose roll interval setting has been changed. The bentonite production method further includes: a crushing process S13 of crushing the bentonite pellet so that a size distribution thereof approaches the distribution set as a buffer material; and a mixing process S14 of mixing the pellets with a powder bentonite so as to optimize the size distribution.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a bentonite pellet manufacturing method for manufacturing bentonite pellets containing bentonite, and particularly to a technique for manufacturing high-density bentonite pellets.

  In a high-level radioactive waste disposal site, a method of constructing an artificial barrier (buffer material) around the waste has been considered as a method for burying a radioactive waste waste. In recent years, a pellet filling method in which bentonite pellets, which are relatively easy to operate, is filled around a waste body as a buffer material has attracted attention. Since high shielding performance is required for the buffer material, the bentonite pellet used in the pellet filling method is required to have a high density.

  For example, as a method for producing high density bentonite pellets, for example, drum granulation, bread granulation, extrusion granulation method, CIP (Cold Isostatic Pressing) method and the like are known.

  For example, a technique described in Patent Document 1 is known as a technique related to a method of manufacturing bentonite pellets using an extrusion granulation method.

JP, 2015-206736, A

  Machines used in drum granulation, extrusion granulation method, and CIP method are not general-purpose machines but special machines, and the total number of machines is relatively small. Further, the amount that can be produced at one time by drum granulation, extrusion granulation method, and CIP method is relatively small. Further, in the extrusion granulation method, it is necessary to dry the pellets formed by extrusion, and it takes time to complete the final pellets. For this reason, there is a problem that the manufacturing cost of high density bentonite pellets is very high.

  This invention is made | formed in view of the said situation, The objective is to provide the technique which can reduce the manufacturing cost of a high density bentonite pellet.

  In order to achieve the above object, a bentonite pellet manufacturing method according to an aspect of the present invention is a bentonite pellet manufacturing method in which bentonite pellets are manufactured using a roll press machine capable of compression molding by passing a treatment target between two rolls. A first press molding process for producing primary bentonite pellets by introducing a bentonite-containing material into a roll press machine and compression molding, and a roll press set differently from the first compression molding process. A first bentonite pellet obtained by the first compression molding process is put into the machine to produce a second bentonite pellet that is thicker than the first bentonite pellet.

  In the bentonite pellet manufacturing method, the roll interval of the roll press machine in the second compression molding step may be set larger than the roll interval of the roll press machine in the first compression molding step.

  In the bentonite pellet manufacturing method, the roll interval of the roll press machine in the first compression molding step may be 0 mm, and the roll interval of the roll press machine in the second compression molding step may be 2 mm.

  In the bentonite pellet manufacturing method, the bentonite-containing material may be powdered bentonite.

  Moreover, in the said bentonite pellet manufacturing method, 137.2 N / mm or more may be sufficient as the linear pressure of the roll of a roll press machine.

  Moreover, in the said bentonite pellet manufacturing method, 15.7 mm / s or less may be sufficient as the feed rate of the roller of a roll press machine.

In the bentonite pellet manufacturing method, the second bentonite pellet may have a thickness of 3.5 mm or more and a bulk density of 1.93 Mg / m ³ or more.

  According to the present invention, the manufacturing cost of high density bentonite pellets can be reduced.

It is a lineblock diagram showing typically a roll press machine used for a shock absorbing material manufacturing method concerning one embodiment of the present invention. It is a figure which shows an example of the bentonite pellet obtained by compression molding with a roll press. It is a flowchart of the shock absorbing material manufacturing method which concerns on one Embodiment of this invention. It is a figure which shows the content and result of each experiment example which concern on one Embodiment of this invention.

  Hereinafter, based on an accompanying drawing, a buffer material manufacturing method including a bentonite pellet manufacturing method concerning one embodiment of the present invention is explained.

  First, the roll press machine utilized for the buffer material manufacturing method concerning one embodiment of the present invention is explained.

  FIG. 1 is a configuration diagram schematically showing a roll press machine used in a cushioning material manufacturing method according to an embodiment of the present invention.

  The roll press 10 is not a device unique to the production of bentonite pellets, but a device that is widely used in general. The roll press machine 10 includes a pair of rolls 11 and 12 arranged opposite to each other, a hopper 13 for introducing a processing target to be compressed, and a workpiece that is compression-molded through the rolls 11 and 12. And a workpiece receiving portion 14 for receiving the workpiece.

