Method for modifying bentonite, modified bentonite, modified bentonite slurry, and method for producing a high-viscosity modified bentonite slurry.

Abstract

To provide a method for modifying bentonite by which the bentonite can be modified to have such characteristics that the viscosity of the bentonite when the bentonite is formed into a slurry is sufficiently low and the slurry can be easily thickened to a much higher viscosity without using a thickener or the like, modified bentonite obtained by this modification method, a modified bentonite slurry obtained by using this modified bentonite, and a method for producing a highly viscous modified bentonite slurry.SOLUTION: A method for modifying bentonite includes subjecting a hydro-kneaded product of bentonite powder containing cristobalite as a main contaminant mineral and having a swelling power to water of 18 ml / 2 g or more to a shearing treatment and then dry-grinding.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for modifying bentonite, modified bentonite, a modified bentonite slurry, and a method for producing a highly viscous modified bentonite slurry.

Background Art

[0002] Bentonite is a clay mainly composed of montmorillonite, has very high swelling property (infinite swelling property), and exhibits excellent thickening effect. Bentonite is a natural product, mined from a mine, dried and pulverized to obtain a powdery product. Since bentonite swells and thickens in water, it is also used as a lubricant for excavation work and an excavation stabilizing fluid for hole wall stability by utilizing its characteristics.

[0003] A slurry obtained by dispersing bentonite in water is adjusted to an appropriate viscosity according to its use. As a general method for thickening a bentonite slurry, increasing the bentonite concentration in the slurry or adding a thickening agent such as carboxymethyl cellulose is known. Further, for example, Patent Document 1 describes an organophilic modified bentonite that does not require the combined use of a highly polar organic compound for a hydrocarbon solvent system, has easy dispersibility and high thickening property. Patent Document 1 describes that this modified bentonite is obtained by adding one or more alkyltrialkoxysilanes having a specific structure to bentonite in an amount within a range where the product does not lose its water dispersibility, stirring and pulverizing in an anhydrous atmosphere, and adding an alkylsilyl group partially to the surface of bentonite, and that this modified bentonite has a function of dispersing in water and adjusting the rheology of an aqueous fluid. Further, Patent Document 2 describes a modified bentonite characterized in that bentonite is treated with an aminated alkyltriethoxysilane solution and modified, and that this modified bentonite has excellent thickening property for an aqueous dispersion. Furthermore, Patent Document 3 describes a modified bentonite in which a specific calcium compound and / or magnesium compound is added and a strong mechanical shear force is applied to impart a disordered basic surface period to the montmorillonite in the bentonite, and it is stated that applying this shear force improves the viscosity when the slurry of this modified bentonite is dispersed in 4% saline solution. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 5-254823 [Patent Document 2] Japanese Patent Application Publication No. 8-198617 [Patent Document 3] Japanese Patent Application Publication No. 56-140062 [Overview of the project] [Problems that the invention aims to solve]

[0005] For example, when bentonite slurry is used as backfill for tunnel boring shield machines, the bentonite slurry is usually prepared on the surface and sent to the tip of the shield machine by pumping. Since high viscosity makes pumping difficult, it is desirable for the bentonite slurry to have low viscosity during pumping. On the other hand, high viscosity is required for backfilling, so the bentonite slurry needs to be made even more viscous at the tip of the shield machine. As mentioned above, the viscosity of bentonite slurry can be increased by adding thickeners, but from the perspective of reducing the complicated work at the mining site, there has been a need to develop a method that can easily increase the viscosity without adding thickeners.

[0006] The present invention aims to provide a method for modifying bentonite, a modified bentonite obtained by this modification method, a modified bentonite slurry using this modified bentonite, and a method for producing a high-viscosity modified bentonite slurry, which can modify bentonite to have a sufficiently low viscosity when it is made into a slurry (aqueous dispersion), and to modify the slurry to have a significantly higher viscosity without the use of thickeners or the like. [Means for solving the problem]

[0007] In view of the above problems, the inventors conducted diligent research. As a result, they found that when a hydrolyzed mixture of bentonite powder containing cristobalite as the main impurity mineral and having a swelling capacity in water above a specific value is subjected to a predetermined strong shear force and then dried and pulverized, the resulting pulverized material becomes a slurry with sufficiently low viscosity. Furthermore, they found that when the slurry is heated, its viscosity is significantly increased. In other words, they found that the slurry has low viscosity during preparation, allowing for smooth pumping and other processes, but can be sufficiently thickened by heating during use to change its properties to those suitable for backfilling and other applications. This invention was completed after further consideration based on these findings.

