Preparation method and application of eucalyptus man-made forest waste biochar

Abstract

The invention provides a preparation method of eucalyptus man-made forest waste biochar, which comprises the following steps: collecting eucalyptus man-made forest waste, removing soil and impurities on the surface of the eucalyptus man-made forest waste, cleaning with water, naturally airing for 8 hours, drying at 60-80 DEG C until the water content is 15%, and crushing to obtain crushed eucalyptus man-made forest waste; and heating to 300-700 DEG C at a heating rate of 20 DEG C / min in the presence of nitrogen or argon, carrying out constant-temperature carbonization for 2-4 hours, cooling to room temperature, crushing, and screening with a 100-mesh sieve to obtain the eucalyptus artificial forest waste biochar. The eucalyptus man-made forest waste biochar prepared by the invention can be used as a soil conditioner for practical application, can effectively relieve soil acidification of the eucalyptus man-made forest, improve soil fertility and reduce the risk of heavy metal cadmium, lead and arsenic pollution of the soil, has a good removal effect on pesticides paraquat, glyphosate and thiophanate methyl, and has a good application prospect. The yield and the quality of the pakchoi in the heavy metal contaminated soil are improved, and good application prospects are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of eucalyptus plantation waste treatment, and specifically relates to a preparation method of eucalyptus plantation waste biochar and application thereof. Background Art

[0002] Biochar is a carbon-rich solid substance produced by pyrolysis of biomass materials in an oxygen-free environment. It has strong adsorption properties and high thermal stability. It has a certain repair effect on soil fertility, soil heavy metal pollution and residual pesticides. The potential environmental benefits of biochar have attracted widespread attention. So far, research on biochar has mostly focused on agricultural straw, feces and sludge wastes such as wheat, corn and rice, while the preparation of biochar from woody forestry waste raw materials, its method system and biochar properties are quite different.

[0003] Eucalyptus is one of the three fastest-growing tree species in the world, and my country's eucalyptus plantation area ranks second in the world. Eucalyptus plantations are mostly managed in a short cycle of 4 to 5 years. During the management of eucalyptus plantations, a large amount of forestry waste is generated, mainly branches and bark. Most of them are removed from the forest and burned in the open air, which greatly affects the nutrient balance of the forest soil. The added value of direct burning is low, which is easy to cause environmental pollution and waste of resources, and is not conducive to the sustainable development of eucalyptus plantations. Therefore, exploring resource utilization methods for eucalyptus plantation waste branches and bark with high added value and environmental friendliness is an urgent problem that technicians in this field need to solve. Turning eucalyptus plantation waste into biochar is expected to create more economic value while solving the problem of forestry waste disposal.

[0004] At present, in the prior art, there has been no report on the research and development of preparing biochar using a mixture of eucalyptus plantation waste branches and bark as raw materials and its application potential. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing biochar from eucalyptus plantation waste and its application in view of the deficiencies of the above-mentioned prior art. The biochar from eucalyptus plantation waste prepared by the present invention can be used as a soil conditioner for practical application, can effectively alleviate soil acidification and improve soil fertility in eucalyptus plantation, reduce the risk of soil heavy metal cadmium, lead and arsenic pollution, has good removal effect on the pesticides paraquat, glyphosate and methyl thiophanate, improves the yield and quality of Chinese cabbage in heavy metal contaminated soil, can be effectively applied in the fields of agriculture, forestry and environment, is suitable for large-scale production and promotion, and has good application prospects.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing biochar from eucalyptus plantation waste, the method comprising:

[0007] S1. Collect eucalyptus plantation waste, remove soil and impurities on the surface, wash with water, dry naturally for 8 hours, and then dry at a temperature of 60° C. to 80° C. until the moisture content is 15%, and then crush to obtain crushed eucalyptus plantation waste;

[0008] S2. The crushed eucalyptus plantation waste obtained in S1 is heated to 300°C-700°C at a heating rate of 20°C / min under a nitrogen or argon atmosphere, carbonized at a constant temperature for 2h-4h, then cooled to room temperature, crushed, and passed through a 100-mesh sieve to obtain eucalyptus plantation waste biochar.

[0009] Preferably, the eucalyptus plantation waste in S1 is leafy branches and bark.

[0010] Preferably, the mass ratio of the leafy branches to the bark is 3:1.

[0011] Preferably, the gas flow rate of the nitrogen or argon in S2 is 200 mL / min.

