Preparation method of liquid humic acid salt fertilizer

Abstract

The present application belongs to the technical field of comprehensive utilization of weathered coal, and particularly relates to a preparation method of a humic acid salt liquid fertilizer. The preparation method provided by the present application comprises the following steps: mixing weathered coal powder, an alkaline extracting agent and water to obtain an alkaline extracting solution, and mixing the alkaline extracting solution with an oxidizing agent to obtain an oxidized raw material solution; injecting an inorganic acid solution into the oxidized raw material solution, and performing an oxidation reaction on a mixed solution obtained in the step to obtain an oxidized reaction solution; the injection speed of the inorganic acid is calculated according to the decrease of 0.3-0.5 of the pH value of the mixed system of the oxidized raw material solution and the inorganic acid solution per 10 min; the pH value of the oxidized reaction solution is less than 6.6; and the oxidized reaction solution is subjected to solid-liquid separation to obtain the humic acid salt liquid fertilizer. The present application realizes effective improvement of the extraction rate of humic acid salt under the condition of not using a heavy metal salt catalyst by changing the oxidation capacity of the alkaline extracting agent and the oxidizing agent under different pH value conditions, is environmentally friendly, and is suitable for industrial promotion.

Description

Technical Field

[0001] This invention belongs to the field of comprehensive utilization technology of weathered coal, specifically relating to a method for preparing humic acid phytate liquid fertilizer. Background Technology

[0002] Weathered coal is rich in humic acid, which is widely used in agriculture, forestry, animal husbandry, petroleum, medicine, and environmental protection due to its excellent physiological activity and functions such as absorption, complexation, and exchange. Humic acid can be classified into black humic acid, brown humic acid, and fulvic acid according to its molecular weight, with brown and fulvic acids having relatively smaller molecular weights. Black humic acid is soluble under alkaline conditions, while brown humic acid is soluble in organic solvents and alkaline aqueous solutions. Flavvic acid is directly soluble in water, and its aqueous solution is acidic. Flavvic acid is the smallest molecular weight and most active component of humic acid, representing its most essential component and making it easily absorbed and utilized by plants. Flavvic acid contains various oxygen-containing functional groups, such as hydroxyl, carboxyl, quinone, methoxy, and phenolic hydroxyl groups, exhibiting a strong ability to complex metal ions.

[0003] Fulvic acid possesses anti-flocculation and anti-precipitation properties in high-calcium and magnesium water bodies. In northern regions with high-hardness water, it has been proven effective in fertilization and irrigation via drip irrigation systems in conjunction with other fertilizers, achieving integrated water and fertilizer management. Its application in agriculture has demonstrated multiple benefits, including saving on chemical fertilizer use, enhancing plant stress resistance, and improving the quality of agricultural products. Therefore, research on obtaining low-molecular-weight fulvic acid has garnered significant attention. Currently, humic acid is mainly extracted from low-cost coals such as weathered coal and lignite. Common extraction methods include "alkali dissolution and acid precipitation" and "fractional centrifugation," but these methods have low extraction rates and large residue emissions, especially for humic acid. Therefore, researchers are focusing on how to effectively prepare low-molecular-weight fulvic acid from the high- and medium-molecular-weight black and brown humic acids in weathered coal.

[0004] Chinese Patent Application No. 201610262629.2 discloses a method for in-situ catalytic preparation of fulvic acid and its salts via a thermal dissolution method. Specifically, it involves mixing low-rank coal powder obtained by pulverizing and sieving with a mixed solution of copper salt solution, oxidant, and strong alkali solution to form a mixture reaction. The solid and liquid products are then separated, and the liquid product is dried to obtain a solid product of fulvic acid. The copper salt solution used is a solution prepared with water from one of copper chloride, copper sulfate, or copper nitrate. Chinese Patent Application No. 201310069033.7 discloses a method for improving the preparation of fulvic acid from weathered coal. The method for increasing phytate yield first requires adding the residue from weathered coal or lignite after humic acid extraction to a reaction vessel at ambient temperature and pressure, along with 0.01% to 10% of the residue mass of catalyst and 1 to 30 times the residue mass of oxidant aqueous solution. The catalyst is a composite of one or more oxides of metal elements such as Fe, Cu, and Zn. Chinese Patent Application No. 201610267074.0 discloses a method for producing fulvic acid from weathered coal by catalytic oxidation of weathered coal using nanocatalysts, where the nanocatalysts are Fe and / or Cu and / or Zn metal oxides.