[0008] The above-mentioned problems of the present invention were solved by the following means. [1] A method for modifying bentonite, comprising subjecting a hydrated kneaded bentonite powder containing cristobalite as the main impurity mineral and having a water swelling capacity of 18 ml / 2 g or more to shear treatment, followed by drying and grinding. [2] The method for modifying bentonite according to [1], wherein the content of cristobalite in the impurities contained in the bentonite powder is 60% by mass or more. [3] The method for modifying bentonite according to [1] or [2] above, wherein the shearing treatment is performed by a three-roll mill. [4] The method for modifying bentonite according to any one of the above [1] to [3], wherein the modified bentonite powder obtained by the method for modifying bentonite satisfies the following (a). (a) When comparing slurries with the same bentonite concentration, the slurry obtained by dispersing the modified bentonite powder in water has lower viscosity than the slurry obtained by dispersing the bentonite powder in water. [5] The method for modifying bentonite according to [4], wherein the modified bentonite powder obtained by the method for modifying bentonite satisfies the following (b). (b) When comparing slurries with the same bentonite concentration, the slurry in which the modified bentonite powder is dispersed in water and subjected to heat treatment at 80°C for 24 hours has a higher viscosity than the slurry in which the modified bentonite powder is dispersed in water and not subjected to heat treatment. [6] The method for modifying bentonite described in [5] above, wherein the modified bentonite powder obtained by the method for modifying bentonite satisfies the following (c). (c) When comparing slurries with the same bentonite concentration, the slurry obtained by dispersing the modified bentonite powder in water and heating it at 80°C for 24 hours has a higher viscosity than the slurry obtained by dispersing the bentonite powder in water and heating it at 80°C for 24 hours. [7] Modified bentonite obtained by the method for modifying bentonite described in any of [1] to [6] above. [8] A modified bentonite slurry comprising the modified bentonite described in [7] above dispersed in an aqueous medium. [9] A method for producing a high-viscosity modified bentonite slurry, comprising the steps of: dispersing the modified bentonite described in [7] above in an aqueous medium to obtain a low-viscosity modified bentonite slurry; and heating the modified bentonite slurry to increase its viscosity.

[10] A method for producing a high-viscosity modified bentonite slurry according to [9], wherein the heating temperature is 80°C or higher.

Advantages of the Invention

[0009] According to the method for modifying bentonite of the present invention, bentonite can be modified to have characteristics such that when slurried, its viscosity is sufficiently low, and the slurry can be easily thickened to a significantly higher viscosity without using a thickening agent or the like. The modified bentonite of the present invention has a sufficiently low viscosity when slurried, and the slurry can be easily thickened to a significantly higher viscosity without using a thickening agent or the like. The modified bentonite slurry of the present invention, in one embodiment, has a sufficiently low viscosity and can be easily thickened to a significantly higher viscosity without using a thickening agent or the like. Also, in another embodiment, the modified bentonite slurry of the present invention exhibits a significantly higher viscosity compared to a normal bentonite slurry. According to the method for producing a high-viscosity modified bentonite slurry of the present invention, a bentonite slurry with a significantly higher viscosity can be easily obtained from a low-viscosity bentonite slurry without using a thickening agent or the like.

Modes for Carrying Out the Invention

[0010] Preferred embodiments of the present invention will be specifically described, but the present invention is not limited to these embodiments other than as defined in the present invention.

[0011] [Method for Modifying Bentonite] <Raw Material Bentonite Powder> The bentonite powder (raw material bentonite powder) modified by the method for modifying bentonite of the present invention (hereinafter, also referred to as "the modification method of the present invention") is a clay mainly composed of montmorillonite, which is a kind of layered silicate mineral mainly composed of silica and alumina. The raw material bentonite powder is preferably of natural origin.

[0012] Montmorillonite forms a layered structure composed of thin plate-like crystals with a thickness of about 1 nm. Between the crystals, cations such as alkali metals and alkaline earth metals generally exist in the interlayer space. In the bentonite used in the present invention, there is no particular limitation on the cations existing between the crystal layers of montmorillonite. For example, one or more bentonites selected from Na (sodium) type, Li (lithium) type, K (potassium) type, NH4 (ammonium) type, Ca (calcium) type, Mg (magnesium) type, Ba (barium) type, Al (aluminum) type, Fe (iron) type, Cu (copper) type, and Zn (zinc) type bentonites can be used. Among them, from the viewpoint of improving the swelling property of bentonite, the cation is preferably a monovalent metal ion, and more preferably lithium ion and / or sodium ion.

[0013] Also, from the viewpoint of improving the swelling property of bentonite during its water dispersion, the cation exchange capacity (CEC: Cation Exchange Capacity) of the raw bentonite powder is preferably 20 meq (milli-equivalent) / 100 g or more, more preferably 25 meq / 100 g or more, and even more preferably 30 meq / 100 g or more. Usually, the cation exchange capacity of the raw bentonite powder is 250 meq / 100 g or less.

[0014] The swelling power of the raw bentonite powder is 18 ml / 2 g or more. From the viewpoint of further promoting the thickening of the bentonite slurry by heating, the swelling power is preferably 19 ml / 2 g or more, and more preferably 20 ml / 2 g or more. The swelling power is determined in accordance with the swelling power test method (Japan Bentonite Industry Association JBAS - 104 - 77) with the measurement temperature set at 20°C. More specifically, 2.0 g of the raw bentonite powder is added in 10 portions into a stoppered graduated cylinder containing 100 mL of purified water so that the raw bentonite powder smoothly settles to the bottom of the cylinder. Then, when left standing at 20°C for 24 hours, the apparent volume of the raw bentonite powder deposited in the purified water is read to determine the above-mentioned swelling power.

