Corn straw-agricultural film co-pyrolysis biomass charcoal as well as preparation method and application thereof

Abstract

The invention provides corn straw-agricultural film co-pyrolysis biomass charcoal as well as a preparation method and application thereof, and belongs to the technical field of agricultural waste resource utilization. The method comprises the following steps: mixing corn straw and an agricultural film according to a mass ratio of 10: (0.1-0.5), crushing, and co-pyrolyzing to obtain the corn straw-agricultural film co-pyrolyzed biomass charcoal. According to the invention, agricultural film plastic residues and corn crop straw wastes in agricultural production are co-processed in a co-pyrolysis manner to obtain the corn straw-agricultural film co-pyrolysis biomass charcoal, and the corn straw-agricultural film co-pyrolysis biomass charcoal can improve the physicochemical properties, fertility condition and microbial environment of soil and improve the yield and quality of crops; effective heavy metals in soil are reduced, enrichment of heavy metals in soil by crops is inhibited, and absorption of heavy metals in polluted soil by crops is reduced. The corn straw-agricultural film co-pyrolysis biomass charcoal can be used as a soil conditioner and a soil heavy metal passivator to improve the health of a soil-crop system.

Description

Technical Field

[0001] The present invention belongs to the technical field of agricultural waste resource utilization, and in particular relates to a corn straw-agricultural film co-pyrolysis biochar, a preparation method and application thereof. Background Art

[0002] A large amount of waste is generated during agricultural production, mainly including livestock and poultry manure and crop straw. Crop straw has very high nutritional potential and can improve the sustainable production capacity of soil. The traditional method of burning and discarding it not only causes environmental pollution, but also wastes a lot of precious biomass resources. Plastic products in agricultural production are mainly used for crop shading and protection, fertilizer and pesticide packaging, irrigation pipes, soil covering, flower pots, trays, etc. Among them, soil covering mulch is widely used, but the recycling of agricultural film is not optimistic. Since plastic film is mainly composed of polyethylene, the residual film is not easy to degrade in the soil and accumulates continuously, causing "white pollution". The residual film will hinder the internal circulation system of the soil, affect the growth of microorganisms in the soil, change the normal transportation of water and nutrients, and lead to a decrease in crop yields. The plastic particles remaining in the agricultural mulch will also be absorbed by microorganisms in the soil and transferred to crops, and passed along the food chain, causing damage to human health.

[0003] At present, there are many ways to deal with agricultural waste, but there are various problems. For example, returning agricultural biomass waste directly to the field is the simplest way to use it as fertilizer, but this method may lead to crop pests and diseases and continuous cropping problems; biomass resources can be used to efficiently produce hydrogen through pyrolysis and gasification, but CO will be generated in the process. 2 , CO and other gases. The presence of plastics will make the gas composition in the product more complex. The preparation of pure hydrogen still needs to be separated and purified, and the process is complicated and the cost is high. Composting is a low-cost and environmentally friendly option, but this method is based on the sole utilization of biomass waste. The presence of plastic waste will seriously affect the quality of composting, and the composting of agricultural waste will transfer microplastics to the soil again, which cannot completely solve the environmental pollution caused by agricultural plastic residues. Incineration is widely accepted as a way to deal with agricultural waste plastics, which will release many toxic pollutants, such as polycyclic aromatic hydrocarbons, polychlorinated biphenyls, dust, dioxins, heavy metals, etc. These pollutants will cause environmental deterioration and damage the health of organisms.

[0004] Co-pyrolysis technology refers to the high-temperature pyrolysis of two or more mixtures to obtain different value-added products. It is an efficient and convenient thermochemical technology. There is no significant difference in the operation of co-pyrolysis technology and single pyrolysis, but plastics and biomass will interact with each other during the pyrolysis process to produce a synergistic effect, making the pyrolysis products different from single pyrolysis. Biochar as a soil conditioner has attracted attention from agricultural and environmental integrated strategies worldwide. Applying biochar to the soil can increase soil organic carbon sequestration, reduce greenhouse gas emissions, increase soil pH and nutrient utilization efficiency, and increase crop yields.

[0005] At present, there are still difficulties in the treatment of agricultural plastic waste and mixed waste of agricultural biomass and plastic. Therefore, it is very necessary to find an efficient, reasonable and resource-based method to utilize agricultural biomass and plastic waste. Summary of the invention

[0006] In view of this, the object of the present invention is to provide a corn straw-agricultural film co-pyrolysis biochar, a preparation method and application thereof.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing corn straw-agricultural film co-pyrolysis biochar, comprising the following steps:

[0009] Corn straw and agricultural film are mixed and crushed in a mass ratio of 10:(0.1-0.5) and then co-pyrolyzed to obtain corn straw-agricultural film co-pyrolysis biomass charcoal.

[0010] Preferably, the co-pyrolysis temperature is 400-600° C., and the co-pyrolysis time is 1-3 hours.

[0011] Preferably, the heating rate of the co-pyrolysis is 3-7°C / min.

[0012] Preferably, the crushing is performed to 3-5 cm.