[0005] The methods disclosed in the aforementioned patents have improved the extraction rate of humic acid, but all of them use heavy metals as catalysts, which cause serious environmental pollution. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing humic acid liquid fertilizer. The preparation method provided by this invention has a high humic acid extraction rate without the use of heavy metal catalysts, is environmentally friendly, and is suitable for industrial promotion.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for preparing humic acid phytate liquid fertilizer, comprising the following steps:

[0009] Weathered coal powder, an alkaline extractant, and water are mixed for extraction, and a first solid-liquid separation is performed to obtain an alkaline extract; the alkaline extractant is any one or more of alkali metal hydroxides and alkali metal pyrophosphates;

[0010] The alkaline extract and the oxidant are mixed to obtain an oxidized raw material solution; the pH value of the oxidized raw material solution is ≥10; the oxidant is an alkali metal hypochlorite.

[0011] An inorganic acid solution is injected into the oxidizing raw material solution to carry out an oxidation reaction, thereby obtaining an oxidizing reaction solution; the injection rate of the inorganic acid is calculated based on a decrease in pH value of the mixture of the oxidizing raw material solution and the inorganic acid solution by 0.3 to 0.5 per 10 minutes; the pH value of the oxidizing reaction solution is <6.6;

[0012] The second solid-liquid separation of the oxidation reaction solution yields the humate liquid fertilizer.

[0013] Preferably, the injection of the inorganic acid solution is carried out in stages for the oxidation reaction, including a first continuous injection stage and a second continuous injection stage performed sequentially.

[0014] The first continuous injection stage is as follows: the inorganic acid solution is continuously injected into the oxidizing raw material solution until the pH value is 7.2 to 7.4, and then the first mixed solution is obtained. The oxidation reaction is continued for 30 to 40 minutes to obtain the second mixed solution.

[0015] The second continuous injection stage is as follows: the inorganic acid solution is continuously injected into the second mixed solution until the pH value is 6 to 6.6, and then the third mixed solution is obtained. The oxidation reaction is continued for 30 to 60 minutes to obtain the oxidation reaction solution.

[0016] Preferably, the mass ratio of the alkaline extractant to the weathered coal powder is 1:(10-20).

[0017] Preferably, the alkaline extractant is any two or three of alkali metal sodium hydroxide and alkali metal pyrophosphate.

[0018] Preferably, the oxidant is mixed with the alkaline extract in the form of an aqueous oxidant solution;

[0019] The oxidant aqueous solution has a mass percentage content of 6-12%;

[0020] The aqueous oxidant solution accounts for 5-20% of the volume of the alkaline extract.

[0021] Preferably, the inorganic acid solution is any one of hydrochloric acid, sulfuric acid, or nitric acid.

[0022] Preferably, the inorganic acid solution has a mass percentage content of 6-15%.

[0023] Preferably, the liquid phase component is collected after the second solid-liquid separation; the method further includes concentrating the liquid phase component to obtain the fulvic acid humate liquid fertilizer; the solid content of the fulvic acid humate liquid fertilizer is 20-25%.

[0024] Preferably, the mass ratio of the weathered coal powder to water is 1:(5-7).

[0025] Preferably, both the first solid-liquid separation and the second solid-liquid separation are centrifugal separations;

[0026] The centrifugal separation speed is independently 2500–3500 r / min.

