Liquid humic acid and method for producing liquid humic acid

Abstract

A purpose of the present invention is to provide liquid humic acid which can be stably stored over a long period. The liquid humic acid has a concentration of nitric acid radicals of 2,000 μg / g or less and, by adding hydrochloric acid to the liquid humic acid to adjust the pH to 1, is separated into a sedimentation portion and a soluble portion. When the total organic-carbon concentration of the sedimentation portion is expressed by A mg / L and the total organic-carbon concentration of the soluble portion is expressed by B mg / L, then the value of B / A×100 is 15-1,000.

Description

Liquid humic acid and method for producing liquid humic acid

[0001] The present invention relates to a liquid humic acid and a method for producing the same.

[0002] Humic acid is a natural high molecular weight organic substance found in soil and land water. Examples of humic acid include humic acid found in lignite and peat, natural humic acid derived from bacterial metabolic products, and natural humic acid derived from plants and animals. Humic acid is believed to have the effect of promoting plant growth, and its use as a fertilizer has been proposed.

[0003] Humic acid can be classified into humin, which is the insoluble fraction, humic acid (also called humic acid), which is alkali-soluble but acid-insoluble, and fulvic acid, which is acid-soluble. The difference between humic acid and fulvic acid is determined only by their solubility at pH 1.0.

[0004] In order to use humic acid as a liquid fertilizer, an effective method for extracting humic acid has been proposed. For example, it is described that this humic acid extract is produced by extracting it from a crude humic acid product obtained by oxidizing young coal such as brown coal or lignite with nitric acid (Patent Document 1).

[0005] Japanese Patent Application Laid-Open No. 2017-71522

[0006] As described in Patent Document 1, the production of liquid humic acid involves a step of reacting lignite with nitric acid, but since the production is carried out using nitric acid, nitrate radicals may remain in the produced liquid humic acid. If nitrate radicals are present in liquid humic acid, there is a concern that the nitrate radicals may be generated as nitric acid gas during long-term storage. Therefore, it has been necessary to take complicated storage measures, such as storing the liquid humic acid in a cool, dark place with good ventilation, avoiding direct sunlight. Therefore, there has been a demand for liquid humic acid that can be stored safely. In addition, since the production is carried out using nitric acid, NOx may be released during the reaction. Ｘ There were concerns that gas would be generated, placing a heavy burden on the environment. This required complicated storage measures, such as storing the product in a cool, dark place with good ventilation and avoiding direct sunlight. Furthermore, with growing environmental awareness in recent years, there has been a movement to reduce the use of chemical fertilizers, and it is expected that in the future, even cleaner manufacturing processes will be required.

[0007] The present invention has been made in view of the above circumstances, and aims to provide a liquid humic acid that can be stably stored for a long period of time. Furthermore, the present invention aims to provide a method for producing liquid humic acid that reduces the environmental load.

[0008] The present inventors have conducted extensive research to solve the above problems, and have found that by keeping the concentration of nitrate ions at a predetermined concentration or less, it is possible to suppress the generation of nitric acid gas during long-term storage, and by keeping the ratio of the total organic carbon concentrations of the precipitated part and the soluble part within a predetermined range, it is possible to further improve the growth of crops, and have completed the present invention. In addition, by having a reaction step in which young charcoal and hydrogen peroxide are subjected to an oxidation reaction in the presence of a metal catalyst, it is possible to produce liquid humic acid, and NO ＸThe inventors have found that gas generation can be suppressed by adding hydrochloric acid to the liquid humic acid, and have completed the present invention. That is, the present invention is as follows: [1] Liquid humic acid having a nitrate ion concentration of 2,000 μg / g or less, which is separated into a precipitate and a soluble portion by adjusting the pH of the liquid humic acid to 1 with hydrochloric acid, and when the total organic carbon concentration of the precipitate is A mg / L and the total organic carbon concentration of the soluble portion is B mg / L, the value of B / A x 100 is 15 to 1,000. [2] A liquid humic acid containing humic acid and fulvic acid, having a nitrate ion concentration of 2,000 μg / g or less, which is separated into a precipitate containing the humic acid and a soluble portion containing the fulvic acid by adding hydrochloric acid to adjust the pH of the liquid humic acid to 1, and where the total organic carbon concentration of the precipitate is A mg / L and the total organic carbon concentration of the soluble portion is B mg / L, the liquid humic acid has a B / A x 100 value of 15 to 1,000. [3] A liquid humic acid containing humic acid and fulvic acid, having a nitrate ion concentration of 2,000 μg / g or less, and where the total organic carbon concentration of the humic acid is C mg / L and the total organic carbon concentration of the fulvic acid is D mg / L, the liquid humic acid has a D / C x 100 value of 15 to 1,000. [4] The liquid humic acid according to [2] or [3], wherein the total organic carbon concentration of the sum of the total organic carbon concentrations of the humic acid and the fulvic acid is 4,000 to 150,000 mg / L. [5] The liquid humic acid according to [2] or [3], wherein the total organic carbon concentration of the humic acid is 2,000 to 148,000 mg / L. [6] The liquid humic acid according to [2] or [3], wherein the total organic carbon concentration of the fulvic acid is 2,000 to 50,000 mg / L. [7] The liquid humic acid according to any one of [1] to [6], wherein the tungsten concentration in the liquid humic acid is 5 μg / g or more and 500 μg / g or less. [8] The liquid humic acid according to any one of [1] to [7], wherein the sodium concentration in the liquid humic acid is 200 μg / g or more and 3,000 μg / g or less. [9] The liquid humic acid according to any one of [1] to [8], having a pH of 5 to 10.

