Potassium-type or ammonium-type smectite slurry and method for producing the same, and dehydrated cake

Abstract

To provide K-type or NH4-type smectite slurry excellent in dispersion stability and a method of producing the same, and dehydrated cake suitable for preparing K-type or NH4-type smectite slurry.SOLUTION: The method of producing K-type or NH4-type smectite slurry includes steps of mixing Na-type smectite and a potassium salt or an ammonium salt, and water to subject the Na-type smectite to cation exchange, subsequently removing the salt, dehydrating the slurry to obtain dehydrated cake, and mixing the dehydrated cake and water to obtain K-type or NH4-type smectite slurry.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a K-type or NH4-type smectite slurry, a method for producing the same, and a dewatered cake.

Background Art

[0002] Smectite, which is a clay mineral, is an aluminosilicate layer (hereinafter also referred to as "crystalline layer"), which is a crystalline layered compound of silicate and aluminate constituting smectite. It is known that water molecules intercalate into the gap (bottom surface gap) between the bottom surfaces of the crystalline layers, and the bottom surface gap expands to exhibit swelling properties. In particular, Na-type smectite, in which the interlayer cation (exchangeable cation) of smectite is Na (sodium) ion, has a relatively weak electric attraction between the crystalline layers due to the presence of Na ions. When Na-type smectite is dispersed in water, water molecules successively intercalate between the crystalline layers, showing osmotic swelling in which the bottom surface gap of the crystalline layer expands to 4 nm or more, and further interlayer peeling occurs and infinite swelling occurs. On the other hand, for example, smectite having a monovalent cation such as K (potassium) ion or NH4 (ammonium) ion, or a divalent cation such as Ca (calcium) ion or Mg (magnesium) ion as an interlayer cation shows crystalline swelling, which is limited microscopic swelling with a bottom surface interval of less than 4 nm, in which the intercalation of water molecules into the bottom surface gap is limited. It is considered that whether smectite exhibits osmotic swelling or crystalline swelling is determined by the valence and ionic radius of the interlayer cation. The smaller the valence of the ion and the smaller the ionic radius, the easier it is to exhibit osmotic swelling.

[0003] Smectite is known to exhibit various properties depending on the type of intercalation cation it contains. By performing cation exchange using naturally occurring Na-type smectite as a raw material, various types of smectite with intercalation cations other than Na ions can be obtained. Methods for cation exchange include adding Na-type smectite to an aqueous solution of a salt containing the target cation and stirring, or passing a dispersion of Na-type smectite through a column packed with a resin for exchanging the target cation. The cation-exchanged smectite is then dried and pulverized and stored in powder form. On the other hand, smectite that is not Na-type generally has poor water swelling properties or dispersion stability, limiting its applications. Therefore, technologies to improve the water swelling properties or dispersion stability of smectite with intercalation cations other than Na ions are being investigated. For example, Patent Document 1 discloses a dried clay powder in which 70-99 mol% of the interlayer cations are hydrogen ions and the secondary particles are in a rosette shape. It has been shown that secondary particles of clay obtained by drying clay in which the interlayer cations have been replaced with hydrogen ions using a specific method are uniformly finely dispersed in water or a hydrophilic solvent, and also thicken and swell. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2013-112568 [Overview of the project] [Problems that the invention aims to solve]

[0005] The present invention aims to provide a K-type or NH4-type smectite slurry with excellent dispersion stability and a method for producing the same. Furthermore, the present invention aims to provide a dehydrated cake suitable for preparing the aforementioned K-type or NH4-type smectite slurry. [Means for solving the problem]

[0006] The inventors of this invention conducted thorough research in view of the above problems. As a result, they discovered that a dehydrated cake obtained by replacing the interlayer cations of Na-type smectite with K-ions or NH4-ions by cation exchange, then removing the salt and dehydrating it, can be mixed with water to form a slurry with excellent smectite dispersion stability, even though it is a dehydrated cake of K-type or NH4-type smectite. The present invention was completed based on these findings and further research.

