CN109603749B - Preparation method and application of modified straw stalk biochar - Google Patents

Preparation method and application of modified straw stalk biochar Download PDF

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CN109603749B
CN109603749B CN201811599794.2A CN201811599794A CN109603749B CN 109603749 B CN109603749 B CN 109603749B CN 201811599794 A CN201811599794 A CN 201811599794A CN 109603749 B CN109603749 B CN 109603749B
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fly ash
biochar
straw
straw stalk
modified
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CN109603749A (en
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彭娜
王开峰
成卓鸿
刘映婷
郭远凯
王赢利
王春英
黄晓霞
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Jiaying University
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/10Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising silica or silicate
    • B01J20/16Alumino-silicates
    • B01J20/165Natural alumino-silicates, e.g. zeolites
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/20Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising free carbon; comprising carbon obtained by carbonising processes
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00Treatment of water, waste water, or sewage
    • C02F1/28Treatment of water, waste water, or sewage by sorption
    • C02F1/281Treatment of water, waste water, or sewage by sorption using inorganic sorbents
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00Treatment of water, waste water, or sewage
    • C02F1/28Treatment of water, waste water, or sewage by sorption
    • C02F1/283Treatment of water, waste water, or sewage by sorption using coal, charred products, or inorganic mixtures containing them
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2220/00Aspects relating to sorbent materials
    • B01J2220/40Aspects relating to the composition of sorbent or filter aid materials
    • B01J2220/48Sorbents characterised by the starting material used for their preparation
    • B01J2220/4812Sorbents characterised by the starting material used for their preparation the starting material being of organic character
    • B01J2220/485Plants or land vegetals, e.g. cereals, wheat, corn, rice, sphagnum, peat moss
    • CCHEMISTRY; METALLURGY
    • C02TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02FTREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00Nature of the contaminant
    • C02F2101/30Organic compounds
    • C02F2101/308Dyes; Colorants; Fluorescent agents

Abstract

The invention discloses a preparation method and application of modified straw biochar, belonging to the technical field of biological environmental protection and comprising the following steps of 1) preparation of raw materials, namely collecting fly ash of a power plant and straw stalks of farmland and drying respectively, and crushing the straw stalks; 2) mixing the fly ash obtained in the step 1) with sodium hydroxide and then roasting to obtain alkali fusion fly ash; 3) adding the alkali-fused fly ash obtained in the step 2) into the straw stalks obtained in the step 1), adding deionized water, shaking up, oscillating, drying and crushing to obtain a mixture of the straw stalks and the alkali-fused fly ash; 4) pyrolyzing and crushing the mixture of the straw stalks obtained in the step 3) and the alkali fusion fly ash to obtain modified straw stalk biochar; the preparation raw materials of the invention are industrial and agricultural wastes, are cheap and easily available, the preparation method is simple, the preparation cost is low, the removal rate of pollutants is high, the adsorption capacity is large, no secondary pollution is caused to the environment, and the invention is beneficial to the management and control and treatment of environmental pollution.

Description

Preparation method and application of modified straw stalk biochar
Technical Field
The invention relates to a preparation method of modified biochar, in particular to a preparation method of modified straw biochar. The invention also relates to the application of the modified biochar.
Background
The discharge amount of the printing and dyeing wastewater is large, according to European statistics, the weight ratio of the fabric to the discharged wastewater is 1: 150-1: 200, and the weight ratio of the fabric to the discharged wastewater is about 1: 200-1: 400 in China. The textile industry wastewater in China is the sixth grade of national industrial wastewater discharge, and 80% of the wastewater belongs to printing and dyeing wastewater. The treatment method of the printing and dyeing wastewater is various and mainly comprises adsorption, oxidation, membrane separation, flocculation, biodegradation and the like. Adsorption processes are particularly well established in the field of wastewater treatment due to their ability to selectively enrich certain compounds. Activated carbon is one of the most effective adsorbents at present, but because the activated carbon is difficult to regenerate, the treatment cost is high, and the application range is narrow. Therefore, the search for an economically efficient adsorbent is the key to the current technological development.