[0015] The raw material bentonite powder, excluding the main component montmorillonite, contains associated minerals (interfering minerals) such as cristobalite, quartz, feldspar, zeolite, calcite, and mica. In the raw material bentonite powder used in the present invention, the main interfering mineral among the aforementioned interfering minerals is cristobalite. In this invention and specification, "main interfering mineral" means the interfering mineral with the highest content among the aforementioned interfering minerals. The type of the aforementioned interfering mineral can be identified according to conventional methods. Cristobalite is a type of crystalline polymorph of silicon dioxide (silica), also known as cristobalite. The cristobalite contained in the raw material bentonite powder is usually low-temperature cristobalite.

[0016] In the impurities of the raw bentonite powder, the content of cristobalite is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. Furthermore, this content may be 100% by mass, 99% by mass or less, 90% by mass or less, or 80% by mass or less. A preferred range for this content is 50 to 100% by mass, more preferably 60 to 100% by mass, and even more preferably 70 to 100% by mass. Furthermore, the cristobalite content in the raw bentonite powder is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more. The cristobalite content is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less. The preferred range for this content is 10 to 40% by mass, more preferably 15 to 35% by mass, and even more preferably 20 to 30% by mass.

[0017] From the viewpoint of suppressing gelation in the bentonite slurry, the raw material bentonite powder is preferably dispersed in distilled water at a concentration of 7.4% by mass, and the conductivity of the slurry (at 20°C) is preferably 2000 μS / cm or less, more preferably 1600 μS / cm or less, and even more preferably 1200 μS / cm or less.

[0018] <Method of modification> In the modification method of the present invention, raw material bentonite powder is mixed with water to obtain a hydrated mixture, this hydrated mixture is subjected to a shearing treatment, and then dried and pulverized. This makes it possible to obtain the desired modified bentonite. In the aforementioned hydration and kneading process, it is preferable to mix 10 to 30 parts by mass of water with 100 parts by mass of the raw bentonite powder, and more preferably 10 to 20 parts by mass of water. The kneader used for hydration and kneading is not particularly limited, and a general-purpose kneader can be widely used. The shearing process described above is not particularly limited as long as a desired shearing force can be applied. For example, a twin-screw extruder or a shearing machine (preferably a three-roll mill) that can forcibly pass the water-mixed material between two or more rolls can be used. In the latter, the shearing force can be controlled by adjusting the distance (clearance) between the rolls. Examples of equipment that can be used for the shearing process include the three-roll mill manufactured by Ashizawa Finetech, the BR-300HCV III manufactured by AIMEX, the HHCtype THREE ROLL MILL manufactured by Inoue Seisakusho, the Three-roll mill Trinomic manufactured by Bühler, and the NR-120A manufactured by Noritake. The aforementioned shearing process can be repeated multiple times to apply sufficient shear force.

[0019] The bentonite, after the shearing treatment, is then processed into a powder by drying and grinding. The drying temperature is preferably 80-120°C, and more preferably 100-110°C. The drying time can be appropriately set depending on the amount of bentonite and the drying temperature, and can be 2-48 hours, 2-24 hours, or 2-12 hours. By crushing the dried material obtained through the drying process using a pulverizer, powdered modified bentonite can be obtained. Furthermore, the above-described drying and grinding process may be carried out simultaneously (grinding while drying).

[0020] <Properties of Modified Bentonite>

[0021] When comparing slurries with the same bentonite concentration, a slurry obtained by dispersing modified bentonite powder in water using the modification method of the present invention can have a lower viscosity than a slurry obtained by dispersing the aforementioned bentonite powder in water.

[0022] The modified bentonite slurry obtained by the modification method of the present invention has low viscosity, but its viscosity can be significantly increased by heating. Specifically, when comparing slurries with the same bentonite concentration, the slurry obtained by dispersing the modified bentonite powder in water and subjecting it to a heat treatment at 80°C for 24 hours has higher viscosity than the slurry obtained by dispersing the modified bentonite powder in water and subjecting it to a heat treatment. Furthermore, for example, when comparing slurries with the same bentonite concentration, the slurry obtained by dispersing the modified bentonite powder obtained by the modification method of the present invention in water and subjecting it to a heat treatment at 80°C for 24 hours can have a higher viscosity than the slurry obtained by dispersing the raw bentonite powder in water and subjecting it to a heat treatment at 80°C for 24 hours. For example, in an aqueous dispersion with a bentonite powder concentration of 7.4% by mass, the relationship between the funnel viscosity (I) of the slurry obtained by dispersing the modified bentonite powder obtained by the modification method of the present invention in water and subjecting it to a heat treatment at 80°C for 24 hours and the viscosity (II) of the slurry obtained by dispersing the raw bentonite powder in water and subjecting it to a heat treatment at 80°C for 24 hours is preferably such that viscosity (I) - viscosity (II) (value obtained by subtracting viscosity (II) from viscosity (I)) is 10 to 40 seconds (s), and more preferably 20 to 40 seconds. In the present invention, "funnel viscosity" is a value measured with a slurry temperature of 20°C.