[0013] The present invention also provides corn straw-agricultural film co-pyrolysis biomass charcoal prepared by the preparation method, wherein the specific surface area of ​​the corn straw-agricultural film co-pyrolysis biomass charcoal is 1.91 to 2.39 m 2 ·g -1 The average pore size is 10.86-12.37 nm, and the total pore volume is 0.05-0.08 cm 3 ·g -1 .

[0014] The present invention also provides the use of the corn straw-agricultural film co-pyrolysis biomass charcoal as a soil conditioner in promoting crop growth and improving crop quality.

[0015] Preferably, the crop is non-heading cabbage.

[0016] Preferably, the corn straw-agricultural film co-pyrolysis biochar and soil are mixed to plant non-heading cabbage.

[0017] The present invention also provides the use of the corn straw-agricultural film co-pyrolysis biomass charcoal as a soil heavy metal passivator in improving the health of the soil-crop system.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention uses a co-pyrolysis method to synergistically process agricultural film plastic residues and corn crop straw waste in agricultural production in a certain proportion to obtain corn straw-agricultural film co-pyrolysis biomass charcoal. The corn straw-agricultural film co-pyrolysis biomass charcoal can improve the physical and chemical properties, fertility and microbial environment of the soil, increase the yield quality of crops, reduce the effective heavy metals in the soil, inhibit the enrichment of crops in the soil heavy metals, and reduce the absorption of crops by heavy metals in contaminated soil. The corn straw-agricultural film co-pyrolysis biomass charcoal can be used as a soil conditioner and soil heavy metal passivator to improve the health of the soil-crop system.

[0020] The physicochemical properties of the corn straw-agricultural film co-pyrolysis biochar of the present invention are affected by the proportion of agricultural film added. The specific surface area and total pore volume of the biochar increased when the agricultural film was added at a medium or low proportion (1%, 2.5%), and the number of C=C functional groups increased. The specific surface area, total pore volume and average pore diameter of the biochar decreased, the mineral composition decreased, and the oxygen-containing functional groups increased when the agricultural film was added at a high proportion (5%). Compared with corn straw charcoal, the corn straw-agricultural film co-pyrolysis charcoal had higher contents of available phosphorus and available potassium.

[0021] The present invention adds corn straw-agricultural film co-pyrolysis biomass charcoal to lead and cadmium composite contaminated soil to plant non-heading cabbage. The addition of corn straw-agricultural film co-pyrolysis biomass charcoal increases the pH and organic matter content of the soil, increases the nutrient content and effectiveness of the soil, and increases the soil microbial biomass; significantly reduces the CaCl in the contaminated soil 2 The content of extractable Pb and Cd was different from the enrichment of Pb and Cd in non-heading cabbage; the yield and vitamin C content of non-heading cabbage were significantly increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the corn straw-agricultural film co-pyrolysis biomass char after pyrolysis carbonization (wherein, CB0: corn straw char; CB1%: corn straw char containing 1% agricultural film; CB2.5%: corn straw char containing 2.5% agricultural film; CB5%: corn straw char containing 5% agricultural film);

[0023] Figure 2The SEM-EDS image of corn straw-agricultural film co-pyrolysis biochar (where a, b, c, and d are the SEM-EDS spectra of CB0, CB1%, CB2.5%, and CB5%, respectively);

[0024] Figure 3 This is the FT-IR spectrum of corn straw-agricultural film co-pyrolysis carbon;

[0025] Figure 4 This is the XRD pattern of corn straw-agricultural film co-pyrolysis carbon;

[0026] Figure 5 Effects of different corn straw-agricultural film co-pyrolysis biochar on soil CaCl 2 The influence of the content of leached Pb and Cd;

[0027] Figure 6 The effect of applying different corn straw-agricultural film co-pyrolysis biochar on the DTPA-extractable Pb and Cd content in soil. DETAILED DESCRIPTION

[0028] The present invention provides a method for preparing corn straw-agricultural film co-pyrolysis biochar, comprising the following steps:

[0029] Corn straw and agricultural film are mixed and crushed in a mass ratio of 10:(0.1-0.5) and then co-pyrolyzed to obtain corn straw-agricultural film co-pyrolysis biomass charcoal.

[0030] In the present invention, the mass ratio of corn straw to agricultural film is preferably 10:(0.2-0.4); the crushing to 3-5 cm, further crushing to 3.5-4.5 cm; the co-pyrolysis temperature is preferably 400-600°C, more preferably 450-550°C; the co-pyrolysis time is preferably 1-3h, more preferably 1.5-2.5h; the co-pyrolysis heating rate is preferably 3-7°C / min, more preferably 4-6°C / min.

[0031] The present invention also provides corn straw-agricultural film co-pyrolysis biomass charcoal prepared by the preparation method, wherein the specific surface area of ​​the corn straw-agricultural film co-pyrolysis biomass charcoal is 1.91 to 2.39 m 2 ·g -1 The average pore size is 10.86-12.37 nm, and the total pore volume is 0.05-0.08 cm 3 ·g -1 .

[0032] The present invention also provides the use of the corn straw-agricultural film co-pyrolysis biomass charcoal as a soil conditioner in promoting crop growth and improving crop quality.

