NL2034400B1

NL2034400B1 - Biochar—based compound fertilizer

Info

Publication number: NL2034400B1
Application number: NL2034400A
Authority: NL
Inventors: Liu Buyou
Original assignee: Qingdao Yingkunyuan Mineral Tech Co Ltd
Priority date: 2022-04-02
Filing date: 2023-03-22
Publication date: 2024-01-19
Also published as: CN114538991A; NL2034400A; CN114538991B

Abstract

The present application relates to the ﬁeld of comprehensive utilization of solid wastes, and speciﬁcally discloses a biochar-based compound fertilizer, including a biochar 5 composition. A method for preparing the biochar composition includes the following steps: drying biomass, pulverizing and granulating it to prepare biomass particles for later use, drying red mud for later use, mixing the red mud and additives, adding them from the kiln tail of a rotary kiln, blowing the biomass particles from the kiln head, heating up, and performing pyrolysis treatment to prepare calcined material, cooling 10 the calcined material, finely grinding, and performing magnetic separation to obtain non-magnetic slags, and finely grinding and winnowing the non-magnetic slags to obtain the biochar composition. An amount of biomass particles is 20 to 25% of that of the red mud, and an amount of the additives is 4 to 8% of that of the red mud.

Description

BIOCHAR-BASED COMPOUND FERTILIZER

TECHNICAL FIELD

[01] The present application relates to the field of solid waste comprehensive utilization, and more particularly to a biochar-based compound fertilizer.

BACKGROUND ART

[02] Biochar is a solid material produced by pyrolysis of biomass at high temperatures under hypoxia or anoxic conditions. It has the characteristics of rich carbon, large specific surface area, high porosity, and alkalinity. As an environment-friendly improver and passivator, biochar has a wide application prospect in improving soil fertility, stimulating crop growth, and stabilizing heavy metals in soil.

However, the contents of potassium, nitrogen and other nutrients in ordinary biochar are very low, which cannot reach the fertility of chemical fertilizer in the traditional sense.

[03] Red mud is a by-product of alumina production in alumina factories. Generally, for every ton of alumina produced, about 1 to 1.5 tons of red mud is a by-product. The red mud has the characteristics of strong alkalinity, compound components, large utilization limitation, a comprehensive utilization rate of only 4.5%, mainly stockpiling, and serious environmental pollution.

[04] In view of the above-mentioned related art, the inventors believe that the red mud and biomass have not been combined to prepare biochar compositions, which are used in the research of compound fertilizers.

SUMMARY

[05] In order to improve the comprehensive utilization of waste agricultural and forestry substances, such as large solid wastes such as wheat straw, waste sawdust, etc., and also to solve the problem of environmental damage caused by red mud, iron is extracted from the red mud by pyrolysis and gasification of biomass particles formed by the solid wastes such as wheat straw and waste sawdust, and a biochar-based compound fertilizer is generated by the comprehensive utilization of the red mud. The present application provides a biochar-based compound fertilizer.

[06] In a first aspect, the present application provides a method for preparing a biochar-based compound fertilizer, adopting the following technical solution.

A method for preparing a biochar-based compound fertilizer includes a biochar composition, and the following steps: drying biomass, pulverizing and granulating it to prepare biomass particles for later use; drying red mud for later use; mixing the red mud and additives, adding them from the kiln tail of a rotary kiln, blowing the biomass particles from the kiln head, heating up, and performing pyrolysis treatment to prepare calcined material; quenching the calcined material with water, finely grinding, and performing magnetic separation to obtain non-magnetic slags; and finely grinding and winnowing the non-magnetic slags to obtain the biochar composition; where an amount of biomass particles is 20 to 25% of that of the red mud, and an amount of the additives is 4 to 8% of that of red mud.

[07] By adopting the above-mentioned technical solution, the biomass is mainly composed of cellulose, hemicellulose, and lignin, etc. which can produce volatile substances such as carbon monoxide, hydrogen, methane gas and tar after pyrolysis and gasification, as well as biochar composition and ash such as silicon, potassium, calcium and iron, and these volatile substances and carbon in biomass can completely provide heat and reducing agents for the red mud reduction and calcination; After reduction and calcination, biomass generates a porous structure with well-developed pores, and the metal oxides produced after the pyrolysis of red mud are loaded on the pores and surfaces of the porous structure, which can enrich the element types of the biochar composition, increase the content of each element in the biochar composition, improve the fertility of the biochar composition and enhance the soil improvement effect when it is used in compound fertilizer; in addition, the iron oxide loaded on the porous structure of the biochar composition can reduce the loss of carbon, and enhance the improvement effect of the biochar composition in improving soil, promoting the absorption and growth of crop nutrients and passivating heavy metals in soil, not only reduce the red mud using biomass to extract iron by calcination, but also produce the biochar composition, which not only fertilizes the soil, but also has carbon negativity, and carbon fixation and emission reduction.