[0027] This invention provides a method for preparing humic acid phosphate liquid fertilizer, comprising the following steps: mixing weathered coal powder, an alkaline extractant, and water for extraction; performing a first solid-liquid separation to obtain an alkaline extract; wherein the alkaline extractant is any one or more of alkali metal hydroxides and alkali metal pyrophosphates; mixing the alkaline extract with an oxidizing agent to obtain an oxidizing raw material solution; wherein the pH value of the oxidizing raw material solution is ≥10; wherein the oxidizing agent is an alkali metal hypochlorite; injecting an inorganic acid solution into the oxidizing raw material solution to carry out an oxidation reaction to obtain an oxidation reaction solution; wherein the injection rate of the inorganic acid is calculated based on a decrease in pH value of the mixture of the oxidizing raw material solution and the inorganic acid solution by 0.3 to 0.5 per 10 minutes; wherein the pH value of the oxidation reaction solution is <6.6; and performing a second solid-liquid separation of the oxidation reaction solution to obtain the humic acid phosphate liquid fertilizer. The preparation method provided by this invention first mixes weathered coal powder, an alkaline extractant, and water. Humic acid (including high-molecular-weight black humic acid) in the weathered coal powder is fully dissolved in the alkaline environment formed by the alkaline extractant and water. Furthermore, the black humic acid molecules are fully extended in the alkaline extract, which is conducive to molecular chain breakage. Then, the alkali metal hypochlorite is utilized as an oxidant. The hypochlorite oxidizing capacity varies within different pH ranges; as the pH decreases, the hypochlorite redox potential increases, enhancing the oxidizing capacity. This oxidizes high and medium molecular weight black humic acid, breaking down the large molecular chains into smaller molecule fulvic acid. Finally, after solid-liquid separation, fulvic acid liquid fertilizer is obtained. This preparation method, by utilizing the changes in the oxidizing capacity of the alkaline extractant and oxidant under different pH conditions at different stages, effectively improves the extraction rate of fulvic acid without using heavy metal salt catalysts. It is environmentally friendly and suitable for industrial application.

[0028] Meanwhile, the preparation method provided by the present invention has the advantages of low reaction temperature, short time consumption, simple operation and low energy consumption.

[0029] Furthermore, in this invention, the injection of the inorganic acid solution is carried out in stages for the oxidation reaction, including a first continuous injection stage and a second continuous injection stage performed sequentially. The first continuous injection stage involves continuously injecting the inorganic acid solution into the oxidation raw material solution until the pH value reaches 7.2–7.4, obtaining a first mixed solution, and continuing the oxidation reaction for 30–40 minutes to obtain a second mixed solution. The second continuous injection stage involves continuously injecting the inorganic acid solution into the second mixed solution until the pH value reaches 6–6.6, obtaining a third mixed solution, and continuing the oxidation reaction for 30–60 minutes to obtain the oxidation reaction solution. This invention, by adjusting the pH value during the oxidation reaction in stages, can effectively enhance the oxidation capacity of hypochlorite and obtain a high-yield humic acid oxidation product. Attached Figure Description

[0030] Figure 1This is a flowchart illustrating the preparation process of humic acid phytate liquid fertilizer provided in an embodiment of the present invention. Detailed Implementation

[0031] This invention provides a method for preparing humic acid phytate liquid fertilizer, comprising the following steps:

[0032] Weathered coal powder, an alkaline extractant, and water are mixed for extraction, and a first solid-liquid separation is performed to obtain an alkaline extract; the alkaline extractant is any one or more of alkali metal hydroxides and alkali metal pyrophosphates;

[0033] The alkaline extract and the oxidant are mixed to obtain an oxidized raw material solution; the pH value of the oxidized raw material solution is ≥10; the oxidant is an alkali metal hypochlorite.

