Alkali agent

Abstract

This alkaline agent is characterized by containing magnesium oxide particles having a crystallite diameter of 80 nm to 300 nm, a BET specific surface area of 0.1 m2 / g to 1.2 m2 / g, and an MgO content of 95.0 mass% or more. (The MgO content ratio is a value when the total of the content ratios (mass%) of the five elements, namely Mg, Ca, Si, Fe, and Al, detected by X-ray fluorescence measurement, converted into MgO, CaO, SiO2, Fe2O3, and Al2O3 is 100. ).

Description

Technical Field

[0001] The present invention relates to an alkali agent. Background Art

[0002] Sometimes, it is necessary to modify and maintain the environment such as water quality and soil to be alkaline (alkaline agent). Such alkaline agents are also used in fertilizers, coatings, etc. For example, Patent Document 1 describes a soil modification material that suppresses the soil modification effect brought about by magnesium oxide or calcium oxide by combining with a base material and a pH adjuster. In addition, Patent Document 2 describes a coated steel material having a non-water-soluble coating film having an alkali metal concentrated area formed on the surface of a steel material having a specific composition.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-044110

[0006] Patent Document 2: Japanese Patent Application Publication No. 2015-151571 Summary of the invention

[0007] Problems to be solved by the invention

[0008] From the perspective of environmental modification, the alkali agent, which is the source of the modification effect, has an appropriate dissolution rate and can be expected to maintain the effect for a long time. However, the dissolution rate of the alkali agent itself has not been paid much attention to and has not been fully studied.

[0009] Therefore, an object of the present invention is to provide an alkali agent which has an appropriate dissolution rate and can exert a stable effect over a long period of time.

[0010] Means for solving problems

[0011] The alkali agent of the present invention is characterized in that it contains magnesium oxide particles, wherein the crystallite diameter of the magnesium oxide particles is 80nm to 300nm and the BET specific surface area is 0.1m 2 / g~1.2m 2 / g, and the MgO content is 95.0 mass% or more.

[0012] Effects of the Invention

[0013] According to the present invention, it is possible to provide an alkali agent which has an appropriate dissolution rate and can exert a stable effect over a long period of time. DETAILED DESCRIPTION

[0014] The present inventors have conducted intensive studies and have found that magnesium oxide particles having a crystallite diameter and a BET specific surface area within a predetermined range and containing a predetermined amount of magnesium oxide have an appropriate dissolution rate, thereby completing the present invention.

[0015] Hereinafter, embodiments of the present invention will be described in detail.

[0016] The alkali agent of the present invention contains magnesium oxide particles (MgO particles) whose crystallite diameter and BET specific surface area are within specified ranges. The MgO particles contain magnesium oxide at a content of 95% by mass or more, and may contain impurities.

[0017] The crystallite diameter of the MgO particles in the present invention is 80nm to 300nm. By making the crystallite diameter within the range of 80nm to 300nm, appropriate dissolution can be ensured. The MgO particles have a tendency to dissolve faster as the crystallite diameter is smaller. The crystallite diameter of the MgO particles is preferably 85nm to 275nm, more preferably 90nm to 250nm. The crystallite diameter is a value obtained by processing the MgO (002) plane peak in the XRD pattern with analysis software. Usually, a particle is a polycrystal composed of multiple single crystals, and the crystallite diameter represents the average value of the size of the single crystals in the polycrystal.

[0018] As described later, the MgO particles in the present invention are obtained by sintering a magnesium oxide sintered body formed by sintering a magnesium compound, and the crystallite diameter can be controlled by the sintering temperature at this time. Magnesium oxide is mostly produced by thermal decomposition of a magnesium compound as a raw material, and after fine crystals are produced, crystal growth is carried out according to the sintering temperature. The crystallite diameter of the MgO particles can also be adjusted by the impurity content. Si and the like have a tendency to promote crystal growth, and are particularly prone to promote crystal growth in a magnesium oxide sintered body having an MgO content of less than 99% by mass. Furthermore, the magnesium oxide sintered body can also be crushed to reduce the crystallite diameter of the MgO particles.