[10] The liquid humic acid according to any one of [1] to [9], diluted with water.

[11] A method for producing liquid humic acid, comprising a reaction step of subjecting young charcoal and hydrogen peroxide to an oxidation reaction in the presence of a metal catalyst.

[12] The method for producing liquid humic acid according to

[11] , wherein the young coal is lignite.

[13] The method for producing liquid humic acid according to

[11] or

[12] , wherein the metal catalyst is sodium tungstate.

[14] The method for producing liquid humic acid according to any one of

[11] to

[13] , wherein the reaction step is a step of preparing a crude humic acid product, and includes a step of extracting humic acid from the crude humic acid product with an alkali to obtain a humic acid extract, and a step of subjecting the humic acid extract to solid-liquid separation to obtain liquid humic acid.

[15] The method for producing liquid humic acid according to any one of

[11] to

[14] , wherein the amount of fulvic acid and humic acid in the liquid humic acid is adjusted by adjusting the blending ratio of the young coal and the hydrogen peroxide.

[16] By increasing the amount of the young charcoal mixed with the hydrogen peroxide, the amount of humic acid in the liquid humic acid is increased, and by increasing the amount of the hydrogen peroxide mixed with the young charcoal, the amount of fulvic acid is increased.

[15] A method for producing liquid humic acid.

[0009] According to the present invention, it is possible to provide a liquid humic acid that can be stably stored for a long period of time, and a method for producing liquid humic acid that reduces the environmental load.

[0010] FIG. 1 shows the results of a cultivation test.

[0011] The liquid humic acid and the method for producing the liquid humic acid of the present invention will be described in detail below, but the present invention is not limited to these embodiments. In this specification, "%" is based on mass unless otherwise specified. Furthermore, a numerical range defined using the symbol "to" includes both the upper and lower limits of the range. In this embodiment, the humic acid fraction and the fulvic acid fraction, which have nearly continuous properties, are collectively referred to as humic acid.

[0012] [Liquid Humic Acid] The liquid humic acid of the present invention has a nitrate ion concentration of 2,000 μg / g or less, and is separated into a precipitate and a soluble portion by adding hydrochloric acid to adjust the pH of the liquid humic acid to 1. When the total organic carbon concentration of the precipitate is A mg / L and the total organic carbon concentration of the soluble portion is B mg / L, the value of B / A×100 is 15 to 1,000.

[0013] (Nitrate ion concentration) The liquid humic acid of the present invention has a nitrate ion concentration of 2,000 μg / g or less. Conventional liquid humic acid has been produced by a method including a step of reacting lignite with nitric acid, but the liquid humic acid of the present invention does not contain nitric acid and can be produced, for example, by a method described below. This makes it possible to make the nitrate ion concentration contained in the liquid humic acid 2,000 μg / g or less. By making the nitrate ion concentration 2,000 μg / g or less, it is possible to prevent the generation of nitric acid during long-term storage. The nitrate ion concentration is preferably 1,000 μg / g or less, more preferably 500 μg / g or less. In this specification, "nitrate ion" refers to nitrate ion (NO ３ － ), nitrite ion (NO ２ － This is a general term for nitrogen oxide ions such as nitroxide, nitrite, and nitrite.

[0014] (B / A x 100 Value) The liquid humic acid according to this embodiment is separated into a precipitate and a soluble portion by adjusting the pH of the liquid humic acid to 1 by adding hydrochloric acid. When the total organic carbon concentration of the precipitate is A mg / L and the total organic carbon concentration of the soluble portion is B mg / L, the value of B / A x 100 is 15 to 1000. If the value of B / A x 100 is less than 15, the short-term growth-promoting effect may be insufficient, and the crop growth-promoting effect of the liquid humic acid may be reduced. On the other hand, if the value of B / A x 100 is greater than 1000, the long-term growth-promoting effect may be insufficient, and the crop growth-promoting effect of the liquid humic acid may be reduced. From this perspective, the value of B / A x 100 is preferably 20 to 800. The preferred value of B / A x 100 varies depending on the condition of the soil in which liquid humic acid is used or the type of crop, and is preferably 15 to 100, more preferably 20 to 80, when the soil pH is high or when the crop is a leafy vegetable or root vegetable. When the soil pH is low or when the crop is a fruit or flower, the preferred value is 80 to 1000, more preferably 100 to 800. The total organic carbon concentrations of the precipitate and soluble fractions can be measured by the methods described in the Examples below.

