CN117884095B - A method for preparing composite modified sand-granulated microcrystalline activated carbon - Google Patents

Abstract

The invention relates to a preparation method of composite modified sand-grained microcrystalline activated carbon, which comprises the following steps: s1: cleaning the raw materials of microcrystalline activated carbon and sand particles, mixing and stirring in ammonia water, and carrying out first ammonia water modification to obtain a first modified product; s2: putting the primary modified product and the sand grains remained in the step S1 into extrusion equipment for granulating and molding to obtain granulated microcrystalline activated carbon; s3: mixing plant biomass, sand grains and water into paste, uniformly mixing the paste with the sand-grained microcrystalline activated carbon, and then feeding the mixture into a muffle furnace for high-temperature calcination to obtain remolded activated carbon; s4: adding the remolded activated carbon into ammonia water, and carrying out secondary ammonia water modification to obtain a secondary modified product; s5: uniformly spraying polytetrafluoroethylene solution on the surface of the secondary modified product, carrying out hydrophobic modification, airing, and then sending into a muffle furnace for drying to obtain the final composite modified granulated microcrystalline activated carbon.

Description

A method for preparing composite modified sand-granulated microcrystalline activated carbon

Technical Field

The invention belongs to the technical field of activated carbon modification, and in particular relates to a method for preparing composite modified sand-granulated microcrystalline activated carbon.

Background technique

Microcrystalline activated carbon is a carbon material with a special structure, with a specific surface area of ^70-900m2 /g. It contains a large number of relatively complete graphite-like microcrystalline structures with a size of 1-3nm. Compared with ordinary activated carbon, it has more obvious crystal characteristics and maintains a larger interlayer spacing. The interlayer spacing of graphite microcrystals is between 0.365-0.385nm. Microcrystalline activated carbon has a developed pore structure, a large specific surface area, strong adsorption and catalytic functions. As an excellent adsorbent, it is widely used in the field of water treatment and is an effective means to remove organic pollutants in water.

However, after using microcrystalline activated carbon to treat wastewater, it is not easy to separate from aerobic activated sludge due to its light weight. In addition, since the surface of microcrystalline activated carbon contains a large number of polar functional groups such as carboxyl and phenolic hydroxyl groups, it has strong hydrophilicity. The water molecules and pollutant molecules in the wastewater produce competitive adsorption, which makes the adsorption effect of microcrystalline activated carbon on pollutant molecules worse, thereby accelerating the "aging" process of microcrystalline activated carbon.

In addition, in the process of wastewater treatment, the remaining pollutants that are difficult to degrade in the biochemical effluent are mostly hydrophobic organic matter. The hydrophilic microcrystalline activated carbon has an unsatisfactory adsorption effect on such organic matter, and it is necessary to use advanced oxidation methods to remove organic matter, which is costly. In addition, if membrane-related technologies are used in sewage treatment, microcrystalline activated carbon is prone to cause membrane blockage.

Summary of the invention

In view of the above problems, the present invention provides a method for preparing composite modified sand-granulated microcrystalline activated carbon, comprising the following steps:

S1: Clean the raw material microcrystalline activated carbon and sand particles, mix and stir them in ammonia water, perform the first ammonia water modification, and obtain a first modified product;

S2: putting the first modified product and the remaining sand particles in step S1 into an extrusion device for granulation to obtain sand-granulated microcrystalline activated carbon;

S3: mixing plant biomass, sand and water into a paste, mixing the paste with the sanded microcrystalline activated carbon evenly, and then calcining at high temperature in a muffle furnace to obtain re-plasticized activated carbon;

S4: adding the remolded activated carbon into ammonia water to perform a second ammonia modification to obtain a secondary modified product;

S5: Use polytetrafluoroethylene solution to evenly spray the surface of the secondary modified product for hydrophobic modification, and then send it into a muffle furnace for drying after drying to obtain the final composite modified sand-granulated microcrystalline activated carbon.

