CN111423280A

CN111423280A - 3D-structure biochar fertilizer and preparation method and application thereof

Info

Publication number: CN111423280A
Application number: CN201910017118.8A
Authority: CN
Inventors: 周南; 姚登辉; 钟美娥; 周智
Original assignee: Hunan Agricultural University
Current assignee: Hunan Agricultural University
Priority date: 2019-01-08
Filing date: 2019-01-08
Publication date: 2020-07-17

Abstract

The invention belongs to the field of biofertilizer, and particularly relates to a preparation method of a 3D (three-dimensional) structure biochar fertilizer, which comprises the steps of carbonizing a raw material aqueous solution containing biomass powder, hydrophilic colloid and phosphoric acid at 80-270 ℃ in an oxygen-containing atmosphere; adding an ammonium source and a potassium source into a carbonization reaction system; and then separating to obtain the biochar fertilizer. The fertilizer material has wide sources, can be directly produced near farmlands, has low cost, can be reasonably prepared according to soil properties, slowly releases the fertilizer in the farmlands, can reduce the excessive use of the fertilizer, can keep soil moisture and adsorb heavy metals in the soil due to loose and porous structures and functional groups on the surfaces of the loose and porous structures, and is a very safe and healthy fertilizer preparation method.

Description

3D-structure biochar fertilizer and preparation method and application thereof

The technical field is as follows:

the invention belongs to the field of material processing and the field of agricultural technology, and particularly relates to a preparation method and application of a 3D (three-dimensional) biochar fertilizer.

Technical background:

the application amount of the chemical fertilizer in China is close to 1/3 of the total amount of the world, but the cultivated land area is less than 10 percent of the total amount of the world, so that the excessive application of the chemical fertilizer is a very serious problem in China, and the excessive application of the chemical fertilizer can cause the following harm to the soil: firstly, the proportion of soil nutrients can be disordered; secondly, the physiological acid or alkaline fertilizer is applied, so that the acid-base environment of the soil is easily damaged, the soil is usually acidified, the mineral composition of the soil is damaged, and the soil is hardened; then, salt damage or soil salinization can be caused due to overhigh salt ion concentration, and soil nutrient deficiency and fertility imbalance can be caused due to the antagonistic action among fertilizer elements; and finally, excessive fertilizer is applied excessively, and excessive elements inevitably flow to a water body, so that the water body is eutrophicated, and environmental pollution is caused. However, China is also a large population country, and the yield relation of grains is a problem of people, so that the search for a fertilizing mode which has little influence on the environment is not slow.

Crop production produces a large amount of biological waste, such as crop straw. In the prior art, biological straws are carbonized and recycled as fertilizer in crop production. The carbonized product of the crops (namely the biochar) is directly recycled, so that better fertility is difficult to obtain, and in order to solve the problems, various nutrient materials are generally physically doped in the biochar in the prior art. For example, CN108191586A the present invention discloses a fertilizer capable of reducing lead pollution, which is prepared from the following raw materials in parts by weight: 60-80 parts of charcoal, 20-30 parts of livestock and poultry manure, 10-12 parts of compound fertilizer, 10-12 parts of phosphorus pentoxide, 3-5 parts of potassium oxide, 2-4 parts of compound microbial agent, 10-15 parts of potassium fulvate, 3-5 parts of cellulose and 6-10 parts of auxiliary agent.

The invention discloses a fruit tree fertilizer capable of improving yield, which is prepared from the following raw materials in parts by weight: 40-60 parts of charcoal, 30-50 parts of livestock and poultry manure, 15-25 parts of compound fertilizer, 10-20 parts of additive, 1-2 parts of amino acid, 2-4 parts of compound microbial agent, 2-4 parts of cellulose and 1-3 parts of medium trace element.

The invention discloses a crop fertilizer which comprises the following components in parts by weight: 20-40 parts of wormcast; 5-10 parts of calcium superphosphate; 6-9 parts of ammonium nitrate; 3-5 parts of copper sulfate; 2-5 parts of potassium chloride; 15-30 parts of cellulose; 15-25 parts of egg shells; 20-30 parts of bean curd residues; 9-12 parts of biochar; 20-30 parts of sapropel; 6-9 parts of lophatherum gracile; 8-12 parts of rare earth elements; 10-15 parts of chicken droppings.