[0023] The reason why the modified bentonite slurry of the present invention can be made low viscosity and further thickened by heating is not clear, but it is presumed to be achieved by the following mechanism. Quartz, one of the impurities that can be found in bentonite, is generally a mineral with large grain size and high hardness. Therefore, when a hydrated kneaded bentonite mixture containing a large amount of quartz as an impurity (with quartz being the main impurity) is subjected to shearing treatment, the quartz destroys the layered structure of montmorillonite itself, reducing the viscosity of the slurry. In this case, even if the slurry is subjected to heat treatment after shearing, the layered structure of montmorillonite does not recover, and the thickening of the slurry is limited. In contrast, cristobalite, a type of impurity mineral, has a small grain size and lower hardness compared to quartz. Therefore, even if a hydrolyzed bentonite mixture containing a large amount of cristobalite as an impurity mineral (where cristobalite is the main impurity mineral) is subjected to shearing treatment, it is thought that it will not destroy the layered structure of montmorillonite, or if it does, the degree of destruction will be considerably less than that of the above-mentioned mixture where quartz is the main impurity mineral. On the other hand, cristobalite is thought to have the effect of binding the montmorillonite layers together like glue, and this is thought to be one of the reasons why the viscosity of the modified bentonite slurry decreases. On the other hand, when such a slurry is heated, the binding effect of cristobalite disappears, and the delamination between the montmorillonite layers is further promoted. In other words, it is thought that heating can significantly increase the viscosity of the modified bentonite slurry.

[0024] [Modified Bentonite] The modified bentonite of the present invention is bentonite obtained through the modification method of the present invention. Therefore, it is bentonite obtained by subjecting a hydrated kneaded mixture of bentonite powder containing cristobalite as the main impurity mineral and having a swelling capacity in water of 18 ml / 2 g or more to shear treatment, followed by drying and pulverization.

[0025] [Modified bentonite slurry] The modified bentonite slurry of the present invention is a slurry obtained by dispersing the modified bentonite of the present invention in an aqueous medium. As described above, this slurry can have a desired low viscosity when not subjected to heat treatment (for example, not exposed to temperatures above 50°C). Furthermore, by heating this low-viscosity slurry, it can be increased to a desired high viscosity. Therefore, the modified bentonite slurry of the present invention can have either a low viscosity or a high viscosity depending on the purpose.

[0026] Examples of the aqueous medium include water, and may also include a water-soluble medium that is miscible with water. Examples of water-soluble mediums include alcohols, polyhydric alcohols, ethers, etc. When the aqueous medium contains a water-soluble medium along with water, the water content in the aqueous medium is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more.

[0027] The aforementioned heat treatment for thickening is not particularly limited as long as it can achieve the desired high viscosity of the bentonite slurry. For example, the slurry can be left to stand in a constant temperature oven or dryer, or it can be heated by irradiating it with microwaves while it is flowing. The heating temperature is preferably 70°C or higher, more preferably 80°C or higher, and even more preferably 90°C or higher. Furthermore, from the viewpoint of suppressing deterioration of bentonite due to excessive heating and from the viewpoint of the performance of the heating device, the heating temperature is preferably 120°C or lower, more preferably 110°C or lower, and even more preferably 105°C or lower. The heating time is not particularly limited and can be set appropriately depending on the bentonite content in the slurry. For example, it can be 12 to 24 hours, 1 to 12 hours, or 0.2 to 6 hours.

[0028] The bentonite concentration in the modified bentonite slurry of the present invention is not particularly limited. For example, it can be 8 to 20% by mass, or 2 to 8% by mass.

[0029] [Method for producing a high-viscosity modified bentonite slurry] The present invention provides a method for producing a high-viscosity modified bentonite slurry, comprising the steps of: dispersing the modified bentonite of the present invention in an aqueous medium to obtain a low-viscosity modified bentonite slurry; and heating the modified bentonite slurry to increase its viscosity. The details of each step are as described above. [Examples]

[0030] The present invention will be described in more detail below based on examples, but the present invention is not limited thereto.

[0031] [Raw material: Bentonite powder] The physical properties of the bentonite powder used to prepare each bentonite slurry are shown in Table 1 below. The physical properties of each bentonite powder were measured using the methods described below.

[0032] (moisture content) After measuring the mass of bentonite powders A to F, they were dried in a constant temperature incubator set to 105°C for 24 hours. The moisture content (mass%) of bentonite A to F was then measured again by measuring the mass of the dried bentonite A to F.

[0033] (swelling power) The swelling force of bentonite powders A to F at a temperature of 20°C was measured in accordance with the swelling force test method described above (Japan Bentonite Industry Association JBAS-104-77).

[0034] (pH) 2g each of bentonite powders A through F was added to 100ml of distilled water and stirred to form an aqueous dispersion. The pH of this aqueous dispersion was then measured using a personal pH meter (model number: SPH71, manufactured by Sansho Co., Ltd.).

