Preparation method of insoluble humic acid

Abstract

The invention discloses a preparation method of insoluble humic acid, which comprises the following steps: step 1, preparing pure humic acid for later use; the method comprises the following steps of 1, preparing pure humic acid, 2, treating the pure humic acid obtained in the step 1 to prepare insoluble humic acid, and 3, carrying out impurity removal treatment on the insoluble humic acid obtained in the step 2 to obtain the high-purity insoluble humic acid. Impurities in natural humic acid are effectively removed through the alkali dissolution characteristic and centrifugal separation of humic acid, and extraction of high-purity humic acid is achieved; the solubility of the humic acid is reduced from 23% reported in the literature to 1% or below through long-term heating condensation at 330 DEG C, so that the humic acid is stable under the environmental condition; the preparation efficiency is improved by increasing the initial material ratio, the preparation rate of dozens of grams per time is achieved on the laboratory scale, and the material requirements of most natural science experiments are met.

Description

Technical Field

[0001] The invention relates to the technical field of organic matter, and in particular to a method for preparing insoluble humic acid. Background Art

[0002] Organic matter is a natural substance widely present in the earth's surface environment, controlling the surface cycle of elements and participating in the regulation of the earth's habitability. On the one hand, organic matter is an important carbon sink that affects global climate conditions. The organic carbon content in the soil is as high as 1550 Pg C, followed by the ocean, with a content of 640 Pg C, and the organic carbon content in ocean floor sediments is 150 Pg C, the total amount is higher than the total organic carbon content of all aquatic and terrestrial organisms in the world (1200 Pg C) (Findlay and Sinsabaugh, 2003). On the other hand, organic matter contains abundant functional groups, including carboxyl, hydroxyl, thiol, amine, etc., which can react with trace metal elements in oxidation-reduction, precipitation and complexation, affecting the migration, transformation and fate of trace metal elements. Therefore, the surface geochemical cycle of organic matter and its environmental effects are important topics in earth science and environmental science research.

[0003] Humic acid is an important component of soil and water organic matter. It has typical carboxyl and hydroxyl functional groups of organic matter and is often used as a model organic matter in research. However, natural humic acid has extremely high solubility under environmental pH conditions and cannot be separated after reacting with metal ions in solution, which hinders the study of the environmental effects of humic acid. Therefore, reducing the solubility of humic acid and synthesizing insoluble particles is the first step in establishing model organic matter.

[0004] However, there is no mature patent technology for preparing insoluble humic acid. The relevant papers published (Seki and Suzuki, 1995; Baker and Khalili et al., 2004; Ling et al., 2022) also have contradictory technical descriptions in the preparation method. Seki and Suzuki (1995) proposed the concept of hydrothermal condensation method and suggested the use of 1h rapid hydrothermal condensation method with a condensation temperature of 330℃, which is much higher than the 65℃±5℃ recommended by Ling et al. (2022); Baker and Khalili (2004) even proposed anhydrous condensation. In addition, these articles only give technical suggestions without specific method parameters, which are difficult to repeat; more importantly, there is a lack of solubility performance testing, and the solubility of the synthesized product cannot be determined. We repeated the 1h rapid hydrothermal condensation technology (Seki and Suzuki, 1995), which has the most citations, and found that the solubility of the product synthesized by this technology is as high as 23% (pH=10). In summary, there is currently a lack of preparation technology for insoluble humic acid.

[0005] Therefore, a method for preparing insoluble humic acid is provided to solve the above technical problems. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing insoluble humic acid. The present invention uses natural humic acid as a substrate and explores the optimal condensation conditions based on the theory of organic matter heating condensation to prepare insoluble humic acid.

[0007] The object of the present invention is achieved in that: A method for preparing insoluble humic acid comprises the following steps: Step 1, preparing pure humic acid for later use; Step 2: The pure humic acid obtained in step 1 is treated to prepare insoluble humic acid, as follows: Step 2.1, dissolving 5-20 g of pure humic acid obtained in step 1 into 100 mL of ultrapure water, stirring thoroughly for 12 h to dissolve the pure humic acid, and obtaining a first suspension; Step 2.2, adding a 4M calcium chloride solution of the same volume as the ultrapure water in step 2.1 to the first suspension in step 2.1, so that the concentration of calcium chloride in the solution is 2M calcium chloride solution, and the volume ratio (m:v) of the mass of humic acid to the 2M calcium chloride solution is 1:(10-40), to obtain a second suspension, and the second suspension is stirred for 1 hour to allow the humic acid and calcium chloride to fully react; Step 2.3, after the reaction of humic acid and calcium chloride is completed, the second suspension is placed in a muffle furnace and fired at 330° C. for 1-6 hours to promote dehydration condensation of humic acid; Step 2.4, after the firing is completed, the solid matter is collected and dispersed in ultrapure water to form a third suspension, the suspension pH is adjusted to 8, stirred at room temperature for 48 hours and allowed to stand for 12 hours, the overlying solution is removed to remove the slightly soluble humic acid, and the remaining insoluble solid is the insoluble humic acid, thereby obtaining the insoluble humic acid; Step 3: performing impurity removal treatment on the insoluble humic acid in step 2 to obtain high-purity insoluble humic acid.

