Kaolin-based powder

Abstract

To provide a kaolin-based powder capable of preventing viscosity increase and rapid setting of geopolymer.SOLUTION: A geopolymer composition includes a kaolin-based powder derived from coal seam kaolin, having an ignition loss of 1.5 mass% or more and 10 mass% or less, and an amorphous content of 56 mass% or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a kaolin powder, particularly to a kaolin powder used for a solidified body capable of fixing low-level radioactive waste and toxic substances subject to emission regulations, particularly solutions, dried residues, incineration ash, sludge, ion exchange resins, etc. [Background technology]

[0002] Low-level radioactive waste such as waste liquid, sludge, and ion exchange resin generated from operating nuclear power plants is subjected to solvent removal, incineration, melting, and reduction in volume, and then mixed with cement or asphalt in drums to solidify it into waste bodies. After that, it is stored for a certain period in storage facilities within the power plant, and then, depending on the radioactivity level, it is disposed of in shallow or medium-depth burial sites. After burial disposal, the disposal site will be able to be used for general land use after a management period of 300 to 400 years.

[0003] Traditionally, cement-based materials have been mainly used as solidification materials for radioactive waste. In addition to this, geopolymers have been considered as a new solidification material in recent years. Geopolymers are amorphous aluminosilicates in which aluminum and silicon are three-dimensionally connected via oxygen. Geopolymers are prepared by kneading alkali-activated fillers such as metakaolin and fly ash, water glass, caustic soda / caustic potash, and water. The kneaded mixture maintains a slurry state for a certain period of time. For this reason, if the mixture in a slurry state is mixed with radioactive waste such as waste liquid, filter sludge, and ion exchange resin and allowed to stand, it can then be solidified and turned into a waste body.

[0004] Currently, metakaolin is often used as an alkaline-active filler in research on waste disposal using geopolymers. However, the metakaolin used is a kaolin powder made for resin additives and building materials, and is calcined kaolin with whiteness as a quality. No kaolin powder prepared for radioactive waste solidification is known. Calcined kaolin is partially or completely amorphous metakaolin, and is usually called metakaolin. Since the whiteness is adjusted by the calcination temperature reflecting the geological characteristics of the kaolin deposit, the alkaline activity may not be constant for each metakaolin. In that case, the setting time of the slurry varies for each material, and metakaolin with high alkaline activity may set too quickly. In addition, depending on the metakaolin, it may not be possible to disperse it well in the alkaline silicate solution, and the powder may clump, making it impossible to knead uniformly.

[0005] Inorganic and organic substances have been considered as additives for controlling the hardening time (potable time) of geopolymers (see, for example, Patent Document 1). The effect of additives varies depending on the geopolymer raw material, fly ash, slag, or metakaolin. For example, phosphate-based retarders have a retarding effect on alkali-activated slag containing Ca by chelating Ca ions and inhibiting the rapid reaction between calcium silicate hydrate and calcium aluminosilicate hydrate. On the other hand, the use of phosphate-based retarders reduces the strength of the solidified body. In addition, phosphate-based retarders may not be effective on metakaolin, which contains almost no Ca.

[0006] Phosphate ester compounds have been disclosed as viscosity reducers for geopolymers (see, for example, Patent Document 2). Patent Document 2 reports that although the mortar flow value does not change with or without a viscosity reducer, the load power of the kneader is halved, and there is a viscosity reducer effect. However, since the setting time cannot be changed, phosphate ester compounds have no effect on improving the pot life. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 2021-506708 [Patent Document 2] JP 2020-138899 A Summary of the Invention [Problem to be solved by the invention]

[0008] Waste forms to be processed at actual nuclear power plants, i.e., full-scale waste forms, are usually drum-sized (200L). This requires large mixing equipment, and the entire process of mixing geopolymers takes about three hours. Any increase in viscosity or rapid solidification during this time will cause the mixer to stop and result in breakdowns, so stable solidification cannot be guaranteed. To make the pot life longer than the working time, metakaolin is required for full-scale waste forms, with suppressed alkaline activity and good dispersibility in alkali silicate.