The existing fertilizer containing biochar is generally obtained by physically mixing the ready-made biochar with fertilizer nutrient elements, the fertilizer efficiency of the fertilizer needs to be improved, and the fertility duration is limited.

Disclosure of Invention

The first purpose of the invention is to provide a preparation method of a biochar fertilizer with a 3D (three-dimensional) structure, and to provide the biochar fertilizer with a slow release function and a certain function of fixing heavy metals.

The second purpose of the invention is to provide the biochar fertilizer prepared by the preparation method.

A preparation method of a biochar fertilizer with a 3D (three-dimensional) structure comprises the steps of carbonizing a raw material aqueous solution containing biomass powder, hydrophilic colloid and phosphoric acid at 80-270 ℃ in an oxygen-containing atmosphere;

adding an ammonium source and a potassium source into a carbonization reaction system; and then separating to obtain the biochar fertilizer.

By the method, raw material aqueous solution containing biomass powder, hydrophilic colloid and phosphoric acid is carbonized in advance under oxygen-containing atmosphere (hydrothermal carbonization under non-closed and oxygen-free conditions), so that biochar with a three-dimensional structure, larger granularity and good blocky appearance can be prepared, and the surface of the biochar is modified with rich active groups; further contacting with ammonia source and potassium source, and converting active group into form (ammonium/potassium salt form) favorable for heavy metal adsorption by ion exchange reaction to obtain fertilizer NH₄ ⁺/K⁺And the effective nutrient elements are bonded to the surface of the biochar in situ, so that the purposes of slow release and heavy metal fixation are realized.

The biochar with the 3D structure prepared by the invention not only has nutrient elements required by plants, but also can enhance the water-retaining capacity of soil due to the good pore structure, so that the soil can be kept loose, the growth of the root systems of the plants is facilitated, the application speed of fertilizer nutrients can be slowed down, the utilization rate of the fertilizer is improved, the application of the fertilizer is reduced, and good ecological environmental benefits are brought.

The main innovation points of the technical scheme of the invention are as follows: hydrophilic colloid is newly added in raw material aqueous solution and then is cooperated with carbonization under oxygen-containing atmosphere and the temperature condition, so that a carbonization product with a good three-dimensional structure and surface active functional groups is formed, and is further innovatively cooperated with an ammonium source and a potassium source for conversion, so that active group ions of the carbonization product are converted, and the double effects of in-situ bonding of nutrient elements and heavy metal adsorption are realized.

Preferably, the hydrophilic colloid is at least one of HPMC, xanthan gum and guar gum.

It has been found that the use of preferred hydrocolloids helps to improve the performance of the biochar fertilizer produced.

Still more preferably, the hydrocolloid is HPMC. The research of the inventor finds that the biochar waste prepared by HPMC has better performance in aspects of appearance, fertility retention and heavy metal adsorption compared with other hydrophilic colloids.

Preferably, the mass ratio of the biomass powder to the hydrophilic colloid is 1: 0.001 to 0.2.

Further preferably, the mass ratio of the biomass powder to the hydrophilic colloid is 1: 0.01 to 0.07. The structure form of the prepared biochar fertilizer is better and the 3D structure is not easy to break by controlling the optimal range; moreover, the adsorption of heavy metals is better, and ammonium and potassium in the heavy metals are further released through the adsorption of the heavy metals, so that the slow release effect is further achieved. The research shows that the prepared biochar fertilizer has unexpected effects in the aspects of water retention rate, crop yield increase rate, heavy metal adsorption, biochar fertilizer recovery rate and the like by controlling the content in the preferable range.

Preferably, the biomass powder is powder of lignocellulose biomass; such as various plant stalks (e.g., fruit peels and agricultural waste).

Preferably, the biomass powder is at least one of durian shell powder, tobacco stems, grape vines, sawdust and peanut shells.

The biomass powder can be obtained by drying, crushing and sieving a biomass raw material.

Preferably, the granularity of the biomass powder is not more than 60 meshes; preferably 60-100 mesh. Under the preferable particle size range, the biochar with a three-dimensional structure can be prepared more favorably by matching with the additive components and the control of carbonization conditions.