[08] Preferably, a temperature of the pyrolysis treatment is 850 to 950°C for 80 to 100 minutes.

[09] By adopting the above-mentioned technical solution, low pyrolysis temperature or short pyrolysis time leads to a low degree of biomass pyrolysis, so that it is difficult for the biochar composition to obtain a rich porous structure, and the effect on improving the soil permeability is reduced; excessive pyrolysis temperature or long pyrolysis time causes excessive pyrolysis of biochar composition and collapse of the porous structure.

[10] Preferably, a temperature of the pyrolysis treatment is 900°C for 90 minutes.

[11] By adopting the above-mentioned technical solution, when the pyrolysis temperature of the biochar composition and the red mud is controlled at 900°C for 90 minutes, a stable biochar composition with a porous structure can be formed, and the red mud is fully reduced.

Preferably, the biomass is selected from one or more of waste wood, straw, and fast-growing plants.

[12] By adopting the above-mentioned technical solution, the waste wood, straw and fast-growing plants are all renewable clean energy sources, which can replace coal and become excellent heat sources and reducing agents for the red mud. The straw is rich in proteins, vitamins, nitrogen, phosphorus, potassium, trace elements, etc. After pyrolysis treatment, the straw forms a pore structure.

[13] Preferably, the straw is selected from one or more of corn straw, rice straw, wheat straw, sesame straw, and cotton straw.

[14] By adopting the above-mentioned technical solution, the straw has a low water content, very little corrosive gases such as sulfur dioxide after burning, and the resulting biochar composition is rich in potassium and silicon, which can enhance the disease resistance of plants, so the straw can be used as a potassium fertilizer for organic agriculture and as an acidic soil improvement material.

[15] Preferably, the biomass includes waste wood and straw with a mass ratio of 0.1 to 0.3: 1, the straw includes corn straw, rice straw, and wheat straw with a mass ratio of 1: 0.1t0 0.3: 0.3 to 0.5, and the waste wood is sawdust.

[16] By adopting the above-mentioned technical solution, a mixture of the straw and the waste wood is used as biomass to generate reducing gas after combustion, and three substances, corn straw, rice straw and wheat straw are adopted because the reducing gas content is high after pyrolysis.

[17] Preferably, the additive includes calcium oxide.

[18] By adopting the above-mentioned technical solution, the addition of calcium oxide can promote the decomposition of complex oxides, enhance the activity of main metal oxides and reduce the starting temperature of their reduction decomposition.

[19] Preferably, the additive further includes fluorite and a mass ratio of calcium oxide to fluorite is 1: 0.3 to 0.5.

[20] By adopting the above-mentioned technical solution, low-grade fluorite can be used because the low-grade fluorite belongs to industrial solid wastes, which cannot be effectively utilized, and produces waste of resources and environmental pollution. The use of fluorite, as an additive, can reduce the melting point of refractory substances in red mud, promote the flow of slags, and enable the good separation of the slags and metal, so that the yield of the biochar composition can be increased.

[21] Preferably, a drying temperature of the biomass is < 80°C with a pulverized particle size of 5 to 10 mm.

[22] By adopting the above-mentioned technical solution, the temperature of the biomass is controlled at lower than 80°C, which can prevent the biomass from being decomposed, deteriorated and burned, and the biomass is pulverized, which can make the biomass burn more fully and a higher utilization rate.

[23] Preferably, the red mud is dried by rotary flash drying at an inlet temperature of 230 to 250°C and an outlet temperature of 70 to 85°C for 2 to 3 hours.

[24] By adopting the above-mentioned technical solution, the red mud particles 5 have characteristics: fine, large specific surface area, well-developed network structure, high viscosity, high adherence to water, extremely difficult removal of capillary water, and the red mud has a plastic state stage in the dehydration process, and the red mud is dispersed into irregular particles in the drying chamber by adopting rotary flash drying, so that the red mud is not easy to reunite with fast drying speed and thorough drying.