[0009] By adjusting the water content and alkali content of the metakaolin used on the spot each time and adjusting the alkali activity and dispersibility, it is possible to prevent rapid setting and achieve uniform mixing. However, because records must be kept of the waste bodies that were created according to the established procedures, once the mix has been approved, it cannot be changed arbitrarily. This approach is based on the premise that the quality of the materials is always constant and that the compressive strength and distribution coefficient of the created waste bodies are determined by the mix of materials. For these reasons, it is necessary to prepare a kaolin powder with sufficient dispersibility that will realize a slurry with a sufficiently long pot life and low viscosity. [Means for solving the problem]

[0010] As a result of extensive research, the inventors have solved the problems by using kaolin ore derived from a specific mineral deposit as a material and by carrying out a calcination treatment within a specific low temperature range, thereby completing the present invention.

[0011] That is, according to one embodiment, the present invention relates to a kaolin powder derived from coal seam kaolin, having an ignition loss of 1% by mass or more and 10% by mass or less, and having an amorphous content of 56% by mass or more.

[0012] The kaolin powder preferably has an Al / Si molar ratio of 0.4 to 1.2. Alternatively, one or more components selected from silicon dioxide, aluminum oxide, and aluminosilicate salts are added before calcination, and the kaolin powder preferably has an Al / Si molar ratio of 0.4 or less or 1.2 or more.

[0013] The kaolin powder preferably contains organic matter derived from humus. Effect of the Invention

[0014] The kaolin powder according to the present invention can ensure the necessary pot life in the preparation of solidified bodies or waste bodies, and can uniformly knead the raw material mixture of geopolymers without rapid solidification. In addition, since no additives are required, there is no need to consider the deterioration of performance due to additives. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a graph showing the relationship between the calcination temperature (° C.) and the ignition loss (mass %) of kaolin. [Diagram 2] FIG. 2 shows the calcination temperature of kaolin, and the proportion (mass %) of kaolin and the proportion (%) of amorphous matter in the resulting powder. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described. However, the present invention is not limited to the embodiment described below.

[0017] According to one embodiment, the present invention relates to a kaolin powder. The kaolin powder is derived from coalbed kaolin, has an ignition loss of 1% to 10% by mass, and is amorphous at 56% by mass or more. In one embodiment, the kaolin powder preferably has an Al / Si molar ratio of 0.4 to 1.2. Alternatively, in another embodiment, the kaolin powder preferably has one or more components selected from silicon dioxide, aluminum oxide, and aluminosilicate salts added before calcination, and has an Al / Si molar ratio of 0.4 or less or 1.2 or more. Hereinafter, kaolin is used to mean a substance that contains metakaolin as its main component and may contain inorganic and organic substances such as iron oxide, titanium oxide, silicon dioxide, and aluminosilicates as impurities, and kaolin powder is used to mean a powder that contains metakaolin as its main component and may contain inorganic and organic substances such as iron oxide, titanium oxide, silicon dioxide, and aluminosilicates as impurities, or as additives for adjusting the composition or improving workability.

[0018] The kaolin powder according to this embodiment can be produced by a method including the following steps. (1) A step of calcining a coalbed kaolin powder having an Al / Si molar ratio of 0.4 to 1.2 at an atmospheric temperature of 900°C or less. (2) Classifying the calcined kaolin The production method will now be described in detail.