[0015] Another form of liquid humic acid according to this embodiment is a liquid humic acid containing humic acid and fulvic acid. By adding hydrochloric acid to adjust the pH of the liquid humic acid to 1, the liquid humic acid is separated into a precipitate containing humic acid and a soluble portion containing fulvic acid. When the total organic carbon concentration of the precipitate is A mg / L and the total organic carbon concentration of the soluble portion is B mg / L, the value of B / A x 100 is 15 to 1000. If the value of B / A x 100 is less than 15, the short-term growth-promoting effect of the fulvic acid may be insufficient, resulting in a reduced crop growth-promoting effect of the liquid humic acid. On the other hand, if the value of B / A x 100 is greater than 1000, the long-term growth-promoting effect of the humic acid may be insufficient, resulting in a reduced crop growth-promoting effect of the liquid humic acid. From this perspective, the value of B / A x 100 is preferably 20 to 800. The preferred value of B / A x 100 varies depending on the condition of the soil in which liquid humic acid is used or the type of crop, and is preferably 15 to 100, more preferably 20 to 80, when the soil pH is high or when the crop is a leafy vegetable or root vegetable. When the soil pH is low or when the crop is a fruit or flower, the preferred value is 80 to 1000, more preferably 100 to 800. The total organic carbon concentrations of the precipitate and soluble fractions can be measured by the methods described in the Examples below.

[0016] Furthermore, when the organic matter contained in the precipitate portion is primarily composed of humic acid, the total organic carbon concentration of the precipitate portion is substantially equal to that of humic acid, and when the organic matter contained in the soluble portion is primarily composed of fulvic acid, the total organic carbon concentration of the soluble portion is substantially equal to that of fulvic acid. As described above, humic acid can be classified into humin, which is the insoluble fraction, alkali-soluble, acid-insoluble humic acid (also referred to as humic acid), and acid-soluble fulvic acid. Therefore, the precipitate portion of liquid humic acid may be referred to as humic acid, and the soluble portion may be referred to as fulvic acid. Therefore, the total organic carbon concentration of the precipitate portion of liquid humic acid according to this embodiment may be referred to as the total organic carbon concentration of humic acid in the liquid humic acid according to this embodiment, and the total organic carbon concentration of the soluble portion of liquid humic acid according to this embodiment may be referred to as the total organic carbon concentration of fulvic acid in the liquid humic acid according to this embodiment. Therefore, when the total organic carbon concentration of humic acid in the liquid humic acid according to this embodiment is C mg / L and the total organic carbon concentration of the fulvic acid is D mg / L, the value of D / C x 100 is 15 to 1000, preferably 20 to 800. The preferred value of D / C x 100 varies depending on the soil conditions or the type of crop in which the liquid humic acid is used. When the soil pH is high or the crop is a leafy vegetable or root vegetable, the preferred value is 15 to 100, more preferably 20 to 80. When the soil pH is low or the crop is a fruit or flower, the preferred value is 80 to 1000, more preferably 100 to 800.

[0017] (Total organic carbon concentration of soluble portion) The total organic carbon concentration of soluble portion in the liquid humic acid according to this embodiment is preferably 2,000 to 50,000 mg / L. When the total organic carbon concentration of soluble portion is 2,000 to 50,000 mg / L, the short-term growth-promoting effect of the liquid humic acid on crops can be further improved. From this viewpoint, the total organic carbon concentration of soluble portion is more preferably 2,000 to 45,000 mg / L, and even more preferably 2,500 to 40,000 mg / L.

[0018] (Total Organic Carbon Concentration of Fulvic Acid) The total organic carbon concentration of the fulvic acid in the liquid humic acid according to this embodiment is preferably 2,000 to 50,000 mg / L. When the total organic carbon concentration of the fulvic acid is 2,000 to 50,000 mg / L, the short-term growth-promoting effect of the liquid humic acid on crops can be further improved. From this perspective, the total organic carbon concentration of the fulvic acid is more preferably 2,000 to 45,000 mg / L, and even more preferably 2,500 to 40,000 mg / L. The total organic carbon concentration of the fulvic acid in the liquid humic acid is substantially the same as the total organic carbon concentration of the soluble portion.