According to the research of the invention, under the innovative raw material aqueous solution system, the content of acid is further controlled, the three-dimensional structure and surface active groups of the biochar can be regulated and controlled, and the slow release effect and the heavy metal fixing performance of the prepared biochar are improved.

Preferably, the concentration of phosphoric acid in the raw material aqueous solution is 40 to 85 wt%.

More preferably, the concentration of phosphoric acid in the raw material aqueous solution is 50 to 70 wt%. Researches show that the carbonization degree can be further improved and the performance of the prepared biochar fertilizer can be improved by controlling the range and the synergism of the HPMC and the open carbonization condition.

In the invention, the biomass powder and the hydrophilic colloid are dispersed in phosphoric acid solution with the concentration of 40-85 wt% (preferably 50-70 wt%), and are stirred and then kept stand for 0.5-2 h for structural infiltration to obtain the water solution of the raw materials. And standing after stirring for structure infiltration, which is favorable for further improving the slow release effect of the subsequently prepared biochar and the fixing performance of heavy metal. The research of the invention finds that the water retention rate, the crop yield increasing rate, the slow release performance and the recovery rate of the obtained biochar fertilizer can be unexpectedly improved by carrying out the structural infiltration.

Further preferably, the solid-to-liquid ratio of the solid weight of the biomass powder and the hydrophilic colloid to the phosphoric acid solution is 1 g: 2-20 ml.

In the invention, the raw material aqueous solution system is innovatively carbonized in an oxygen-containing atmosphere at the temperature, so that the biochar which is three-dimensional, large in particle size, rich in active groups, better in slow release performance and better in heavy metal adsorption can be obtained.

The oxygen-containing atmosphere may be an atmosphere containing oxygen, such as oxygen; a mixed atmosphere of oxygen and a protective atmosphere. The protective atmosphere is, for example, nitrogen or an inert gas.

Preferably, the oxygen-containing atmosphere is air.

Preferably, the aqueous feedstock solution is placed in an open vessel and carbonized at the temperature.

In the invention, the carbonization is performed in an oxygen-containing atmosphere and at the temperature innovatively under the raw material aqueous solution system, and the active group, the structure and the carrying effect of valuable elements of the prepared biochar can be regulated, so that the biochar which is three-dimensional, large in particle size, rich in active groups and more beneficial to slow release and heavy metal adsorption can be obtained.

Preferably, the carbonization temperature is 150 to 220 ℃. Researches show that under the carbonization system, the control of the preferable temperature is helpful for further improving the structural stability of the prepared biochar and improving the slow release effect of the biochar, and in addition, the conversion of phosphoric acid into pyrophosphate and metaphosphate can be reduced, so that the biochar is beneficial to absorption and utilization of plants.

Further preferably, the carbonization temperature is 160-210 ℃.

Preferably, the carbonization time is 2 to 24 hours.

In the invention, an ammonium source and a potassium source are added into a carbonization reaction system; and then removing part of the solvent to obtain the biochar fertilizer.

In the invention, an ammonium source and a potassium source are added into a carbonization reaction system, N/K is bonded into the biochar by an ion exchange method, and the exchanged biochar is also beneficial to exchange with heavy metal, so that the heavy metal is fixed, and nutrient elements such as N/K are slowly released.

Preferably, the ammonium source is capable of ionizing NH₄ ⁺Preferably ionizable to form NH₄ ⁺The alkali (b) is more preferably at least one of ammonia water, ammonium carbonate, ammonium bicarbonate, ammonium sulfate and ammonium nitrate.

Preferably, the potassium source is K⁺The compound (2) is preferably potassium hydroxide or carbonic acidAt least one of potassium, potassium bicarbonate, potassium nitrate and potassium sulfate.

Further preferably, at least one of the ammonium source and the potassium source has basicity. By means of this preferred material, the reactive groups in the carbonized product obtained by carbonization can be converted (ammonified and potassified); the converted biochar has stronger heavy metal complexing adsorption performance; in the process of adsorbing heavy metals, ammonium and potassium are released; thereby achieving the slow release of the nutrient elements while adsorbing heavy metals.

