Method for producing humic acid-containing powder, humic acid-containing water, method for improving soil, and method for promoting plant growth

Abstract

Provided is a humic acid-containing powder having a median diameter D50 of 10-50 μm and a loose bulk density of 0.40-0.8 g / cm3. Also provided is a method for producing humic acid-containing water in which the humic acid-containing powder is dissolved or dispersed in water to produce humic acid-containing water. Also provided is a method for improving soil, in which the humic acid-containing water is sprayed onto soil. Also provided is a method for promoting plant growth, in which the humic acid-containing water is supplied to a plant.

Description

Technical Field

[0001] The present invention relates to a method for producing a humic acid-containing powder, a humic acid-containing water, a method for improving soil, and a method for promoting plant growth. More specifically, the present invention relates to a humic acid-containing powder having predetermined properties, a method for producing a humic acid-containing water using the humic acid-containing powder, a method for improving soil using the humic acid-containing water, and a method for promoting plant growth using the humic acid-containing water.

Background Art

[0002] Humic acid is said to have effects such as promoting plant growth. For this reason, it has been proposed to use humic acid as a fertilizer. Humic acid is present in soil and surface water. Specifically, humic acid is contained in lignite or peat, or exists as a metabolite of bacteria. There is also natural humic acid derived from animals and plants. Industrially, humic acid that is an oxidative decomposition product of young coal such as lignite, or an alkali metal salt or alkaline earth metal salt of the oxidative decomposition product is known.

[0003] Patent Documents 1 and 2 describe a method for producing a humic acid extract and a specific humic acid extract.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Patent Documents 1 and 2 describe a humic acid extract, that is, liquid humic acid. On the one hand, considering the ease of transportation and storage, powdered humic acid can be manufactured in advance, dissolved in water at the time of use to form an aqueous solution, and this aqueous solution can also be used as a fertilizer or soil conditioner. In fact, powdered humic acid is also circulating in the market.

[0006] However, according to the findings of the present inventors, the powdered humic acid that has been circulating in the market conventionally is difficult to dissolve in water and may take time to form an aqueous solution. This leads to a decrease in work efficiency when using powdered humic acid as a fertilizer or soil conditioner.

[0007] The present invention has been made in view of such circumstances. One of the objects of the present invention is to provide a humic acid-containing powder that is easily soluble in water.

Means for Solving the Problems

[0008] The present inventors have completed the invention provided below and solved the above problems.

[0009] 1. Median diameter D 50 is 10 to 50 μm, and the loose bulk density is 0.40 to 0.8 g / cm 3 of humic acid-containing powder. 2. The humic acid-containing powder according to 1., wherein the water content is 15% by mass or less. 3. The humic acid-containing powder according to 1. or 2., wherein the roundness of the particles in the humic acid-containing powder is 0.90 to 1. 4. The humic acid-containing powder according to any one of 1. to 3., wherein the humic acid-containing powder is obtained by drying a humic acid extract extracted from a crude humic acid obtained by oxidizing young coal with nitric acid using an aqueous solution having a pH of 1 to 7. 5. The humic acid-containing powder according to any one of 1. to 4., Integrated 10% diameter D 10 The humic acid-containing powder has an integrated 10% diameter of 10 μm or more. 6. The humic acid-containing powder according to any one of 1. to 5., When the integrated 10% diameter is D 10 (D 50 - D 10 ) / D 50 is 0.1 to 0.50, the humic acid-containing powder. 7. A method for producing humic acid-containing water, which comprises dissolving or dispersing the humic acid-containing powder according to any one of 1. to 6. in water to produce humic acid-containing water. 8. A method for improving soil, which comprises spraying the humic acid-containing water produced by the production method according to 7. on the soil. 9. A method for promoting plant growth, which comprises supplying the humic acid-containing water produced by the production method according to 7. to plants.

Advantages of the Invention

[0010] The humic acid-containing powder of the present invention has good solubility in water.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described in detail. In this specification, the notation "X to Y" in the description of a numerical range represents X or more and Y or less, unless otherwise specified. For example, "1 to 5 mass%" means "1 mass% or more and 5 mass% or less".

[0012] <Humic Acid-Containing Powder> The humic acid-containing powder of the present embodiment has a median diameter D of 10 to 50 μm 50 and has a bulk density of 0.40 to 0.8 g / cm 3 .

