Biochar as a carrier of slow-release potassium fertilizer and its preparation method
By ball milling modified biochar and using polyvinyl alcohol coating technology, slow-release potassium fertilizer was prepared, which solved the problems of low potassium fertilizer utilization and excessively rapid release of biochar-based fertilizers, and achieved stable, controllable release and efficient utilization of potassium, thereby reducing environmental impact.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZUNYI CITY BRANCH OF GUIZHOU TOBACCO COMPANY
- Filing Date
- 2026-03-19
- Publication Date
- 2026-05-29
AI Technical Summary
Existing chemical potassium fertilizers have low utilization rates and serious losses, leading to resource waste and environmental pollution. Meanwhile, biochar-based fertilizers release nutrients too quickly and have poor slow-release effects.
By employing ball milling technology to modify biochar and polyvinyl alcohol coating technology, slow-release potassium fertilizer with biochar as the carrier was prepared. Ball milling increases the specific surface area and the number of functional groups, and polyvinyl alcohol is combined to form a dense film, thereby synergistically achieving stable slow release of potassium.
It significantly improves potassium fertilizer utilization, reduces fertilization frequency and environmental impact, enhances potassium adsorption capacity, achieves controlled slow release of potassium, has a wide range of applications, and the preparation process is simple and environmentally friendly.
Smart Images
Figure CN122102796A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of slow-release fertilizer technology, specifically relating to a slow-release potassium fertilizer using biochar as a carrier and its preparation method. Background Technology
[0002] With the continuous growth of the global population, food security has become one of the most serious challenges facing the world, and ensuring a stable increase in food production has become a core requirement for current agricultural development. In agricultural production, fertilizer input is a key means to increase food yield. Among them, potassium, as an essential nutrient element indispensable for crop growth and development, plays an irreplaceable and crucial role in a series of physiological and biochemical processes, such as regulating plant photosynthetic efficiency, maintaining cell osmotic balance, regulating stomatal conductance, and promoting protein synthesis.
[0003] Currently, the supply of potash fertilizer in agricultural production mainly relies on chemical potash fertilizers. While these can quickly provide crops with potassium nutrition and meet their growth needs, they have significant limitations: Firstly, the production cost of chemical potash fertilizers is high, and their raw materials are mostly derived from non-renewable silicate minerals, which will exacerbate the risk of resource depletion in the long term. Secondly, due to the high solubility of potassium ions, chemical potash fertilizers applied to the soil are easily lost through rainwater leaching and soil seepage, resulting in a utilization rate of only about 35% in the current season. This low utilization rate not only causes serious resource waste, but the lost potassium ions also lead to a series of environmental problems such as eutrophication of water bodies and deterioration of soil physical and chemical properties, hindering the sustainable development of agriculture.
[0004] To address the aforementioned issues, slow-release fertilizers, due to their ability to precisely regulate nutrient release rates and dynamically match nutrient supply with crop growth needs, have become a research hotspot in the fertilizer field. This significantly improves fertilizer utilization efficiency while reducing the negative environmental impact of nutrient loss. In the development of slow-release fertilizer carriers, biochar, with its unique advantages such as wide availability of raw materials (derived from agricultural and forestry waste), high chemical stability, rich pore structure, and diverse surface functional groups, has been widely applied in soil structure improvement, contaminated soil remediation, and the fixation of heavy metals and organic pollutants. Furthermore, biochar itself contains a certain amount of mineral nutrients and can be directly used as a slow-release fertilizer carrier to continuously supply nutrients to the soil. Therefore, research on the preparation of slow-release fertilizers using biochar has received widespread attention and importance from scholars both domestically and internationally in recent years.
[0005] Among biochar modification technologies, ball milling, as a more environmentally friendly, economical, and efficient physical modification method compared to chemical modification, has been widely used in the industrial field. This process, through mechanical force, can significantly increase the specific surface area of biochar, expand its pore volume, and increase the number of its surface functional groups. These characteristics directly affect the adsorption and loading capacity of biochar for nutrients, thus playing a key regulatory role in the nutrient release behavior of biochar-based slow-release fertilizers, providing a reliable technical path for optimizing the performance of biochar-based slow-release fertilizers.
