JP5339185B2 - Process for producing bentonite compact - Google Patents

Description

The present invention relates to a method for producing a bentonite molded body used, for example, as a backfill material for backfilling a disposal tunnel of a waste burial disposal facility where radioactive waste has been disposed of.

  For example, it is considered to bury high-level (or low-level) radioactive waste in the deep underground. At this time, the radioactive waste is mixed with glass and solidified, and this vitrified body is disposed as a waste body sealed with an overpack made of carbon steel or the like. Further, as shown in FIGS. 10 and 11, the waste body is disposed in a relatively stable natural ground G in the deep underground, and a main tunnel 1 connected in a substantially annular shape, and a disposal tunnel formed so as to be connected to the main tunnel 1. A waste burying / disposal facility A including a disposal hole (hereinafter referred to as a disposal mine 2) is constructed and disposed in the disposal mine 2 of the waste burying / disposal facility A (see, for example, Patent Document 1).

  Moreover, if the disposal tunnel 2 where the waste is disposed is left as it is, loosening of the ground G around the disposal tunnel 2 will be expanded, and an excellent waterway will be formed in the groundwater. There is a risk of lowering the barrier performance. For this reason, it is necessary to backfill the disposal tunnel 2 with a low water permeability material (backfill material 3) equal to or higher than that of the natural ground G. As the backfill material 3, the swelling property and the adsorptivity of radioactive substances are improved. The use of excellent bentonite has been studied. And when such a bentonite is used as the backfill material 3, the groundwater that has entered the disposal tunnel 2 from the natural ground G comes into contact with it, and the bentonite swells and presses the natural ground G to further infiltrate the groundwater. Infiltration of groundwater can be prevented by reducing the water permeability coefficient of the backfill material 3 with swelling. This makes it possible to reliably dispose of radioactive waste from the outside natural environment.

  Then, bentonite crushed material obtained by crushing bentonite ore, bentonite compacted into a plate shape, bentonite crushed material obtained by crushing this bentonite plate, bentonite pellets formed by compacting bentonite into a cylindrical shape, for example, and isotropically pressurized bentonite It is considered that bentonite molded bodies (bentonite granular bodies) formed to a size of several millimeters to several tens of millimeters, such as bentonite balls compacted into a spherical shape by pressure treatment, are filled into the disposal tunnel 2 as the backfill material 3. (For example, see Patent Document 2, Patent Document 3, and Patent Document 4).

  On the other hand, in order to exhibit excellent barrier performance using bentonite compacts, that is, to form a high-density bentonite impermeable layer, it is important how much mass of bentonite can be packed in a given space. Therefore, it is necessary to form a bentonite molded body at a high density and to fill (construct) this high-density bentonite molded body at a high filling rate.

  On the other hand, when using bentonite crushed material crushed bentonite ore, the density of bentonite ore is not high, and there is a possibility that further density reduction may occur when crushing bentonite ore. It will be necessary to compact later. In addition, bentonite crushed material obtained by crushing such bentonite ore is irregular in particle shape, and the filling rate does not increase only by throwing it into a predetermined space by free fall. It becomes necessary. Furthermore, even in the bentonite crushed material obtained by crushing the bentonite plate, there is a possibility that the density may be lowered by crushing the bentonite plate.

  On the other hand, bentonite balls that are compacted into a spherical shape by isotropic pressure treatment are bent into a spherical shape, so when a single particle size bentonite ball is thrown into a predetermined space by free fall, Thus, it is possible to fill with a high filling rate of about 75%. However, forming a bentonite ball having a particle diameter of several mm to several tens of mm by isostatic pressing at a pressure of several hundred MPa requires a very large apparatus and a complicated manufacturing process. Therefore, there is a problem that a great deal of cost is required for manufacturing.

  In contrast, the inventors of the present application add water to powdered bentonite and mix them together, and form a wet cylindrical bentonite compact using a disk die (extrusion granulator) in the extrusion granulation process. Then, the bentonite molded body formed in the extrusion granulation process is formed into a spherical shape in the rolling granulation process, and the spherical bentonite molded body formed in the rolling granulation process is further densified by drying shrinkage. Has proposed a method for producing bentonite compacts (Japanese Patent Application No. 2008-127737).

