Basic aluminum lactate solution

Abstract

An object of the present invention is to develop a basic aluminum lactate solution having excellent storage stability. 【Solution means】The solution means is a basic aluminum lactate solution that satisfies the following requirements (1) to (3). That is, (1) it contains D-lactic acid, which is an optical isomer of lactic acid, and the ratio of D-lactic acid in total lactic acid (L-lactic acid + D-lactic acid) is 5 mol% or more; (2) the range of total lactic acid / Al2O3 (molar ratio) = 1.0 to 4.0; and (3) it contains a sulfuric acid component.

Description

Technical Field

[0001] The present invention relates to a basic aluminum lactate solution.

Background Art

[0002] Basic aluminum lactate solutions have been used, for example, as additives for alkaline refractories to improve air permeability and suppress digestion of basic aggregates, or as aluminum dopants for raw materials of composite oxides.

[0003] There are many known documents regarding basic aluminum lactate solutions, including Patent Document 1. Although not specified in most documents, basic aluminum lactate solutions are somewhat difficult in storage stability and tend to precipitate when stored for a long time.

[0004] In order to maintain long-term stability, Patent Document 2 discloses a method of controlling the contents of Fe, Ca, Mg, Si, carbonate ions, sulfate ions, and phosphate ions (hereinafter collectively referred to as "sub-components") to be low during production. The production method involves mixing an aluminum chloride solution, an alkali metal aluminate solution, and water to form a gel of aluminum hydroxide, washing the gel with water, adding water to obtain an aluminum hydroxide slurry, and then adding lactic acid and reacting them.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The basic aluminum lactate solution described in Patent Document 2 is suitable for use in forming ceramics because it contains a small amount of secondary components. However, in applications where it is applied to the mixing with raw materials containing secondary components, even if the basic aluminum lactate solution contains secondary components, it does not pose a problem. For example, in refractory applications where the basic aluminum lactate solution is mixed with magnesia aggregate, alumina cement, silica, etc., there is no problem even if the basic aluminum lactate solution contains secondary components.

[0007] An object of the present invention is to develop a basic aluminum lactate solution having excellent storage stability by a method different from the method of controlling secondary components.

Means for Solving the Problems

[0008] As a result of intensive studies on the above problems, the present inventors have surprisingly found that by containing a predetermined amount of D-lactic acid (D-lactic acid), which is an optical isomer of lactic acid, as lactic acid, a basic aluminum lactate solution having long-term stability can be obtained, and the present invention has been completed based on such findings.

[0009] The present invention is as follows. [1] A basic aluminum lactate solution satisfying the following requirements (1) to (3). (1) It contains D-lactic acid (D-lactic acid), which is an optical isomer of lactic acid, and the ratio of D-lactic acid in total lactic acid (L-lactic acid + D-lactic acid) is 5 mol% or more. (2) The range of total lactic acid / Al2O3 (molar ratio) is 1.0 to 4.0. (3) It contains a sulfuric acid component. [2] The basic aluminum lactate solution according to [1] above, in which the aluminum index is in the range of 0.90 to 1.10 in the following storage test. 〔Storage Test〕 As the Al2O3 concentration before the test, the Al2O3 concentration of the basic aluminum lactate solution before the storage test is measured. Weigh 20 g of the above basic aluminum lactate solution and transfer it to a 50 mL Ibo PP wide-mouth bottle sold by AS ONE Corporation, then seal it. After standing it still in a thermostatic bath set at 50 °C for 2 weeks, measure the Al2O3 concentration of the portion from the upper surface to a depth of 5 mm, and this is defined as the Al2O3 concentration after the test. Calculate the aluminum index from the following formula. Aluminum index = Al2O3 concentration after the test ÷ Al2O3 concentration before the test [3] A method for producing the basic aluminum lactate solution according to [1] or [2] above, including the following steps. (1) A first step of mixing an aqueous aluminum sulfate solution and lactic acid to prepare a mixed solution (2) A second step of precipitating sulfate ions in the above mixed solution as alkaline earth metal sulfates with an alkaline earth metal [4] A powder obtained by drying the basic aluminum lactate solution according to [1] or [2] above.

Mode for Carrying Out the Invention

[0010] Hereinafter, the present invention will be described in detail based on preferred embodiments. However, the present invention is not limited to the following embodiments, and various modifications can be made within the scope shown in the claims. In the present invention, the notation "numerical value 1 to numerical value 2" regarding a numerical range means a numerical range including both numerical values 1 and 2 with numerical value 1 as the lower limit value and numerical value 2 as the upper limit value, and is synonymous with "numerical value 1 or more and numerical value 2 or less".

