Preparation process of mineral source potassium fulvate

Abstract

The invention relates to a preparation process of mineral source potassium fulvic acid, which comprises the following steps: carrying out jaw breaking and fine grinding on weathered coal, lignite or peat to obtain powder, leaching with dilute nitric acid, and carrying out solid-liquid separation to obtain a first clear liquid and a first precipitate; removing heavy metals in the first clear liquid by using an ammonia water / flocculation method or chelating macroporous resin to obtain a second clear liquid; adding potassium hydroxide into the first precipitate and the second clear liquid, heating and reacting to obtain a third clear liquid containing potassium fulvate and a third precipitate; acidifying the third clear liquid to remove silicate, calcium salt and the like contained in the third clear liquid to obtain a fourth clear liquid containing potassium fulvate and a fourth precipitate; combining the third precipitate and the fourth precipitate to form a base fertilizer; concentrating the fourth clear liquid under negative pressure by adopting a double-effect evaporation concentrator to obtain a potassium fulvate concentrated aqueous solution product; and adding granulation auxiliary materials into the concentrated solution, and carrying out spray granulation to obtain a solid particle product. According to the invention, weathered coal, lignite or peat can be fully recycled, resource waste is reduced, and heavy metal residues in the product are effectively reduced.

Description

Technical Field

[0001] The invention relates to the technical field of humic acid, and more specifically to a preparation process of mineral-source potassium humate. Background Art

[0002] As an efficient organic fertilizer and soil conditioner, potassium humate is widely used in agriculture, horticulture, environmental protection and other fields. Its main uses include: ① Promote plant growth, stimulate root development, increase chlorophyll content, and improve photosynthesis efficiency. ② Improve soil structure: Enhance soil permeability and water retention, prevent soil compaction, and facilitate root expansion. ③ Regulate pH value: It can help regulate soil acidity and alkalinity to create a more suitable environment for crop growth. ④ Chelate trace elements: Form stable complexes with trace elements in the soil to prevent these elements from being fixed and unable to be absorbed by plants. ⑤ Enhance stress resistance: Improve plant resistance to abiotic stresses such as drought and cold. Therefore, the preparation of potassium humate is of great significance to promoting agricultural development and improving agricultural productivity. At the same time, it can also achieve high added value transformation of waste for natural resources such as weathered coal, lignite or peat, which is in line with the concept of circular economy.

[0003] The current preparation method of potassium humate is mainly alkaline extraction, which uses alkaline solutions such as potassium hydroxide (KOH) or sodium hydroxide (NaOH) to extract humic acid from weathered coal, lignite or peat and form corresponding salts (such as potassium humate).

[0004] Weathered coal, lignite or peat contain similar ingredients, the main components include: (1) Organic components: Humic acid: high content, including fulvic acid, these organic acids give weathered coal good soil improvement properties. Lignin derivatives: residual plant fiber structure, with certain adsorption capacity and water retention properties. (2) Inorganic components: Minerals: such as silicon dioxide (SiO2), aluminum oxide (Al2O3), iron oxide (Fe2O3), calcium and magnesium compounds, etc., derived from the ash in the original coal and impurities introduced during the weathering process. Trace elements: such as potassium (K), phosphorus (P), sulfur (S), nitrogen (N) and heavy metals (such as Zn, Cu, Pb, Cd, Cr, etc.). (3) Lignite and peat also contain incompletely decomposed plant remains, undecomposed plant debris, such as cell walls, lignin, etc. (4) Water.

[0005] Among them, the raw materials (such as weathered coal and lignite) may contain a certain amount of heavy metals. If not handled properly, these harmful elements may remain in the final product, affecting its safety and scope of application. In addition, although the alkaline leaching method is mature in technology, it consumes a lot of water, and wastewater treatment and other issues need to be considered in the subsequent treatment process. At present, the remaining slag is not fully utilized after extracting humic acid from weathered coal, lignite or peat. Summary of the invention

[0006] 1. Technical issues to be resolved

[0007] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a preparation process of mineral-based potassium humate, which can not only fully utilize weathered coal, lignite or peat to reduce resource waste, but also effectively reduce the residual amount of heavy metals in potassium humate, and fully utilize water resources, and can produce a compound fertilizer containing potassium humate and nitrogen fertilizer.