[0019] The raw material of the kaolin powder according to this embodiment is a coal layer kaolin ore. The coal layer kaolin ore may be kaolin obtained from a coal deposit, for example, kaolin derived from a deposit in the UK, Scotland, the USA, Australia, or China. Coal layer kaolin ore is commercially available, and commercially available coal layer kaolin ore can be used. More specifically, the coal layer kaolin ore is a black-brown ore containing fulvic acid and humic acid, which are humus substances. Fulvic acid and humic acid are organic substances with large molecular weights that contain aromatic and linear hydrocarbons, carboxylic acids, and the like, and contain hydrogen, oxygen, sulfur, nitrogen, and the like in addition to carbon, but since they are derived from living organisms and have been denatured over a long period of time, their molecular weights and structures are indefinite, and they do not have a single chemical structure. The fact that the coal layer kaolin ore contains fulvic acid and humic acid, which are humus substances, and the quantitative analysis method thereof can be confirmed by humus analysis by a general analysis agency.

[0020] The raw material of the kaolin powder may include an additional component added from the outside in addition to the coal seam kaolin ore. The additional component can be optionally used to adjust the Al / Si molar ratio to 0.4 or less, or 1.2 or more. More preferably, the Al / Si molar ratio can be adjusted to 0.1 or more and 0.4 or less, or 1.2 or more and 2.0 or less. The additional component may be one or more selected from silicon dioxide, aluminum oxide, and aluminosilicate salt. The additional component can be added to the coal seam kaolin ore before the next step, the crushing step. Alternatively, the additional component can be added to the raw powder after the crushing step.

[0021] The obtained raw stone or the mixture of the raw stone and the additional component can be optionally crushed and classified to obtain a powder of a desired particle size to obtain a raw powder. Crushing can be carried out using a normal crushing device such as a roller mill, a vertical mill, or a pot mill. For example, primary crushing is performed using a dry roller mill, followed by secondary crushing using a wet pot mill. Classification can also be carried out using a sieve with a predetermined size of openings.

[0022] The raw powder obtained through optional pulverization and classification is then washed, suction filtered, dried and disintegrated. Washing can be performed using water, and drying can be performed using an electric furnace, a hot plate, or other methods.

[0023] Next, the dried and washed raw powder is calcined. Calcination is performed at 900°C or less, at which mullite crystal phase is not formed. This makes it possible to obtain kaolin powder that retains organic matter derived from humus contained in coalbed kaolin. Calcination is preferably performed for 1 to 6 hours at an atmospheric temperature of 900°C or less, which is a temperature at which the alkaline activity of coalbed kaolin is not lost, more preferably for 2 to 5 hours at an atmospheric temperature of 450°C or more and 900°C or less, and most preferably for 3 to 4 hours at an atmospheric temperature of 550°C or more and 750°C or less. Alkaline activity refers to the solubility of aluminic acid and silicic acid in an alkaline solution, and whether the alkaline activity has not been lost can be confirmed by dispersing the calcined kaolin in an alkaline solution and measuring the aluminum and silicon concentrations in the alkaline solution after a certain temperature and time. The concentrations can be measured by atomic absorption spectroscopy, mass spectrometry, or ion chromatography. Calcination can be performed in an air atmosphere using a device such as a gas furnace or an electric furnace. In order to maintain the amount of organic matter, the calcination may be carried out under a nitrogen gas or argon gas atmosphere. The kaolin powder thus obtained is calcined and then naturally cooled.

[0024] The cooled kaolin powder can be optionally classified after crushing. For the purpose of producing a solidified body or waste body described in detail in the second embodiment, the low-temperature calcined kaolin powder can be classified, for example, with a sieve having an opening of 75 μm or less, preferably 35 μm or less. The kaolin powder according to the first embodiment of the present invention obtained in this manner is also referred to as low-temperature calcined kaolin powder in this specification.

[0025] Low-temperature calcined kaolin powder is Al4Si4O 10It is believed that organic matter derived from humus that was attached to the raw stone remains on the surface and inside of the kaolinite, which has a chemical composition of (OH)8. Organic matter derived from humus includes fulvic acid and humic acid, just like the raw stone, and these can be identified and quantified by excitation and fluorescence intensity measurement at specific wavelengths (three-dimensional fluorescence spectrum measurement). In addition, according to time-of-flight secondary ion mass spectrometry, it includes aromatic hydrocarbons, aliphatic hydrocarbons, ammonia, phthalic acid and its esters, and sulfur oxides. In addition to organic matter, the low-temperature calcined kaolin powder also contains Si oxides, cations derived from elements such as Li, Na, Mg, Al, K, and Ca, and anions derived from elements such as F and Cl. In addition, additional components added before calcination remain in their original form at calcination temperatures of 900°C or less.