[0033] In the present invention, the crop is non-heading cabbage; corn straw-agricultural film co-pyrolysis biomass charcoal and soil are mixed to plant non-heading cabbage, and the added amount of corn straw-agricultural film co-pyrolysis biomass charcoal is preferably 0.5-1.5% of the total mass of corn straw-agricultural film co-pyrolysis biomass charcoal and soil, and further preferably 0.7-1.4% of the total mass of corn straw-agricultural film co-pyrolysis biomass charcoal and soil.

[0034] The present invention also provides the use of the corn straw-agricultural film co-pyrolysis biomass charcoal as a soil heavy metal passivator in improving the health of the soil-crop system.

[0035] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0036] Example 1

[0037] Corn straw and agricultural film were mixed in a mass ratio of 10:0.25, air-dried and crushed to 4 cm, heated to 500°C at a heating rate of 5°C / min, maintained for 2 h after reaching the set temperature, cooled to room temperature and taken out to obtain corn straw-agricultural film co-pyrolysis biochar.

[0038] Example 2

[0039] Corn straw and agricultural film were mixed in a mass ratio of 10:0.1, air-dried and crushed to 3 cm, heated to 400°C at a heating rate of 4°C / min, maintained for 1 h after reaching the set temperature, cooled to room temperature and taken out to obtain corn straw-agricultural film co-pyrolysis biochar.

[0040] Example 3

[0041] Corn straw and agricultural film were mixed in a mass ratio of 10:0.5, air-dried and crushed to 5 cm, heated to 600°C at a heating rate of 6°C / min, maintained for 3 h after reaching the set temperature, cooled to room temperature and taken out to obtain corn straw-agricultural film co-pyrolysis biochar.

[0042] Experimental Example 1

[0043] Corn straw and agricultural film were mixed at a mass ratio of 10:0; 10:0.1; 10:0.25; 10:0.5, respectively, and then air-dried and crushed to 3-5 cm. The temperature was raised to 500°C at a heating rate of 5°C / min, and maintained for 2 hours after reaching the set temperature. The corn straw and agricultural film were cooled to room temperature and taken out to obtain corn straw-agricultural film co-pyrolysis biochar (CB0, CB1%, CB2.5%, CB5%) after corn straw and agricultural film were mixed in different proportions. Figure 1 The biomass obtained by carbonization was passed through 20-mesh and 100-mesh nylon sieves respectively and stored in a sealed bag for later use.

[0044] 1. Determination of basic physical and chemical properties of corn straw-agricultural film co-pyrolysis biochar:

[0045] 1. The calculation of biochar yield is as follows:

[0046]

[0047] 2. Determination of pH value: After the biochar was extracted with ultrapure water at a ratio of m:v=1:20 for 10 min, it was allowed to stand and measured using a pH meter (Shanghai Leici PHB-5 portable pH meter) within 2 h.

[0048] 3. Determination of organic carbon content: After oxidizing the biochar with 0.8 M potassium dichromate and concentrated sulfuric acid solution under external heating conditions, the remaining potassium dichromate was titrated with ferrous sulfate to calculate the organic carbon content.

[0049] 4. Determination of total C, H, O, N, and S content: Determined using an organic element analyzer (Elementar Unicube, Germany).

[0050] 5. Determination of total potassium and phosphorus: The biochar sample was subjected to H 2 SO 4 -H 2 O 2 After digestion, the total potassium content was determined using a flame photometer (FP6410, Shanghai analyzer electricity co., ltd.), the test solution was colored by vanadium molybdenum yellow colorimetry, and the total phosphorus content was determined using a spectrophotometer (ultraviolet spectrophotometer: A360 spectrophotometer, Beijing Puxi General Instrument Co., Ltd.).

[0051] 6. Determination of available potassium: The biochar sample was subjected to 1M neutral NH 4 After extraction with OAc solution, the content of biochar was measured using a flame photometer (FP6410, Shanghai Analyzer Electric Co., Ltd.), where the ratio of biochar to the extractant was 1:10 (m:v).

[0052] 7. Determination of available phosphorus: 2% formic acid solution extraction - vanadium molybdenum yellow colorimetric method, where the ratio of biochar to leaching agent is 1:100 (m:v) (UV spectrophotometer: A360 spectrophotometer, Beijing Puxi General Instrument Co., Ltd.).

[0053] 8. Determination of specific surface area, average pore diameter and total pore volume: Determination by BET method (Quantachrome Autosorb IQ3).

[0054] 9. Determination of the total amount of heavy metal elements Fe, Mn, Cu, Zn, Pb, Cd: The biochar sample was subjected to 85% HNO 3 +15% HClO 4 After the mixed acid solution was digested, it was measured using an inductively coupled plasma mass spectrometer (ICP-MS, Thermo Fisher ICAP-Q).

[0055] 10. Determination of polycyclic aromatic hydrocarbons (PAHs) content in biochar: After dehydration, the biochar was mixed evenly with anhydrous sodium sulfate and ground into particles, and the alternative intermediate solution was added. The acetone-n-hexane mixed solution was used for Soxhlet extraction for 16-18 hours, and the extract was collected. The extract was concentrated by nitrogen blowing, purified by silica gel chromatography, and the test solution was concentrated. The internal standard intermediate solution was added and the volume was fixed to 1 ml. The gas chromatography-mass spectrometry was used for determination (gas chromatography-mass spectrometry: Shimadzu GCMS-QP2010 SESY-001).