[0013] The reason why such a humic acid-containing powder dissolves well in water can be explained as follows. Just to be on the safe side, the following explanation includes speculation, and the present invention is not limited by the following explanation.

[0014] Median diameter D 50 Humic acid-containing powder with too small a size is likely to form "lumps" on the water surface when put into water, making it difficult to dissolve in water. On the other hand, for humic acid-containing powder with too large a median diameter D 50 it is less likely to form lumps, but the surface area relative to the volume of the powder becomes small. That is, since the contact area with water per unit volume of the powder decreases, it is considered that the dissolution rate in water becomes small. Median diameter D 50 is 10 to 50 μm, that is, due to the median diameter D 50 being neither too large nor too small, it is less likely to form lumps when put into water, and the contact area with water per unit volume of the powder is sufficient, so it is considered that the solubility in water is good.

[0015] Also, when the loose bulk density is 0.8 g / cm 3 or less, it is ensured that there are gaps for water to enter between the particles constituting the humic acid-containing powder, and it is considered that the solubility in water is increased. Incidentally, in terms of ensuring gaps for water to enter, the smaller the loose bulk density, the better. However, from the viewpoints of manufacturing suitability and reducing the space required for storing the humic acid-containing powder, in this embodiment, the lower limit value of the loose bulk density is 0.40 g / cm 3 is set.

[0016] The humic acid-containing powder of this embodiment can be manufactured by using appropriate raw materials and passing through an appropriate manufacturing process. As an appropriate manufacturing process, preferably, a process of atomizing while evaporating water from the humic acid extract by an atomizer disk method can be mentioned. As far as the inventors' limited-time study is concerned, in a powdering process other than the atomizer disk method, a median diameter D of 10 to 50 μm 50 is possessed, and 0.40 to 0.8 g / cm 3It is difficult to obtain the humic acid-containing powder having a loose bulk density. However, this does not mean that the manufacturing method of the humic acid-containing powder of the present embodiment is limited. The raw materials and the manufacturing process will be described in detail later.

[0017] Continue the description of the humic acid-containing powder of the present embodiment.

[0018] (Particle size distribution) As described above, the median diameter D of the humic acid-containing powder of the present embodiment 50 is 10 to 50 μm. D 50 is preferably 15 to 45 μm, more preferably 20 to 40 μm. The median diameter D 50 being a relatively large value of 10 μm or more also leads to the fact that the alteration of the humic acid in the humic acid-containing powder of the present embodiment is suppressed. This is because when the humic acid extract is dried to obtain the humic acid-containing powder, as will be described later, if the particle size is relatively large, the influence of the hot air during drying can be mitigated.

[0019] When the cumulative 10% diameter of the humic acid-containing powder of the present embodiment is D 10 then D 10 is preferably 10 μm or more, more preferably 10 to 25 μm, still more preferably 10 to 20 μm. D 10 being 10 μm or more, in other words, the fine particles less than 10 μm in the humic acid-containing powder being less than 10% suppresses the scattering of the humic acid-containing powder due to static electricity, and the handleability of the humic acid-containing powder tends to be improved (fine particles tend to be easily scattered by static electricity).

[0020] From the same viewpoint, the value of (D 50 - D 10 ) / D 50 is preferably 0.1 to 0.50, more preferably 0.10 to 0.50, still more preferably 0.2 to 0.5, particularly preferably 0.20 to 0.50, most preferably 0.3 to 0.5, and extremely preferably 0.30 to 0.50. (D 50 - D10 ) / D 50 being 0.5 or less means that in the particle size distribution of the humic acid-containing powder, the particle size distribution on the smaller particle size side than D 50 is sharp. That is, (D 50 -D 10 ) / D 50 being 0.5 or less can be said to mean that the ratio of fine particles that are likely to scatter due to static electricity in the humic acid-containing powder is small.