[0006] Furthermore, overcoming the limitation of excessively rapid nutrient release in biochar-based fertilizers and further enhancing their slow-release effect has become a key research focus. Combining biodegradable films with functionalized biochar to construct a slow-release system with both nutrient adsorption and retention and diffusion barrier mechanisms is one innovative approach to solving this problem. Polyvinyl alcohol (PVA), as a non-toxic and biodegradable polymer material, possesses excellent film-forming properties and shows promising application prospects in the coating modification of slow-release fertilizers. It can effectively slow down the nutrient release rate, further enhancing the application value of slow-release fertilizers. Summary of the Invention
[0007] This invention aims to overcome the problems of low utilization rate and serious loss of conventional potassium fertilizers, as well as the problems of excessively rapid nutrient release and poor slow-release effect of biochar-based fertilizers. It provides a slow-release potassium fertilizer using biochar as a carrier and its preparation method. This method is simple, operates under mild conditions, and is environmentally friendly. The prepared potassium fertilizer exhibits significant slow-release nutrient effect and has a wide range of applications, providing both technical and theoretical support for the development and application of biochar-based slow-release potassium fertilizers.
[0008] The objective of this invention can be achieved through the following technical solutions: This invention provides a slow-release potassium fertilizer using biochar as a carrier and its preparation method, comprising the following steps: (1) Mix tobacco stalk biochar (BC) and potassium sulfate (K2SO4) evenly to obtain a mixture; (2) The mixture was placed in a planetary ball mill for ball milling to obtain potassium-rich ball-milled tobacco biochar, denoted as BM-KBC; (3) Prepare a polyvinyl alcohol (PVA) solution by adding BM-KBC, concentrated hydrochloric acid and glutaraldehyde to the PVA solution in sequence and stirring until the system is mixed evenly. (4) Let the mixture obtained in step (3) stand until it gels; (5) After the gel-forming product is frozen, it is freeze-dried to obtain PVA-coated potassium-rich ball-milled tobacco biochar, denoted as PVA / BM-KBC, which is the slow-release potassium fertilizer with biochar as carrier.
[0009] Preferably, in step (1), the mass ratio of tobacco biochar to potassium sulfate is 1~3:1.
[0010] Preferably, in step (2), the ball milling conditions of the planetary ball mill are: ball milling time 1~3 h, ball milling speed 160~200 rpm.
[0011] As a preferred option, in step (3), the concentration and dosage ratio of each raw material are as follows: the concentration of PVA solution is 4~6wt%, the concentration of concentrated hydrochloric acid is 36wt%, and the concentration of glutaraldehyde solution is 20~30wt%; the dosage ratio of the above-mentioned concentrations of PVA solution, BM-KBC, concentrated hydrochloric acid, and glutaraldehyde solution is 10mL:1g:0.3mL:0.25mL.
[0012] Preferably, in step (5), the freezing conditions are: placed in a freezer at -20°C for 4 to 8 hours.
[0013] The beneficial effects of this invention are reflected in: 1. This invention significantly slows down the release rate of potassium in biochar through the synergistic effect of ball milling and polyvinyl alcohol coating, achieving stable and controllable slow release of potassium, effectively improving the utilization rate of potassium fertilizer, and helping to reduce the frequency and total amount of fertilization, thereby mitigating the potential environmental impact on soil and water bodies.
[0014] 2. This invention utilizes ball milling to increase the number of surface functional groups in biochar, thereby enhancing its potassium adsorption capacity. Furthermore, polyvinyl alcohol coating further forms a dense film on the biochar surface, delaying potassium diffusion through a physical barrier effect. The combination of these two methods achieves a dual slow-release effect of adsorption and barrier in its structure, providing a reliable technical path for developing efficient and environmentally friendly slow-release potassium fertilizers.