[0034] An inorganic acid solution is injected into the oxidizing raw material solution to carry out an oxidation reaction, thereby obtaining an oxidizing reaction solution; the injection rate of the inorganic acid is calculated based on a decrease in pH value of the mixture of the oxidizing raw material solution and the inorganic acid solution by 0.3 to 0.5 per 10 minutes; the pH value of the oxidizing reaction solution is <6.6;

[0035] The second solid-liquid separation of the oxidation reaction solution yields the humate liquid fertilizer.

[0036] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0037] This invention involves mixing weathered coal powder, an alkaline extractant, and water for extraction, followed by a first solid-liquid separation to obtain an alkaline extract; the alkaline extractant is any one or more of alkali metal hydroxides and alkali metal pyrophosphates.

[0038] In this invention, the method for preparing the weathered coal powder preferably includes the following steps: sequentially pulverizing and sieving the weathered coal to obtain the weathered coal powder. This invention does not have specific requirements for the specific implementation of the pulverization process. In this invention, the mesh size of the sieve used for sieving is preferably 80 mesh.

[0039] In this invention, the particle size of the weathered coal powder is preferably ≤0.178mm.

[0040] In this invention, the alkali metal hydroxide is preferably sodium hydroxide and / or potassium hydroxide.

[0041] In this invention, the alkali metal pyrophosphate is preferably sodium pyrophosphate and / or potassium pyrophosphate.

[0042] In this invention, the alkaline extractant is preferably any two or three of alkali metal sodium hydroxide and alkali metal pyrophosphate.

[0043] As one or more embodiments of the present invention, the alkaline extractant is potassium hydroxide and sodium pyrophosphate; the mass ratio of potassium hydroxide and sodium pyrophosphate is preferably 1:1 or 4:1.

[0044] In this invention, the water is preferably tap water.

[0045] In this invention, the mass ratio of the alkaline extractant to the weathered coal powder is preferably 1:(10-20), more preferably 1:(12-18).

[0046] In this invention, the mass ratio of the weathered coal powder to water is preferably 1:(5-7), more preferably 1:(5.5-6).

[0047] In this invention, the extraction temperature is preferably room temperature, and the extraction time is preferably 30 to 60 minutes; the extraction is preferably carried out under stirring conditions.

[0048] In this invention, the first solid-liquid separation is preferably centrifugal separation; the centrifugal separation speed is preferably 2500-3500 r / min, more preferably 2500 r / min.

[0049] After obtaining the alkaline extract, the present invention mixes the alkaline extract with an oxidizing agent to obtain an oxidizing raw material solution; the pH value of the oxidizing raw material solution is ≥10; the oxidizing agent is an alkali metal hypochlorite.

[0050] In this invention, the alkali metal hypochlorite is preferably sodium hypochlorite and / or potassium hypochlorite. In this invention, both sodium hypochlorite and potassium hypochlorite are industrial-grade products.

[0051] In this invention, the oxidant is preferably mixed with the alkaline extract in the form of an aqueous oxidant solution.

[0052] In this invention, the mass percentage of the oxidant aqueous solution is preferably 6-12%, more preferably 6.6-11.5%.

[0053] In this invention, the volume percentage of the oxidant aqueous solution in the alkaline extract is preferably 5-20%, more preferably 6-18%.

[0054] In this invention, the mixing temperature of the alkaline extract and the oxidant is preferably room temperature, the mixing time is preferably 30 minutes, and the mixing is preferably carried out under stirring conditions.

[0055] In this invention, the pH value of the oxidizing raw material solution is ≥10, preferably 10-11.

[0056] After obtaining the oxidizing raw material solution, the present invention injects an inorganic acid solution into the oxidizing raw material solution, and the resulting mixed solution undergoes an oxidation reaction to obtain an oxidizing reaction solution; the injection rate of the inorganic acid is calculated based on the pH value of the mixed system of the oxidizing raw material solution and the inorganic acid solution decreasing by 0.3 to 0.5 every 10 minutes; the pH value of the oxidizing reaction solution is <6.6.

[0057] In this invention, the injection preferably includes a first continuous injection phase and a second continuous injection phase performed sequentially.

