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

Abstract

The application discloses a kind of preparation and application of compound biochar for improving acidification soil improvement effect, first of all, agricultural waste biomass is used as raw material in preparation process, after washing, drying, grinding, high-temperature pyrolysis under argon protection, biochar is prepared, then the biochar obtained is mixed with KOH, after ultrasonic dispersion, standing, suction filtration and drying, secondary pyrolysis activation under argon protection, modified biochar is obtained, finally, the modified biochar is mixed with alkaline material in proportion to obtain compound biochar.The method of the application significantly improves the pH value adjustment effect of the biochar on acid soil by optimizing the preparation process of the biochar and adjusting the compounding ratio of the modified biochar and the alkaline material.The method of the application has the advantages of simple operation, low cost, long-lasting effect, etc., is suitable for large-scale acid soil improvement, and has wide application prospect and ecological and economic benefits.

Description

Technical Field

[0001] This invention relates to the field of soil improvement technology, and more specifically to the preparation and application of a compound biochar for improving the improvement effect of acidified soil. Background Technology

[0002] In recent years, with the continuous improvement of industrialization and agricultural production levels, the problem of large-scale acidic soils has become increasingly prominent. Acidic soils not only inhibit crop root growth and affect nutrient absorption, but also lead to the leaching of harmful metal ions, reducing crop yield and quality. Traditional soil improvement methods, such as lime amendment, can increase soil pH, but they suffer from drawbacks such as large usage, high cost, uneven distribution, soil compaction, and short-lasting improvement effects. Meanwhile, biochar, as a novel environmentally friendly material, has attracted widespread attention due to its excellent pore structure, large surface area, and diverse functional groups. In many applications, biochar can be used to adsorb pollutants, improve soil structure, and enhance soil water retention. In recent years, methods for modifying biochar have been continuously explored. Among these, the activation modification of biochar using alkaline substances (such as KOH) can significantly increase its alkaline functional groups and specific surface area, thereby enhancing its ability to improve acidic soils.

[0003] However, current research on the use of biochar-based alkaline materials for acidic soil improvement, both domestically and internationally, still suffers from the following shortcomings: a lack of systematic research on biochar modification and compounding processes makes it difficult to achieve optimal ratios; the synergistic effect between alkaline materials and modified biochar has not been fully utilized; and there is a lack of verification regarding long-term improvement effects and agricultural application results. A search revealed Chinese patent CN 118791341A, which discloses an environmentally friendly acidified soil conditioner, its preparation method, and application scenarios. The conditioner comprises: 70-100 parts organic waste, 1-4 parts silica powder, 50-70 parts limestone powder, 5-10 parts fly ash, 5-10 parts slag, 0.5-1 part urease inhibitor, 5-10 parts calcium magnesium phosphate potassium fertilizer, 3-5 parts zinc oxide, 3-7 parts dissociation agent, 1-3 parts conditioner, 0.1-0.7 parts penetrant, and 120-200 parts water. The specific contents of the preparation method are as follows: Step S1, raw material slurrying; Step S2, raw material homogenization; Step S3, solid-liquid separation; Step S4, filter cake activation; Step S5, material granulation; Step S6, material mixing; Step S7, material composting. Although this patent provides a multi-component composite soil conditioner for acidified soil, it has certain limitations in terms of raw material selection, preparation process, acid reduction effect, environmental friendliness, economy, and technological novelty. For example, the use of chemical additives such as urease inhibitors and zinc oxide increases the preparation cost; and while the application of industrial waste such as fly ash and slag achieves resource utilization, these materials 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 that is structurally sound, easy to operate, economical, environmentally friendly, and has significant improvement effects, in order to meet the needs of modern agriculture for acidified soil improvement technology. Summary of the Invention

[0005] In view of this, the present invention provides a biochar compounding method that can significantly improve the effect of acidic soil improvement, which has the advantages of low cost, simple process, environmental friendliness and long-term stable improvement effect.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing compound biochar to improve the remediation effect of acidified soil includes the following steps: (1) Biochar was prepared by using agricultural waste biomass as raw material, which was cleaned, dried and ground and then pyrolyzed at high temperature under argon protection; (2) The biochar obtained in step (1) is mixed with KOH, and after ultrasonic dispersion, standing, filtration and drying, it is activated by secondary pyrolysis under argon protection to obtain modified biochar; (3) The modified biochar obtained in step (2) is mixed with alkaline materials in a certain proportion to obtain compound biochar.

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

[0008] Preferably, the grinding process described in step (1) is followed by passing through a 100-mesh sieve.

[0009] Preferably, in step (1), the pyrolysis is oxygen-limited pyrolysis, the pyrolysis temperature is 700℃, 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, in step (2), the secondary pyrolysis temperature 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 present invention also provides an application of the compound biochar prepared by the method described above to improve the effect of acidified soil, characterized in that, when applied to the improvement of acidified soil, the modified biochar is mixed with alkaline materials and added to the acidified soil.