[0035] (conductivity) 2g each of bentonite powders A through F was added to 100ml of distilled water and stirred to form an aqueous dispersion. The conductivity of this aqueous dispersion was measured using an electrical conductivity meter (model: ES-51, manufactured by Horiba, Ltd.).

[0036] (Amount of methylene blue adsorbed) Utilizing the property that methylene blue specifically adsorbs between clay (montmorillonite) layers, the amount of methylene blue adsorbed onto bentonite powders A to F was measured. The amount of methylene blue adsorbed by montmorillonite was measured according to the JBAS-107-77 method (filter paper method), a standard of the Japan Bentonite Industry Association. Bentonite powders A to F were dried at 105°C for 2 hours and then pulverized. The amount of methylene blue adsorbed (unit: mmol / 100g) was measured for each of the resulting dried powders.

[0037] (Identification of contaminating minerals) The types and content of impurities in the bentonite powders A to F were determined by measuring the diffraction spectrum using X-ray diffraction with the bentonite powder to identify the type of mineral, determining the peak intensity of each mineral from the obtained diffraction spectrum, and then determining the content using a calibration curve prepared separately.

[0038] [Table 1]

[0039] [Experimental Example 1] 15 parts by mass of water were added to 100 parts by mass of bentonite powder A, and the mixture was kneaded for 3 minutes in an Eirich intensive mixer (model: R02, manufactured by Nippon Eirich Co., Ltd.). The resulting hydrated mixture was then subjected to shearing force in a three-roll mill (manufactured by Ashizawa Finetech Co., Ltd.), and this shearing process was repeated a total of 5 times. In the three-roll mill, the distance between the first roll (loading roll) and the second roll (intermediate roll) was set to approximately 1 mm. The mixture after the shearing process was placed in a constant temperature oven set to 105°C and dried until the moisture content was approximately 8% by mass. The dried material was then pulverized in a hammer mill (manufactured by Fuji Powder Co., Ltd.) to obtain a bentonite powder sample (modified bentonite powder). 48 g of the powder sample obtained above was added to 600 ml of distilled water and stirred for 15 minutes in a Hamilton Beach mixer to obtain a modified bentonite slurry. The funnel viscosity (FV (seconds: s)) of the slurry at 20°C was measured using a funnel viscometer (manufactured by Nishinihon Shikiki Co., Ltd.).

[0040] The modified bentonite slurry, whose funnel viscosity was measured, was allowed to stand overnight at room temperature (20°C) (without heating). After standing, the slurry was stirred again in a Hamilton Beach mixer for 5 minutes, and the funnel viscosity was measured in the same manner as above. The pH and conductivity of the slurry after stirring were also measured in the same manner as above. The results are shown in Table 2 below.

[0041] [Experimental Example 2] A modified bentonite slurry was obtained from the powder sample in the same manner as in Experimental Example 1. This modified bentonite slurry was placed in a plastic bottle, sealed, and left to stand overnight in an 80°C constant temperature bath. After standing, the slurry was stirred again for 5 minutes in a Hamilton Beach mixer, and the funnel viscosity, pH, and conductivity were measured in the same manner as above. The results are shown in Table 2 below.

[0042] [Reference example 1-1] 48 g of bentonite powder A was added to 600 ml of distilled water and stirred in a Hamilton-Beach mixer for 15 minutes to obtain a bentonite slurry. The funnel viscosity of this slurry was measured in the same manner as above. The slurry whose funnel viscosity was measured was allowed to stand overnight at room temperature. After standing, the slurry was stirred again in a Hamilton-Beach mixer for 5 minutes, and the funnel viscosity, pH, and conductivity were measured in the same manner as above. The results are shown in Table 2 below.

[0043] [Reference example 1-2] 48 g of bentonite powder A was added to 600 ml of distilled water and stirred in a Hamilton-Beach mixer for 15 minutes to obtain a bentonite slurry. The funnel viscosity of this slurry was measured in the same manner as above. The slurry with the measured funnel viscosity was placed in a plastic bottle, sealed, and left to stand overnight in an 80°C constant temperature bath. After standing, the slurry was stirred again in a Hamilton-Beach mixer for 5 minutes, and the funnel viscosity, pH, and conductivity were measured in the same manner as above. The results are shown in Table 2 below.

[0044] [Reference example 1-3] 15 parts by mass of water were added to 100 parts by mass of bentonite powder A, and the mixture was kneaded for 3 minutes in an Eirich intensive mixer (model: R02, manufactured by Eirich Japan). The resulting hydrated mixture was then placed in a constant temperature oven set to 105°C and dried until the moisture content was approximately 8% by mass. The dried material was then pulverized in a hammer mill (manufactured by Fuji Powder Co., Ltd.) to obtain a powder sample. 48 g of the powder sample obtained above was added to 600 ml of distilled water and stirred for 15 minutes in a Hamilton Beach mixer to obtain a bentonite slurry. The funnel viscosity of this slurry was measured in the same manner as above. The results are shown in Table 2 below.