[0058] In this invention, the injection of the inorganic acid solution for the oxidation reaction is preferably carried out in stages, preferably including a first continuous injection stage and a second continuous injection stage in sequence.

[0059] In this invention, the first continuous injection stage is preferably: the inorganic acid solution is continuously injected into the oxidizing raw material solution until the pH value is preferably 7.2 to 7.4, more preferably 7.2, and then the injection is stopped to obtain a first mixed solution. The oxidation reaction is preferably continued for 30 to 40 minutes, preferably 30 minutes, to obtain a second mixed solution.

[0060] In this invention, the second continuous injection stage is preferably: the inorganic acid solution is continuously injected into the second mixed solution until the pH value is preferably 6 to 6.6, more preferably 6.5 to 6.6, to obtain a third mixed solution, and preferably the oxidation reaction is continued for 30 to 60 minutes, preferably 60 minutes, to obtain the oxidation reaction solution.

[0061] In this invention, the inorganic acid solution is preferably any one of hydrochloric acid, sulfuric acid, or nitric acid.

[0062] In this invention, the inorganic acid solution preferably has a mass percentage content of 6-15%, more preferably 6.6-14%.

[0063] After obtaining the oxidation reaction solution, the present invention performs a second solid-liquid separation of the oxidation reaction solution to obtain the humic acid phytate liquid fertilizer.

[0064] In this invention, the second solid-liquid separation is preferably centrifugal separation; the centrifugal separation speed is preferably 2500-3500 r / min, more preferably 3500 r / min.

[0065] In this invention, the liquid phase component is collected after the second solid-liquid separation; preferably, this invention also includes concentrating the liquid phase component to obtain the humate liquid fertilizer.

[0066] The preferred mass percentage of humic acid in the humic acid liquid fertilizer is 13.3% to 28.4%.

[0067] Compared with existing technologies, this invention has the following advantages: First, it utilizes the fact that humic acid is fully dissolved under alkaline conditions, and its molecular structure is fully extended; second, it fully utilizes the fact that hypochlorite has different oxidizing abilities under different pH conditions—as pH decreases, the redox potential increases, and the oxidizing ability is enhanced: in solutions with a pH greater than 7.2, it mainly exists as ClO₂. - As pH decreases, the redox potential increases; solutions with pH 2.2–7.2 are mainly composed of HOCl, and the redox potential increases with decreasing pH; at pH below 2.2, chlorine mainly exists as Cl2. Oxidation of high and medium molecular weight black humic acid breaks down the large molecular chains into smaller molecule fulvic acid. After solid-liquid separation, the acid is further concentrated to obtain fulvic acid salt liquid fertilizer. This method has a high extraction rate, low reaction temperature, short processing time, simple operation, and low energy consumption; furthermore, it improves nitrogen fertilizer utilization efficiency and reduces costs while increasing efficiency in cotton cultivation.

[0068] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0069] Example 1

[0070] The weathered coal was pulverized and passed through an 80-mesh sieve to obtain coal powder. 100 kg of weathered coal was mixed with 7 kg of alkaline extractant, including 5 kg of potassium hydroxide and 2 kg of sodium pyrophosphate. 600 kg of tap water was added, and the mixture was stirred for 30 minutes. The solid and liquid were separated using a high-speed centrifuge at 2500 rpm. After solid-liquid separation, the separated liquid was placed in a reaction vessel, and 5% (by volume) of industrial sodium hypochlorite solution (10 wt%) was added. The mixture was stirred for 30 minutes, and then hydrochloric acid solution (20 wt%) was injected. The pH was adjusted by decreasing the pH by 0.5 every 10 minutes until it reached 7.2. After stirring and reacting for 30 minutes, the acid solution was continued to be injected until the pH reached 6.5. The mixture was stirred and reacted for another 60 minutes until the reaction was complete. The reaction solution was centrifuged at 3500 rpm to separate the solid and liquid components. The separated liquid was concentrated to a solid content of 20% to obtain humic acid salt liquid fertilizer. The humic acid salt liquid fertilizer contained 13.30% humic acid salt by mass.