[0007] The above-mentioned problems of the present invention were solved by the following means. [1] A method for producing a K-type or NH4-type smectite slurry, comprising mixing Na-type smectite with a potassium salt or ammonium salt and water, subjecting the Na-type smectite to cation exchange, then removing the salt and dehydrating to obtain a dehydrated cake, and mixing this dehydrated cake with water to obtain a K-type or NH4-type smectite slurry. [2] A method for producing a K-type or NH4-type smectite slurry according to [1], wherein the water content of the dehydrated cake is 70 to 85% by mass. [3] A method for producing a K-type or NH4-type smectite slurry according to [1] or [2], wherein the average particle size of the smectite contained in the dehydrated cake is 1000 nm or less. [4] A dehydrated cake of K-type or NH4-type smectite obtained by mixing Na-type smectite, a potassium salt or ammonium salt, and water, subjecting the Na-type smectite to cation exchange, then removing the salt and dehydrating, and which is used to obtain a K-type or NH4-type smectite slurry when mixed with water. [5] The dehydrated cake according to [4], wherein the moisture content of the dehydrated cake is 70 to 85% by mass. [6] The dehydrated cake according to [4] or [5], wherein the average particle size of the smectite contained in the dehydrated cake is 1000 nm or less. [7] A K-type or NH4-type smectite slurry obtained by mixing the dehydrated cake described in any of [4] to [6] above with water. [Effects of the Invention]

[0008] The K-type or NH4-type smectite slurry of the present invention exhibits excellent dispersion stability. Furthermore, the method for producing the K-type or NH4-type smectite slurry of the present invention makes it possible to obtain a slurry with excellent dispersion stability of K-type or NH4-type smectite. In addition, by mixing the dewatered cake of the present invention with water, a slurry in which K-type or NH4-type smectite is stably dispersed in water can be obtained. [Brief explanation of the drawing]

[0009] [Figure 1] This graph shows the X-ray diffraction results of various smectite slurries. [Modes for carrying out the invention]

[0010] Preferred embodiments of the present invention will be described in detail, but the present invention is not limited to these forms other than those specified herein.

[0011] [Method for producing K-type or NH4-type smectite slurry] In the method for producing K-type or NH4-type smectite slurry of the present invention (hereinafter also referred to as "the method of production of the present invention"), a dehydrated cake containing K-type or NH4-type smectite is first produced (hereinafter, this method of producing the dehydrated cake is also referred to as "the method of producing the dehydrated cake of the present invention").

[0012] <Method for manufacturing dehydrated cake> The present invention provides a method for producing a dehydrated cake, comprising a cation exchange step in which interlayer cations of Na-type smectite are exchanged for K-type or NH4-type ions, a desalting step in which salt is removed after cation exchange, and a dehydration step in which water is removed after desalting. The dehydrated cake obtained in the dehydration step can then be mixed with water to obtain a K-type or NH4-type smectite slurry with excellent dispersion stability. We will explain each step in detail.

[0013] (Cation exchange process) In the manufacturing method of the present invention, the cation exchange step is a step of mixing Na-type smectite, potassium salt or ammonium salt, and water as described above, and ion-exchanging the Na ions, which are interlayer cations of Na-type smectite, for K ions or NH4 ions to obtain K-type smectite or NH4-type smectite in the mixture. In the cation exchange step, "mixing Na-type smectite, potassium salt or ammonium salt, and water" means that at least Na-type smectite, potassium salt or ammonium salt, and water are mixed, and the mixing order is not particularly limited. That is, they may be mixed independently, or one of them may be mixed beforehand. For example, potassium salt or ammonium salt may be mixed into a Na-type smectite aqueous dispersion in which Na-type smectite is dispersed in water beforehand, or Na-type smectite may be mixed into an aqueous solution in which potassium salt or ammonium salt is dissolved in water beforehand, or the Na-type smectite aqueous dispersion and the aqueous solution may be mixed. Hereinafter, smectite obtained by ion-exchanging the interlayer cations of Na-type smectite for a target cation (a cation other than Na ions) will also be referred to as "cation-exchange smectite."