[0008] The specific operation of step 1 is as follows: step 1.1, placing natural humic acid in a NaOH solution, stirring it sufficiently for a set time to make the natural humic acid dissolve quickly, while other impurities are insoluble, thereby obtaining a reaction solution; step 1.2, placing the reaction solution in a centrifuge and centrifuging it, collecting the supernatant after centrifugation as the first supernatant; in order to fully separate the humic acid and impurities, the collected first supernatant is centrifuged again and the second supernatant is collected; step 1.3, adjusting the collected second supernatant to a pH value of 1 with 6M hydrochloric acid, at which time the naked eye can see A black humic acid solid is seen precipitating from the solution, and a suspension is obtained; the suspension with a pH value of 1 is transferred to a centrifuge tube for centrifugation, and the solid after centrifugation is collected, which is the first solid; step 1.4, the first solid collected in step 1.3 is dispersed in ultrapure water, and centrifuged, and then the supernatant is poured out, and step 1.4 is repeated 5 times to wash away the residual impurity ions to obtain a second solid; step 1.5, the collected second solid is placed in an oven, and the second solid is dried at 75°C for 48 hours to obtain pure humic acid.

[0009] In the step 1.1, the concentration of the NaOH solution is 0.1 M; stirring for 15 minutes promotes the rapid dissolution of natural humic acid.

[0010] In the step 1.2, the reaction solution is placed in a centrifuge for centrifugation at a speed of 10000 r / min and a centrifugation time of 10 min.

[0011] In the step 1.3, the suspension with pH=1 is transferred to a centrifuge tube and centrifuged at 5000 r / min for 10 min.

[0012] In the step 1.4, the first solid collected in the step 1.3 is dispersed in ultrapure water, and centrifuged at 5000 r / min for 10 min using a centrifuge.

[0013] The specific operation of step 3 is as follows: step 3.1, dispersing the insoluble humic acid in step 2 into ultrapure water, using a centrifuge to centrifuge for 10 minutes at 10000r / min, separating and collecting the solid, and obtaining a first insoluble humic acid solid; step 3.2, repeating step 3.1 three times to remove residual calcium chloride to obtain a second insoluble humic acid solid; step 3.3, drying the obtained second insoluble humic acid solid at 75°C to obtain high-purity insoluble humic acid.

[0014] The beneficial effects of the present invention are: 1. The present invention effectively removes impurities in natural humic acid through the alkali solubility of humic acid and centrifugal separation, thereby realizing the extraction of high-purity humic acid; reduces the solubility of humic acid through long-term heating condensation at 330°C, reducing it from 23% reported in the literature to below 2%, thereby achieving stability under environmental conditions; increases the preparation efficiency by increasing the initial material ratio, and realizes a preparation rate of tens of grams per time on a laboratory scale, thereby ensuring the material requirements of most natural science experiments; the product prepared by the present invention has the characteristics of low solubility and high purity, can be used as a natural model organic matter, and has a very broad application prospect in natural science research.

[0015] 2. The method used in the present invention is simple, low-cost, safe and environmentally friendly, does not involve strong acids, strong bases, or harmful reagents, and does not use high temperature or high pressure operations. It is an environmentally friendly technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The X-ray diffraction spectrum (XRD) diagram of humic acid before and after purification of the present invention; Figure 2 The FTIR spectra of humic acid before firing and after firing for 6 hours are shown in the figure; Figure 3 The dissolution diagrams of different fired products of the present invention under different conditions; (a) the solubility of humic acid at different firing times at pH = 9; (b) the solubility of humic acid fired for 1h and 6h at different pH values. DETAILED DESCRIPTION

[0017] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0018] A method for preparing insoluble humic acid comprises the following steps: Step 1: prepare pure humic acid for later use.