[0021] From another perspective, when the cumulative 90% diameter of the humic acid-containing powder of the present embodiment is D 90 , D 90 is preferably 30 to 70 μm, more preferably 35 to 65 μm, and even more preferably 35 to 60 μm. When D 90 is 70 μm or less, in other words, when the fine particles exceeding 70 μm in the humic acid-containing powder are less than 10%, the remaining undissolved coarse particles are reduced, and the solubility of the humic acid-containing powder in water tends to be better. Also, the value of (D 90 -D 50 ) / D 50 is preferably 0.6 to 1.00, more preferably 0.60 to 1.00, even more preferably 0.65 to 0.9, and still more preferably 0.65 to 0.90. (D 90 -D 50 ) / D 50 being 1.0 or less means that in the particle size distribution of the humic acid-containing powder, the particle size distribution on the larger particle size side than D 50 is sharp. That is, (D 90 -D 50 ) / D 50 being 1.0 or less can be said to mean that the ratio of coarse particles that are likely to remain undissolved in the humic acid-containing powder is small.

[0022] D 10 、D 50 and D 90 values can be measured dry by the laser diffraction / scattering method. The D 10 , D 50 and D90 The value of 10 D 50 and 90 D The measurement can be carried out using, for example, an apparatus manufactured by HORIBA.

[0023] (Loose bulk density) As described above, the loose bulk density of the humic acid-containing powder of the present embodiment is 0.40 to 0.80 g / cm 3 . The loose bulk density is preferably 0.40 to 0.70 g / cm 3 , more preferably 0.40 to 0.60 g / cm 3 . As a method for measuring the loose bulk density, the method described in the examples below can be adopted.

[0024] (Moisture content) The moisture content of the humic acid-containing powder of the present embodiment is preferably 15% by mass or less, more preferably 1 to 15% by mass, still more preferably 3 to 12% by mass, and particularly preferably 5 to 10% by mass. By not having too high a moisture content, it is possible to expect an improvement in storage properties such as suppression of caking during storage and suppression of deterioration of humic acid. Also, by not having too high a moisture content, the humic acid-containing powder tends to be less likely to adhere to the container wall surface. That is, by not having too high a moisture content, the handleability of the humic acid-containing powder tends to be improved. The moisture content may be small, but there is a balance between the energy cost for removing moisture and the improvement in storage properties and handleability described above, so it does not necessarily have to be a value close to zero.

[0025] (Roundness) The particles in the humic acid-containing powder of the present embodiment preferably have an appropriate roundness. The roundness can be determined by analyzing an electron microscope image of the particles in the humic acid-containing powder. Specifically, it can be determined by the following steps (1) to (3). (1) Based on 100 arbitrary particles in the electron microscope image of the humic acid-containing powder, the area s and perimeter l of each particle are determined. The area s and perimeter l can be determined using image analysis software. (2) From the above s, l, and the pi π, 4πs / l 2 The circularity of each particle is calculated by the formula of. (3) The arithmetic mean value of the circularity of each particle obtained in the above (2) is adopted as the circularity in this specification.

[0026] The above circularity is preferably 0.90 to 1, more preferably 0.90 to 1.00, still more preferably 0.9 to 0.98, particularly preferably 0.90 to 0.98, especially preferably 0.9 to 0.97, and most preferably 0.90 to 0.97. When the average circularity is moderately large, the contact area between particles becomes small, so effects such as the particles becoming smoother, the handleability improving, and the tendency to agglomerate decreasing can be expected. Also, a further improvement in solubility in water can be expected.

[0027] (Melanic Index (MI)) The humic acid-containing powder of this embodiment preferably has an appropriate melanic index (MI). The MI is preferably 2 to 5, more preferably 2.0 to 5.0, still more preferably 2 to 3, and particularly preferably 2.0 to 3.0. That the MI is within this numerical range is considered to mean that the humic acid in the humic acid-containing powder has an appropriate amount of hydrophilic groups. The presence of an appropriate amount of hydrophilic groups is considered to further improve the water solubility or water dispersibility of the powder. The measurement method of MI is described as procedures (1) to (5) in the item of "Method for Producing Crude Humic Acid" described later. However, when the particle size of the humic acid-containing powder is sufficiently small, the pulverization and sieving in procedure (1) may not be necessary.

[0028] (Raw Material of Humic Acid-Containing Powder) As an example, the humic acid-containing powder can be produced using a humic acid extract as a raw material. As an example, the humic acid extract can be produced by first oxidizing young coals such as lignite with nitric acid to obtain a crude humic acid product, and then extracting the humic acid from the crude humic acid product. Hereinafter, the method for producing the crude humic acid product and the method for extracting the humic acid from the crude humic acid product will be described.