[0014] It is preferable to allow cation exchange to occur in a mixture of Na-type smectite, potassium salt or ammonium salt, and water while stirring. Furthermore, from the viewpoint of improving cation exchange efficiency, the stirring time is preferably 1 to 24 hours. Furthermore, from the perspective of further improving the cation exchange efficiency, it is preferable to concentrate or dehydrate the mixed solution after the stirring, and then mix the concentrated or dehydrated smectite with the water and the salt (or the aqueous solution), and stir again to mix them. For example, it is preferable to mix the Na-type smectite, the potassium salt or ammonium salt, and water two or more times, and more preferably three or more times. In addition, the conditions for concentration or dehydration can be the conditions usually used in the cation exchange process of smectite, and for example, the dehydration conditions described in the following desalination process can also be applied.

[0015] -Na-type smectite- In the present invention, when referring to "X-type smectite" (X is the type of cation), it means a smectite in which the amount of X ions (unit: meq / 100 g) in the amount of leached cations of smectite (that is, the total amount of leached cations, unit: meq / 100 g, the same hereinafter) is 70% or more (preferably 80% or more, more preferably 90% or more, more preferably 92% or more, and still more preferably 95% or more). For example, in the case of Na-type smectite, it means a smectite in which the amount of Na ions (unit: meq / 100 g) in the amount of leached cations of smectite is 70% or more (preferably 80% or more, more preferably 90% or more, more preferably 92% or more, and still more preferably 95% or more). In this specification, the amount of leached cations of smectite shall be measured by the method (SFSA improved method) described in the examples.

[0016] Smectite forms a layered structure in which thin plate-like crystals with a thickness of about 1 nm are stacked, and generally cations such as alkali metals and alkaline earth metals exist between the crystals in the interlayer. In this ion exchange process, the main cation existing in the crystal interlayer of the raw material smectite for substituting the interlayer cation of smectite with K ions or NH4 ions is Na ions (that is, the raw material smectite is Na-type smectite). The type of smectite used in the production method of the present invention is not particularly limited, and it may be natural smectite or synthetic smectite. Examples of the smectite used in the production method of the present invention include montmorillonite, beidellite, nontronite, saponite, hectorite, sauconite, and stibnite, and montmorillonite is preferably used.

[0017] - Potassium salt or ammonium salt - Examples of the potassium salt include potassium chloride, potassium acetate, potassium carbonate, potassium sulfate, etc. Examples of the ammonium salt include ammonium chloride, ammonium acetate, ammonium carbonate, ammonium sulfate, etc. The amount of the salt to be mixed is not particularly limited, and by adjusting the amount of the salt, the ratio of the target cation (K ion, NH4 ion) in the leached cation of the obtained cation-exchanged smectite can be appropriately adjusted.

[0018] - Water - The water is not particularly limited, and for example, water such as tap water, distilled water, deionized water can be used. From the viewpoint of improving the dispersibility of Na-type smectite and obtaining a high-purity smectite ion-exchanged with the target cation (K ion, NH4 ion), the water is preferably deionized water. The mixing amount of water can be appropriately set according to the mixing amount of the Na-type smectite to be mixed. For example, the mixing amount can also be set so that the content of Na-type smectite in the mixed solution is 1 to 10% by mass.

[0019] (Desalting step) The mixture containing cation-exchanged smectite obtained by the above cation exchange step is then subjected to a desalting step. This desalting step removes the salt mixed in the cation exchange step, ions derived from the salt, and Na ions released from between the crystalline layers of smectite by ion exchange. The desalting method is not particularly limited, and any ordinary method capable of desalting from the mixture can be used. Examples include washing with water or desalting using a semipermeable membrane. In this specification, "removal" includes both complete removal and reduction. In a preferred embodiment of the present invention, the desalination step can be carried out by washing with water. Preferably, this washing with water includes a dehydration step and a running water washing step. By going through these dehydration and running water washing steps, salts or ions released into the mixture can be removed with high efficiency. The dehydration step and the running water washing step will be described below.

[0020] -Dehydration stage- The dehydration conditions in the above dehydration stage are not particularly limited as long as they allow for a reduction in water content. For example, filtration methods such as natural filtration, reduced pressure filtration, pressure filtration, and centrifugal filtration can be employed, and the filter media can be the same as those used in normal filtration.