[0056] 11. Toxicity determination of polycyclic aromatic hydrocarbons in biochar: PAHs mainly include 16 components: naphthalene (Nap), acenaphthylene (Acpy), acenaphthene (Acp), fluorene (Flu), phenanthrene (Phe), anthracene (Ant), fluoranthene (Fla), pyrene (Pyr), benzo[a]anthracene (BaA), (Chr), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[a]pyrene (Bap), dibenzo[a,h]anthracene (IND), benzo[g,h,i]perylene (DBA) and indeno[1,2,3-c,d]pyrene (Bghip). The toxicity of different components is different, that is, the toxicity equivalent factor is different. Formulas 2 and 3 are the calculation formulas for the toxicity of polycyclic aromatic hydrocarbons. Table 1 shows the toxicity equivalent factors of different components:

[0057] TEQ=PAH×TEF (Formula 2)

[0058] TEQ=TEQ (Formula 3)

[0059] Among them, TEFi is the toxicity equivalent factor of a single PAH monomer, TEQi is the toxicity equivalent of a PAH monomer, PAHi is the toxicity equivalent factor of PAH monomer i, and TEQ is the sum of the toxicity equivalents of multiple PAH monomers detected in biochar.

[0060] Table 1 Toxicity equivalence factors of PAHi

[0061]

[0062] Experimental results: as shown in Table 2.

[0063] Table 2 Basic physical and chemical properties of biochar

[0064]

[0065]

[0066] Note: a IBI stands for International Biochar Initiative, which is an international biochar initiative organization; b EBC stands for European Biochar Certificate, which is the European biochar certificate. EBC-AgroOrganic and EBC-Agro respectively represent the standards set by the European Biochar Certificate for the heavy metal and organic pollutant content of biochar used in organic farming and agriculture; the test value is mean ± standard deviation (n = 3), and different letters indicate significant differences between biochars p < 0.05.

[0067] As shown in Table 2, the yields of CB1% and CB2.5% are 38.13% and 38.02% respectively, which are lower than corn straw charcoal. This is because corn straw is mainly composed of lignin, cellulose and hemicellulose, while agricultural film is mainly composed of hydrocarbons. In comparison, corn straw is more stable during the carbonization process and has a higher yield. The yield of CB5% is 0.62% higher than that of CB0. Due to the high proportion of plastic added and wrapped on the surface of biochar after melting, the release of volatile substances during pyrolysis of corn straw is inhibited, and a higher biochar yield is obtained.

[0068] The pH of corn straw charcoal was 9.9, and the pH of CB1%, CB2.5% and CB5% decreased by 0.5, 0.6 and 1.0 units respectively, indicating that the pH of biomass charcoal decreased with the increase of the proportion of agricultural film added.

[0069] The elemental analysis results of corn straw-agricultural film co-pyrolysis charcoal show that compared with CB0, the content of C, H, O, and N in CB1% increased, the content of C in CB2.5% increased, the content of H, O, N, and S decreased, and the content of C, H, O, N, and S in CB5% decreased. The above results show that the mixing of corn straw and agricultural film in different proportions leads to different effects on the element content of biochar, which in turn leads to differences in the types, quantities, and adsorption capacity of functional groups of biochar. Among them, the H / C and O / C values ​​of CB2.5% are lower than those of corn straw charcoal, indicating that its charcoal morphology has strong aromaticity and stability.

[0070] The total phosphorus content of corn straw-agricultural film co-pyrolysis charcoal was higher than that of CB0, and the total potassium content of CB2.5% and CB5% was higher than that of CB0; the available phosphorus and available potassium contents of CB1%, CB2.5%, and CB5% were 60.0%, 60.0%, 150.0% and 11.5%, 23.0%, and 8.9% higher than those of CB0, respectively. This indicates that the nutrient content of corn straw-agricultural film co-pyrolysis charcoal is higher than that of corn straw charcoal, because the plastic wrapping inhibits the volatilization of phosphorus and potassium in the biomass or the agricultural film is mixed with farmland soil, which increases the nutrient content in the biomass charcoal after pyrolysis.

[0071] The specific surface area of ​​CB1% and CB2.5% is higher than that of CB0, and the specific surface area of ​​CB5% is the lowest. Plastics are mainly composed of C and H elements, which are easy to volatilize during pyrolysis, resulting in a porous structure of biochar. A high proportion of agricultural film addition may wrap the biochar during pyrolysis, resulting in a decrease in specific surface area and total pore volume, which is consistent with the results of biochar yield. The average pore size of corn straw-agricultural film co-pyrolysis charcoal is lower than that of corn straw charcoal, indicating that there are more microporous structures in the co-pyrolysis charcoal, which is due to the more complex microstructure of plastic charcoal.