[0029] · Method for producing crude humic acid product As described above, the crude humic acid product can be obtained by oxidizing young coals such as lignite with nitric acid. Young coal is coal with a low carbon content and is defined as coal with a carbon content of 83% by mass or less. Preferably, young coal with a carbon content of 78% by mass or less is used. Such young coal is in the process of coalification and contains a large amount of aliphatic hydrocarbon structures, so it is easily decomposed by oxidation with nitric acid. As young coal, one or more of peat, sub-bituminous coal, lignite, sub-bituminous coal, etc. can be used.

[0030] When oxidizing with nitric acid, it is preferable to mix 500 - 1000 kg of concentrated nitric acid in terms of anhydrous per 1000 kg of young coal. Also, the mixing time can be, for example, 20 - 60 minutes. Oxidation with nitric acid is an intense chemical reaction and is accompanied by foaming. When the foaming is intense, it may be difficult to control the chemical reaction, so an antifoaming agent may be used. Considering that humic acid is used for soil improvement, it is preferable to use hydrophobic silica, which is a component close to soil, as the antifoaming agent. Examples of commercially available products of hydrophobic silica include the SIPERNAT series of Evonik Corporation.

[0031] By adjusting the addition amount of nitric acid, the melanic index (hereinafter abbreviated as MI) of the obtained crude humic acid product can be made 2.0 - 3.0. MI is an index used for the classification of humic acid and is the ratio of the absorbances (A 450 / A 520 ) at wavelengths 450 nm and 520 nm of the absorption spectrum of the sodium hydroxide extract. (Reference: Koichi Kumada, Chemistry of Soil Organic Matter, 2nd Edition, The Chemical Society of Japan Press (1981); Journal of the Japanese Society of Soil Science and Plant Nutrition, Vol. 71, No. 1, pp. 82 - 85 (2000)).

[0032] More specifically, MI can be calculated by the following procedure. (1) Grind the sample in a mortar, and then use a 250 - μm sieve to obtain the undersize fraction of 250 μm. (2) Take about 10 g of the above - mentioned 250 - μm undersize fraction and accurately weigh it into a weighing bottle with a known mass. Leave this weighing bottle in a dryer maintained at a temperature of 105°C for about 12 hours, then return it to room temperature in a desiccator and weigh it accurately again. Consider the mass reduction as moisture and determine the moisture content of the sample. (3) Put 0.10 g of the above - mentioned 250 - μm undersize fraction, equivalent to the dry mass, and 45 mL of 0.5 mol / L sodium hydroxide aqueous solution into a 50 - mL centrifuge tube, and shake at a speed of 250 rpm at room temperature (20°C) for about 1 hour. (4) After the shaking is completed, perform centrifugation at 3,000 x g for about 10 minutes. Filter the obtained supernatant with No. 5C filter paper manufactured by Advantec to obtain a filtrate. Measure the absorbance of the filtrate at 450 nm and 520 nm, using distilled water as a blank. At this time, if the absorbance at 450 nm shows 1.0 or more, add 0.1 mol / L sodium hydroxide aqueous solution to adjust the absorbance to be between 0.8 and 1.0, and then measure the absorbance at 520 nm. (5) Calculate the ratio of (absorbance at 450 nm / absorbance at 520 nm) and define it as MI.

[0033] The fact that MI measured as described above is 2.0 or more means that the humic acid in the crude humic acid product has sufficient hydrophilic groups, resulting in good water solubility. That is, the extraction rate with water (specifically, water with a pH of 7.0 or less) is improved. Also, if MI is 3.0 or less, it leads to the suppression of excessive oxidation reactions and a reduction in nitric acid costs.

[0034] The increase or decrease of MI can be achieved by changing the amount of nitric acid during the production of crude humic acid. Generally, increasing the amount of nitric acid will increase MI. From the above perspective, it is preferable to increase MI by increasing the amount of nitric acid. However, considering the balance with cost, MI is preferably 3.0 or less. From the perspective of achieving both improved extraction rate and cost-effectiveness, MI is more preferably in the range of 2.2 to 3.0, and even more preferably in the range of 2.2 to 2.4. Incidentally, the MI of natural humic acid is generally 1.7 or less.

