Preparation and application of compound biochar for improving acidified soil improvement effect

Abstract

The invention discloses preparation and application of compound biochar capable of improving the acidified soil improvement effect, in the preparation process, firstly, agricultural waste biomass serves as a raw material, high-temperature pyrolysis is conducted under argon protection after cleaning, drying and grinding are conducted, biochar is prepared and obtained, then the obtained biochar is mixed with KOH, and after ultrasonic dispersion, standing, suction filtration and drying are conducted, the compound biochar is obtained. Performing secondary pyrolysis activation under the protection of argon to obtain modified biochar, and finally mixing the modified biochar with an alkaline material in proportion to obtain the compound biochar. According to the method, by optimizing the preparation process of the biochar and adjusting the compounding proportion of the modified biochar and the alkaline material, the adjusting effect of the biochar on the pH value of the acid soil is remarkably improved. The method has the advantages of being easy and convenient to operate, low in cost, lasting in effect and the like, is suitable for large-scale acid soil improvement, and has wide application prospects and ecological economic benefits.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of soil improvement, more particularly to a preparation and application of a compound biochar for improving the effect of acidified soil improvement. BACKGROUND

[0002] In recent years, with the continuous improvement of industrialization and agricultural production level, the problem of large-area acid soil has become increasingly prominent. Acid soil not only inhibits the growth of plant roots and affects nutrient absorption, but also leads to the dissolution of harmful metal ions, reducing crop yield and quality. Traditional soil improvement methods, such as lime improvement, can increase soil pH, but have defects such as large usage, high cost, uneven distribution, soil compaction, and non-persistent improvement effect. At the same time, biochar, as a new type of environmentally friendly material, has attracted widespread attention due to its good pore structure, large surface area, and the presence of various functional groups. Among many applications, biochar can be used for adsorbing pollutants, improving soil structure, and increasing soil water retention. In recent years, methods for modifying biochar have been explored, and the use of alkaline substances (such as KOH) for activation and modification of biochar can significantly increase its alkaline functional groups and specific surface area, thereby enhancing its ability to improve acid soil.

[0003] However, current research on the use of biochar and alkaline materials for acid soil improvement still has the following shortcomings: the modification and compounding process of biochar lacks systematic research, it is difficult to achieve optimal compounding, the synergistic effect between alkaline materials and modified biochar is not fully utilized, and the long-term improvement effect and agricultural application effect are not verified. Through retrieval, Chinese patent CN 118791341A discloses an environmentally friendly acid soil conditioner, a preparation method, and application scenarios. The composition of the conditioner includes: organic waste 70-100 parts, silicon powder 1-4 parts, limestone powder 50-70 parts, fly ash 5-10 parts, slag 5-10 parts, urease inhibitor 0.5-1 part, calcium-magnesium-phosphorus-potassium fertilizer 5-10 parts, zinc oxide 3-5 parts, dissociation agent 3-7 parts, conditioning agent 1-3 parts, penetration agent 0.1-0.7 parts, and 120-200 parts of water. The specific content of the preparation method is: step S1, slurry of raw materials; step S2, homogenization of raw materials; step S3, solid-liquid separation; step S4, activation of filter cake; step S5, material granulation; step S6: material mixing; step S7: material composting. Although this patent provides a multi-component composite acid soil conditioner, it has certain limitations in terms of raw material selection, preparation process, acid reduction effect, environmental friendliness, economy, and technical novelty, such as the use of urease inhibitors, zinc oxide, and other chemical additives, which increases the cost of preparation; the use of fly ash, slag, and other industrial waste materials, while achieving resource utilization, may contain harmful substances such as heavy metals, posing a risk of secondary pollution.

[0004] Therefore, there is an urgent need for a biochar compounding method with strict structure, simple operation, economic and environmental protection, and significant improvement effect to meet the needs of modern agriculture for acid soil improvement technology. SUMMARY

[0005] Therefore, the present application provides a biochar compounding method which can significantly improve the acid soil improvement effect, has the advantages of low cost, simple process, environmental friendliness and long-term stable improvement effect.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: A preparation method of a compounded biochar for improving the acid soil improvement effect, comprising the following steps: (1) Using agricultural waste biomass as raw material, after cleaning, drying and grinding, biochar is prepared by high-temperature pyrolysis under argon protection; (2) The biochar obtained in step (1) is mixed with KOH, and after ultrasonic dispersion, standing, suction filtration and drying, the modified biochar is obtained by secondary pyrolysis activation under argon protection; (3) The modified biochar obtained in step (2) is mixed with alkaline material in proportion to obtain compounded biochar.