Optionally, in step S1, the raw material microcrystalline activated carbon and sand particles are cleaned, including surface pretreatment of the microcrystalline activated carbon and surface pretreatment of the sand particles;

The surface pretreatment of microcrystalline activated carbon includes: (1) washing the microcrystalline activated carbon with distilled water to clean the ash on the surface of the microcrystalline activated carbon, and then filtering; (2) immersing the drained microcrystalline activated carbon in excess distilled water, and ultrasonically cleaning it for 2-3 hours to remove inorganic impurities in the pores of the microcrystalline activated carbon and dredge the microcrystalline activated carbon pores; (3) washing with 1-3 mol/L sodium hydroxide solution to remove organic impurities on the surface of the microcrystalline activated carbon, and then washing with tap water until it is neutral, draining the water, drying, and setting aside;

The surface pretreatment of the sand particles includes: washing and scrubbing the sand particles with tap water to clean the dirt, impurities, dust, etc. on the surface of the sand particles, then rinsing with distilled water, drying, and setting aside.

Optionally, in step S1, after cleaning, the particle size of the microcrystalline activated carbon is 0.5-1.2 mm, and the sand is crushed and ground to 300-500 mesh; the mass ratio of the microcrystalline activated carbon to the sand is (2-2.5):1.

Optionally, in step S1, the first ammonia modification is specifically as follows: first, add microcrystalline activated carbon into a reactor, add 25-28wt% ammonia water, and the mass volume ratio of microcrystalline activated carbon to ammonia water is 1g:(10-20)mL; stir to fully disperse the microcrystalline activated carbon, then add sand particles, and stir and mix at 50-80°C; the reactor is sealed and provided with an exhaust pipe, which is connected to the top and bottom of the reactor, and the volatilized ammonia gas is extracted and returned to the inside of the reactor, forming ammonia aeration at the bottom of the reactor, and the temperature in the reactor is conducive to the ammonia gas re-dissolving into water;

After the modification, the ammonia water is discharged, and clean water is added several times, and stirring is continued until the pH in the reactor is 7-8, thereby obtaining the primary modified product and the remaining sand particles.

After the surface of the microcrystalline activated carbon is initially modified by ammonia water, the acid-base properties of the surface will change, the reducing functional groups on the surface will increase, and the adsorption performance of non-polar substances will be improved. At the same time, ammonia water can promote the formation and development of pores on the surface of the microcrystalline activated carbon, and increase its specific surface area and porosity. Inside the reactor, the microcrystalline activated carbon and sand particles are in a mechanically mixed state, which is conducive to the embedding of sand particles with smaller particle size into the internal pores of the microcrystalline activated carbon, so that the microcrystalline activated carbon has sand particles inside, which helps to increase the internal solid weight of the microcrystalline activated carbon, making it easy to separate the modified microcrystalline activated carbon from aerobic sludge in subsequent applications.

After the microcrystalline activated carbon is fully dispersed, the mass of a single microcrystalline activated carbon particle is sampled and detected, which is recorded as the initial mass. During the first ammonia modification process, the microcrystalline activated carbon in the reactor is sampled and the mass of a single sample particle is detected until the weight of the single sample particle increases to 120-140% of the initial mass, indicating that the first ammonia modification is completed.

Optionally, in step S2, the once modified product and the remaining sand particles of step S1 contain a certain amount of water after being discharged from the reactor, with a water content of 10-15wt%, and can be directly granulated. The solidified microcrystalline activated carbon and the crushed sand particles are mixed into sand-granulated microcrystalline activated carbon with a particle size of 0.6-2.5mm, and then naturally cooled to room temperature.

Optionally, in step S3, the plant biomass is selected from one or more of crops, herbs, and aquatic plants, and the roots, stems, and leaves of crops, herbs, and aquatic plants may be used; the sand used in step S3 is the above-mentioned crushed and ground sand (300-500 mesh), and the plant biomass is crushed, dried, and then ground to a particle size of 300-500 mesh;

The mass ratio of plant biomass to sand is (1.5-2.5):1, and the mass ratio of sand to sand-granulated microcrystalline activated carbon is (0.7-1.3):1. There is no limit on the amount of water added, as long as it can be made into a paste;

The granulated microcrystalline activated carbon obtained in step S2 is stirred and mixed evenly with the above-mentioned paste, so that the surface of the granulated microcrystalline activated carbon is evenly covered with the paste, and then the mixture is sieved as a whole, leaving the granulated microcrystalline activated carbon covering the paste on the sieve, and then the sieve material is collected and sent to a muffle furnace. The heating temperature of the muffle furnace is 900-1100°C, and the heating is carried out for 5-7 hours. After heating, it is taken out and cooled naturally.