According to the report of the environmental planning agency of the united nations, crops planted in the world can provide about 20 hundred million t of various straws every year, the annual output of the crop straws in China is about 7 hundred million t, and the first of the world is that the amount of the straws accounts for about 30 percent of the total amount of the straws in the world, which is converted into 3.53 hundred million t of standard coal. The amount of crop straw resources accounts for nearly half of the amount of biomass resources every year in China. Crop straws are a precious renewable resource, but for a long time, due to the influence of consumption concept and life style, the rural straw resources in China are completely in the conditions of high consumption, high pollution and low yield, and a considerable part of crop straws are abandoned or incinerated and are not reasonably developed and utilized. According to investigation, the utilization rate of the straws in China is about 33 percent at present, most of the straws are not treated, and the straws are only utilized by about 2.6 percent after technical treatment. Therefore, the comprehensive utilization of the crop straw resources has important practical significance for saving resources, protecting the environment, increasing the income of farmers and promoting the sustainable development of agriculture. The straw carbonization technology provides a good method which is environment-friendly, has high technological content and has market prospect for solving the problem of comprehensive utilization of straws in China.
As a novel environment-friendly repair material, the biochar has the advantages of large specific surface area, high porosity, rich surface functional groups and strong ion exchange capacity, and has strong application potential in removing pollutants in water. However, the traditional charcoal has low adsorption efficiency, light charcoal density and small particles, and is difficult to separate solid from liquid after adsorption, easy to cause secondary pollution, and not beneficial to the regeneration and reutilization of the charcoal. Research shows that the adsorption effect of the common composite material on pollutants is better than that of a single material. Therefore, at present, some researchers pay attention to the combination of the biochar and other materials, and the biochar and other materials are combined by physical and chemical methods to prepare materials with new performance and new structures, so that the comprehensive performance of the materials is superior to that of the original materials, and various different requirements can be met. The biochar composite material is generally prepared by adding other materials (magnetic materials, nano materials, inorganic salts and the like) into a biomass raw material and then performing high-temperature pyrolysis on the mixture to prepare the composite material. After the biochar is prepared into the composite material, the specific surface area and the pore size are increased, the removal capacity of pollutants due to the increase of surface functional groups is obviously improved, and the solid-liquid separation is easy after the adsorption. However, these composite materials are often expensive, too small particles are easy to agglomerate, and have certain toxicity, which can reduce the types and amounts of environmental microorganisms, and these disadvantages limit the popularization and application of these composite materials. At present, biochar and composite materials thereof are mainly used for adsorbing inorganic pollutants (such as heavy metals, fluorine and the like) and organic pollutants (such as dyes, petroleum hydrocarbons, pesticides, antibiotics and the like) in the environment and researching the adsorption effect and action mechanism of the biochar.
Disclosure of Invention
The invention aims to provide a preparation method and application of modified straw stalk biochar. The preparation raw materials of the invention are industrial and agricultural wastes, are cheap and easily available, the preparation method is simple, the preparation cost is low, the removal rate of pollutants is high, the adsorption capacity is large, no secondary pollution is caused to the environment, and the invention is beneficial to the management and control and treatment of environmental pollution.
The technical scheme of the invention is realized in such a way that the preparation method of the modified straw stalk biochar comprises the following steps:
1) preparing raw materials, namely collecting fly ash and straw stalks, and drying the fly ash; drying and crushing straw stalks;
2) preparing alkali fusion fly ash, namely mixing the fly ash obtained in the step 1) with sodium hydroxide and then roasting to obtain alkali fusion fly ash;
3) mixing the straw stalk and the alkali fusion fly ash, namely adding the alkali fusion fly ash obtained in the step 2) into the straw stalk obtained in the step 1), adding a certain volume of deionized water, and sequentially shaking up, oscillating, drying and crushing to obtain a mixture of the straw stalk and the alkali fusion fly ash;
4) preparing the modified straw stalk biochar, namely pyrolyzing and crushing the mixture of the straw stalks obtained in the step 3) and the alkali fusion fly ash in sequence to obtain the modified straw stalk biochar.