[0021] The above dehydration step forms a dehydrated cake (also referred to as "dehydrated cake A") with a reduced moisture content, before desalting (before washing with running water). Preferably, the moisture content of the dehydrated cake A obtained in the above dehydration step is 85% by mass or less, more preferably 82% by mass or less, and even more preferably 80% by mass or less. The moisture content of the dehydrated cake A is usually 50% by mass or more, and from the viewpoint of preventing the dehydrated cake A from drying out, it is practical to set it at 60% by mass or more.

[0022] -Rinsing stage- The dehydrated cake A obtained in the above dehydration step is then washed by running water through it in a running water washing step. This removes the salt contained in the dehydrated cake A. In this specification, "running water washing" means a method of washing the smectite by passing water through it while maintaining the shape of the cake to some extent, by simultaneously adding and draining water. In the running water washing stage, it is preferable to add water at least 100 times the mass of the smectite (solid content) contained in the dewatered cake A, more preferably 150 times the mass, and even more preferably 200 times the mass. Normally, however, water at least 500 times the mass is added. It is preferable that the added water be drained by natural filtration. For example, if the dewatering in the dewatering stage is filtered by vacuum filtration or the like, the water can be added on the filter media used and then naturally filtered. The water addition rate is preferably about the same as the drainage rate. The above-mentioned "desalination process" shall be terminated when the mixture of smectite and water is in a state with a higher water content than a so-called dehydrated cake. That is, the mixture of smectite and water obtained in the desalination process is subjected to the subsequent dehydration process to obtain the desired dehydrated cake. Note that the dehydration process, which is the process following the desalination process, can also remove any remaining salt along with the water, so the dehydration process may also serve as a desalination treatment. In other words, in this invention, "removing salt and dehydrating to obtain a dehydrated cake" encompasses all methods of obtaining a dehydrated cake from which salt has been removed from the mixture after the cation exchange process.

[0023] (Dehydration process) The mixture after the desalting process is then subjected to a dehydration process. This dehydration process forms a dehydrated cake with reduced moisture content. The dewatering method used in the dewatering process is not particularly limited, and filtration methods such as vacuum filtration, pressure filtration, and centrifugal filtration can be employed. The filter media can also be the same as that used in normal filtration.

[0024] From the perspective of further improving the handling property by reducing the volume, the water content of the dehydrated cake is preferably 85% by mass or less, more preferably 83% by mass or less, and still more preferably 80% by mass or less. Further, from the perspective of further improving the dispersion stability of the K-type or NH4-type smectite contained in the dehydrated cake in water when the dehydrated cake is mixed with water, the water content of the dehydrated cake is preferably 60% by mass or more, more preferably 65% by mass or more, and still more preferably 70% by mass or more.

[0025] <Preparation of K-type or NH4-type smectite slurry> The dehydrated cake obtained through the above dehydration step is mixed with water to obtain a K-type or NH4-type smectite slurry. The K-type or NH4-type smectite contained in this dehydrated cake is excellent in dispersion stability in water. That is, even though the interlayer cation of the smectite is a K ion or an NH4 ion, the smectite can be well redispersed in water to form a slurry with stable properties. As the water, the same water as that mixed in the above ion exchange step can be used. The solid content concentration of the K-type or NH4-type smectite slurry obtained by mixing the dehydrated cake obtained in the dehydration step and water is not particularly limited and is appropriately set according to the purpose. For example, it can be 0.1 to 5.0% by mass, or can also be 5.0 to 20.0% by mass.

[0026] The mixing of the dehydrated cake and water may be carried out by mixing with water immediately after the production of the dehydrated cake, or may be carried out by mixing with water after storing the dehydrated cake after production. For example, after the production of the dehydrated cake, it can be transported in the state of the dehydrated cake to the site where the slurry is actually used, and then mixed with water and stirred at the site to obtain a slurry. During the storage period, the dehydrated cake is stored without being dried. The storage is preferably carried out so that the dehydrated cake can maintain the above water content, and the storage period is preferably within 5 years, more preferably within 3 years, and still more preferably within 1 year.

