Biomass charcoal composite hydrogel slow release fertilizer as well as preparation method and application thereof

Abstract

The invention discloses a biomass charcoal composite hydrogel slow-release fertilizer as well as a preparation method and application thereof, and belongs to the field of composite hydrogel and fertilizer preparation. The invention provides a biomass charcoal composite hydrogel slow release fertilizer, which comprises biomass charcoal, hydrogel fixed on the pores and surface of the biomass charcoal, and an element fertilizer mixed in the hydrogel, and the hydrogel is prepared from metal cations and alginate. The invention provides a strategy of'in-hole in-situ gelation ', hydrogel is prepared in situ in gaps of the biochar, and the biomass charcoal composite hydrogel slow-release fertilizer is prepared. The biochar and the hydrogel in the slow-release fertilizer are high in bonding strength and mechanical strength, so that the slow-release fertilizer has the slow-release function of the fertilizer and also has the capability of improving soil.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of composite hydrogel and fertilizer preparation, and particularly relates to a biomass charcoal composite hydrogel slow-release fertilizer and a preparation method and application thereof. BACKGROUND

[0002] Traditional slow-release fertilizers can delay nutrient release through coating or chemical modification, but the sulfur coating, polymer coating and other processes make the price of slow-release fertilizer reach 3-5 times of ordinary fertilizer, and lack the ability of soil improvement.

[0003] Biomass charcoal can be prepared into biomass charcoal fertilizer, which can improve the soil water holding capacity, cation exchange capacity (CEC) and can sequester carbon, reduce emissions, and adsorb heavy metals and organic pollutants. However, the nutrient content of biomass charcoal itself is low, N / P / K < 3%, and direct use as fertilizer has limited effect, and needs to rely on exogenous nutrient supplement. In the existing modification method, such as through physical adsorption or simple loading of nutrients (such as inorganic salt) combined with biomass charcoal, the binding force is weak, and under the conditions of rainwater leaching or irrigation, it is easy to be lost, the slow-release period is short, and there is a problem of easy loss of nutrients; or lack of precise control mechanism, the nutrient release rate increases rapidly under high temperature or high humidity environment, and the release is stagnant at low temperature, which cannot match the demand of crop growth cycle, and there are problems such as uncontrollable release.

[0004] Hydrogel (such as alginate, cellulose derivative) can lock water and nutrients through three-dimensional network structure, and realize controllable release in the process of swelling-shrinking. However, the slow-release fertilizer based on hydrogel has the following problems: (1) insufficient mechanical strength: the three-dimensional network structure of traditional hydrogel (such as sodium alginate) is fragile, and is easy to break in the process of soil pressure or tillage, resulting in nutrient leakage. (2) risk of burst release after swelling: after water absorption and swelling, the network pore increases, and the nutrients are easy to release quickly, which cannot realize long-term slow supply (such as nitrogen release rate exceeding 60% within 72 hours). (3) weak environmental adaptability: in acidic soil (pH < 5.5) or high salt environment, the swelling performance decreases, and the nutrient release efficiency decreases; at low temperature, the stability of cross-linking bond is poor, which affects the slow-release effect. (4) poor long-term stability: easy to be degraded by soil microorganisms (such as cellulose-based hydrogel), or the network structure is fatigue broken due to repeated swelling-shrinking. SUMMARY

[0005] In view of the problems of serious microplastic pollution of traditional slow-release fertilizer, low nutrient content of biomass charcoal fertilizer, poor mechanical strength and insufficient stability of hydrogel-based charcoal fertilizer, the present application aims to provide a biomass charcoal composite hydrogel slow-release fertilizer and a preparation method and application thereof. The present application proposes an "in-situ gelation in hole" strategy to prepare hydrogel in-situ in the space of biomass charcoal, and prepares a biomass charcoal composite hydrogel slow-release fertilizer. The slow-release fertilizer has high bonding strength between biomass charcoal and hydrogel and large mechanical strength, which not only has the function of slow-release fertilizer, but also has the ability of soil improvement.

