CN110577219A - A kind of magnetic sludge straw-based activated carbon and preparation method thereof - Google Patents

Abstract

A magnetic sludge straw-based activated carbon and a preparation method thereof, the activated carbon is mainly made from the following raw materials: dry sludge, dry straw, foaming agent, carbonate and iron salt. The method is as follows: (1) crushing the dry sludge and dry straw, drying, crushing and sieving; (2) adding a foaming agent, mixing evenly, then adding an aqueous solution of carbonate, shaking and activating, and drying (3) in an inert atmosphere, after heating and carbonization, cooling, ultrasonic cleaning, water washing, suction filtration, and drying; (4) adding an aqueous solution of iron salts, oscillating adsorption, and drying; (5) under an inert atmosphere, After heating and carbonization, cooling, ultrasonic cleaning, water washing, suction filtration, drying, and finished. The magnetic sludge straw-based activated carbon has a wide range of raw materials, is cheap and easy to obtain, has abundant pore structure, stable magnetic properties, high compressive strength, good wear resistance, good water resistance, and can be reused; the method of the invention is simple, low in cost, and suitable for in industrial production.

Description

A kind of magnetic sludge straw-based activated carbon and preparation method thereof

technical field

The invention relates to an activated carbon and a preparation method thereof, in particular to a magnetic sludge straw-based activated carbon and a preparation method thereof.

Background technique

At present, most of the commercial activated carbons on the market are prepared from coal, wood and fruit shells, etc. However, these raw materials have limited resources and high cost. With the development of industrialization and the improvement of environmental protection requirements, the demand for activated carbon is gradually increasing, and it is increasingly urgent to seek a high-performance and low-cost activated carbon preparation technology.

Municipal sludge is the main by-product of domestic sewage treatment plants. With the increase of urbanization rate, the amount of municipal sludge is also increasing year by year. At present, the total annual output of municipal sludge in my country exceeds 40 million tons per year (with a moisture content of 80%), and it is increasing at a rate of 15-18% year by year, but more than 80% of the municipal sludge in my country has not been properly disposed of. Municipal sludge accumulates 30-50% of COD and 40-70% of organic matter in sewage, which is a carbon resource with high carbon content and can be used as a raw material to prepare activated carbon. The preparation of sludge-based activated carbon can be used as a substitute for traditional activated carbon prepared from precious materials such as coal and wood. Use, the purpose of treating waste with waste.

Sludge-based activated carbon is granular, which has the advantages of low price and fast adsorption speed. However, due to the high sand content in municipal sludge, the quality of activated carbon is not high, and there are disadvantages such as difficulty in recycling in practical applications. The application in the field of environmental protection is greatly restricted. Moreover, in the traditional use process of activated carbon, there are problems such as blockage of the filtration separation method or the loss of activated carbon.

CN103521179A discloses a one-step method for preparing sludge-based shaped activated carbon. The sludge-based shaped magnetic activated carbon is prepared by mixing sludge with nanoscale Fe ₃ O ₄ , adding a binder and a foaming agent to form the activated carbon. However, the high sand content in the sludge will adversely affect the specific surface area and pore structure of the sludge-based activated carbon, and the cost of nano-scale Fe ₃ O ₄ is also relatively high.

CN103521180A discloses a preparation method of sludge-based shaped magnetic activated carbon, which uses sludge as raw material, KOH or ZnCl ₂ as activator, nano-scale Fe ₃ O ₄ as magnetic source, and organic-inorganic composite agent as foaming agent and binder. However, the disadvantages of insufficiently developed specific surface area and pore structure of magnetic sludge-based activated carbon are also not solved; in addition, the activator in the process of this method is highly corrosive or toxic, which is likely to cause secondary pollution and the cost is relatively high. .

CN107175078A discloses a preparation method of sludge buckwheat-based magnetic activated carbon, which is prepared by mixing sludge and buckwheat straw, impregnating with ZnCl ₂ and FeCl ₃ mixed solution and then carbonizing. However, in this method, toxic ZnCl ₂ is used as an activator, which is likely to bring about secondary pollution problems.