In the preparation method of the modified straw stalk biochar, the fly ash in the step 1) is coal-fired power plant fly ash, the particle size is less than 0.045mm, and the fly ash is dried at the temperature of 100-110 ℃;
the straw stalks are farmland straw stalks, are dried at the temperature of 70-90 ℃, and are crushed to have the grain diameter of less than 1.00 mm.
The preparation method of the modified straw stalk biochar comprises the step 2) of uniformly mixing the fly ash obtained in the step 1) with sodium hydroxide according to a mass ratio of 1: 1-1.5, roasting for 0.5-2 hours at 600-700 ℃, and crushing the roasted product until the particle size is smaller than 1.00mm to obtain the fly ash subjected to alkali fusion treatment, namely the alkali fusion fly ash.
In the preparation method of the modified straw stalk biochar, the sodium hydroxide in the step 2) is an analytically pure chemical reagent.
The preparation method of the modified straw stalk biochar comprises the following steps of mixing the straw stalks and the alkali fused fly ash in the step 3) according to a mass ratio of 1: 0.1-0.5; the mass volume ratio of the mixture of the alkali fused fly ash and the straw stalks to the deionized water is 1:10 g/ml; the oscillation time is 2-6 h; the drying temperature is 70-90 ℃; the particle size after crushing is less than 1.00 mm.
In the step 4), the pyrolysis is specifically carried out by heating from room temperature to 650-750 ℃ at a heating rate of 10 ℃/min, carrying out heat preservation pyrolysis for 1-2 h, and naturally cooling after pyrolysis is finished; the particle size after crushing is less than 1.00 mm.
The invention discloses application of modified straw stalk biochar disclosed by claim 1 in removing methylene blue and cation red in a water body in sewage.
The modified straw stalk biochar is used for removing methylene blue and cation red in a water body from sewage, and can treat methylene blue wastewater within the range of pH being more than or equal to 7 and less than or equal to 13 and treat cation red wastewater within the range of pH being more than or equal to 1 and less than or equal to 13.
The modified straw stalk biochar is used for removing methylene blue and cation red in a water body in sewage, the adsorption balance time of the prepared modified straw stalk biochar to the methylene blue and the cation red is 2-24 hours, and the adsorption balance time to the methylene blue is preferably 4-24 hours.
After the method is adopted, compared with the prior art, the method has the following advantages and effects:
1) the fly ash adopted by the invention contains a large amount of porous glass bodies, is in a porous honeycomb structure, has a large specific surface area, and has a large amount of active groups such as Si-O-Si bonds, Al-O-Al bonds and the like on the surface, so that the adsorption activity is high. However, in the forming process of the fly ash, part of gas escapes to form open holes, and the surface of the fly ash is in a honeycomb shape; part of the gas does not escape and is wrapped in the particles to form closed cavities, and the interior of the particles is also in a honeycomb shape. The former has adsorption property because the holes are exposed on the surface; the latter has a very small adsorption capacity and requires physical or chemical means to open the closed pores to increase the porosity and specific surface area. The alkali fusion treatment can not only open the holes, but also generate a large number of new tiny pores through the action of alkali, thereby increasing the specific surface area and the porosity, and greatly improving the effect of treating the wastewater.
2) The invention carries out resource utilization on agricultural waste comprising straw stalks to prepare the adsorbing material biochar, and improves the adsorption efficiency through alkali fusion fly ash modification to obtain the modified straw stalk biochar efficient adsorbent.