[0027] The K-type or NH4-type smectite slurry of the present invention, obtained by mixing the dewatered cake with water, is practically difficult to directly and appropriately define in terms of its technical features, structure, composition, and properties. Therefore, in order to clarify the invention by clearly indicating the differences from the prior art, the present invention specifies the manufacturing method (process) for the K-type or NH4-type smectite slurry.

[0028] [Dehydrated cake] The dehydrated cake of the present invention is a dehydrated cake obtained through the cation exchange step, desalting step, and dehydration step described above. That is, it is a dehydrated cake of K-type or NH4-type smectite obtained by mixing Na-type smectite, a potassium salt or ammonium salt, and water, subjecting the Na-type smectite to cation exchange, then removing the salt, and dehydrating, and is a dehydrated cake for obtaining a K-type or NH4-type smectite slurry by mixing with water. This mixing of the dehydrated cake with water means mixing with water without drying the dehydrated cake.

[0029] Despite being a dehydrated cake of K-type or NH4-type smectite, the dehydrated cake of the present invention exhibits excellent dispersion stability in water. While K-type or NH4-type smectite is known to have poor dispersion stability in water, the dehydrated cake of the present invention, when mixed directly with water without drying, yields a slurry with excellent dispersion stability of K-type or NH4-type smectite. The reason for this is unclear, but the following is considered. When cation exchange is performed by dispersing Na-type smectite in water, it is presumed that the resulting cation-exchanged smectite maintains a certain degree of interlayer delamination immediately after cation exchange, because the Na-type smectite is dispersed in water. In particular, when the interlayer cations are K ions or NH4 ions, the electrical attraction is relatively weaker compared to divalent cations, so even if the crystal layers are aligned, they are less likely to stack. Therefore, even if the smectite comes into close proximity after subsequent dehydration, the delamination state can be maintained as long as a certain level of water content is maintained, and it is considered to have excellent dispersion stability in water. However, in cation-exchanged smectite where the cations are divalent cations instead of K ions or NH4 ions, even if a dehydrated cake is obtained by the same method as above, the dispersion stability in water is inferior, as shown in the [Examples] section below.

[0030] In this invention, "having dispersion stability" and "excelling dispersion stability" mean, for example, that when smectite is dispersed in water and allowed to stand, no free water is generated, or very little free water is generated. As an example, if smectite is mixed with water to form a slurry with a solid content of 3% by mass, and allowed to stand overnight at 25°C, and the amount of free water generated is 5% or less, then the smectite can be evaluated as having "dispersion stability" and "excelling dispersion stability." The amount of free water can be calculated using the following formula (Equation 1). Note that "free water" refers to the supernatant obtained when the slurry is allowed to stand and phase separation occurs. Percentage of free water (%) = [Volume of free water / Total volume of dispersion] × 100 ... (Equation 1) When evaluating the proportion of free water by mixing the dehydrated cake of the present invention with water, the proportion of free water is preferably 5% or less, more preferably 3% or less, more preferably 1% or less, and even more preferably 0% (no free water is generated).

[0031] (pH) From the viewpoint of further improving the dispersion stability in water, the pH of the slurry (at 25°C) of the dehydrated cake of the present invention dispersed in water at a concentration of 2.0% by mass is preferably 6.5 to 10.5, more preferably 7.0 to 9.0, and even more preferably 7.0 to 8.5. The pH can be measured, for example, using a personal pH meter (model number: SPH71, manufactured by Sansho Co., Ltd.).

[0032] (conductivity) From the viewpoint of further improving the dispersion stability in water, the dehydrated cake of the present invention preferably has an electrical conductivity of 600 μS / cm or less, more preferably 300 μS / cm or less, and more preferably 150 μS / cm or less, when dispersed in water at a concentration of 2.0 mass% (at 25°C). This electrical conductivity can be measured, for example, using an electrical conductivity meter (model number: ES-51, manufactured by Horiba, Ltd.).

[0033] (Average particle size) In the dehydrated cake of the present invention, the average particle diameter of smectite is preferably 2000 nm or less, more preferably 1500 nm or less, and even more preferably 1000 nm or less. Furthermore, the average particle diameter is usually 200 nm or more. Note that the average particle diameter is the cumulant diameter determined by cumulant analysis. The average particle diameter of smectite in the dehydrated cake can be measured according to conventional methods. For example, it can be measured by the method described in the examples.