Step S3: uniformly coat a layer of mixed slurry of biomass and sand on the surface of the sand-granulated microcrystalline activated carbon, and then calcine at high temperature in a muffle furnace to carbonize the biomass, forming a layer of carbonized material on the surface and near the surface of the activated carbon, and having micropores and internal pore structure, with a large specific surface area, which makes up for the reduction of pores and specific surface area of the activated carbon due to the embedding of sand particles; at the same time, the mixed slurry contains sand particles, which is conducive to the embedding of sand particles into the pores of the newly formed carbonized material, and promotes the combination of carbonized material and activated carbon. The particle size of the remolded activated carbon is 0.8-3mm, and sand particles are embedded inside and near the outside, so that the sand modification of the activated carbon is more uniform and thorough, and the sand particles are not easy to lose in subsequent applications.

Optionally, in step S4, the reactor of step S1 is used, the remolded activated carbon is added into the reactor, 25-28wt% ammonia water is added, and the mass volume ratio of the remolded activated carbon to the ammonia water is 1g:(5-10)mL; the remolded activated carbon is stirred at 50-80°C to fully disperse and mix with the ammonia water; the exhaust pipe of the reactor extracts the volatilized ammonia gas and returns it to the inside of the reactor, forming ammonia aeration at the bottom of the reactor;

Mix for 10-12 hours, then drain the ammonia water, add clean water several times, and continue stirring until the pH in the reactor is 7-8 to obtain the secondary modified product, and then dry it in an oven at 100°C for 5-6 hours.

The present invention performs a second ammonia modification on the remolded activated carbon, using ammonia as a reducing modifier. Ammonia is cheaper than sodium hydroxide, and can generate free radicals such as · _NH2 , ·NH and ·H at a higher temperature. These free radicals react with the acidic groups on the surface of the remolded activated carbon to generate substances such as amino derivatives, which can effectively remove the acidic oxygen-containing groups on the surface of the activated carbon, and introduce nitrogen-containing basic groups to increase the number of basic groups on the surface of the activated carbon, thereby enhancing the non-polarity of the surface of the microcrystalline activated carbon. At the same time, ammonia can promote the formation and development of pores on the surface of the remolded activated carbon, further increasing its specific surface area and porosity.

Optionally, in step S5, the concentration of the polytetrafluoroethylene solution is 30-40wt%, and the medium is water; the mass volume ratio of the secondary modified product to the sprayed polytetrafluoroethylene solution is 1g:(0.01-0.25)mL, and the polytetrafluoroethylene forms a hydrophobic layer on the surface of the secondary modified product to improve the hydrophobicity of the activated carbon;

The standard for drying is that the surface of activated carbon particles is not sticky;

The activated carbon particles are dried in a muffle furnace by programmed temperature increase, from 8-10°C to 80°C for 40 minutes; from 5-7°C to 150°C for 20 minutes; from 5-7°C to 200°C for 20 minutes; after heating, the material is taken out and cooled naturally.

The above heating can cure the polytetrafluoroethylene coating. While the polytetrafluoroethylene coating is curing, since part of the polytetrafluoroethylene will penetrate into the pore channels of the secondary modified product, the programmed temperature increase and the selection of the heating temperature can make the polytetrafluoroethylene cure slowly and maintain fluidity, thereby performing hydrophobic modification on the pore channels of the secondary modified product, rather than quickly curing on the particle surface and blocking the pores; the above programmed temperature increase conditions.

In the aspect of hydrophobic modification, the present invention uses polytetrafluoroethylene, which has the characteristics of corrosion resistance, aging resistance, high lubricity, non-adhesion, etc. In addition, as a dispersion liquid with low surface energy, it exhibits the characteristics of stable properties and non-toxicity, and is loaded on the surface of microcrystalline activated carbon, which can improve its surface hydrophobicity and slow down the "aging" process of the microcrystalline activated carbon.

The present invention adopts a composite modification method of ammonia water modification and polytetrafluoroethylene hydrophobic coating loading, which can further enhance the hydrophobic property of the surface of microcrystalline activated carbon, and at the same time, after ammonia water modification, the loss of polytetrafluoroethylene, a low surface energy substance loaded on the surface of microcrystalline activated carbon, can be avoided. The prepared hydrophobic activated carbon has a good adsorption effect on non-polar substances and stable adsorption performance.

