Synthesis method of hard-water-resistant potassium fulvate for preparing fertilizer

Abstract

The invention provides a synthesis method of hard-water-resistant potassium fulvic acid for preparing a fertilizer, which comprises the following steps: mixing a nitric acid aqueous solution and an H2SO4 aqueous solution to obtain a mixed acid solution, then adding potassium fulvic acid into the mixed acid solution, then adding ZnSO4, and heating to fully react to obtain a first liquid; then, pouring out the first liquid, adjusting the pH value of the first liquid to 7, and then evaporating water in the first liquid to dryness to obtain a first solid; adding a sufficient amount of water into the first solid, and dissolving to obtain a first solid water solution; then adding 2-acrylamide-2-methylpropanesulfonic acid into the first solid aqueous solution, fully stirring, then adding ammonium persulfate, and heating for reaction to obtain a second liquid; and evaporating the solvent of the second liquid to dryness to obtain a second solid, and drying the second solid to obtain the hard-water-resistant potassium fulvate. When the obtained hard-water-resistant potassium fulvate is prepared into a solution for irrigation, the flocculation phenomenon is avoided, pipeline blockage is avoided, and the potassium fulvate absorption capacity of plants can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of hard water resistant agents and relates to a method for synthesizing hard water resistant potassium fulvic acid for preparing fertilizers. Background Art

[0002] Humic acid in lignite exists in two main forms: bound calcium humate and magnesium humate; and free humic acid. Separating bound humic acid and extracting free humic acid are two important processes for obtaining humic acid. The methods that have been used include: 1) Organic solvent extraction method An appropriate concentration of sulfuric acid is added to a coal sample, causing the bound humic acid in the coal to react with the sulfuric acid to produce humic acid and sulfate. Since most humic acid is soluble in organic solvents, acetone or other organic solvents are added to dissolve the humic acid. The humic acid is then separated from the organic solvent and extracted. Alternatively, an organic solvent can be added directly to the lignite to dissolve the free humic acid, yielding a humic acid product using the same method. This method can also be used to extract humic acid from weathered coal. Using ethanol can yield a higher yield of humic acid than acetone. Furthermore, ethanol is non-toxic and non-volatile, offering significant advantages over acetone as a solvent for humic acid extraction.

[0003] 2) Alkali dissolution and acid precipitation method The principle of alkali dissolution and acid precipitation is that the acidic groups of humic acid, such as carboxyl and hydroxyl groups, can react with strong bases (sodium hydroxide, potassium hydroxide, etc.) to generate soluble salts. The clear liquid after removing the residue reacts with strong acid, and the black and brown humic acid salts are called black and brown humic acids. However, black and brown humic acids cannot dissolve in acidic solutions. Acid is added to precipitate black and brown humic acids, and part of yellow humic acid dissolves in the acid solution and can be obtained by evaporation. This method is easy to operate and can separate yellow humic acid from black and brown humic acid. However, the extraction rate of yellow humic acid is low. The basic process is as follows: Figure 2 shown.

[0004] The sulfuric acid precipitation method is to directly add an appropriate amount of sulfuric acid to the coal sample, so that the complexation state of metal ions and carboxyl groups in the humates in the coal is destroyed by hydrogen ions, generating free humic acid that dissolves in water, and fulvic acid is obtained by evaporation. This method is suitable for extracting soluble fulvic acid.

[0005] 3) Chemical oxygenation method The method of extracting humic acid from low-rank coal has been studied by many scholars in recent years. The chemical oxidation method mainly focuses on oxidants and oxidation catalysts, and there has been a lot of research on these two aspects. Oxidants such as ozone, potassium permanganate, sodium hypochlorite, peracetic acid, and oxygen have all been used in the oxidation research of low-rank coal. The oxidation of coal by nitric acid and hydrogen peroxide has been studied the most. The addition of nitric acid can increase the yield of humic acid in lignite. Nitric acid has strong oxidizing properties and a high oxidation efficiency for coal. However, when using nitric acid to oxidize coal, nitric acid is highly corrosive and releases toxic nitrogen oxides (thick yellow smoke) during the reaction process, causing pollution and damage to the environment. Therefore, it is necessary to find a greener and safer oxidant for coal oxidation.

[0006] As a green oxidant, hydrogen peroxide produces no environmentally harmful waste during the oxidation process and is increasingly being used by researchers in the production of humic acid from coal. Hydrogen peroxide can break down the long chains and aromatic rings of coal, producing small molecules.

[0007] In addition, there are methods for preparing humic acid such as ion exchange and biochemical methods, but they generally have limitations such as long process routes, complex purification, and high process costs, which urgently need to be improved.

[0008] Weathered coal, a type of coal at a higher stage of formation than lignite, is commonly known as "outcrop coal," "low-grade coal," or "lead coal." It is the product of long-term exposure of surface or shallow-sediment lignite, bituminous coal, and anthracite to the combined effects of the atmosphere, sunlight, rain, snow, groundwater, and mineral erosion (commonly known as "weathering"). Weathered coal increases in moisture, becomes lighter in color, darkens in luster, and increases in volatile matter, decreasing its mechanical strength, cohesiveness, calorific value, and ignition point. Its elemental composition undergoes significant changes, with an increase in oxygen and a decrease in carbon and hydrogen, leading to the formation of regenerated humic acid. The total humic acid content in weathered coal generally ranges from 30% to 70%, but can reach over 80%. Its chemical activity (such as ion exchange and complexing properties) is even higher than that of lignite and peat humic acid, but its anti-flocculation properties in electrolytes are inferior to those of the latter two.

[0009] Lignite, also known as wood coal, is the lowest grade of coal produced. It is a low-grade coal with a brownish-black, dull color, intermediate between peat and bituminous coal. It is highly chemically reactive, easily weathered by air, and difficult to store and transport. Its combustion also causes significant air pollution.

[0010] Currently, commercially available potassium humate products have low resistance to hard water. When configured into solution for irrigation, flocculation often occurs, blocking pipes and making it difficult for plants to absorb.