The mol ratio of the ammonium source to the potassium source is 1: 3-3: 1.

preferably, an ammonium source and a potassium source are added into the carbonization reaction system, the pH value of the solution system is regulated to be neutral, and then part of solvent is evaporated to obtain the biochar fertilizer with the 3D spatial structure.

Preferably, the amount of solvent evaporated is 40 to 60 wt% of the amount of solution before evaporation.

The invention relates to a preparation method of a more preferable biochar fertilizer with a 3D structure, which comprises the following steps:

(1) drying biomass powder raw materials (such as agricultural and forestry waste) in the sun or in an oven;

(2) sieving powder with a certain mesh number after being crushed by a crusher to obtain biomass powder;

(3) mixing the biomass powder and the HPMC to obtain a mixed raw material;

(4) weighing mixed raw material powder in an open container, adding a phosphoric acid solution in a certain proportion, uniformly stirring, and standing for a period of time;

(5) putting the containers into a heating device together, and reacting at the temperature of 150 ℃ and 220 ℃ for 2-24h to obtain a precursor carbon material;

(6) after cooling, directly adding a certain proportion of mixed solution of potassium carbonate and ammonia water into a container until the mixed solution is neutral.

(7) And (5) drying the mixture and the container to be semi-dry, and taking out the mixture to obtain the biochar fertilizer with the 3D spatial structure.

In the step (1), the agricultural and forestry waste is naturally dried in the sun and air, the drying temperature of an instrument is 60-110 ℃, and the drying time is 6-20 h.

And (3) sieving the crushed powder in the step (2) by using a sieve, wherein the granularity is 60-100 meshes.

The HPMC provides a carbon source on one hand, and is assisted in carbonization under the oxygen-containing condition and at the temperature by virtue of abundant functional groups and structural characteristics of the HPMC on the other hand, so that the HPMC is beneficial to preparing the biochar which has abundant active groups formed on the surface and has a good three-dimensional structure, and further is beneficial to improving the slow-release effect and the heavy metal fixing effect of the prepared biochar.

Preferably, the HPMC is added in the step (3) to be 0.1-20% of the mass of the biomass powder.

And (4) weighing the powder to be used in a reaction vessel, adding 40-85% phosphoric acid solution into the reaction vessel, wherein the weight-volume ratio of the powder to the phosphoric acid solution is 1 kg: 2-20L, uniformly stirring, and standing for 30min-2h for structure infiltration.

The molar ratio of the ammonia water to the potassium carbonate in the step (6) is 1: 3-3: 1.

phosphoric acid is used for corroding and catalyzing and carbonizing raw materials to manufacture a pore structure; in addition, a source of phosphorus in the fertilizer is provided, and the phosphorus reacts with potassium carbonate and ammonia water in the step (5) to produce a fertilizer source such as potassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, ammonium phosphate and the like. And finally adjusting the proportion and the amount of ammonia water and potassium carbonate according to the fertility and the pH value of the soil to obtain the corresponding fertilizer.

The drying temperature of the step (7) is 60-110 ℃, the drying time is 6-20h, and the semi-wet state is kept when the material is taken out.

The invention also provides the 3D three-dimensional structure biochar fertilizer prepared by the preparation method.

Advantageous effects

The fertilizer applied in the invention not only contains rich elements such as nitrogen, phosphorus, potassium and the like, but also effectively ensures nutrients required in the growth process of crops; moreover, the biochar with the 3D stereo structure can enhance the water-retaining capacity of the soil, enables the soil to keep loose, is beneficial to the root growth of plants, can slow down the application speed of fertilizer nutrients, improves the utilization rate of the fertilizer, and reduces the application of the fertilizer, thereby bringing good ecological environmental benefits.

Drawings

FIG. 1 is an SEM image of the biochar fertilizer prepared in example 1;

FIG. 2 is an SEM image of the biochar fertilizer prepared in example 2;

fig. 3 is an SEM image of the biochar fertilizer prepared in example 3.

Detailed Description

The present invention is described in further detail below with reference to specific embodiments.

The following examples and comparative examples, HPMC were used and purchased from chemical industries, Inc. in Shijia.