[0012] The present invention also provides the use of the eucalyptus plantation waste biochar prepared by the above-mentioned preparation method, wherein the eucalyptus plantation waste biochar is used for returning the eucalyptus plantation to the field and for improving the soil.

[0013] The present invention also provides the use of the eucalyptus plantation waste biochar prepared by the above-mentioned preparation method, wherein the eucalyptus plantation waste biochar is used for ecological restoration of soil contaminated by heavy metals cadmium, lead and / or arsenic.

[0014] Preferably, the eucalyptus plantation waste biochar is used to improve the yield and quality of Chinese cabbage in soil contaminated by heavy metal cadmium, lead and / or arsenic.

[0015] The present invention also provides the use of the eucalyptus plantation waste biochar prepared by the above-mentioned preparation method, wherein the eucalyptus plantation waste biochar is used to remove paraquat, glyphosate and / or thiophanate-methyl in the soil.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. The present invention selects for the first time a mixture of eucalyptus plantation waste with leaves, branches and bark as the raw material for biochar preparation. The mixture is abundant in quantity, low in price and extremely easy to obtain, and the preparation method is simple, which reduces the cost of biochar preparation, turns waste into treasure, and effectively solves the problem of insufficient resource utilization of eucalyptus plantation waste in the prior art, reduces the pollution to the environment caused by burning or discarding of eucalyptus plantation waste, and is beneficial to environmental protection. The present invention can realize on-site carbonization of eucalyptus plantation waste, avoiding the problem of raw material storage and transportation that is difficult to overcome in large-scale centralized treatment.

[0018] 2. The biochar prepared by the present invention has a high yield, a high pH value, a large specific surface area, a high cation exchange capacity, and the heavy metal elements chromium, lead, arsenic and cadmium are not exceeded, and mercury is not detected, which has the advantages of environmental friendliness and sustainable development; the mineral elements are of various types and rich in content, and returning them to the fields on the spot is an effective compensation measure for the lack of soil nutrients caused by the removal of forestry waste. It can be used as a soil conditioner to improve soil fertility and effectively alleviate soil acidification, and has good prospects for large-scale application and promotion.

[0019] 3. The biochar prepared by the present invention has rich surface functional groups and strong adsorption properties. It can be used as an environmental remediation material, can reduce the risk of soil heavy metal cadmium, lead and arsenic pollution, has a good removal effect on the pesticides paraquat, glyphosate and methyl thiophanate, can increase the yield and quality of Chinese cabbage in heavy metal contaminated soil, and has good ecological, environmental and economic effects.

[0020] The present invention is further described in detail below in conjunction with embodiments. DETAILED DESCRIPTION

[0021] Example 1

[0022] The method for preparing biochar from eucalyptus plantation waste in this embodiment is as follows:

[0023] S1. Collect eucalyptus plantation waste, remove soil and impurities on the surface, wash with water, dry naturally for 8 hours, and then dry at 60° C. to a moisture content of 15%, and then crush to obtain crushed eucalyptus plantation waste;

[0024] The eucalyptus plantation waste is leaf branches and bark, and the mass ratio of the leaf branches to the bark is 3:1;

[0025] S2. Put the crushed eucalyptus plantation waste obtained in S1 into a movable carbonization furnace, heat it to 300°C at a heating rate of 20°C / min in an atmosphere of nitrogen with a gas flow rate of 200 mL / min, carbonize it at a constant temperature for 4 hours, then cool it to room temperature, crush it, and pass it through a 100-mesh sieve to obtain eucalyptus plantation waste biochar.

[0026] Analysis of biochar quality indicators: Accurately weigh the cooled biochar and calculate the yield of biochar; use nitrogen as the adsorption medium and use a specific surface area and porosity tester to determine the specific surface area and pore volume. The cation exchange capacity was determined by the ammonium acetate exchange method, and the pH value was determined by a Sartorius PP-20 pH meter. The number of surface acidic (alkaline) oxygen-containing functional groups was determined by the Boehm titration method. Ash content was determined using the charcoal test method (GB / T 17664-1999). The carbon, nitrogen and sulfur contents were determined using the German Elementar Vario EL III elemental analyzer. Total phosphorus was decomposed by sulfuric acid-hydrogen peroxide and determined by vanadium-molybdenum yellow colorimetry; available phosphorus was extracted by sodium bicarbonate and molybdenum-antimony anti-colorimetry; total potassium was determined by flame photometry. The contents of calcium, magnesium, iron, copper, manganese, zinc, etc. were determined by inductively coupled plasma emission spectrometer (ICP, PE optima5300DV, USA).