Since the loading of polytetrafluoroethylene coating will inevitably lose part of the original pores of activated carbon, the adsorption performance will be reduced. The present invention creatively adopts a method of twice ammonia modification combined with biomass carbon coating. After the first ammonia modification, the microcrystalline activated carbon is first treated to promote the growth of pores and channels, and favorable conditions are prepared in advance. Then, a paste of plant biomass and sand particles is configured, and under roasting conditions, the structure of the activated carbon is reshaped to increase its overall specific surface area and pore channels. At the same time, the first ammonia modification promotes the entry of sand particles into the interior of the activated carbon and improves the solidity; extrusion granulation molding and paste coating can increase the loading amount of sand particles on the surface or outside of the activated carbon. After the second ammonia modification and hydrophobic modification, a composite modified sand-granulated microcrystalline activated carbon with high specific surface area, high porosity, high sand particle loading amount and good hydrophobicity is finally obtained.

Detailed ways

Example 1

The present embodiment provides a method for preparing a composite modified sand-granulated microcrystalline activated carbon, comprising the following steps:

S1: Clean the raw material microcrystalline activated carbon (20 g coconut shell activated carbon) and sand, mix and stir in ammonia water, perform the first ammonia water modification, and obtain a first modified product;

S2: putting the first modified product and the remaining sand particles in step S1 into an extrusion device for granulation to obtain sand-granulated microcrystalline activated carbon;

S3: mixing plant biomass, sand and water into a paste, mixing the paste with the sanded microcrystalline activated carbon evenly, and then calcining at high temperature in a muffle furnace to obtain re-plasticized activated carbon;

S4: adding the remolded activated carbon into ammonia water to perform a second ammonia modification to obtain a secondary modified product;

S5: Use polytetrafluoroethylene solution to evenly spray the surface of the secondary modified product for hydrophobic modification, and then send it into a muffle furnace for drying after drying to obtain the final composite modified sand-granulated microcrystalline activated carbon.

In step S1, the raw material microcrystalline activated carbon and sand particles are cleaned, including surface pretreatment of the microcrystalline activated carbon and surface pretreatment of the sand particles;

The surface pretreatment of the microcrystalline activated carbon includes: (1) washing the microcrystalline activated carbon with distilled water to clean the ash on the surface of the microcrystalline activated carbon, and then filtering; (2) immersing the drained microcrystalline activated carbon in excess distilled water, and ultrasonically cleaning it for 2 hours to remove inorganic impurities in the pores of the microcrystalline activated carbon and dredge the microcrystalline activated carbon pores; (3) washing with 2 mol/L sodium hydroxide solution to remove organic impurities on the surface of the microcrystalline activated carbon, and then washing with tap water until it is neutral, draining the water, drying it, and setting it aside;

The surface pretreatment of the sand particles includes: washing and scrubbing the sand particles with tap water to clean the dirt, impurities, dust, etc. on the surface of the sand particles, then rinsing with distilled water, drying, and setting aside.

In step S1, after cleaning, the particle size of the microcrystalline activated carbon is 0.5-0.8 mm, and the sand is crushed and ground to 300-500 mesh; the mass ratio of the microcrystalline activated carbon to the sand is 2:1.

In step S1, the first ammonia modification is specifically as follows: first, add microcrystalline activated carbon into a reactor, add 25wt% ammonia water, and the mass volume ratio of microcrystalline activated carbon to ammonia water is 1g:10mL; stir to fully disperse the microcrystalline activated carbon, then add sand particles, and stir and mix at 80°C; the reactor is sealed and provided with an exhaust pipe, which is connected to the top and bottom of the reactor, and the volatilized ammonia gas is extracted and returned to the reactor, forming ammonia aeration at the bottom of the reactor, and the temperature in the reactor is conducive to the ammonia gas re-dissolving into water;

After the modification, the ammonia water is discharged, and clean water is added several times, and stirring is continued until the pH in the reactor is 7-8, thereby obtaining the primary modified product and the remaining sand particles.

After the microcrystalline activated carbon is fully dispersed, the mass of a single microcrystalline activated carbon particle is tested by sampling. The sampling is tested 10 times, and the average value is calculated and recorded as the initial mass. During the first ammonia modification process, the microcrystalline activated carbon in the reactor is sampled and the mass of a single sample particle is tested until the weight of the single sample particle increases to 120% of the initial mass, indicating that the first ammonia modification is completed.

In step S2, after the primary modified product and the remaining sand particles in step S1 are discharged from the reactor, the moisture content is 10wt%, and granulation can be directly performed. The solidified microcrystalline activated carbon and the crushed sand particles are mixed into sand-granulated microcrystalline activated carbon with an average particle size of 1.5mm, and then naturally cooled to room temperature.