[0019] The specific operations of step 1 are as follows: Step 1.1, placing natural humic acid in a 0.1M NaOH solution, stirring thoroughly for 15 minutes to make the natural humic acid dissolve quickly, while other impurities are insoluble, to obtain a reaction solution; Step 1.2, placing the reaction solution in a centrifuge for centrifugation at a speed of 10000 r / min for 10 min, collecting the supernatant after centrifugation as the first supernatant; in order to fully separate the humic acid and impurities, the collected first supernatant is centrifuged again and the second supernatant is collected; Step 1.3, adjusting the collected second supernatant to a pH of 1 with 6M hydrochloric acid, at which time black humic acid solids can be seen precipitating from the solution with the naked eye, thereby obtaining a suspension; transferring the suspension with a pH of 1 to a centrifuge tube for centrifugation, centrifuging at 5000 r / min for 10 min, and collecting the solid after centrifugation, which is the first solid; Step 1.4, dispersing the first solid collected in step 1.3 in ultrapure water and centrifuging at 5000 r / min for 10 min, then discarding the supernatant, repeating step 1.4 5 times to wash away residual impurity ions, and obtaining a second solid; Step 1.5: Place the collected second solid in an oven and dry the second solid at 75° C. for 48 hours to obtain pure humic acid.

[0020] Step 2: The pure humic acid obtained in step 1 is treated to prepare insoluble humic acid, as follows: Step 2.1, dissolve 5-20g of pure humic acid obtained in step 1 into 100mL of ultrapure water, stir thoroughly for 12h to dissolve the pure humic acid, and obtain a first solution.

[0021] Step 2.2, add a 4M calcium chloride solution of the same volume as the ultrapure water in step 2.1 to the first suspension in step 2.1, so that the concentration of calcium chloride in the solution is 2M calcium chloride solution, and the volume ratio (m:v, in g / mL) of the mass of humic acid to the 2M calcium chloride solution is 1:(10-40), to obtain a second suspension, and continue to stir the second suspension for 1 hour to allow the humic acid and calcium chloride to fully react; Step 2.3, after the reaction of humic acid and calcium chloride is completed, the second solution is placed in a muffle furnace and fired at 330° C. for 6 hours to promote dehydration condensation of humic acid; Step 2.4, after the firing is completed, the solid matter is collected and dispersed in ultrapure water, the suspension pH is adjusted to 8, stirred at room temperature for 48 hours and then allowed to stand for 12 hours, the overlying solution is removed to remove the slightly soluble humic acid, and the remaining insoluble solid is the insoluble humic acid, thereby obtaining the insoluble humic acid; Step 3: performing impurity removal treatment on the insoluble humic acid in step 2 to obtain high-purity insoluble humic acid.

[0022] The specific operations of step 3 are as follows: Step 3.1, dispersing the insoluble humic acid in step 2 into ultrapure water, using a centrifuge to centrifuge at 10000r / min for 10min, separating and collecting the solid, and obtaining a first insoluble humic acid solid; Step 3.2, repeating step 3.1 three times to remove residual calcium chloride and obtain a second insoluble humic acid solid; Step 3.3: Dry the obtained second insoluble humic acid solid at 75° C. to obtain high-purity insoluble humic acid.

[0023] Purification effect evaluation: Figure 1 The XRD spectra of humic acid before and after purification are shown. The spectra show that the humic acid before purification contains soil particle impurities, and the XRD signals of these impurities disappear after purification, leaving only the signal of humic acid, indicating that the centrifugal separation and purification technology used in the present invention has a good effect.

[0024] Firing impact assessment: Figure 2 The Fourier transform infrared spectra (FTIR) of humic acid before firing and after firing for 6 hours are shown. The spectra show that the FTIR spectral characteristics remain unchanged before and after firing, indicating that heating condensation will not change the essential properties of humic acid, and the product after firing is still humic acid.

[0025] Solubility test: Weigh a certain amount of humic acid particles and disperse them in ultrapure water so that the solid-liquid ratio is 2.5g / L. Adjust the pH of the suspension to 4-10, put it in a constant temperature shaking table, set the reaction temperature to 25°C, the shaking speed to 120r / min, and the reaction time to 48h. After the reaction is completed, centrifuge the suspension (speed 1000r / min, centrifugation 10min), then take the supernatant, and use the TOC-LCPN instrument to measure the dissolved organic carbon (TOC) concentration.

[0026] Calculation of solubility: Weigh a certain amount of unfired humic acid and disperse it in ultrapure water so that the solid-liquid ratio is 2.5g / L. Adjust the pH to alkaline so that the humic acid is completely dissolved and measure the TOC concentration using a TOC-LCPN instrument, which is used as the total concentration. By comparing the total TOC concentration of the fully dissolved sample with the TOC concentration data of the above experimental sample, the solubility is obtained in %.