[0008] (II) Technical solution

[0009] In a first aspect, the present invention provides a process for preparing mineral-derived potassium humate, comprising:

[0010] S1. Jaw-crushing, fine grinding and screening of weathered coal, lignite or peat to obtain 300-mesh powder, leaching the powder with dilute nitric acid, and separating the solid and liquid to obtain a first clear liquid and a first precipitate; then, treating in any of the following ways:

[0011] Method 1: adding ammonia water and flocculant to the first clear liquid to carry out precipitation reaction, and separating the solid and liquid to obtain a second precipitate and a second clear liquid from which heavy metals have been removed;

[0012] Method 2: adding a chelating macroporous resin to the first clear solution, and after adsorption reaction, performing solid-liquid separation to obtain a second precipitate and a second clear solution from which heavy metals have been removed;

[0013] S2, the first precipitate: the second clear liquid and the total amount of water are mixed in a mass ratio of 1:3-8 (when the amount of the second clear liquid is sufficient, no water is added), potassium hydroxide is added in an amount of 10-20% of the dry mass of the first precipitate, the pH of the mixed system is adjusted to between 10-14, the temperature is raised to 60-90° C. and stirred or ultrasonically reacted for 1-1.5 hours; after the reaction is completed, the solid and liquid are separated to obtain a third precipitate and a third clear liquid;

[0014] S3, adding dilute sulfuric acid to the third clear liquid for acidification until the pH reaches 2-3, stirring or ultrasonically reacting for 10-20 minutes, and separating the solid and the liquid to obtain a fourth precipitate and a fourth clear liquid;

[0015] S4. Combine the third precipitate and the fourth precipitate and send them to the fertilizer processing workshop to be processed into base fertilizer; concentrate the fourth clear liquid by double-effect evaporation concentrator under negative pressure to obtain a potassium humate concentrated aqueous solution product; or after concentration, add granulation auxiliary materials to perform spray granulation to obtain a potassium humate solid particle product. If no auxiliary materials are added, directly spray drying is performed to obtain a potassium humate powder product.

[0016] According to a preferred embodiment of the present invention, in method 1 of S1, the flocculant is bentonite, PAM, PDADMAC or a natural organic flocculant (starch, cellulose and its derivatives, gelatin, chitosan, lignin); the amount of PAM, PDADMAC or a natural organic flocculant added is 0.1-2 mg / L; the amount of bentonite added is 5-10% of the volume of the reaction system; the second precipitate is harmlessly landfilled or sintered at high temperature and then used as a concrete filler to make a building material.

[0017] According to a preferred embodiment of the present invention, in S1, the concentration of dilute nitric acid is 5-10%, the mass ratio of powder to dilute nitric acid is 1:2-4; the amount of ammonia water added is to adjust the pH of the reaction system to 8-9; the second clear liquid obtained in method one contains ammonium nitrate.

[0018] According to a preferred embodiment of the present invention, in the second mode of S1, the chelating macroporous resin is a macroporous resin containing aminophosphoric acid, mercapto or pyridyl groups, and the amount of the chelating macroporous resin added is 10-20% of the volume of the reaction system. This type of chelating macroporous resin can specifically bind certain heavy metal ions (such as Hg 2+ , Pb 2+ 、Cd 2+ 、Zn 2+ The second precipitate produced by the second method is subjected to a regeneration treatment by 0.1-1M dilute sulfuric acid for 0.5-5h and then reused; the second clear solution obtained by the second method contains nitrate.

[0019] According to a preferred embodiment of the present invention, in S2, ammonia vapor is collected with dilute nitric acid during stirring at 60-90° C. or ultrasonic reaction to obtain an aqueous solution of ammonium nitrate, which is then used in step S1 or in S2.