[0071] Comparative Example 1

[0072] Weathered coal was pulverized and passed through an 80-mesh sieve to obtain coal powder. 100 kg of weathered coal was mixed with 7 kg of alkaline extractant, including 5 kg of potassium hydroxide and 2 kg of sodium pyrophosphate. 600 kg of tap water was added, and the mixture was stirred for 30 minutes. The solid and liquid components were separated using a high-speed centrifuge at 2500 rpm. After solid-liquid separation, the separated liquid was placed in a reaction vessel and stirred for 30 minutes. Hydrochloric acid solution (20 wt%) was injected, and the pH was adjusted by decreasing it by 0.5 every 10 minutes until the pH reached 7.2. The mixture was stirred and reacted for 30 minutes. Then, the acid solution was continued to be injected until the pH reached 6.5, and the mixture was stirred and reacted for another 60 minutes. The reaction was then completed. The reaction solution was centrifuged at 3500 rpm to separate the solid and liquid components. The separated liquid was concentrated to a solid content of 20%, yielding a fulvic acid salt liquid fertilizer. The fulvic acid salt liquid fertilizer contained 3.48% fulvic acid salt by mass.

[0073] Compared with Comparative Example 1, the mass percentage of humic acid salts in the humic acid salt liquid fertilizer prepared in Example 1 increased by 2.83 times.

[0074] Example 2

[0075] The weathered coal was pulverized and passed through an 80-mesh sieve to obtain coal powder. 100 kg of weathered coal was mixed with 10 kg of alkaline extractant, including 8 kg of potassium hydroxide and 2 kg of sodium pyrophosphate. 700 kg of tap water was added, and the mixture was stirred for 60 minutes. The solid and liquid were separated using a high-speed centrifuge at 2500 rpm. After solid-liquid separation, the separated liquid was placed in a reaction vessel, and 8% (10%) of the volume of the separated liquid was added to an industrial sodium hypochlorite solution. The mixture was stirred for 30 minutes, and then a 20% hydrochloric acid solution was injected. The pH was adjusted by decreasing the pH by 0.5 units every 10 minutes until it reached 7.2. After stirring and reacting for 30 minutes, the acid solution was continued to be injected until the pH reached 6.6. The mixture was stirred and reacted for another 60 minutes until the reaction was complete. The reaction solution was centrifuged at 3500 rpm to separate the solid and liquid components. The separated liquid was concentrated to a solid content of 20% to obtain humic acid salt liquid fertilizer. The humic acid salt liquid fertilizer contained 21.53% humic acid salt by mass.

[0076] Comparative Example 2

[0077] Weathered coal was pulverized and passed through an 80-mesh sieve to obtain coal powder. 100 kg of weathered coal was mixed with 10 kg of alkaline extractant, including 8 kg of potassium hydroxide and 2 kg of sodium pyrophosphate. 700 kg of tap water was added, and the mixture was stirred for 60 minutes. The solid and liquid components were separated using a high-speed centrifuge at 2500 rpm. After solid-liquid separation, the separated liquid was placed in a reaction vessel and stirred for 30 minutes. A 20% hydrochloric acid solution was then injected, and the pH was adjusted by decreasing the pH by 0.5 units every 10 minutes until it reached 7.2. The mixture was stirred and reacted for 30 minutes. Then, the acid solution was continued to be injected until the pH reached 6.6, and the mixture was stirred and reacted for another 60 minutes. The reaction was then terminated. The reaction solution was centrifuged at 3500 rpm to separate the solid and liquid components. The separated liquid was concentrated to a solid content of 20%, yielding a fulvic acid salt liquid fertilizer. The fulvic acid salt liquid fertilizer contained 3.82% fulvic acid salt by mass.

