CN113293001A - Preparation and application of phosphorus-rich biochar based on mulberry branch waste - Google Patents
Preparation and application of phosphorus-rich biochar based on mulberry branch waste Download PDFInfo
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Abstract
The invention belongs to the technical field of agricultural waste recycling and soil improvement, and particularly relates to preparation and application of phosphorus-rich biochar based on mulberry branch waste. The invention can greatly reduce the mulberry branch waste and can effectively utilize the mulberry branch waste as resources.
Description
Technical Field
The invention belongs to the technical field of agricultural waste recycling and soil improvement, and particularly relates to preparation and application of phosphorus-rich biochar based on mulberry branch waste.
Background
China is a big agricultural country, and with the rapid development of modern agriculture, large-area agriculture and forestry industries can generate wastes while harvesting fruits and wood. The annual output of agricultural and forestry wastes is reported to be close to 20 billion tons, and except that a small part of the agricultural and forestry wastes are recycled, most of the agricultural and forestry wastes are directly incinerated and wasted, so that direct or indirect environmental pollution is caused. The mulberry branch waste is a typical agricultural and forestry waste. 1522t of mulberry branches produced in mulberry gardens in forestation in China accounts for more than 60% of the mulberry gardens. At present, most of mulberry twig wastes are not fully utilized. How to effectively utilize the mulberry branch waste and recycle the mulberry branch waste into better resources becomes one of the technical problems which need to be solved in recent years. At present, the recycling of the mulberry twig waste mainly comprises medicine extraction, edible fungus cultivation, flocculant research and development and the like. However, the amount of mulberry twig processed by medicine extraction, edible fungus cultivation and the like is very limited, most of mulberry twig waste is still directly combusted, and the process still has the problem of waste processing. Therefore, development of a treatment method capable of more effectively reducing and recycling the mulberry twig waste is urgently needed.
At present, the heavy metal pollution of soil is increasingly serious, particularly the heavy metal content in agricultural products is seriously exceeded due to the heavy metal pollution of farmland cultivated land soil, and great threat is caused to the health of people. At present, the area of polluted cultivated land in China is close to 1.5 hundred million mu, the cultivated land is irrigated by sewage about 3250 ten thousand mu, the direct economic loss caused by cultivated land pollution reaches more than 200 hundred million yuan every year, and meanwhile, in recent years, cases of diseases caused by eating agricultural products with heavy metal pollution exceeding the standard are continuously reported. Agricultural product safety issues have threatened the health and nice life of people. Therefore, it is necessary to develop effective soil heavy metal pollution treatment technology.
At present, reports on preparing phosphorus-rich biochar from ramulus mori waste and applying the phosphorus-rich biochar to improvement of heavy metal contaminated soil are not available.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a preparation method of phosphorus-rich biochar based on mulberry branch waste, and the prepared phosphorus-rich biochar can be used as an efficient carbon-based soil conditioner for soil remediation, is applied to the treatment of heavy metal pollution of farmland soil, can greatly reduce mulberry branch waste, and can effectively recycle the mulberry branch waste.
In order to achieve the purpose, the invention adopts the technical scheme that:
the invention provides a preparation method of phosphorus-rich biochar based on mulberry branch waste, which comprises the following steps:
s1, washing and drying the mulberry twig waste and crushing the mulberry twig waste into particles;
s2, alkalizing the crushed mulberry twig waste by using NaOH solution, and drying to obtain biomass;
s3, adding an initiator and a surfactant into the alkalized biomass for etherification, and performing microwave digestion in the etherification process to promote the etherification reaction; after etherification, biomass raw materials are activated at high temperature, wherein the activation temperature is 150-200 ℃;
s4, mixing the activated biomass with water, stirring, adding a potassium dihydrogen phosphate solution in the stirring process, maintaining the temperature at 75-85 ℃, stirring for 3-5 hours, and drying after stirring to obtain a phosphorus-rich biomass material;
s5, putting the phosphorus-rich biomass material in a vacuum closed environment for pyrolysis treatment: firstly heating to 250-300 ℃ at a speed of 3-5 ℃/min, then heating to 650 ℃ at a speed of 30-50 ℃/min, and carrying out thermal pyrolysis for 3-5h to obtain biomass carbon;
and S6, cooling the pyrolyzed biomass carbon to room temperature, grinding and sieving, activating by using alkali liquor, and finally drying to obtain the phosphorus-rich biochar.
Preferably, the concentration of the NaOH solution in step S2 is 6% -10%. Further, the concentration of the NaOH solution was 6%.
Preferably, in the alkalization treatment in the step S2, the feed-liquid ratio of the ramulus mori waste to the NaOH solution is 1: 5-1: 15, the time of alkalization treatment is 2-6 h. Further, the feed-liquid ratio of the mulberry twig waste to the NaOH solution is 1: and 10, the time of alkalization treatment is 4 hours.