[0019] In addition, the BET specific surface area of ​​MgO particles is specified as 0.1 m 2 / g~1.2m 2 / g. Thus, appropriate dissolution can be ensured. The BET specific surface area of ​​MgO particles is preferably 1.0 m 2 / g or less, more preferably 0.8m 2 / g or less, more preferably 0.6m 2 / g or less. In addition, the BET specific surface area of ​​the MgO particles is preferably 0.15 m 2 / g or more, more preferably 0.25m 2 / g or above.

[0020] The BET specific surface area of ​​the MgO particles can be controlled by the firing temperature of the magnesium oxide sintered body. The higher the firing temperature, the smaller the BET specific surface area tends to be. In addition, the BET specific surface area can also be increased by crushing the fired magnesium oxide sintered body. In addition, by classifying the fired and / or crushed magnesium oxide sintered body, particles mainly composed of particles with any BET specific surface area can also be screened.

[0021] The MgO particles of the present invention have a crystallite diameter and a BET specific surface area within a specified range, and a MgO content of 95% or more, so that alkali can be dissolved at a moderate rate, and a stable effect can be exerted for a long time. The MgO content is preferably 99.0% by mass or less in the MgO particles, more preferably 95.5% to 98.5% by mass, and further preferably 96.0% to 98.0% by mass.

[0022] The MgO content in the MgO particles is obtained by converting the five elements Mg, Ca, Si, Fe, and Al detected by fluorescent X-ray measurement into MgO, CaO, SiO, and 2 , Fe 2 O 3 、Al 2 O 3 The total of the contents (mass %) at 100 is the MgO content at 100.

[0023] In the determination of the alkali dissolution rate, a MgO suspension prepared by dispersing 50 mg of MgO particles in 100 mL of ion exchange water and 0.05 mol / L of sulfuric acid were used. The pH of the MgO suspension was maintained at 3 by dropping sulfuric acid using a potentiometric automatic titration device, and the sulfuric acid consumption required to maintain the pH was calculated. Specifically, the dissolution rate test value X shown in the following formula (2) can be used for evaluation.

[0024] X=m / t (2)

[0025] (In the above formula (2), m is (mol of sulfuric acid at the end point / mol of MgO) in the dissolution test in which the pH of the MgO suspension is maintained at 3, and t is the titration time (seconds).)

[0026] If the dissolution rate test value X thus obtained is 0.00035 or less, it has a moderate dissolution rate and can function for a long time. The dissolution rate test value X is more preferably 0.00025 or less, and further preferably 0.00020 or less. The lower limit of the dissolution rate test value X is not particularly limited, but is preferably 0.00003 or more, more preferably 0.00005 or more, and further preferably 0.00010 or more.

[0027] The MgO particles may contain, for example, Ca, Si, Fe, Al, etc. as impurities. The impurities can be evaluated using the S / M ratio represented by the following formula (1).

[0028] S / M=XRF(S) / XRF(M) (1)

[0029] XRF (S) and XRF (M) convert the five elements Mg, Ca, Si, Fe, and Al detected by fluorescent X-ray measurement into MgO, CaO, and SiO, respectively. 2 , Fe 2 O 3 、Al 2 O 3 When the total content (mass %) of SiO is 100 2 Content (S) and MgO content (M).

[0030] When the (S / M ratio) is 0.004 to 0.040, there is a tendency that the stability is improved and the moisture resistance is maintained even when a large load is applied to the surface during pulverization and classification. It is presumed that the heterogeneous phase (Si-Mg compound) formed when the magnesium oxide sintered body is sintered delays the internal penetration of the deterioration caused by moisture absorption, etc. The (S / M ratio) is preferably 0.006 to 0.035, and more preferably 0.007 to 0.020.

[0031] The 50% volume cumulative particle size (D50) of the MgO particles is preferably 1 μm to 200 μm. By making D50 within this range, a moderate dissolution rate can be achieved. The higher the sintering temperature, the greater the D50 tends to be. In addition, by crushing the fired magnesium oxide sintered body, D50 can also be reduced. In addition, by classifying the fired and / or crushed magnesium oxide sintered body, D50 can also be adjusted to an arbitrary range. The D50 of the MgO particles is more preferably 10 μm to 150 μm, and further preferably 20 μm to 100 μm.