[0034] Despite the smectite interlayer cations being either K ions or NH4 ions, the dehydrated cake of the present invention redisperses well in water, forming a slurry with stable properties. Therefore, it can be stored and transported in a volume-reduced state by filtration, and then redispersed in water as needed to form a stable slurry that can be used for various applications. Furthermore, since a drying and grinding process is not required, manufacturing costs can be reduced. [Examples]

[0035] The present invention will be described in more detail below based on examples, but the present invention is not limited thereto.

[0036] <Experimental Example 1: Production of Dehydrated Cake> (Example 1) -Cation exchange process- To 1000 ml of 0.7 mol / l potassium chloride aqueous solution (potassium chloride: special grade, manufactured by Kanto Chemical Co., Ltd.), 50 g (0.5 mass%) of Na-type smectite (product name: Kunipia F, manufactured by Kunimine Industries Co., Ltd.) was added to make a mixture, which was stirred overnight at 25°C. The mixed solution, after stirring, was poured into a Buchner funnel lined with filter paper (hard filter paper No. 4A, manufactured by Advantec Co., Ltd.), and suction filtration was performed using a vacuum pump with a suction pressure of 700 mmHg (approximately 93.31 kPa, calculated assuming 1 mmHg = 0.1333 kPa). The smectite after suction filtration was then added entirely to 1000 ml of the potassium chloride aqueous solution and stirred (second time), followed by suction filtration. The smectite after suction filtration was then added entirely again to 1000 ml of the potassium chloride aqueous solution and stirred (third time), obtaining a mixed solution containing K-type smectite, in which the interlayer cations of the smectite were exchanged from Na ions to K ions.

[0037] -Desalination process- After the cation exchange process was completed (after the third stirring), suction filtration was performed in the same manner as above (dehydration stage). Before the surface of the smectite after suction filtration dried, 10 L of distilled water was slowly poured over the smectite to perform running water washing (filtration washing by natural filtration) (running water washing stage).

[0038] -Dehydration process- Subsequently, dehydration was performed by suction filtration under the same conditions as described above to obtain a dehydrated cake of K-type smectite.

[0039] The degree of dehydration, desalting, and cation exchange in the obtained dehydrated cake was confirmed by the following method.

[0040] -Moisture content of dehydrated cake- After measuring the mass of a portion of the dehydrated cake, it was dried in a constant temperature oven set to 105°C for 24 hours. The mass of the dried cake was then measured again to calculate the moisture content (mass %) of the dehydrated cake after suction filtration. The results are shown in Table 1 below.

[0041] -pH, conductivity- A portion of the dehydrated cake was dried overnight at 105°C and then pulverized in a cup mill. This dried pulverized material was dispersed in water to a concentration of 2% by mass to form an aqueous dispersion, and the pH and conductivity of this aqueous dispersion were measured. A personal pH meter (model number: SPH71, manufactured by Sansho Co., Ltd.) was used to measure pH, and an electrical conductivity meter (model number: ES-51, manufactured by Horiba, Ltd.) was used to measure conductivity. The measurement temperature was room temperature (25°C). As a control sample, smectite powder (Na-type smectite, trade name: Kunipia F, manufactured by Kunimine Industries Co., Ltd.) was used as the smectite powder in Reference Example 1, and the pH and conductivity were measured as an aqueous dispersion in the same manner as above. The results are shown in Table 1 below.

[0042] -Cational composition- The interlayer cation composition of each smectite was measured using the SFSA improvement method (Japanese Geotechnical Society Journal, Vol. 17, No. 1, 61-71) with the aforementioned dried pulverized material (dried pulverized material of the dehydrated cake from Example 1) and the smectite powder from Reference Example 1. The measurement results are shown in Table 1 below.

[0043] (Example 2) Except for using a 0.7 mol / l aqueous solution of ammonium chloride (ammonium chloride: special grade, manufactured by Kanto Chemical Co., Ltd.) instead of a 0.7 mol / l aqueous solution of potassium chloride, a dehydrated cake of NH4-type smectite was obtained by following the same procedure as in Example 1 above, including cation exchange, desalting, and dehydration steps. The dehydrated cake was subjected to measurements of moisture content, pH, and conductivity in the same manner as described above. The results are shown in Table 1 below.