Preferably, the initiator in step S3 is Fe2+/H2O, cetyl trimethyl ammonium bromide (C) as surfactant19H42BrN) or sodium dodecylbenzenesulfonate (C)18H29NaO3S)。
Preferably, in step S3, the concentration of the initiator is 2-10g/L, the addition amount is 1-2L/kg, the concentration of the surfactant is 5-10mol/L, and the addition amount is 3-4L/kg. Furthermore, the concentration of the initiator is 4g/L, the addition amount is 1L/kg, the concentration of the surfactant is 5mol/L, and the addition amount is 3L/kg.
Preferably, in step S3, microwave digestion is carried out for 1h, the microwave power is 800W-1200W, and then stirring and dipping are continued for 12-24 h. Further, the microwave power was 800W, and then the stirring and impregnation were continued for 12 hours.
Preferably, in step S3, the temperature of the high-temperature activation is 150-200 ℃, and the activation time is 6-8 h. Further, the temperature of high-temperature activation is 150 ℃, and the activation time is 6 h.
The concentration of the potassium dihydrogen phosphate solution is 1-15g/L, and the solution is slowly dripped at the speed of 200-1000mL/h, and the dripping time is 20-40 h. Further, the potassium dihydrogen phosphate solution was added dropwise at a rate of 500mL/h and a concentration of 10g/L over a period of 20 h.
Preferably, the mulberry branch waste is waste left by cutting branches of mulberry gardens.
Preferably, the pulverization of step S1 is to a powder with a particle size of 10-100 mm.
Preferably, in step S5The pyrolysis treatment adopts an anaerobic pyrolysis furnace, and is performed by vacuumizing and introducing protective gas (CO)2) So that the cavity in the device is in a vacuum or oxygen-insulated state.
Preferably, in step S6, the biomass carbon is activated by soaking it for 2-6h using an acid solution or an alkali solution with a concentration of 1-3mol/L as an activating agent. Further, the biomass carbon is activated by soaking the biomass carbon for 4 hours by using an acid solution or an alkali solution with the concentration of 1mol/L as an activating agent.
Preferably, in step S6, the mixture is ground and sieved through a 20-100 mesh sieve.
The invention also provides the phosphorus-rich biochar based on the mulberry branch waste prepared by the method.
The invention also provides application of the phosphorus-rich biochar based on the mulberry branch waste in improvement of heavy metal contaminated soil.
The phosphorus-rich biochar prepared by the method disclosed by the invention is prepared from waste mulberry twigs, the lignin content of the biochar is higher, the biochar still contains various oxygen-containing functional groups (carboxyl, hydroxyl, carbonyl, lactone acid and the like) on the surface after high-temperature pyrolysis and activation, and the groups can adsorb heavy metals in soil and water through complexation, pi-pi action and the like, so that the process of passivating the heavy metals by the biochar is realized.
Meanwhile, the phosphorus-rich biochar prepared by the pre-loading technology process contains rich phosphate ash, and phosphate radicals have the capabilities of regulating the pH of soil and complexing heavy metals, so that the harm of the heavy metals is further reduced, the adsorption capacity of the biochar is improved, and the growth of plants can be promoted by taking phosphoric acid as a necessary nutrient element for crops.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides a preparation method of phosphorus-rich biochar based on mulberry branch waste, which is characterized in that the mulberry branch waste is subjected to continuous pyrolysis through a pre-loading combined pyrolysis technology to prepare the phosphorus-rich biochar, and the prepared phosphorus-rich biochar is applied to the pollution treatment of farmland soil heavy metal, can effectively passivate soil heavy metal, inhibit the process of absorbing and accumulating heavy metal by crops, and simultaneously promote the nutrition supply of soil to the crops, and can be used as an efficient carbon-based soil conditioner for soil remediation. The invention can greatly reduce the mulberry branch waste and can effectively utilize the mulberry branch waste as resources. Overall, the invention has the following advantages:
(1) compared with the prior art, the phosphorus-rich biochar prepared by the method can realize the mass reduction of the mulberry twig waste.
At present, the main treatment mode of the mulberry twig waste is to directly discard the mulberry twig waste without treatment. The discarded branches can not rapidly reduce mulberry branch wastes, thereby causing pollution to rural orchards and surrounding environment. The invention provides a process technology for effectively reducing mulberry twig waste, which can realize the fast pyrolysis treatment of the mulberry twig waste in a relatively short time through a pyrolysis process technology, and simultaneously can treat the mulberry twig waste in a large amount at one time, thereby overcoming the defect that the existing mulberry twig waste treatment process can not rapidly eliminate the mulberry twig waste in a large batch.
(2) Compared with the prior art, the method for preparing the phosphorus-rich biochar improves the resource utilization rate of the mulberry twig waste.