[0006] To achieve the above object, the technical scheme of the present application is: In the first aspect, the present application provides a biomass charcoal composite hydrogel slow-release fertilizer, which comprises biomass charcoal, hydrogel fixed in the pores and surface of the biomass charcoal, and element fertilizer mixed in the hydrogel, wherein the hydrogel is prepared from metal cations and alginate.

[0007] In the present application, hydrogel is present in the interior and surface of the biomass charcoal, and element fertilizer is present in the hydrogel. The hydrogel is mainly present in the interior pores of the biomass charcoal. The second soaking of metal cations is to improve the cross-linking strength of the outermost hydrogel.

[0008] The mass ratio of biomass charcoal, element fertilizer and hydrogel is 1:0.3-0.45:3.2-3.65. The ratio of biomass charcoal to hydrogel is mainly determined by the pore structure of the biomass charcoal. If the ratio of element fertilizer is too high, the gel strength will be reduced, and if the ratio of element fertilizer is too low, the fertilizer load will be reduced.

[0009] In the second aspect, the present application provides a preparation method of the above biomass charcoal composite hydrogel slow-release fertilizer, which comprises the following steps: S1: soaking the biomass charcoal in a solution of multivalent metal cations, and then filtering; S2: adding element fertilizer to an alginate solution to form a hydrogel precursor solution, placing the filtered biomass charcoal of step S1 in the solution, and then filtering after standing and reaction; S3: soaking the filtered product of step S2 in a solution of multivalent metal cations, standing, filtering and drying to obtain the product.

[0010] In one or more embodiments, in step S1, the biomass charcoal is obtained by thermal chemical depolymerization of biomass. The biomass charcoal needs to be sieved to 10-30 mesh. The biomass charcoal can be prepared by pyrolysis of agricultural and forestry waste, and has high specific surface area, rich pore structure (micropore-mesopore classification) and stable carbon skeleton. The biomass charcoal fertilizer can improve the water holding capacity and cation exchange capacity (CEC) of the soil, and can sequester carbon, reduce emissions, and adsorb heavy metals and organic pollutants.

[0011] Further, biomass refers to organic material that is renewable, derived from living or recently living biological organisms, including the organisms themselves, their metabolites, byproducts and waste. The biological organisms include but are not limited to plants, animals and microorganisms. The forms of biomass include but are not limited to: wood and forestry residues, crops, agricultural residues and energy crops, algae and aquatic plants, animal manure, organic fractions of municipal waste, food processing waste, sewage sludge, and intermediates or derivatives produced by physical, chemical and / or biological treatment processes from any of the foregoing. For example, the biomass is lignin, sawdust, rice husk, etc.

[0012] Further, the thermo-chemical depolymerization includes pyrolysis, hydrothermal carbonization and the like. The step of hydrothermal carbonization can be hydrothermal reaction at 200-300°C (such as 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, etc.) for 2-6h (such as 2h, 3h, 4h, 5h, 6h, etc.). The step of pyrolysis can be high-temperature calcination at 600-800°C (such as 600°C, 650°C, 700°C, 750°C, 800°C, etc.) for 5-60min (such as 5min, 10min, 15min, 20min, 25min, 30min, 40min, 50min, 60min, etc.), and the heating rate is 10-20°C / min.

[0013] In one or more embodiments, in steps S1 and S3, the multivalent metal cation is one or more of calcium, magnesium, barium, strontium, zinc, copper, iron, aluminum ion solution. Among them, the multivalent metal cations in steps S1 and S3 can be the same or different.

[0014] In one or more embodiments, in step S1, the concentration of the multivalent metal cation is 0.01-0.4 mol / L. Such as 0.01mol / L, 0.05mol / L, 0.1mol / L, 0.15mol / L, 0.2mol / L, 0.25mol / L, 0.3mol / L, 0.35mol / L, 0.4mol / L, etc. and specific numerical values between the above point values.

[0015] In one or more embodiments, in step S3, the concentration of the multivalent metal cation is 0.4-1.0mol / L. Such as 0.45mol / L, 0.5mol / L, 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L, 1mol / L, etc. and specific numerical values between the above point values.