[0020] According to a preferred embodiment of the present invention, the solid-liquid separation in S2 and S3 is performed by centrifuge at 3000 rpm for 30-40 min.

[0021] According to a preferred embodiment of the present invention, in S3, the solid-liquid separation further includes a microfiltration or an ultrafiltration device.

[0022] According to a preferred embodiment of the present invention, in S1, the humic acid content in the weathered coal, lignite or peat used as the raw material is greater than 10%. If the humic acid content in the raw material is less than 10%, the raw material should be subjected to oxidative degradation treatment to increase the humic acid content in the raw material.

[0023] According to a preferred embodiment of the present invention, in S4, during the evaporation and concentration process using a double-effect evaporation concentrator, steam is collected and condensed, and the condensate is recovered. The condensate is applied to the preparation of dilute nitric acid in step S1, or is reused in S2 for mixing with the second clear liquid, or is reused in S3 for preparing dilute sulfuric acid.

[0024] According to a preferred embodiment of the present invention, in S4, concentrated crystals are collected during the concentration process, and the concentrated crystals are potassium humate crystal products.

[0025] According to a preferred embodiment of the present invention, in S4, the granulation auxiliary material is at least one of PVA, CMC, cyclodextrin, starch, bentonite and attapulgite. During the granulation process, appropriate trace elements such as ferrous sulfate (FeSO4), zinc sulfate (ZnSO4), ammonium molybdate (NH4MoO4), etc. can be added according to the needs of the target crops.

[0026] (III) Beneficial effects

[0027] 1. The preparation process of potassium humate of the present invention comprises the following steps: firstly, grinding the raw material and then leaching it with dilute nitric acid, at which time most of the heavy metal ions enter the solution, then forming hydroxides with ammonia water, removing them in the form of precipitation under the flocculation of a flocculant, or using a chelating macroporous resin for specific adsorption to remove the heavy metal ions, a small amount of humic acid enters the second clear liquid, and a large amount of humic acid remains in the first precipitate; the first precipitate: the second clear liquid is mixed with the total amount of water and potassium hydroxide is added for heating reaction, so that the humic acid in the first precipitate is promoted to form potassium humate and enter the solution; then, acidification treatment is performed with dilute sulfuric acid to promote the precipitation of silicates and calcium salts in the solution (precipitation of a small amount of humic acid), purifying the potassium humate solution, and preparing better solution conditions for subsequent evaporation and concentration; then, the solution containing potassium humate is subjected to double-effect evaporation and concentration to obtain a humic acid concentrated aqueous product, or after concentration, a certain amount of granulation auxiliary materials are added for spray granulation to obtain a humic acid granule product. The method of the invention can reduce the residual amount of heavy metals in the prepared potassium humate product, and the product contains no or very low content of heavy metals, thereby improving the safety of the fertilizer.

[0028] 2. In the present invention, after leaching with dilute nitric acid and then precipitating ammonia water, ammonium nitrate can be obtained in the second clear liquid, and this part of ammonium nitrate finally enters the concentrated aqueous product of potassium humate, forming a composite fertilizer of potassium humate and nitrate nitrogen and ammonium nitrogen. When a chelating macroporous resin is used to specifically adsorb and remove heavy metal ions, the second clear liquid contains nitrate, which also enters the concentrated aqueous product or granular product of potassium humate, and a composite containing potassium humate and nitrogen is obtained.

[0029] 3. When bentonite is selected as the flocculant, bentonite is rich in sodium, calcium, potassium and magnesium ions. When it is used as a flocculant to flocculate heavy metal hydroxides, the sodium, potassium and magnesium ions introduced enter the second clear liquid and eventually enter the concentrated aqueous product or granular product of potassium humate, which helps to supplement metal trace elements for crops.