At present, the resource utilization approach of the mulberry planting waste is mushroom planting, however, after the mushroom planting, mulberry twig waste still exists, a further treatment technology is needed, the treatment capacity of the mushroom planting is limited, and the resource utilization rate is low. The invention provides a new resource utilization approach for mulberry twig waste, and the mulberry twig waste is converted into the phosphorus-rich biochar through the combined preloading pyrolysis technology, and the phosphorus-rich biochar can be used as an effective soil conditioner, can be applied to the conditioning of agricultural heavy metal contaminated soil, and greatly improves the resource utilization rate of the mulberry twig waste.
(3) Compared with the traditional biochar, the phosphorus-rich biochar prepared by the method has higher phosphate content, and the capability of biochar for passivating heavy metals is improved.
The biochar disclosed by the invention contains a large amount of phosphate, and the phosphate can be combined with heavy metals in soil through complexation and precipitation, so that the form of the heavy metals in the soil is changed, the process of transferring the heavy metals from the soil to crops is reduced, and the effect of passivating the heavy metals by the biochar is improved.
(4) Compared with the traditional biological carbon, the phosphorus-rich biological carbon prepared by the method has better phosphate content and can provide abundant and necessary nutrient elements for crops.
Compared with the traditional biochar, the phosphorus-rich biochar disclosed by the invention contains more abundant phosphate which is an essential nutrient element for plants, and can provide more abundant phosphorus for crops, so that the nutrient requirement of the crops on the phosphorus is met, and the growth of the crops is promoted.
Drawings
FIG. 1 is a process flow diagram of example 1;
FIG. 2 shows the yields of various biochar;
FIG. 3 is a Fourier Infrared Spectroscopy (FTIR) of biochar;
FIG. 4 shows the adsorption removal rate of Cd by biochar;
FIG. 5 shows the change in biomass of Shuidong mustard.
Detailed Description
The following further describes the embodiments of the present invention. It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The experimental procedures in the following examples were carried out by conventional methods unless otherwise specified, and the test materials used in the following examples were commercially available by conventional methods unless otherwise specified.
Example 1 preparation of phosphorus-rich biochar based on ramulus mori waste and application of phosphorus-rich biochar in improvement of heavy metal contaminated soil
The process flow of this example is shown in fig. 1:
1. method for preparing phosphorus-rich biochar based on mulberry twig waste
1.1 preparation of conventional biochar
Removing impurities from the collected ramulus mori waste, crushing the ramulus mori waste into powder, putting the biomass into an anaerobic pyrolysis furnace (vacuum tube furnace BTF-1400C, Bei Yike equipment and technology Co., Ltd., Anhui) for pyrolysis at 500 ℃ for 5 hours, taking out the biomass, grinding the biomass, and sieving the biomass with a 20-100-mesh sieve to obtain the conventional biochar.
1.2 preparation of phosphorus-rich biochar 1, comprising the following steps:
(1) removing impurities from collected ramulus Mori waste (waste left by cutting branches of mulberry garden), cleaning with tap water, air drying, oven drying at 60 deg.C for 24 hr, and pulverizing into powder with particle diameter of 10-100 mm.
(2) Soaking the crushed ramulus mori waste (1kg) in 10L NaOH solution (with the concentration of 6%) for 4h, stirring for 1h for alkalization, and drying at 80 ℃ for 3h to obtain biomass;
(3) 1L of initiator (Fe) with a concentration of 4g/L was added to 1kg of alkalized biomass2+/H2O), and 3L of a surfactant (cetyltrimethylammonium bromide, C) at a concentration of 5mol/L19H42BrN), mixing, then carrying out etherification treatment, firstly carrying out microwave digestion on the soaked mixed solution, wherein the power of microwaves is 800W, the time is 1h, the etherification reaction is promoted, and continuously stirring and soaking for 12h after microwave digestion; after etherification reaction, taking out the biomass raw material, drying, then performing high-temperature activation in an oven at the activation temperature of 150 ℃ for 6 hours, and grinding after activation to obtain an activated biomass raw material;
(4) mixing 1kg of activated biomass raw material with 2L of water, stirring by using a stirrer, dropwise adding 10L of prepared potassium dihydrogen phosphate solution (with the concentration of 10g/L) into the raw material water mixed solution at the dropping speed of 500mL/h (the dropwise adding time is 20h) in the stirring process, uniformly mixing, maintaining the temperature of 80 ℃, stirring for 4h, taking out the phosphorus-rich biomass raw material, and drying in an oven at the temperature of 60 ℃ to obtain the phosphorus-rich biomass material;
(5) putting the dried phosphorus-rich biomass particles into an anaerobic pyrolysis furnace (vacuum tube furnace BTF-1400C, Anhui Beiyi)Ke equipment technologies Co., Ltd.), sealing, evacuating, and introducing CO2The protective gas is slowly heated to 300 ℃ at the speed of 3 ℃/min, then is rapidly heated to 350 ℃ at the speed of 30 ℃/min, and is kept for 3 hours to obtain the phosphorus-rich biomass carbon, and byproducts of the pyrolysis furnace are respectively water, sulfide, combustible gas and pyroligneous liquor, and are collected and stored;
(6) and taking out the biomass carbon after pyrolysis, cooling to room temperature, grinding, sieving with a 20-100-mesh sieve, soaking for 4 hours by using 1.0mol/L NaOH solution for activation, washing with water, and drying for 3 hours at 80 ℃ to obtain the phosphorus-rich biochar 1.