CN104028221A discloses a preparation method of magnetic activated carbon, which is prepared by using cow dung, sludge, crop straw and coal powder as raw materials, KOH solution as activator, iron powder core or iron-silicon-aluminum powder core as magnetic source, and microwave heating to prepare . However, the preparation procedure of this method is relatively complicated, the requirements for raw materials and magnetic source materials are relatively high, and the selected activator has strong corrosiveness.

In summary, there are many related literatures and reports on the preparation of sludge-based activated carbon and its magnetic loading, but due to the limitation of raw materials, it is not conducive to the development of the specific surface area and pore structure of magnetic sludge-based activated carbon, and it is easy to corrode equipment and produce. secondary pollution, etc.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art, and to provide a kind of raw material with wide source, cheap and easy to obtain, large specific surface area, small average pore size, large total pore volume, abundant pore structure, stable magnetic properties, high resistance to High compressive strength, good abrasion resistance, good water resistance, reusable magnetic sludge straw-based activated carbon.

The further technical problem to be solved by the present invention is to overcome the above-mentioned defects in the prior art, and to provide a preparation method of magnetic sludge straw-based activated carbon with simple process, low cost and suitable for industrial production.

The technical scheme adopted by the present invention to solve the technical problem is as follows: a magnetic sludge straw-based activated carbon is mainly made from the following raw materials: dry sludge, dry straw, foaming agent, carbonate and iron salt. Adding straw to the sludge can increase the carbon content in the raw materials, thereby increasing the pore structure inside the sludge-based activated carbon and improving its adsorption performance; at the same time, straw is agricultural waste, and it is used as an auxiliary raw material to prepare activated carbon, which achieves a waste-free life. Reuse, with the purpose of treating waste with waste. The pore structure of sludge-based activated carbon can be regulated by blowing agent and carbonate. Adding foaming agent to the mixed material of sludge and straw can not only promote the formation of pore structure in the activation stage, but also enhance the strength and flexibility of the mixed material, and improve the material hardness of sludge-based activated carbon; At this stage, carbonate can not only adjust the pore structure of sludge-based activated carbon, but also promote the formation of mesoporous structure of sludge-based activated carbon. By loading variable valence metal materials, the chemical adsorption process of sludge-based activated carbon can be improved, and the adsorption performance of sludge-based activated carbon can be further improved, and it can be recovered by magnetic separation during use to solve technical defects such as filtration and separation blockage or activated carbon loss. Dry sludge and dry straw are preferably obtained by natural air drying.

Preferably, the weight parts of each raw material of the magnetic sludge straw-based activated carbon are: 20-40 parts of dry sludge, 60-80 parts of dry straw, 5-10 parts of foaming agent, 5-15 parts of carbonate and iron 5 to 10 parts of salt. Too much sludge will cause high sand content in the raw materials, which is not conducive to the improvement of the pore structure and specific surface area of the sludge straw-based activated carbon. If the straw content is too high, the yield and compressive strength of the product will be reduced.

Preferably, the dry sludge has a moisture content of 50-60% and a carbon content of 15-30%, wherein the fixed carbon content is 5-10%.

Preferably, the sludge is one or more of municipal sludge, papermaking sludge or farm wastewater sludge.

Preferably, the dry straw has a moisture content of 50-60% and a carbon content of 30-50%, wherein the fixed carbon content is 5-10%. The sum of the moisture content and carbon content is less than 100%.

Preferably, the straw is one or more of corn straw, rice straw or sorghum straw.

Preferably, the foaming agent is one or more of azodicarbonamide, azoformamide or p-toluenesulfonyl hydrazide. The foaming agents are all organic foaming agents, which are non-toxic, and will decompose when the temperature exceeds 200° C. to generate a large amount of nitrogen, which is beneficial to the pore-forming behavior of the internal pore structure of the sludge straw-based activated carbon.

Preferably, the carbonate is one or more of potassium carbonate, calcium carbonate or sodium carbonate. The carbonates are all neutral salts, which are less corrosive, and can be decomposed to generate CO ₂ gas under high temperature conditions, which is conducive to the further pore-forming behavior of the internal pore structure of the sludge straw-based activated carbon, and can also affect the sludge straw-based activated carbon. The pore structure inside the activated carbon is adjusted.

Preferably, the iron salt is one or more of ferric nitrate, ferric chloride or ferric sulfate, and hydrates thereof.