[0019] (Total Organic Carbon Concentration of Humic Acid) The total organic carbon concentration of humic acid in the liquid humic acid according to this embodiment is preferably 2,000 to 148,000 mg / L. When the total organic carbon concentration of humic acid is 2,000 to 148,000 mg / L, the long-term growth-promoting effect of the liquid humic acid on crops can be further improved. From this perspective, the total organic carbon concentration of humic acid is more preferably 2,500 to 128,000 mg / L, and even more preferably 3,000 to 117,500 mg / L. The total organic carbon concentration of humic acid in the liquid humic acid is substantially the same as the total organic carbon concentration of the precipitate.

[0020] (Total Organic Carbon Concentration of Liquid Humic Acid) The total organic carbon concentration of the liquid humic acid according to this embodiment is preferably 4,000 to 150,000 mg / L. When the total organic carbon concentration of the liquid humic acid is 4,000 to 150,000 mg / L, the short-term and long-term growth-promoting effect of the liquid humic acid on crops can be further improved. From this perspective, the total organic carbon concentration of the liquid humic acid is more preferably 5,000 to 130,000 mg / L, and even more preferably 5,000 to 120,000 mg / L.

[0021] (Sum of Total Organic Carbon Concentrations of Humic Acid and Fulvic Acid) The sum of the total organic carbon concentrations of humic acid and fulvic acid in the liquid humic acid according to this embodiment is preferably 4,000 to 150,000 mg / L. When the sum of the total organic carbon concentrations of humic acid and fulvic acid in the liquid humic acid is 4,000 to 150,000 mg / L, the short-term and long-term growth-promoting effect of the liquid humic acid on crops can be further improved. From this perspective, the sum of the total organic carbon concentrations of humic acid and fulvic acid in the liquid humic acid is more preferably 5,000 to 130,000 mg / L, and even more preferably 5,000 to 120,000 mg / L. The sum of the total organic carbon concentrations of humic acid and fulvic acid in the liquid humic acid is substantially the same as the total organic carbon concentration of the liquid humic acid.

[0022] (Tungsten concentration) The tungsten concentration in the liquid humic acid according to this embodiment is preferably 5 μg / g or more and 500 μg / g or less, more preferably 8 μg / g or more and 400 μg / g or less, and even more preferably 10 μg / g or more and 200 μg / g or less. In addition, the tungsten concentration in the liquid humic acid can be achieved by adjusting the concentration of tungsten acid, heterotungstic acid, and their salts, which are metal catalysts used when producing liquid humic acid. In addition, the tungsten concentration can be measured by ICP emission spectrometry.

[0023] (Sodium concentration) The sodium concentration in the liquid humic acid according to this embodiment is preferably 200 μg / g or more and 3,000 μg / g or less, more preferably 300 μg / g or more and 2,000 μg / g or less, and even more preferably 400 μg / g or more and 800 μg / g or less. The sodium concentration in the liquid humic acid can be achieved by adjusting the concentration of sodium tungstate and sodium heterotungstate, which are metal catalysts used when producing liquid humic acid. The sodium concentration can be measured by ICP emission spectrometry.

[0024] (pH) The pH of the liquid humic acid according to this embodiment is preferably 5 to 10. When the pH of the liquid humic acid is 5 to 10, precipitation of humic acid and fulvic acid in the liquid humic acid can be suppressed. Furthermore, when the pH of the liquid humic acid is 5 to 10, the liquid humic acid can be handled more safely and the solubility of the liquid humic acid with fertilizer components can be further improved. From these viewpoints, the pH of the liquid humic acid according to this embodiment is more preferably 6.5 to 8, and even more preferably 6.5 to 7.5. The pH of the liquid humic acid can be measured by the method described in the Examples below.

[0025] The liquid humic acid according to this embodiment may be diluted with water. This makes the liquid humic acid according to this embodiment even easier to use as a fertilizer. In this case, the water content in the liquid humic acid according to this embodiment is not particularly limited, as long as the total organic carbon concentration of the diluted liquid humic acid according to this embodiment is preferably 0.1 to 100 mg / L, more preferably 0.5 to 50 mg / L, and even more preferably 1 to 20 mg / L. The total organic carbon concentration of the liquid humic acid when diluted with water can be measured by the method described in the Examples below.

[0026] [Method for producing liquid humic acid] The method for producing liquid humic acid of the present invention will be described below. Note that the method for producing liquid humic acid of the present invention is not limited to this, and various modifications are possible within the scope of the gist thereof.