1.3 preparation of phosphorus-enriched biochar 2
The preparation method is different from the phosphorus-rich biochar 1 in that: in the step (5), the temperature is slowly increased to 300 ℃ at the speed of 4 ℃/min, and then the temperature is rapidly increased to 450 ℃ at the speed of 40 ℃/min, so as to obtain the phosphorus-rich biochar 2.
1.4 preparation of phosphorus-enriched biochar 3
The preparation method is different from the phosphorus-rich biochar 1 in that: in the step (5), the temperature is slowly increased to 300 ℃ at the speed of 5 ℃/min, and then the temperature is rapidly increased to 550 ℃ at the speed of 50 ℃/min, so that the phosphorus-rich biochar 3 is obtained.
1.5 preparation of phosphorus-enriched biochar 4
The preparation method is different from the phosphorus-rich biochar 1 in that: in the step (5), the temperature is slowly increased to 300 ℃ at the speed of 5 ℃/min, and then is rapidly increased to 650 ℃ at the speed of 50 ℃/min, so as to obtain the phosphorus-rich biochar 4.
1.6 determination of biochar yield
The yields of conventional biochar, phosphorus-rich biochar 1, phosphorus-rich biochar 2, phosphorus-rich biochar 3, and phosphorus-rich biochar 4 were calculated by equation (1):
wherein Y represents the yield, M1Mass of biomass before combustion, M2Is the biomass mass after combustion.
As shown in fig. 2, the yields of the conventional biochar and the four phosphorus-rich biochar were: 39.85%, 68.35%, 55.67%, 45.36% and 49.76%. Wherein the yield of the conventional biochar is lower and is 39.85 percent. This is because the conventional biochar has a high moisture content and is not subjected to etherification and alkalization, so that the material is more easily volatilized during pyrolysis. The yield of the phosphorus-rich biochar 1 is the highest in the phosphorus-rich biochar, which shows that the yield of the biochar is greatly influenced by the pyrolysis temperature, the temperature is lower, the biomass gasification is slow, and volatile substances are less generated, so that the yield is higher. It can be seen that the pyrolysis temperature is optimal for example 1.
1.7 determination of phosphorus content of biochar
The phosphorus content of conventional biochar, phosphorus-rich biochar 1, phosphorus-rich biochar 2, phosphorus-rich biochar 3 and phosphorus-rich biochar 4 was determined at the southern china agricultural university test center using an elemental analyzer (ThermoFisher-flash smart).
As shown in table 1, the total phosphorus contents of the conventional biochar, the phosphorus-rich biochar 1, the phosphorus-rich biochar 2, the phosphorus-rich biochar 3, and the phosphorus-rich biochar 4 were 0.32%, 4.59%, 5.45%, 6.01%, and 7.6%, respectively. From the results, the phosphorus content of the phosphorus-rich biochar is far higher than that of the conventional biochar, wherein the phosphorus content of the phosphorus-rich biochar 4 is the highest and reaches 7.6%.
Meanwhile, the effective phosphorus content released by the conventional biochar and the four phosphorus-rich biochar in water is measured by sodium bicarbonate leaching-molybdenum-antimony anti-spectrophotometry (HJ 704-. As shown in Table 1, the available phosphorus content of the conventional biochar in water is 35.69mg/kg, and the available phosphorus content of the phosphorus-rich biochar 1-4 among the four phosphorus-rich biochar is 802.0mg/kg (phosphorus-rich biochar 1), 3564.5mg/kg (phosphorus-rich biochar 2), 2867.5mg/kg (phosphorus-rich biochar 3) and 1112.0mg/kg (phosphorus-rich biochar 4), respectively. Wherein the available phosphorus content of the phosphorus-rich biochar 2 is the highest. This is mainly determined by the self-structural properties and the inherent physicochemical shape of biochar. The porosity and specific surface area of the biochar are higher along with the increase of the temperature, phosphate in the biochar stays in pores and cannot be quickly released from the pores, and the content of available phosphorus is reduced.