[0032] The ratio of the 50% volume cumulative particle size (D50) to the crystallite diameter (D50 / crystallite diameter) of the MgO particles is preferably in the range of 100 to 600. It is believed that the smaller the (D50 / crystallite diameter), the higher the possibility that the fracture surface of the crystal structure is exposed on the particle surface, and the lower the stability such as moisture resistance. If it is in the range of 100 to 600, the moisture resistance can be improved. (D50 / crystallite diameter) is preferably 150 to 550, and more preferably 200 to 500.

[0033] The moisture resistance of MgO particles can be evaluated based on the mass increase rate in a humidity test. When kept in an atmosphere of 50°C and 85% humidity for 120 hours, the mass increase rate is preferably 2% or less. The mass increase rate is more preferably 1.5% or less, and further preferably 1.0% or less.

[0034] The alkali agent of the present invention can be obtained by pulverizing a magnesium oxide sintered body and classifying it as necessary.

[0035] The magnesium oxide sintered body can be obtained by sintering magnesium compounds such as magnesium hydroxide, magnesium carbonate, magnesium chloride, magnesium nitrate, and magnesium sulfate. As magnesium hydroxide, magnesium hydroxide precipitated by the reaction of magnesium salts in seawater with calcium hydroxide can be used. As magnesium carbonate, magnesite ore can be used.

[0036] The magnesium compound is preferably calcined at 1300°C to 2800°C in the atmosphere. When the temperature is less than 1300°C, the crystallite diameter is less than the prescribed range and the BET specific surface area is greater than the prescribed range, which tends to make the material have an excessive dissolution rate. On the other hand, if the temperature exceeds 2800°C, the crystallite diameter is greater than the prescribed range and the BET specific surface area is less than the prescribed range, which tends to make the material insufficient as an alkali agent. The calcination temperature is more preferably 1400°C to 2400°C. The calcination time is preferably set to 10 minutes to 10 hours.

[0037] The content of components in the MgO particles including the MgO content can be adjusted when firing the magnesium oxide sintered body. Specifically, it can be controlled by selecting the magnesium compound as the firing raw material and using additives corresponding to impurities such as Si. If the manufacturing efficiency is considered, it is preferred to refer to the amount of impurities in the magnesium compound as the raw material and adjust it by selecting and combining the magnesium compound.

[0038] The Si content can be adjusted by any additive. The additive is not particularly limited, and examples thereof include silica fume, silica sand, sodium silicate, etc. As the magnesium compound, a circulating product can also be used, but a magnesium compound with adjusted components can also be prepared by known means. It should be noted that, in the case where a magnesium oxide sintered body that meets the specified conditions can be obtained, the magnesium oxide sintered body can also be used.

[0039] When the magnesium oxide sintered body contains a large amount of coarse particles, it can be crushed to a particle size that is easy to handle. As a crushing device, crushing devices such as hammer crusher, roll crusher, jaw crusher, impact crusher, disc mill, rolling ball mill, vibrating ball mill, pin mill, bead mill, jet mill, cyclone mill, etc. can be cited. Such a device can be used alone or in combination of two or more.

[0040] After pulverization, coarse powder and / or fine powder can be removed by classification to form a preferred particle size distribution. The classification method is not particularly limited, and a vibrating screen, a wind classifier, a cyclone classifier, etc. can be used alone or in combination of two or more.

[0041] The magnesium oxide sintered body can be subjected to the above-mentioned crushing and / or classification treatment as needed to adjust the particle size to a specified value. The crushing step and the classification step can be appropriately combined according to the magnesium oxide sintered body, and the order and number of times are not particularly limited. Either the classification step or the crushing step can be performed first, or the crushing step can be further performed after the classification step is performed on the magnesium oxide sintered body that has undergone the crushing step.

[0042] When the particle size of the magnesium oxide sintered body to be used satisfies the desired properties, it can be used without performing the pulverization step and the classification step.

[0043] As long as the MgO particles have the conditions of crystallite diameter, BET specific surface area and MgO content, they can be effectively used as the alkali agent of the present invention. Since they have a moderate dissolution rate and can exert a stable effect for a long time, the material of the present invention can be suitably used as an alkali agent.

[0044] Example

[0045] Hereinafter, the present invention will be specifically described based on Examples, but these do not limit the purpose of the present invention, and the present invention is not limited to these Examples.