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

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

[0018] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a preparation and application of compound biochar to improve the effect of acidified soil remediation, which has the following beneficial effects: The technical solution of this invention involves preparing biochar from biomass raw materials such as corn stalks and reed stalks, and then modifying it by activation with KOH to obtain modified biochar with high specific surface area and abundant alkaline functional groups. Subsequently, it is compounded 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 acidic soil to rapidly increase the soil pH value and maintain its stability for a long period of time. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 Preparation of compound biochar to improve the remediation effect of acidified soil: (1) Corn stalks and reed stalks were selected as raw materials. The outer waxy hard shell of the stalks was removed by mechanical stripping to obtain stalk base material that meets the requirements of the next test. After washing, drying, grinding and passing through a 100-mesh sieve, the stalks were heated to 700°C at a rate of 10°C / min under argon protection and subjected to oxygen-limited high-temperature pyrolysis for 2 hours to prepare corn stalk biochar (JBC) and reed stalk biochar (LBC). (2) Biochar was modified by alkali post-treatment-melting method. Biochar and KOH were mixed at a mass-volume ratio of 2:1, stirred for 1 hour, ultrasonically dispersed for 30 minutes, allowed to stand for 24 hours, vacuum filtered and dried, and placed in a muffle furnace and heated to 500°C at a rate of 10°C / min. It was then activated by secondary pyrolysis for 2 hours under argon protection 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 in a certain mass ratio to obtain compound biochar.

[0021] Example I. Verification of the acid-reducing performance of modified biochar Unmodified biochar JBC and LBC, and alkali-treated-melt modified KJBC and KLBC were mixed at proportions of 0.3%, 0.5%, and 1.0% of the soil dry weight, respectively. The mixture was thoroughly stirred to ensure that the alkaline material was fully distributed in the pores of the biochar, thereby enhancing the uniformity and compounding effect of the material.

[0022] The treatment groups were set up as follows: 100 g of soil was weighed into several plastic cups, and different amounts of biochar and modified biochar were added at 0.3%, 0.5%, and 1.0% of the soil weight, respectively. The treatment without added biochar served as the control (CK). The soil samples and biochar were mixed evenly, and then an appropriate amount of deionized water was added to make the moisture content 60% of the soil field capacity. The cups were sealed with plastic wrap, and several 2 mm holes were punched in the surface to allow for air exchange. The soil was placed in a constant temperature incubator at 25 ℃ for 60 days, and weighed every 3 days, with deionized water added to maintain a relatively constant soil moisture content. All treatments were repeated 3 times. Soil samples were taken on days 0, 5, 10, 15, 30, 45, and 60 after the start of the incubation experiment to determine their pH values. The effects of different gradient amounts of biochar and modified biochar on reducing acidity in acidified black soil were analyzed. The results are shown in Table 1.

[0023] Table 1 Soil pH values ​​after biochar application

[0024] Modified biochar (KJBC and KLBC) treatments showed significant pH regulation effects within 60 days, and were generally superior to the unmodified treatments (JBC and LBC). The 1.0% KJBC and KLBC treatments reached pH values ​​of 6.58 and 6.55, respectively, at 60 days. JBC and LBC showed slower and smaller pH increases, reaching a maximum of 6.37. The overall pH regulation effect of different biochar addition ratios within 60 days was 1.0% > 0.5% > 0.3%, but there were no significant differences between the different ratios. The 1.0% treatment rapidly increased soil pH in the early stages of cultivation, but the rate of pH increase gradually leveled off after 30 days. Therefore, the 1.0% biochar addition ratio is suitable for short-term, rapid pH regulation. Compared to the 1.0% treatment, the 0.3% and 0.5% treatments demonstrated long-term effectiveness in regulating soil acidification, making them suitable for long-term soil pH adjustment. Furthermore, from an economic perspective, the 0.3%-0.5% biochar addition ratio offers greater cost savings and meets the needs of field applications. Therefore, the 0.3%-0.5% addition ratio can be considered the optimal proportion for regulating moderately acidified soils in the black soil region.

[0025] II. Verification of the optimal blending ratio of modified biochar and alkaline materials Mix 0.5% KJBC and KLBC with alkaline materials (wood ash and oyster shell powder) at ratios of 0.3%, 0.5%, and 1.0% of the dry weight of the soil, respectively; stir thoroughly to ensure that the alkaline materials are fully distributed in the pores of the biochar, thereby enhancing the uniformity and compounding effect of the materials.