[25] Preferably, the biochar composition accounts for 15 to 25% of a total amount of the biochar-based composite, and an application amount of the biochar-based composite is 300 to 600 kg/hm?.

[26] By adopting the above-mentioned technical solution, the addition of biochar composition to compound fertilizer with an application amount of 750 to 1125 kg/hm? can effectively increase the content of soil nutrients, enhance the permeability of the soil and enhance the absorption capacity of crops for nutrients.

[27] In summary, the present application has the following beneficial effects. 1. As the metallurgical solid waste red mud and recyclable resource biomass in the present application are used as raw materials with wide sources and low costs, a large amount of residual iron in the red mud can be recovered, and at the same time, the secondary slag can be used to prepare the biochar composition, which turns wastes into treasures and has extremely high economic value and environmental protection value, that is, the recovery of iron resources from red mud is realized, the problem of red mud stockpiling is solved, the types of metal oxides in the biochar composition are enriched, the fertility effect of the biochar composition on soil is enhanced, the preparation process is short, the operation is simple, and large-scale production is facilitated.

[28] 2. In the present application, pyrolysis treatment at 850 to 950°C is preferred, which can make the biochar composition form a stable pore structure with large pore volume and increase the carbon content of the biochar composition; during pyrolysis,

metal oxides are loaded on the surface or pores of the biochar composition, which reduces the loss of carbon and achieves the effect of carbon locking and emission reduction.

[29] 3. In the present application, corn straw, rice straw, wheat straw, and sawdust are preferably used as biomass, which has wide sources, large output and low price, reduces the utilization of non-renewable resources such as coal and tar, and adjusts the content of reducing gas generated by the biochar composition to fully reduce iron in the red mud; in addition, it can increase the carbon content in the biochar composition and improve the fertility of the biochar composition.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[30] The chemical analysis results of red mud by Bayer process in Example 1 are shown in Table 1.

[31] Table 1 Chemical composition of red mud by Bayer process

Ingredient | S102 | CaO | AbOs | Fe:05; | MgO | Na:0 | K:O | TiO; | Loss on ignition

Example 1: a biochar-based compound fertilizer included a biochar composition accounting for 25% of the total amount of the biochar-based composite fertilizer, 5% of bentonite, and 70% of an NPK fertilizer, the NPK fertilizer being composed of nitrogen, phosphorus, and potassium with a mass ratio of 1.5: 1: 0.7. A method for preparing the biochar composition included the following steps.

At Sl, biomass was dried, pulverized, and sprayed with a polyvinyl alcohol solution with an amount of 15% of that of the biomass, then granulated to prepare biomass particles for later use. The biomass was prepared by mixing waste wood and straw with a mass ratio of 0.3: 1, the straw included corn straw, rice straw, and wheat straw with a mass ratio of 1: 0.3: 0.5, and the waste wood was sawdust.

The red mud by Bayer process was taken, dried, and crushed until an average particle size was < 0.074 mm for later use. The chemical analysis results of the red mud by

Bayer process were shown in Table 1.

At S2, 100 kg of the red mud and additives were mixed, and added from the kiln tail of a rotary kiln, then the biomass particles were blown from the kiln head and heated up to 900°C for pyrolysis treatment for 90 minutes to prepare a calcined material. An amount of biomass particles was 25% of that of the red mud, an amount of the additives was 8% of that of the red mud, and the additives were calcium oxide and fluorite with a mass ratio of 1: 0.5.

At S3, the calcined material was cooled by water quenching, and finely ground for 30 minutes until the content of particles with a particle size of < 0.03 mm reached 96%, and magnetic separation was performed with an excitation current of 2A (1940 Oe) to obtain non-magnetic slags.

At S4, the non-magnetic slags were finely ground for 10 minutes and winnowed to obtain the biochar composition.

[32] Example 2: a biochar-based compound fertilizer differed from Example 1 in that the additive in step S2 was calcium oxide.

[33] Example 3: a biochar-based compound fertilizer differed from Example 2 in that the biomass was straw including rice straw and sesame straw with a mass ratio of 1. 0.5.

[34] Example 4: a bio-based compound fertilizer differed from Example 2 in that the pyrolysis temperature was 950°C for 80 minutes.

[35] Example 5: a bio-based compound fertilizer differed from Example 2 in that the pyrolysis temperature was 850°C for 100 minutes.

[36] Example 6: a biochar-based composite differed from Example 2 in that the pyrolysis treatment temperature was 700°C.