[0027] The biochar yield of the eucalyptus plantation waste prepared in Example 1 was 63.57% and the specific surface area was 78.76 m 2 / g, average pore size 3.16nm, cation exchange capacity 43.48cmol / kg, ash content 23.42%, pH value 7.25, acidic functional group 1.04mmol / g, basic functional group 0.89mmol / g, total functional group 1.93mmol / g, total carbon content 61.79%, total nitrogen content 1.23%, total phosphorus content 3.47g / kg, total potassium content 23.77g / kg, total sulfur content 0.41%, effective phosphorus content 79.95mg / kg, calcium content 11.58mg / g, magnesium content 9.85mg / g, iron content 6.68mg / g, copper content 2.29mg / g, manganese content 1.17mg / g, zinc content 1.22mg / g. The heavy metal elements chromium are 4.01 mg / kg, lead content is 3.82 mg / kg, arsenic content is 1.99 mg / kg, cadmium content is 0.088 mg / kg, and mercury element is not detected.

[0028] Example 2

[0029] The method for preparing biochar from eucalyptus plantation waste in this embodiment is as follows:

[0030] S1. Collect eucalyptus plantation waste, remove soil and impurities on the surface, wash with water, dry naturally for 8 hours, and then dry at 70° C. to a moisture content of 15%, and then crush to obtain crushed eucalyptus plantation waste;

[0031] S2. Put the crushed eucalyptus plantation waste obtained in S1 into a movable carbonization furnace, heat it to 500°C at a heating rate of 20°C / min in an argon atmosphere with a gas flow rate of 200 mL / min, carbonize it at a constant temperature for 3 hours, then cool it to room temperature, crush it, and pass it through a 100-mesh sieve to obtain eucalyptus plantation waste biochar.

[0032] The biochar yield of eucalyptus plantation waste prepared in this example is 58.79%, and the specific surface area is 155.87m 2 / g, average pore size 4.98nm, cation exchange capacity 76.77cmol / kg, ash content 46.31%, pH value 9.87, acidic functional group 0.94mmol / g, basic functional group 1.58mmol / g, total functional group 2.52mmol / g, total carbon content 68.95%, total nitrogen content 1.87%, total phosphorus content 6.85g / kg, total potassium content 56.21g / kg, total sulfur content 0.89%, effective phosphorus content 176.87mg / kg, calcium content 25.98mg / g, magnesium content 19.97mg / g, iron content 17.17mg / g, copper content 5.16mg / g, manganese content 3.86mg / g, zinc content 3.89mg / g. The heavy metal elements chromium content was 5.08 mg / kg, lead content was 4.98 mg / kg, arsenic content was 2.13 mg / kg, cadmium content was 0.101 mg / kg, and mercury was not detected.

[0033] Example 3

[0034] The method for preparing biochar from eucalyptus plantation waste in this embodiment is as follows:

[0035] S1. Collect eucalyptus plantation waste, remove soil and impurities on the surface, wash with water, dry naturally for 8 hours, and then dry at 80° C. to a moisture content of 15%, and then crush to obtain crushed eucalyptus plantation waste;

[0036] S2. Put the crushed eucalyptus plantation waste obtained in S1 into a movable carbonization furnace, heat it to 700°C at a heating rate of 20°C / min in an atmosphere of nitrogen with a gas flow rate of 200 mL / min, carbonize it at a constant temperature for 2 hours, then cool it to room temperature, crush it, and pass it through a 100-mesh sieve to obtain eucalyptus plantation waste biochar.

[0037] The yield of the eucalyptus plantation waste biochar prepared in this example is 42.23%, and the specific surface area is 114.66m 2 / g, average pore size 6.87nm, cation exchange capacity 75.44cmol / kg, ash content 48.75%, pH value 10.58, acidic functional group 0.65mmol / g, basic functional group 1.36mmol / g, total functional group 2.01mmol / g, total carbon content 72.11%, total nitrogen content 1.35%, total phosphorus content 5.91g / kg, total potassium content 52.14g / kg, total sulfur content 0.66%, effective phosphorus content 130.05mg / kg, calcium content 19.54mg / g, magnesium content 11.76mg / g, iron content 11.49mg / g, copper content 4.97mg / g, manganese content 4.19mg / g, zinc content 4.26mg / g. The heavy metal elements chromium content was 5.51 mg / kg, lead content was 5.09 mg / kg, arsenic content was 2.31 mg / kg, cadmium content was 0.109 mg / kg, and mercury was not detected.