[0045] [Table 2]

[0046] In Experimental Examples 1 and 2, the modified bentonite slurry, by using modified bentonite powder that had been pre-sheared using a three-roll mill, showed a significantly lower funnel viscosity after slurry preparation (before heating) compared to the bentonite slurries in Reference Examples 1-1 and 1-2, which used unmodified bentonite powder that had not been pre-sheared using a three-roll mill. Furthermore, as shown in the results of Experimental Example 1, even after leaving the modified bentonite slurry at room temperature overnight, the funnel viscosity remained low compared to Reference Example 1-1, in which the slurry of unmodified bentonite powder, without the application of shear force by a three-roll mill, was left at room temperature overnight. On the other hand, as shown in the results of Experimental Example 2, allowing the modified bentonite slurry to stand overnight under heating conditions resulted in a significant increase in funnel viscosity compared to Reference Examples 1-2, in which the slurry of unmodified bentonite powder, without the application of shear force by a three-roll mill, was allowed to stand overnight under heating conditions.

[0047] Furthermore, in the unmodified bentonite powder slurry of Reference Examples 1-3, where no shear force was applied by a three-roll mill after the raw bentonite powder was mixed with water, no decrease in funnel viscosity was observed; rather, the viscosity tended to increase.

[0048] [Experimental Example 3] 48 g of the modified bentonite powder obtained in Experimental Example 1 was added to 600 ml of distilled water, and the mixture was stirred for 15 minutes in a Hamilton Beach mixer to obtain a modified bentonite slurry. The viscosity of this slurry at 20°C was measured using a Brookfield-type (Type B) viscometer (model number: B8M, manufactured by Tokyo Keiki Co., Ltd., spindle size: rotor No. 3, No. 4). Rotor No. 3 or No. 4 was selected according to the viscosity of the sample, and the viscosity at 60 rpm and 6 rpm was measured using the selected rotor. Furthermore, the slurry was left to stand overnight at room temperature, and after standing, the slurry was stirred again for 5 minutes in a Hamilton Beach mixer. The viscosity was then measured using a Type B viscometer in the same manner as described above. The results are shown in Table 3 below.

[0049] [Experimental Example 4] 200g of the slurry (slurry before overnight standing) whose viscosity was measured using a B-type viscometer in Experimental Example 3 was sent to a microwave reactor once and heated under the following microwave heating conditions. After that, the viscosity was measured using a B-type viscometer in the same manner as in Experimental Example 3. The results are shown in Table 3 below. -Microwave heating conditions- Equipment: Microwave reactor MR-2G-100, manufactured by Linghe Electronics Co., Ltd. Heating power: 42W Sample temperature: Approximately 87°C Teflon (registered trademark) tube diameter: φ1mm Fluid delivery rate: 7g / min

[0050] [Reference example 2-1] In Reference Example 1-1, viscosity was measured using a B-type viscometer instead of funnel viscosity measurement. The results are shown in Table 3 below.

[0051] [Reference example 2-2] The heat treatment was carried out in the same manner as in Experimental Example 4 above, and the viscosity was measured using a B-type viscometer instead of measuring the viscosity with a funnel, except that the procedure was the same as in Reference Example 1-2. The results are shown in Table 3 below.

[0052] [Table 3]

[0053] The modified bentonite slurries in Experimental Examples 3 and 4, which used modified bentonite powder that had been pre-sheared using a three-roll mill, showed a significantly lower viscosity after slurry preparation (before heating) compared to the unmodified bentonite powder slurries in Reference Examples 2-1 and 2-2, which did not have shearing applied using a three-roll mill. Furthermore, as shown in the results of Experimental Example 3, even after leaving the bentonite aqueous dispersion at room temperature overnight, the viscosity remained lower compared to Reference Example 2-1, in which a slurry of unmodified bentonite powder, without the application of shear force by a three-roll mill, was left at room temperature overnight. On the other hand, as shown in the results of Experimental Example 4, the viscosity of the modified bentonite slurry increased significantly when heated to a sample temperature of 87°C by microwave irradiation, compared to Reference Example 2-2, in which a slurry of unmodified bentonite powder without shear force applied by a three-roll mill was heated to a sample temperature of 87°C by microwave irradiation.

[0054] [Experimental Example 5] A modified bentonite slurry was obtained in the same manner as in Experimental Example 1, except that bentonite powder B was used instead of bentonite powder A as the raw material. The funnel viscosity, pH, and conductivity of this slurry were measured in the same manner as above. The results are shown in Table 4 below.

[0055] [Experimental Example 6] A modified bentonite slurry was obtained in the same manner as in Experimental Example 1, except that bentonite powder B was used instead of bentonite powder A as the raw material bentonite powder. This slurry was heat-treated in the same manner as in Experimental Example 2, and the funnel viscosity, pH, and conductivity were measured in the same manner as above. The results are shown in Table 4 below.