TABLE 1 physicochemical Properties of various biochar
| Biochar | pH | Organic carbon (%) | Total phosphorus (%) | Available phosphorus (mg/kg) |
| Phosphorus-rich biochar 1 | 7.2 | 72.40 | 4.59 | 802.0 |
| Phosphorus- |
10.0 | 50.82 | 5.45 | 3564.5 |
| Phosphorus- |
10.2 | 33.75 | 6.01 | 2867.5 |
| Phosphorus- |
9.9 | 33.78 | 7.63 | 1112.0 |
| Conventional biochar | 7.1 | 51.37 | 0.32 | 35.69 |
1.8 determination of pH value of biochar
The pH values of the conventional biochar and the four phosphorus-rich biochar were measured using a pH meter (mettlerlitosan 405-60-SC). As shown in table 1, the pH of the conventional biochar was 7.1, and the basicity was weak; the pH values of the four phosphorus-rich biochar are alkaline, the pH value of the phosphorus-rich biochar 1 is 7.2, the pH value of the phosphorus-rich biochar 2 is 10.0, the pH value of the phosphorus-rich biochar 3 is 10.2, and the pH value of the phosphorus-rich biochar 4 is 9.9. The phosphorus-rich biochar 2 and the phosphorus-rich biochar 3 are the most basic, the pH value of the phosphorus-rich biochar 2 is more than 10, and the pH value of the phosphorus-rich biochar 4 is close to 10, so that the phosphorus-rich biochar 2, the phosphorus-rich biochar 3 and the phosphorus-rich biochar 4 have better capacity of adjusting the pH value of soil, namely the phosphorus-rich biochar contains higher basic components and plays a role in slowing down soil acidification.
1.9 calculation of specific surface area and pore size Structure of biochar
By N2The adsorption-desorption isotherms calculated the surface area and pore size structure of the conventional biochar and the four phosphorus-rich biochar.
As shown in Table 2, the specific surface area of the conventional biochar was as small as 1.03 (m)2(iv)/g); the comparative area of the phosphorus-rich biochar is larger than that of the conventional biochar. Wherein the specific surface area value of the phosphorus-rich biochar 4 is the largest, and the micropore volume thereof is also the largest, because the higher the temperature is, the biomass heat isThe more pores are exposed during the solution process, the larger the resulting specific surface area. However, the average pore size of the phosphorus-rich biocarbon 2 is larger than that of the phosphorus-rich biocarbon 4 because the interior of pores may collapse under high temperature conditions as the temperature increases, and thus, the pore volume may become smaller as the temperature increases. The pore diameter of the phosphorus-rich biochar is also a very important index for controlling the adsorption capacity, and the analysis result shows that the average pore diameter of the phosphorus-rich biochar 2 is the largest, so that pollutants can enter the pores, an internal diffusion process is formed, and the adsorption capacity of the phosphorus-rich biochar on the pollutants is further promoted.
TABLE 2 specific surface area and pore size of various biochar
1.10 surface functional group determination of biochar
The surface functional groups of the conventional biochar and the four phosphorus-rich biochar were characterized by fourier-infrared spectroscopy.
As shown in fig. 3, four different phosphorus-rich biochar surfaces all have abundant functional group structures. Compared with the conventional biochar, the phosphorus-rich biochar has more abundant hydroxyl functional groups and carboxyl functional groups, and the functional groups have the capacity of complexing soil heavy metals under alkaline conditions, so that the adsorption capacity of the phosphorus-rich biochar is promoted. In particular, the high content of aromatic functional groups on the surface of the phosphorus-rich biochar 3 and the phosphorus-rich biochar 4 promotes the stability of the phosphorus-rich biochar in soil.
The analysis shows that the four phosphorus-rich biochar types have better yield and stronger alkalinity compared with the conventional biochar, have the capability of teaching the soil pH value, are rich in nutrient elements required by plants, particularly contain higher phosphorus elements, can further promote the growth of crops and passivate soil heavy metals through the release of phosphate, and also have certain pores and oxygen-containing functional groups, so that the heavy metals can be adsorbed through mechanisms such as complexation, van der Waals force and the like, and the migration of the heavy metals in the crops is reduced.
Second, heavy metal adsorption test of biochar
In order to verify the heavy metal adsorption capacity of the phosphorus-rich biochar, experiments of adsorbing heavy metals in a water phase by the phosphorus-rich biochar are developed in southern plant nutrition and fertilizer key laboratories of the Ministry of agriculture of the Guangdong province academy of agricultural sciences. The specific contents of the experiment are as follows:
respectively preparing heavy metal cadmium (Cd) aqueous solutions with low concentration (0.5mg/L) and high concentration (10.0mg/L), adding conventional biochar and four kinds of phosphorus-rich biochar into the aqueous solutions, wherein the concentration of the biochar and the four kinds of phosphorus-rich biochar in water is 1.0g/L, respectively carrying out oscillation adsorption in a constant-temperature oscillator, and calculating removal efficiency according to the residual concentration of the heavy metal cadmium (Cd) in the adsorbed solution after oscillation for 24 hours.