[0011] The present invention relates to a basic aluminum lactate solution satisfying the following requirements (1) to (3). (1) It contains D-lactic acid, which is an optical isomer of lactic acid, and the proportion of D-lactic acid in total lactic acid (L-lactic acid + D-lactic acid) is 5 mol% or more. (2) The range of total lactic acid / Al2O3 (molar ratio) is 1.0 to 4.0. (3) It contains a sulfuric acid component.

[0012] (Requirement 1) Lactic acid has L-form and D-form as optical isomers, which are called L-lactic acid and D-lactic acid respectively. In the literature, when simply described as "lactic acid", it is common technical knowledge that it is intended to be L-lactic acid. Generally, when described as "L-lactic acid", it is often necessary to distinguish it from D-lactic acid.

[0013] The basic aluminum lactate solution of the present invention contains D-lactic acid as lactic acid, and the ratio of D-lactic acid in total lactic acid, that is, [L-lactic acid + D-lactic acid] (hereinafter referred to as "D-form ratio") is 5 mol% or more. In other words, when 100 mol of total lactic acid is contained, 5 mol or more of D-lactic acid is contained.

[0014] Due to the D-form ratio being 5 mol% or more, the basic aluminum lactate solution of the present invention includes, in addition to the mode containing both L-lactic acid and D-lactic acid, a mode in which L-lactic acid is not contained, that is, a mode containing only D-lactic acid. It should be noted that when the D-form ratio is less than 5 mol%, precipitation is likely to occur. The D-form ratio is preferably 7 mol% or more, more preferably 8 mol% or more, and particularly preferably 10 mol% or more.

[0015] In the present invention, the measurement method for obtaining the D-form ratio is as follows. (Treatment of basic aluminum lactate solution) For the basic aluminum lactate solution to be measured, in order to measure the specific rotation of lactic acid, a treatment is performed to dissolve aluminum in the solution in hydrochloric acid. Specifically, concentrated hydrochloric acid is added to the basic aluminum lactate solution in the range of Cl in concentrated hydrochloric acid / Al2O3 in basic aluminum lactate solution (molar ratio) = 3 to 10, and then boiled for 10 minutes. Then, the cooled one is used as a sample for measurement. It should be noted that during the above boiling, it is gently boiled so as not to evaporate to dryness. (Preparation of calibration curve) The lactic acids used to obtain the calibration curve are DL-lactic acid (a 50 mol% mixture of L-lactic acid and D-lactic acid) and L-lactic acid. As the DL-lactic acid, "DL-Lactic Acid Special Grade" manufactured by Kishida Chemical Co., Ltd. (Product Code: 000-43525) is used. As the L-lactic acid, "L-Lactic Acid Special Grade" manufactured by Fujifilm Wako Pure Chemical Corporation (Product Code: 129-02666) is used. Weigh precisely about 0.5 g each of the above DL-lactic acid and L-lactic acid using an analytical balance as a guide, put them into a 100 mL volumetric flask, add about 20 mL of distilled water and 2 mL of concentrated hydrochloric acid, then boil for 10 minutes. After cooling, make up to the mark with distilled water to prepare the standard solution. Note that during the above boiling, boil gently so as not to evaporate to dryness. The discrimination of optical isomers (L-form, D-form) is carried out by measuring the specific rotation. As the measuring device, the polarimeter P-2200 manufactured by JASCO Corporation is used. Note that if the same measured values as those of the said measuring device can be obtained, another measuring device may be used. Using the standard solutions of DL-lactic acid and L-lactic acid prepared above, measure each specific rotation with the above measuring device to create a calibration curve. Next, measure the specific rotation of the sample and determine the D-form ratio of the sample from the calibration curve. Note that distilled water is used for the blank measurement. In this measurement method, since a standard solution consisting only of D-lactic acid is not used, depending on the calibration curve, for example, when measuring D-lactic acid, the D-form ratio may exceed 100 mol%. However, even if it exceeds, there is no problem at all, and the value exceeding 100 mol% can be adopted as it is. By the way, when determining the D-form ratio using the lactic acid used as the raw material as the sample, the addition of concentrated hydrochloric acid and heat treatment for the sample and the standard solution are not necessary. On the other hand, when using the basic aluminum lactate solution as the sample as described above, by performing the addition of concentrated hydrochloric acid and heat treatment on the standard solution in the same way as the sample, a D-form ratio value consistent with the D-form ratio of the lactic acid used as the raw material can be obtained.