[0027] The method for producing liquid humic acid of the present invention preferably includes a step of oxidizing young coal with hydrogen peroxide, preferably young coal with aqueous hydrogen peroxide, in the presence of a metal catalyst. First, young coal is oxidized with aqueous hydrogen peroxide to remove H from the young coal. ２ O ２ A crude humic acid product, which is an oxide, is prepared. It is also preferable to use a metal catalyst when preparing the crude humic acid product. After preparing the crude humic acid product, an alkali is added and an extraction operation is performed to obtain a humic acid extract. Furthermore, the unreacted residue is subjected to solid-liquid separation from the humic acid extract to obtain liquid humic acid.

[0028] Young coal is coal with a lower carbon content than bituminous coal, and is defined as having a carbon content of 83% by mass or less. Examples of young coal include peat, lignite, brown coal, and subbituminous coal. Among these, lignite is preferred because it produces a high yield of humic acid. A mixture of two or more of the above coals can also be used.

[0029] The hydrogen peroxide solution used to produce liquid humic acid is usually an aqueous solution containing 20 to 90% by mass of hydrogen peroxide. The amount of hydrogen peroxide used is preferably 5 to 500 parts by mass, more preferably 10 to 300 parts by mass, per 100 parts by mass of young charcoal.

[0030] Furthermore, by adjusting the ratio of young charcoal to hydrogen peroxide, the concentration ratio of humic acid to fulvic acid in the produced liquid humic acid can be adjusted. By increasing the amount of young charcoal relative to hydrogen peroxide, humic acid can be predominantly produced. Furthermore, by increasing the amount of hydrogen peroxide relative to young charcoal, fulvic acid can be predominantly produced. Note that a high amount of humic acid has the effect of promoting the growth of crop leaves and roots, and a high amount of fulvic acid has the effect of promoting the growth of fruits and flowers, so it is preferable to adjust the amounts of humic acid and fulvic acid depending on the purpose.

[0031] As the metal catalyst used in the production of liquid humic acid, tungstic acid and its salts can be used. ２ W ２ O ７ , H ２ WO ４ Examples of the salts of these compounds include alkali metal tungstates such as lithium salts, sodium salts, and potassium salts. Among these compounds, sodium tungstate (Na ２ WO ４ ) is preferred. Heterotungstic acid and its salts can be used as the metal catalyst. Heterotungstic acid is a compound in which a heteroatom such as phosphorus or silicon is inserted into a tungstic acid skeleton, and examples thereof include silicotungstic acid (H ３ (SiW １２ O４０ ) nH ２ O) and phosphotungstic acid (H ３ (P.W. １２ O ４０ ) nH ２ Examples of the salts of these compounds include alkali metal heterotungstates such as lithium salts, sodium salts, and potassium salts. Among these, sodium heterotungstate (Na(PW)) is particularly preferred because of its high catalytic activity. １２ O ４０ ) nH ２ These may be used alone or in combination of two or more.

[0032] When a metal catalyst is added, the amount of the metal catalyst used is preferably 3 parts by mass or less, more preferably 1.5 parts by mass or less, per 100 parts by mass of young coal. The amount of the metal catalyst used is preferably 0.001 parts by mass or more, more preferably 0.002 parts by mass or more, per 100 parts by mass of young coal. Adding a metal catalyst can increase the reaction rate. Furthermore, by setting the amount used within the above range, the function of the metal catalyst can be effectively expressed.

[0033] The temperature for producing liquid humic acid is preferably from room temperature (20°C) to 90°C, more preferably from 35°C to 90°C, even more preferably from 45°C to 85°C, and particularly preferably from 75°C to 85°C. By setting the temperature for producing liquid humic acid within the above range, the reaction between young charcoal and hydrogen peroxide solution can be promoted. Furthermore, the reaction time is preferably from 30 minutes to 6 hours, more preferably from 1 to 5 hours.

[0034] By oxidizing the young coal with hydrogen peroxide, the H ２ O ２An oxide (crude humic acid product) is prepared. After the reaction is completed, water and an alkali are added to the reaction solution (crude humic acid product) to adjust the pH to 5 to 10. For example, while measuring the pH, water or an alkali is added as needed to adjust the pH to a range of 5 to 10. By adjusting the pH to a range of 5 to 10, humic acid can be extracted at a high concentration. The pH is preferably adjusted to 6 to 10. Examples of alkalis include hydroxides and ammonia. As the hydroxide, an alkali metal hydroxide is preferred. As the alkali metal hydroxide, one or more of potassium hydroxide, sodium hydroxide, and ammonium hydroxide (aqueous ammonia) are preferred.

[0035] The concentration of the alkaline aqueous solution used in the extract is preferably an aqueous solution containing 10 to 50% by weight of alkali, more preferably an aqueous solution containing 20 to 40% by weight, and even more preferably an aqueous solution containing 25 to 35% by weight. Furthermore, according to the method for producing liquid humic acid of this embodiment, by not using nitric acid in the reaction, it is possible to reduce the amount of reagent used for neutralization compared to a production method using nitric acid.