[0038] The pH values ​​of the eucalyptus plantation waste biochars prepared in Examples 1-3 of the present invention are all alkaline; the biochars have a variety of mineral nutrient elements such as carbon, nitrogen, phosphorus, and potassium, and have high contents, which can be used as an external input source of soil nutrient elements; referring to the standard of "Biocal-based Organic Fertilizer" (NY / T3618-2020), the heavy metal elements chromium, lead, arsenic, and cadmium in the biochars are not exceeded, mercury is not detected, and the biochars are environmentally friendly without secondary pollution; the biochars have large specific surface area and cation exchange capacity, and are rich in surface functional groups, which can provide more adsorption sites for the removal of heavy metals and residual pesticides in contaminated soils. In particular, the physical properties, surface composition, and mineral element content of the biochars obtained at 500°C in Example 2 are relatively good in terms of comprehensive quality.

[0039] Example 4

[0040] Soil improvement effect 1: The eucalyptus plantation waste biochar prepared in Example 1 was returned to the field on site and applied to the 0-30 cm soil of the eucalyptus plantation at one time, with a mass ratio of 0% (control, no biochar), 1%, 2%, 4%, 6% and 8% to the dry weight of the soil, for a total of 6 treatments, 4 replicates per treatment, and fully mixed. The soil is acidic soil. The experimental method used for soil analysis in the example is a conventional method.

[0041] One year after application, compared with the control, the soil bulk density (BD, g / cm 3) decreased by 4.85% to 20.61%, soil pH increased by 0.11 to 0.9, natural water content (SWC, %) increased by 2.85% to 26.11%, soil organic carbon (SOC, g / kg) increased by 3.85% to 43.18%, total nitrogen (TN, g / kg) increased by 3.03% to 54.55%, total phosphorus (TP, g / kg) increased by 12.0% to 52.0%, total potassium (TK, g / kg) increased by 8.4% to 36.89%, available nitrogen (AN, mg / kg) increased by 3.28% to 22.85%, available phosphorus (AP, mg / kg) increased by 2.29% to 48.85%, and available potassium (AK, mg / kg) increased by 3.97% to 26.72%. Total calcium (TCa, mg / kg) increased by 0.54% to 39.86%, total magnesium (TMg, mg / kg) increased by 0.51% to 5.27%, total sodium (TNa, mg / kg) decreased by 2.23% to 19.50%, total aluminum (TAI, mg / kg) decreased by 1.57% to 17.67%, exchangeable calcium (EXCa, mg / kg) increased by 4.10% to 42.74%, exchangeable magnesium (EXMg, mg / kg) increased by 3.08% to 32.74%, exchangeable sodium (EXNa, mg / kg) decreased by 5.15% to 18.76%, exchangeable aluminum (EXAI, cmol / kg) decreased by 1.77% to 48.61%, exchangeable acid (EXAc, cmol / kg) decreased by 3.18% to 42.40%, and exchangeable hydrogen (EXHy, cmol / kg) decreased by 6.43% to 28.07%.

[0042] Table 1 Changes in physical and chemical properties of eucalyptus forest soil after one year of using biochar prepared from eucalyptus plantation waste in Example 1

[0043] deal with BD pH SWC SOC TN TP TK AN AP AK CK 1.65 5.34 18.92 5.72 0.66 0.25 4.88 56.14 1.31 30.76 T1 1.57 5.45 19.46 5.94 0.68 0.28 5.29 57.98 1.34 31.98 T2 1.48 5.81 20.75 6.75 0.71 0.31 5.78 61.42 1.39 34.47 T4 1.44 5.96 21.66 7.44 0.85 0.35 6.25 64.26 1.77 35.75 T6 1.36 6.11 22.78 8.19 1.02 0.38 6.68 68.97 1.95 38.98 T8 1.31 6.24 23.86 7.12 0.94 0.36 6.19 67.11 1.81 36.59 deal with TCa TMg TNa TAI EXCa EXMg EXNa EXAI EXAc EXY CK 2286.63 300.25 64.45 2887.48 2102.55 169.99 61.02 3.95 5.66 1.71 T1 2298.95 301.78 63.01 2842.11 2188.79 175.22 57.88 3.88 5.48 1.60 T2 2495.21 307.46 61.59 2755.62 2300.24 187.95 54.02 3.75 5.23 1.48 T4 2679.89 311.21 58.57 2612.55 2545.58 205.44 51.65 3.66 5.08 1.42 T6 2991.97 316.06 54.69 2482.65 2887.95 220.15 51.22 2.93 4.24 1.31 T8 3198.01 310.65 51.88 2377.24 3001.26 225.65 49.57 2.03 3.26 1.23