3) The invention adopts cheap and easily available industrial and agricultural wastes as raw materials, can control the pollution of industrial and agricultural solid wastes to a certain extent, reduces the treatment pressure of the industrial and agricultural wastes, realizes high-value utilization of the industrial and agricultural wastes, changes waste into valuables and is expected to be produced in a commercialized way.
4) The modified straw stalk biochar prepared by the invention has obvious adsorption effect on methylene blue and cationic red which are commonly existing in printing and dyeing wastewater, improves the treatment efficiency, is beneficial to water pollution treatment, and has good application prospect.
Drawings
Fig. 1 is SEM images of fly ash, alkali fused fly ash, biochar, and modified straw stalk biochar of the present invention, wherein fig. 1(a) is an SEM image of fly ash, fig. 1(b) is an SEM image of alkali fused fly ash, fig. 1(c) is an SEM image of straw stalk biochar, and fig. 1 (d) is an SEM image of modified straw stalk biochar.
FIG. 2 is a Fourier characterization diagram of the rice straw biochar and the modified rice straw biochar of the invention.
FIG. 3 is EDS energy spectra of the rice straw biochar and the modified rice straw biochar of the invention.
FIG. 4 is a graph showing the results of adsorption equilibrium experiments of modified straw stalk biochar on methylene blue and cation red in example 4 of the present invention.
FIG. 5 is a graph showing the results of the modified straw stalk biochar in example 5 of the present invention on methylene blue and cation red adsorption kinetics experiments.
FIG. 6 is a graph showing the results of adsorption experiments of modified straw stalk biochar in example 6 of the present invention on methylene blue and cation red at different initial pH values of the solution.
Detailed Description
The present invention will be described in further detail with reference to the following examples, but the present invention is not limited thereto.
The invention discloses a preparation method of modified straw biochar, which comprises the following steps:
1) preparing raw materials, namely collecting coal-fired power plant fly ash and farmland straw straws with the particle size of less than 0.045mm, and drying the fly ash at the temperature of 100-110 ℃; the rice straw is dried at 70-90 ℃ and then crushed to a particle size of less than 1.00 mm.
Wherein the chemical components of the fly ash of the coal-fired power plant are shown in a table 1,
TABLE 1 chemical composition (mass fraction) of fly ash in:%
2) And (2) preparing the alkali fusion fly ash, namely uniformly mixing the fly ash obtained in the step 1) with sodium hydroxide according to a mass ratio of 1: 1-1.5, roasting for 0.5-2 h at a temperature of 600-700 ℃, and crushing a roasted product to obtain the fly ash subjected to alkali fusion treatment, namely the alkali fusion fly ash, wherein the particle size of the roasted product is less than 1.00 mm. The sodium hydroxide is an analytical pure chemical reagent.
3) Mixing the straw stalks and the alkali-fusion fly ash, namely adding the alkali-fusion fly ash obtained in the step 2) into the straw stalks obtained in the step 1), wherein the mixing ratio of the straw stalks to the alkali-fusion fly ash is 1: 0.1-0.5, adding deionized water, wherein the mass-volume ratio of the mixture of the alkali-fusion fly ash and the straw stalks to the deionized water is 1:10g/ml, shaking uniformly, drying at 70-90 ℃ after oscillating for 2-6 h, and crushing to obtain a mixture of the straw stalks and the alkali-fusion fly ash, wherein the particle size of the mixture is smaller than 1.00 mm;
4) and (3) preparing the modified straw stalk biochar, namely putting the mixture of the straw stalks obtained in the step 3) and alkali fusion fly ash into a corundum crucible, covering the crucible with a cover tightly, putting the crucible into a muffle furnace, heating the mixture from room temperature to 650-750 ℃ at the heating rate of 10 ℃/min, carrying out thermal pyrolysis for 1-2 h, naturally cooling the mixture in the muffle furnace after pyrolysis is finished, taking out a sample, and crushing the sample until the particle size is less than 1.00mm to obtain the modified straw stalk biochar.