As shown in the experimental results of fig. 4, four kinds of phosphorus-rich biochar can effectively remove heavy metal pollutants in the water phase. For the low-concentration heavy metal solution, the removal rate of the heavy metal of the conventional biochar is 23.6%, and the removal efficiency of the phosphorus-rich biochar 1-4 is 83.5%, 96.7%, 90.3% and 92.3% respectively, which are far higher than that of the conventional biochar. Wherein the removal rate of the phosphorus-rich biochar 2 is highest. For a high-concentration heavy metal solution, the removal rate of the conventional biochar is 15.9%, and the removal efficiencies of the phosphorus-rich biochar 1-4 are 53.4%, 69.7%, 63.1% and 69.1%, respectively, which are also higher than that of the conventional biochar, and thus the phosphorus-rich biochar provided by the invention has stronger adsorption capacity on heavy metals compared with the conventional biochar.
Third, potted plant culture test
The pot culture test was carried out in a greenhouse of the academy of agricultural sciences of Guangdong province, and the phosphorus-rich biochar 2 having the best adsorption performance was selected as the soil conditioner material (and the conventional biochar was used as a control) according to the adsorption result of heavy metals in the "heavy metal adsorption test". Three kinds of soil with different physicochemical properties are set for soil culture, wherein the soil 1 is farmland soil (111 degrees 03 'W, 22 degrees 22' N) in Yunhuo city in Guangdong province, the soil 2 is farmland soil (112052 'E, 35013' N) in Jiyuan city in Henan province, and the soil 3 is farmland soil (113 degrees 30 'W, 25 degrees 27' N) in Shaoguan city in Guangdong province. Respectively adding 0 percent, 3 percent of conventional biochar and 3 percent of biochar into three kinds of soilThe phosphorus-rich biochar 2 is used for treatment (conventional biochar and the phosphorus-rich biochar 2 are scattered on the surface layer of the soil and turned over), 9 treatments are performed in total, each treatment is repeated for 3 times, the water amount in the soil field is maintained at 60%, the soil is placed in a greenhouse for culture, the soil is weighed every 3 days, and the soil moisture is balanced by deionized water. After the soil of each group is cultured for 60 days, respectively planting the Shuidong mustards in the soil, detecting the physicochemical properties of the soil and the content of Cd in the Shuidong mustards during harvesting, and performing qualitative and quantitative analysis on heavy metal pollutants by using CaCl2And (3) extracting, and analyzing the available heavy metals in the soil sample by using an inductively coupled plasma emission spectrometer (ICP-OES). The results of the measurement were as follows:
3.1 Effect of biochar on raising pH of soil
As shown in table 3, the pH in the soil was hardly changed after the conventional biochar was applied to three kinds of soil. After the phosphorus-rich biochar is treated, the pH of the three soils is improved, wherein the pH of the soil 1 is improved from 7.22 to 7.44, the pH of the soil 2 is improved from 7.40 to 7.54, and the pH of the soil 3 is improved from 4.40 to 4.95. The phosphorus-rich biochar can obviously improve the pH value of soil, inhibit the acidification of the soil and further reduce the harm brought by the acidification of the soil.
3.2 Effect of biochar on improving total phosphorus in soil
The content of available phosphorus in the soil before and after the treatment by the biochar is detected, and the detection results in table 3 show that the content of phosphorus in the soil is basically unchanged by applying the conventional biochar, because the content of phosphorus in the conventional biochar is less, the total amount of phosphorus in the soil cannot be changed. After the treatment of the phosphorus-rich biochar, the total phosphorus content of the soil 1 is improved from 2.37g/kg to 2.57g/kg, the total phosphorus content of the soil 2 is improved from 1.4g/kg to 1.7g/kg, and the total phosphorus content of the soil 3 is improved from 1.16g/kg to 1.39. From the results of three soils, the phosphorus-rich biochar disclosed by the invention can effectively improve the phosphorus content in the soil, and because the phosphorus-rich biochar contains rich phosphate mineral components, after the phosphorus-rich biochar is input into the soil, phosphate is slowly released into the soil, so that the available phosphorus content in the soil is improved.
3.3 passivation effect of biochar on soil available heavy metal Cd
The phosphorus-rich biochar has a good effect on adsorbing heavy metals, and in order to further test the passivation effect of the phosphorus-rich biochar on soil heavy metals, the concentration of the soil available heavy metals before and after the conventional biochar and phosphorus-rich biochar are treated is detected.
As can be seen from the detection results in Table 3, when the conventional biochar is applied to the soil 3, the effective concentration of the heavy metal Cd in the soil is reduced from 3.3mg/kg to 3.02mg/kg, while the effective concentration of the Cd in the soil 1 and the soil 2 cannot be reduced by applying the conventional biochar. This shows that the conventional biochar has a certain Cd passivating effect on acid soil, but has an insignificant heavy metal passivating effect on neutral soil. After the treatment of the phosphorus-rich biochar, the content of the effective Cd in the soil 1 is reduced from 0.72mg/kg to 0.67mg/kg, the content of the effective Cd in the soil 2 is reduced from 5.85mg/kg to 5.26mg/kg, and the content of the effective Cd in the soil 3 is reduced from 3.30mg/kg to 2.97 mg/kg. It can be seen that the phosphorus-rich biochar can effectively reduce the effective content of Cd in soil after being applied to the soil, and the effective concentration of Cd in acid soil or neutral soil is remarkably reduced because phosphate in the phosphorus-rich biochar can adsorb heavy metal in the soil through various mechanisms such as complexation and coprecipitation, so that the mobility of the heavy metal in the soil is reduced, and the content of the effective heavy metal in the soil is reduced.