  The roll 11 is, for example, a solid cylindrical member, and has a diameter of 300 mm and an axial length of 300 mm, for example. The roll 11 can be rotated in the clockwise direction in FIG. 1 by a motor 15 that transmits a rotational force to the roll shaft 11A. The rotation speed of the roll 11 can be adjusted. Further, a load can be applied to the roll 11 by, for example, a hydraulic jack 17 or the like. In the roll press 10, for example, a load of 4.0 ton or more can be applied so as to press the roll 11 in the direction of the roll 12.

  The roll 12 is a solid cylindrical member, for example, and has a diameter of 300 mm and an axial length of 300 mm, for example. The roll 12 can be rotated counterclockwise in FIG. 1 by a motor 16 that transmits a rotational force to the roll shaft 12A. The rotation speed of the roll 12 can be adjusted. Basically, the rotation speed of the roll 12 is the same as the rotation speed of the roll 11.

  In the roll press 10, the distance between the roll 11 and the roll 12 (roll interval G) can be adjusted. In the present embodiment, for example, the roll press machine 10 can adjust the roll interval in units of 1 mm, for example, from a roll interval G where the roll 11 and the roll 12 are in contact with each other.

  According to the roll press machine 10, when a processing object is put into the hopper 13 while a load is applied to the roll 11 and the roll 11 and the roll 12 are rotated, the processing object put into the hopper 13 is turned into the roll 11. Are swallowed between the roll 12 and the roll 12, are compressed and formed by the roll 11 and the roll 12, become a processed product, and are discharged to the workpiece receiving unit 14. In this embodiment, the base material of bentonite pellets (for example, powdered bentonite) and the workpiece (bentonite pellets) compression-molded by the roll press 10 are input to the hopper 13, and the workpiece receiving portion is used as bentonite pellets. 14 is discharged.

  Next, bentonite pellets, which are workpieces compression-molded by the roll press machine 10, will be described.

  FIG. 2 is a diagram showing an example of bentonite pellets obtained by compression molding using a roll press.

  The bentonite pellets P have a flat plate shape, for example, as shown in FIG. In the present embodiment, the plane of the bentonite pellets P may have a size of about several tens mm × several tens mm, for example. In this specification, the distance between planes in the bentonite pellets P is expressed as a thickness D as shown in the figure.

  Next, a buffer material manufacturing method including a bentonite pellet manufacturing method will be described.

  FIG. 3 is a flowchart of a cushioning material manufacturing method according to an embodiment of the present invention.

  It is assumed that a base material for the buffer material is prepared in advance before executing the buffer material manufacturing method. As the base material, a bentonite-containing material such as powdered bentonite can be used.

  First, the first compression molding process (first compression molding process) is performed using the roll press 10 (step S11). In the first compression molding process, the roll press 10 is operated with the roll interval of the roll press 10, the load applied to the roll 11, and the rotation speed of the rolls 11 and 12 as predetermined settings for the first compression molding process. Next, the base material powder bentonite is put into the hopper 13 of the roll press 10. Thereby, a plurality of compression-molded bentonite pellets (primary bentonite pellets) are discharged to the workpiece receiver 14 of the roll press machine 10.

  Next, a second compression molding process (second compression molding process) is performed using the roll press 10 (step S12). In the second compression molding process, the roll press machine 10 is operated with the roll interval of the roll press machine 10, the load on the roll 11, and the rotation speed of the rolls 11 and 12 set for the second compression molding process. Here, the setting for the second compression molding step is different from the setting for the first compression molding step. Specifically, in this embodiment, the roll interval in the setting for the second compression molding step is set to be larger than the roll interval in the first setting. Next, a plurality of bentonite pellets obtained in the first compression molding step are put into the hopper 13 of the roll press machine 10. As a result, a plurality of compression-molded bentonite pellets (corresponding to secondary bentonite pellets) are discharged to the workpiece receiver 14 of the roll press 10. The bentonite pellets obtained by the second compression molding step are thicker than the bentonite pellets obtained by the first compression molding step. The process so far is a process for producing high-density bentonite pellets (bentonite pellet manufacturing method). In addition, when the thickness of the bentonite pellet obtained by a 2nd compression molding process is less than desired thickness, the setting of the roll press 10 is changed by making the bentonite pellet obtained at the last process into a process target ( For example, the third and subsequent compression molding steps may be performed by increasing the roll interval.