The specific surface area of the straw stalk biochar at the temperature of 650-750 ℃ is 76.25-84.69m2The specific surface area of the modified biochar is greatly increased to 311.6-352.4m2The micropores with the diameter less than 1nm are obviously increased. Comparing the fly ash and the alkali fusion fly ash in fig. 1(a) and (b), it can be seen that the sodium hydroxide not only opens the closed pores of the fly ash, but also generates a large number of new tiny pores, and increases the specific surface area and the porosity. Before and after the biochar is modified by comparing fig. 1(c) and (d), it can be seen that the surface of the straw stalk biochar can be rougher by the method of the invention, the number and the volume of micropores are increased, a layer of alkali fused fly ash fluffy film is well formed on the biochar surface, the specific surface area is increased, and the adsorption performance can be enhanced. As can be seen from the figure 2 of the drawings,the method obviously enhances the wavelength range of 1100-450 cm-1In the interval, the absorbances of active groups such as Si-O-Si bonds, Al-O-Al bonds and the like are shown in fig. 3(a) and (b), and meanwhile, the method obviously increases the contents of main elements O, Si and Al contained in the alkali fusion fly ash on the surface of the modified straw stalk biochar, so that the modified biochar can be judged to be successfully loaded with the alkali fusion fly ash, and the modification effect can be achieved by the method.
Example 1
Drying the fly ash collected in a power plant at 105 ℃, uniformly mixing the dried fly ash and sodium hydroxide according to the mass ratio of 1:1.2, putting the mixture into a corundum crucible, roasting the mixture for 1 hour at 650 ℃ by using a muffle furnace, cooling the mixture in a hearth, taking the cooled mixture out, and crushing the mixture until the particle size is less than 1.00mm to obtain the alkali fusion fly ash. Drying the farmland straw stalks at the temperature of 80 ℃, wherein the grain diameter of the crushed straw stalks is less than 1.00 mm. Uniformly mixing the dried and crushed straw stalks with alkali fused fly ash according to the mass ratio of 10:3, namely, the adding mass of the alkali fused fly ash is 30% of the mass of the straw stalks, adding deionized water into the mixture, oscillating for 2 hours, drying at 80 ℃ and crushing to obtain the straw stalks with the particle size of less than 1.00mm, wherein the mass volume ratio of the mixture to the deionized water is 1:10 g/ml.
Placing the mixture of the dried straw stalks and the alkali fusion fly ash into a corundum crucible, covering the crucible with a cover, placing the corundum crucible into a muffle furnace, heating the pyrolysis temperature to 650 ℃ at the heating rate of 10 ℃/min, preserving the heat and pyrolyzing for 1.5h, naturally cooling in the muffle furnace after pyrolysis is finished, taking out a sample, and crushing to obtain the modified straw stalk biochar with the grain size of less than 1.00 mm.
The application effect is that the modified straw stalk biochar prepared by the method is added into an aqueous solution containing 10mg/L of methylene blue or cation red, the pH value is 6-8, the adding concentration is 0.25g/L, the mixture is placed on a constant temperature shaking table, and the shaking table oscillates at 150r/min for 2 hours at the temperature of 25 +/-1 ℃. The result shows that the modified straw stalk biochar can effectively adsorb methylene blue and cation red in a water body. The adsorption capacity of the prepared modified straw stalk biochar to methylene blue is 22.7mg/g, and the adsorption capacity is improved by more than 5 times compared with that of pure straw stalk biochar prepared under the same condition; the adsorption capacity to the cation red is 27.8mg/g, and is improved by about 65 percent compared with the pure straw stalk biochar prepared under the same condition.