[0016] It should be noted that the concentration of the multivalent metal cation solution in step S3 is equal to or higher than the concentration of the multivalent metal cation solution in step S1, in order to achieve better technical effects, preferably the concentration of the multivalent metal cation solution in step S3 is higher than the concentration of the multivalent metal cation solution in step S1. Because the metal ions first enter the inside of the biochar, and then the alginate solution enters the biochar, resulting in the later the alginate entering the inside of the biochar, the lower the cross-linking density of the hydrogel formed by the alginate. Step S3 is to soak the metal cation again in order to improve the cross-linking density of the hydrogel in the outermost layer (late entering the biochar), which can improve the strength of the hydrogel and its slow-release effect.

[0017] In one or more embodiments, in step S2, the concentration of alginate in the precursor solution of hydrogel is 2-5 wt%, such as 2 wt%, 3 wt%, 4 wt%, 5 wt%, and specific values between the above-mentioned point values. The alginate is sodium alginate or potassium alginate.

[0018] The reason for choosing alginate is that after the biomass charcoal is soaked and filtered in the solution of multivalent metal cations in step S1, a large amount of metal cations will be left in the pores of the biomass charcoal. At this time, the addition of alginate will cause a displacement reaction between the metal cations in the pores of the biomass charcoal and the metal ions (such as sodium ions) in the alginate, realizing in-situ gelation of the biomass charcoal pores. In the process, the element fertilizer in the hydrogel precursor solution is also fixed in the pores of the biomass charcoal, realizing the fixed filling of element fertilizer and gel in the pores of the biomass charcoal.

[0019] In one or more embodiments, in step S2, the element fertilizer includes one or more of urea, ammonium nitrate, diammonium phosphate, calcium superphosphate, triple superphosphate, potassium nitrate, potassium chloride, ammonium polyphosphate, potassium sulfate, and potassium dihydrogen phosphate. The addition amount of each element in the element fertilizer is 10-20% of the hydrogel precursor solution. If multiple elements are added, the addition amount of each element can be in a ratio of 1:1.

[0020] In one or more embodiments, in step S2, the concentration of element fertilizer in the precursor solution of hydrogel is 0-300 g / L. Such as 0 g / L, 1 g / L, 25 g / L, 50 g / L, 100 g / L, 150 g / L, 200 g / L, 250 g / L, 300 g / L, and specific values between the above-mentioned point values. Too much addition of element fertilizer will affect the in-situ gelation of alginate and metal cations in the pores.

[0021] In one or more embodiments, in step S2, the standing time is 20-60 min, such as 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, and specific values between the above-mentioned point values. The standing for a certain time can cause sufficient displacement reaction between alginate and metal cations, so that the in-situ gelation of biomass charcoal is realized at the same time, and the slow-release fertilizer elements are also in-situ fixed in the pores of the biomass charcoal.

[0022] In one or more embodiments, in step S3, the standing time is 2-15 min, such as 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, and the like, as well as specific values between the above-mentioned point values. In step S3, the biomass charcoal composite hydrogel slow-release fertilizer preliminarily formed in step S2 is again placed in a higher concentration of metal cation buffer solution to allow the residual unreacted completely alginate and metal cations to fully react.

[0023] In one or more embodiments, in steps S2 and S3, the crosslinking temperature used is room temperature. As a preferred embodiment, the preparation method of the biomass charcoal composite hydrogel slow-release fertilizer comprises: (1) preparing biomass charcoal by thermal chemical depolymerization of biomass.

[0024] (2) placing the biomass charcoal in a solution containing multivalent metal cations, soaking for a sufficient time, and then filtering out.

[0025] (3) preparing a precursor solution of hydrogel, and adding a large amount of element fertilizer into the precursor solution.

[0026] (4) placing the filtered biomass charcoal in step (2) into the hydrogel precursor solution containing nitrogen, phosphorus, and potassium fertilizer obtained in step (3) to stand and react.

[0027] (5) placing the biomass charcoal after the reaction in step (4) is filtered into a high-concentration multivalent metal cation solution for sufficient soaking.

[0028] (6) filtering the biomass charcoal obtained in step (5) to obtain a biomass charcoal composite hydrogel, and drying to obtain a biomass charcoal composite hydrogel slow-release fertilizer.

[0029] In a third aspect, the present application provides the use of the above-mentioned biomass charcoal composite hydrogel slow-release fertilizer in the field of agriculture.