[0011] Patent application publication CN114524910A discloses a method for preparing a light-resistant, salt-water-resistant, durable humic acid drought-resistant and water-retaining agent. Potassium fulvic acid is used as a synthetic raw material, and then polymer monomers containing carbon-carbon double bonds and good water solubility are added, including acrylic acid, potassium acrylate, acrylamide, and 2-acrylamide-2-methylpropane sulfonic acid. Finally, the cross-linking agent N,N'-methylenebisacrylamide MBA is added. Subsequently, aqueous solution free radical polymerization is carried out under the initiation of ammonium persulfate. However, the product obtained by this method has extremely low hard water resistance and cannot be used as an anti-hard water agent.

[0012] Patent application publication CN105801879A discloses a method for producing humic acid by catalytic oxidation of weathered coal using nanocatalysts. The method involves adding weathered coal to a reactor at room temperature and pressure, followed by the addition of a nanocatalyst (Fe and / or Cu and / or Zn metal oxides) at a concentration of 0.1% to 20% by weight of the weathered coal. Distilled water (5 to 20 times the weight of the weathered coal) is then added dropwise with stirring to form a suspension. Depending on the pH of the suspension, an excess of alkali may be added to control the pH within a neutral to alkaline range. After 0.5 to 60 hours of reaction, stirring is stopped, and the residue and humate solution are separated by suction or centrifugation. The humate solution contains yellow, brown, and black humates. The pH of the humate solution is adjusted to a range of 1 to 2 to precipitate the brown and black humic acids, and then the humic acid solution is separated by centrifugation. The humic acid solution obtained by this method also has extremely low resistance to hard water and cannot be used as an anti-hard water agent.

[0013] Patent application publication CN102584470A discloses a composite water-soluble fertilizer for hard water resistance and its preparation method. The fertilizer uses weathered coal, sulfuric acid, phosphoric acid, nitric acid, ammonium nitrate, potassium hydroxide, and potassium nitrate as the main raw materials; a mixture of potassium pyrophosphate, polyvinyl pyrrolidone, polyacrylamide, ammonium polyphosphate, sodium lauryl sulfate, methylsilane, xanthan gum, carrageenan, and konjac gum as auxiliary hard water resistance and sustained-release agents; and ferrous sulfate, zinc sulfate, potassium octaborate, copper sulfate, manganese sulfate, and ammonium molybdate as trace element additives. The fertilizer is prepared through processes such as degradation, modification, chelation, and stabilization. However, the hard water resistance obtained by this method needs to be improved, and the product uses a large number of strong acids and bases, making the subsequent purification process difficult and costly. Summary of the Invention

[0014] The technical problem to be solved by the present invention is that the commercially available potassium humate products have low resistance to hard water. When configured into a solution for irrigation, flocculation often occurs, which can block the pipeline and make it difficult for plants to absorb.

[0015] In order to solve the above problems, the present invention provides a method for synthesizing hard water resistant potassium fulvic acid for preparing fertilizer, comprising: 50 mL of 65% nitric acid aqueous solution and 10 mL of 4 mol / L H2SO4 aqueous solution were mixed to obtain a mixed acid solution, and then 10 g to 30 g of potassium fulvic acid and 0.5 g of ZnSO4 were added to the mixed acid solution. The mixture was heated to 80°C under stirring and fully reacted to obtain a first liquid. Subsequently, the first liquid is poured out, and the pH value of the first liquid is adjusted to 7, and then the water in the first liquid is evaporated, and the solid remaining after the water in the first liquid is evaporated is dried to obtain a first solid; Sufficient water is added to 5-10 g of the first solid to fully dissolve the solid to obtain a first solid aqueous solution; 1-2 g of 2-acrylamide-2-methylpropanesulfonic acid is then added to the first solid aqueous solution, the mixture is stirred thoroughly, and then 0.5 g of ammonium persulfate is added. The mixture is heated to 75° C. and maintained at this temperature for a thorough reaction to obtain a second liquid; The solvent of the second liquid is evaporated to dryness to obtain a second solid, and the second solid is dried to obtain hard water resistant potassium fulvic acid.

[0016] The present invention copolymerizes potassium humate with a small amount of environmentally friendly hydrophilic monomers to obtain hard water-resistant potassium humate. When the hard water-resistant potassium humate is configured into a solution for irrigation, no flocculation occurs, no pipe blockage occurs, and the absorption capacity of plants for potassium humate can be improved.

[0017] According to the above-mentioned synthesis method of hard water resistant potassium fulvic acid for preparing fertilizers of the present invention, the pH regulating liquid for adjusting the pH value of the first liquid to 7 is a KOH or K2CO3 regulating solution.

[0018] According to the above-mentioned synthesis method of potassium fulvic acid for preparing hard water-resistant fertilizer of the present invention, the preparation method of potassium fulvic acid is as follows: The cleaned coal slag is added into a KOH aqueous solution and stirred thoroughly to obtain a reaction solution; separating the filtrate and the solid in the reaction solution; Adding HCl aqueous solution dropwise to the filtrate, monitoring the pH value of the filtrate, and stopping the addition of hydrochloric acid when the pH value of the filtrate is 2-3; The brown-black solid precipitate in the filtrate was collected; The collected brown-black solid is washed with water and then dried to obtain potassium fulvic acid.

[0019] Optionally, the coal slag includes at least one of lignite or weathered coal.

[0020] Optionally, the weathered coal includes at least one of Xinjiang weathered coal and Inner Mongolia weathered coal.

[0021] Optionally, the cleaning liquid for the coal slag is deionized water or distilled water.