[0046] <Manufacturing of magnesium oxide>

[0047] As a raw material magnesium compound, magnesium hydroxide obtained by reaction of seawater and slaked lime is prepared. The content of components in magnesium hydroxide is determined by impurities from slaked lime, the presence or absence of an impurity removal step, and additives.

[0048] Magnesium hydroxide was sintered to produce a magnesium oxide sintered body, and pulverization and classification were combined to produce MgO particles as examples and comparative examples. When producing MgO particles, the sintering temperature and pulverization / classification were controlled so that the crystallite diameter and the BET specific surface area became the values ​​of Table 1. The sintering temperature and the presence or absence of pulverization / classification are shown in Table 1. An impact crusher and a cyclone mill were used in pulverization 1, screening and wind screening were used in classification, and a cyclone mill was used in pulverization 2.

[0049] The crystallite diameter, BET specific surface area, content and volume cumulative particle size of the obtained MgO particles were determined. The respective evaluation methods are as follows.

[0050] <Crystalline Diameter>

[0051] First, an XRD pattern was obtained under the following conditions using an X-ray diffractometer (NEW D8 ADVANCE manufactured by Bruker AXS).

[0052] X-ray source: CuKα (Ni filter)

[0053] Tube voltage: 40kV

[0054] Tube current: 40 mA

[0055] Detector: One-dimensional semiconductor high-speed detector LynxEye

[0056] Divergent slit: 0.30 degrees

[0057] Step size: 0.015 degrees

[0058] Counting time: 0.65 seconds / step

[0059] For the obtained XRD pattern, using analysis software (DIFFRAC.EVA V.3.2 manufactured by Bruker AXS), the crystallite diameter was calculated. The MgO (002) plane peak in the XRD pattern was specified, and the value calculated as the crystallite diameter based on the half-value width was used.

[0060] <BET specific surface area>

[0061] Using a specific surface area meter (MONOSORB manufactured by YUASA IONICS), as a pretreatment, after degassing at 180 °C for 10 minutes, the measurement was carried out using the BET single-point method.

[0062] <Determination of contained components>

[0063] The contained components of the MgO particles were determined by the glass bead method using lithium tetraborate as the melting material through a fluorescence X-ray analyzer (Supermini 200 manufactured by Rigaku). In the quantitative analysis of the detected characteristic X-rays, a standard curve prepared from magnesia refractories for fluorescence X-ray analysis (JRRM401 - 410) of the Refractories Society standard substance was used.

[0064] The five elements Mg, Ca, Si, Fe, and Al detected by fluorescence X-ray measurement were respectively converted to MgO, CaO, SiO 2 , Fe 2 O 3 , Al 2 O 3 When the total content rate (mass %) at this time was set to 100, the SiO 2 content rate and the MgO content rate were denoted as XRF(S) and XRF(M), respectively. Using the thus obtained XRF(S) and XRF(M), the S / M ratio was calculated by the following formula (1).

[0065] S / M = XRF(S) / XRF(M) (1)

[0066] The obtained results were summarized in Table 1 below together with the crystallite diameter and the BET specific surface area.

[0067] <Volume Cumulative Particle Size (D50)>

[0068] The volume-based particle size distribution was determined as the average of three repeated measurements using a laser diffraction particle size distribution analyzer (MICROTRAC MT3300EX manufactured by MicrotracBEL Co., Ltd.) using a laser beam having a wavelength of 780 nm, and the 50% volume cumulative particle size D50 was obtained.

[0069] The obtained results are summarized in Table 2 below together with D50 / crystallite diameter.

[0070] [Table 1]

[0071]

[0072] [Table 2]

[0073]

[0074] The MgO particles in the examples all have a crystallite diameter of 80 nm to 300 nm and a BET specific surface area of ​​0.1 m 2 / g~1.2m 2 In contrast, the crystallite diameter of the MgO particles of Comparative Example 1 is less than 80 nm, and the BET specific surface area of ​​the MgO particles of Comparative Examples 2 and 3 exceeds 1.2 m 2 / g.

[0075] The MgO particles of Examples and Comparative Examples were evaluated for dissolution and moisture resistance. The methods are as follows.