[0044] Example 5

[0045] Soil improvement effect 2: The eucalyptus plantation waste biochar prepared in Example 2 was returned to the field on site and applied to the 0-30 cm soil of the eucalyptus plantation at one time. The mass ratio to the dry weight of the soil was 0% (control, no biochar application), 1%, 2%, 4%, 6% and 8%, with a total of 6 treatments, 4 replicates per treatment, and fully mixed. The soil is acidic soil. After one year of application, compared with the control, based on the average value of the 0-30 cm soil layer, the soil bulk density (BD, g / cm 3) decreased by 8.48% to 26.06%, soil pH increased by 0.37 to 1.18, natural water content (SWC, %) increased by 10.94% to 32.98%, soil organic carbon (SOC, g / kg) increased by 26.05% to 79.9%, total nitrogen (TN, g / kg) increased by 24.24% to 106.06%, total phosphorus (TP, g / kg) increased by 28.0% to 108.0%, total potassium (TK, g / kg) increased by 25.20% to 86.68%, available nitrogen (AN, mg / kg) increased by 13.73% to 81.67%, available phosphorus (AP, mg / kg) increased by 7.63% to 74.05%, and available potassium (AK, mg / kg) increased by 13.07% to 51.33%. Total calcium (TCa, mg / kg) increased by 11.75% to 56.68%, total magnesium (TMg, mg / kg) increased by 2.21% to 15.43%, total sodium (TNa, mg / kg) decreased by 6.72% to 30.16%, total aluminum (TAI, mg / kg) decreased by 6.49% to 30.63%, exchangeable calcium (EXCa, mg / kg) increased by 9.91% to 60.14%, exchangeable magnesium (EXMg, mg / kg) increased by 12.43% to 47.74%, exchangeable sodium (EXNa, mg / kg) decreased by 7.29% to 30.73%, exchangeable aluminum (EXAI, cmol / kg) decreased by 6.33% to 68.86%, exchangeable acid (EXAc, cmol / kg) decreased by 7.77% to 60.07%, and exchangeable hydrogen (EXHy, cmol / kg) decreased by 11.11% to 39.77%.

[0046] Table 2 Changes in physical and chemical properties of eucalyptus plantation soil after one year of application of eucalyptus plantation waste biochar prepared in Example 2

[0047] deal with BD pH SWC SOC TN TP TK AN AP AK CK 1.65 5.34 18.92 5.72 0.66 0.25 4.88 56.14 1.31 30.76 T1 1.51 5.71 20.99 7.21 0.82 0.32 6.11 63.85 1.41 34.78 T2 1.45 6.01 22.12 7.53 0.98 0.41 7.22 71.88 1.52 40.66 T4 1.35 6.29 23.98 9.77 1.19 0.46 8.04 90.85 2.19 43.89 T6 1.24 6.48 24.79 10.29 1.36 0.52 9.11 101.99 2.28 46.55 T8 1.22 6.52 25.16 9.89 1.25 0.48 8.59 100.02 2.14 42.74 deal with TCa TMg TNa TAI EXCa EXMg EXNa EXAI EXAc EXY CK 2286.63 300.25 64.45 2887.48 2102.55 169.99 61.02 3.95 5.66 1.71 T1 2555.26 306.88 60.12 2700.11 2311.01 191.12 56.57 3.70 5.22 1.52 T2 2671.22 320.06 57.89 2586.02 2514.25 208.88 51.89 3.44 4.85 1.41 T4 3091.36 332.54 54.26 2402.15 2922.74 221.26 49.55 2.40 3.65 1.25 T6 3582.58 346.59 51.22 2109.44 3242.48 251.15 45.62 1.23 2.44 1.21 T8 3469.98 332.12 45.01 2002.98 3366.97 248.75 42.27 1.23 2.26 1.03