[0036] After adjusting the pH, water is added to achieve the desired solid-liquid ratio (mass ratio). The final solid-liquid ratio is 1:3 or more, preferably 1:3 to 1:12, and more preferably 1:5 to 1:10. In this specification, the amount of extraction solvent relative to the amount of raw material young charcoal used to prepare the humic acid crude product is defined as the solid-liquid ratio. For example, when 100 g (100 mL) of solvent (water) is added to humic acid crude product prepared from 10 g of young charcoal, the solid-liquid ratio is 1:10.

[0037] The amount of alkali to be used can be determined in advance by conducting tests in which different amounts of alkali are used for the crude humic acid product, and determining the desired pH and amount of alkali to be used for the liquid humic acid. The alkali to be added to adjust the pH during extraction can be selected depending on the intended use, such as potassium hydroxide, which can be used as a fertilizer component.

[0038] The extraction is performed using a hot water bath or the like, maintaining the liquid temperature at 40 to 90°C for 0.5 to 24 hours to extract a humic acid extract. If the liquid temperature and retention time are within the above ranges, the extract will not freeze, ensuring the quality of the extract. From this perspective, the liquid temperature is preferably 45 to 90°C, more preferably 50 to 80°C. Furthermore, the retention time is preferably 0.5 to 12 hours, more preferably 1 to 6 hours. After extraction, the humic acid extract is preferably cooled to 40°C or below. Unreacted residue is separated from the humic acid extract by, for example, centrifugation or a filter press. The supernatant obtained after solid-liquid separation is used as liquid humic acid. Furthermore, the liquid humic acid of this embodiment has high solubility in water even when dehydrated and powdered, and can also be used by powdering it using spray drying, freeze drying, or the like.

[0039] According to the method for producing liquid humic acid of this embodiment, nitric acid is not used in the reaction, so NO is not produced. Ｘ Gas generation can be suppressed, and the environmental load can be reduced.

[0040] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to these examples.

[0041] [Confirmation of the presence of humic acid and fulvic acid in humic acid solution] FT-IR (Fourier transform infrared spectroscopy) and １３ The presence of humic acid and fulvic acid in the humic acid solution was confirmed by C-NMR (carbon-13 nuclear magnetic resonance) spectroscopy.

[0042] <FT-IR Measurement> The liquid humic acids obtained in each Example and Comparative Example were subjected to FT-IR measurement using a Fourier transform infrared spectrometer (manufactured by PerkinElmer, product name "Frontier FT IR") (measurement method: KBr method, measurement range: 4000 to 400 cm －１ , resolution: 8cm －１, number of scans: 32, measurement temperature: room temperature, reference: KBr). The following paper was referenced for the measurement: Fukushima, M., S. Tanaka, H. Nakamura, and S. Ito: Acid-base characterization of molecular weight fractionated humic acid. Talanta, 43, 383-390 (1996). －１ The band at 2920 cm is attributed to OH stretching vibration and NH stretching vibration. －１ The band at 1720 cm is assigned to the aliphatic CH stretching vibration. －１ The band at 1610 cm is attributed to the C=O stretching vibration of COOH. －１ The band at 1230 cm is attributed to the antisymmetric stretching vibration of COO- or aromatic C=C stretching vibration. －１ is attributed to the CO stretching vibration or the COOH bending vibration of the COOH and phenol groups.

[0043] < １３ C-NMR Measurement> The liquid humic acids obtained in each Example and Comparative Example were measured using a nuclear magnetic resonance apparatus (manufactured by Bruker, trade name "Avance Neo500 (Bruker)"). １３ C-NMR measurement was carried out (magnetic field strength: 11.74 T, measurement nucleus: １３ C, solvent: D ２O, Reference: Trimethylsilylpropanoic acid, Measurement temperature: Room temperature). The following paper was referenced for the measurements: K.A. Thorn, D.W. Folan, P. MacCarthy (1989), Characterization of the International Humic Substances Society Standard and Reference Fulvic and Humic Acids by Solution State Carbon-13 (13C) and Hydrogen-1 (1H) Nuclear Magnetic Resonance Spectrometry, US Geological Survey, Water-Resources Investigations Report 89-4196, Denver, CO, 93 pp. The peaks from 5 to 65 ppm are assigned to aliphatic compounds, those from 65 to 110 ppm to acetal and heteroaliphatic compounds, those from 110 to 165 ppm to aromatic compounds, those from 165 to 191 ppm to carboxyl groups, and those from 191 to 220 ppm to carbonyl groups.

[0044] [pH Measurement] The pH was measured by the glass electrode method while stirring the suspension (humic acid extract) with a magnetic stirrer.