TABLE 3 Change in pH, Total phosphorus in soil and available Cd before and after application of phosphorus-enriched biochar
| Soil(s) | Treatment of | pH | Total phosphorus (gkg-1) | Available state Cd (mgkg-1) |
| Soil 1 | Blank space | 7.22±0.08 | 2.37±0.04 | 0.72±0.01a |
| Phosphorus- |
7.44±0.02 | 2.57±0.17 | 0.67±0.00b | |
| Conventional biochar | 7.21±0.07 | 2.14±0.08 | 0.73±0.02a | |
| |
Blank space | 7.40±0.04 | 1.40±0.13b | 5.85±0.11a |
| Phosphorus- |
7.54±0.06 | 1.70±0.06a | 5.26±0.26b | |
| Conventional biochar | 7.33±0.04 | 1.27±0.18b | 5.90±0.07a | |
| |
Blank space | 4.40±0.14c | 1.16±0.03b | 3.30±0.11a |
| Phosphorus- |
4.95±0.17b | 1.39±0.07c | 2.97±0.09b | |
| Conventional biochar | 4.39±0.37c | 1.11±0.13a | 3.02±0.06a |
3.4 Biomass of Shuidong mustard is improved by charcoal
To study the effect of the phosphorus-rich biochar on soil improvement, after soil 1, soil 2 and soil 3 were mixed with conventional biochar and phosphorus-rich biochar, arabidopsis thaliana was planted in the soil (with the soil without biochar applied as a control).
The statistics of biomass are given in figure 5. As can be seen from the figure, the Shuidong mustard can grow normally in the soil 1, the yield is reduced when the conventional biochar is applied, the yield is obviously increased after the biochar rich in phosphorus is applied, and the yield of the Shuidong mustard in the soil 1 is statistically increased from 3.6 g/pot to 4.8 g/pot after the biochar rich in phosphorus is applied. The phosphorus-rich biochar can effectively promote the growth of vegetables, and mainly because the phosphorus content in the phosphorus-rich biochar is high, phosphorus released by the biochar can effectively enhance the photosynthesis and carbohydrate transport of crops, promote the metabolism of nitrogen elements, improve the adaptability to the outside and further promote the growth of the crops.
The content of heavy metals in the soil 2 is higher because the yield of the Shuidong brassica juncea in the soil 2 is only 2.66 g/pot due to abnormal growth, the content of heavy metal is 5.85mg/kg, which far exceeds that of soil 1, therefore, the heavy metal toxic action causes the abnormal growth of Shuidong mustard, when the conventional biochar is applied, the yield of the Shuidong mustard is not improved, after the phosphorus-rich biochar is added, the biomass of the Shuidong mustard in the soil 2 is increased from 2.66 g/pot to 3.22 g/pot, the yield of the Shuidong mustard is greatly improved, the reason is that the phosphorus-rich biochar passivates heavy metals in soil through the actions of adsorption, complexation, coprecipitation and the like, reduces the mobility of the heavy metals in the soil, further reducing the heavy metal absorption amount of the Shuidong mustard, reducing the toxic action of the heavy metal in the soil on the Shuidong mustard and promoting the growth of the Shuidong mustard.
The water-east mustard in soil 3 hardly grew, so the crop biomass was 0 without added biochar. When conventional biochar was added, Shuidong mustard still failed to grow. This is because soil 3 is highly acidic (pH <4.5) and is not suitable for growth of arabidopsis thaliana, whereas conventional biochar cannot change the pH of soil and inhibit soil acidification. When the phosphorus-rich biochar of the invention is applied to soil 3, the Shuidong mustard can survive and grow slowly. This is because the phosphorus-rich biochar can adjust the pH of the soil, inhibiting acidification of the soil 3, and thus allowing the arabidopsis thaliana to start growing in the soil 3.
Therefore, the phosphorus-rich biochar disclosed by the invention can improve the soil environment, improve the fertilizer efficiency of the soil, promote the growth of the Shuidong brassica juncea and further prove that the phosphorus-rich biochar has remarkable effects on improving the soil and improving the soil fertility.
3.5 Effect of biochar on reducing Cd content in edible part of Shuidong mustard
In order to further verify the effect of the phosphorus-rich biochar on inhibiting the crops from absorbing the heavy metals in the soil, the content of the heavy metals in the edible parts of the Shuidong brassica juncea is detected. Since the soil 3 cannot normally grow the Shuidong mustard and cannot contrast the heavy metal content before and after the biochar is applied, only the heavy metal content of the Shuidong mustard in the soil 1 and the soil 2 is detected.