[0076] <Dissolution rate test>

[0077] First, 50 mg of MgO particles were dispersed in 100 mL of ion exchange water to prepare a MgO suspension. A potentiometric automatic titrator (manufactured by Kyoto Electronics Industry, AT-510 model) was used to drip 0.05 mol / L of sulfuric acid while stirring the MgO suspension, thereby maintaining the pH of the MgO suspension at 3, and the sulfuric acid consumption (CS(1)) (sulfuric acid mol / MgO mol) required to maintain the pH was calculated. The endpoint of the measurement was the time when 1 hour had passed since the start of the measurement or when the total amount of MgO in the suspension was determined to have been consumed based on the sulfuric acid consumption, and the time from the start of the measurement to the end point was taken as the titration time (seconds).

[0078] The same measurement was performed on 100 mL of ion exchange water to determine the sulfuric acid consumption (CS(0)) (sulfuric acid mol / MgOmol) of the blank. The sulfuric acid consumption (CS(0)) (sulfuric acid mol / MgOmol) of the magnesium oxide suspension at the end time was subtracted from the sulfuric acid consumption (CS(1)) (sulfuric acid mol / MgOmol) of the magnesium oxide suspension at the end time to determine the (sulfuric acid mol / MgOmol at the end time) based on the magnesium oxide powder.

[0079] The thus obtained (sulfuric acid mol / MgO mol at the end point) is defined as m, and the titration time (seconds) is defined as t, and the dissolution rate test value X is calculated by the following formula (2).

[0080] X=m / t (2)

[0081] When the dissolution rate test value X is 0.00035 or less, the dissolution rate is appropriate.

[0082] <Humidity resistance test>

[0083] 20 g of MgO particles were placed in a glass weighing bottle and weighed, and kept in a constant temperature and humidity chamber at a temperature of 50°C and a humidity of 85% for 120 hours. Then, the MgO particles were taken out of the constant temperature and humidity chamber, and the mass (M(1)) of the MgO particles was weighed. The mass of the MgO particles before the holding (M(0)) was used to calculate the weight increase rate by the following formula. If the mass increase rate is 2% or less, the moisture resistance is sufficient.

[0084] Mass increase rate = ((M(1) - M(0)) / M(0)) × 100 (%)

[0085] The obtained results are summarized in Table 3 below together with the dissolution rate test values.

[0086] [Table 3]

[0087]

[0088] The crystallite diameter of the MgO particles in the embodiment is 80 nm to 300 nm, and the BET specific surface area is 0.1 m 2 / g~1.2m 2 In contrast, in Comparative Example 1, where the crystallite diameter of the MgO particles is as small as less than 80 nm and the BET specific surface area exceeds 1.2 m 2 In Comparative Examples 2 and 3 where the elution rate was too high, the elution rate was too high. If one of the crystallite diameter and the BET specific surface area was not met, the function could not be exhibited for a long time.

Claims

1. An alkaline agent, characterized in that It contains magnesium oxide particles, the crystallite diameter of the magnesium oxide particles is 80nm to 300nm, and the BET specific surface area is 0.1m 2 / g~1.2m 2 / g, MgO content is 95.0 mass % or more, The MgO content is a value when the total of the contents (mass %) when the five elements Mg, Ca, Si, Fe, and Al detected by fluorescent X-ray measurement are converted into MgO, CaO, SiO2, Fe2O3, and Al2O3, respectively, is set to 100.

2. The alkaline agent according to claim 1, wherein The magnesium oxide particles have an S / M ratio represented by the following formula (1) of 0.004 to 0.040, S / M=XRF(S) / XRF(M) (1) XRF (S) and XRF (M) are the SiO2 content and MgO content when the total content (mass %) of the five elements Mg, Ca, Si, Fe, and Al detected by fluorescent X-ray measurement converted into MgO, CaO, SiO2, Fe2O3, and Al2O3 is set to 100, respectively.

3. The alkali agent according to claim 1, wherein The ratio of 50% volume cumulative particle size D50 of the magnesium oxide particles to the crystallite diameter, ie, D50 / crystalline diameter, is 100-600.

4. The alkali agent according to claim 1, wherein The magnesium oxide particles have a dissolution rate test value X represented by the following formula (2) of 0.00035 or less. X=m / t (2) In the above formula (2), m is (mol of sulfuric acid at the end point / mol of MgO) in the dissolution test in which the pH of the MgO suspension is maintained at 3, and t is the titration time in seconds.

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