Example 2
Drying the fly ash collected in a power plant at 100 ℃, uniformly mixing the dried fly ash and sodium hydroxide according to the mass ratio of 1:1, putting the mixture into a corundum crucible, roasting the mixture for 2 hours at 600 ℃ by using a muffle furnace, cooling the mixture in a hearth, taking the mixture out, and crushing the mixture until the particle size is less than 1.00mm to obtain the alkali fusion fly ash. Drying the farmland straw stalks at the temperature of 70 ℃, wherein the grain diameter of the crushed straw stalks is less than 1.00 mm. Uniformly mixing the dried and crushed straw stalks with the alkali fused fly ash according to the mass ratio of 10:1, namely, the adding mass of the alkali fused fly ash is 10% of the mass of the straw stalks, adding a certain amount of deionized water into the mixture, oscillating for 4 hours, drying at 70 ℃, and crushing to obtain the straw stalks with the particle size of less than 1.00 mm.
And putting the mixture of the dried straw stalks and the alkali fusion fly ash into a corundum crucible, covering the crucible with a cover, putting the corundum crucible into a muffle furnace, heating the pyrolysis temperature to 700 ℃ at the heating rate of 10 ℃/min, pyrolyzing for 1h at the temperature, naturally cooling in the muffle furnace after pyrolysis is finished, taking out a sample, and crushing to obtain the modified straw stalk biochar with the particle size of less than 1.00 mm.
The application effect is that the modified straw stalk biochar prepared by the method is added into an aqueous solution containing 10mg/L of methylene blue or cation red, the pH value is 6-8, the adding concentration is 0.25g/L, the mixture is placed on a constant temperature shaking table, and the shaking table oscillates at 150r/min for 4 hours at the temperature of 25 +/-1 ℃. The result shows that the modified straw stalk biochar can effectively adsorb methylene blue and cation red in a water body. The adsorption capacity of the prepared modified straw stalk biochar to methylene blue is 21.5mg/g respectively; the amount of adsorbed cationic red was 25.1 mg/g.
Example 3
Drying the fly ash collected in a power plant at 110 ℃, uniformly mixing the dried fly ash and sodium hydroxide according to the mass ratio of 1:1.5, putting the mixture into a corundum crucible, roasting the mixture for 0.5h at 700 ℃ by using a muffle furnace, cooling the mixture in a hearth, taking the cooled mixture out, and crushing the mixture until the particle size is less than 1.00mm to obtain the alkali fusion fly ash. Drying the farmland straw stalks at the temperature of 90 ℃, wherein the grain diameter of the crushed straw stalks is less than 1.00 mm. Uniformly mixing the dried and crushed straw stalks with alkali fused fly ash according to the mass ratio of 10:5, namely the adding mass of the alkali fused fly ash is respectively 50% of the mass of the straw stalks, adding deionized water into the mixture, oscillating for 24h, drying at 90 ℃ and crushing to obtain the straw stalks with the particle size of less than 1.00mm, wherein the mass volume ratio of the mixture to the deionized water is 1:10 g/ml.
Placing the mixture of the dried straw stalks and the alkali fusion fly ash into a corundum crucible, covering the crucible with a cover, placing the corundum crucible into a muffle furnace, respectively heating the pyrolysis temperature to 750 ℃ at the heating rate of 10 ℃/min, respectively pyrolyzing the mixture for 2 hours at the temperature, naturally cooling the mixture in the muffle furnace after the pyrolysis is finished, taking out a sample, and crushing the sample until the particle size is less than 1.00mm to obtain the modified straw stalk charcoal.
The application effect is that the modified straw stalk biochar prepared by the method is added into an aqueous solution containing 10mg/L of methylene blue or cation red, the pH value is 6-8, the adding concentration is 0.25g/L, the mixture is placed on a constant temperature shaking table, and the shaking is carried out for 6 hours at the temperature of 25 +/-1 ℃ and at the speed of 150 r/min. The result shows that the modified straw stalk biochar can effectively adsorb methylene blue and cation red in a water body. The adsorption capacity of the prepared modified straw stalk biochar to methylene blue is 24.3 mg/g; the amount of adsorbed cationic red was 30.8 mg/g.