[0072] With the increase of the proportion of agricultural film added to corn straw, the content of PAHs in the co-pyrolysis charcoal did not show a regular trend of change. Compared with corn straw charcoal, the content of PAHs in CB1% increased by 44.78%, while the content of PAHs in CB2.5% was not significantly different from CB0, and the content of PAHs in CB5% increased by 111.74% compared with CB0. The above results may be due to the increase in the carbon-hydrogen ratio in the raw material with the addition of plastic, which makes more biomass converted into PAHs. At the same time, the oxygen-containing compounds in the biomass will further promote the cracking of plastics, thereby reducing the content of PAHs in biomass charcoal. This interaction is a complex process, and the above two situations may occur at the same time. The content of PAHs in corn straw charcoal and corn straw-agricultural film co-pyrolysis charcoal is lower than the standard limit of agricultural biomass charcoal specified in IBI and EBC.

[0073] The toxic equivalent of corn straw charcoal and corn straw-agricultural film co-pyrolysis charcoal is much lower than the IBI's regulations on the toxic equivalent of polycyclic aromatic hydrocarbons in biomass charcoal. The PAHs toxic equivalent of MB500 is 0.19, which is much lower than the IBI regulations.

[0074] 2. Surface morphology analysis of corn straw-agricultural film co-pyrolysis biochar

[0075] Scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS) were used for characterization (Hitachi Regulus 8100).

[0076] Experimental results: Figure 2As shown. The proportion of agricultural film added affects the surface morphology and pore structure of corn straw-agricultural film co-pyrolysis charcoal. Compared with corn straw charcoal, there are obvious particles on the surface of corn straw-agricultural film co-pyrolysis charcoal, which are volatiles and condensates such as tar in the pyrolysis process of plastics, among which CB5% is the most obvious. CB5% contains a high proportion of agricultural film. During pyrolysis, the molten plastic wraps the surface of biochar, blocking the porous structure of biochar, resulting in a small number of pores and a small pore structure of CB5%. In the co-pyrolysis charcoal with a low proportion of agricultural film added, KCl in the biomass will catalyze the pyrolysis of plastic charcoal during the co-pyrolysis process, aggravating the fragmentation of plastic. This synergistic effect leads to an increase in the specific surface area and total pore volume of CB1% and CB2.5%, further affecting the adsorption performance of biochar. The EDS spectrum shows that the surface of biochar is composed of C and O, in addition to elements such as Na, Si, Ca, K, and Cl.

[0077] 3. Determination of surface functional groups of biochar from corn straw-agricultural film co-pyrolysis

[0078] Fourier transform infrared spectroscopy (FTIR) was used for characterization (Thermo Scientific Nicolet iS20).

[0079] Experimental results: Figure 3 Compared with CB0, the peaks of CB1% and CB5% are enhanced, which may be due to the influence of the "carbon chain" structure in the plastic. 1400-1440cm -1 The vibration peak corresponds to the stretching vibration of the carboxyl salt (-COO), 1100cm -1 The vibration peaks of COC at 2922cm and 2922cm correspond to the vibration peaks of COC. Compared with corn straw charcoal, the peaks of corn straw-agricultural film co-pyrolysis charcoal at these two locations are enhanced, proving that the co-pyrolysis charcoal contains more carboxyl, ether and phenol. This may be because the encapsulation of plastics during the pyrolysis process inhibits the release of macromolecular substances and retains oxygen-containing functional groups. In addition, the peaks at 2922cm -1 、857cm -1 、408~607cm -1 The stretching vibration peaks at come from CH, CC and Si-O / Al-O respectively.

[0080] 4. Characterization of minerals in biochar from co-pyrolysis of corn straw and agricultural film

[0081] X-ray diffractometer (XRD) was used for characterization (Rigaku MiniFlex600).

[0082] Experimental results: Figure 4 In addition to KCl, the main components of corn straw charcoal and corn straw-agricultural film co-pyrolysis charcoal are SiO 2,Compared with the diffraction peaks of CB0, the number of diffraction peaks of CB5% is less, indicating that the co-pyrolysis char of straw and agricultural film with a high proportion of agricultural film addition will affect the mineral composition of biomass char.

[0083] Experimental Example 2

[0084] The soil used in the potted experiment was collected from the surface soil (0-15 cm) samples in the rice fields of Tongling County, Anhui Province (30°58′58″N, 118°4′11″E). The soil was contaminated with heavy metals lead and cadmium due to industrial emissions. After collection, the soil was naturally air-dried, and the plant residues, stones and other debris were picked out. It was smashed into pieces with a wooden hammer, crushed and passed through a 10-mesh nylon mesh sieve for potted experiments. Another part of the soil was taken, ground with an agate mortar, and passed through 20-mesh and 100-mesh nylon mesh sieves respectively, and stored in a ziplock bag for soil analysis. The basic physical and chemical properties of the soil are as follows: pH, 5.73; organic matter, 28.50 g·kg -1 ; Total nitrogen, 1.70 g kg -1 ; Total phosphorus, 0.31 g·kg -1 ; Total potassium, 11.95 g·kg -1 ; Available phosphorus, 25.19 mg kg -1 ; Fast-acting potassium, 110.33 mg kg -1 ; The element contents of iron, manganese, lead, cadmium, copper and zinc are 16.36 g·kg -1 , 272.77mg·kg -1 , 180mg·kg -1 , 1.79mg·kg -1 , 20.77mg·kg -1 and 142.57 mg kg -1 .