[0027] Experimental results: The experimental results are as follows Figure 3 As shown in the figure, the solubility of humic acid increases with the increase of pH. Prolonging the firing time helps to reduce the solubility. As the firing time increases from 1h to 6h, the solubility of humic acid decreases from 23% to <2%, and changing the material-liquid ratio (1: (10-40), m:v) does not affect the solubility.

Claims

1. A method for preparing insoluble humic acid, characterized in that: The following steps are involved: Step 1, preparing pure humic acid for standby use; Step 2: The pure humic acid obtained in step 1 is treated to prepare insoluble humic acid, as follows: Step 2.1, dissolving 5-20 g of pure humic acid obtained in step 1 into 100 mL of ultrapure water, stirring thoroughly for 12 h to dissolve the pure humic acid, and obtaining a first suspension; Step 2.2, adding a 4M calcium chloride solution of the same volume as the ultrapure water in step 2.1 to the first suspension in step 2.1, so that the concentration of calcium chloride in the solution is 2M calcium chloride solution, and the volume ratio of the mass of humic acid to the 2M calcium chloride solution is 1: (10-40), to obtain a second suspension, and the second suspension is further stirred for 1 hour to allow the humic acid and calcium chloride to fully react; Step 2.3, after the reaction of humic acid and calcium chloride is completed, the second suspension is placed in a muffle furnace and fired at 330° C. for 1-6 hours to promote dehydration condensation of humic acid; Step 2.4, after the firing is completed, the solid matter is collected and dispersed in ultrapure water to form a third suspension, the suspension pH is adjusted to 8, stirred at room temperature for 48 hours and then allowed to stand for 12 hours, the overlying solution is removed to remove the slightly soluble humic acid, and the remaining insoluble solid is the insoluble humic acid, thereby obtaining the insoluble humic acid; Step 3: performing impurity removal treatment on the insoluble humic acid in step 2 to obtain high-purity insoluble humic acid.

2. The method for preparing insoluble humic acid according to claim 1, characterized in that: The specific operation of step 1 is as follows: step 1.1, placing natural humic acid in a NaOH solution, stirring it sufficiently for a set time to make the natural humic acid dissolve quickly, while other impurities are insoluble, thereby obtaining a reaction solution; step 1.2, placing the reaction solution in a centrifuge and centrifuging it, collecting the supernatant after centrifugation as the first supernatant; in order to fully separate the humic acid and impurities, the collected first supernatant is centrifuged again and the second supernatant is collected; step 1.3, adjusting the collected second supernatant to a pH value of 1 with 6M hydrochloric acid, at which time the naked eye can see A black humic acid solid is seen precipitating from the solution, and a suspension is obtained; the suspension with a pH value of 1 is transferred to a centrifuge tube for centrifugation, and the solid after centrifugation is collected, which is the first solid; step 1.4, the first solid collected in step 1.3 is dispersed in ultrapure water, and centrifuged, and then the supernatant is poured out, and step 1.4 is repeated 5 times to wash away the residual impurity ions to obtain a second solid; step 1.5, the collected second solid is placed in an oven, and the second solid is dried at 75°C for 48 hours to obtain pure humic acid.

3. The method for preparing insoluble humic acid according to claim 2, characterized in that: In the step 1.1, the concentration of the NaOH solution is 0.1 M; stirring for 15 minutes promotes the rapid dissolution of natural humic acid.

4. The method for preparing insoluble humic acid according to claim 2, characterized in that: In the step 1.2, the reaction solution is placed in a centrifuge for centrifugation at a speed of 10000 r / min and a centrifugation time of 10 min.

5. The method for preparing the insoluble humic acid according to claim 2, characterized in that: In the step 1.3, the suspension with pH=1 is transferred to a centrifuge tube and centrifuged at 5000 r / min for 10 min.

6. The method for preparing the insoluble humic acid according to claim 2, characterized in that: In the step 1.4, the first solid collected in the step 1.3 is dispersed in ultrapure water, and centrifuged at 5000 r / min for 10 min using a centrifuge.

7. The method for preparing insoluble humic acid according to claim 1, characterized in that: The specific operation of step 3 is as follows: step 3.1, dispersing the insoluble humic acid in step 2 into ultrapure water, using a centrifuge to centrifuge for 10 minutes at 10000r / min, separating and collecting the solid, and obtaining a first insoluble humic acid solid; step 3.2, repeating step 3.1 three times to remove residual calcium chloride to obtain a second insoluble humic acid solid; step 3.3, drying the obtained second insoluble humic acid solid at 75°C to obtain high-purity insoluble humic acid.

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