[0045] [Total Organic Carbon Concentration] The total organic carbon concentration (hereinafter also referred to as "TOC") of the humic acid solution was measured using a combustion catalytic oxidation method with a total organic carbon analyzer (TOC-L manufactured by Shimadzu Corporation). Compared to the complicated humic acid quantification method (e.g., International Humic Substances Society method, see Fujitake, Humic Substances Research Vol. 3, pp. 1-9), the present embodiment uses TOC, which is easily quantifiable, as an indicator. There is a strong correlation between TOC and the amount of humic acid obtained by the humic acid quantification method. Although this varies depending on the type of lignite used as raw material, the amount of humic acid can be estimated to be 1.4 to 1.8 times the amount of TOC. The liquid humic acid was adjusted to pH 1 by adding hydrochloric acid, and then centrifuged at 5,000 × g for 10 minutes to form a precipitate from the liquid humic acid. The TOC of the supernatant (soluble portion) from which the precipitate was removed was then measured. The TOC of the precipitate was calculated by subtracting the measured TOC value of the soluble portion from the measured TOC value of the liquid humic acid.

[0046] [Measurement of Nitrate Ion Concentration] The concentration of nitrate ions in liquid humic acid was measured using ion chromatography (for example, HIC-SP manufactured by Shimadzu Corporation).

[0047] [Example 1] In a draft chamber, 2.00 g of lignite with a carbon content of 77% by mass was placed in a 100 mL beaker, and 12 g of 30% by mass hydrogen peroxide solution (3.60 g of hydrogen peroxide) and 20.0 mg of sodium tungstate were added. The oxidation reaction was carried out for 0.5 hours in an 80 ° C water bath. The crude humic acid obtained by this operation was subjected to the following extraction operation.

[0048] To this crude humic acid product, 6.00 g of a 30% by weight aqueous solution of potassium hydroxide was added, and extraction was carried out at 80° C. for 1 hour. The pH at this time was 12.

[0049] The crude extract was cooled to 40°C or below, the volatilized water was added, and the total volume was adjusted to 10 mL, followed by centrifugation at 3,500 x g for 20 minutes. The resulting liquid humic acid was appropriately diluted, and the nitrate concentration, TOC of the liquid humic acid, TOC of the precipitate (humic acid), TOC of the soluble portion (fulvic acid), and pH of the liquid humic acid were measured using the above-mentioned methods. The results are shown in Table 1.

[0050] [Examples 2-5] Liquid humic acid was produced in the same manner as in Example 1, except that raw materials having the masses shown in Table 1 were placed in a 500 mL beaker and produced under the conditions shown in Table 1.

[0051] [Examples 6 and 7] Liquid humic acid was produced in the same manner as in Example 1, except that a 500 mL beaker and a hot stirrer were used to carry out the oxidation reaction under the mass and production conditions of the raw materials shown in Table 1.

[0052] [Comparative Example 1] In a draft chamber, 20 g of lignite with a carbon content of 77% by mass was placed in a 500 mL beaker, and 41.7 g of 48% by mass nitric acid (100 parts by mass of 100% nitric acid per 100 parts by mass of young coal) was added. The oxidation reaction was carried out in a water bath at 80 ° C for 3 hours. The crude humic acid obtained by this operation was subjected to the following extraction operation.

[0053] Approximately 80 mL of water was added to this humic acid crude product, and 8 g of potassium hydroxide was added and stirred. While monitoring with a pH meter, 1.0 mol / L of potassium hydroxide aqueous solution was added appropriately while stirring to adjust the pH to 6.5. The total volume was adjusted to 200 mL with water (solid-liquid ratio was 1:10), and the mixture was extracted at 80 ° C for 1 hour.

[0054] This crude extract was cooled to 40°C or below, evaporative water was replenished to make the total volume 200 mL, and the extract was centrifuged at 3,500 xg for 20 minutes to obtain liquid humic acid.

[0055] In addition, in all of the liquid humic acids in the Examples and Comparative Examples, FT-IR and １３ The presence of humic acid and fulvic acid was confirmed by C-NMR.

[0056]

[0057] As shown in Table 1, the liquid humic acid of Examples 1 to 7 has a low nitrate concentration of less than 100 μg / g (below the detection limit), so it is thought that the generation of nitric acid gas can be suppressed during storage and stable long-term storage is possible. In addition, since the liquid humic acid of Examples 1 to 7 does not contain nitric acid as a raw material, NOx gas is not generated during production, and environmental load can be reduced.