[0016] (Requirement 2) The basic aluminum lactate solution of the present invention has a total lactic acid / Al2O3 (molar ratio) in the range of 1.0 to 4.0. When the total lactic acid / Al2O3 (molar ratio) is less than 1.0, precipitation is likely to occur, and the solution stability tends to be impaired. On the other hand, when it exceeds 4.0, a stable basic aluminum lactate solution can be obtained regardless of the ratio of the optical isomers of lactic acid, but it is not economical to contain a large amount of lactic acid. The lower limit of this range is preferably 1.1, more preferably 1.2. Therefore, more preferable ranges can be exemplified as 1.1 to 4.0 and 1.2 to 4.0.

[0017] (Requirement 3) The basic aluminum lactate solution of the present invention contains a sulfuric acid component. In the sulfuric acid component, in addition to sulfate ions, when there are dispersed particles of alkaline earth metal sulfates, the sulfuric acid in the salt is included. The sulfuric acid component preferably has a range of SO4 / Al2O3 (molar ratio) = 0.01 to 0.5. The concentration of sulfate ions is not particularly limited as long as it is below the maximum concentration that can be contained as ions.

[0018] The Al2O3 concentration of the basic aluminum lactate solution of the present invention is preferably in the range of 1 to 20% by mass. From the viewpoints of economy in production and transportation, the lower limit is more preferably 3% by mass, still more preferably 5% by mass. The upper limit is more preferably 15% by mass.

[0019] A preferred form of the basic aluminum lactate solution of the present invention contains an alkaline earth metal component. In addition to alkaline earth metal ions, the alkaline earth metal component includes the alkaline earth metal in the salt when there are dispersed particles of alkaline earth metal sulfate. Preferred examples of the alkaline earth metal are calcium, strontium, barium, etc., and calcium is particularly preferred. The alkaline earth metal component preferably has a range of alkaline earth metal oxide / Al2O3 (molar ratio) = 0.01 to 0.3. Here, the alkaline earth metal oxide is, for example, CaO when the alkaline earth metal is calcium. The concentration of the alkaline earth metal ions is not particularly limited as long as it is below the maximum concentration that can be contained as ions.

[0020] (Aluminum index) Another preferred form of the basic aluminum lactate solution of the present invention has an aluminum index in the range of 0.90 to 1.10 in the following storage test. 〔Storage test〕 As the Al2O3 concentration before the test, measure the Al2O3 concentration of the basic aluminum lactate solution before the storage test. Measure 20 g of the basic aluminum lactate solution into a 50 mL Ibo PP wide-mouth bottle sold by AS ONE Corporation, seal it, and let it stand in a constant temperature bath set at 50 °C for 2 weeks. Then, measure the Al2O3 concentration of the portion from the upper surface to a depth of 5 mm, and use it as the Al2O3 concentration after the test. Calculate the aluminum index from the following formula. Aluminum index = Al2O3 concentration after the test ÷ Al2O3 concentration before the test In the above, for the measurement of the Al2O3 concentration after the test, it is preferable to collect the portion from the upper surface to a depth of 5 mm and measure the Al2O3 concentration in the collected portion. When collecting, it is preferable to collect as gently as possible, that is, carefully collect in a state where the fluidity is suppressed as much as possible. As the collecting instrument, a pipette, a syringe, etc. are preferable.

[0021] If the aluminum index is in the range of 0.90 to 1.10, it can be evaluated that the storage stability is high because the change in the Al2O3 concentration of the basic aluminum lactate solution before and after the test is small, and long-term stability can also be expected. The lower limit value of the range is preferably 0.95. The upper limit value of the range is preferably 1.05. Therefore, as preferred ranges, 0.95 to 1.10, 0.90 to 1.05, and 0.95 to 1.05 can be exemplified.

[0022] (Total light transmittance) In a preferred form of the basic aluminum lactate solution of the present invention, when measuring the total light transmittance of the basic aluminum lactate solution of the present invention adjusted to 9.0% by mass as the Al2O3 concentration, it is preferably 80% or more. A more preferred form is one in which the total light transmittance after being sealed and left standing at 50 °C for 2 weeks is 80% or more. As a method for adjusting the Al2O3 concentration to 9.0% by mass, methods such as dilution with distilled water and heating and concentration are preferred.