[0015] 3. The preparation conditions of this invention are mild, the steps are simple, the requirements for instruments and equipment are low, the process is simple, and it is suitable for large-scale preparation and production. It has stable effects under a wide range of pH conditions. The carrier used is derived from biomass, which is safe, non-toxic, naturally degradable, and inexpensive. Attached Figure Description
[0016] Figure 1 The image shows a scanning electron microscope (SEM) image of the PVA-coated potassium-rich ball-milled tobacco biochar (PVA / BM-KBC) prepared in Example 3 of this invention. Figure 2 The Fourier transform infrared (FT-IR) spectra of Embodiment 2 (BM-KBC), Embodiment 3 (PVA / BM-KBC), and Comparative Example 2 (BC) of the present invention are shown below. Figure 3The static water release curves of potassium in Examples 1 (BM-BC), 2 (BM-KBC), and 3 (PVA / BM-KBC) of the present invention, and Comparative Example 1 (K2SO4) and Comparative Example 2 (BC) are shown. Figure 4 The static water release curves of potassium element prepared by PVA / BM-KBC under different pH conditions in Example 3 of this invention. Detailed Implementation
[0017] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to specific comparative examples and embodiments, but the scope of protection of the present invention is not limited thereto.
[0018] Comparative Example 1 Pure potassium sulfate (K2SO4), without any treatment, was used as a blank control.
[0019] Comparative Example 2 Untreated tobacco straw biochar (BC) served as a control sample of unmodified biochar.
[0020] Example 1 Prepare ball-milled tobacco biochar (BM-BC) according to the following steps: Take an appropriate amount of tobacco stalk biochar and place it in a planetary ball mill. Set the ball milling speed to 180 rpm and continue milling for 2 hours to obtain ball-milled tobacco stalk biochar, denoted as BM-BC.
[0021] Example 2 Prepare potassium-rich ball-milled tobacco biochar (BM-KBC) according to the following steps: (1) Mix tobacco biochar and potassium sulfate (K2SO4) evenly at a mass ratio of 2:1 to obtain a mixture. (2) The above mixture was placed in a planetary ball mill, the ball milling speed was set to 180 rpm, and the ball milling was continued for 2 hours to obtain potassium-rich ball milled tobacco biochar, denoted as BM-KBC.
[0022] Example 3 PVA-coated potassium-rich ball-milled tobacco biochar (PVA / BM-KBC) was prepared according to the following steps: (1) Mix tobacco biochar and potassium sulfate (K2SO4) evenly at a mass ratio of 2:1 to obtain a mixture. (2) The above mixture was placed in a planetary ball mill, the ball milling speed was set to 180 rpm, and the ball milling was continued for 2 hours to obtain potassium-rich ball milled tobacco biochar, denoted as BM-KBC; (3) Prepare 10 mL of 5 wt% polyvinyl alcohol (PVA) solution, add 1 g BM-KBC, 0.3 mL of 36 wt% concentrated hydrochloric acid and 0.25 mL of 25 wt% glutaraldehyde to the PVA solution in sequence, and stir until the system is mixed evenly. (4) Let the above mixture stand until the system is completely gelled; (5) The gel-formed product was pre-frozen in a freezer at -20℃ for 6 h, and then freeze-dried (temperature -40℃, vacuum degree ~100 pa) to obtain PVA-coated potassium-rich ball milled tobacco biochar, denoted as PVA / BM-KBC.
[0023] Using BM-BC, BM-KBC, and PVA / BM-KBC prepared in Examples 1-3, as well as pure potassium sulfate and untreated tobacco biochar from Comparative Examples 1-2, as test samples, a series of performance characterization experiments were conducted, as detailed below: 1. Morphology measurement (SEM) Take an appropriate amount of the PVA / BM-KBC sample prepared in Example 3, and evenly adhere it onto the conductive adhesive to complete the sample preparation. Observe its microstructure using a scanning electron microscope (SEM). Figure 1 As shown, PVA successfully formed a uniform and dense coating film on the surface of tobacco biochar, and a rich porous network structure was formed inside the PVA / BM-KBC particles, with the tobacco biochar particles uniformly embedded within it. This morphological feature confirms the effectiveness of the preparation method of the present invention: the dense surface coating film can effectively encapsulate the biochar and the loaded exogenous potassium, while the internal porous network structure can extend the diffusion path of potassium ions, thereby improving the sustained-release effect.