[0007] Preferably, the waste biomass in step (1) is one or more of corn stalks or reed stalks.

[0008] Preferably, the grinding in step (1) is passed through a 100-mesh sieve.

[0009] Preferably, the pyrolysis in step (1) adopts limited oxygen pyrolysis, the pyrolysis temperature is 700°C, the heating rate is 10°C / min, and the residence time is 2h.

[0010] Preferably, the mass-volume ratio of biochar to KOH in step (2) is 2:1.

[0011] Preferably, the secondary pyrolysis temperature in step (2) is 500°C, the heating rate is 10°C / min, and the pyrolysis time is 2h.

[0012] Preferably, the alkaline material in step (3) is one or more of wood ash and oyster shell powder.

[0013] Preferably, the mass ratio of modified biochar to alkaline material in step (3) is (3-5):(5-10).

[0014] More preferably, the mass ratio of modified biochar to alkaline material in step (3) is 1:1.

[0015] The application further provides application of the compound biochar for improving the improvement effect of acidified soil prepared by the method.

[0016] Further, the adding amount of the modified biochar is 0.3%-0.5% and the adding amount of the alkaline material is 0.5%-1.0% based on the weight of the acidified soil.

[0017] Preferably, the adding amount of the modified biochar is 0.5% and the adding amount of the alkaline material is 0.5% based on the weight of the acidified soil.

[0018] Compared with the prior art, the application provides the preparation and application of the compound biochar for improving the improvement effect of acidified soil, and has the following beneficial effects: The technical scheme of the application selects corn stalks, reed stalks and other biomass raw materials to prepare biochar, then modifies the biochar by using KOH activation to obtain modified biochar with high specific surface area and rich alkaline functional groups, and then mixes the modified biochar with alkaline materials such as wood ash and oyster shell powder in a certain proportion to form a compound mixture, which is directly applied to acid soil to rapidly increase the pH value of the soil and keep the pH value stable for a long time. DETAILED DESCRIPTION

[0019] The technical scheme of the application will be described clearly and completely below with reference to the embodiments of the application. Obviously, the described embodiments are only some of the embodiments of the application but not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0020] Embodiment 1 Preparation of the compound biochar for improving the improvement effect of acidified soil: (1) Corn stalks and reed stalks are selected as raw materials, and the waxy hard shell on the outer layer of the stalks is removed by mechanical stripping to obtain stalk base materials meeting the requirements of the next test; then after cleaning, drying and grinding through a 100-mesh sieve, the stalk base materials are pyrolyzed under the protection of argon at a rate of 10°C / min to 700°C for 2h to prepare corn stalk biochar (JBC) and reed stalk biochar (LBC); (2) The biochar was modified by alkali post-treatment-melting method. The biochar was mixed with KOH at a mass-volume ratio of 2:1, stirred for 1 h, and then ultrasonically dispersed for 30 min. After standing for 24 h, the mixture was vacuum filtered and dried. The modified biochar was placed in a muffle furnace and heated to 500°C at a rate of 10°C / min. The modified biochar was twice pyrolyzed and activated under argon protection for 2 h to obtain modified corn straw biochar (KJBC) and modified reed straw biochar (KLBC). (3) The modified biochar was mixed with alkaline materials such as wood ash and oyster shell powder at a mass ratio to obtain a compounded biochar.

[0021] Examples I. Verification of the acid reduction performance of modified biochar The unmodified biochar JBC, LBC, and the modified biochar KJBC and KLBC obtained by alkali post-treatment-melting method were mixed at a ratio of 0.3%, 0.5%, and 1.0% of the dry weight of the soil, respectively. The mixture was thoroughly stirred to ensure that the alkaline materials were evenly distributed in the pores of the biochar, enhancing the uniformity and compounding effect of the materials.

