Nano-hydroxyapatite / carbon ball composite fertilizer and preparation method thereof

Abstract

The invention discloses a nano-hydroxyapatite / carbon ball composite fertilizer and a preparation method thereof, and belongs to the technical field of composite fertilizers. The invention adopts waste biomass containing sugars as raw materials, couples the extraction process of sugar substances with the synthesis process of nano-hydroxyapatite, has no waste acid discharge, does not need to use organic solvents, has a short process flow, and is green and environmentally friendly. The sugar substances are derived into carbon balls through hydrothermal reaction, and at the same time, the phosphorus source and calcium source in the precursor are self-assembled into rod-shaped nano-hydroxyapatite on the surface of the carbon balls, and the nano-hydroxyapatite load is stably loaded on the surface of the carbon balls without agglomeration. After the composite fertilizer is applied, under the action of crop root secretions, the hydroxyapatite nanorods fall off from the surface of the carbon balls and are directly absorbed by the crops, which can effectively prevent phosphorus from being fixed by the soil, thereby improving the utilization rate of the phosphorus element, and then improving the fertilizer effect of the nano-hydroxyapatite / carbon ball composite fertilizer.

Description

Technical Field

[0001] The invention belongs to the technical field of compound fertilizers, and in particular relates to a nano hydroxyapatite / carbon ball compound fertilizer and a preparation method thereof. Background Art

[0002] Phosphorus is the second most essential macronutrient for crops. It comes from phosphate rock, a non-renewable resource. Global phosphate resources are expected to be exhausted within 50 to 400 years. Conventional phosphate fertilizers such as monoammonium phosphate and diammonium phosphate (MAP and DAP) and triple superphosphate (TSP) are easily oxidized by Ca in the soil. 2+ 、Al 3+ and Fe 3+ Phosphorus is fixed by the reaction, and the utilization rate of phosphorus in the season is only 15-20%. The inefficient use of phosphorus fertilizers has led to environmental problems such as soil pollution and eutrophication of water bodies. New fertilizers prepared by nanotechnology are increasingly considered to have good prospects for promoting sustainable agricultural development.

[0003] Nanohydroxyapatite (nHA) is a new type of phosphorus-based nanofertilizer that has attracted the attention of researchers in recent years. nHA has the characteristics of small particle size, high specific surface area, and high biocompatibility. It can also be used as a carrier to load a variety of nutrients and play a good role in nutrient slow release. It is expected to meet the dual needs of agricultural production that fertilizers can increase crop yields and reduce environmental pollution. In recent years, some patent applications related to nanohydroxyapatite have been disclosed, such as the Chinese patent application number 201611268306.0, which discloses a one-step synthesis method for preparing hydroxyapatite pesticide and fertilizer slow-release complexes; the Chinese patent application number 201980097395.2 discloses a method for preparing hydroxyapatite coated with humic acid or monomer phenol polymers; the Chinese patent application number 202010878165.4 discloses a method for preparing a hydroxyapatite-based nanoscale slow-release nitrogen fertilizer.

[0004] However, like other nanomaterials, due to the high surface energy of nanoparticles, nHA is easy to agglomerate during synthesis and application, which reduces the small size effect of nHA and is not conducive to the direct absorption of nano-nHA particles by crops. The nHA agglomerates gradually release phosphorus and calcium ions in the soil like conventional fertilizers, and still cannot avoid being fixed by the soil. The current preparation process lacks an effective method to inhibit the agglomeration of nHA, and mostly physical means are used, but the effect is limited. For example, the Chinese patent application number 201010524021.5 discloses a method for preparing nano-apatite fertilizer, which is to mix a phosphorus-based solution and a calcium-based solution to cause a precipitation reaction or a hydrothermal reaction, and the obtained nano-hydroxyapatite powder is only ground by a mortar and mortar to crush the particles, which cannot destroy the nano-particle agglomerates. The Chinese patent with application number 201610816945.X prepared a hydroxyapatite modified biochar fertilizer. The method first synthesized humic acid modified hydroxyapatite, then added it to the phosphorylated carbon powder solution, and finally added the remaining raw materials for spray drying to obtain the fertilizer. The physical mixing of hydroxyapatite and phosphorylated carbon powder cannot effectively disperse nHA nanoparticles. The Chinese patent with application number 201911362725.4 disclosed a method for preparing a nutrient slow-release acidic soil conditioner. The method ball-milled hydroxyapatite with rice husk charcoal, selenium-rich chitosan and other raw materials, mixed them with a binder for a second time, and then granulated them. Ball milling is beneficial to reducing the particle size of hydroxyapatite and deagglomerating agglomerates, but a dispersant needs to be added to prevent secondary agglomeration of nanoparticles. In addition, the ball milling process has high energy consumption and low production efficiency, which is not conducive to industrial application. Summary of the invention