The technical solution adopted by the present invention to further solve the technical problem is as follows: a preparation method of magnetic sludge straw-based activated carbon, comprising the following steps:

(1) Crushing the dry sludge and dry straw, drying to constant weight, pulverizing and sieving to obtain the mixed powder of sludge and straw;

(2) adding a foaming agent to the mixed powder of sludge and straw obtained in step (1), mixing evenly, then adding an aqueous solution of carbonate, shaking and activating, and drying to obtain a precursor of sludge and straw-based activated carbon;

(3) The sludge straw-based activated carbon precursor obtained in step (2) is heated and carbonized in an inert atmosphere, cooled to room temperature with the furnace, ultrasonically cleaned, washed with water, suction filtered, and dried to constant weight to obtain the sludge straw-based activated carbon precursor. activated carbon;

(4) adding an aqueous solution of iron salt to the sludge straw-based activated carbon obtained in step (3), oscillating and dipping, and drying to obtain a magnetic sludge straw-based activated carbon precursor;

(5) The magnetic sludge straw-based activated carbon precursor obtained in step (4) is heated and carbonized in an inert atmosphere, cooled to room temperature with the furnace, ultrasonically cleaned, washed with water, suction filtered, and dried to constant weight to obtain magnetic sludge. Straw-based activated carbon.

Preferably, in step (1), the drying temperature is 90-110°C.

Preferably, in step (1), the mesh number of the sieve is 40-80 mesh. Under the mesh size, the sludge and straw can be uniformly mixed.

Preferably, in step (2), the mass fraction of the carbonate aqueous solution is 5-15%. The aqueous carbonate solution is preferably prepared with carbon dioxide-free deionized water.

Preferably, in step (2), the oscillation activation rate is 80-120 r/min, and the time is 4-8 h. The vibration activation can promote the carbonate solution to fully impregnate the sludge straw mixture and mix evenly.

Preferably, in step (2), the drying temperature is 100-110° C., and the time is 10-14 h.

Preferably, in step (3), the inert atmosphere is one or more of nitrogen, argon or helium.

Preferably, in step (3), the heating rate is 2-8°C/min, and the temperature is raised to 750-900°C. During the heating process, the organic matter in the sludge and straw is decomposed by heat to form water vapor and small molecular hydrocarbons to escape, thereby forming a porous structure with well-developed pore structure. Among them, straw is beneficial to the increase of micropore content, and sludge is beneficial to the formation of carbon skeleton and the increase of activated carbon hardness. If the heating rate is too slow, the carbon production efficiency will be affected, and if the heating rate is too fast, the formation of the microporous structure will be affected.

Preferably, in step (3), the time for the carbonization at elevated temperature is 0.5-2.0 h. When the carbonization time is less than 0.5h, the organic matter in the raw materials will not be completely decomposed, and the aromatization will not be sufficient, which is not conducive to the formation of the internal pore structure of the activated carbon; and when the carbonization time is more than 2h, on the one hand, it will cause energy waste, on the other hand. On the one hand, the solidification reaction, shrinkage effect or collapse effect of the internal pore structure of the carbonized product will be induced, resulting in the reduction of the specific surface area and pore volume of the activated carbon.

Preferably, in step (3), the temperature of the ultrasonic cleaning is 60-100° C., the ultrasonic frequency is 20-40 kHz, and the time is 15-25 min. The purpose of ultrasonic cleaning is to remove ash in carbonized substances, thereby increasing the specific surface area and pore structure of activated carbon. Heating and ultrasonic treatment are beneficial to improve the removal rate of ash in carbonized materials.

Preferably, in step (3), the water washing and suction filtration are repeated ≥ 1 time until the pH value of the water washing solution is neutral.

Preferably, in step (4), the concentration of the iron salt aqueous solution is 0.5-1.5 mol/L.

Preferably, in step (4), the vibration impregnation rate is 100-140 r/min, and the time is 4-8 h. The purpose of oscillating impregnation is to mix the sludge straw-based activated carbon matrix with the iron salt solution evenly, so that the iron salt can be fully and uniformly loaded on the surface of the sludge straw-based activated carbon.

Preferably, in step (4), the drying temperature is 70-90° C., and the drying time is 10-20 h.