[0022] The treatment groups were set as follows: 100 g of soil was weighed into several plastic cups, and different biochar and modified biochar were added at a ratio of 0.3%, 0.5%, and 1.0% of the soil weight, respectively. The treatment without adding biochar served as a control (CK). The soil sample was mixed with the biochar, and then an appropriate amount of deionized water was added to maintain a water content of 60% of the soil field water capacity. The plastic wrap was sealed, and several 2 mm holes were punched in the surface to maintain air exchange. The soil was placed in a 25°C constant temperature incubator for 60 days, and the weight was measured every 3 days and deionized water was added to maintain the soil water content basically constant. All treatments were repeated three times. The pH value of the soil sample was measured at 0, 5, 10, 15, 30, 45, and 60 days after the start of the incubation experiment. The acid reduction effect of different gradient inputs of biochar and modified biochar on acidified black soil was analyzed. The results are shown in Table 1.

[0023] Table 1 Soil pH value after biochar application

[0024] The modified biochar (KJBC and KLBC) treatment groups showed significant pH adjustment effects within 60 days, and overall better than the unmodified treatment groups (JBC and LBC). The 1.0% treatment groups of KJBC and KLBC reached pH values of 6.58 and 6.55, respectively, at 60 days. The pH values of JBC and LBC were increased more slowly and to a lesser extent, with the highest reaching 6.37. The pH adjustment effects of different biochar addition ratios within 60 days showed a general trend of 1.0%>0.5%>0.3%, but there was no significant difference between different proportions. The 1.0% treatment can rapidly increase the soil pH value in the early stage of cultivation, but the pH value increases gradually after 30 days, so the 1.0% biochar addition ratio is suitable for short-term rapid pH adjustment. Compared with the 1.0% treatment, the 0.3% and 0.5% treatments showed long-term soil acidification adjustment and were suitable for long-term soil pH adjustment. From the perspective of economic applicability, the 0.3%-0.5% biochar addition ratio can save more costs and meet the needs of field application. Therefore, the 0.3%-0.5% addition ratio can be considered as the best ratio for adjusting moderately acidified soil in the black soil region.

[0025] II. Verification of the Optimal Compound Ratio of Modified Biochar and Alkaline Materials Mix 0.5% of KJBC and KLBC with alkaline materials (wood ash, oyster shell powder) at a ratio of 0.3%, 0.5%, and 1.0% of soil dry weight, respectively. Mix thoroughly to ensure that the alkaline materials are evenly distributed in the pores of the biochar, enhancing the uniformity and compound effect of the materials.

[0026] The treatment groups are set as follows: 100 g of soil is weighed into several plastic cups, and the compound modified biochar materials are added according to the above ratios of soil dry weight. The control group (CK) is not added with compound biochar. Mix the three groups evenly and add an appropriate amount of deionized water to maintain a water content of 60% of the soil field water capacity. Seal with plastic wrap and make several 2 mm holes on the surface to maintain air exchange. Place the soil in a 25°C constant temperature incubator for 60 days, weigh every 3 days and add deionized water to maintain the soil water content basically constant. All treatments are repeated three times. Take soil samples at 0, 5, 10, 15, 30, 45, and 60 days after the start of the incubation experiment to determine the pH value. Analyze the effect of the compound ratio of modified biochar and different gradient alkaline materials on the acid reduction of acidified soil. The results are shown in Table 2.

[0027] Table 2 Soil pH value after compound of modified biochar and alkaline materials