[0005] In view of the above-mentioned prior art, the present invention provides a nano-hydroxyapatite / carbon ball composite fertilizer and a preparation method thereof, so as to solve the technical problems of the existing nano-hydroxyapatite fertilizers being difficult to synthesize and easy to agglomerate.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is to provide a method for preparing nano-hydroxyapatite / carbon ball composite fertilizer, comprising the following steps:

[0007] S1: Mix the sugar-containing waste biomass dry powder with phosphoric acid solution at a solid-liquid ratio of 1 g: 5-100 mL, reflux extract at 80-100 °C for 90-150 min, filter and collect the filtrate to obtain an extract;

[0008] S2: Add calcium hydroxide suspension to the extract under stirring conditions until the calcium-phosphorus atomic ratio in the system is 1:1, and continue stirring the reaction for 45-90 min to obtain a precursor solution;

[0009] S3: The precursor solution is heated to 160-200 °C under closed conditions, kept warm for 8-16 h, and then naturally cooled to room temperature to obtain a suspension;

[0010] S4: Centrifuge the suspension, collect the solid, wash and dry it.

[0011] Based on the above technical solution, the present invention can also be improved as follows.

[0012] Furthermore, the sugar-containing waste biomass dry powder is obtained by the following steps: drying the sugar-containing waste biomass at a temperature of 40-50° C. to a moisture content of less than 5%, and then crushing it through an 80-mesh sieve.

[0013] Furthermore, the sugar contained in the sugar-containing waste biomass is at least one of pectin, glucose, sucrose, fructose and cellulose.

[0014] Further, the sugar-containing waste biomass is at least one of citrus peels, orange peels, apple pomace, sunflower discs, banana peels, wine waste and sugarcane bagasse.

[0015] Furthermore, the phosphoric acid solution is obtained by diluting or concentrating wet-process phosphoric acid, thermal-process phosphoric acid or raffinate acid, wherein the concentration of phosphoric acid is 0.1-10 mol / L.

[0016] Furthermore, the concentration of the calcium hydroxide suspension is 0.1-10 mol / L.

[0017] Furthermore, the reaction temperature in S2 is 20-30 °C.

[0018] Furthermore, the heating rate in S3 is 5 °C / min.

[0019] Furthermore, in S4, the centrifugal speed was 4000 rpm, the centrifugal time was 5 min, the drying temperature was 80 °C, and the drying time was 24 h.

[0020] The invention also discloses a nano hydroxyapatite / carbon ball composite fertilizer. The nano hydroxyapatite / carbon ball composite fertilizer is prepared by the above preparation method.

[0021] The beneficial effects of the present invention are:

[0022] The present invention adopts common waste biomass containing sugar as raw material, and sugar is dissolved from cell wall by phosphoric acid extraction, and the process flow is short and green and environmentally friendly, and the extraction process of sugar substances and the synthesis process of nano hydroxyapatite are coupled, and compared with the traditional process, there is no waste acid discharge, and it is not necessary to use organic solvents, so it is more green and environmentally friendly. Sugar substances are derived into carbon balls by hydrothermal reaction, and at the same time, the phosphorus source and calcium source in the precursor are self-assembled into rod-shaped nano hydroxyapatite on the surface of carbon balls, and nano hydroxyapatite and carbon balls are combined by the POC group on the surface of carbon balls, and the dispersion is good, and the stability is high, and the nano hydroxyapatite is stably loaded on the surface of carbon balls, and agglomeration will not occur. After using the nano hydroxyapatite / carbon ball composite fertilizer in the present invention, under the action of crop root secretions, hydroxyapatite nanorods fall off from the surface of carbon balls, and therefore, crops can directly absorb hydroxyapatite nanorods, and phosphorus can be effectively prevented from being fixed by soil, so as to improve the utilization rate of phosphorus element, and then promote the fertilizer effect of nano hydroxyapatite / carbon ball composite fertilizer. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The scanning electron microscope test image of the nano-hydroxyapatite / carbon ball composite fertilizer obtained in Example 1, wherein (a) and (b) are the test results at 2 μm and 200 nm scales, respectively;