  Next, a crushing step is performed for crushing the plurality of bentonite pellets obtained in the second compression molding step so that the particle size distribution approaches a predetermined distribution set as a buffer material (step S13).

  Next, by mixing powder bentonite with the resultant product obtained in the crushing step, the particle size distribution in the mixture is optimized, that is, the particle size distribution is made closer to a predetermined distribution set as a buffer material. (Mixing step: step S14). By performing this mixing step, it is possible to replenish powder bentonite as a small particle size (fine fraction) that is insufficient only with the resultant product obtained by crushing bentonite pellets in step S13. The particle size distribution in the mixture obtained through the mixing step can be made to coincide with or be closer to a predetermined distribution set as a buffer material. In this way, the mixture obtained through the mixing step can be used as a cushioning material when the radioactive waste waste is disposed of.

  Next, each experimental example regarding the bentonite pellet manufacturing method in the buffer material manufacturing method will be described in detail.

  FIG. 4 is a diagram showing the state of each experimental example and the experimental results.

  In Experimental Example 1 to Experimental Example 6, the same roll press machine 10 was used. The rolls 11 and 12 of the roll press machine 10 had a diameter of 300 mm and a length of 300 mm. The load on the roll 11 in the roll press 10 was 4.2 ton (linear pressure 137.2 N / mm (= 4.2 ton × 1000 kg × 9.8 N / 300 mm)). Further, Na-type bentonite was used as the powdery bentonite of the base material. Specifically, Kunigel V1 (Kunimine Kogyo Co., Ltd .: Kunigel is a trademark) was used. The initial moisture content of the powder bentonite was unadjusted as shipped, and was 10.3%. When powder bentonite is used as a base material, impurities contained in the obtained bentonite pellets can be reduced, and reliability required as a buffer material for radioactive waste waste can be ensured.

[Experimental Example 1]
In Experimental Example 1, in the roll press machine 10, the roll interval was 3 mm, and the rotation speeds of the rolls 11 and 12 were 6 rpm (feed speed was 94.2 mm / s (≈300 mm × π × 6 rpm / 60 s)). . Between the hopper 13 and the rolls 11 and 12, 0.4 kg of powdered bentonite was charged for 3.0 minutes, that is, at a charging speed of 0.1 kg / min.

  The work piece obtained by the roll press 10 was a small particle that could not be used as bentonite pellets, and was judged to be defective (NG).

[Experiment 2]
In Experimental Example 2, in the roll press machine 10, the roll interval was set to 0 mm, and the rotation speeds of the rolls 11 and 12 were set to 1 rpm (feed speed was 15.7 mm / s (≈300 mm × π × 1 rpm / 60 s)). . Between the hopper 13 and the rolls 11 and 12, 3.4 kg of powdered bentonite was charged at 15.0 minutes, that is, at a charging speed of 0.2 kg / min.

When a plurality of bentonite pellets (primary bentonite pellets) in a workpiece compression-molded by the roll press 10 are sampled and measured, the thickness is 1.39 mm and the bulk density is 1 .98 Mg / m ³ . The bulk density is a dry density. The wet density was measured according to the paraffin method of the soil wet density test (JIS A 1225), and the dry density was determined from the water content ratio. The bulk density was determined by the same method in other experimental examples.

[Experiment 3]
In Experimental Example 3, in the roll press machine 10, the roll interval was set to 0 mm, and the rotation speeds of the rolls 11 and 12 were set to 4 rpm (feeding speed was 62.8 mm / s). Between the hopper 13 and the rolls 11 and 12, 0.5 kg of powdered bentonite was charged for 1.5 minutes, that is, at a charging rate of 0.3 kg / min.

  The rotation speed of the rolls 11 and 12 of the roll press machine 10 is fast, and a sufficient amount of bentonite cannot be supplied between the rolls 11 and 12 to obtain bentonite pellets. Was not obtained, and it was determined to be defective (NG).