[0022] The technical effects of this application are: (1) When preparing the first liquid in the present invention, potassium fulvate is added to the mixed acid solution, and ZnSO4 is added and heated at the same time. The Zn²⁺ in ZnSO4 can react with the active functional groups (such as carboxyl, phenolic hydroxyl, etc.) in potassium fulvate to form a stable chelate, which helps to regulate the concentration of metal ions in the solution, prevent the free metal ions from interfering with the subsequent process, and improve the stability of potassium fulvate. After obtaining the first liquid, the present invention uses alkaline substances to condition the pH value of the first liquid to 7 so that the first liquid When the liquid is neutral or weakly alkaline, Zn²⁺ can form a chelate with the active functional groups in fulvic acid. Therefore, other impurities in the first liquid (such as Fe³⁺, Cu²⁺, etc.) are separated from potassium fulvate, and metal ions can be precipitated under alkaline conditions, thereby promoting the separation of metal impurities and improving the purity of potassium fulvate. On the other hand, Zn²⁺ is a trace element required by plants and can be directly used in fertilizers. On the other hand, high-purity potassium fulvate can combine with more 2-acrylamido-2-methylpropanesulfonic acid.

[0023] (2) The present invention uses specific coal in the preparation of potassium fulvate. The organic components contained in the Xinjiang weathered coal, Inner Mongolia weathered coal, and lignite used are mainly organic small molecules containing C, N, and O. The organic components do not contain carbon chains in the form of polymers, which can improve the hard water resistance of the final product. The potassium element in Xinjiang weathered coal and Inner Mongolia weathered coal is K + exists in the form of K + Chelation with organic matter. Potassium nitrate exists in Xinjiang weathered coal and Inner Mongolia weathered coal, which has high solubility and can further improve the product's resistance to hard water.

[0024] (3) The present invention uses AMPS (2-acrylamide-2-methylpropanesulfonic acid) in combination with the first solid. AMPS is a multifunctional water-soluble anionic surfactant with a hydrophilic sulfonic acid group that can complex calcium and magnesium ions in hard water and fertilizers, and can further improve the water solubility of potassium humate after it is configured as a fertilizer.

[0025] (4) The hard water-resistant potassium humate synthesized by this method can effectively solve the flocculation problem of potassium humate products and does not clog pipes during irrigation. The method provided by the present invention can achieve the synthesis of the target product using inexpensive and readily available reagents, without the need for any additional auxiliary reagents or any other gradient temperature control devices, resulting in safe production and low cost. The method provided by the present invention is used for halogenation catalysis, and since the reaction system is closed and the reaction temperature is moderate, no three wastes are discharged during the preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the full XPS spectrum of Xinjiang weathered coal A2; Figure 2 This is the C 1s spectrum of Xinjiang weathered coal A2; Figure 3 This is the K 2p spectrum of Xinjiang weathered coal A2; Figure 4 is the S 2p spectrum of Xinjiang weathered coal A2; Figure 5 This is the O 1s spectrum of Xinjiang weathered coal A2; Figure 6 This is the XRD spectrum of Xinjiang weathered coal A2; Figure 7 This is the thermogravimetric analysis spectrum of Xinjiang weathered coal A2; Figure 8 This is the UV spectrum analysis spectrum of Xinjiang weathered coal A2; Figure 9 These are SEM images of Xinjiang weathered coal A2: a) 1,000 times magnification; b) 2,000 times magnification; c) 5,000 times magnification; d) 1,000 times magnification; e) 2,000 times magnification; Figure 10 This is the full XPS spectrum of Inner Mongolia weathered coal A2; Figure 11 This is the C 1s spectrum of Inner Mongolia weathered coal A2; Figure 12 This is the K 2p spectrum of Inner Mongolia weathered coal A2; Figure 13 This is the S 2p spectrum of Inner Mongolia weathered coal A2; Figure 14 This is the N 1s spectrum of Inner Mongolia weathered coal A2; Figure 15 This is the O 1s spectrum of Inner Mongolia weathered coal A2; Figure 16 This is the XRD spectrum of Inner Mongolia weathered coal A2; Figure 17 This is the thermogravimetric analysis spectrum of Inner Mongolia weathered coal A2; Figure 18 This is the UV spectrum analysis spectrum of Inner Mongolia weathered coal A2; Figure 19 These are SEM images of Inner Mongolia weathered coal A2: a) 500x magnification; b) 1,000x magnification; c) 2,000x magnification; d) 1,000x magnification; Figure 20 This is the full XPS spectrum of lignite A2; Figure 21 is the C 1s spectrum of lignite A2; Figure 22 is the N 1s spectrum of lignite A2; Figure 23 is the K 2p spectrum of lignite A2; Figure 24 is the S 2p spectrum of lignite A2; Figure 25 This is the O 1s spectrum of lignite A2; Figure 26 is the XRD spectrum of lignite A2; Figure 27 This is the UV spectrum analysis spectrum of lignite A2; Figure 28 These are SEM images of lignite A2: a) 250-fold magnification; b) 1,000-fold magnification; c) 2,000-fold magnification; d) 1,000-fold magnification. DETAILED DESCRIPTION

[0027] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0028] Example 1 Weigh 25 g of crushed Xinjiang weathered coal (produced in Yiwu County, Xinjiang) and rinse it twice with 250 mL of tap water and then twice with 250 mL of distilled water.

[0029] Place the washed solid particles in 50 mL of 8% (mass percent) KOH aqueous solution and magnetically stir for 1 hour. Then, centrifuge (using a laboratory centrifuge) and collect the filtrate. Combine the filtrates (also collect the solids and store separately).

[0030] Add 3 mol / L aqueous HCl dropwise to the filtrate obtained above. Monitor the pH of the solution until the pH reaches 2.5, then stop adding HCl. A brownish-black solid precipitate (the target product, potassium fulvate) will precipitate. Collect the solid using a Büchner funnel and wash twice with 50 mL of distilled water. Finally, dry the resulting precipitate at 60°C to a constant weight, weigh it, and calculate the yield.