[0030] 4. The third precipitate is mainly the unleached slag (lignin derivatives, minerals, trace elements, undecomposed plant remains) from weathered coal, lignite or peat; the fourth precipitate is mainly humic acid or its insoluble salts precipitated by acidification. Both parts have been free of heavy metals and contain plant nutrients. After mixing, they are sent to the fertilizer processing workshop to be processed into base fertilizer, reducing resource waste and improving utilization rate.

[0031] 5. The condensate recovered by negative pressure double-effect evaporation concentration can be applied to the above steps to prepare dilute nitric acid, or dilute the second clear liquid or prepare dilute sulfuric acid for acidification, thereby reducing water resource consumption.

[0032] 6. The present invention can prepare concentrated aqueous products, granular products or potassium humate crystal products of potassium humate, which are concentrated to a relatively high density and then directly spray-dried to obtain potassium humate powder products; the products have various forms. In order to improve the purity of potassium humate, a combination of centrifugation, microfiltration and ultrafiltration can be used during solid-liquid separation, which can greatly improve the purity of the final potassium humate product. DETAILED DESCRIPTION

[0033] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below in conjunction with specific implementation methods.

[0034] Example 1

[0035] This embodiment provides a preparation process of mineral-source potassium humate, and the steps are as follows:

[0036] (1) Dry weathered coal (humic acid content 40-50%) is coarsely sieved, and the part with a particle size less than 5 cm is retained for jaw crushing, and finely ground through a 300-mesh sieve to obtain a powder.

[0037] (2) preparing dilute nitric acid with a concentration of 5%, mixing the powder with the dilute nitric acid at a mass ratio of 1:3, stirring and leaching for 2.5 hours at room temperature, and centrifuging at 3000 rpm to obtain a first clear liquid and a first precipitate.

[0038] (3) Ammonia water is added to the first clear liquid to adjust the pH to 9, and after stirring or ultrasonic reaction for 0.5 h, 10% of the volume of the reaction system of bentonite is added, and the reaction is allowed to stand for 1 h, and centrifuged at 3000 rpm to obtain a second clear liquid and a second precipitate. The second precipitate is landfilled harmlessly.

[0039] (4) The first precipitate and the second clear liquid are mixed in a mass ratio of 1:4, potassium hydroxide is added at 15% of the dry weight of the first precipitate, the pH of the mixed system is adjusted to about 13, the temperature is raised to 80-85°C, and the mixture is reacted under 40KHz ultrasound for 1 hour; after the reaction is completed, the mixture is centrifuged at 3000rpm to obtain a third precipitate and a third clear liquid. During the reaction, ammonia vapor is collected with dilute nitric acid to obtain an aqueous solution of ammonium nitrate, which is used in this step.

[0040] (5) Add dilute sulfuric acid to the third clear liquid for acidification until the pH is 2, stir or ultrasonically react for 15 minutes, let stand for 0.5 hours, and centrifuge at 3000 rpm to obtain a fourth precipitate and a fourth clear liquid.

[0041] (6) The third precipitate and the fourth precipitate are combined and sent to the fertilizer processing workshop to be processed into base fertilizer. The fourth clear liquid is concentrated by a double-effect evaporation concentrator at -0.06 to -0.09 MPa to obtain a potassium humate concentrated aqueous solution product with a temperature of 25° C. and a relative density of 1.3.

[0042] During the evaporation and concentration process, the steam is collected and condensed, and the condensate is recovered. The condensate is then used in step (2) to prepare dilute nitric acid.

[0043] Example 2

[0044] This embodiment provides a preparation process of mineral-source potassium humate, and the steps are as follows:

[0045] (1) Dry weathered coal (humic acid content 40-50%) is coarsely sieved, and the part with a particle size less than 5 cm is retained for jaw crushing, and finely ground through a 300-mesh sieve to obtain a powder.

[0046] (2) preparing dilute nitric acid with a concentration of 5%, mixing the powder with the dilute nitric acid at a mass ratio of 1:4, stirring and leaching at room temperature for 3 hours, and centrifuging at 3000 rpm to obtain a first clear liquid and a first precipitate.