[0056] [Reference example 3-1] A bentonite slurry was obtained in the same manner as in Reference Example 1-1, except that bentonite powder B was used instead of bentonite powder A as the raw material. The funnel viscosity, pH, and conductivity of this slurry were measured in the same manner as above. The results are shown in Table 4 below.

[0057] [Reference example 3-2] A bentonite slurry was obtained in the same manner as in Reference Example 1-1, except that bentonite B was used instead of bentonite powder A as the raw material bentonite powder. This slurry was heat-treated in the same manner as in Reference Example 1-2, and the funnel viscosity, pH, and conductivity were measured in the same manner as above. The results are shown in Table 4 below.

[0058] [Table 4]

[0059] Similar to the case where bentonite powder A was used as the raw material, using bentonite powder B, which has cristobalite as the main contaminating mineral, yielded the same results as in Experimental Examples 1, 2, Reference Examples 1-1, and 1-2, which used bentonite powder A. Specifically, in Experimental Examples 5 and 6, using modified bentonite powder that had been pre-sheared by a three-roll mill resulted in a lower funnel viscosity of the slurry. After being left to stand overnight at a temperature of 80°C, the funnel viscosity was significantly increased, as shown in the results of Experimental Example 6.

[0060] [Comparative Example 4-1] A bentonite slurry was obtained in the same manner as in Experimental Example 1, except that bentonite powder C was used instead of bentonite powder A as the raw material. The funnel viscosity, pH, and conductivity of this slurry were measured in the same manner as above. The results are shown in Table 5 below.

[0061] [Comparative Example 4-2] A bentonite slurry was obtained in the same manner as in Experimental Example 1, except that bentonite powder C was used instead of bentonite powder A as the raw material. This slurry was heat-treated in the same manner as in Experimental Example 2, and the funnel viscosity, pH, and conductivity were measured in the same manner as above. The results are shown in Table 5 below.

[0062] [Reference example 4-1] A bentonite slurry was obtained in the same manner as in Reference Example 1-1, except that bentonite powder C was used instead of bentonite powder A as the raw material. The funnel viscosity, pH, and conductivity of this slurry were measured in the same manner as above. The results are shown in Table 5 below.

[0063] [Reference example 4-2] A bentonite slurry was obtained in the same manner as in Reference Example 1-1, except that bentonite powder C was used instead of bentonite powder A as the raw material bentonite powder. This slurry was heat-treated in the same manner as in Reference Example 1-2, and the funnel viscosity, pH, and conductivity were measured in the same manner as above. The results are shown in Table 5 below.

[0064] [Comparative Example 4-3] A bentonite slurry was obtained in the same manner as in Experimental Example 1, except that bentonite powder D was used instead of bentonite powder A as the raw material. The funnel viscosity, pH, and conductivity of this slurry were measured in the same manner as above. The results are shown in Table 5 below.

[0065] [Comparative Example 4-4] A bentonite slurry was obtained in the same manner as in Experimental Example 1, except that bentonite powder D was used instead of bentonite powder A as the raw material. This slurry was heat-treated in the same manner as in Experimental Example 2, and the funnel viscosity, pH, and conductivity were measured in the same manner as above. The results are shown in Table 5 below.

[0066] [Reference example 4-3] A bentonite slurry was obtained in the same manner as in Reference Example 1-1, except that bentonite powder D was used instead of bentonite powder A as the raw material. The funnel viscosity, pH, and conductivity of this slurry were measured in the same manner as above. The results are shown in Table 5 below.

[0067] [Reference example 4-4] A bentonite slurry was obtained in the same manner as in Reference Example 1-1, except that bentonite powder D was used instead of bentonite powder A as the raw material. This slurry was heat-treated in the same manner as in Reference Example 1-2, and the funnel viscosity, pH, and conductivity were measured in the same manner as above. The results are shown in Table 5 below.

[0068] [Comparative Example 4-5] A bentonite slurry was obtained in the same manner as in Experimental Example 1, except that bentonite powder E was used instead of bentonite powder A as the raw material. The funnel viscosity, pH, and conductivity of this slurry were measured in the same manner as above. The results are shown in Table 5 below.

[0069] [Comparative Examples 4-6] A bentonite slurry was obtained in the same manner as in Experimental Example 1, except that bentonite powder E was used instead of bentonite powder A as the raw material. This slurry was heat-treated in the same manner as in Experimental Example 2, and the funnel viscosity, pH, and conductivity were measured in the same manner as above. The results are shown in Table 5 below.

[0070] [Reference example 4-5] A bentonite slurry was obtained in the same manner as in Reference Example 1-1, except that bentonite powder E was used instead of bentonite powder A as the raw material. The funnel viscosity, pH, and conductivity of this slurry were measured in the same manner as above. The results are shown in Table 5 below.

[0071] [Reference example 4-6] A bentonite slurry was obtained in the same manner as in Reference Example 1-1, except that bentonite powder E was used instead of bentonite powder A as the raw material. This slurry was heat-treated in the same manner as in Reference Example 1-2, and the funnel viscosity, pH, and conductivity were measured in the same manner as above. The results are shown in Table 5 below.