[0058] [Cultivation Test] Four uniformly grown cabbage seedlings (manufactured by Sakata Seed Corporation, product name "Early Ball," two weeks after sowing) were prepared in polyethylene seedling pots. The liquid humic acid from Example 2 was diluted with water to a TOC concentration of 50 mg / L to prepare diluted liquid humic acid. Each pot of cabbage seedlings was then given 500 mL of diluted liquid humic acid every week. Ten weeks after the initial application of liquid humic acid, the masses of the heads of the four cabbage plants were measured and the average value was calculated. For comparison, a control cultivation area (Blank) was also set up in which cabbage seedlings were grown without the liquid humic acid. Ten weeks later, the masses of the heads of the four cabbage plants in the control area were also measured and the average value was calculated.

[0059] The mass of the underground parts (roots) of four cabbages grown as described above was also measured and the average was calculated. As a control, the mass of the underground parts of four cabbage seedlings not given liquid humic acid was also measured and the average was calculated. The results for the head part are shown in Figure 1(a), and the results for the underground part are shown in Figure 1(b).

[0060] As shown in FIG. 1, it was confirmed that the use of the liquid humic acid of the present invention as a fertilizer resulted in greater growth in both the head and underground parts of cabbages than the control cabbages not treated with liquid humic acid, confirming the effectiveness of the liquid humic acid of the present invention as a fertilizer.

[0061] The liquid humic acid of the present invention can be stably stored for a long period of time and has the effect of promoting crop growth, so it can be widely used as a fertilizer for crops.

Claims

1. A liquid humic acid having a nitrate ion concentration of 2,000 μg / g or less, which can be separated into a precipitate and a soluble portion by adding hydrochloric acid to adjust the pH of the liquid humic acid to 1, and in which, when the total organic carbon concentration of the precipitate is A mg / L and the total organic carbon concentration of the soluble portion is B mg / L, the value of B / A x 100 is 15 to 1000.

2. A liquid humic acid containing humic acid and fulvic acid, the concentration of nitrate ions being 2,000 μg / g or less, the liquid humic acid being separated into a precipitate containing the humic acid and a soluble portion containing the fulvic acid by adding hydrochloric acid to adjust the pH of the liquid humic acid to 1, the total organic carbon concentration of the precipitate being A mg / L and the total organic carbon concentration of the soluble portion being B mg / L, and the value of B / A x 100 being 15 to 1000.

3. A liquid humic acid containing humic acid and fulvic acid, the liquid humic acid having a nitrate ion concentration of 2,000 μg / g or less, and a D / C x 100 value of 15 to 1,000 when the total organic carbon concentration of the humic acid is C mg / L and the total organic carbon concentration of the fulvic acid is D mg / L.

4. The liquid humic acid according to claim 2 or 3, wherein the total organic carbon concentration of the sum of the total organic carbon concentration of the humic acid and the total organic carbon concentration of the fulvic acid is 4,000 to 150,000 mg / L.

5. The liquid humic acid according to claim 2 or 3, wherein the total organic carbon concentration of the humic acid is 2,000 to 148,000 mg / L.

6. The liquid humic acid according to claim 2 or 3, wherein the total organic carbon concentration of the fulvic acid is 2,000 to 50,000 mg / L.

7. A liquid humic acid according to any one of claims 1 to 3, wherein the concentration of tungsten in the liquid humic acid is 5 μg / g or more and 500 μg / g or less.

8. A liquid humic acid according to any one of claims 1 to 3, wherein the concentration of sodium in the liquid humic acid is 200 μg / g or more and 3,000 μg / g or less.

9. A liquid humic acid according to any one of claims 1 to 3, having a pH of 5 to 10.

10. A liquid humic acid according to any one of claims 1 to 3, diluted with water.

11. A method for producing liquid humic acid, comprising a reaction step of oxidizing young charcoal with hydrogen peroxide in the presence of a metal catalyst.

12. The method for producing liquid humic acid according to claim 11, wherein the young coal is lignite.

13. The method for producing liquid humic acid according to claim 11 or 12, wherein the metal catalyst is sodium tungstate.

14. The method for producing liquid humic acid according to claim 11 or 12, wherein the reaction step is a step of preparing a crude humic acid product, and includes a step of extracting humic acid from the crude humic acid product with an alkali to obtain a humic acid extract, and a step of subjecting the humic acid extract to solid-liquid separation to obtain liquid humic acid.

15. A method for producing liquid humic acid according to claim 11 or 12, wherein the amount of fulvic acid and humic acid in the liquid humic acid is adjusted by adjusting the compounding ratio of the young charcoal and the hydrogen peroxide.

16. A method for producing liquid humic acid as described in claim 15, wherein the amount of humic acid in the liquid humic acid is increased by increasing the amount of young charcoal mixed with the hydrogen peroxide, and the amount of fulvic acid is increased by increasing the amount of hydrogen peroxide mixed with the young charcoal.

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