[0085] The pot experiment was conducted in the greenhouse of Baima Base of Nanjing Agricultural University. The experimental settings included: (1) control without biochar (CK), (2) corn straw char treatment (CB0), (3) corn straw pyrolysis char treatment with 1% agricultural film (CB1%), (4) corn straw pyrolysis char treatment with 2.5% agricultural film (CB2.5%), and (5) corn straw pyrolysis char treatment with 5% agricultural film (CB5%), a total of five treatments, each with 3 replicates, and the amount of biochar added was 1%.

[0086] The potted test used a plastic pot with a height of 20 cm and a diameter of 25 cm, with a drainage hole at the bottom of the plastic pot and a base. 2 kg of air-dried soil passing through a 10-mesh nylon mesh was added to the CK treatment, and 1.98 kg of air-dried soil passing through a 10-mesh nylon mesh and 20 g of biochar were fully mixed and added to the plastic pot in the other four treatments. 0.65 g of urea, 0.44 g of diammonium phosphate, and 0.74 g of potassium sulfate were added to each pot, and no fertilizer was added later. After the above work was completed, water was watered to about 70% of the field water holding capacity, the temperature was maintained at 20-25 ° C, and the soil moisture was maintained stable by weighing within 5 days. Planting was carried out after the soil was stabilized. The planting crop of the present invention selected a common edible vegetable-non-heading cabbage, and the non-heading cabbage was sown after germination, and 10 seeds were sown per pot. Thinning was carried out when the non-heading cabbage grew the third true leaf, and the seedling spacing was controlled to be 3-4 cm, leaving 4 plants per pot. The non-heading cabbage seeds were sown on August 13, 2023 and harvested on September 25, 2023.

[0087] When the potted plants are harvested, the aboveground and underground parts of the non-heading cabbage are harvested separately, washed with tap water and then rinsed three times with ultrapure water, and the surface moisture of the plants is absorbed with absorbent paper. The aboveground parts of the non-heading cabbage are weighed, and the fresh weight of the aboveground parts of each pot of non-heading cabbage is recorded. Some aboveground leaves are randomly selected from each pot to determine the quality of the non-heading cabbage. The remaining aboveground and underground parts of the non-heading cabbage are weighed and placed in an oven at 105°C for half an hour, then adjusted to 60°C and dried to constant weight, the dry weight is recorded and the moisture content is calculated, and the aboveground and underground parts of the dried non-heading cabbage are crushed and stored for subsequent index determination.

[0088] 1. Properties and nutrient content of potted soil under different corn straw-agricultural film co-pyrolysis biochars

[0089] After removing the plant debris and roots, take about 200g of fresh soil from the pot. The collected fresh soil was divided into two parts by quartering. One part was stored in a refrigerator at 4℃ and the soil microbial biomass was measured within one week. The other part was naturally air-dried, ground with an agate mortar, passed through 20-mesh and 100-mesh nylon sieves, and stored in a sealed bag for subsequent index determination.

[0090] 12.5 g of fresh soil sample was taken and fumigated in a vacuum dryer with or without chloroform for 24 h, and then condensed with K 2 SO 4 Extract, centrifuge and filter, and then use a carbon and nitrogen analyzer (multiN / C3100, Jena, Germany) to measure the concentration of soil microbial biomass C and N. Mix the soil and water in a ratio of 1:2.5 (m / v), and use a pH meter (Shanghai Leici PHB-5 portable pH meter) to measure the soil pH within 2 hours. 2 Cr2 O 7 The content of organic matter in soil was determined by oxidation method. 3 The available phosphorus content was determined by leaching-molybdenum antimony colorimetry. The available potassium content was determined by NH 4 OAc extraction-flame photometer method.

[0091] Experimental results: as shown in Table 3.

[0092] Table 3 Effects of applying different biochars on soil physical and chemical properties

[0093]

[0094] Note: The test value is mean ± standard deviation (n = 3), different letters indicate significant differences between treatments p < 0.05

[0095] As shown in Table 3, the pH of each treated soil increased significantly after the application of biochar. Biochar treatment significantly increased the organic matter content of the soil. The organic matter content in the soil was CB2.5%>CB5%>CB0>CB1%. Corn straw-agricultural film co-pyrolysis carbon significantly increased the organic matter level of the soil. Observation of the nutrient content in the soil showed that corn straw-agricultural film co-pyrolysis carbon had no significant effect on the improvement of soil total nitrogen, and CB0, CB1%, and CB2.5% had no significant effect on the soil available phosphorus content. Biochar treatment significantly increased the available potassium content of the soil, proving that biochar is rich in available potassium, which is consistent with the results of the basic physical and chemical properties of biochar. Corn straw-agricultural film co-pyrolysis carbon treatment had no significant effect on the soil microbial carbon content, but significantly increased the soil microbial nitrogen content. Compared with CK, CB2.5% had the most significant effect on the improvement of soil microbial nitrogen content, reaching 195.2%.