Example 4
Drying the fly ash collected in a power plant at 105 ℃, uniformly mixing the dried fly ash and sodium hydroxide according to the mass ratio of 1:1.2, putting the mixture into a corundum crucible, roasting the mixture for 1 hour at 650 ℃ by using a muffle furnace, cooling the mixture in a hearth, taking the cooled mixture out, and crushing the mixture until the particle size is less than 1.00mm to obtain the alkali fusion fly ash. Drying the farmland straw stalks at the temperature of 80 ℃, wherein the grain diameter of the crushed straw stalks is less than 1.00 mm. Uniformly mixing the dried and crushed straw stalks with the alkali-fused fly ash according to the mass ratio of 10:1, namely, the adding mass of the alkali-fused fly ash is 10% of the mass of the straw stalks, adding a certain amount of deionized water into the mixture, wherein the mass-volume ratio of the mixture to the deionized water is 1:10g/ml, oscillating for 2h, drying at 80 ℃, and crushing to obtain the straw stalks with the particle size of less than 1.00 mm.
And putting the mixture of the dried straw stalks and the alkali fusion fly ash into a corundum crucible, covering the crucible with a cover, putting the corundum crucible into a muffle furnace, heating the pyrolysis temperature to 700 ℃ at the heating rate of 10 ℃/min, pyrolyzing for 2 hours at the temperature, naturally cooling in the muffle furnace after pyrolysis is finished, taking out a sample, and crushing to obtain the modified straw stalk biochar with the particle size of less than 1.00 mm.
The application effect is that the modified straw stalk biochar prepared by the method is added into aqueous solutions respectively containing 5, 10, 15, 20, 30, 40, 60 and 80mg/L of methylene blue or cation red, the pH value is within the range of 6-8, the adding concentration is 0.25g/L, the modified straw stalk biochar is placed on a constant temperature shaking table, and the modified straw stalk biochar is oscillated for 3 hours at the temperature of 25 +/-1 ℃ at the speed of 150 r/min. The experimental result is shown in fig. 4, and fig. 4 shows that the modified straw stalk biochar can effectively adsorb methylene blue and cation red in the water body. Pyrolyzing for 2 hours at 700 ℃, wherein the maximum adsorption capacity of the prepared modified straw stalk biochar to methylene blue can reach 40.8mg/g under the condition that the adding mass of the alkali fusion fly ash is 10% of the mass of the straw stalks; the maximum adsorption capacity to the cationic red can reach 63.1 mg/g.
Example 5
The modified straw stalk biochar prepared in the embodiment 4 of the invention is added into an aqueous solution containing 10mg/L methylene blue or cation red, the pH value is within the range of 6-8, the adding concentration is 0.25g/L, the mixture is placed on a constant temperature shaking table, and the shaking table is oscillated at 150r/min for 10min, 30min, 1, 2, 4, 8, 16 and 24h within the temperature range of 25 +/-1 ℃. The experimental result is shown in fig. 5, and fig. 5 shows that the modified straw stalk biochar can effectively adsorb methylene blue and cation red in the water body. Pyrolyzing for 2 hours at 700 ℃, wherein the maximum adsorption capacity of the prepared modified straw stalk biochar to methylene blue can reach 34.9mg/g under the condition that the adding mass of the alkali fusion fly ash is 10% of the mass of the straw stalks; the maximum adsorption capacity to the cationic red can reach 36.7 mg/g.
Example 6
The modified straw stalk biochar prepared in the embodiment 4 of the invention is added into an aqueous solution containing 10mg/L of methylene blue or cation red, the initial pH values of the aqueous solution are respectively adjusted to be 1, 3, 5, 7, 9, 11 and 13, the adding concentration is 0.25g/L, the mixture is placed on a constant temperature shaking table, and the shaking is carried out for 2 hours at the temperature of 25 +/-1 ℃ and at the speed of 150 r/min. The experimental result is shown in fig. 6, and fig. 6 shows that the modified straw stalk biochar can effectively adsorb methylene blue and cation red in the water body. The modified straw stalk biochar prepared by pyrolyzing the raw materials at 700 ℃ for 2h and under the condition that the adding mass of the alkali fusion fly ash is 10% of the mass of the straw stalks has a good adsorption effect when the initial pH value of the solution is greater than 5, and the maximum adsorption capacity (pH value is 13) to methylene blue can reach 32.2 mg/g; the maximum adsorption capacity (pH 11) for cationic red can reach 38.7 mg/g.