[0024] Figure 2 The scanning electron microscope test image of the nano-hydroxyapatite / carbon ball composite fertilizer obtained in Example 2, wherein (a) and (b) are the test results at 2 μm and 200 nm scales, respectively;

[0025] Figure 3 The scanning electron microscope test image of the nano-hydroxyapatite / carbon ball composite fertilizer obtained in Example 3, wherein (a) and (b) are the test results at 2 μm and 200 nm scales, respectively;

[0026] Figure 4 The scanning electron microscope test image of the nano-hydroxyapatite / carbon ball composite fertilizer obtained in Example 4, wherein (a) and (b) are the test results at 2 μm and 200 nm scales, respectively;

[0027] Figure 5 The scanning electron microscope test image of the nano-hydroxyapatite / carbon ball composite fertilizer obtained in Comparative Example 1, wherein (a) and (b) are the test results at 2 μm and 200 nm scales, respectively;

[0028] Figure 6 The Raman spectra of the nano-hydroxyapatite / carbon ball composite fertilizers obtained in Example 3, Example 4 and Comparative Example 1 are shown. DETAILED DESCRIPTION

[0029] The specific implementation modes of the present invention are described in detail below with reference to the embodiments.

[0030] Example 1

[0031] A nano-hydroxyapatite / carbon ball composite fertilizer is prepared by the following steps:

[0032] S1: drying orange peel at 45°C until the water content is less than 5%, and then crushing and passing through an 80-mesh sieve to obtain orange peel powder; diluting wet-process phosphoric acid with a phosphoric acid content of 25.8wt% into a phosphoric acid solution with a phosphoric acid concentration of 0.7 mol / L; the chemical composition and elemental composition of the orange peel powder are shown in Table 1, and the non-metal and metal oxide contents of the orange peel powder and the wet-process phosphoric acid are shown in Table 2;

[0033] Table 1 Chemical composition and elemental composition of orange peel powder (dry basis)

[0034]

[0035] Table 2 Non-metal and metal oxide contents in wet-process phosphoric acid and waste orange peel

[0036]

[0037] S2: Add 9.5 g of orange peel powder to 50 mL of phosphoric acid solution, reflux and extract at 90 °C for 120 min, then filter and collect the filtrate to obtain an extract containing pectin;

[0038] S3: The extract was placed in a water bath at 25°C, and then a 0.7 mol / L calcium hydroxide suspension was added dropwise to the extract under stirring conditions until the calcium-phosphorus atomic ratio (Ca:P) in the system was 1:1; after the addition was completed, the reaction was continued with heat preservation and stirring for 60 min to obtain a precursor solution containing dihydrate calcium hydrogen phosphate / pectin complex;

[0039] S4: Add the precursor solution into a polytetrafluoroethylene liner with a total volume of 100 mL, load it into a hydrothermal synthesis reactor, put it into an oven, heat it to 180 °C at a heating rate of 5 °C / min, and keep it warm for hydrothermal reaction. The hydrothermal reaction time is 16 h. After the hydrothermal reaction is completed, the reactor is naturally cooled to room temperature to obtain a suspension.

[0040] S5: The suspension was centrifuged at 4000 rpm for 5 min, the solid was collected, and the solid was washed with deionized water for 3 times, and then the solid was placed in an electric constant temperature forced air drying oven at 80°C and dried for 24 h to obtain nano-hydroxyapatite / carbon ball composite fertilizer.

[0041] Example 2

[0042] A nano-hydroxyapatite / carbon ball composite fertilizer, the preparation process of which is based on Example 1, wherein the amount of orange peel powder added is adjusted to 7.0 g, the hydrothermal reaction time is adjusted to 8 h, and the other conditions are the same as Example 1.

[0043] Example 3

[0044] A nano-hydroxyapatite / carbon ball composite fertilizer, the preparation process of which is based on Example 1, with the addition amount of orange peel powder adjusted to 7.0 g, the hydrothermal reaction time adjusted to 12 h, and the other conditions being the same as Example 1.