[37] Example 7: a biochar-based compound fertilizer differed from Example 2 in that the pyrolysis treatment temperature was 1050°C.

[38] Example 8: a biochar-based composite differed from Example 2 in that the pyrolysis treatment time was 150 minutes.

[39] Example 9: a biochar compound fertilizer differed from Example 1 in that it included the biochar composition accounting for 15% of the total amount of the biochar-based composite fertilizer, 10% of bentonite, and 75% of an NPK fertilizer.

[40] Example 10: a biochar compound fertilizer differed from Example 1 in that it included the biochar composition accounting for 35% of the total amount of the biochar-based composite fertilizer, 5% of bentonite, and 60% of an NPK fertilizer.

[41] Example 11: a biochar compound fertilizer differed from Example 1 in that it included the biochar composition accounting for 5% of the total amount of the biochar-based composite fertilizer, 15% of bentonite, and 80% of an NPK fertilizer.

[42] Comparative Example 1: a biochar-based compound fertilizer differed from

Example 2 in that the amount of biomass in step S2 was 35% of that of the red mud.

[43] Comparative Example 2: a biochar-based compound fertilizer differed from

Example 2 in that the amount of the additives in step S2 was 10% of that of red mud.

[44] Comparative Example 3: a biochar-based compound fertilizer differed from

Example 2 in that the calcined material was cooled at normal temperature in step S3.

[45] Comparative Example 4: 1000 g of a biochar-based compound fertilizer included 100 g of biochar and 900 g of chemical fertilizer. The biochar was a pyrolysis product of rice straw, and the chemical fertilizer was urea, ammonium hydrogen phosphate, ammonium nitrate, potassium chloride and potassium hydrogen phosphate as equivalent amounts of the compound fertilizer.

[46] The method for preparing the biochar-based compound fertilizer included the steps: (1) preparation of biochar: taking fresh rice straw, drying and fully pulverizing by a pulverizer to a maximum particle size of 10-mesh sieve; placing the pulverized rice straw (the volume of rice straw was not greater than 2/5 of the inner volume of carbonization furnace) into a carbonization furnace, heating in isolation from the air, setting a temperature at 320°C, starting the time when the temperature reaching 320°C, and closing the carbonization furnace after 4 hours, cooling to room temperature, and performing secondary pulverization by the pulverizer to the maximum particle size of 20-mesh sieve; (2) pre-granulation treatment of biochar: soaking the screened biochar into a 3% oxalic acid solution, with a weight ratio of the biochar to the oxalic acid solution of 1: 20, filtering out the liquid using fine mesh film after soaking for 36 hours, and drying the residue portion at 60°C; (3) melting granulation of the biochar and the chemical fertilizer: melting urea, ammonium hydrogen phosphate, ammonium nitrate, potassium chloride, and potassium hydrogen phosphate in the chemical fertilizer in a high tower, dissolving the biochar into absolute ethanol with a weight ratio of the biochar to the absolute ethanol of 1: 2.5, mixing a mixed solution of the absolute ethanol and the biochar into the melted chemical fertilizer, and uniformly stirring for granulation.

[47] Detection method

In the Jiaozhou area of Qingdao, the basic fertility of tested soil in 0-20 cm depth was pH 8.2, organic matter 25.96 g/kg, total nitrogen 1.72 g/kg, alkali-hydrolyzable nitrogen 157.37 mg/kg, available phosphorus 19.30 mg/kg, and available potassium 143.81 mg/kg.

[48] The experiment adopted a random block design, and had 12 treatments, namely, bio-based compound fertilizer treatment and compound fertilizer treatment (compound fertilizer includes 30% of bentonite and 70% of NPK fertilizer) made by examples and Comparative Examples, and each treatment was repeated 3 times. The soil without any treatment was taken as the control group, and the fertilizer application amount of each soil treatment was 500 kg/hm?. The fertilization method was a one-time application of base fertilizer, the cultivation method was 0.65m uniform ridge planting with a planting density of 75,000/hm?, and the planting crop was Zhengdan 958 corn.

[49] The rhizosphere soil of maize was taken at the seedling stage, jointing stage, tasseling stage, dough stage, and maturation stage, and the contents of organic matter, total nitrogen, available phosphorus, and available potassium in the soil were detected.

The detection results of total nitrogen content in the soil were recorded in Table 2, organic matter in Table 3, available phosphorus in Table 4, available potassium in

Table 5, and growth traits and yield in Table 6.