[0035] · Method for extracting humic acid from crude humic acid Water is added to the crude humic acid obtained as described above, or to a crude humic acid obtained by other methods, and an alkali such as potassium hydroxide is appropriately added, for example, to achieve a pH of 1 to 7, preferably pH 5 to 7, or pH ~ 3. The resulting liquid is typically stirred at 40 to 90 °C for 0.5 to 1 hour and then cooled to 40 °C or lower. An unreacted residue can be separated from the cooled liquid by methods such as centrifugation or filter press to obtain a humic acid extract.

[0036] Incidentally, for the method of manufacturing a humic acid extract, reference can be made to the descriptions in Patent Documents 1 and 2.

[0037] (Method for manufacturing humic acid-containing powder) A humic acid-containing powder can be manufactured by drying the humic acid extract obtained as described above, or a humic acid extract obtained by other methods. In this embodiment, it is preferable to dry the humic acid extract by the atomizer disk method to form a powder. By adopting this method, a humic acid-containing powder having a median diameter D of 10 to 50 μm 50 and a bulk density of 0.40 to 0.8 g / cm 3 can be stably manufactured. Although the details are unknown, it is considered that the characteristics of the humic acid extract match these powder-forming methods, enabling the production of the desired humic acid-containing powder. Incidentally, as the inventor's finding, when water is evaporated and powdered from a humic acid extract by a method other than these methods (for example, a spray drying method), it is difficult to produce a humic acid-containing powder having a loose bulk density within the above numerical range. 50

[0038] The atomizer disk method is a method of drying and powdering a liquid raw material by spraying the liquid raw material into a space where hot air is blown using a disk-shaped high-speed rotating body (disk). When the atomizer disk method is adopted, it is particularly preferable to adopt the following conditions from the viewpoint of obtaining a powder having a desired D or loose bulk density. 50 · Hot air temperature (hot air inlet temperature): preferably 150 to 300°C, more preferably 170 to 260°C · Throughput of raw material: preferably 0.5 to 10 kg / hr, more preferably 1 to 5 kg / hr · Rotational speed of disk: preferably 10,000 to 40,000 rpm, more preferably 15,000 to 30,000 rpm

[0039] Examples of apparatuses capable of powdering by the atomizer disk method include apparatuses manufactured by Okawara Chemical Machinery Co., Ltd., product number: L-8i.

[0040] <Method for producing humic acid-containing water> The above-mentioned humic acid-containing powder can be dissolved or dispersed in water to produce a humic acid-containing water. This humic acid-containing water is preferably sprayed on the soil for soil improvement. The ratio of the humic acid-containing powder to water when producing the humic acid-containing water is not particularly limited, but in the case of spraying on the soil, it is preferable to dissolve or disperse 1 part by mass of the humic acid-containing powder in 100 to 30,000 parts by mass of water.

[0041] <Method for improving soil and method for promoting plant growth> By spraying the above-mentioned humic acid-containing water on the soil, the soil can be improved, specifically, the soil can be improved to be suitable for plant growth. Similarly, by applying the above-mentioned humic acid-containing water to plants, the growth of the plants can be promoted. Specifically, the growth of plants can be promoted by spraying the above-mentioned humic acid-containing water onto the soil where the plants have grown or been planted. Various edible plants can be mentioned as the plants.

[0042] The spraying amount onto the soil is not particularly limited, but from the viewpoint of obtaining a sufficient soil improvement effect or plant growth promotion effect and the balance with cost, the spraying amount of the humic acid-containing water can be, for example, 10 to 50 t / ha. Also, when converted to humic acid-containing powder, the spraying amount can be 0.01 to 0.1 kg / ha.

[0043] As described above, the embodiments of the present invention have been described, but these are examples of the present invention, and various configurations other than the above can be adopted. Also, the present invention is not limited to the above-described embodiments, and modifications, improvements, etc. within the scope that can achieve the object of the present invention are included in the present invention.

Examples

[0044] The embodiments of the present invention will be described in detail based on examples and comparative examples. Just to be clear, the present invention is not limited only to the examples.