In step S3, the plant biomass includes straw and weeds, and roots, stems and leaves can all be used; the sand used in step S3 is the above-mentioned crushed and ground sand (300-500 mesh), and the plant biomass is crushed, dried and then ground to a particle size of 300-500 mesh;

The mass ratio of plant biomass to sand is 1.5:1, and the mass ratio of sand to sand-granulated microcrystalline activated carbon is 0.7:1. There is no limit on the amount of water added, as long as it can be made into a paste;

The granulated microcrystalline activated carbon obtained in step S2 is stirred and mixed evenly with the above-mentioned paste, so that the surface of the granulated microcrystalline activated carbon is evenly covered with the paste, and then the mixture is sieved as a whole, leaving the granulated microcrystalline activated carbon covering the paste on the sieve, and then the sieved material is collected and sent to a muffle furnace. The muffle furnace is heated to a temperature of 1000°C for 5 hours, and then taken out and naturally cooled after heating.

In step S4, the reactor of step S1 is used, the remolded activated carbon is added into the reactor, 25 wt% ammonia water is added, and the mass volume ratio of the remolded activated carbon to the ammonia water is 1 g:5 mL; the remolded activated carbon is stirred at 80° C. to fully disperse and mix with the ammonia water; the exhaust pipe of the reactor extracts the volatilized ammonia gas and returns it to the reactor, forming ammonia aeration at the bottom of the reactor;

The mixture was mixed for 10 hours, and then the ammonia water was discharged, and clean water was added several times and stirred continuously until the pH in the reactor was 7-8 to obtain the secondary modified product, which was then dried in an oven at 100° C. for 5-6 hours.

In step S5, the concentration of the polytetrafluoroethylene solution is 30wt%, and the medium is water; the mass volume ratio of the secondary modified product to the polytetrafluoroethylene solution used for spraying is 1g:0.01mL;

The standard for drying is that the surface of activated carbon particles is not sticky;

The activated carbon particles are dried by programmed temperature increase in a muffle furnace, with the temperature increased from 10°C to 80°C for 40 minutes; the temperature increased from 5°C to 150°C for 20 minutes; the temperature increased from 5°C to 200°C for 20 minutes; after heating, the material is taken out and cooled naturally to obtain the final composite modified sand-granulated microcrystalline activated carbon.

The total mass of the final composite modified sand-granulated microcrystalline activated carbon prepared in this embodiment is 58 g, which is a significant increase in weight.

Comparative Example 1

The preparation method of a composite modified sand-granulated microcrystalline activated carbon provided in this comparative example is the same as that in Example 1, except that the first ammonia modification and the second ammonia modification are not performed, and step S3 is not implemented.

After the raw materials of step S1, the microcrystalline activated carbon and sand are cleaned, the microcrystalline activated carbon and sand are directly mixed evenly in water to obtain a mixture with a moisture content of 10wt%, and then put into an extrusion device for granulation to obtain sand-granulated microcrystalline activated carbon; then step S5 is implemented, and the surface of the sand-granulated microcrystalline activated carbon is evenly sprayed with a polytetrafluoroethylene solution, and the subsequent steps are the same as in Example 1.

Comparative Example 2

The preparation method of a composite modified sand-granulated microcrystalline activated carbon provided in this comparative example is the same as that in Example 1, except that the first ammonia modification is not performed.

After the raw materials of the microcrystalline activated carbon and the sand particles in step S1 are cleaned, the microcrystalline activated carbon and the sand particles are directly mixed evenly in water to obtain a mixture with a moisture content of 10 wt%, and then put into an extrusion device for granulation to obtain sand-granulated microcrystalline activated carbon.

Comparative Example 3

The preparation method of a composite modified sand-granulated microcrystalline activated carbon provided in this comparative example is the same as that of Example 1, except that step S3 is not implemented, and the sand-granulated microcrystalline activated carbon is directly subjected to a second ammonia modification.

Comparative Example 4

The preparation method of a composite modified sand-granulated microcrystalline activated carbon provided in this comparative example is the same as that of Example 1, except that no second ammonia modification is performed, and polytetrafluoroethylene solution is used to evenly spray the re-plasticized activated carbon for hydrophobic modification.