[50] Organic matter was detected according to NT/Y 1121.6-2006 "Soil Detection

Part 6: Detection of Soil Organic Matter", and total nitrogen was digested with potassium dichromate-sulfuric acid accelerator and determined by SKD-2000 automatic Kjeldahl Nitrogen Meter; available phosphorus was detected according to

NY/T1121.7-2014 "Soil Detection Part 7: Determination of Available Phosphorus in

Soil"; available potassium was detected according to NY/T889-2004 "Determination of Available Potassium and Slow-Released Potassium in Soil".

[51] Table 2 Effect of biochar-based compound fertilizer on total nitrogen content in soil (%)

Item Seedling | Jointing Tasseling | Dough Maturation stage stage stage stage stage

Example 5 0.21 0.22 0.22

Comparative | 0.20 0.21 0.21 0.21 0.20

Example

Comparative | 0.20 0.20 0.21 0.21 0.20

Example 2

Comparative | 0.19 0.19 0.20 0.20 0.20

Example 3 eames

Compound 0.20 0.21 0.22 0.21 0.20 fertilizer treatment

Null 0.19 0.19 0.19 0.19 0.19 treatment

As could be seen from the data in Table 2, the total nitrogen content in the soil treated with the biochar-based compound fertilizer in Examples 1-5 and Example 9 was significantly higher than that in the blank control group; while in Examples 6 and 7, the total nitrogen content in the soil treated with the biochar-based compound fertilizer was lower than that in Example 1 due to the change of the pyrolysis treatment temperature; and in Examples 10 and 11, the amount of the biochar composition increased and decreased relative to the compound fertilizer, as shown in Table 2, the promotion of total nitrogen in corn decreased at dough stage and continued to decrease until maturation stage, indicating that the mixture ratio of biochar composition and compound fertilizer could improve the total nitrogen content in the soil.

[52] Compared with Example 1, the amount of biomass in Comparative Example 1 was higher than that of the red mud, while compared with Example 1, the amount of biomass in Comparative Example 2 was lower than that of the red mud, and the total nitrogen content of biochar-based compound fertilizers made in Comparative Example 1 and Comparative Example 2 decreased at maturation stage.

[53] Using a normal temperature cooling method, the biochar-based compound fertilizer in Comparative Example 3 did not significantly increase the total nitrogen content in the soil at dough stage and maturation stage.

[54] In Comparative Example 4, the compound fertilizer containing biochar prepared by the prior art did not significantly improve the total nitrogen content in the soil.

[55] Table 3 Effect of biochar-based compound fertilizer on organic matter content in soil (mg/kg)

Item Seedling Jointing Tasseling Dough Maturation stage stage stage stage stage

Example 8 | 28.15 | 29.38 | 28.26 31.54 33.68 33.48 30.67 29.87 29.41

Comparative | 27.68 28.54 29.47 30.21 28.35

Example 1

Comparative | 26.94 28.81 29.97 28.91 27.39

Example 2

Comparative | 28.91 29.31 29.75 30.51 28.34

Example 3

Comparative 26.94 29.21 28.64

Example 4

Compound | 26.37 28.34 24.39 fertilizer treatment

Null 25.23 26.35 25.58 22.67 23.64 treatment

The biochar-based compound fertilizers made in Examples 1-5 and 9 promoted the soil organic matter content of corn at seedling stage, jointing stage, tasseling stage, dough stage, and maturation stage, and the promotion effect was obviously better than that of the compound fertilizer treatment group. [S6] Compared with Example 1, Example 6 and Example 7 decreased and increased the pyrolysis temperature, respectively. The promotion effect of biochar-based compound fertilizer made in Examples 6-7 on organic matter in soil was not as good as that in Example 1.

[57] When the pyrolysis time was prolonged, the biochar-based compound fertilizer in Example 8 had a poor effect on the organic matter content of corn during its growth.

[58] In Example 10, the application amount of compound fertilizer decreased and the application amount of biochar composition increased, and the content of organic matter in the soil increased, but the persistence was insufficient.

[59] In Example 11, the amount of biochar composition decreased, the amount of compound fertilizer increased, and the organic matter content in soil decreased, indicating that biochar composition could provide a large amount of organic matter for soil and form biochar-based compound fertilizer with compound fertilizer, which had a more lasting effect on improving soil fertility.