[0031] Mix 65% nitric acid aqueous solution (50 mL) with 4 mol / L H2SO4 aqueous solution (10 mL), then add all the potassium fulvic acid obtained in the previous step, and then add ZnSO4 (0.5 g, catalyst), and heat to 80 o C for 1 hour. Then, the liquid was decanted (the remaining solid was collected and stored separately), and the pH of the solution was adjusted to 7 with KOH or K2CO3. The water was evaporated and the remaining solid was dried to obtain solid A1.

[0032] Weigh solid A1 (6.0 g) into a 250 mL three-necked flask, add 30 mL of deionized water, and stir magnetically at room temperature until it is basically dissolved. Subsequently, add 2-acrylamide-2-methylpropanesulfonic acid (AMPS, 1.0 g) and continue stirring for 10 minutes. Then add ammonium persulfate ((NH4)2S2O8, 0.5 g), heat to 75 °C in a water bath (or oil bath), and maintain this temperature for 2 hours. Evaporate the solvent and dry the resulting solid in an oven (60 o C, 4 hours), and the Xinjiang weathered coal sample A2 was obtained.

[0033] Example 2 Weigh 25 g of crushed Inner Mongolia weathered coal (produced in Wuhai City, Inner Mongolia) and rinse it twice with 250 mL of tap water and then twice with 250 mL of distilled water.

[0034] Place the washed solid particles in 50 mL of 8% (mass percent) KOH aqueous solution and magnetically stir for 1 hour. Then, centrifuge (using a laboratory centrifuge) and collect the filtrate. Combine the filtrates (also collect the solids and store separately).

[0035] Add 3 mol / L aqueous HCl dropwise to the filtrate obtained above. Monitor the pH of the solution until the pH reaches 2.5, then stop adding HCl. A brownish-black solid precipitate (the target product, potassium fulvate) will precipitate. Collect the solid using a Büchner funnel and wash twice with 50 mL of distilled water. Finally, dry the resulting precipitate at 60°C to a constant weight, weigh it, and calculate the yield.

[0036] Mix 65% nitric acid aqueous solution (50 mL) with 4 mol / L H2SO4 aqueous solution (10 mL), then add all the potassium fulvic acid obtained in the previous step, and then add ZnSO4 (0.5 g, catalyst), and heat to 80 o C for 1 hour. Then, the liquid was decanted (the remaining solid was collected and stored separately), and the pH of the solution was adjusted to 7 with KOH or K2CO3. The water was evaporated and the remaining solid was dried to obtain solid A1.

[0037] Weigh sample A1 (6.0 g) and place it in a 250 mL three-necked flask. Add 30 mL of deionized water and stir magnetically at room temperature until the sample is essentially dissolved. Subsequently, add 2-acrylamide-2-methylpropanesulfonic acid (AMPS, 1.0 g) and continue stirring for 10 minutes. Then add ammonium persulfate ((NH4)2S2O8, 0.5 g) and heat in a water bath (or oil bath) to 75 °C and maintain this temperature for 2 hours. Evaporate the solvent and dry the resulting solid in an oven (60 °C). oC, 4 hours), and the sample Inner Mongolia weathered coal A2 was obtained.

[0038] Example 3 Weigh 25 g of crushed lignite and rinse it twice with 250 mL of tap water and then twice with 250 mL of distilled water.

[0039] Place the washed solid particles in 50 mL of 8% (mass percent) KOH aqueous solution and magnetically stir for 1 hour. Then, centrifuge (using a laboratory centrifuge) and collect the filtrate. Combine the filtrates (also collect the solids and store separately).

[0040] Add 3 mol / L aqueous HCl dropwise to the filtrate obtained above. Monitor the pH of the solution until the pH reaches 2.5, then stop adding HCl. A brownish-black solid precipitate (the target product, potassium fulvate) will precipitate. Collect the solid using a Büchner funnel and wash twice with 50 mL of distilled water. Finally, dry the resulting precipitate at 60°C to a constant weight, weigh it, and calculate the yield.

[0041] Mix 65% nitric acid aqueous solution (50 mL) with 4 mol / L H2SO4 aqueous solution (10 mL), then add all the potassium fulvic acid obtained in the previous step, and then add ZnSO4 (0.5 g, catalyst), and heat to 80 o C for 1 hour. Then, the liquid was decanted (the remaining solid was collected and stored separately), and the pH of the solution was adjusted to 7 with KOH or K2CO3. The water was evaporated and the remaining solid was dried to obtain solid A1.

[0042] Weigh sample A1 (6.0 g) and place it in a 250 mL three-necked flask. Add 30 mL of deionized water and stir magnetically at room temperature until the sample is essentially dissolved. Subsequently, add 2-acrylamide-2-methylpropanesulfonic acid (AMPS, 1.0 g) and continue stirring for 10 minutes. Then add ammonium persulfate ((NH4)2S2O8, 0.5 g) and heat in a water bath (or oil bath) to 75 °C and maintain this temperature for 2 hours. Evaporate the solvent and dry the resulting solid in an oven (60 °C). o C, 4 hours), and the lignite sample A2 was obtained.

[0043] Xinjiang weathered coal A2 was subjected to XPS analysis, and the results are shown in Table 1.

[0044] Table 1 Element binding energy and chemical composition of Xinjiang weathered coal A2 a Binding energy (eV), the value in parentheses is the atomic percentage (at%). As can be seen from Table 1: The experimental molecular formula of Xinjiang weathered coal A2 is: 20.81 C 58.82 N 0.37 K 14.81 S 4.37 B 0.82 The molecular weight is 1772.6093. The mass percentages are: O% = 18.78%; C% = 39.85%; N% = 0.29%; K% = 32.66%; S% = 7.90%; and B% = 0.50%.

[0045] Depend on Figure 1 It can be seen that Xinjiang weathered coal A2 contains all the elements reported in Table 1, but no other impurity elements.