[0023] (Powder) The basic aluminum lactate solution of the present invention may be made into a powder by drying it. The powder can be used as it is or dispersed in water. As the drying method, commonly used methods such as spray drying, static drying, and fluidized bed drying can be adopted. Regarding the drying temperature, it is preferably 300 °C or lower.

[0024] (Production method) A preferred production method of the basic aluminum lactate solution of the present invention includes the following steps. (1) The first step of mixing an aqueous aluminum sulfate solution and lactic acid to prepare a mixed solution (2) The second step of precipitating sulfate ions in the mixed solution as alkaline earth metal sulfates with alkaline earth metals

[0025] In the first step, the aqueous aluminum sulfate solution preferably has, for example, an Al2O3 concentration of 1 to 14% by mass. Alternatively, a basic aluminum sulfate aqueous solution may be used instead of the aqueous aluminum sulfate solution. The lactic acid only needs to contain at least D-lactic acid. That is, the total amount may be D-lactic acid, or a combination of D-lactic acid and L-lactic acid may also be used. The method of mixing the aqueous aluminum sulfate solution and lactic acid is not particularly limited, and lactic acid may be added to the aqueous aluminum sulfate solution, or vice versa. As shown in Requirement 2, the mixing ratio of the aqueous aluminum sulfate solution and lactic acid is in the range of total lactic acid / Al2O3 (molar ratio) = 1.0 to 4.0.

[0026] The second step is a step of precipitating sulfate ions in the mixed solution obtained in the first step as alkaline earth metal sulfates using an alkaline earth metal. However, it is not necessary to completely precipitate, and the remaining of sulfate ions is allowed. Preferred examples of the alkaline earth metal are calcium, strontium, barium, etc. It is preferable to heat to efficiently generate alkaline earth metal sulfates. The heating temperature is preferably, for example, 50 to 100°C. The heating time may be appropriately set according to the heating temperature, and is preferably, for example, 0 to 12 hours. In the above, a heating time of 0 hours means stopping heating when the predetermined heating temperature is reached after starting heating.

[0027] As a step of removing the alkaline earth metal sulfates precipitated in the second step, it is preferable to use methods such as filtration, sedimentation separation, and centrifugation. Note that the dispersed particles of the alkaline earth metal sulfates may remain in the basic aluminum lactate solution of the present invention.

[0028] Furthermore, if necessary, a concentration adjustment step, a concentration step, etc. may be carried out.

Examples

[0029] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.

[0030] (Type of lactic acid) The types of lactic acid used are as follows. · DL-lactic acid: "DL-Lactic Acid Special Grade" manufactured by Kishida Chemical Co., Ltd. (Product Code: 000-43525) (Lactic acid concentration described in the test report issued by the company: 91.8% by mass) · L-lactic acid: "L-Lactic Acid Special Grade" manufactured by Fujifilm Wako Pure Chemical Corporation (Product Code: 129-02666) (Lactic acid concentration described in the inspection certificate issued by the company: 88.3% by mass) · D-lactic acid: "D-Lactic Acid" manufactured by Corbion (Lactic acid concentration described in the analysis certificate issued by the company: 92.3% by mass)

[0031] (Examples 1 to 8 and Comparative Examples 1 to 2) Common to Examples 1 to 8 and Comparative Examples 1 to 2, a basic aluminum lactate solution was prepared by the following production method. Table 1 shows the addition amounts of each raw material (aqueous aluminum sulfate solution, lactic acid solution, calcium carbonate). The aqueous aluminum sulfate solution had an Al2O3 concentration of 8% by mass. The lactic acid solution was prepared by previously mixing those described in Table 1 among the above DL-lactic acid, L-lactic acid, and D-lactic acid.

[0032] <Production Method> The lactic acid solution was added to the aqueous aluminum sulfate solution. This mixed solution was heated with stirring until it reached 90°C, calcium carbonate was slowly added, and then heating was carried out at 90°C for 1 hour. After cooling, centrifugation (5000 rpm, 20 minutes) was performed, and the supernatant was collected. This supernatant was used as the basic aluminum lactate solution. Note that the heating conditions for Example 8 were 140°C for 1 hour.