Example 2

The method for preparing a composite modified sand-granulated microcrystalline activated carbon provided in this embodiment is the same as that in Embodiment 1, except that the mass volume ratio of the microcrystalline activated carbon to the ammonia water in step S1 is 1 g:20 mL.

Example 3

The preparation method of a composite modified sand-granulated microcrystalline activated carbon provided in this embodiment is the same as that in Embodiment 1, except that the mass volume ratio of the microcrystalline activated carbon to the ammonia water in step S1 is 1 g:9 mL.

Example 4

The method for preparing a composite modified sand-granulated microcrystalline activated carbon provided in this embodiment is the same as that in Embodiment 1, except that the mass ratio of plant biomass to sand in step S3 is 2.5:1.

Example 5

The method for preparing a composite modified sand-granulated microcrystalline activated carbon provided in this embodiment is the same as that in Embodiment 1, except that the mass ratio of plant biomass to sand in step S3 is 1.4:1.

Example 6

The method for preparing a composite modified sand-granulated microcrystalline activated carbon provided in this embodiment is the same as that in Embodiment 1, except that in step S3, the mass ratio of sand to sand-granulated microcrystalline activated carbon is 1.3:1.

Example 7

The method for preparing a composite modified sand-granulated microcrystalline activated carbon provided in this embodiment is the same as that in Embodiment 1, except that in step S3, the mass ratio of sand to sand-granulated microcrystalline activated carbon is 0.6:1.

Example 8

The present embodiment provides a method for preparing a composite modified sand-granulated microcrystalline activated carbon, which is the same as that of Embodiment 1, except that the mass volume ratio of the remolded activated carbon to the ammonia water in step S4 is 1 g:10 mL.

Embodiment 9

The present embodiment provides a method for preparing a composite modified sand-granulated microcrystalline activated carbon, which is the same as that of Embodiment 1, except that the mass volume ratio of the remolded activated carbon to the ammonia water in step S4 is 1 g:4 mL.

Example 10

The preparation method of a composite modified sand-granulated microcrystalline activated carbon provided in this embodiment is the same as that in Embodiment 1, except that the mass volume ratio of the secondary modified product to the sprayed polytetrafluoroethylene solution in step S5 is 1 g:0.25 mL.

Embodiment 11

The preparation method of a composite modified sand-granulated microcrystalline activated carbon provided in this embodiment is the same as that in Embodiment 1, except that the mass volume ratio of the secondary modified product to the sprayed polytetrafluoroethylene solution in step S5 is 1 g:0.26 mL.

Example 12

The preparation method of a composite modified sand-granulated microcrystalline activated carbon provided in this embodiment is the same as that in Embodiment 1, except that in step S5, the muffle furnace is heated at 200° C. for 80 min.

Table 1 Comparison of specific surface areas of composite modified sand-granulated microcrystalline activated carbon of the embodiment and the comparative example

Table 2 Comparison of hydrophobicity of composite modified sand-granulated microcrystalline activated carbon in the examples

It can be seen from Table 1 and Table 2 that the present invention provides a method for preparing a composite modified sand-granulated microcrystalline activated carbon, which still has a large specific surface area on the basis of obvious weight gain, does not affect its adsorption or catalytic performance, and after hydrophobic modification, the contact angle reaches more than 170°.

Claims (9)

1. The preparation method of the composite modified granulated microcrystalline activated carbon is characterized by comprising the following steps of:

S1: cleaning the raw materials of microcrystalline activated carbon and sand particles, mixing and stirring in ammonia water, and carrying out first ammonia water modification to obtain a first modified product;

S2: putting the primary modified product and the sand grains remained in the step S1 into extrusion equipment for granulating and molding to obtain granulated microcrystalline activated carbon;

S3: mixing plant biomass, sand grains and water into paste, uniformly mixing the paste with the sand-grained microcrystalline activated carbon, and then feeding the mixture into a muffle furnace for high-temperature calcination to obtain remolded activated carbon;

S4: adding the remolded activated carbon into ammonia water, and carrying out secondary ammonia water modification to obtain a secondary modified product;

S5: uniformly spraying polytetrafluoroethylene solution on the surface of a secondary modified product, carrying out hydrophobic modification, airing, and then sending into a muffle furnace for drying to obtain the final composite modified granulated microcrystalline activated carbon;