[Experimental Example 4]
In Experimental Example 4, the bentonite pellets obtained in Experimental Example 2 were set as treatment targets to be charged into the roll press machine 10. That is, Experimental Example 4 is an example in which the roll press machine 10 is passed twice and the compression molding process is performed twice. In the roll press 10, the roll interval was 2 mm, and the rotation speed of the rolls 11 and 12 was 1 rpm (feeding speed was 15.7 mm / s). Between the hopper 13 and the rolls 11 and 12, 3.1 kg of bentonite pellets was charged for 1.5 minutes, that is, at a charging speed of 2.1 kg / min.

When a plurality of bentonite pellets (secondary bentonite pellets) in the work piece compression-molded by the roll press 10 are sampled and measured, the thickness is 3.59 mm and the bulk density is 2. 02Mg / m ³ .

[Experimental Example 5]
In Experimental Example 5, the bentonite pellets obtained in Experimental Example 2 were set as treatment targets to be charged into the roll press machine 10. That is, Experimental Example 5 is an example in which the roll press machine 10 is passed twice and the compression molding process is performed twice. In the roll press 10, the roll interval was 3 mm, and the rotation speeds of the rolls 11 and 12 were 1 rpm (feeding speed was 15.7 mm / s). Between the hopper 13 and the rolls 11 and 12, 0.5 kg of bentonite pellets was charged for 0.5 minutes, that is, at a charging speed of 1.0 kg / min.

When a plurality of bentonite pellets (secondary bentonite pellets) in a work product compression-molded by the roll press 10 are sampled and measured, the thickness is 3.63 mm, and the bulk density is 1 .93 Mg / m ³ .

[Experimental Example 6]
In Experimental Example 6, the bentonite pellets obtained in Experimental Example 4 were set as treatment targets to be charged into the roll press machine 10. That is, Experimental Example 6 is an example in which the roll press machine 10 is passed three times and the compression molding process is performed three times. In the roll press 10, the roll interval was 3 mm, and the rotation speeds of the rolls 11 and 12 were 1 rpm (feeding speed was 15.7 mm / s). Between the hopper 13 and the rolls 11 and 12, 2.7 kg of bentonite pellets was charged at 1.0 minutes, that is, at a charging speed of 2.7 kg / min.

When a plurality of bentonite pellets in a workpiece compression-molded by the roll press 10 are sampled and measured, the thickness is 4.13 mm and the bulk density is 1.98 Mg / m ³ . there were.

  Next, the experimental results of Experimental Example 1 to Experimental Example 6 will be compared and described.

  In Experimental Examples 1 to 3, the processing object was powder bentonite, and the roll press machine 10 was passed once, that is, the compression molding process by the roll press machine 10 was performed once.

  As shown in Experimental Example 1 and Experimental Example 3, when the roll feed rate was 62.8 mm / s or higher, bentonite pellets having an effective size could not be produced by the roll press machine 10. Moreover, as shown in Experimental Example 1, when the roll interval was 3 mm, bentonite pellets having an effective size could not be produced. This is considered to be because the powder bentonite to be treated is in a state where it is passed through without being sufficiently compressed between the rolls 11 and 12 of the roll press 10.

On the other hand, in Experimental Example 2, since the roll interval is as narrow as 0 mm and the feed speed of the roll is as low as 15.7 mm / s, the powder bentonite is sufficiently compressed to have a relatively large flat plate shape. Of bentonite pellets were obtained. From this, it was found that when the processing target is powdered bentonite, relatively large bentonite pellets can be obtained when the roll interval is narrow and the roll feed rate is low. The obtained bentonite pellets have a bulk density of 1.98 Mg / m ³ and are relatively high, but are relatively thin at 1.39 mm.

  In Experimental Example 4 and Experimental Example 5, the roll interval in the compression molding process in the roll press machine 10 is larger than that in Experimental Example 2. In Experimental Example 4 and Experimental Example 5, the experimental example 5 has a larger roll interval in the compression molding process in the roll press machine 10 than in Experimental Example 4.