According to this bentonite molded body manufacturing method, a high-density and spherical bentonite molded body can be efficiently and easily manufactured without using a high pressure or requiring a complicated process. Further, it is theoretically possible to fill the bentonite molded body thus produced with a filling rate of about 75% by simply dropping it into a predetermined space by free fall.
JP 2003-215297 A Japanese Patent No. 4036975 JP-A-6-41513 Japanese Patent No. 3539928

  On the other hand, multiple types of bentonite compacts (bentonite compacts with particle size distribution) with different particle sizes compared to the case where a single particle size bentonite compact is charged into a predetermined space by free fall Can be filled at a higher filling rate.

  However, the conventional spherical bentonite molded body is formed by forming a bentonite molded body having a substantially single size using a disk die having an extrusion hole of the same diameter in the extrusion granulation process. The molded body was formed into a spherical shape by a rolling granulation process. For this reason, when a predetermined space is filled with bentonite compacts having a particle size distribution (a mixture of bentonite compacts), a plurality of types of bentonite compacts having different particle diameters are produced individually, A plurality of types of bentonite compacts having different values are mixed in advance at a predetermined ratio and then filled into a predetermined space. Therefore, in order to increase the filling rate, a complicated work of mixing a plurality of types of bentonite compacts having different particle sizes is required.

 In addition, when mixing multiple types of bentonite compacts with different particle sizes, it takes a lot of labor and time for the mixing operation, so it is difficult to use multiple types of bentonite compacts with different particle sizes, For example, as shown in FIG. 12, the particle size distribution has a stepped shape, and the filling rate may not be increased as expected.

In view of the above circumstances, the present invention eliminates the need for mixing a plurality of types of bentonite compacts having different particle sizes, and easily and reliably has a smooth particle size distribution (mixture of bentonite compacts). It aims at providing the manufacturing method of the bentonite molded object which can manufacture .

  In order to achieve the above object, the present invention provides the following means.

The manufacturing method of bentonite molded body of the present invention includes an extrusion granulation step in which water is added to and mixed with bentonite powder, and a bentonite molded body in a wet state is molded by extrusion granulation, and molding is performed in the extrusion granulation step. In the bentonite molded body manufacturing method comprising the rolling granulation step of forming the bentonite molded body into a substantially spherical shape by rolling granulation, bentonite molded bodies having different sizes are molded in the extrusion granulation step. Basically , in the rolling granulation step, bentonite compacts having different sizes are simultaneously formed into a substantially spherical shape.

  Here, since it is difficult to make a bentonite molded body into a true sphere by rolling granulation, in the present invention, “substantially spherical (substantially spherical bentonite molded body)” means a range that can be molded by rolling granulation. The bentonite molded body is connected in a smooth curve and has a substantially spherical shape.

  In this invention, by simultaneously rolling and granulating bentonite compacts having different sizes formed in the extrusion granulation process in the rolling granulation process, a plurality of types of bentonite compacts having different particle diameters can be produced simultaneously. Is possible. This makes it possible to easily produce a mixture of bentonite compacts with different particle sizes, and mix conventional bentonite compacts with different particle sizes at a specified ratio. Work can be made unnecessary. In addition, bentonite compacts with a smooth particle size distribution (bentonite molding) are formed by molding various types of bentonite compacts with different sizes in the extrusion granulation process and rolling granulation at the same time in the rolling granulation process. Body mixture) can be produced easily and reliably.

In the bentonite molded body manufacturing method of the present invention, bentonite molding is performed using a disk die provided with a plurality of extrusion holes through which the bentonite kneaded material mixed with the bentonite and the water is extruded in the extrusion granulation step. A plurality of disc dies having different sizes of the extrusion holes are prepared, and bentonite compacts having different sizes are formed while exchanging the disc dies .

  In this invention, a plurality of disk dies having different sizes of extrusion holes, that is, a single size of the extrusion holes of each disk die, a plurality of disk dies having different sizes of the extrusion holes between the disk dies, By extruding and granulating the bentonite kneaded material while exchanging these disk dies, it is possible to easily and reliably produce a plurality of bentonite compacts having different particle sizes. In addition, by using various types of disc dies having different sizes of extrusion holes, it is possible to easily and surely manufacture bentonite compacts having a smooth particle size distribution.