[0024] 2. Functional group determination (FT-IR) Infrared spectroscopy was used to analyze the changes in surface functional groups of the samples in Examples 2-3 (BM-KBC, PVA / BM-KBC) and Comparative Example 2 (BC) before and after ball milling modification and PVA coating treatment. The results are as follows: Figure 2 As shown. All samples were at 3420 cm. -1 With 2941 cm -1 1630 cm -1 With 1408 cm -1 1115 cm -1 With 620 cm -1 Characteristic absorption peaks appear at 3420 cm⁻¹, and the functional groups corresponding to each characteristic peak are as follows: -1 The absorption peak at 2941 cm⁻¹ corresponds to the OH stretching vibration of the hydroxyl (-OH) or carboxyl (-COOH) group; -1 The absorption peak at 1620 cm⁻¹ corresponds to the stretching vibration of aliphatic CH. -1The absorption peak at 1430 cm⁻¹ corresponds to the aromatic C=O stretching vibration. -1 The absorption peak at 1034 cm⁻ corresponds to the -COO⁻ tensile vibration; -1 The absorption peak at 620 cm⁻¹ corresponds to the CO bending vibration. -1 The absorption peak at that point corresponds to the stretching vibration of aromatic CH.
[0025] Depend on Figure 2 It is known that untreated tobacco biochar (BC) contains abundant surface functional groups, which can enhance the interaction between potassium ions and biochar, thereby slowing down the release rate of endogenous potassium. After ball milling, the content of oxygen-containing functional groups in BM-KBC is significantly increased compared to BC, especially the characteristic absorption peak intensity of the CO bond is significantly improved. This indicates that the ball milling process can not only effectively load exogenous potassium (potassium sulfate) onto the surface and pores of tobacco biochar, but also enhance the interaction between potassium ions and tobacco biochar. At the same time, the C=O peak position redshifted after ball milling, further confirming the stable interaction between tobacco biochar and potassium ions. After PVA coating treatment, the content of oxygen-containing functional groups in PVA / BM-KBC is further increased compared to BM-KBC, providing more binding sites for potassium ion fixation and helping to further slow down the release rate of potassium ions.
[0026] 3. Static water release experiment Take each test sample (Examples 1-3, Comparative Examples 1-2), place them in a 100-mesh nylon mesh bag, and put the mesh bag in a beaker containing 200 mL of distilled water. Allow the samples to stand for a static release experiment. At 3 h, 6 h, 9 h, 12 h, 24 h, 36 h, 48 h, and 96 h, take 1 mL of the released liquid from the beaker. Immediately after each sampling, add 1 mL of distilled water to ensure a constant volume of the release system.
[0027] Method for determining the initial total potassium content: Accurately weigh 10 mg of each test sample and place it in a 3 cm diameter glass tube. Add 10 mL of concentrated nitric acid. Place a 4 cm diameter curved-neck glass funnel at the mouth of the glass tube and place the glass tube in a temperature-controlled far-infrared digestion furnace. Set the temperature to 300℃ for heating and digestion. After digestion, transfer the digestion solution to a 100 mL volumetric flask and dilute to volume. Take 1 mL of the diluted solution for potassium content determination.
[0028] The potassium content in the released liquid and sample digest at each time point was determined by flame atomic absorption spectrophotometry (according to GB11904-1989 standard), and potassium release curves were plotted. The results are as follows: Figure 3 As shown.