[0047] (3) Ammonia water was added to the first clear liquid to adjust the pH to 9, and after stirring or ultrasonic reaction for 0.5 h, 1 mg / L PAM was added, and the reaction was allowed to stand for 1 h, and centrifuged at 3000 rpm to obtain a second clear liquid and a second precipitate. The second precipitate was landfilled harmlessly.

[0048] (4) The first precipitate and the second clear liquid are mixed in a mass ratio of 1:3, potassium hydroxide is added at 12% of the dry weight of the first precipitate, the pH of the mixed system is adjusted to 12.5, the temperature is raised to 75-80°C, and the mixture is reacted under 40KHz ultrasound for 1.5 hours; after the reaction is completed, the mixture is centrifuged at 3000rpm to obtain a third precipitate and a third clear liquid. During the reaction, ammonia vapor is collected with dilute nitric acid to obtain an aqueous solution of ammonium nitrate, which is used in this step.

[0049] (5) Add dilute sulfuric acid to the third clear liquid for acidification until the pH is 2, stir or ultrasonically react for 15 minutes, let stand for 0.5 hours, and centrifuge at 3000 rpm to obtain a fourth precipitate and a fourth clear liquid.

[0050] (6) The third precipitate and the fourth precipitate are combined and sent to a fertilizer processing workshop to be processed into base fertilizer. The fourth clear liquid is concentrated at -0.06 to -0.09 MPa using a double-effect evaporation concentrator to obtain a potassium humate concentrated aqueous solution product at 25° C. and a relative density of 1.3. During the evaporation and concentration process, steam is collected and condensed, and the condensate is recovered, and the condensate is applied to the preparation of dilute nitric acid in step (2).

[0051] Example 3

[0052] This embodiment provides a preparation process of mineral-source potassium humate, and the steps are as follows:

[0053] (1) Dry weathered coal (humic acid content 40-50%) is coarsely sieved, and the part with a particle size less than 5 cm is retained for jaw crushing, and finely ground through a 300-mesh sieve to obtain a powder.

[0054] (2) preparing dilute nitric acid with a concentration of 5%, mixing the powder with the dilute nitric acid at a mass ratio of 1:3, stirring and leaching at room temperature for 3 hours, and centrifuging at 3000 rpm to obtain a first clear liquid and a first precipitate.

[0055] (3) Add 10% of the reaction system of chelating macroporous resin (1.0-1.6 mm), the surface of which is grafted with aminophosphoric acid and thiol, to the first clear solution, let it stand for 1 hour, and centrifuge at 3000 rpm to obtain a second clear solution and a second precipitate.

[0056] The second precipitate is subjected to analytical regeneration treatment with 0.5M dilute sulfuric acid and can be reused after being soaked for 3 hours.

[0057] Steps (4) to (6) are the same as those in Example 1. During the evaporation and concentration process, the steam is collected and condensed, and the condensate is recovered. The condensate is used to prepare dilute sulfuric acid in step (5). Finally, a potassium humate concentrated aqueous solution product with a temperature of 25° C. and a relative density of 1.3 is obtained.

[0058] Example 4

[0059] In this embodiment, when concentrating in a double-effect evaporation concentrator in Example 1, the solution is first concentrated to 33% of the initial volume, then cooled to 0-4°C, solid-liquid separated, and potassium humate crystals are collected.

[0060] Example 5

[0061] This embodiment is based on Example 3, and the fourth clear liquid is concentrated at -0.06 to -0.09 MPa by a double-effect evaporation concentrator to obtain a potassium humate concentrated aqueous solution at 25°C and a relative density of 1.5, and then cyclodextrin, starch (cyclodextrin and starch are added in an amount of 20%) and trace elements ferrous sulfate (Fe, 3.4%), zinc sulfate (Zn, 3.4%), and ammonium molybdate (Mo, 0.6%) are added for spray granulation to obtain a potassium humate granule product.