[0048] Example 6

[0049] Soil improvement effect 3: The eucalyptus plantation waste biochar prepared in Example 3 was returned to the field on site and applied to the 0-30 cm soil of the eucalyptus plantation at one time. The mass ratio to the dry weight of the soil was 0% (control, no biochar application), 1%, 2%, 4%, 6% and 8%, for a total of 6 treatments, 4 replicates per treatment, and fully mixed. The soil is acidic soil. After one year of application, compared with the control, based on the average value of the 0-30 cm soil layer, the soil bulk density (BD, g / cm 3) decreased by 10.30% to 28.48%, soil pH increased by 0.44 to 1.27, natural water content (SWC, %) increased by 11.79% to 34.99%, soil organic carbon (SOC, g / kg) increased by 22.55% to 75.0%, total nitrogen (TN, g / kg) increased by 7.58% to 68.18%, total phosphorus (TP, g / kg) increased by 20.0% to 80.0%, total potassium (TK, g / kg) increased by 21.72% to 59.63%, available nitrogen (AN, mg / kg) increased by 6.91% to 59.49%, available phosphorus (AP, mg / kg) increased by 5.34% to 62.6%, and available potassium (AK, mg / kg) increased by 6.18% to 36.02%. Total calcium (TCa, mg / kg) increased by 5.60% to 46.50%, total magnesium (TMg, mg / kg) increased by 1.44% to 7.86%, total sodium (TNa, mg / kg) decreased by 3.63% to 19.08%, total aluminum (TAI, mg / kg) decreased by 5.07% to 27.24%, exchangeable calcium (EXCa, mg / kg) increased by 6.07% to 55.36%, exchangeable magnesium (EXMg, mg / kg) increased by 9.55% to 38.38%, exchangeable sodium (EXNa, mg / kg) decreased by 9.44% to 32.78%, exchangeable aluminum (EXAI, cmol / kg) decreased by 2.03% to 48.61%, exchangeable acid (EXAc, cmol / kg) decreased by 4.06% to 44.35%, and exchangeable hydrogen (EXHy, cmol / kg) decreased by 8.77% to 34.50%.

[0050] Table 3 Changes in physical and chemical properties of eucalyptus plantation soil after one year of application of eucalyptus plantation waste biochar prepared in Example 3

[0051]

[0052]

[0053] It can be seen from the above Examples 4 to 6 that the eucalyptus plantation waste biochar prepared in Examples 1-3 increases the soil nutrient content, can increase the soil organic carbon, total nitrogen and total phosphorus content, increase the soil pH value and the content of mineral elements such as calcium and magnesium, while reducing the content of sodium, aluminum, exchangeable acid and exchangeable hydrogen, effectively alleviating soil acidification, and showing a high soil improvement effect. Among them, the eucalyptus plantation waste biochar prepared in Example 2 has the best comprehensive performance, and 6% is the optimal application amount.

[0054] Example 7

[0055] Remediation effect of soil contaminated by heavy metals cadmium (Cd), lead (Pb) and arsenic (As): An experiment on potted pakchoi contaminated with heavy metals of cadmium, lead and arsenic at a concentration of 500 mg / kg was set up. Biochar 1, biochar 2 and biochar 3 prepared from eucalyptus plantation waste prepared in Examples 1 to 3 were applied to soil contaminated by heavy metals cadmium, lead and arsenic, respectively. The mass ratio of biochar from eucalyptus plantation waste to the dry weight of potted soil was 5%. No biochar was used as the control (CK). There were 4 treatments, 5 repetitions per treatment, and a total of 60 pots. The remediation effect on the total amount of cadmium, lead and arsenic in the soil. Table 4 shows the changes in the content of cadmium, lead and arsenic in the planted pakchoi in the potted soil contaminated by heavy metals of cadmium, lead and arsenic at a concentration of 500 mg / kg. Compared with the control, the application of eucalyptus plantation waste biochar 1 (Example 1), biochar 2 (Example 2) and biochar 3 (Example 3) significantly reduced the concentrations of heavy metal cadmium, lead and arsenic in Chinese cabbage. The cadmium in the aboveground part of Chinese cabbage decreased by 69.01% to 78.91%, and the cadmium in the underground part decreased by 86.62% to 92.67%; the lead in the aboveground part of Chinese cabbage decreased by 67.22% to 77.45%, and the lead in the underground part decreased by 83.78% to 90.90%; the arsenic in the aboveground part of Chinese cabbage decreased by 68.97% to 73.13%, and the arsenic in the underground part decreased by 89.01% to 90.86%.

[0056] Table 4 Effect of biochar on heavy metal content in Chinese cabbage (mg / kg)

[0057]

[0058]

[0059] Note: The letters in Table 4 indicate significant differences at the P<0.05 level, the same as in the following tables.