[0030] One or some of the above technical solutions have the following advantages or beneficial effects: (1) The present application is prepared by the "in-pore in-situ gelation" strategy to prepare a biomass charcoal composite hydrogel slow-release fertilizer, in which the hydrogel is prepared in-situ in the pores of the biomass charcoal, and the fertilizer is also fixed in-situ in the pores of the biomass. The biomass charcoal skeleton enhances the mechanical strength of the hydrogel, delays microbial decomposition, and the carbon pores adsorb free nutrients to form a double slow-release barrier with the hydrogel controlling the diffusion rate. The biomass charcoal composite hydrogel slow-release fertilizer has the functions of delaying fertilizer release and improving soil.

[0031] (2) The biomass charcoal composite hydrogel slow-release fertilizer prepared by the application can realize long-time slow-release effect, and the slow-release proportion of the fertilizer is more than 95% in 48 days, and the slow-release proportion of the fertilizer is more than 97% in 60 days. BRIEF DESCRIPTION OF DRAWINGS

[0032] The drawings accompanying the specification of the application form a part of the application and serve to further illustrate the application, the illustrative embodiments thereof, and the description thereof. The drawings do not, however, limit the application.

[0033] Figure 1 The biomass charcoal and the biomass charcoal composite hydrogel slow-release fertilizer prepared by the application are shown in the figures, wherein a is a biomass charcoal figure, and b is a biomass charcoal composite hydrogel slow-release fertilizer figure; Figure 2 The SEM figures of the biomass charcoal and the biomass charcoal composite hydrogel slow-release fertilizer prepared by the application are shown in the figures, wherein a is an SEM figure of the biomass charcoal, and b is an SEM figure of the biomass charcoal composite hydrogel slow-release fertilizer; Figure 3 The infrared spectrograms of the biomass charcoal and the biomass charcoal composite hydrogel slow-release fertilizer prepared by the application are shown in the figures. DETAILED DESCRIPTION

[0034] In the application, unless otherwise specified, other test materials and instruments and equipment are conventional test materials in the art, and can be purchased through commercial channels.

[0035] In order for those skilled in the art to more clearly understand the technical solutions of the application, the technical solutions of the application will be described in detail below with specific examples.

[0036] Example 1 Take 20 g of dry lignin, place it in a quartz tube, and directly put it into a tube furnace at a temperature of 650 DEG C under a nitrogen atmosphere, and keep it warm for 10 min. Naturally cool to room temperature, grind through a 20-mesh sieve, and obtain lignin biomass charcoal. Put the biomass charcoal into a 0.1 mol / L calcium chloride solution and magnetically stir for 30 min, filter, and then put it into a solution of sodium alginate (3 wt%) and urea (15 wt%), stand for 30 min, and filter again. Put the biomass carbon composite hydrogel after filtering again into a 0.8 mol / L calcium chloride solution, stand for 5 min, filter and wash, and finally obtain a biomass carbon composite hydrogel slow-release fertilizer.

[0037] Example 2 Take 50 g of dry pine sawdust and place it in a high-pressure reaction kettle. Add 300 mL of deionized water for hydrothermal carbonization: heat to 220°C and hold for 4 hours. Allow to cool naturally to room temperature, grind through a 20-mesh screen, and obtain pine biomass charcoal. Place the biomass charcoal in a 0.1 mol / L calcium chloride solution and magnetically stir for 30 min. After filtering, place in a sodium alginate (3 wt%), potassium nitrate (10 wt%), diammonium phosphate (10 wt%) solution, and stand for 30 min before filtering again. Place the biomass carbon composite hydrogel after filtering again into a 0.8 mol / L calcium chloride solution, stand for 5 min, filter and wash, and finally obtain the biomass carbon composite hydrogel slow-release fertilizer.