[0026] The presence of organic matter derived from humus in low-temperature calcined kaolin powder can be confirmed by the ignition loss being between 1% and 10% by mass when heated at 1000°C for 3 hours. Since the calcined kaolin powder does not contain inorganic matter with a decomposition temperature below 1000°C, the ignition loss at 500°C or higher can be considered to be mainly derived from organic matter. The heating conditions can be an electric furnace under atmospheric conditions. The ignition loss (mass%) can be calculated using the following formula. Ignition loss = (mass of sample before ignition - mass of sample after ignition) / mass of sample before ignition x 100 Here, the pre-ignition sample is the mass of the dried low-temperature calcined kaolinite powder before ignition, and the post-ignition sample is the mass of the sample allowed to cool after ignition.

[0027] The low-temperature calcined kaolin powder also contains 56% by mass or more of amorphous matter. Preferably, it contains 77% by mass or more of amorphous matter, more preferably 80% by mass or more. The amount of amorphous matter in the low-temperature calcined kaolin powder can be quantified by Rietveld analysis using an internal standard substance in an X-ray diffraction method, and silicon dioxide can be used as the internal standard substance. The Al / Si molar ratio of the low-temperature calcined kaolin powder is preferably 0.4 to 1.2, more preferably 0.8 to 1.0, and even more preferably 0.85 to 0.95, when the low-temperature calcined kaolin powder does not substantially contain any additional components added from the outside other than the raw coalbed kaolin ore. On the other hand, when the raw coalbed kaolin ore contains one or more additional components selected from silicon dioxide, amorphous silicon dioxide such as silica fume, aluminum oxide, aluminum hydroxide, and aluminosilicate salts, the Al / Si molar ratio can be 0.4 or less, or 1.2 or more. The Al / Si molar ratio can be preferably set to 0.1 to 0.4, or 1.2 to 2.0. The Al / Si molar ratio can be evaluated by using fluorescent X-ray analysis.

[0028] The low-temperature calcined kaolin powder according to the present embodiment can be used as a geopolymer raw material, and when mixed with alkali silicate and water to produce a geopolymer, it can have a low viscosity and a long usable time. Although there is no intention to be bound by theory, this is thought to be due to the action of organic matter derived from humus remaining in the kaolin powder due to low-temperature calcination. Since humus consists of humic acid, which dissolves in an alkaline environment, and fulvic acid, which dissolves in an acidic environment, when a geopolymer is made using low-temperature calcined kaolin powder, the humic acid of the humus is eluted from the metakaolin. These have aromatic, hydrocarbon, and carboxylic acids, and are therefore thought to have surface activity and lubricating effects. Although the details are still unknown, it is thought that the slurry using the low-temperature calcined kaolin powder has a low viscosity due to these remaining organic matters, and since the organic matter remains on the metakaolin surface, the solubility in alkali is suppressed, which leads to a longer hardening time.

[0029] By mixing the above-mentioned kaolin powder with an alkali silicate, water, and an alkali to prepare a mixture, a hardening reaction starts at room temperature and normal pressure, and a hardened product (hardened geopolymer product) can be prepared. By using the low-temperature calcined kaolin powder according to this embodiment, the viscosity of the mixture slurry can be set to, for example, 25 Pa·s or less, preferably 10 Pa·s or less, at 20 to 23°C for 5 hours after mixing. By maintaining such a low viscosity, good workability can be obtained when preparing the hardened product, and the solidification work can be performed safely.