[0028] The modified biochar and alkaline material compound treatment has a significant effect on the pH value adjustment of the acidic soil, and the compound ratio has a greater influence on the effect. The data in Table 2 show that, in the 60-day cultivation period, with the increase of the compound ratio, the pH value adjustment effect gradually increases. In the KJBC+wood ash group, the compound ratio of 0.5% KJBC+0.5% wood ash is gradually increased from the initial pH value of 5.5 to 6.74, showing a stable and continuous pH value increase effect. Although the initial increase amplitude of the 0.5% ratio is relatively small, the pH value increases obviously during 10 d to 30 d, and the growth is stable in the later period, which is suitable for the medium and long-term pH value adjustment requirement. Similarly, the compound effect of KJBC and oyster shell powder is also significant, wherein the pH value of the 0.5% KJBC+1.0% oyster shell powder compound treatment group reaches 6.70 after 60 d, and remains stable and increases during 15 d to 60 d, but the pH value of the 0.5% KJBC+0.5% oyster shell powder compound ratio is also stably increased to 6.68 within 60 d, and the pH value changes uniformly and stably at each time point, showing good long-acting property. For the 0.5% KLBC treatment group, the pH value of the 0.5% KLBC+1.0% wood ash compound ratio is increased to 6.75 after 60 d, showing the most significant pH value increase effect, and the pH value stably increases at each time point; and the pH value of the 0.5% KLBC+0.5% oyster shell powder compound ratio reaches 6.71 at 60 d, which has an effect close to that of the 1.0% treatment group, and has a higher cost performance. Although the 1.0% ratio also has a significant effect, the pH value adjustment increase amplitude tends to be saturated in the later period, and has a lower cost performance than the 0.5% group. In the whole test period, the pH value of the control group remains at 5.5 without obvious change, which proves that the acidic environment is maintained stable without the addition of modified biochar and alkaline material, further indicating that the modified biochar and alkaline material compound has a significant effect on the soil pH value adjustment.

[0029] In summary, the KJBC and KLBC compound wood ash and oyster shell powder in the present application show better acid reduction performance at a higher ratio (1.0%), but considering the economic applicability and long-acting property, the acid reduction effect of the 0.5% compound ratio is close to that of the 1.0% application amount, and the use amount is more economical, has a higher cost performance, and can stably increase and maintain a high pH value level within 60 d, which is suitable for long-term improvement of the acidic soil. Especially, the 0.5% compound ratio of KJBC and alkaline material not only effectively reduces the amount of alkaline material, but also maintains a high pH value adjustment stability within the whole 60 d period, which is suitable for long-term improvement of the acidic soil.

[0030] The various embodiments described in this specification are intended to be illustrative only and are not intended to limit the scope of the present application. Numerous modifications to the embodiments described herein will be readily apparent to those skilled in the art and the general principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a compound biochar for improving the effect of acidified soil improvement, characterized in that, The method comprises the following steps: (1) taking agricultural waste biomass as raw material, cleaning, drying and grinding, and then pyrolyzing under argon protection to obtain biochar; (2) mixing the biochar obtained in step (1) with KOH, ultrasonic dispersion, standing, suction filtration and drying, and then second pyrolysis activation under argon protection to obtain modified biochar; (3) mixing the modified biochar obtained in step (2) with alkaline material in a certain proportion to obtain compound biochar.

2. The preparation method of the compound biochar for improving the effect of acidified soil improvement according to claim 1, characterized in that, The waste biomass in step (1) is one or more of corn stalks or reed stalks.

3. The preparation method of the compound biochar for improving the effect of acidified soil improvement according to claim 1, characterized in that, In step (1), the ground material is sieved through a 100-mesh sieve.

4. The preparation method of the compound biochar for improving the effect of acidified soil improvement according to claim 1, characterized in that, In step (1), the pyrolysis is carried out by limited oxygen pyrolysis, the pyrolysis temperature is 700°C, the heating rate is 10°C / min, and the residence time is 2h.

5. The preparation method of the compound biochar for improving the effect of acidified soil improvement according to claim 1, characterized in that, In step (2), the mass-volume ratio of biochar to KOH is 2:

1.

6. The preparation method of the compound biochar for improving the effect of acidified soil improvement according to claim 1, characterized in that, In step (2), the second pyrolysis temperature is 500°C, the heating rate is 10°C / min, and the pyrolysis time is 2h.

7. The preparation method of the compound biochar for improving the effect of acidified soil improvement according to claim 1, characterized in that, The alkaline material in step (3) is one or more of wood ash and oyster shell powder.

8. The preparation method of the compound biochar for improving the effect of acidified soil improvement according to claim 1, characterized in that, In step (3), the mass ratio of modified biochar to alkaline material is (3-5):(5-10).

9. The use of the compound biochar for improving the effect of acidified soil improvement prepared by the method of any one of claims 1-8, characterized in that, The modified biochar and alkaline material are mixed and added to acidified soil for acidified soil improvement.

10. Use according to claim 9, characterized in that, The addition amount of the modified biochar is 0.3%-0.5% and the addition amount of the alkaline material is 0.5%-1.0% based on the weight of the acidified soil.

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