According to the bentonite molded product manufacturing method of the present invention, bentonite molded products having different sizes formed in the extrusion granulation step are simultaneously rolled and granulated in the rolling granulation step, and dried in the drying step. It is possible to produce a plurality of bentonite compacts having different diameters while mixing them at the same time. This eliminates the need for a mixing operation in which bentonite molded bodies having different particle sizes, which are individually molded as in the prior art, are mixed at a predetermined ratio, and makes a bentonite molded body (a mixture of bentonite molded bodies) having a smooth particle size distribution. It becomes possible to manufacture easily and reliably.

  The bentonite molded body thus manufactured can be filled at a higher filling rate than when a bentonite molded body having a single particle diameter is used by simply dropping it into a predetermined space. Therefore, for example, when used as a backfill material when refilling a disposal tunnel of a radioactive waste burial disposal facility, it is possible to reliably form a bentonite impermeable layer with excellent barrier performance, Radioactive waste can be reliably separated from the outside natural environment and disposed of, and a highly reliable waste disposal facility can be obtained.

  Hereinafter, with reference to FIGS. 1 to 11, a bentonite molded body manufacturing method and bentonite molded body according to an embodiment of the present invention will be described. The present embodiment relates to a bentonite molded body used as a backfill material 3 in a disposal mine channel 2 of a waste burial disposal facility A that disposes radioactive waste, and a bentonite molded body manufactured by this manufacturing method. .

  As shown in FIG. 1, in the manufacturing method of the bentonite molded body of the present embodiment, first, a predetermined amount of water is added to and mixed with powdered bentonite. At this time, the water content of the bentonite in the powder is generally about 7 to 10%, and water is added to the bentonite and mixed so that the water content is about 25 to 28%, for example. The water content ratio in a state where a predetermined amount of water is added to and mixed with bentonite powder is not necessarily limited to about 25 to 28%, but the characteristics of bentonite used (such as bentonite production area) and molding It adjusts suitably according to the particle size etc. to do. That is, if the moisture content is small relative to the bentonite powder, the amount of air in the wet bentonite molded body formed in the extrusion granulation process described later increases, and the bentonite during granulation in the rolling granulation process described later. The molded body is not molded into a spherical shape and is shattered. In addition, if the amount of water is large, a large number of bentonite compacts formed in the extrusion granulation process or rolling granulation process adhere to large particles, and the bentonite compacts become peanut molds or have a large air layer. Including (low density) will be formed. For this reason, the amount of water added to the bentonite powder is set to an amount that allows the bentonite compact to be molded into a predetermined shape in the extrusion granulation process or the rolling granulation process in accordance with the characteristics of the bentonite or the particle size to be molded.

  Then, at the stage where the bentonite powder and water are kneaded, the extruded bentonite (bentonite kneaded product) is extruded and granulated using an extrusion granulator to form a large amount of wet columnar bentonite compacts. (Extrusion granulation process).

At this time, as a reference example of the disk die of the extrusion granulator, as shown in FIG. 2, the hole diameter (size) of a plurality of extrusion holes 5a into which bentonite kneaded material is extruded, such as 1 mm, 2 mm, 4 mm, 15 mm, and 20 mm. May be prepared at the same time in a state in which a plurality of bentonite compacts having different sizes (diameters) are mixed .

In the bentonite molded body manufacturing method of this embodiment, as shown in FIG. 3 (FIGS. 3A and 3B), a plurality of disc dies 6 having different hole diameters (sizes) of the extrusion holes 6a and 7a. , 7, that is, a plurality of disk dies 6, 7 having a single hole diameter of the extrusion holes 6 a, 7 a of each disk die 6, 7 and different hole diameters of the extrusion holes 6 a, 7 a between the disk dies 6, 7, By extruding and granulating the bentonite kneaded material while exchanging the disk dies 6 and 7, a large number of molded bentonite bodies having different sizes (diameters) are mixed.

  Next, as shown in FIG. 1, by supplying a plurality of bentonite compacts having different sizes formed in the extrusion granulation process to the rolling granulator, by rolling and granulating with the rolling granulator, A plurality of types of bentonite compacts having different sizes are mixed and formed into a substantially spherical shape simultaneously (rolling granulation step). At this time, for example, a large amount of bentonite compact is supplied to a drum of a rolling granulator, and the bentonite compact is formed into a substantially spherical shape by rotating the drum at a high speed.