Example 1:

drying grape vines at 80 ℃, crushing the grape vines into powder, screening out powder with a particle size smaller than 80 meshes, mixing the powder with 5% of HPMC (based on the weight of the grape vine powder) to obtain mixed raw materials, adding 5kg of the mixed raw materials and 10L 50% of phosphoric acid solution into an open container according to the solid-liquid ratio of 1kg to 2L, uniformly stirring, standing for 45min for structural infiltration, putting the container into an oven, burning for 10h at 160 ℃ to obtain a precursor, cooling, adding a mixed solution of potassium carbonate and ammonia water with the molar mass ratio of 3: 2.5, adjusting to be neutral, drying to be semi-dry at 60 ℃ in the oven, and taking out to obtain the finished product of the biochar fertilizer.

Example 2:

drying corn straws at 60 ℃, crushing the corn straws into powder, screening out powder with a particle size of less than 80 meshes, mixing the powder with 1% of HPMC (based on the weight of the corn straw powder) to obtain mixed raw materials, adding 5kg of the mixed raw materials and 8L 65% of phosphoric acid solution into an open container according to the solid-liquid ratio of 1kg to 1.6L, uniformly stirring, standing for 1h for structural infiltration, putting the container into an oven, heating for 6h at 220 ℃ to obtain a precursor, cooling, adding a mixed solution of potassium carbonate and ammonia water with the molar mass ratio of 2: 1.5, adjusting to be neutral, drying to be semi-dry at 60 ℃ in the oven, and taking out to obtain the finished product of the biochar fertilizer.

Example 3:

drying soybean straws at 75 ℃, crushing the soybean straws into powder, screening out powder with a particle size of less than 80 meshes, mixing with 7% HPMC (based on the weight of the soybean straw powder) to obtain a mixed raw material, adding 5kg of the mixed raw material and 6L 70% phosphoric acid solution into an open container according to the solid-to-liquid ratio of 1kg to 1.2L, uniformly stirring, standing for 45min for structural infiltration, putting the container into an oven, baking for 8h at 170 ℃ to obtain a precursor, cooling, adding a mixed solution of potassium carbonate and ammonia water with the molar mass ratio of 1: 2, adjusting to be neutral, baking to be semi-dry at 60 ℃ in the oven, and taking out to obtain the finished product of the biochar fertilizer.

Example 4:

the main difference compared to example 1 is that it is carried out at a higher carbonization temperature, as follows:

drying grape vines at 80 ℃, crushing the grape vines into powder, screening out powder with a particle size smaller than 80 meshes, mixing the powder with 5% of HPMC (based on the weight of the grape vine powder) to obtain mixed raw materials, adding 5kg of the mixed raw materials and 10L 50% of phosphoric acid solution into an open container according to the solid-to-liquid ratio of 1 kg: 2L, uniformly stirring, standing for 45min for structural infiltration, putting the container into an oven, burning for 10h at 270 ℃ to obtain a precursor, cooling, adding a mixed solution of potassium carbonate and ammonia water with the molar mass ratio of 3: 2.5, adjusting to be neutral, drying to be semi-dry at 60 ℃ by using the oven, and taking out to obtain the finished product of the biochar fertilizer

Example 5:

the main difference compared to example 1 is that it is carried out at a lower carbonization temperature, as follows:

drying grape vines at 80 ℃, crushing the grape vines into powder, screening out powder with a particle size smaller than 80 meshes, mixing the powder with 5% of HPMC (based on the weight of the grape vine powder) to obtain mixed raw materials, adding 5kg of the mixed raw materials and 10L 50% of phosphoric acid solution into an open container according to the solid-liquid ratio of 1kg to 2L, uniformly stirring, standing for 45min for structural infiltration, putting the container into an oven, baking for 10h at 80 ℃ to obtain a precursor, cooling, adding a mixed solution of potassium carbonate and ammonia water with the molar mass ratio of 3: 2.5, adjusting to be neutral, baking to be semi-dry at 60 ℃ in the oven, and taking out to obtain the finished product of the biochar fertilizer.