[0096] 2. Yield, quality and nutrient absorption of non-heading cabbage under different corn straw-agricultural film co-pyrolysis biochars

[0097] Determination of total N, P, and K: The dried plant samples were 2 SO 4 -H 2 O 2After digestion, the total nitrogen content in the plants was determined using a fully automatic Kjeldahl nitrogen analyzer (KDN-1, Leici Co., Shanghai, China). The total K content was determined using a flame photometer (FP6410, Shanghai analyzer electricity co., ltd). The total P content was determined using an ultraviolet spectrophotometer (A360 spectrophotometer, Beijing Puxi General Instrument Co., Ltd.) after colorimetry using the vanadium molybdenum yellow colorimetry. The biomass of the aboveground part of non-heading cabbage was multiplied by its nutrient content to obtain the nutrient absorption of the aboveground part of non-heading cabbage.

[0098] Quality determination: The soluble sugar content of non-heading cabbage was determined by anthrone colorimetry. The vitamin C content was determined by 2,6-dichlorophenol indophenol titration. The soluble protein was determined by Coomassie brilliant blue colorimetry.

[0099] Experimental results: as shown in Table 4 and Table 5.

[0100] Table 4 Effects of applying different biochars on the yield and quality of non-heading cabbage

[0101]

[0102] Note: The test values ​​are mean ± standard deviation (n = 3), and different letters indicate significant differences between treatments, p < 0.05.

[0103] As shown in Table 4, biochar treatment significantly increased the biomass of non-heading cabbage, and there was no significant difference in the biomass enhancement effect (40.0% to 50.0%) between CB0 and CB1%, CB2.5% and CB5%. Partial co-pyrolysis charcoal significantly improved the quality of non-heading cabbage, and CB5% increased the vitamin C content of non-heading cabbage by 6.5%.

[0104] Table 5 Effects of applying different biochars on nutrient content and nutrient absorption of non-heading cabbage

[0105]

[0106] As shown in Table 5, biochar treatment significantly increased the N and K contents of non-heading cabbage. The N content of non-heading cabbage under different treatments: CB1%>CB0>CB2.5%>CB5%, which significantly increased the N content of non-heading cabbage by 37.5%, 30.3%, 30.1%, and 27.8% compared with CK, respectively. The K content of non-heading cabbage under different treatments: CB2.5%>CB1%>CB5%>CB0, which significantly increased the K content of non-heading cabbage by 23.3%, 23.0%, 20.4%, and 6.17% compared with CK, respectively. There was no significant difference in the effect of CB0, CB1%, CB2.5%, and CB5% on the absorption of N and K in non-heading cabbage.

[0107] 3. Heavy metal content and effectiveness of potted soil under different corn straw-agricultural film co-pyrolysis biochar

[0108] The air-dried soil was treated with HCl-HNO 3 After digestion, the total content of Pb and Cd in the soil was determined using ICP-MS (Thermo Fisher Scientific, Inc., iCAPQ, USA). To evaluate the effective components of Pb and Cd in the soil, 0.01 M CaCl 2 5 g of air-dried soil was extracted with DTPA solution, and the concentrations of available Pb and Cd in the extract were determined by ICP-MS.

[0109] Experimental results: as shown in Table 6.

[0110] Table 6 Effects of applying different biochars on the total heavy metal content in soil

[0111]

[0112]

[0113] Note: The test values ​​are mean ± standard deviation (n = 3), and different letters indicate significant differences between treatments, p < 0.05.

[0114] The comparison showed that CB0 and CB1% treatments significantly reduced soil Fe content, and CB1% treatment soil Zn content was 4.8% lower than CK. CB0 and CB1% significantly reduced soil Pb content, among which CB1% had the most significant passivation effect on the total amount of Pb in the soil, reaching 8.0%. The application of biochar significantly reduced the Cd content in the soil.

[0115] Figure 5 and Figure 6 Soil CaCl under different biochar treatments 2 The contents of Pb and Cd in the extractable and DTPA-extractable states showed that biochar treatment significantly reduced soil CaCl2 Content of extractable Pb and Cd. Soil CaCl 2 The extractable Pb content CB1%=CB5%<CB2.5%<CB0, which makes the soil CaCl 2 The extractable Pb content was reduced by 64.9%, 64.9%, 62.2% and 50.0% compared with CK. 2 The content of Cd in the leached state is CB1%<CB2.5%<CB5%<CB0, which makes the soil CaCl 2 The extractable Cd content was reduced by 30.9%, 27.5%, 21.7% and 12.9% compared with CK. Comparison of the content of DTPA-extractable Pb and Cd in soils treated with different methods showed that CB0, CB1% and CB2.5% significantly reduced the content of DTPA-extractable Pb in soils, and the DTPA-extractable Pb content in soils treated with CB2.5% was reduced by 18.7% compared with CK.

[0116] 4. Contents of heavy metals and polycyclic aromatic hydrocarbons in non-heading cabbage under different corn straw-agricultural film co-pyrolysis biochars

[0117] Determination of heavy metal content: dried plant samples were subjected to HNO 3 -HClO 4 After digestion, the contents of Pb and Cd were determined using ICP-MS (ThermoFisher Scientific, Inc., iCAPQ, USA). The calculation methods for the enrichment coefficient and transport coefficient of non-heading cabbage for heavy metals are shown in Equation 4 and Equation 5, respectively:

[0118]

[0119] Experimental results: as shown in Tables 7 and 8.