In both Examples 4 and 5, bentonite pellets having a thickness of 3.5 mm or more and a bulk density of 1.93 Mg / m ³ or more were obtained. According to Experimental Example 4 and Experimental Example 5, bentonite pellets thicker than the bentonite pellets obtained in Experimental Example 2 as a treatment target were obtained. The bentonite pellet of Experimental Example 4 has a bulk density of 2.02 Mg / m ³ and is 2.0 Mg / m ³ or more, and is more preferable than the bentonite pellet of Experimental Example 5 from the viewpoint of bulk density.

In Experimental Example 6, a bentonite pellet thicker than the bentonite pellet obtained in Experimental Example 4 as a treatment target and having a thickness of 4.13 mm was obtained. The resulting bentonite pellets have a bulk density of 1.98 Mg / m ³ and are relatively high. In Experimental Example 6, since it is necessary to pass the roll press machine 3 three times to obtain bentonite pellets, Experimental Example 4 and Experimental Example 5 are preferable in terms of reducing the manufacturing cost.

  According to the experimental results of Experimental Example 1 to Experimental Example 6 described above, for example, the bentonite pellets may have a thickness of 3.5 mm or more. What is necessary is just to manufacture. Specifically, a process of producing bentonite pellets by passing the powder bentonite through the roll press 10 with the roll feed speed of the roll press 10 set to 15.7 mm / s and the roll interval set to 0 mm (first) Compression molding step: equivalent to Experimental Example 2), then the roll feed rate was set to 15.7 mm / s and the roll interval was set to 2 mm, and the resulting bentonite pellets were passed through the roll press 10 to be bentonite. What is necessary is just to perform the process (2nd compression molding process) which manufactures a pellet.

  As described above, in the bentonite pellet manufacturing method according to the present embodiment, the first bentonite pellet is manufactured by charging the powdered bentonite into the roll press 10 and compressing it, The first bentonite pellet obtained by the first compression molding process is put into a roll press machine set differently from the first compression molding process, and the second bentonite pellet is thicker than the first bentonite pellet. Therefore, it is possible to easily and rapidly produce a high-density bentonite pellet having a relatively large thickness. Moreover, as the roll press machine 10, a general roll press machine can be used. Thereby, the manufacturing cost of bentonite pellets can be reduced. Moreover, even if it does not perform a drying process with respect to the bentonite pellet after a compression molding process, a comparatively high bulk density can be obtained.

  The present invention is not limited to the above-described embodiments and examples, and can be appropriately modified and implemented without departing from the spirit of the present invention.

  For example, in the above embodiment, only powder bentonite is used as the base material of bentonite pellets, but the present invention is not limited to this, and as a base material, for example, bentonite mixed soil containing bentonite and sand. May be used, and bentonite raw ore may be used. In short, any bentonite-containing material may be used.

DESCRIPTION OF SYMBOLS 10 ... Roll press machine, 11 ... Roll, 12 ... Roll, 13 ... Hopper, 14 ... Workpiece receiving part, P ... Bentonite pellet

Claims (7)

A bentonite pellet manufacturing method for manufacturing bentonite pellets using a roll press machine capable of compression molding by passing a treatment target between two rolls,
A first compression molding step of producing primary bentonite pellets by introducing a bentonite-containing material into the roll press machine and performing compression molding;
The first bentonite pellet obtained by the first compression molding step is introduced into the roll press machine set differently from the first compression molding step, and the first bentonite pellet is thicker than the first bentonite pellet. A second compression molding step for producing secondary bentonite pellets. The bentonite pellet manufacturing method according to claim 1, wherein a roll interval of the roll press machine in the second compression molding step is set larger than a roll interval of the roll press machine in the first compression molding step. The roll interval of the roll press machine in the first compression molding step is 0 mm,
The bentonite pellet manufacturing method according to claim 2, wherein a roll interval of the roll press machine in the second compression molding step is 2 mm. The bentonite pellet manufacturing method according to any one of claims 1 to 3, wherein the bentonite-containing material is powdered bentonite. The bentonite pellet manufacturing method according to any one of claims 1 to 4, wherein a linear pressure of the roll of the roll press machine is 137.2 N / mm or more. The bentonite pellet manufacturing method according to any one of claims 1 to 5, wherein a feed speed of the roll of the roll press machine is 15.7 mm / s or less. The secondary bentonite pellets is a thickness of more than 3.5 mm, bentonite pellets production method according to claims 1 to any one of claims 6 bulk density of 1.93 mg / m ³ or more.

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