[0045] Example 4

[0046] A nano-hydroxyapatite / carbon ball composite fertilizer, the preparation process of which is based on Example 1, the addition amount of orange peel powder is adjusted to 7.0 g, the hydrothermal reaction temperature is adjusted to 160° C., the hydrothermal reaction time is adjusted to 12 h, and the other conditions are the same as Example 1.

[0047] Example 5

[0048] A nano-hydroxyapatite / carbon ball composite fertilizer is prepared by the following steps:

[0049] S1: drying bagasse at 50°C until the water content is less than 5%, and then crushing and passing through an 80-mesh sieve to obtain bagasse powder; concentrating raffinate with a phosphoric acid content of 10 wt% into a phosphoric acid solution with a phosphoric acid concentration of 10 mol / L;

[0050] S2: Add 10 g of bagasse powder into 50 mL of phosphoric acid solution, reflux and extract at 100 °C for 90 min, then filter and collect the filtrate to obtain the extract;

[0051] S3: Place the extract in a water bath at 25 °C, then add a 10 mol / L calcium hydroxide suspension to the extract under stirring until the calcium-phosphorus atomic ratio (Ca:P) in the system is 1:1; after the addition is completed, continue to stir and react for 45 min to obtain a precursor solution;

[0052] S4: Add the precursor solution into a polytetrafluoroethylene liner with a total volume of 100 mL, load it into a hydrothermal synthesis reactor, put it into an oven, heat it to 200 °C at a heating rate of 5 °C / min, and keep it warm for a hydrothermal reaction for 10 h. After the hydrothermal reaction is completed, the reactor is naturally cooled to room temperature to obtain a suspension.

[0053] S5: The suspension was centrifuged at 4000 rpm for 5 min, the solid was collected, and the solid was washed with deionized water for 3 times, and then the solid was placed in an electric constant temperature forced air drying oven at 80°C and dried for 24 h to obtain nano-hydroxyapatite / carbon ball composite fertilizer.

[0054] Example 6

[0055] A nano-hydroxyapatite / carbon ball composite fertilizer is prepared by the following steps:

[0056] S1: drying winemaking waste at 40°C until the water content is less than 5%, and then crushing and passing through an 80-mesh sieve to obtain winemaking waste powder; diluting thermal phosphoric acid with a phosphoric acid content of 16wt% into a phosphoric acid solution with a phosphoric acid concentration of 0.1 mol / L;

[0057] S2: Add 1 g of brewing waste powder into 100 mL of phosphoric acid solution, reflux and extract at 80 °C for 150 min, then filter and collect the filtrate to obtain an extract;

[0058] S3: Place the extract in a water bath at 25 °C, then add a 0.1 mol / L calcium hydroxide suspension to the extract under stirring until the calcium-phosphorus atomic ratio (Ca:P) in the system is 1:1; after the addition is completed, continue to stir and react for 90 min to obtain a precursor solution;

[0059] S4: Add the precursor solution into a polytetrafluoroethylene liner with a total volume of 100 mL, load it into a hydrothermal synthesis reactor, put it into an oven, heat it to 180 °C at a heating rate of 5 °C / min, and keep it warm for hydrothermal reaction. The hydrothermal reaction time is 16 h. After the hydrothermal reaction is completed, the reactor is naturally cooled to room temperature to obtain a suspension.

[0060] S5: The suspension was centrifuged at 4000 rpm for 5 min, the solid was collected, and the solid was washed with deionized water for 3 times, and then the solid was placed in an electric constant temperature forced air drying oven at 80°C and dried for 24 h to obtain nano-hydroxyapatite / carbon ball composite fertilizer.

[0061] Comparative Example 1

[0062] A nano-hydroxyapatite / carbon ball composite fertilizer, the preparation process of which is based on Example 1, wherein the hydrothermal reaction temperature is adjusted to 140° C., and the other conditions are the same as Example 1.

[0063] Comparative Example 2

[0064] Commercialized nano-hydroxyapatite (Ca 10 (PO4)6(OH)2, rod-shaped) was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0065] Comparative Example 3

[0066] Superphosphate products are purchased from a fertilizer company.

[0067] Results Analysis

[0068] The nano-hydroxyapatite / carbon ball composite fertilizer obtained in Example 1 was tested by scanning electron microscope. Figure 1 As shown in Figure 2, (a) and (b) are the test results at 2 μm and 200 nm scales, respectively. Figure 1 It can be seen that the size of the carbon sphere is 1~2 μm, and rod-shaped nanohydroxyapatite is distributed on its surface, and the nanohydroxyapatite is not agglomerated.