[60] Compared with Example 1, the amounts of biomass in Comparative Example 1 and Comparative Example 2 were higher and lower than that of the red mud, respectively. As shown in Table 3, the content of organic matter in the soil of

Comparative Example 1 and Comparative Example 2 decreased, but the effect was more significant than that of using compound fertilizer alone.

[61] Adopting a normal temperature cooling method, the bio-char compound fertilizer in Comparative Example 3 had no significant effect on promoting the content of organic matter in the soil, and had insufficient persistence in enhancing soil fertility.

[62] Comparative Example 4 was a biochar-based composite fertilizer containing biological carbon prepared in the prior art, and by comparison, it could be seen that the promotion effect was similar to that of soil treated by adding compound fertilizer, but not as good as that of this application.

[63] Table 4 Effect of biochar-based compound fertilizer on available phosphorus content in soil (mg/kg)

Item Seedling Jointing Tasseling Dough Maturation stage stage stage stage stage es [194 a Jos ow or

Example 8 | 8.23 | 8.45 | 8.84 11.37 13.28 13.41

Comparative | 9.02 9.64 9.84 8.64 8.37

Example 1

Comparative | 8.64 8.84 8.97 8.34 8.11

Example 2

Comparative | 8.96 9.65 9.85 8.64 8.34

Example 3

Comparative | 8.15 8.54 8.34 8.24 8.14

Example 4

Compound | 8.14 8.36 8.21 8.17 8.04 fertilizer treatment

Null 7.45 7.98 7.64 7.18 6.94 treatment

As could be seen from the data in Table 4, compared with the compound fertilizer treatment, the biochar-based compound fertilizers prepared in Examples 1-5 and 9 could significantly increase the content of available phosphorus in the soil, while compared with Example 10, in which the amount of biochar composition decreased, the effect of Examples 1-5 is more remarkable, indicating that the application of biochar composition could increase the content of available phosphorus in soil.

[64] Compared with Example 1, the pyrolysis temperature of Example 6 decreased, while compared with Example 1, the pyrolysis temperature of Example 7 increased, and the promotion effect of biochar-based compound fertilizer prepared in Example 6 and Example 7 on available phosphorus content in the soil decreased; in Example 8, due to the shortened pyrolysis time and incomplete pyrolysis, the promotion effect on available phosphorus of biochar-based compound fertilizer was not as good as that of

Example 1.

[65] In Example 11, the amount of compound fertilizer increased and the amount of biochar composition decreased, which had similar results to the promotion of effective phosphorus content in the soil in Example 1, but the amount of compound fertilizer and the cost were increased.

[66] Compared with Example 1, Comparative Example 1 and Comparative

Example 2 increased and decreased the amount of biomass, respectively, and the promotion effect of the biochar-based compound fertilizers prepared in Comparative

Example 1 and Comparative Example 2 on the available phosphorus content in the soil was not significant.

[67] Using a normal temperature cooling method, the promotion effect of available phosphorus content in the soil in Comparative Example 3 was not significant.

[68] In Comparative Example 4, the compound fertilizer containing biochar was prepared by the prior art, but its promotion effect on available phosphorus content in the soil was similar to that of the compound fertilizer treatment.

[69] Table 5 Effect of biochar-based compound fertilizer on available potassium content in soil (mg/kg)

Item Seedling Jointing Tasseling Dough Maturation stage stage stage stage stage

Example 6 126.93 128.61 119.64 127.69 129.24 118.25

Example 8 126.35 129.64 118.21 118.64 116.34 135.14 138.67 123.47 128.53 118.69 132.21 118.52 137.64 140.12 118.47

Comparative | 128.94 131.21 120.31 133.21 120.11

Example 1

Comparative | 124.31 129.56 120.83 121.42 117.92

Example 2

Comparative | 127.64 129.83 122.31 123.14 118.54

Example 3

Comparative | 118.64 122.54 120.38 122.34 118.24

Example 4

Compound 117.54 121.88 118.24 123.73 114.27 fertilizer treatment

Null 115.24 118.44 117.24 117.12 110.14 treatment

It could be seen from the data in Table 5 that the biochar-based compound fertilizer in

Examples 1-5 and Example 9 had a significant promotion effect on the available potassium during the growth period of corn, and the promotion effect lasted until the dough stage, indicating that the combination of biochar composition and compound fertilizer had a rapid and long-lasting effect on improving the content of available potassium in the soil; and the content of available potassium in the soil was higher than that in the compound fertilizer treatment group at the maturation stage of corn.