[0046] Depend on Figure 2 It can be seen that the peak of binding energy at 284.7 eV represents saturated carbon (such as alkyl C, hybridization mode is sp 3 The peak with a binding energy of 285.7 eV represents carbon in CO bonds, while the peak with a binding energy of 287.0 eV represents carbon in carboxyl groups and carbon in C=N bonds. The molar ratio of these three is saturated carbon: carbon in CO bonds: carbon in carboxyl groups = 57.24:17.18:25.57. This indicates that the organic components of Xinjiang weathered coal A2 are small organic molecules containing C, N, and O. (Since there are no peaks after 290 eV, this organic component does not contain polymeric carbon chains, such as polyethylene or polypropylene.)

[0047] Depend on Figure 3 It can be seen that the peak of binding energy at 295.4 eV represents K 2p 1 / 2 The photoelectron binding energy peak at 292.7 eV represents K 2p 3 / 2 The photoelectrons show that the potassium in Xinjiang weathered coal A2 is in the form of K + exists in the form of .

[0048] Depend on Figure 4 It can be seen that the S 2p spectrum of Xinjiang weathered coal contains two components: at 168.7 eV (S 2p 1 / 2 ) and 167.7 eV (S2p 3 / 2 ) represents SO4 2- S.

[0049] Depend on Figure 5 It can be seen that the peak with a binding energy of 531.3 eV represents oxygen on inorganic matter (oxide), while the peaks at 532.4 eV and 532.6 eV represent oxygen on organic matter.

[0050] Depend on Figure 6It can be seen that potassium nitrate (KNO3, PDF No. 71-1558) is present in Xinjiang weathered coal A2. Organic matter does not exhibit a distinct diffraction peak. Potassium nitrate is a chlorine-free nitrogen-potassium compound fertilizer with high solubility. Its active ingredients, nitrogen and potassium, are rapidly absorbed by crops, leaving no chemical residue. As a fertilizer, it is suitable for vegetables, fruits, and flowers, as well as some chlorine-sensitive crops (such as potatoes, strawberries, beans, cabbage, lettuce, peanuts, carrots, onions, blueberries, tobacco, apricots, grapefruit, and avocados). Therefore, Xinjiang weathered coal, after being converted into hard water-resistant Xinjiang weathered coal A2, possesses high fertility.

[0051] Depend on Figure 7 It can be seen that Xinjiang weathered coal A2 is in the range of 30-150 o The weight loss of C (2.86%) represents the thermal runaway of adsorbed water. o The continuous weight loss of C (35.04%) represents the continuous thermal volatilization of organic matter.

[0052] Depend on Figure 8 It can be seen that the absorption peak of Xinjiang weathered coal A2 at 300 nm represents the π→π* transition of organic matter. In addition, Xinjiang weathered coal A2 does not contain metal ions and no charge transfer transition was found.

[0053] Depend on Figure 9 It can be seen that Xinjiang weathered coal A2 is a micron-sized flake material with a thickness of 50-100 nm.

[0054] Inner Mongolia weathered coal A2 was subjected to XPS analysis, and the results are shown in Table 2.

[0055] Table 2 Element binding energy and chemical composition of Inner Mongolia weathered coal A2 a Binding energy (eV), the value in parentheses is the atomic percentage (at%). As can be seen from Table 2: The experimental molecular formula of Inner Mongolia weathered coal A2 is: 63.19 C 9.87 N 5.32 K 16.78 S 14.16 B 0.46 The molecular weight is 2322.6711. The mass percentages are: O% = 43.52%; C% = 5.10%; N% = 3.20%; K% = 28.39%; S% = 19.54%; and B% = 0.21%.

[0056] Depend on Figure 10 It can be seen that, in addition to the elements reported in Table 2, Inner Mongolia weathered coal A2 does not contain other impurity elements.

[0057] Depend on Figure 11 It can be seen that the peak with binding energy at 285.1 eV represents the carbon atoms on the alkyl chain (hybridization mode sp 3 ), the peak with a binding energy of 286.4 eV represents the carbon in the CO bond. The molar ratio is alkyl carbon:CO carbon = 53.50:46.50.

[0058] Depend on Figure 12 It can be seen that the peak of binding energy at 295.7 eV represents K 2p 1 / 2 The photoelectron binding energy peak at 293.1 eV represents K 2p 3 / 2 The photoelectrons indicate that the potassium in Inner Mongolia weathered coal A2 is in the form of K + exists in the form of .

[0059] Depend on Figure 13 It can be seen that the S 2p spectrum of Inner Mongolia weathered coal contains two components: at 168.9 eV (S 2p 1 / 2 ) and 167.9 eV (S 2p 3 / 2 ) represents SO4 2- S.

[0060] Depend on Figure 14 It can be seen that the N 1s spectrum of Inner Mongolia weathered coal A2 contains four parts: the peak with a binding energy of 399.7 eV represents the -NH- group, which is derived from the amide group of the organic raw material; the peak with a binding energy of 401.5 eV represents the amino or tertiary amine group, which is derived from the organic raw material; the peak with a binding energy of 407.3 eV represents the NO3 - , which is introduced during the production process of Inner Mongolia weathered coal A2.

[0061] Depend on Figure 15 It can be seen that the peak at the binding energy of 531.4 eV represents oxygen on inorganic matter (oxides or acid radicals), while the peak at 532.7 eV represents oxygen on organic matter.

[0062] Depend on Figure 16As can be seen, Inner Mongolian weathered coal A2 contains two inorganic components: potassium nitrate (KNO3, PDF No. 71-1558) and potassium sulfate (K2SO4, PDF No. 05-0613). Potassium nitrate is a chlorine-free, nitrogen-potassium compound fertilizer with high solubility. Its active ingredients, nitrogen and potassium, are quickly absorbed by crops, leaving no chemical residue. As a fertilizer, it is suitable for vegetables, fruits, and flowers, as well as some chlorine-sensitive crops (such as potatoes, strawberries, beans, cabbage, lettuce, peanuts, carrots, onions, blueberries, tobacco, apricots, grapefruit, and avocados). Potassium sulfate is generally pale yellow in appearance, has low hygroscopicity, is non-caking, has excellent physical properties, and is easy to apply. It is an excellent water-soluble potassium fertilizer and the main raw material for the production of chlorine-free, nitrogen-phosphorus-potassium compound fertilizers. Therefore, after Inner Mongolian weathered coal is converted into hard water-resistant Inner Mongolian weathered coal A2, it possesses high fertility.