[0038] Example 3 Take 20 g of dry lignin and place it in a quartz tube. Place the tube in a tube furnace at a temperature of 650°C under a nitrogen atmosphere and hold for 10 min. Allow to cool naturally to room temperature, grind through a 20-mesh screen, and obtain lignin biomass charcoal. Place the biomass charcoal in a 0.05 mol / L magnesium sulfate solution and magnetically stir for 30 min. After filtering, place in a sodium alginate (3 wt%), urea (10 wt%), diammonium phosphate (10 wt%) solution, and stand for 30 min before filtering again. Place the biomass carbon composite hydrogel after filtering again into a 0.4 mol / L magnesium sulfate solution, stand for 5 min, filter and wash, and finally obtain the biomass carbon composite hydrogel slow-release fertilizer.

[0039] Example 4 Take 20 g of dry rice husk and place it in a quartz tube. Heat to 600°C at a rate of 15°C / min under a nitrogen atmosphere and hold for 1 hour. Allow to cool naturally to room temperature, grind through a 20-mesh screen, and obtain lignin biomass charcoal. Place the biomass charcoal in a 0.1 mol / L zinc chloride solution and magnetically stir for 30 min. After filtering, place in a potassium alginate (3 wt%), urea (10 wt%), diammonium phosphate (10 wt%) solution, and stand for 30 min before filtering again. Place the biomass carbon composite hydrogel after filtering again into a 0.4 mol / L magnesium sulfate solution, stand for 5 min, filter and wash, and finally obtain the biomass carbon composite hydrogel slow-release fertilizer.

[0040] Comparative Example 1 Unlike Example 1, the process of soaking in the metal cation solution twice is omitted.

[0041] If not soaked in the metal cation solution, the alginate and metal cations cannot undergo a displacement crosslinking reaction, and thus a hydrogel cannot be formed.

[0042] Comparative Example 2 Different from example 1, the initial biomass charcoal is retained in the soaking process in the metal cation solution, but the last metal cation soaking process is omitted. If the second metal cation soaking process is omitted, the fertilizer slow-release effect will decrease.

[0043] Comparative example 3 Different from example 1, the alginate and metal cation are first formed into a hydrogel, and then the biomass charcoal and element fertilizer are added. At this time, the hydrogel, element fertilizer and biomass charcoal are separated from each other, and cannot form a slow-release fertilizer.

[0044] Comparative example 4 Different from example 1, the biomass charcoal and element fertilizer such as urea are mixed to obtain a biomass charcoal loaded with urea, and then the metal cation and alginate are added to form a hydrogel. The hydrogel is crosslinked on the surface of the porous biomass charcoal loaded with urea to form a porous biomass charcoal loaded with urea wrapped by a hydrogel. At this time, the hydrogel can only adhere to the surface of the biomass charcoal, and cannot enter the inside of the biomass charcoal, so that the double-effect slow-release effect of the hydrogel plus the biomass charcoal cannot be formed, and the slow-release effect decreases.

[0045] Comparative example 5 Different from example 1, the biomass charcoal, urea, metal cation and alginate are mixed at this time, and the hydrogel cannot be formed, and there is no slow-release effect.

[0046] Comparative example 6 Different from example 1, the metal cation, alginate and urea are mixed, and then mixed with the biomass charcoal. At this time, the hydrogel is only doped with the biomass charcoal, and cannot enter the inside of the biomass charcoal, so that the double-effect slow-release effect of the hydrogel plus the biomass charcoal cannot be formed, and the slow-release effect decreases.

[0047] Figure 2 The SEM images of the biomass charcoal and the biomass charcoal composite hydrogel slow-release fertilizer prepared in the application; wherein a is the SEM image of the biomass charcoal, and b is the SEM image of the biomass charcoal composite hydrogel slow-release fertilizer. Figure 2 It can be seen that: the pores on the surface of the biomass charcoal have all disappeared and are filled with the hydrogel.

[0048] Figure 3 The infrared spectrum of the biomass charcoal and the biomass charcoal composite hydrogel slow-release fertilizer prepared in the application. From Figure 3 And Table 1, it can be seen that the biomass charcoal composite hydrogel slow-release fertilizer is indeed synthesized, which contains element fertilizer, sodium alginate and other components.

[0049] Table 1: Assignment of some absorption peaks in the infrared spectrum

[0050] Fertilizer slow-release effect detection method: After mixing 1.0 g sample with 60 g dry soil, the mixture was added into the experimental device, and distilled water was added to saturate the soil with water. Every time interval, 20 mL distilled water was added into the device, and the drain valve was kept open, and the leachate was collected for nitrogen nutrient content determination.