  And the bentonite molded object shape | molded by the spherical shape in the wet state as mentioned above is dried (drying process). At this time, for example, as shown in FIG. 4, a bentonite molded body 10 formed by a rolling granulation process is provided in a drying furnace 9 in which hot air 8 flows and heat is forced convection (that is, bentonite molded body 10 is heated). In an air environment with forced convection). Alternatively, for example, as shown in FIG. 5, the bentonite molded body 10 is provided and dried in an air environment in which heat 12 generated from the heat source 11 is naturally convected. The bentonite molded body 10 provided in the air environment in which the hot air 8 is circulated and the heat is forced to convection or in the air environment in which the heat 12 is naturally convected is densified by drying shrinkage.

  Here, when the bentonite molded body 10 is dried by forced convection of heat, as shown in FIG. 6, the bentonite molded body 10 in a wet state is 60 minutes even if the blowing temperature is 40 to 50 ° C. It is dried to a water content ratio (about 7 to 10%) equivalent to that of bentonite powder in a drying time of about. In addition, when the bentonite molded body 10 is dried by natural convection of heat 12, the bentonite molded body 10 in a wet state is about 1440 minutes (about 1 day) at 50 ° C. as shown in FIG. Dry slowly at a temperature of 240 minutes with a drying time of about 240 minutes.

FIG. 8 shows the dry density of the bentonite compact 10 dried in the case where the heat shown in FIG. 6 is forced convection and in the case where the heat 12 shown in FIG. 7 is naturally convected. . As shown in this figure, when the temperature is 50 ° C. or lower, even when heat is forced to convection, the heat shrinks and densifies with heat, and the dry density becomes 1.8 Mg / m ³ without taking time. A bentonite molded body 10 having a higher density is produced. On the other hand, when natural convection of heat 12 is performed, drying shrinkage occurs more favorably by drying more slowly than when forced convection is performed, and the drying density is about 2.0 Mg / m ^3, which is a higher density. The bentonite molded body 10 is manufactured.

Production of a mixture of bentonite compacts 10 having different particle diameters (bentonite compact 10) can be achieved by bagging at the stage where the plurality of bentonite compacts 10 having different particle diameters are dried. Complete. Moreover, the mixture of bentonite molded body 10 can be obtained by using various types of disk dies 6 and 7 (see FIG. 3) having different sizes of the extrusion holes 6a and 7a in the extrusion granulation step , for example, as shown in FIG. Furthermore, it is manufactured as a mixture of bentonite compact 10 having a smooth particle size distribution easily and reliably.

  And when using the mixture of the bentonite molded body 10 manufactured in this way as, for example, the backfilling material 3 when backfilling the disposal tunnel 2 of the radioactive waste embedding disposal facility A, a plurality of types having already different particle sizes are used. Since the bentonite molded body 10 is manufactured in a mixed state, there is no need for a mixing operation in which bentonite molded bodies having different particle diameters, which are individually molded as in the past, are mixed at a predetermined ratio. By simply dropping into a predetermined space by free fall, it is filled at a higher filling rate than when a bentonite molded body having a single particle size is used.

  Therefore, in the manufacturing method of the bentonite molded body 10 according to the present embodiment, the bentonite molded body 10 having a different size formed in the extrusion granulation process is simultaneously subjected to rolling granulation in the rolling granulation process, thereby reducing the particle size. Different types of bentonite compacts 10 can be produced simultaneously. This makes it possible to easily manufacture a plurality of types of bentonite compacts 10 having different particle sizes, and mix bentonite compacts having different particle sizes that are individually molded at a predetermined ratio as in the prior art. Mixing work can be eliminated. Moreover, the bentonite molded object 10 (smooth particle size distribution is formed by shape | molding many types of bentonite molded object 10 from which a magnitude | size differs by an extrusion granulation process, and carrying out rolling granulation simultaneously at a rolling granulation process. It is possible to easily and reliably produce the bentonite compact 10).

The extrusion hole 6a, a plurality of disks dies 6,7 having different sizes of 7a, thus to granulating extruded bentonite kneaded product while exchanging these disks die 6, easily and reliably particle It is possible to produce a plurality of bentonite compacts 10 having different diameters. In this case, the bentonite molded body 10 having a smooth particle size distribution can be easily and surely manufactured by using various types of disc dies 6 and 7 having different sizes of the extrusion holes 6a and 7a. It becomes possible.