In the soil 1, the content of heavy metal in the Shuidong brassica juncea is 17.3mg/kg without adding the biochar, the content of heavy metal in the Shuidong brassica juncea is reduced to 16.5mg/kg after adding the conventional biochar, and the content of heavy metal in the Shuidong brassica juncea is reduced to 13.6mg/kg after adding the biochar rich in phosphorus. This shows that the phosphorus-rich biochar has stronger capacity of reducing the heavy metal content in vegetables.
In the soil 2, the content of heavy metal in the Shuidong brassica juncea without adding the biochar is 35.7mg/kg, and after the conventional biochar is added, the content of heavy metal in the Shuidong brassica juncea is 37.89, but the content of heavy metal in the Shuidong brassica juncea is increased. The heavy metal content of the Shuidong mustard added with the phosphorus-rich biochar is reduced to 19.6mg/kg, so that the heavy metal content of the Shuidong mustard is greatly reduced. Therefore, the phosphorus-rich biochar disclosed by the invention can promote the growth of crops, can inhibit the accumulation of heavy metals in vegetable crops, and can improve the safety of the vegetable crops, so that the phosphorus-rich biochar disclosed by the invention is a soil conditioner with a good application prospect.
The embodiments of the present invention have been described in detail, but the present invention is not limited to the described embodiments. It will be apparent to those skilled in the art that various changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, and the scope of protection is still within the scope of the invention.
Claims (10)
1. A preparation method of phosphorus-rich biochar based on mulberry branch waste is characterized by comprising the following steps:
s1, washing and drying the mulberry twig waste and crushing the mulberry twig waste into particles;
s2, alkalizing the crushed mulberry twig waste by using NaOH solution, and drying to obtain biomass;
s3, adding an initiator and a surfactant into the alkalized biomass for etherification, and performing microwave digestion in the etherification process to promote the etherification reaction; after etherification, biomass raw materials are activated at high temperature, wherein the activation temperature is 150-200 ℃;
s4, mixing the activated biomass with water, stirring, adding a potassium dihydrogen phosphate solution in the stirring process, maintaining the temperature at 75-85 ℃, stirring for 3-5 hours, and drying after stirring to obtain a phosphorus-rich biomass material;
s5, putting the phosphorus-rich biomass material in a vacuum closed environment for pyrolysis treatment: firstly heating to 250-300 ℃ at a speed of 3-5 ℃/min, then heating to 650 ℃ at a speed of 30-50 ℃/min, and carrying out thermal pyrolysis for 3-5h to obtain biomass carbon;
and S6, cooling the pyrolyzed biomass carbon to room temperature, grinding and sieving, activating by using alkali liquor, and finally drying to obtain the phosphorus-rich biochar.
2. The method for preparing phosphorus-rich biochar based on mulberry branch waste as claimed in claim 1, wherein the concentration of NaOH solution in step S2 is 6% -10%.
3. The method for preparing phosphorus-rich biochar based on mulberry branch waste as claimed in claim 1, wherein in the alkalization treatment of the step S2, the feed-liquid ratio of the mulberry branch waste to NaOH solution is 1: 5-1: 15, the time of alkalization treatment is 2-6 h.
4. The method for preparing phosphorus-rich biochar based on mulberry branch waste as claimed in claim 1, wherein the initiator in step S3Is Fe2+/H2O, cetyl trimethyl ammonium bromide (C) as surfactant19H42BrN) or sodium dodecylbenzenesulfonate (C)18H29NaO3S)。
5. The method for preparing phosphorus-rich biochar based on mulberry branch waste as claimed in claim 1, wherein in step S3, the concentration of the initiator is 2-10g/L, the addition amount is 1-2L/kg, the concentration of the surfactant is 5-10mol/L, and the addition amount is 3-4L/kg.
6. The method for preparing phosphorus-rich biochar based on mulberry branch waste as claimed in claim 1, wherein in step S3, microwave digestion is carried out for 1h with the microwave power of 800W-1200W, and then stirring and dipping are continued for 12-24 h.
7. The method for preparing phosphorus-rich biochar based on mulberry branch waste as claimed in claim 1, wherein in step S3, the temperature of high-temperature activation is 150-200 ℃, and the activation time is 6-8 h.
8. The method as claimed in claim 1, wherein in step S4, the concentration of the potassium dihydrogen phosphate solution is 1-15g/L, and the solution is slowly added dropwise at a rate of 200-1000mL/h for 20-40 h.
9. The phosphorus-rich biochar based on the mulberry branch waste prepared by the method of any one of claims 1 to 8.
10. Use of the phosphorus-rich biochar based on mulberry branch waste of claim 9 for improving heavy metal contaminated soil.
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