[0030] According to another embodiment, the present invention relates to a geopolymer composition comprising kaolin powder. The geopolymer composition comprises kaolin powder and one or more components selected from silicon dioxide, aluminum oxide, and aluminosilicate salts, and has an Al / Si molar ratio of 0.4 or less or 1.2 or more.

[0031] The kaolin powder may be a kaolin powder having an Al / Si molar ratio of 0.4 to 1.2 that does not substantially contain additional components added from the outside, among the kaolin powders described in the above embodiments. In addition to the kaolin powder, one or more components selected from silicon oxide, aluminum oxide, and aluminosilicate salts are added to the composition. Therefore, among these, only one component may be included, or any combination of two or three may be included. In addition, minerals containing these additional components may be added, and examples of such minerals include clay minerals such as illite and mordenite, but are not limited thereto. The amount of the added material may be an amount that allows the Al / Si molar ratio to be adjusted to a desired value. The Al / Si molar ratio may be preferably 0.1 to 0.4, or 1.2 to 2.0.

[0032] The composition can be prepared by adding one or more components selected from silicon oxide, aluminum oxide, and aluminosilicate salts to the kaolin powder obtained by calcination, and mixing the mixture.

[0033] The geopolymer composition can be used to prepare a mixture by mixing an alkali silicate, water, and an alkali, which initiates a curing reaction at room temperature and pressure, and to prepare a cured product (cured geopolymer product). Compared to kaolin powder with an Al / Si molar ratio of 0.4 to 1.2, a geopolymer composition with an Al / Si molar ratio adjusted to 0.4 or less is useful because it can improve the waste immobilization ability when the waste loading amount is increased when fixing waste with a geopolymer. In addition, compared to kaolin powder with an Al / Si molar ratio of 0.4 to 1.2, a geopolymer composition with an Al / Si molar ratio adjusted to 1.2 or more is expected to improve the heat resistance and chemical resistance of the cured product. EXAMPLES

[0034] The present invention will be described in more detail below with reference to examples, but the following examples are not intended to limit the present invention.

[0035] [Example 1] Coal bed kaolin ore (Ig.loss = 21% by mass), which is thought to contain a large amount of humus, was crushed, washed, dried, and then calcined at temperatures of 400 to 1050°C. It was then heated at 1000°C for 3 hours. Figure 1 is a graph showing the relationship between calcination temperature (°C) and ignition loss (% by mass). Ig.loss is thought to indicate the proportion of organic matter in the total mass of the kaolin powder obtained by calcination at each temperature. At a calcination temperature of 400°C, more than 11% by mass of organic matter remained, and at 500°C or higher, the amount rapidly decreased, but about 0.3 to 4.5% by mass of organic matter remained. Figure 2 shows the calcination temperature, the proportion of kaolin (% by mass, Kaoline) and the proportion of amorphous matter (% by mass, Amorphous) in the obtained powder. The proportion of amorphous matter was quantified by Rietveld analysis using an X-ray diffractometer (Smartlab Rigaku) ​​and silicon dioxide as a standard substance. The proportion of kaolin was quantified based on the area value of the diffraction peak. When the calcination temperature was 600°C or higher, kaolin almost disappeared and the amount of amorphous matter increased rapidly. This indicates that kaolin became metakaolin. From the above, calcination at 500°C or higher can obtain a kaolin-based powder with a large amount of amorphous matter (metakaolin) and about 0.3 to 4.5 mass% of organic matter remaining. The amount of organic matter such as surfactants required to improve the dispersibility and flowability of inorganic powders is generally a few mass% or less. Therefore, it is considered that the properties due to the remaining organic matter can be fully exhibited.