In step S1, the first ammonia modification specifically includes: firstly, adding microcrystalline active carbon into a reactor, and adding 25-28wt% ammonia water, wherein the mass volume ratio of the microcrystalline active carbon to the ammonia water is 1g (10-20) mL; stirring to disperse microcrystalline active carbon, adding sand grains, and stirring and mixing at 50-80deg.C;

the reactor is sealed and is provided with an exhaust pipe, the exhaust pipe is communicated with the top and the bottom of the reactor, volatilized ammonia gas is extracted and returned to the inside of the reactor, ammonia gas aeration is formed at the bottom of the reactor, and the temperature in the reactor is favorable for the ammonia gas to be dissolved into water again;

And (3) discharging ammonia water after modification, adding clear water for a plurality of times, and continuing stirring until the pH value in the reactor is 7-8, so as to obtain the primary modified product and the residual sand grains.

2. The method for producing a composite modified grittized activated carbon according to claim 1, wherein in step S1, after cleaning, the particle size of the activated carbon is 0.5 to 1.2mm, and the grittized activated carbon is crushed and ground to 300 to 500 mesh; the mass ratio of the microcrystalline active carbon to the sand grains is (2-2.5): 1.

3. The method for preparing composite modified sand-granulated activated carbon according to claim 2, wherein after the microcrystalline activated carbon is sufficiently dispersed, sampling and detecting the mass of single grain of the microcrystalline activated carbon, and recording as the initial mass; in the first ammonia water modification process, sampling microcrystalline activated carbon in the reactor, and detecting the mass of single sample particles until the weight of the single sample particles is increased to 120-140% of the initial mass, wherein the end of the first ammonia water modification is indicated.

4. The method for producing composite modified and micronized microcrystalline activated carbon according to claim 2, wherein in step S2, after the primary modified product and the remaining sand grains of step S1 are discharged from the reactor, the water content is 10-15wt%, granulation can be directly performed, and the solidified microcrystalline activated carbon and the crushed sand grains are mixed to form granulated microcrystalline activated carbon with a grain size of 0.6-2.5mm, and naturally cooled to room temperature.

5. The method for preparing composite modified sand-granulated activated carbon according to claim 2, wherein in step S3, the plant biomass includes straw and weeds, and roots, stems and leaves can be used;

The sand grain used in the step S3 is crushed and ground, and the grain size is 300-500 meshes.

6. The method for producing a composite modified, grittized, microcrystalline activated carbon according to claim 5, wherein the mass ratio of the plant biomass to the sand is (1.5-2.5): 1, and the mass ratio of the sand to the grittized, microcrystalline activated carbon is (0.7-1.3): 1.

7. The method for producing composite modified gritty activated carbon according to claim 6, wherein the gritty activated carbon obtained in step S2 is stirred and mixed with the paste uniformly so that the surface of the gritty activated carbon is covered with the paste uniformly, the mixture is sieved as a whole, the gritty activated carbon covered with the paste is left on the sieve, the oversize is collected and fed into a muffle furnace, the muffle furnace is heated at 900-1100 ℃ for 5-7h, and the mixture is taken out after being heated and cooled naturally.

8. The method for preparing composite modified sand-grained activated carbon according to claim 2, wherein in the step S4, the reactor of the step S1 is used, the remolded activated carbon is added into the reactor, 25-28wt% of ammonia water is added, and the mass-volume ratio of the remolded activated carbon to the ammonia water is 1g (5-10) mL;

Stirring at 50-80deg.C to disperse the remolded activated carbon, and mixing with ammonia water; the exhaust pipe of the reactor extracts the volatilized ammonia gas and returns the volatilized ammonia gas to the inside of the reactor, so that ammonia gas aeration is formed at the bottom of the reactor;

mixing for 10-12h, discharging ammonia water, adding clear water for a plurality of times, continuously stirring until the pH value in the reactor is 7-8, obtaining the secondary modified product, and drying in a drying oven at 100 ℃ for 5-6h.

9. The method for producing a composite modified grittized microcrystalline activated carbon according to claim 1, wherein in step S5, the concentration of the polytetrafluoroethylene solution is 30 to 40wt%; the mass volume ratio of the secondary modified product to the sprayed polytetrafluoroethylene solution is 1g (0.01-0.25) mL;

The active carbon particles are subjected to programmed heating drying in a muffle furnace, and heated to 80 ℃ at 8-10 ℃ for 40min; heating to 150 deg.C at 5-7deg.C for 20min; heating to 200 deg.C at 5-7deg.C for 20min; and after heating, taking out the materials and naturally cooling.