[0120] Table 7 Effects of applying different biochars on the contents of Pb and Cd in the aboveground and underground parts of non-heading cabbage

[0121]

[0122] Note: The test values ​​are mean ± standard deviation (n = 3), and different letters indicate significant differences between treatments, p < 0.05.

[0123] As shown in Table 7, the co-pyrolysis char treatment significantly reduced the content of Pb and Cd in the aboveground part of non-heading cabbage. Compared with CK, CB1%, CB2.5%, and CB5% reduced the content of Pb in the aboveground part of non-heading cabbage by 42.0%, 47.1%, and 53.6%, respectively. The Cd content in the aboveground part of non-heading cabbage under different biochar treatments was reduced by 25.2% to 37.8% compared with CK, and the difference was not significant. The application of biochar significantly reduced the content of Pb and Cd in the underground part of non-heading cabbage. The co-pyrolysis char of corn straw and agricultural film reduced the content of Pb in the underground part of non-heading cabbage by 49.3% to 58.3%, and the corn straw char reduced the content of Pb in the underground part of non-heading cabbage by 30.4%, indicating that the addition of agricultural film in corn straw to prepare biochar is helpful to reduce the content of Pb in the underground part of non-heading cabbage. Compared with CK, the Cd content in the underground part of non-heading cabbage was reduced by 29.2%, 24.2%, 36.7% and 25.0% in the CB0, CB1%, CB2.5% and CB5% treatments, respectively.

[0124] Table 8 Effects of different biochar applications on the enrichment and transport coefficients of Pb and Cd in non-heading cabbage

[0125]

[0126]

[0127] As shown in Table 8, the co-pyrolysis char treatment significantly reduced the enrichment coefficients of Pb and Cd in the aboveground and underground parts of non-heading cabbage. Corn straw-agricultural film co-pyrolysis char reduced the Pb enrichment coefficient of the aboveground part of non-heading cabbage by 37.3% to 55.4%, while corn straw char had no significant effect on the Pb enrichment coefficient of the aboveground part of non-heading cabbage. The enrichment coefficient of Pb in the underground part of non-heading cabbage: CB5%<CB2.5%<CB1%<CB0, indicating that the inhibitory ability of biomass charcoal on the enrichment of Pb in the underground part of non-heading cabbage: corn straw-agricultural film co-pyrolysis charcoal>corn straw charcoal. Compared with CK, there was no significant difference in the inhibitory effect of corn straw-agricultural film co-pyrolysis charcoal on the enrichment of Cd in the aboveground part of non-heading cabbage. The CB0, CB1%, CB2.5%, and CB5% treatments reduced the Cd enrichment coefficient in the underground part of non-heading cabbage by 19.7%, 11.0%, 30.8%, and 20.5% respectively compared with CK. Biochar treatment had no significant effect on the Pb transport coefficient of non-heading cabbage, while CB1% and CB5% significantly reduced the Cd transport coefficient of non-heading cabbage.

[0128] It can be seen from the above embodiments and experimental examples that the corn straw-agricultural film co-pyrolysis biomass charcoal prepared by the present invention can improve the physical and chemical properties, fertility and microbial environment of the soil, increase the yield quality of crops, reduce the effective heavy metals in the soil, inhibit the enrichment of heavy metals in the soil by crops, and reduce the absorption of heavy metals in contaminated soil by crops. It can be used as a soil conditioner and soil heavy metal passivator to improve the health of the soil-crop system.

[0129] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing corn straw-agricultural film co-pyrolysis biochar, characterized in that: The following steps are involved: Corn straw and agricultural film are mixed and crushed in a mass ratio of 10:(0.1-0.5) and then co-pyrolyzed to obtain corn straw-agricultural film co-pyrolysis biomass charcoal.

2. The preparation method according to claim 1, characterized in that: The co-pyrolysis temperature is 400-600° C., and the co-pyrolysis time is 1-3 hours.

3. The preparation method according to claim 1 or 2, characterized in that: The heating rate of the co-pyrolysis is 3-7°C / min.

4. The preparation method according to claim 1, characterized in that: The crushing is to 3-5 cm.

5. The corn straw-agricultural film co-pyrolysis biochar prepared by the preparation method according to any one of claims 1 to 4, characterized in that: The specific surface area of ​​the corn straw-agricultural film co-pyrolysis biomass charcoal is 1.91 to 2.39 m 2 ·g -1 The average pore size is 10.86-12.37 nm, and the total pore volume is 0.05-0.08 cm 3 ·g -1 .

6. The use of the corn straw-agricultural film co-pyrolysis biochar as claimed in claim 5 as a soil conditioner in promoting crop growth and improving crop quality.

7. The use according to claim 6, characterized in that: The crop is non-heading cabbage.

8. The use according to claim 7, characterized in that: The corn straw-agricultural film co-pyrolysis biochar was mixed with soil to plant non-heading cabbage.

9. The use of the corn straw-agricultural film co-pyrolysis biochar as claimed in claim 5 as a soil heavy metal passivator in improving the health of the soil-crop system.

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