[0062] After testing, ICP-MS was used to test the aqueous product, and a portable X-ray fluorescence spectrometer was used to test the crystalline and granular products. The results confirmed that the potassium humate products prepared in Examples 1-5 did not contain heavy metal ions such as Cu, Pb, Cd, and Cr. In addition, the potassium humate concentrated aqueous solution of Examples 1-2 also contained a small amount of ammonium nitrate. The potassium humate granular product of Example 5 was dissolved in water, and nitrate nitrogen could also be detected. Nitrogen is a very important plant nutrient.

[0063] The product prepared in Example 1 is used to plant peppers. The potassium humate concentrated aqueous solution is diluted at 1:500 (i.e., 2 ml of potassium humate concentrate is added per liter of water), and 1 kg of concentrated aqueous solution is used per mu each time. Mineral potassium humate is applied during the pepper seedling period (seedling nursery bed), sprayed once before emergence, and sprayed a second time one week after emergence, which can make the pepper seedlings uniform and strong. Compared with the unapplied nursery bed, it can be transplanted to the greenhouse or field 7-10 days earlier, so that the vegetables can be put on the market earlier.

[0064] The potassium humate granule product of Example 5 was dissolved in water at a ratio of 1:800 and applied to the demonstration field (pepper) in Hejing County, Bayinguoleng Mongolian Autonomous Prefecture. Drip irrigation was carried out at 1 kg of granule product per mu. After using potassium humate twice, the root development of the pepper was promoted, and the utilization rate of soil moisture and fertilizer was improved, the plant's stress resistance was enhanced, the growth of the pepper was promoted, and the yield was increased.

[0065] The potassium humate granule product of Example 5 was dissolved in water at a ratio of 1:800 and applied to the demonstration field (cotton) in Yongku Tuanjie Village, Qiman Town, Kuqa. Drip irrigation was carried out at 1 kg of granule product per mu. After using potassium humate twice, the root surface area and the number of root hairs of the cotton increased significantly, the stems were thick, and the root system was well-developed, which promoted the growth and branching of the cotton plants, and the leaf area and the number of leaves increased.

[0066] The potassium humate granule product of Example 5 was dissolved in water at a ratio of 1:800 and applied to the demonstration field of Gansu Yasheng Industrial Co., Ltd. (silage corn Kenyu 1608). Drip irrigation was carried out at 2 kg of granule product per mu. After two uses, the leaves were darker green than those in the control group, the plants maintained green better, the secondary roots of the root system increased significantly, the growth potential was enhanced, and there were obvious effects of promoting rooting, promoting filling, and promoting starch accumulation, thereby increasing dry matter yield.

[0067] The mineral source potassium humate granule product of Example 5 and the concentrated aqueous solution product of Example 1 were used in oats (first crop, irrigated land) in Dongle Town, Shandan, with 5kg / mu of base fertilizer granules + 1kg per mu sprayed by drone (2 times). The granules were directly sprinkled into the soil, and the concentrated aqueous solution was diluted and sprayed at 1:500. Demonstration data: 400 mu of oat fields were applied with Qingtianzi-mineral source potassium humate liquid fertilizer. The average plant height of oats was 1.7m (up to 1.8m), the average ear length was 45cm, the rhizome was thick, the leaf surface was wide, and the yield per mu was 810kg, which was 20cm higher than the same plot last year, and the yield per mu increased by 150kg.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may still be modified, or some or all of the technical features therein may be replaced by equivalents. These modifications or replacements, or the technical features in the above embodiments may be combined in the manner described in the embodiments if they do not conflict with each other, and these modifications, replacements or combinations do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for preparing mineral-derived potassium humate, characterized in that: It includes: S1. Jaw-crushing, fine grinding and screening of weathered coal, lignite or peat to obtain 300-mesh powder, leaching the powder with dilute nitric acid, and separating the solid and liquid to obtain a first clear liquid and a first precipitate; then, treating in any of the following ways: Method 1: adding ammonia water and flocculant to the first clear liquid to carry out precipitation reaction, and separating the solid and liquid to obtain a second precipitate and a second clear liquid from which heavy metals have been removed; Method 2: adding a chelating macroporous resin to the first clear solution, and after adsorption reaction, performing solid-liquid separation to obtain a second precipitate and a second clear solution from which heavy metals have been removed; S2, the first precipitate: the second clear liquid and the total amount of water are mixed in a mass ratio of 1:3-8, 10-20% of the dry mass of the first precipitate of potassium hydroxide is added, the pH of the mixed system is adjusted to between 10-14, the temperature is raised to 60-90 ° C and stirred or ultrasonically reacted for 1-1.5h; after the reaction is completed, the solid and liquid are separated to obtain a third precipitate and a third clear liquid; S3, adding dilute sulfuric acid to the third clear liquid for acidification until the pH reaches 2-3, stirring or ultrasonically reacting for 10-20 minutes, and separating the solid and the liquid to obtain a fourth precipitate and a fourth clear liquid; S4. Combine the third precipitate and the fourth precipitate and send them to a fertilizer processing workshop to be processed into base fertilizer; concentrate the fourth clear liquid by using a double-effect evaporation concentrator under negative pressure to obtain a potassium humate concentrated aqueous solution product; or after concentration, add granulation auxiliary materials to perform spray granulation to obtain a potassium humate solid particle product.