[0063] Depend on Figure 17 It can be seen that the weathered coal A2 in Inner Mongolia is 30-150 o The weight loss of C (3.04%) represents the thermal runaway of adsorbed water. o The continuous weight loss of C (38.86%) represents the continuous thermal volatilization of organic matter.

[0064] Depend on Figure 18 It can be seen that the absorption peak of Inner Mongolia weathered coal A2 at 295 nm represents the π→π* transition of organic matter. In addition, Inner Mongolia weathered coal A2 does not contain metal ions and no charge transfer transition was found.

[0065] Depend on Figure 19 It can be seen that the Inner Mongolia weathered coal A2 has a micron-sized flake-like superimposed morphology. In addition to the flake-like morphology with smooth edges, there is also a flake-like morphology with a rectangular structure.

[0066] The lignite A2 was subjected to XPS analysis, and the results are shown in Table 3.

[0067] Table 3 Element binding energy and chemical composition of lignite A2 a Binding energy (eV), the value in parentheses is the atomic percentage (at%). As can be seen from Table 3: The experimental molecular formula of lignite A2 is: 19.66 C 55.38 N 7.13 K 13.95 S 3.48 Si 0.40The molecular weight is 1747.8149. The mass percentages are: O% = 17.99%; C% = 38.05%; K% = 31.20%; S% = 6.38%; and Si% = 0.64%.

[0068] Depend on Figure 20 It can be seen that, apart from the elements reported in Table 3, lignite A2 does not contain other impurity elements.

[0069] Depend on Figure 21 As can be seen, the peak with a binding energy of 285.6 eV represents the carbon in the CO bond, and the peak with a binding energy of 287.2 eV represents the carbon in the carboxyl group. The molar ratio is 48.47:51.53.

[0070] Depend on Figure 22 It can be seen that the N 1s spectrum of lignite A2 contains four parts: the peak with a binding energy of 399.8 eV represents the -NH- group, which is derived from the amide group of the organic raw material; the peak with a binding energy of 401.8 eV represents the amino or tertiary amine group, which is derived from the organic raw material; the peak with a binding energy of 407.8 eV represents the nitro group, and the peak with a binding energy of 409.3 eV represents the NO3 - , originating from groups introduced during the production of lignite A2.

[0071] Depend on Figure 23 It can be seen that the peak of binding energy at 296.0 eV represents K 2p 1 / 2 The peak of binding energy at 293.3 eV represents K 2p 3 / 2 photoelectrons, indicating that the potassium in lignite A2 is in the form of K + exists in the form of .

[0072] Depend on Figure 24 It can be seen that the S 2p spectrum of lignite A2 contains two components: 1 / 2 ) and 168.7 eV (S2p 3 / 2 ) represents SO4 2- The S comes from the organic matter introduced during the synthesis of lignite A2 (such as sulfonation with sulfuric acid, etc.).

[0073] Depend on Figure 25 It can be seen that the peak at the binding energy of 532.0 eV represents the oxygen on the CO bond of the organic matter, while the broad peak at 533.2 eV represents the oxygen on the C=O bond.

[0074] Depend on Figure 26 It can be seen that lignite A2 contains potassium nitrate (KNO3, PDF No. 71-1558) and potassium sulfate (K2SO4, PDF No. 72-0354), and has high fertility.

[0075] Depend on Figure 27 It can be seen that the absorption peak of lignite A2 at 300 nm represents the π→π* transition of organic matter. In addition, lignite A2 does not contain metal ions and no charge transfer transition was found.

[0076] Depend on Figure 28 It can be seen that lignite A2 has a micron-sized columnar morphology.

[0077] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that in Comparative Example 1, zinc sulfate ZnSO4 is replaced by zinc oxide ZnO, specifically as follows: Weigh 25 g of crushed Xinjiang weathered coal and rinse it twice with 250 mL of tap water and then twice with 250 mL of distilled water.

[0078] Place the washed solid particles in 50 mL of 8% (mass percent) KOH aqueous solution and magnetically stir for 1 hour. Then, centrifuge (using a laboratory centrifuge) and collect the filtrate. Combine the filtrates (also collect the solids and store separately).

[0079] Add 3 mol / L aqueous HCl dropwise to the filtrate obtained above. Monitor the pH of the solution until the pH reaches 2.5, then stop adding HCl. A brownish-black solid precipitate (the target product, potassium fulvate) will precipitate. Collect the solid using a Büchner funnel and wash twice with 50 mL of distilled water. Finally, dry the resulting precipitate at 60°C to a constant weight, weigh it, and calculate the yield.

[0080] Mix 65% nitric acid aqueous solution (50 mL) and 4 mol / L H2SO4 aqueous solution (10 mL), then add all the potassium fulvic acid obtained in the previous step, and then add ZnO (0.5 g). Heat to 80 o C for 1 hour. Then, the liquid was decanted (the remaining solid was collected and stored separately), and the pH of the solution was adjusted to 7 with KOH or K2CO3. The water was evaporated and the remaining solid was dried to obtain solid A1.

[0081] Weigh solid A1 (6.0 g) into a 250 mL three-necked flask, add 30 mL of deionized water, and stir magnetically at room temperature until it is basically dissolved. Subsequently, add 2-acrylamide-2-methylpropanesulfonic acid (AMPS, 1.0 g) and continue stirring for 10 minutes. Then add ammonium persulfate ((NH4)2S2O8, 0.5 g), heat to 75 °C in a water bath (or oil bath), and maintain this temperature for 2 hours. Evaporate the solvent and dry the resulting solid in an oven (60 o C, 4 hours), and the sample was obtained.

[0082] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that zinc sulfate ZnSO4 is not added in Comparative Example 2, specifically as follows: Weigh 25 g of crushed Xinjiang weathered coal and rinse it twice with 250 mL of tap water and then twice with 250 mL of distilled water.