[0044] (Comparative Example 1) Except for using a 0.7 mol / l aqueous solution of calcium chloride (calcium chloride: special grade, manufactured by Kanto Chemical Co., Ltd.) instead of a 0.7 mol / l aqueous solution of potassium chloride, a dehydrated cake of Ca-type smectite was obtained by following the same procedure as in Example 1 above, including cation exchange, desalting, and dehydration steps. The dehydrated cake was subjected to measurements of moisture content, pH, conductivity, and interlayer cation composition in the same manner as described above. The results are shown in Table 1 below.

[0045] (Comparative Example 2) Except for using a 0.7 mol / l magnesium chloride aqueous solution (magnesium chloride: special grade, manufactured by Kanto Chemical Co., Ltd.) instead of a 0.7 mol / l potassium chloride aqueous solution, a dehydrated cake of Mg-type smectite was obtained by following the same procedure as in Example 1 above, including cation exchange, desalting, and dehydration steps. The dehydrated cake was subjected to measurements of moisture content, pH, and conductivity in the same manner as described above. The results are shown in Table 1 below.

[0046] (Comparative Example 3) Except for using a 0.7 mol / l aqueous solution of cesium chloride (cesium chloride: special grade, manufactured by Kanto Chemical Co., Ltd.) instead of an aqueous solution of potassium chloride, a dehydrated cake of Cs (cesium) type smectite was obtained by following the same procedure as in Example 1 above, including cation exchange steps, desalting steps, and dehydration steps. The dehydrated cake was subjected to measurements of moisture content, pH, and conductivity in the same manner as described above. The results are shown in Table 1 below.

[0047] (Comparative Example 4) Except for using a 0.7 mol / l aqueous solution of aluminum chloride (aluminum chloride: special grade, manufactured by Kanto Chemical Co., Ltd.) instead of a 0.7 mol / l aqueous solution of potassium chloride, a dehydrated cake of Al (aluminum) type smectite was obtained by following the same procedure as in Example 1 above, including cation exchange steps, desalting steps, and dehydration steps.

[0048] <Example Test> The dehydrated cakes obtained in Examples 1 and 2, and Comparative Examples 1 to 4, were subjected to the following tests to evaluate their dispersibility.

[0049] (X-ray diffraction) The dehydrated cakes of Examples 1 and 2, and Comparative Examples 1 to 3, were spread onto the recessed portion of a glass slide with a depression, the surface was flattened, and the slide was set in the apparatus. X-ray diffraction was then performed under the following conditions. -X-ray diffraction conditions- X-ray diffractometer: Ultima IV, manufactured by Rigaku Corporation. X-ray: 40kV / 20mA Monochromemeter: Fixed monochromemeter Divergence slit: 1° Divergence vertical limiting slit: 10mm Scattering slit: 1° Light-receiving slit: 0.3mm Monochrome light-receiving slit: 0.8mm

[0050] The results of X-ray diffraction are shown in Figure 1. In Figure 1, the positions indicated by "*" are at 12.5 Å, "**" are at 15 Å, and "***" are at 18 Å, respectively. These correspond to the widths of one (12.5 Å), two (15 Å), and three (18 Å) layers of water molecules intercalated between the crystalline layers of smectite. In other words, the peaks at each position indicate the presence of a certain amount of smectite that is not exfoliated and dispersed but stacked in layers. The presence or absence of peaks due to X-ray diffraction was determined from the distribution in Figure 1. The results are shown in Table 1 below.