Example 6:

compared with example 1, the main difference is that a lower HPMC addition amount is adopted, specifically as follows:

drying grape vines at 80 ℃, crushing the grape vines into powder, screening out powder with a particle size smaller than 80 meshes, mixing the powder with 0.1% of HPMC (based on the weight of the grape vine powder) to obtain mixed raw materials, adding 5kg of the mixed raw materials and 10L 50% of phosphoric acid solution into an open container according to the solid-to-liquid ratio of 1kg to 2L, uniformly stirring, standing for 45min for structural infiltration, putting the container into an oven, heating for 10h at 160 ℃ to obtain a precursor, cooling, adding a mixed solution of potassium carbonate and ammonia water with the molar mass ratio of 3: 2.5, adjusting to be neutral, drying to be semi-dry at 60 ℃ in the oven, and taking out to obtain the finished product of the biochar fertilizer.

Example 7:

compared with the example 1, the main difference is that a higher HPMC adding amount is adopted, and the specific steps are as follows:

drying grape vines at 80 ℃, crushing the grape vines into powder, screening out powder with a particle size smaller than 80 meshes, mixing the powder with 20% of HPMC (based on the weight of the grape vine powder) to obtain mixed raw materials, adding 5kg of the mixed raw materials and 10L 50% of phosphoric acid solution into an open container according to the solid-liquid ratio of 1kg to 2L, uniformly stirring, standing for 45min for structural infiltration, putting the container into an oven, burning for 10h at 160 ℃ to obtain a precursor, cooling, adding a mixed solution of potassium carbonate and ammonia water with the molar mass ratio of 3: 2.5, adjusting to be neutral, drying to be semi-dry at 60 ℃ in the oven, and taking out to obtain the finished product of the biochar fertilizer.

Example 8:

compared with example 1, the main difference is that the grapevine powder is not subjected to structural infiltration with phosphoric acid, as follows:

drying grape vines at 80 ℃, crushing the grape vines into powder, screening out powder with a particle size smaller than 80 meshes, mixing the powder with 5% of HPMC (based on the weight of the grape vine powder) to obtain mixed raw materials, adding 5kg of the mixed raw materials and 10L 50% of phosphoric acid solution into an open container according to the solid-liquid ratio of 1kg to 2L, uniformly stirring, putting the container into an oven, baking for 10 hours at 160 ℃ to obtain a precursor, cooling, adding a mixed solution of potassium carbonate and ammonia water with the molar mass ratio of 3: 2.5, adjusting to be neutral, baking to be semi-dry at 60 ℃ in the oven, and taking out to obtain the finished product of the biochar fertilizer.

Comparative example 1:

the difference compared to example 1 is that no HPMC was added. The water holding rate and crop yield of the prepared biochar fertilizer are further lower than those of example 6.

Comparative example 2:

the difference from example 1 is that carbonization was performed under a closed condition. The study found that the biochar fertilizer with the three-dimensional structure as described in the example could not be obtained.

Comparative example 3

The difference compared to example 1 is that no treatment with ammonia and potassium carbonate was carried out. The obtained biochar can not enable crops to grow.

The biochar fertilizer prepared in each case was tested as follows:

1. determination of the Effect of sustained Release

Burying the fertilizer in soil with a depth of 20cm, collecting a batch of samples at 5, 15 and 30 days without planting any crop, and timely determining the content of residual nitrogen, phosphorus and potassium nutrients. The content detection method is carried out according to the detection standard of the compound fertilizer.

2. Water content of soil

And (5) and (20) respectively taking soil samples at positions 5 and 20cm away from the plant at the 30 th day after watering, wherein the positions are 10 and 40cm deep and 4. The water content is measured by a drying and weighing method, the drying temperature is 105, the drying time is 12h, and the soil weight before and after drying is weighed by a high-precision electronic balance.

3. Fruit and food yield

And weighing each treated dried fruit respectively, and calculating the yield.

Yield enhancement and water retention data are shown in table 1:

TABLE 1

As can be seen from Table 1, the yield and water retention are improved under the preferable conditions of examples 1 to 3 (carbonization temperature is 160 to 220 ℃; HMPC content is 1 to 7 wt%); with higher carbonization temperatures (example 4) and lower carbonization temperatures (example 5), higher HPMC loading (example 7), lower HPMC loading (example 6) and no infiltration of biomass feedstock with phosphoric acid (example 8), the performance of the biochar fertilizer was somewhat reduced.