[0036] [Example 2] Slurry using metakaolin calcined at 550°C The kaolin ore was crushed, classified, washed, dried, and then calcined at 550°C in air. It was then sieved to 35μm or less to obtain low-temperature calcined metakaolin powder. At this time, the Al / Si molar ratio was 0.89 by fluorescent X-ray analysis. The Ig.loss of this powder was 4.5% by mass. In addition, using an X-ray diffractometer (Smartlab, Rigaku), Rietveld analysis was performed using silicon dioxide as a standard substance, and the amorphous ratio of the low-temperature calcined metakaolin powder was quantified to be 56.8% by mass. 90g of alkali silicate (100% water glass No. 1, 20% sodium metasilicate nonahydrate, 17% water), 0.9g of NaOH, and 14.4g of water were added to 86.4g of this metakaolin, and the mixture was kneaded by hand in air for 5 minutes to create a slurry. The slurry was placed in a plastic container (HIT ONE) and the viscosity was measured (TV-35H, Toki Sangyo) to find that the initial viscosity was 4.5 Pa s, and the rate of viscosity increase over the next 5 hours was 0.3 Pa s / h. When the plastic container was sealed, it solidified within 24 hours at 25°C to become a geopolymer.

[0037] [Example 3] Slurry using metakaolin calcined at 650°C A low-temperature calcined metakaolin powder was prepared in the same manner as in Example 1, except that the calcination temperature was 650°C. The Ig.loss of this powder was 2.1% by mass. The Al / Si molar ratio by fluorescent X-ray analysis was 0.90. The slurry prepared in the same manner as in Example 1 was placed in a plastic container (HIT ONE) and the viscosity was measured (TV-35H, Toki Sangyo Co., Ltd.). The initial viscosity was 3.4 Pa·s, and the rate of viscosity increase up to 5 hours thereafter was 0.7 Pa·s / h. When the plastic container was sealed, it solidified at 25°C within 24 hours and became a geopolymer.

[0038] [Example 4] Slurry using metakaolin calcined at 850°C A low-temperature calcined metakaolin powder was prepared in the same manner as in Example 1, except that the calcination temperature was 850°C. The Ig.loss of this powder was 0.86% by mass. The Al / Si molar ratio by fluorescent X-ray analysis was 0.91. The amorphous fraction was 81.6% by mass. The slurry prepared in the same manner as in Example 1 was placed in a plastic container (HIT ONE) and the viscosity was measured (TV-35H, Toki Sangyo Co., Ltd.). The initial viscosity was 7.9 Pa·s, and the rate of viscosity increase up to 5 hours thereafter was 3.1 Pa·s / h. When the plastic container was sealed, it solidified at 25°C within 24 hours and became a geopolymer.

[0039] [Comparative Example] Slurry using commercially available metakaolin The initial viscosity and viscosity rise rate of a slurry using Sobuekree metakaolin, which was made from the same kaolin ore, were measured. The powder had a mass content of 1.4%. X-ray fluorescence analysis revealed that the Al / Si molar ratio was 1.03. The initial viscosity was 4.6 Pa·s, and the rate of viscosity rise over the next 5 hours was 18.1 Pa·s / h. When sealed in a plastic container, it solidified within 24 hours at 25°C to become a geopolymer.

[0040] The results of Examples 2 to 4 and the Comparative Example are shown in Table 1. [Table 1] [Industrial Applicability]

[0041] The kaolin powder and geopolymer composition of the present invention can be used to produce geopolymers, and are useful in producing waste bodies solidified by mixing radioactive waste and metal elements, and solidified bodies that do not contain radioactive waste.

Claims

1. A kaolin powder derived from coal seam kaolin, having an ignition loss of 1.5% by mass or more and 10% by mass or less, and an amorphous content of 56% by mass or more.

2. 2. The kaolin powder according to claim 1, wherein the Al / Si molar ratio is 0.4 to 1.

2.

3. 2. The kaolin-like powder according to claim 1, wherein one or more components selected from silicon dioxide, aluminum oxide, and aluminosilicate salts are added before calcination, and the Al / Si molar ratio is 0.4 or less or 1.2 or more.

4. The kaolin powder according to claim 1 , wherein the kaolin powder contains organic matter derived from humus.

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