Thereby, according to the manufacturing method of the bentonite molded body 10 of the present embodiment, the bentonite molded body 10 is simply dropped into a predetermined space by free fall, compared to the case of using a bentonite molded body having a single particle size. It becomes possible to fill at a high filling rate. Therefore, for example, when it is used as the backfill material 3 or the like when the disposal mine 2 of the radioactive waste burial disposal facility A is backfilled, it becomes possible to form a bentonite impermeable layer with excellent barrier performance. It is possible to reliably dispose of radioactive waste from the outside natural environment for an extremely long period of time and to make it a highly reliable waste burying facility.

As mentioned above, although one embodiment of the manufacturing method of the bentonite forming object concerning the present invention was described, the present invention is not limited to the above-mentioned one embodiment, and if it is the range which does not deviate from the meaning , that is, extrusion molding The bentonite molded body 10 is molded while exchanging a plurality of disk dies 6 and 7 having different hole diameters of the extrusion holes 6a and 7a in the graining process, and a plurality of types of bentonite molded bodies 10 having different sizes (diameters) are mixed. As long as it is molded with, it can be appropriately changed.

  Moreover, it is not necessary to limit the drying process which dries the bentonite molded object 10 shape | molded by the rolling granulation process to the method shown to this embodiment.

It is a flowchart which shows the manufacturing method of the bentonite molded object which concerns on one Embodiment of this invention. It is a diagram showing a reference example of Lud Isukudai used in extrusion granulation step of the manufacturing method of the base bentonite moldings. It is a figure which shows an example of the disk die used at the extrusion granulation process of the manufacturing method of the bentonite molded object which concerns on one Embodiment of this invention. It is a figure which shows the state which provided the bentonite molded object in the air environment which forced the convection of the heat in the drying process of the manufacturing method of the bentonite molded object which concerns on one Embodiment of this invention. It is a figure which shows the state which provided the bentonite molded object in the air environment which carried out the natural convection of the heat | fever in the drying process of the manufacturing method of the bentonite molded object which concerns on one Embodiment of this invention. It is a figure which shows an example of the time change of the moisture content of the bentonite molded object in the case of carrying out heat forced convection. It is a figure which shows an example of the time change of the moisture content of a bentonite molded object in the case of carrying out natural convection of heat. It is a figure which shows an example of the dry density of the bentonite molded object when heat is forcedly convected and when heat is naturally convected. It is a figure which shows an example of the particle size distribution of the bentonite molded object shape | molded by the extrusion granulation process of the manufacturing method of the bentonite molded object which concerns on one Embodiment of this invention. It is a perspective view which shows a waste burial disposal facility. It is a perspective view which shows the main tunnel of the waste burial disposal facility of FIG. 10, and a disposal tunnel. It is a figure which shows an example of the particle size distribution at the time of mixing the multiple types of bentonite molded object from which the particle size manufactured with the manufacturing method of the conventional bentonite molded object differs.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Main tunnel 2 Disposal tunnel 3 Backfill material 5 Disc die 5a Extrusion hole 6 Disc die 6a Extrusion hole 7 Disc die 7a Extrusion hole 8 Hot air 9 Drying furnace 10 Bentonite compact 11 Heat source 12 Heat A Waste disposal disposal facility

Claims (1)

Water is added to and mixed with the bentonite powder, and an extruded granulation step for forming a wet bentonite molded body by extrusion granulation, and the bentonite molded body formed by the extrusion granulation process by rolling granulation A rolling granulation process to form a substantially spherical shape,
In the extrusion granulation step, molded bentonite compacts having different sizes,
In the rolling granulation step, in the method for producing a bentonite molded body in which the bentonite molded bodies having different sizes are simultaneously formed into a substantially spherical shape,
In the extrusion granulation step, a bentonite molded body is formed using a disk die provided with a plurality of extrusion holes into which the bentonite kneaded product mixed with the bentonite is extruded.
A method for producing a bentonite molded body, comprising preparing a plurality of disk dies having different sizes of the extrusion holes and molding the bentonite molded bodies having different sizes while exchanging the disk dies.

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