[0060] Remediation effect on the effective state of soil cadmium, lead and arsenic. As shown in Table 5, compared with the control, after the application of biochar, the content of effective cadmium, effective lead and effective arsenic in the soil decreased to varying degrees, with a decrease of 41.14% to 70.13%, 42.96% to 72.51%, and 45.11% to 72.26% (P < 0.05). This shows that biochar from eucalyptus plantation waste can significantly reduce the absorbability of pakchoi to the total amount and effective state content of heavy metal cadmium, lead and arsenic in the soil, has good soil heavy metal pollution remediation function, and is suitable for the ecological remediation of cadmium, lead and arsenic contaminated soil.

[0061] Table 5 Effects of biochar on soil available cadmium, available lead and available arsenic contents (mg / kg)

[0062] Cabbage potting soil Comparison Biochar 1 Biochar 2 Biochar 3 Effective cadmium content 6.83a 4.02b 2.04c 2.22c Effective lead content 7.24a 4.13b 1.99c 2.15c Available arsenic content 5.01a 2.75b 1.39c 1.50c

[0063] Effects on the growth and quality of pakchoi. Table 6 shows the changes in fresh biomass of pakchoi planted in potted soil contaminated with heavy metals of cadmium, lead and arsenic at a concentration of 500 mg / kg after one growing season. No biochar was applied as the control (CK), 4 treatments, 5 replicates per treatment, and a total of 60 pots. Compared with the control, the fresh weight of pakchoi in heavy metal contaminated soil increased after the application of eucalyptus plantation waste biochar 1, biochar 2 and biochar 3 (P < 0.05). The increases in the aboveground plant biomass of pakchoi were 55.16% to 101.11%, 70.41% to 118.71%, and 61.92% to 108.27%, respectively, and the increases in the underground plant biomass were 32.21% to 76.31%, 53.80% to 97.53%, and 39.08% to 83.92%, respectively. The results showed that the application of biochar from eucalyptus plantation waste significantly promoted the growth of pakchoi in soil contaminated by heavy metals such as cadmium, lead and arsenic, and the relative order of the promoting effect was biochar 2 > biochar 3 > biochar 1 (P < 0.05).

[0064] Table 6 Effects of biochar on aboveground biomass (fresh weight) of Chinese cabbage

[0065] Plant biomass (g / pot) Comparison Biochar 1 Biochar 2 Biochar 3 Cadmium contamination of the aboveground parts of Chinese cabbage 35.28d 54.74c 70.95a 63.87b Cadmium contamination of the underground parts of Chinese cabbage 10.09c 13.34b 17.79a 15.86a Lead contamination of the underground part of Chinese cabbage 35.22d 60.02c 77.03a 66.03b Lead contamination of the underground part of Chinese cabbage 10.13d 15.58c 20.01a 17.54b Arsenic contamination of the underground parts of Chinese cabbage 35.19d 56.98c 73.29a 64.24b Arsenic contamination of the underground parts of Chinese cabbage 10.26d 14.27c 18.87a 16.59b

[0066] As shown in Table 7, compared with the control, the application of biochar from eucalyptus plantation waste increased the vitamin C, soluble protein, soluble sugar and crude fiber contents of Chinese cabbage by 24.50%-37.48%, 36.20%-64.21%, 56.85%-102.03% and 31.48%-62.96%, respectively; and significantly reduced the nitrate content (P < 0.05), with a decrease of 30.52%-43.69%. As can be seen from Table 8, the application of eucalyptus plantation waste significantly increased the activities of nitrate reductase, peroxidase, catalase and superoxide dismutase in pakchoi, with increases of 16.82% to 62.96%, 4.50% to 32.62%, 58.33% to 120.83%, and 27.66% to 114.82%, respectively, and malondialdehyde decreased by 61.99% to 70.18%, indicating that eucalyptus plantation waste biochar has a positive effect on improving the quality of pakchoi in soil contaminated by heavy metal cadmium. The eucalyptus waste biochar prepared at 500°C in Example 2 has a better effect.