[0026] The treatment groups were set up as follows: 100 g of soil was weighed into several plastic cups, and compound modified biochar material was added to each cup according to the above-mentioned ratio based on the dry weight of the soil. The treatment without compound biochar served as the control (CK). All three materials were mixed thoroughly, and an appropriate amount of deionized water was added to bring the moisture content to 60% of the soil's field capacity. The cups were sealed with plastic wrap, and several 2 mm holes were punched in the surface to allow for air exchange. The soil was placed in a 25℃ constant temperature incubator for 60 days, and weighed every 3 days, with deionized water added to maintain a relatively constant soil moisture content. All treatments were repeated three times. Soil samples were taken on days 0, 5, 10, 15, 30, 45, and 60 after the start of the incubation experiment to determine their pH values. The effect of the compound ratio of modified biochar with different gradient alkaline materials on reducing the acidity of acidified soil was analyzed. The results are shown in Table 2.

[0027] Table 2. Soil pH values ​​after mixing modified biochar with alkaline materials

[0028] The combination of modified biochar and alkaline materials significantly improved the pH of acidic soils, with the mixing ratio having a substantial impact on the effect. Table 2 shows that during the 60-day incubation period, the pH regulation effect gradually increased with increasing mixing ratio. In the KJBC + wood ash group, the mixing ratio of 0.5% KJBC + 0.5% wood ash gradually increased from an initial pH of 5.5 to 6.74, demonstrating a stable and continuous pH improvement. Although the initial increase from the 0.5% ratio was relatively small, the pH increase was significant between 10 and 30 days, followed by a stable increase in the later stages, suitable for medium- to long-term pH regulation needs. Similarly, the combination of KJBC and oyster shell powder also showed significant effects. The 0.5% KJBC + 1.0% oyster shell powder combination treatment group reached a pH of 6.70 after 60 days, maintaining a steady increase from day 15 to 60. However, the 0.5% KJBC + 0.5% oyster shell powder combination also steadily increased the pH to 6.68 within 60 days, with uniform and steady pH increases at each time point, demonstrating good long-term effectiveness. For the 0.5% KLBC treatment group, the 0.5% KLBC + 1.0% wood ash combination increased the pH to 6.75 after 60 days, showing the most significant pH increase, with a steady increase at each time point. The 0.5% KLBC + 0.5% oyster shell powder combination reached a pH of 6.71 at 60 days, achieving an effect close to that of the 1.0% treatment group, indicating high cost-effectiveness. While the 1.0% ratio also showed significant effects, its pH-regulating effect tended to saturate in the later stages, making its cost-effectiveness lower than the 0.5% group. Throughout the entire experimental period, the pH value of the control group remained at 5.5 without significant change, demonstrating that the acidic environment remained stable without the addition of modified biochar and alkaline materials. This further indicates that the combination of modified biochar and alkaline materials has a significant effect on soil pH regulation.

[0029] In summary, the compound of KJBC and KLBC with wood ash and oyster shell powder exhibits better acid-reducing performance at a higher ratio (1.0%). However, considering its economic applicability and long-term effectiveness, the acid-reducing effect at a compound ratio of 0.5% is similar to that at a 1.0% application rate, while being more economical in terms of usage and offering higher cost-effectiveness. Furthermore, it can stably raise and maintain a high pH level within 60 days, making it suitable for long-term improvement of acidic soils. In particular, the 0.5% compound ratio of KJBC with alkaline materials not only effectively reduces the amount of alkaline materials used but also maintains high pH regulation stability throughout the 60-day period, making it suitable for long-term improvement of acidic soils.

[0030] The various embodiments described in this specification are presented in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not 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 compound biochar to improve the remediation effect of acidified soil, characterized in that, Includes the following steps: (1) Using agricultural waste biomass as raw material, after cleaning, drying and grinding, it is pyrolyzed at high temperature with limited oxygen under argon protection. The pyrolysis temperature is 700℃, the heating rate is 10°C / min, and the residence time is 2h to prepare biochar. (2) The biochar obtained in step (1) is mixed with KOH at a mass-volume ratio of 2:

1. After ultrasonic dispersion, standing, filtration and drying, it is activated by secondary pyrolysis under argon protection at a temperature of 500℃, a heating rate of 10°C / min and a pyrolysis time of 2h to obtain modified biochar. (3) The modified biochar obtained in step (2) is mixed with alkaline materials in a certain proportion to obtain compound biochar; The alkaline material is one or more of plant ash and oyster shell powder; The mass ratio of modified biochar to alkaline material is (3-5):(5-10).

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

3. The method for preparing compound biochar to improve the effect of acidified soil remediation according to claim 1, characterized in that, The material is ground and then passed through a 100-mesh sieve as described in step (1).

4. The application of a compound biochar prepared by the method according to any one of claims 1-3 to improve the effect of acidified soil remediation, characterized in that, It is applied to the improvement of acidified soil by mixing modified biochar with alkaline materials and adding it to the acidified soil.

5. The application according to claim 4, characterized in that, The modified biochar dosage is 0.3%-0.5% and the alkaline material dosage is 0.5%-1.0% based on the weight of acidified soil.

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