[0069] The nano-hydroxyapatite / carbon ball composite fertilizer obtained in Example 2 was tested by scanning electron microscope. Figure 2 As shown in Figure 2, (a) and (b) are the test results at 2 μm and 200 nm scales, respectively. Figure 2 It can be seen that the size of the carbon sphere is 5~10 μm, and rod-shaped nanohydroxyapatite is distributed on its surface, and the nanohydroxyapatite is not agglomerated.

[0070] The nano-hydroxyapatite / carbon ball composite fertilizer obtained in Example 3 was tested by scanning electron microscope. Figure 3 As shown in Figure 2, (a) and (b) are the test results at 2 μm and 200 nm scales, respectively. Figure 3 It can be seen that the size of the carbon spheres is 1~5 μm, and rod-shaped nanohydroxyapatite is distributed on its surface, and the nanohydroxyapatite is not agglomerated.

[0071] The nano-hydroxyapatite / carbon ball composite fertilizer obtained in Example 4 was tested by scanning electron microscope. The results are as follows: Figure 4 As shown in Figure 2, (a) and (b) are the test results at 2 μm and 200 nm scales, respectively. Figure 4 It can be seen that the size of the carbon sphere is 5~10 μm, and rod-shaped nanohydroxyapatite is distributed on its surface, and the nanohydroxyapatite is not agglomerated.

[0072] The nano-hydroxyapatite / carbon ball composite fertilizer obtained in Comparative Example 1 was tested by scanning electron microscope. The results are as follows: Figure 5 As shown in Figure 2, (a) and (b) are the test results at 2 μm and 200 nm scales, respectively. Figure 5 It can be seen that due to the low hydrothermal temperature, pectin was not converted into carbon spheres, and the short rod-shaped nanohydroxyapatite was evenly embedded in the pectin matrix and agglomerated to form an organic-inorganic hybrid.

[0073] The morphology and structure of the nano-hydroxyapatite / carbon ball composite fertilizer obtained in Example 5 and Example 6 are similar to that of the nano-hydroxyapatite / carbon ball composite fertilizer in Example 1, and will not be described in detail.

[0074] In addition, the nano-hydroxyapatite / carbon ball composite fertilizers prepared in Examples 3 and 4 and Comparative Example 1 were tested by Raman spectroscopy. Figure 6 As shown. Figure 6 It can be seen that the composite fertilizer obtained in Example 3 has a -1 and 1576cm -1 There are two peaks on the left and right, which belong to the characteristic D band and G band of pectin-derived carbon spheres. The D band is related to the degree of structural disorder of the carbon material, and the peak area of ​​the G band is larger, indicating that there is a graphite crystal structure in the compound fertilizer; the peak area ratio between the D band and the G band (ID / IG) represents the degree of surface disorder of the carbon material, and the ID / IG of the sample is 0.80. -1 and 1576 cm -1 Two peaks appeared on the left and right, which were respectively attributed to the characteristic D band and G band of pectin-derived carbon spheres. The ID / IG of the compound fertilizer was 0.64. The two typical bands of carbon were not observed in the compound fertilizer obtained in Comparative Example 1, and no carbon spheres were generated. Figure 5 The results are consistent.

[0075] Experimental example

[0076] A greenhouse hydroponic lettuce experiment was carried out, and the fertilizer efficiency of the above-mentioned embodiments and comparative samples was evaluated. First, the fertilizers in the above-mentioned embodiments and comparative examples were added to the phosphorus-free and calcium-free Hogland nutrient solution, the phosphorus content of the input was controlled to be equal, and the pH of the nutrient solution was adjusted to 6.00. The lettuce seeds were then sterilized with 75% (V / V) ethanol, washed with deionized water, and evenly spread on moist perlite for germination, and grown for 7 days in an environment with a day and night temperature of 25 ℃ / 18 ℃, a day and night cycle of 16 h / 8 h, a humidity of 60%, and an illumination of 5000 lx. Subsequently, the lettuce seedlings were placed in a hydroponic box (2 L) for cultivation, and each treatment was repeated 3 times. Except that the illumination was adjusted to 10000 lx, the other environmental conditions were the same as those in the early stage of seedling cultivation, and the cultivation was carried out for 21 days. After harvesting the plants treated in the examples and comparative examples, the dry weight of the plants was tested to examine the fertilizer efficiency of each fertilizer. The test results are shown in Table 3. The yield increase rate of lettuce seedlings in the table is based on Comparative Example 3.