[70] The biochar-based compound fertilizers made in Examples 6-8 and 10-11 had no significant effect on promoting available potassium in the soil, and the content of available potassium was low at the maturation stage of corn.

[71] The promotion effect of biochar-based compound fertilizer in Comparative

Examples 1-3 on available potassium in the soil was not as good as that in Example 1, and in Comparative Example 4, the biochar compound fertilizer was prepared by the prior art, but its promotion effect on available potassium content was similar to that of compound fertilizer treatment.

[72] Table 6 Characters and yield of corn

Example 6 16.32 0.75 15.32 31.35

Example 7 17.19 1.13 14.65 31.65 17.29 14.76 33.14

Comparative | 17.26 1.14 15.31 32.32 10020.4

Example

Comparative | 16.35 1.18 15.17 31.24 0867.5

Example 2

Comparative | 17.68 1.06 14.65 30.27 9561.4

Example 3

Comparative | 17.64 1.12 14.27 31.58 0652.7

Example 4

Compound 17.34 1.15 14.32 31.34 10253.4 fertilizer treatment

Null 16.24 0.85 14.62 28.91 6231.5 treatment

It could be seen from the data in Table 6 that the biochar-based compound fertilizers prepared in Examples 1-5 and 9 could increase the spike length of corn, reduce the barren tip of corn, increase the number of grains per row of corn and increase the yield of corn.

[73] However, the biochar-based compound fertilizer in Example 6-8 had little effect on the spike length of corn, but it would increase the barren tip length of corn and reduce the number of spikes row and the number of grains per row.

[74] Compared with Example 1, the amount of biomass in Comparative Example 1 and Comparative Example 2 increased and decreased, respectively, relative to the amount of red mud. The results in Table 6 showed that the effect of biochar-based compound fertilizers in Comparative Example 1 and Comparative Example 2 on increasing the number of grains per row of corn was not obvious, and the corn yield in

Example 1 decreased obviously.

[75] The biochar-based compound fertilizer made in Comparative Example 3 had no obvious improvement effect on the bald tip of corn, while compared with Example 1, in Comparative Example 4, the biochar-based compound fertilizer was prepared by the prior art, but its promotion effect on the number of grains per row and the number of spikes row of corn was not good.

[76] The specific example is only an explanation of the present application, and it is not a limitation of the present application. After reading the specification, those skilled in the art can make modifications to the example without creative contribution as needed, but these modifications are all protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

Conclusions l. Method of preparation of a biochar-based composite, which comprises a biochar composition, and includes the following steps: drying, pulverizing and granulating biomass to prepare the biomass particles for later use, drying red mud for later use; mixing the red mud and additives, adding them from a furnace tail of a rotary kiln, blowing the biomass particles from the furnace head, heating, and carrying out pyrolysis treatment to prepare calcined material, quenching the calcined material with water, grinding, and carrying out magnetic separation to obtain non-magnetic slag; and grinding and blowing against the non-magnetic slag to obtain the biochar composition; wherein an amount of biomass particles is 20-25% of that of the red mud, and an amount of the additives is 4-8% of that of the red mud.

A method for preparing a biochar-based composite according to claim 1, wherein a temperature of the pyrolysis treatment is 850-950°C for 80-100 minutes.

A method for preparing a biochar-based composite according to claim 1, wherein the biomass is selected from one or more of waste wood, straw, and fast-growing plants.

A method for preparing a biochar-based composite according to claim 3, wherein the straw is selected from one or more of corn straw, rice straw, wheat straw, sesame straw and cotton straw.

A method for preparing a biochar-based composite according to claim 4, wherein the biomass comprises waste wood and straw with a mass ratio of 0.1-0.3:1, the straw comprising the corn straw, the rice straw and the wheat straw with a mass ratio of 1:0.1-0.3:0.3-0.5, and the waste wood is sawdust.

A method for preparing a biochar-based composite according to claim 1, wherein the additive comprises calcium oxide.

A method for preparing a biochar-based composite according to claim 6, wherein the additive further comprises fluorite, and a mass ratio of calcium oxide to fluorite is 1:0.3-0.5.

A method for preparing a biochar-based composite according to claim 1, wherein the biochar composition constitutes 15-25% of a total amount of the biochar-based composite, and an application rate of a biochar-based composite fertilizer is 300-600 kg/hm ? is.