[0067] Table 7 Effects of biochar on quality indicators of Chinese cabbage

[0068] index Comparison Biochar 1 Biochar 2 Biochar 3 Vitamin C (mg / kg) 211.26d 263.02c 290.44a 278.89b Soluble protein (mg / g) 7.32d 9.97c 12.02a 10.11b Soluble sugar (%) 9.34c 14.65b 18.87a 16.27b Crude fiber (%) 0.54c 0.71b 0.84a 0.88a Nitrate (μg / g) 2306.54a 1602.65b 1311.24c 1298.78d

[0069] Table 8 Effects of biochar on enzyme activities in pakchoi

[0070] index Comparison Biochar 1 Biochar 2 Biochar 3 Nitrate reductase (μg / g·h) 6.48d 7.57c 10.56a 9.35b Peroxidase (U / mg) 2985.79c 3120.22c 3959.88a 3652.08b Superoxide dismutase (U / mg) 168.59d 215.22c 362.17a 284.24b Catalase (U / mg) 0.23c 0.38 0.49a 0.53a Malondialdehyde (umol / g) 1.71a 0.65b 0.54c 0.51c

[0071] Example 8

[0072] Effect of pesticide removal: The eucalyptus plantation waste biochar 1, biochar 2 and biochar 3 prepared in Examples 1 to 3 were mixed with a certain concentration of paraquat, glyphosate and thiophanate-methyl aqueous solution at a solid-liquid ratio of 5%, respectively, and no biochar was used as the control (CK). There were 4 treatments, 5 repetitions per treatment, and a total of 60 experimental tubes. Under light-proof conditions, the adsorption experiment was carried out at a constant temperature of 30°C for 24 hours, and the speed of the shaker was 150rpm. The results showed that the removal rates of paraquat were 89.46%, 93.86% and 91.49% respectively; the removal rates of glyphosate were 90.10%, 95.48% and 92.51% respectively; and the removal rates of thiophanate-methyl were 90.24%, 95.75% and 95.02% respectively. It shows that the eucalyptus plantation waste biochar has a significant removal effect on the pesticides paraquat, glyphosate and thiophanate-methyl, and the eucalyptus plantation waste biochar prepared in Example 2 has a better removal effect.

[0073] In summary, the eucalyptus plantation waste biochar prepared by the present invention has a high content of mineral nutrients, a large specific surface area and cation exchange capacity, and rich surface functional groups, which increases the soil nutrient content and effectively alleviates soil acidification. In particular, the eucalyptus waste biochar obtained at 500°C in Example 2 has the best application effect at a 6% application rate. At the same time, the eucalyptus plantation waste biochar has a significant repair function for soil contaminated by heavy metals cadmium, lead and arsenic, and has a positive effect on improving the yield and quality of Chinese cabbage in heavy metal contaminated soil. The present invention overcomes the current problem of difficult disposal of eucalyptus plantation waste and avoids potential environmental pollution. The present invention is simple to operate, low in cost, high in efficiency, and has good promotion and application value.

[0074] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing biochar from eucalyptus plantation waste, characterized in that: The method is: S1. Collect eucalyptus plantation waste, remove soil and impurities on the surface, wash with water, dry naturally for 8 hours, and then dry at a temperature of 60° C. to 80° C. until the moisture content is 15%, and then crush to obtain crushed eucalyptus plantation waste; S2. The crushed eucalyptus plantation waste obtained in S1 is heated to 300°C-700°C at a heating rate of 20°C / min under a nitrogen or argon atmosphere, carbonized at a constant temperature for 2h-4h, then cooled to room temperature, crushed, and passed through a 100-mesh sieve to obtain eucalyptus plantation waste biochar.

2. The method for preparing biochar from eucalyptus plantation waste according to claim 1, characterized in that: The eucalyptus plantation wastes described in S1 are leafy branches and bark.

3. The method for preparing biochar from eucalyptus plantation waste according to claim 2, characterized in that: The mass ratio of the leafy branches to the bark is 3:

1.

4. The method for preparing biochar from eucalyptus plantation waste according to claim 1, characterized in that: The gas flow rate of the nitrogen or argon in S2 is 200 mL / min.

5. An application of eucalyptus plantation waste biochar prepared by the preparation method according to any one of claims 1 to 4, characterized in that: The eucalyptus plantation waste biochar is used for returning the eucalyptus plantation to the field and for improving the soil.

6. An application of eucalyptus plantation waste biochar prepared by the preparation method according to any one of claims 1 to 4, characterized in that: The eucalyptus plantation waste biochar is used for ecological restoration of soil contaminated by heavy metals cadmium, lead and / or arsenic.

7. The use according to claim 6, characterized in that: The eucalyptus plantation waste biochar is used to improve the yield and quality of Chinese cabbage in soil contaminated by heavy metals cadmium, lead or / and arsenic.

8. An application of eucalyptus plantation waste biochar prepared by the preparation method according to any one of claims 1 to 4, characterized in that: The eucalyptus plantation waste biochar is used to remove paraquat, glyphosate and / or thiophanate-methyl in the soil.

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