[0033] Here, in the case of Example 1 for the above production method, it is as follows. First, 5.54 g of DL-lactic acid and 23.05 g of L-lactic acid were mixed (mixing ratio of D-form and L-form was 10:90) to prepare a lactic acid solution with a D-form rate of 10 mol% in the raw material charge value. 28.59 g of the above lactic acid solution was added to 225.0 g of an aqueous aluminum sulfate solution (Al2O3 concentration: 8% by mass). The mixture was heated to 90 °C with stirring, and 56.67 g of calcium carbonate was slowly added thereto, followed by heating at 90 °C for 1 hour. The addition ratio of calcium carbonate was set so that calcium carbonate / SO4 (molar ratio) = 1.07. After cooling, centrifugation (5000 rpm, 20 minutes) was performed, and the supernatant was collected and used as the basic aluminum lactate solution of Example 1.

[0034]

Table 1

[0035] <D-isomer ratio> For each of the basic aluminum lactate solutions obtained in Examples 1 to 8 and Comparative Examples 1 and 2, the D-isomer ratios in Table 1 are the values determined as follows. (1) Raw material charge value It is a value calculated from the mixing ratio of DL-lactic acid, L-lactic acid, and D-lactic acid used in the preparation of the raw material lactic acid solution. (2) Lactic acid solution analysis value The prepared lactic acid solution was used as a sample (hereinafter referred to as "Sample A"). 0.5 g each of the above DL-lactic acid and L-lactic acid was accurately weighed using an analytical balance as a guide and placed in a 100 mL volumetric flask, dissolved in distilled water, and then made up to the mark to prepare standard solutions of DL-lactic acid and L-lactic acid. For the measurement of the specific rotation, a polarimeter P-2200 manufactured by JASCO Corporation was used and measured according to the measurement procedure. Distilled water was used for the blank measurement, and the specific rotations of the standard solutions of DL-lactic acid and L-lactic acid prepared as described above were measured to create a calibration curve. The calibration curve was y = 0.3271x - 16.317 when the D-isomer ratio was x and the specific rotation was y. Next, the specific rotation of Sample A was measured, and the D-isomer ratio was determined from the above calibration curve. (3) Basic aluminum lactate solution analysis value Concentrated hydrochloric acid was added to the basic aluminum lactate solution at a Cl / Al2O3 (molar ratio) in the concentrated hydrochloric acid to that in the basic aluminum lactate solution of 6, and then it was gently boiled for 10 minutes without a lid. Thereafter, the cooled product was used as a sample for measurement (hereinafter referred to as "Sample B"). Approximately 0.5 g each of the above-mentioned DL-lactic acid and L-lactic acid was precisely weighed using an analytical balance as a guide, placed in a 100 mL volumetric flask, about 20 mL of distilled water and 2 mL of concentrated hydrochloric acid were added, then it was gently boiled for 10 minutes without a lid, and after cooling, it was made up to the mark with distilled water to prepare a standard solution. For the measurement of the specific rotation, a polarimeter P-2200 manufactured by JASCO Corporation was used and measured according to the measurement procedure. Distilled water was used for the blank measurement, and the specific rotations of the standard solutions of DL-lactic acid and L-lactic acid prepared as above were measured to create a calibration curve. The calibration curve was y = -0.0292x + 1.5467 when the D-form ratio was x and the specific rotation was y. Next, the specific rotation of Sample B was measured, and the D-form ratio was determined from the above calibration curve.