[0072] [Table 5]

[0073] When bentonite powders containing quartz as the main contaminating mineral (bentonite powder C, bentonite powder D, bentonite powder E) were used as raw material bentonite powders and subjected to modification treatment to prepare bentonite slurries for Comparative Examples 4-1 to 4-6, the funnel viscosity of these slurries was lower than that of Reference Examples 4-1 to 4-6. On the other hand, even when the bentonite slurries of Comparative Examples 4-2, 4-4, and 4-6 were left to stand overnight under a temperature of 80°C, the funnel viscosity was not increased compared to Reference Examples 4-2, 4-4, and 4-6.

[0074] [Comparative Example 5-1] A bentonite slurry was obtained in the same manner as in Experimental Example 1, except that bentonite powder F was used instead of bentonite powder A as the raw material. The funnel viscosity, pH, and conductivity of this slurry were measured. The results are shown in Table 6 below.

[0075] [Comparative Example 5-2] A bentonite slurry was obtained in the same manner as in Experimental Example 1, except that bentonite powder F was used instead of bentonite powder A as the raw material. This slurry was heat-treated in the same manner as in Experimental Example 2, and the funnel viscosity, pH, and conductivity were measured in the same manner as above. The results are shown in Table 6 below.

[0076] [Reference example 5-1] A bentonite slurry was obtained in the same manner as in Reference Example 1-1, except that bentonite powder F was used instead of bentonite powder A as the raw material bentonite powder. The funnel viscosity, pH, and conductivity of this slurry were measured in the same manner as above. The results are shown in Table 6 below.

[0077] [Reference example 5-2] A bentonite slurry was obtained in the same manner as in Reference Example 1-1, except that bentonite powder F was used instead of bentonite powder A as the raw material bentonite powder. This slurry was heat-treated in the same manner as in Reference Example 1-2, and the funnel viscosity, pH, and conductivity were measured in the same manner as above. The results are shown in Table 6 below.

[0078] [Table 6]

[0079] Bentonite powder F, which contains cristobalite as the main impurity mineral and has a swelling capacity of 17 ml / 2 g, was used as the raw material bentonite powder. When this was modified, bentonite slurries of Comparative Examples 5-1 and 5-2 were prepared. It was found that these slurries actually increased in funnel viscosity compared to the bentonite slurries of Reference Examples 5-1 and 5-2. Furthermore, when the bentonite slurries of Comparative Examples 5-1 and 5-2 were left to stand overnight at room temperature or at 80°C, the viscosity only increased slightly.

Claims

1. A method for modifying bentonite, comprising subjecting a hydrated kneaded bentonite powder, in which the cristobalite content in the impurities is 50% by mass or more and the swelling capacity in water is 18 ml / 2 g or more, to shear treatment, and then drying and grinding.

2. The method for modifying bentonite according to claim 1, wherein the content of cristobalite in the impurities contained in the bentonite powder is 60% by mass or more.

3. The method for modifying bentonite according to claim 2, wherein the shearing treatment is performed by a three-roll mill.

4. The method for modifying bentonite according to claim 3, wherein the modified bentonite powder obtained by the method for modifying bentonite satisfies the following (a). (a) When comparing slurries with the same bentonite concentration, the slurry obtained by dispersing the modified bentonite powder in water has lower viscosity than the slurry obtained by dispersing the bentonite powder in water.

5. The method for modifying bentonite according to claim 4, wherein the modified bentonite powder obtained by the method for modifying bentonite satisfies the following (b). (b) When comparing slurries with the same bentonite concentration, the slurry in which the modified bentonite powder is dispersed in water and subjected to heat treatment at 80°C for 24 hours has a higher viscosity than the slurry in which the modified bentonite powder is dispersed in water and subjected to heat treatment.

6. The method for modifying bentonite according to claim 5, wherein the modified bentonite powder obtained by the method for modifying bentonite satisfies the following (c). (c) When comparing slurries with the same bentonite concentration, the slurry obtained by dispersing the modified bentonite powder in water and heating it at 80°C for 24 hours has a higher viscosity than the slurry obtained by dispersing the bentonite powder in water and heating it at 80°C for 24 hours.

7. A method for producing modified bentonite, comprising subjecting a hydrated kneaded bentonite powder having a cristobalite content of 50% by mass in the impurities and a swelling capacity in water of 18 ml / 2 g or more to shear treatment, and then drying and grinding the mixture to obtain modified bentonite.

8. A method for producing a modified bentonite slurry, comprising obtaining modified bentonite by the method for producing modified bentonite described in claim 7, and dispersing the modified bentonite in an aqueous medium.

9. A method for producing a high-viscosity modified bentonite slurry, comprising the steps of: obtaining modified bentonite by the method for producing modified bentonite described in claim 7; dispersing the modified bentonite in an aqueous medium to obtain a low-viscosity modified bentonite slurry; and heating the modified bentonite slurry to increase its viscosity.

10. A method for producing a high-viscosity modified bentonite slurry according to claim 9, wherein the heating temperature is 80°C or higher.

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