The above-mentioned embodiments are only for convenience of description, and are not intended to limit the present invention in any way, and those skilled in the art will understand that the technical features of the present invention can be modified or changed by other equivalent embodiments without departing from the scope of the present invention.

Claims (6)

1. A preparation method of modified straw stalk biochar is characterized by comprising the following steps:
1) preparing raw materials, namely collecting fly ash and straw stalks, and drying the fly ash; drying and crushing straw stalks;
2) preparing alkali fusion fly ash, namely uniformly mixing the fly ash obtained in the step 1) with sodium hydroxide according to the mass ratio of 1: 1-1.5, roasting for 0.5-2 h at the temperature of 600-700 ℃, and crushing a roasted product to obtain the fly ash subjected to alkali fusion treatment, namely the alkali fusion fly ash, wherein the particle size of the roasted product is less than 1.00 mm;
3) mixing the straw stalk and the alkali fusion fly ash, namely adding the alkali fusion fly ash obtained in the step 2) into the straw stalk obtained in the step 1), adding a certain volume of deionized water, and sequentially shaking up, oscillating, drying and crushing to obtain a mixture of the straw stalk and the alkali fusion fly ash; the mixing ratio of the straw stalks to the alkali fusion fly ash is 1: 0.1-0.5; the mass volume ratio of the mixture of the alkali fused fly ash and the straw stalks to the deionized water is 1:10 g/ml; the oscillation time is 2-6 h; the drying temperature is 70-90 ℃; the particle size after crushing is less than 1.00 mm;
4) preparing modified straw stalk biochar, namely pyrolyzing and crushing the mixture of the straw stalks obtained in the step 3) and alkali fusion fly ash in sequence to obtain the modified straw stalk biochar; the pyrolysis is specifically carried out by heating from room temperature to 650-750 ℃ at a heating rate of 10 ℃/min, carrying out heat preservation pyrolysis for 1-2 h, and naturally cooling after pyrolysis is finished; the particle size after crushing is less than 1.00 mm.
2. The preparation method of the modified straw stalk biochar according to claim 1, wherein the fly ash in the step 1) is coal-fired power plant fly ash with the particle size of less than 0.045mm, and is dried at 100-110 ℃;
the straw stalks are farmland straw stalks, are dried at the temperature of 70-90 ℃, and are crushed to have the grain diameter of less than 1.00 mm.
3. The method for preparing modified straw stalk biochar according to claim 1, wherein the sodium hydroxide in step 2) is an analytical pure chemical reagent.
4. The application of the biochar prepared by the preparation method of the modified straw stalk biochar as claimed in claim 1 in removing methylene blue and cation red in water body in sewage.
5. The application of the biochar prepared by the preparation method of the modified straw stalk biochar as claimed in claim 4 in removing methylene blue and cation red in water bodies in sewage, wherein the prepared modified straw stalk biochar is used for treating methylene blue wastewater within the range of pH being more than or equal to 7 and less than or equal to 13 and treating cation red wastewater within the range of pH being more than or equal to 1 and less than or equal to 13.
6. The application of the biochar prepared by the preparation method of the modified straw stalk biochar according to claim 4 or 5 in removing methylene blue and cation red in a water body in sewage is characterized in that the adsorption equilibrium time of the prepared modified straw stalk biochar to methylene blue and cation red is 2-24 h, and the adsorption equilibrium time to methylene blue is 4-24 h.
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