The sustained release data for each example is shown in table 2:

TABLE 2

As shown in Table 2, the release rate is low and the slow release effect of the biochar fertilizer prepared on the surface is better under the preferable conditions of the examples 1 to 3 (the carbonization temperature is 160 to 220 ℃, the HMPC content is 1 to 7 wt%). The slow release performance of the biochar fertilizer was somewhat reduced with higher carbonation temperature (example 4) and lower carbonation temperature (example 5), higher HPMC loading (example 7), lower HPMC loading (example 6) and no infiltration of biomass feedstock with phosphoric acid (example 8).

1. Determination of lead and cadmium content in peanut

Accurately weighing 1.0000g of peanut, adding into a polytetrafluoroethylene digestion tank, adding 10m L HNO₃Cold digesting for 2H, and adding 4m L H₂O₂Soaking for 30min, digesting in a pressure self-control closed microwave digestion instrument, finally heating in an electric furnace to drive off residual acid, and fixing the volume to 25m L by using distilled water.

The obtained solution is tested by using a graphite furnace atomic absorption spectrometer, and a result is calculated by using a standard curve.

2. Carbon material recovery calculation

And one part of the biochar fertilizer is crushed, put into deionized water for suction filtration, washed and dried, and weighed to obtain the dry weight of the biochar fertilizer. And taking back one part of the collected and cultivated biochar fertilizer, putting the biochar fertilizer into ionized water, performing suction filtration, washing, drying, and weighing to obtain the dry weight of the recovered biochar fertilizer.

The lead and cadmium contents of the peanuts, and the recovery data for the carbon material are shown in table 3:

TABLE 3

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A preparation method of a biochar fertilizer with a 3D (three-dimensional) structure is characterized in that a raw material aqueous solution containing biomass powder, hydrophilic colloid and phosphoric acid is carbonized at 80-270 ℃ in an oxygen-containing atmosphere;

2. The method of claim 1, wherein the hydrocolloid is at least one of HPMC, xanthan gum, guar gum.

3. The preparation method according to claim 2, wherein the mass ratio of the biomass powder to the hydrophilic colloid is 1: 0.001 to 0.2; preferably 1: 0.01 to 0.07.

4. The method according to claim 1, wherein the concentration of phosphoric acid in the aqueous solution of the raw material is 40 to 85 wt%.

5. The method according to claim 1, wherein the biomass powder is a powder of lignocellulosic biomass, preferably having a particle size of not more than 60 mesh; preferably 60-100 mesh.

6. The preparation method of the three-dimensional biochar as claimed in claim 1, wherein the biomass powder and the hydrophilic colloid are dispersed in a phosphoric acid solution with the concentration of 40-85 wt%, and are stirred and then kept stand for 0.5-2 hours for structure infiltration to obtain the water solution of the raw materials;

preferably, the solid-to-liquid ratio of the solid weight of the biomass powder and the hydrophilic colloid to the phosphoric acid solution is 1 g: 2-20 ml.

7. The method according to any one of claims 1 to 6, wherein the aqueous raw material solution is placed in an open container and carbonized at the temperature;

the carbonization temperature is preferably 150-220 ℃;

the carbonization time is preferably 2-24 h.

8. The method of claim 1, wherein the source of ammonium is one that ionizes to form NH₄ ⁺Preferably at least one of ammonia water, ammonium carbonate, ammonium bicarbonate, ammonium sulfate and ammonium nitrate;

the potassium source is K⁺The compound of (4), preferably at least one of potassium hydroxide, potassium carbonate, potassium bicarbonate, potassium nitrate and potassium sulfate;

further preferably, at least one of the ammonium source and the potassium source has basicity;

the mol ratio of the ammonium source to the potassium source is 1: 3-3: 1.

9. the preparation method according to claim 1, wherein a solution containing an ammonium source and a potassium source is added into the carbonization reaction system, the pH of the solution system is regulated to be neutral, and then part of the solvent is evaporated to obtain the 3D spatial structure biochar fertilizer;

10. A3D-structure biochar fertilizer prepared by the preparation method of any one of claims 1 to 9.