[0078] Compared with Comparative Example 2, the mass percentage of humic acid salts in the humic acid salt liquid fertilizer prepared in Example 2 increased by 4.64 times.

[0079] Example 3

[0080] The weathered coal was pulverized and passed through an 80-mesh sieve to obtain coal powder. 5 kg of alkaline extractant, including 4 kg of potassium hydroxide and 1 kg of sodium pyrophosphate, was added to 100 kg of weathered coal. 600 kg of tap water was added, and the mixture was stirred for 60 minutes. The solid and liquid were separated using a high-speed centrifuge at 3000 rpm. After solid-liquid separation, the separated liquid was placed in a reaction vessel, and 10% (by volume) of industrial sodium hypochlorite solution was added. The mixture was stirred for 30 minutes, and then hydrochloric acid solution (20% concentration) was injected. The pH was adjusted by decreasing the pH by 0.5 units every 10 minutes until it reached 7.4. After stirring and reacting for 30 minutes, the acid solution was continued to be injected until the pH reached 6.6. The mixture was stirred and reacted for another 60 minutes until the reaction was complete. The reaction solution was centrifuged at 3500 rpm to separate the solid and liquid components. The separated liquid was concentrated to a solid content of 20% to obtain humic acid salt liquid fertilizer. The humic acid salt liquid fertilizer contained 28.40% humic acid salt by mass.

[0081] Comparative Example 3

[0082] Weathered coal was pulverized and passed through an 80-mesh sieve to obtain coal powder. 100 kg of weathered coal was mixed with 5 kg of alkaline extractant, including 4 kg of potassium hydroxide and 1 kg of sodium pyrophosphate. 600 kg of tap water was added, and the mixture was stirred for 60 minutes. The solid and liquid components were separated using a high-speed centrifuge at 3000 rpm. After solid-liquid separation, the separated liquid was placed in a reaction vessel and stirred for 30 minutes. A 20% hydrochloric acid solution was then injected, and the pH was adjusted by decreasing the pH by 0.5 units every 10 minutes until it reached 7.4. The mixture was stirred and reacted for 30 minutes. Then, the acid solution was continued to be injected until the pH reached 6.6, and the mixture was stirred and reacted for another 60 minutes. The reaction was then terminated. The reaction solution was centrifuged at 3500 rpm to separate the solid and liquid components. The separated liquid was concentrated to a solid content of 20%, yielding a fulvic acid salt liquid fertilizer. The fulvic acid salt liquid fertilizer contained 3.43% fulvic acid salt by mass.

[0083] Compared with Comparative Example 3, the mass percentage of humic acid salts in the humic acid salt liquid fertilizer prepared in Example 3 increased by 7.28 times.

[0084] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a humate liquid fertilizer, characterized in that, Includes the following steps: The weathered coal was pulverized and passed through an 80-mesh sieve to obtain coal powder. 100 kg of this powder was taken and 5 kg of alkaline extractant (containing 4 kg potassium hydroxide and 1 kg sodium pyrophosphate) was added. 600 kg of tap water was added, and the mixture was stirred for 60 minutes. The solid and liquid phases were then separated using a high-speed centrifuge at 3000 rpm. After separation, the liquid was placed in a reaction vessel, and 10% (by volume) of industrial sodium hypochlorite solution (10% by mass) was added. The mixture was stirred for 30 minutes, and then hydrochloric acid was injected. A solution containing 20% ​​hydrochloric acid was continuously injected, with the pH adjusted by decreasing it by 0.5 units every 10 minutes until the pH reached 7.

4. After stirring for 30 minutes, hydrochloric acid was added again to adjust the pH to 6.6, and the reaction was continued for another 60 minutes until the reaction was complete. The reaction solution was then centrifuged at 3500 rpm to separate the solids and liquids. The separated liquid was concentrated to a solid content of 20% to obtain fulvic acid salt liquid fertilizer. The fulvic acid salt liquid fertilizer contained 28.40% fulvic acid salt by mass.

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