[0036] For each of the basic aluminum lactate solutions obtained in Examples 1 to 8 and Comparative Examples 1 to 2, the measurement methods for each analysis item described in "Analytical Values of Basic Aluminum Lactate Solution" in Table 1 are as follows. Note that in Comparative Example 2, precipitation occurred in the obtained basic aluminum lactate solution, so some analysis items were not analyzed. <Al2O3 Concentration> A chelometric titration method according to a conventional method was used. The outline is a method in which the basic aluminum lactate solution is dissolved with hydrochloric acid, aluminum ions are chelated with EDTA / 2Na, the pH is adjusted with sodium acetate, and then xylenol orange is used as an indicator and titrated with a zinc solution. <CaO / Al2O3 (Molar Ratio)> The calcium concentration was measured by atomic absorption spectrophotometry according to a conventional method and calculated from the above Al2O3 concentration. <SO4 / Al2O3 (Molar Ratio)> The sulfuric acid concentration was measured by a turbidimetry method using barium chloride according to a conventional method and calculated from the above Al2O3 concentration. <ph> Measured with the portable pH meter LAQUAact manufactured by Horiba, Ltd. <ec> It was measured with a conductivity meter CM-42X manufactured by Toa DKK Corporation. <Total light transmittance> For the basic aluminum lactate solution immediately after production and after being sealed and allowed to stand at 50°C for 2 weeks, measurements were made using a haze meter "COH7700" manufactured by Nippon Denshoku Industries Co., Ltd. under the conditions of a wavelength of 400 to 700 nm (at 10 nm intervals) and an optical path length of 10 mm. <Aluminum index> The Al2O3 concentration before the storage test of the basic aluminum lactate solution was measured (Al2O3 concentration before the test). 20 g of the basic aluminum lactate solution was measured and sealed in a 50 mL I-Boy PP wide-mouth bottle sold by AS ONE Corporation, and after standing in a thermostatic bath set at 50°C for 2 weeks, the portion from the upper surface to a depth of 5 mm was gently collected with a pipette, and the Al2O3 concentration in the collected portion was measured (Al2O3 concentration after the test). The aluminum index was calculated from the following formula. Aluminum index = Al2O3 concentration after the test ÷ Al2O3 concentration before the test

[0037] Regarding the D-form ratio of each basic aluminum lactate solution obtained in Examples 1 to 8 and Comparative Examples 1 to 2, since the values of (1) the raw material charged value, (2) the lactic acid solution analysis value, and (3) the basic aluminum lactate solution analysis value all showed almost the same values, the analysis method was considered to be appropriate.

[0038] The total light transmittance was measured for each basic aluminum lactate solution obtained in Examples 1 to 8 and Comparative Example 1 as it was. For Examples 2 to 7 in which the Al2O3 concentration was not 9.0% by mass, even if the Al2O3 concentration was adjusted to 9.0% by mass respectively and the total light transmittance was measured, it is presumed that the total light transmittance will be 80% or more both immediately after production and after storage at 50°C for 2 weeks.

[0039] Regarding the aluminum index of each basic aluminum lactate solution obtained in Examples 1 to 8, since all were within the range of 0.90 to 1.10, they were evaluated to have high storage stability.

[0040] (Powder) The basic aluminum lactate solution obtained in Example 5 was allowed to stand and dry at 100 °C in a ventilated dryer to obtain a powder. When ion-exchanged water was added to this powder so as to have the same concentration as before drying and dissolved, a solution was obtained. The properties of this solution were the same as those of the basic aluminum lactate solution before drying. The pH of this solution was 5.5 and the EC was 2.3 mS / cm.< / ec> < / ph>

Claims

1. A basic aluminum lactate solution satisfying the following requirements (1) to (3). (1) It contains D-lactic acid, which is an optical isomer of lactic acid, and the proportion of D-lactic acid in total lactic acid (L-lactic acid + D-lactic acid) is 5 mol% or more. (2) Total lactic acid / Al 2 O 3 (molar ratio) is in the range of 1.0 to 4.

0. (3) It contains a sulfuric acid component.

2. The basic aluminum lactate solution according to Claim 1, wherein in the following storage test, the aluminum index is in the range of 0.90 to 1.

10. 〔Storage test〕 Al before the test 2 O 3 As the concentration, Al before the storage test of the above basic aluminum lactate solution 2 O 3 Measure the concentration. Measure 20 g of the above basic aluminum lactate solution into a 50 mL I-Boy PP wide-mouth bottle sold by AS ONE Corporation, seal it, and let it stand in a thermostatic bath set at 50°C for 2 weeks. Then, measure the Al concentration in the portion from the upper surface to a depth of 5 mm and use it as the Al concentration after the test. 2 O 3 concentration, and use it as the Al concentration after the test. 2 O 3 concentration. The aluminum index is calculated from the following formula. Aluminum index = Al2O3 concentration after the test ÷ Al2O3 concentration before the test 2 O 3 concentration after the test ÷ Al 2 O 3 concentration before the test

3. A method for producing the basic aluminum lactate solution according to Claim 1 or 2, comprising the following steps. (1) A first step of mixing an aqueous aluminum sulfate solution and lactic acid to prepare a mixed solution (2) A second step of precipitating sulfate ions in the mixed solution as alkaline earth metal sulfates with an alkaline earth metal

4. A powder obtained by drying the basic aluminum lactate solution according to Claim 1 or 2.

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