2. The preparation process according to claim 1, characterized in that: In method 1 of S1, the flocculant is bentonite, PAM, PDADMAC or a natural organic flocculant; the amount of PAM, PDADMAC or a natural organic flocculant added is 0.1-2 mg / L; the amount of bentonite added is 5-10% of the volume of the reaction system; the second precipitate is harmlessly landfilled or sintered at high temperature and then used as concrete filler to make building materials.

3. The preparation process according to claim 1, characterized in that: In S1, the concentration of dilute nitric acid is 5-10%, and the mass ratio of powder to dilute nitric acid is 1:2-4; the amount of ammonia water added is to adjust the pH of the reaction system to 8-9; the second clear liquid obtained in method one contains ammonium nitrate.

4. The preparation process according to claim 1, characterized in that: In method 2 of S1, the chelating macroporous resin is a macroporous resin containing a compatible group of aminophosphoric acid, thiol or pyridyl, and its addition amount is 10-20% of the volume of the reaction system; the second precipitate produced by method 2 is subjected to analytical regeneration treatment with 0.1-1M dilute sulfuric acid for 0.5-5h and is reused; the second clear liquid obtained by method 2 contains nitrate.

5. The preparation process according to claim 1, characterized in that: In S2, ammonia vapor is collected with dilute nitric acid during stirring or ultrasonic reaction at 60-90°C to obtain an aqueous solution of ammonium nitrate, which is used in the dilute nitric acid leaching stage in step S1 or in S2.

6. The preparation process according to claim 1, characterized in that: The solid-liquid separation in S2 and S3 was performed by centrifuge at 3000 rpm for 30-40 min.

7. The preparation process according to claim 6, characterized in that: In S3, the solid-liquid separation further includes microfiltration or ultrafiltration.

8. The preparation process according to claim 1, characterized in that: In S1, the humic acid content in the weathered coal, lignite or peat as raw materials is greater than 10%. If the humic acid content in the raw materials is less than 10%.

9. The preparation process according to claim 1, characterized in that: In S4, during the evaporation and concentration process using a double-effect evaporation concentrator, steam is collected and condensed, and the condensate is recovered. The condensate is applied to the preparation of dilute nitric acid in step S1, or is recycled to S2 for mixing with the second clear liquid, or is recycled to S3 for preparing dilute sulfuric acid.

10. The preparation process according to claim 1, characterized in that: In S4, concentrated crystals are collected during the concentration process, and the concentrated crystals are potassium humate crystal products; In S4, the granulation auxiliary material is at least one of PVA, CMC, cyclodextrin, starch, bentonite and attapulgite.