[0045] <Preparation of humic acid extract> The humic acid extract was prepared according to the following procedure. (1) 500 g of lignite with a carbon content of 77% by mass, which was pulverized so as to pass through a sieve with an opening size of 250 μm, was prepared. (2) Using a 2-liter beaker, 500 g of the above lignite and 630 g of nitric acid with a concentration of 48% by mass were subjected to an oxidation reaction for about 1 hour while heating in a water bath at 70°C. At this time, a small amount of defoaming agent (hydrophobic silica) was used to suppress excessive foaming. By this oxidation reaction, a humic acid-containing solution was obtained. (3) The obtained humic acid-containing solution was dried at 105°C to obtain a crude humic acid product. The MI value of this crude humic acid product was 2.20 (measured by the above-described method). (4) To 100 g of the obtained crude humic acid, approximately 900 mL of a 0.5 mol / L potassium hydroxide aqueous solution was added, and while monitoring with a pH meter, a 1.0 mol / L potassium hydroxide aqueous solution was added to adjust the pH to 6.5. Then, in order to finely adjust the solid-liquid ratio to 1:10, a small amount of water was added. (The solid-liquid ratio is defined as the amount of the extraction solvent relative to the crude humic acid. 100 g of the crude humic acid was placed in a 1 L beaker, and the solvent was added to make it 1000 mL, which is defined as a solid-liquid ratio of 1:10.) (5) The liquid obtained in the above (4) was heated at 80 °C for 1 hour. In this way, humic acid was extracted with water to obtain a crude humic acid extraction solution. (6) The above crude humic acid extraction solution was centrifuged under the condition of centrifugal force (xg): 3000. The supernatant obtained thereby was used as a humic acid extraction solution for the production of the following humic acid-containing powder.

[0046] <Production of Humic Acid-Containing Powder> ·Examples 1 to 3 The humic acid extraction solution obtained in the above <Preparation of Humic Acid Extraction Solution> was pulverized by an atomizer disk method. Specifically, an apparatus manufactured by Ohkawara Chemical Machinery Co., Ltd., model number: L-8i was used as the apparatus, and a humic acid-containing powder was produced according to the operating conditions described in Table 1 below.

[0047] ·Comparative Examples 1 to 6 The humic acid extraction solution obtained in the above <Preparation of Humic Acid Extraction Solution> was pulverized by a spray drying method. Specifically, an existing spray drying apparatus was used, and a humic acid-containing powder was produced according to the operating conditions described in Table 1 below.

[0048] <Measurement of Physical Properties of Humic Acid-Containing Powder> ·Particle Size Distribution Using a laser diffraction / scattering type particle size distribution measuring apparatus LA-960 (manufactured by HORIBA), the particle size distribution was measured in a dry state. During the measurement, the refractive index was set to 1.81. Also, the air blowing pressure was set to 0.40 MPa. Under these conditions, the particle size distribution (volume basis) of the powders of each example and comparative example was automatically measured under atmospheric conditions. Then, from the obtained particle size distribution, D10 , D 50 and D 90 values were obtained. Also, based on these values, (D 50 -D 10 ) / D 50 value and (D 90 -D 50 ) / D 50 values were calculated.

[0049] · Loose bulk density The mass of the powder was measured when a stainless steel container with a volume of 25 mL was gently filled with the powder. The measured mass was divided by the volume (25 mL) to obtain the loose bulk density. The measurement was performed 3 times, and the average value of the 3 times was adopted as the loose bulk density.

[0050] · Moisture content The moisture content was measured using a halogen moisture meter HX204 (Mettler Toledo). The drying temperature was set at 105 °C, and 1 g of the powder of each example or comparative example was used to automatically measure the moisture content. The measurement was performed 3 times, and the average value of the 3 times was adopted as the moisture content.

[0051] · Circularity An image of the particles in the humic acid-containing powder was obtained using a scanning electron microscope (Regulus 8220, manufactured by Hitachi High-Tech Corporation). Based on this image, the circularity was determined in the same manner as the above-described procedures (1) to (3). Incidentally, the area s and perimeter l of the particles in the image were determined using image analysis software ImageJ (version 1.53). At this time, 100 points were used as a guide for the measurement points of the area and perimeter.

[0052] · Melanic index (MI) The melanic index (MI) of the humic acid-containing powder of Example 1 was measured by the above-described method. The MI was 2.2.

[0053] <Performance evaluation> (Solubility in water) 1 g of the humic acid-containing powder of each example or comparative example was gently placed into a beaker containing 500 mL of water at room temperature, and then slowly stirred using a glass stirring rod. At this time, if the humic acid-containing powder dissolved rapidly, it was evaluated as having good solubility; if the humic acid-containing powder formed a lump on the water surface and was difficult to dissolve, it was evaluated as having poor solubility.