[0083] Place the washed solid particles in 50 mL of 8% (mass percent) KOH aqueous solution and magnetically stir for 1 hour. Then, centrifuge (using a laboratory centrifuge) and collect the filtrate. Combine the filtrates (also collect the solids and store separately).

[0084] Add 3 mol / L aqueous HCl dropwise to the filtrate obtained above. Monitor the pH of the solution until the pH reaches 2.5, then stop adding HCl. A brownish-black solid precipitate (the target product, potassium fulvate) will precipitate. Collect the solid using a Büchner funnel and wash twice with 50 mL of distilled water. Finally, dry the resulting precipitate at 60°C to a constant weight, weigh it, and calculate the yield.

[0085] Mix 65% nitric acid aqueous solution (50 mL) with 4 mol / L H2SO4 aqueous solution (10 mL), then add all the potassium fulvic acid obtained in the previous step into the mixture, and heat to 80 o C for 1 hour. Then, the liquid was decanted (the remaining solid was collected and stored separately), and the pH of the solution was adjusted to 7 with KOH or K2CO3. The water was evaporated and the remaining solid was dried to obtain solid A1.

[0086] Weigh solid A1 (6.0 g) into a 250 mL three-necked flask, add 30 mL of deionized water, and stir magnetically at room temperature until it is basically dissolved. Subsequently, add 2-acrylamide-2-methylpropanesulfonic acid (AMPS, 1.0 g) and continue stirring for 10 minutes. Then add ammonium persulfate ((NH4)2S2O8, 0.5 g), heat to 75 °C in a water bath (or oil bath), and maintain this temperature for 2 hours. Evaporate the solvent and dry the resulting solid in an oven (60 o C, 4 hours), and the sample was obtained.

[0087] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that 2-acrylamide-2-methylpropanesulfonic acid is not added in Comparative Example 3, specifically as follows: Weigh 25 g of crushed Xinjiang weathered coal (produced in Yiwu County) and rinse it twice with 250 mL of tap water and then twice with 250 mL of distilled water.

[0088] Place the washed solid particles in 50 mL of 8% (mass percent) KOH aqueous solution and magnetically stir for 1 hour. Then, centrifuge (using a laboratory centrifuge) and collect the filtrate. Combine the filtrates (also collect the solids and store separately).

[0089] Add 3 mol / L aqueous HCl dropwise to the filtrate obtained above. Monitor the pH of the solution until the pH reaches 2.5, then stop adding HCl. A brownish-black solid precipitate (the target product, potassium fulvate) will precipitate. Collect the solid using a Büchner funnel and wash twice with 50 mL of distilled water. Finally, dry the resulting precipitate at 60°C to a constant weight, weigh it, and calculate the yield.

[0090] Mix 65% nitric acid aqueous solution (50 mL) with 4 mol / L H2SO4 aqueous solution (10 mL), then add all the potassium fulvic acid obtained in the previous step, and then add ZnSO4 (0.5 g, catalyst), and heat to 80 o C for 1 hour. Then, the liquid was decanted (the remaining solid was collected and stored separately), and the pH of the solution was adjusted to 7 with KOH or K2CO3. The water was evaporated and the remaining solid was dried to obtain solid A1.

[0091] Weigh solid A1 (6.0 g) into a 250 mL three-necked flask, add 30 mL of deionized water, and stir magnetically at room temperature until it is essentially dissolved. Then add ammonium persulfate ((NH4)2S2O8, 0.5 g), heat in a water bath (or oil bath) to 75°C, and maintain this temperature for 2 h. Evaporate the solvent, and dry the resulting solid in an oven (60 o C, 4 hours), and the sample was obtained.

[0092] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the coal used in Comparative Example 4 is Shanxi Datong weakly caking coal, and the other steps are the same as those in Example 1, which are as follows: Weigh 25 g of crushed Datong weakly coking coal and rinse it twice with 250 mL of tap water and then twice with 250 mL of distilled water.

[0093] Place the washed solid particles in 50 mL of 8% (mass percent) KOH aqueous solution and magnetically stir for 1 hour. Then, centrifuge (using a laboratory centrifuge) and collect the filtrate. Combine the filtrates (also collect the solids and store separately).

[0094] Add 3 mol / L aqueous HCl dropwise to the filtrate obtained above. Monitor the pH of the solution until the pH reaches 2.5, then stop adding HCl. A brownish-black solid precipitate (the target product, potassium fulvate) will precipitate. Collect the solid using a Büchner funnel and wash twice with 50 mL of distilled water. Finally, dry the resulting precipitate at 60°C to a constant weight, weigh it, and calculate the yield.

[0095] Mix 65% nitric acid aqueous solution (50 mL) with 4 mol / L H2SO4 aqueous solution (10 mL), then add all the potassium fulvic acid obtained in the previous step, and then add ZnSO4 (0.5 g, catalyst), and heat to 80 o C for 1 hour. Then, the liquid was decanted (the remaining solid was collected and stored separately), and the pH of the solution was adjusted to 7 with KOH or K2CO3. The water was evaporated and the remaining solid was dried to obtain solid A1.

[0096] Weigh solid A1 (6.0 g) into a 250 mL three-necked flask, add 30 mL of deionized water, and stir magnetically at room temperature until it is basically dissolved. Subsequently, add 2-acrylamide-2-methylpropanesulfonic acid (AMPS, 1.0 g) and continue stirring for 10 minutes. Then add ammonium persulfate ((NH4)2S2O8, 0.5 g), heat to 75 °C in a water bath (or oil bath), and maintain this temperature for 2 hours. Evaporate the solvent and dry the resulting solid in an oven (60 o C, 4 hours), and the sample was obtained.