[0029] Depend on Figure 3It can be seen that pure potassium sulfate (Comparative Example 1, K2SO4) has an extremely fast potassium release rate, releasing a large amount of potassium in a short time, with a cumulative release rate of over 50% within 24 hours; the potassium release rate of potassium-enriched ball-milled tobacco biochar (Example 2, BM-KBC) is significantly slowed down, indicating that ball milling treatment can effectively enhance the potassium retention capacity of biochar; while the PVA-coated potassium-enriched ball-milled tobacco biochar (Example 3, PVA / BM-KBC) has the best slow-release effect, with a cumulative potassium release rate of only 23.45% after 24 hours, which is significantly lower than that of BM-KBC.
[0030] The untreated tobacco biochar (Comparative Example 2, BC) and ball-milled tobacco biochar (Example 1, BM-BC) released only their own endogenous potassium. The release rate was not directly comparable to that of the sample loaded with exogenous potassium. However, their release curves also showed that ball milling modification could delay the release of endogenous potassium to some extent.
[0031] The above results indicate that the synergistic effect of ball milling and PVA coating can significantly reduce the release rate of exogenous potassium, thus achieving controlled and sustained release of potassium.
[0032] 4. pH stability measurement The pH of distilled water was adjusted to 5, 6, 7, 8, and 9 using 1 mol / L NaOH and 1.2 mol / L HCl solutions, respectively. Using the PVA / BM-KBC prepared in Example 3 as the test sample, static water release experiments were conducted under different pH conditions, following the same experimental method as above. Potassium release curves under different pH conditions were plotted, and the results are as follows. Figure 4 As shown.
[0033] Depend on Figure 4 It can be seen that within the pH range of 5-9, the potassium release curves of PVA / BM-KBC exhibit similar trends: in the initial release phase (first 12 h), the potassium release rate of samples under different pH conditions showed little difference, with a difference of less than 5%; as the release time increased, the difference in release rate under different pH conditions gradually increased, reaching a peak at 48 h, at which point the potassium release rate of the sample under pH=9 was 62.82%, and the potassium release rate of the sample under pH=6 was 48.95%, with a difference of 13.87%; after 48 h, the difference in release rate under different pH conditions gradually slowed down, and by 96 h, the cumulative potassium release of samples under each pH condition reached approximately 90%. These results indicate that the PVA / BM-KBC prepared in Example 3 of this invention has good slow-release stability under different acidic and alkaline environments, has a wide range of applications, and can adapt to soils with different pH types.
[0034] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for preparing a slow-release potassium fertilizer using biochar as a carrier, characterized in that, Includes the following steps: (1) Mix tobacco straw biochar with potassium sulfate evenly to obtain a mixture; (2) The mixture was placed in a planetary ball mill for ball milling to obtain potassium-rich ball-milled tobacco biochar, denoted as BM-KBC; (3) Prepare a polyvinyl alcohol (PVA) solution by adding BM-KBC, concentrated hydrochloric acid, and glutaraldehyde to the PVA solution in sequence and stirring until the system is evenly mixed. (4) Let the mixture obtained in step (3) stand until it gels; (5) After the gel-forming product is frozen, it is freeze-dried to obtain PVA-coated potassium-rich ball-milled tobacco biochar, denoted as PVA / BM-KBC, which is the slow-release potassium fertilizer with biochar as carrier.
2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of tobacco biochar to potassium sulfate is 1~3:
1.
3. The preparation method according to claim 1, characterized in that, In step (2), the ball milling conditions of the planetary ball mill are: ball milling time 1~3 h, ball milling speed 160~200 rpm.
4. The preparation method according to claim 1, characterized in that, In step (3), the concentration and dosage ratio of each raw material are as follows: PVA solution concentration is 4~6wt%, concentrated hydrochloric acid concentration is 36wt%, and glutaraldehyde solution concentration is 20~30wt%; the dosage ratio of the above-mentioned PVA solution, BM-KBC, concentrated hydrochloric acid, and glutaraldehyde solution is 10mL:1g:0.3mL:0.25mL.
5. The preparation method according to claim 1, characterized in that, In step (5), the freezing conditions are: placed in a freezer at -20℃ for 4~8 hours.
6. A slow-release potassium fertilizer using biochar as a carrier, characterized in that, It is prepared by the preparation method described in any one of claims 1-5.