[0054] (Handling property: Evaluation of scattering due to static electricity) The ease of adhesion of the humic acid-containing powder when sprinkled onto a polyethylene film (negatively charged) was used to evaluate the ease of scattering due to static electricity. Specifically, based on the ease of adhesion when the humic acid-containing powder of Example 1 was sprinkled onto a polyethylene film, when the ease of powder adhesion was about the same as that of Example 1, it was evaluated as having good handling property; when the powder was clearly more likely to adhere than in Example 1, it was evaluated as having poor handling property.

[0055] (Presence or absence of humic acid alteration) Thermal analysis was used to evaluate whether the humic acid had been altered and changed into other components. Specifically, the humic acid-containing powder of each example or comparative example was subjected to thermal analysis under the following apparatus and conditions to obtain TG curves and DTA curves. Also, the freeze-dried product of the humic acid extract obtained in the above <Preparation of humic acid extract> (since it was not heated during drying, the humic acid was not altered in principle) was also subjected to thermal analysis in the same manner. Apparatus: Simultaneous differential thermal and thermogravimetric analyzer TG-DTA2000SR (manufactured by NETZSCH) Measurement temperature: From room temperature to 500 °C Heating rate: 3 °C / min Reference: α-alumina Measurement sample amount: 4.5 mg

[0056] The TG curve (curve 1-1) and DTA curve (curve 1-2) obtained for the humic acid-containing powder of each example or comparative example were compared with the TG curve (curve 2-1) and DTA curve (curve 2-2) obtained for the freeze-dried product of the humic acid extract. When the shapes and peak positions of curve 1-1 and curve 2-1 are substantially the same, and the shapes and peak positions of curve 1-2 and curve 2-2 are substantially the same, it is evaluated that the alteration of humic acid is sufficiently suppressed, and "no alteration" is described in Table 1. On the contrary, when the shapes and / or peak positions of curve 1-1 and curve 2-1 are clearly different, and / or the shapes and peak positions of curve 1-2 and curve 2-2 are clearly different, it is evaluated that the humic acid has been altered, and "alteration present" is described in Table 1.

[0057] The conditions for pulverization (operating conditions), physical properties of the humic acid-containing powder, and evaluation results are summarized in Table 1.

[0058]

Table 1

[0059] As shown in Table 1, the median diameter D 50 is 10 to 50 μm, and the loose bulk density is 0.40 to 0.80 g / cm 3 of the humic acid-containing powders of Examples 1 to 3 dissolved well in water. Also, the handleability of the humic acid-containing powders of Examples 1 to 3 was good, and scattering due to static electricity was suppressed. This is considered to be related to the small D 10 of the humic acid-containing powders of Examples 1 to 3, or the small value of (D 50 -D 10 ) / D 50 . Furthermore, the alteration of humic acid in the humic acid-containing powders of Examples 1 to 3 was suppressed. This is considered to be because the influence of hot air during drying was mitigated due to the particle size being relatively large.

[0060] This application claims the priority based on Japanese Patent Application No. 2023-037236 filed on March 10, 2023, and incorporates all of its disclosures herein.

Claims

1. Median diameter D ５０ is 10 to 50 μm, and the bulk density is 0.40 to 0.8 g / cm ３ of the humic acid-containing powder.

2. The humic acid-containing powder according to Claim 1, wherein the moisture content is 15% by mass or less.

3. The humic acid-containing powder according to Claim 1 or 2, wherein the roundness of the particles in the humic acid-containing powder is 0.90 to 1.

4. The humic acid-containing powder according to Claim 1 or 2, wherein the melanic index is 2 to 5.

5. The humic acid-containing powder according to Claim 1 or 2, Integrated 10% diameter D １０ A humic acid-containing powder having a diameter of 10 µm or more.

6. The humic acid-containing powder according to Claim 1 or 2, When the integrated 10% diameter is D １０ , (D ５０ - D １０ ) / D ５０ is 0.1 to 0.50, a humic acid-containing powder.

7. A method for producing humic acid-containing water, which comprises dissolving or dispersing the humic acid-containing powder according to Claim 1 or 2 in water to produce humic acid-containing water.

8. A method for improving soil, which comprises spraying the humic acid-containing water produced by the production method according to Claim 7 on the soil.

9. A method for promoting plant growth, which comprises supplying the humic acid-containing water produced by the production method according to Claim 7 to plants.

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