[0051] (Measurement test of free water) The dehydrated cakes from Examples 1 and 2, Comparative Examples 1 to 4, and the smectite powder from Reference Example 1 were added to water to a solid content of 3% by mass. The mixture was stirred at 25°C for 24 hours using a shaker (Yamato Scientific SA300, Shaking Speed ​​Memory 4) to obtain a uniform slurry (100 mL). This slurry was then transferred to a graduated cylinder and left to stand overnight at 25°C. The volume of free water generated was measured, and the percentage of free water was calculated using the following formula (Equation 1). The results are shown in Table 1 below. Percentage of free water (%) = [Volume of free water / Total volume of dispersion] × 100 ... (Equation 1)

[0052] (Measurement test of average particle size) The dehydrated cakes from Examples 1 and 2, Comparative Examples 1 and 2, and the smectite powder from Reference Example 1 were added to water to a solid content of 0.05% by mass. The mixture was stirred at 25°C for 24 hours using a shaker (Yamato Scientific SA300, Shaking Speed ​​Memory 4) to obtain a homogeneous slurry. The average particle size of the smectite in the slurry (cumulant diameter determined by cumulant analysis) was measured using a dynamic light scattering device (model: SZ-100, HORIBA). The results are shown in Table 1 below.

[0053] [Table 1]

[0054] The dehydrated cakes of Examples 1 and 2, and Comparative Examples 1 to 3, all had a pH of approximately 7 to 8, and their conductivity was also reduced compared to the smectite powder of Reference Example 1. This indicates that excess ions were sufficiently removed in the "desalting step" during the manufacturing process of the dehydrated cakes. Furthermore, analysis of the cation composition using the smectite powder of Reference Example 1 and the dehydrated cakes of Examples 1 and Comparative Example 1 showed that at least the interlayer cations of Na-type smectite were replaced with the target cations by the method described above. In addition, the water content of the obtained dehydrated cakes was 80% by mass or less, indicating that the volume was sufficiently reduced.

[0055] On the other hand, X-ray diffraction results using the dehydrated cakes of Examples 1 and 2, and Comparative Examples 1 to 3, showed that Comparative Examples 1 to 3 had sharp peaks at 12.5 Å, 15.0 Å, and 18.0 Å, respectively, as shown in Figure 1, while no sharp peaks were detected in the dehydrated cakes of Examples 1 and 2. In other words, it was suggested that the smectite in the dehydrated cakes of Comparative Examples 1 to 3 was ordered and existed in layers, while the smectite in the dehydrated cakes of Examples 1 and 2 had low regularity and high dispersion stability. Furthermore, when the dehydrated cakes of Examples 1 and 2, Comparative Examples 1-4, and the smectite powder of Reference Example 1 were redispersed in water and allowed to stand, a large amount of free water was generated in Comparative Examples 1-4, whereas no free water was generated in Examples 1 and 2 and Reference Example 1. In addition, the average particle size in the aqueous dispersions of Comparative Examples 1 and 2 was 6 μm or larger, while the average particle size in Examples 1 and 2 was 1 μm or smaller, demonstrating superior detachability (dispersion stability).

[0056] <Experimental Example 2: Drying Dehydrated Cake> (Comparative Examples 5 and 6) The dehydrated cakes from Examples 1 and 2 were dried overnight at 105°C and then ground in a cup mill to obtain the resulting dried pulverized products, which were designated as Comparative Examples 5 and 6, respectively. The moisture content of the dried pulverized products of Comparative Examples 5 and 6 was measured in the same manner as described above, and in both cases, the moisture content was 8.0% by mass or less.

[0057] The obtained dried pulverized material was dispersed in water in the same manner as described above, and the free water content and average particle size were measured. The results are shown in Table 2 below.

[0058] [Table 2]

[0059] The results above indicate that subjecting the dehydrated cake to a drying and grinding process significantly reduces the dispersion stability of the dehydrated cake.

Claims

【Request Item 1】 Na-type smectite is mixed with a potassium salt or ammonium salt and water, and the Na-type smectite is subjected to cation exchange, then the salt is removed and dehydrated to obtain a dehydrated cake, and this dehydrated cake is mixed with water to produce K-type or NH ４ This includes obtaining a K-type or NH-type smectite slurry. ４ A method for producing molded smectite slurry. 【Request Item 2】 The K-type or NH-type according to claim 1, wherein the water content of the dehydrated cake is 70 to 85% by mass. ４ A method for producing molded smectite slurry. 【Request Item 3】 The K-type or NH-type according to claim 1 or 2, wherein the average particle size of the smectite contained in the dehydrated cake is 1000 nm or less. ４ A method for producing molded smectite slurry.

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