[0077] Table 3 Performance test results of the embodiments and comparative examples

[0078]

[0079] As can be seen from Table 3, the nano-hydroxyapatite / carbon ball composite fertilizer was successfully prepared by the method of the present invention. The diameter of the nano-hydroxyapatite in the composite fertilizer sample obtained in the embodiment is 50-75 nm, the length is 165-235 nm, the carbon ball diameter is 1-10 nm, the carbon ball content is 4-10%, and the total phosphorus content is close to that of commercial nano-hydroxyapatite (about 18%). The application of the nano-hydroxyapatite / carbon ball composite fertilizer prepared by the present invention increases the dry weight of the lettuce seedlings. Among them, compared with comparative example 3, i.e., conventional phosphate fertilizer superphosphate, the nano-hydroxyapatite / carbon ball composite fertilizer prepared by the embodiment of the present invention significantly increases the yield of the lettuce seedlings, especially in Examples 1-3 and 5-6, the yield increase is more than 50%. It can be seen that compared with commercial nano-hydroxyapatite, the nano-hydroxyapatite composite fertilizer prepared by the present invention using carbon ball dispersion has a higher fertilizer efficiency and promotes the utilization of phosphorus by crops. Nanohydroxyapatite / carbon ball composite fertilizer, as a low-cost, new type of high-efficiency phosphorus-based nanofertilizer, has good application prospects.

[0080] Although the specific implementation of the present invention is described in detail in conjunction with the embodiments, it should not be understood as limiting the scope of protection of this patent. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative work still fall within the scope of protection of this patent.

Claims

1. A method for preparing nano-hydroxyapatite / carbon ball composite fertilizer, characterized in that: The following steps are involved: S1: Mix the sugar-containing waste biomass dry powder with phosphoric acid solution at a solid-liquid ratio of 1 g: 5-100 mL, reflux extract at 80-100° C. for 90-150 min, filter and collect the filtrate to obtain an extract; S2: adding a calcium hydroxide suspension to the extract under stirring conditions until the calcium-phosphorus atomic ratio in the system is 1:1, and continuing the stirring reaction for 45 to 90 minutes to obtain a precursor solution, the reaction temperature is 20 to 30°C; S3: The precursor solution is heated to 160-200°C under closed conditions, kept warm for reaction for 8-16 hours, and then naturally cooled to room temperature to obtain a suspension, and the heating rate is 5°C / min; S4: Centrifuge the suspension, collect the solid, wash and dry it.

2. The method for preparing the nano-hydroxyapatite / carbon ball composite fertilizer according to claim 1, characterized in that: The sugar-containing waste biomass dry powder is prepared by the following steps: drying the sugar-containing waste biomass at a temperature of 40-50° C. until the water content is less than 5%, and then crushing it through an 80-mesh sieve to obtain the dry powder.

3. The method for preparing the nano-hydroxyapatite / carbon ball composite fertilizer according to claim 2, characterized in that: The sugar contained in the sugar-containing waste biomass is at least one of pectin, glucose, sucrose, fructose and cellulose.

4. The method for preparing the nano-hydroxyapatite / carbon ball composite fertilizer according to claim 3, characterized in that: The sugar-containing waste biomass is at least one of citrus peels, orange peels, apple pomace, sunflower discs, banana peels, wine waste and sugarcane bagasse.

5. The method for preparing the nano-hydroxyapatite / carbon ball composite fertilizer according to claim 1, characterized in that: The phosphoric acid solution is obtained by diluting or concentrating wet-process phosphoric acid, thermal-process phosphoric acid or raffinate acid, wherein the concentration of the phosphoric acid is 0.1-10 mol / L.

6. The method for preparing the nano-hydroxyapatite / carbon ball composite fertilizer according to claim 1, characterized in that: The concentration of the calcium hydroxide suspension is 0.1-10 mol / L.

7. The method for preparing the nano-hydroxyapatite / carbon ball composite fertilizer according to claim 1, characterized in that: In S4, the centrifugal speed is 4000 rpm, the centrifugal time is 5 minutes, the drying temperature is 80°C, and the drying time is 24 hours.

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