[0097] The products obtained in the above examples and comparative examples were configured as fertilizers and tested for their hard water resistance. The fertilizer preparation method is as follows: potassium fulvic acid, urea, phosphate fertilizer, and potash fertilizer are mixed in a mass ratio of 30:390:100:480 to prepare the fertilizer, wherein the potassium fulvic acid is respectively derived from the products obtained in the above embodiment and comparative example.

[0098] The hard water resistance test method is to dilute and dissolve the fertilizer obtained by the above-mentioned mixed configuration with 30-degree hard water at a mass ratio of 1:300 to obtain 1L of solution. The flocculation phenomenon is observed after standing for 24h, 72h, 120h, and 168h. See Table 4 for details.

[0099] Table 4 Hard water resistance test table of products obtained in various embodiments and comparative examples As can be seen in Table 4, the products obtained in Examples 1-3, when formulated as fertilizers, exhibit excellent hard water resistance. This is presumably due to the high purity of the potassium fulvate obtained in Examples 1-3, which effectively binds to 2-acrylamide-2-methylpropanesulfonic acid. 2-acrylamide-2-methylpropanesulfonic acid exhibits excellent complexing ability with calcium and magnesium ions in hard water, thereby preventing the phosphate radicals (PO₄³⁻) in phosphate fertilizers (such as monoammonium phosphate and diammonium phosphate) from reacting with calcium and magnesium ions in hard water to form insoluble calcium / magnesium phosphate precipitates and flocculations. Furthermore, 2-acrylamide-2-methylpropanesulfonic acid reduces the salt content of potash fertilizers in hard water, preventing precipitation and flocculation, and improving the fertilizer's hard water resistance.

[0100] Comparative Example 1 showed flocculation when observed after standing for 72 hours, indicating that the hard water resistance obtained in Comparative Example 1 was poor. It is speculated that the impurity content in Comparative Example 1 was high, and ZnO was added in Comparative Example 1, resulting in ZnO consuming part of the OH in the pH adjustment step. - , which results in the inability to effectively remove the metal impurities in the crude potassium fulvic acid, resulting in a large amount of metal impurities, and less 2-acrylamide-2-methylpropanesulfonic acid combined with potassium fulvic acid, causing the final product to have poor hard water resistance and flocculation after standing.

[0101] When comparative example 2 was observed after standing for 120 hours, flocculation occurred, indicating that the hard water resistance obtained in comparative example 2 was poor. It is speculated that the impurity content in comparative example 2 was relatively high, especially the metal impurities. The speculated reason is that some metal impurities in comparative document 2 were combined with organic matter, resulting in the inability to effectively remove the metal impurities in the subsequent metal impurity removal step, resulting in a high metal impurity content. The amount of 2-acrylamide-2-methylpropanesulfonic acid combined with potassium fulvic acid was relatively small, resulting in the poor hard water resistance of the product and flocculation after standing.

[0102] Comparative Example 3 showed flocculation when observed after standing for 72 hours, indicating that the hard water resistance obtained in Comparative Example 3 was poor. It is speculated that the lack of 2-acrylamide-2-methylpropanesulfonic acid in Comparative Example 3 resulted in poor water solubility of the product and flocculation after standing.

[0103] Comparative Example 4 showed flocculation when observed after standing for 72 hours, indicating that the hard water resistance obtained in Comparative Example 4 was poor. It is speculated that the product obtained in Comparative Example 4 contained more macromolecular organic matter, resulting in poor hard water resistance of the product and flocculation after standing.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for synthesizing hard water resistant potassium fulvic acid for preparing fertilizer, characterized in that: include: 50 mL of 65% nitric acid aqueous solution and 10 mL of 4 mol / L H2SO4 aqueous solution were mixed to obtain a mixed acid solution, and then 10 g to 30 g of potassium fulvic acid and 0.5 g of ZnSO4 were added to the mixed acid solution. The mixture was heated to 80°C under stirring and fully reacted to obtain a first liquid. Subsequently, the first liquid is poured out, and the pH value of the first liquid is adjusted to 7, and then the water in the first liquid is evaporated, and the solid remaining after the water in the first liquid is evaporated is dried to obtain a first solid; Sufficient water is added to 5-10 g of the first solid to fully dissolve it, thereby obtaining a first solid aqueous solution; 1-2 g of 2-acrylamide-2-methylpropanesulfonic acid is then added to the first solid aqueous solution, and after thorough stirring, 0.5 g of ammonium persulfate is then added, and the mixture is heated to 75° C. and maintained at this temperature for thorough reaction, thereby obtaining a second liquid; The solvent of the second liquid is evaporated to dryness to obtain a second solid, and the second solid is dried to obtain hard water resistant potassium fulvic acid.

2. The method for synthesizing the hard water resistant potassium fulvic acid for preparing fertilizer according to claim 1, wherein: The pH adjusting liquid for adjusting the pH value of the first liquid to 7 is a KOH or K2CO3 adjusting solution.

3. The method for synthesizing the hard water resistant potassium fulvic acid for preparing fertilizer according to claim 1, wherein: The preparation method of the potassium fulvate is: The cleaned coal slag is added into a KOH aqueous solution and stirred thoroughly to obtain a reaction solution; separating the filtrate and the solid in the reaction solution; Adding HCl aqueous solution dropwise to the filtrate, monitoring the pH value of the filtrate, and stopping the addition of hydrochloric acid when the pH value of the filtrate is 2-3; The brown-black solid precipitate precipitated in the filtrate was collected; The collected brown-black solid is washed with water and then dried to obtain potassium fulvic acid.

4. The method for synthesizing the hard water resistant potassium fulvic acid for preparing fertilizer according to claim 3, wherein: The coal slag includes at least one of lignite and weathered coal.

5. The method for synthesizing the hard water resistant potassium fulvic acid for preparing fertilizer according to claim 4, wherein: The weathered coal includes at least one of Xinjiang weathered coal and Inner Mongolia weathered coal.

6. The method for synthesizing the hard water resistant potassium fulvic acid for preparing fertilizer according to claim 3, wherein: The cleaning liquid for the coal slag is deionized water or distilled water.

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