[0051] The fertilizer slow-release effect of the material prepared in each example and comparative example is shown in Table 2. As shown in Table 2, the biomass carbon composite hydrogel slow-release fertilizer prepared in the examples of the present application achieves slow-release effect for a long time, and the slow-release ratio of the fertilizer is only above 95% at 48 days, and the slow-release ratio of the fertilizer is only above 97% at 60 days. In the comparative examples, such as comparative example 2, the release ratio of 92% is achieved at 13 days, and in comparative examples 4 and 6, the release ratio of 90% is achieved at 7 days. Therefore, the comparative examples do not achieve slow-release effect for a long time, and the technical solution of in-situ formation of hydrogel in pores in the present application can obviously prolong the slow-release effect of the fertilizer.

[0052] Table 2 Release ratio of element fertilizer in slow-release fertilizer at different time (%)

[0053] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A biochar composite hydrogel slow-release fertilizer, characterized in that: The invention comprises biochar, hydrogel fixed in the pores and surface of the biochar, and element fertilizer mixed in the hydrogel, wherein the hydrogel is made of metal cations and alginate.

2. The biochar composite hydrogel slow-release fertilizer according to claim 1, characterized in that: The mass ratio of biochar, elemental fertilizer and hydrogel is 1:0.3-0.45:3.2-3.

65.

3. A method for preparing the biochar composite hydrogel slow-release fertilizer according to claim 1 or 2, characterized in that: The following steps are involved: S1: soaking the biochar in a polyvalent metal cation solution and filtering; S2: adding elemental fertilizer to the alginate solution to form a hydrogel precursor solution, placing the biochar filtered in step S1 therein, allowing it to react and then filtering; S3: soaking the product filtered in step S2 in a polyvalent metal cation solution, allowing it to stand, filtering it, and drying it.

4. The preparation method according to claim 3, characterized in that In step S1, the biochar is obtained by thermochemical depolymerization of biomass; Preferably, the biochar needs to be sieved through 10-30 mesh; Preferably, the thermochemical depolymerization includes pyrolysis and hydrothermal carbonization; Preferably, the temperature of the hydrothermal carbonization is 200-300°C, and the reaction time is 2-6 hours; Preferably, the pyrolysis temperature is 600-800° C., and the pyrolysis time is 5-60 min.

5. The preparation method according to claim 3, characterized in that In step S1 and step S3, the polyvalent metal cations are one or more of calcium, magnesium, barium, strontium, zinc, copper, iron, and aluminum ion solutions; wherein the polyvalent metal cations in step S1 and step S3 may be the same or different.

6. The preparation method according to claim 5, characterized in that In step S1, the concentration of the polyvalent metal cation is 0.01-0.4 mol / L; Preferably, in step S3, the concentration of the polyvalent metal cation is 0.4-1.0 mol / L; The concentration of the polyvalent metal cation solution in step S3 is equal to or higher than that in step S1 , and preferably, the concentration of the polyvalent metal cation solution in step S3 is higher than that in step S1 .

7. The preparation method according to claim 3, characterized in that In step S2, the concentration of alginate in the hydrogel precursor solution is 2-5 wt%; Preferably, the alginate is sodium alginate or potassium alginate.

8. The preparation method according to claim 3, characterized in that In step S2, the elemental fertilizer includes one or more of urea, ammonium nitrate, diammonium phosphate, superphosphate, tripotassium phosphate, potassium nitrate, potassium chloride, ammonium polyphosphate, potassium sulfate, and potassium dihydrogen phosphate; Preferably, in step S2, the concentration of the elemental fertilizer in the hydrogel precursor solution is 0-300 g / L.

9. The preparation method according to claim 3, characterized in that In step S2, the standing time is 20 to 60 minutes; Preferably, in step S3, the standing time is 2 to 15 minutes.

10. Use of the biochar composite hydrogel slow-release fertilizer according to claim 1 or 2 or the biochar composite hydrogel slow-release fertilizer obtained by the preparation method according to any one of claims 3 to 9 in the field of agriculture.

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