Preferably, in step (5), the inert atmosphere is one or more of nitrogen, argon or helium.

Preferably, in step (5), the heating rate is 2-8°C/min, and the temperature is raised to 150-300°C. During the heating process, the iron salt solution undergoes a thermal decomposition reaction, and a magnetic ferromagnetic material is formed inside the activated carbon, which makes the sludge straw-based activated carbon have stable magnetic properties.

Preferably, in step (5), the time for the carbonization at elevated temperature is 0.5-2.0 h.

Preferably, in step (5), the temperature of the ultrasonic cleaning is 60-100° C., the ultrasonic frequency is 20-40 kHz, and the time is 15-25 min.

Preferably, in step (5), the water washing and suction filtration are repeated ≥ 1 time until the pH value of the water washing solution is neutral.

The inert atmosphere used in the present invention is a high-purity atmosphere with a purity of ≥99.9%.

The room temperature in the present invention is 20-30°C.

The beneficial effects of the present invention are as follows:

(1) The magnetic sludge straw-based activated carbon of the present invention has a wide range of raw material sources, is cheap and easy to obtain, and realizes the resource reuse of solid waste. The specific surface area is as high as 596.78m ² /g, the average pore diameter is as small as 2.467nm, and the total pore volume Up to 0.389cm ³ /g, the proportion of micropore volume to total pore volume is as high as 75.96%, rich pore structure, stable magnetic properties, specific saturation magnetization as high as 8.5139emu/g, high compressive strength, good wear resistance, good water resistance ,reusable;

(2) The method of the present invention has simple process and low cost, and is suitable for industrial production;

(3) The magnetic sludge straw-based activated carbon of the present invention has a good application prospect in environmental treatment fields such as sewage purification treatment and soil heavy metal pollution prevention and control, and has good environmental effects and economic benefits.

Description of drawings

Fig. 1 is the nitrogen adsorption/desorption isotherm diagram of the magnetic sludge straw-based activated carbon obtained in Example 1 of the present invention;

2 is a pore size distribution diagram of the magnetic sludge straw-based activated carbon obtained in Example 1 of the present invention.

Detailed ways

The present invention will be further described below with reference to the embodiments and accompanying drawings.

The dried sludge used in the embodiment of the present invention comes from the dehydration workshop of a certain urban sewage treatment plant and is naturally air-dried. The moisture content of the dried sludge is 55% and the carbon content is 23%, wherein the fixed carbon content is 8%. %; the dry straws used in the examples of the present invention all come from a farm and are naturally air-dried. The dry sorghum straw has a moisture content of 57% and a carbon content of 32%, wherein the fixed carbon content is 6%; the carbonate aqueous solution used in the examples of the present invention is prepared with carbon dioxide-free deionized water; the implementation of the present invention The nitrogen and argon used in the examples are high-purity gases with a purity of ≥99.9%; the raw materials or chemical reagents used in the examples of the present invention are obtained through conventional commercial channels unless otherwise specified.

A kind of magnetic sludge straw-based activated carbon Examples 1-3

Table 1 shows the raw materials and parts by weight of the magnetic sludge straw-based activated carbon Examples 1-3.

Table 1 Raw materials and weight parts of examples 1-3 of magnetic sludge straw-based activated carbon

Note: "-" in the table means not added.

A kind of preparation method of magnetic sludge straw-based activated carbon Example 1

(1) According to the weight parts of each raw material in Example 1 in Table 1, crush the dry sludge and dry straw, dry at 105°C to a constant weight, pulverize with a high-speed universal pulverizer, and pass through a 60-mesh sieve to obtain sludge. mixed powder with straw;

(2) According to the weight parts of each raw material in Example 1 in Table 1, in the mixed powder of sludge and straw obtained in step (1), add a foaming agent, mix evenly, and then add an aqueous solution of carbonate with a mass fraction of 10% (configured with 10 parts by weight of potassium carbonate and 90 parts of carbon dioxide-free deionized water), at a rate of 100 r/min, after oscillating activation for 6 hours, and drying at 105 ° C for 12 hours, the sludge straw-based activated carbon precursor was obtained;

(3) The sludge straw-based activated carbon precursor obtained in step (2) was placed in the furnace of the box-type atmosphere electric furnace, and under high-purity nitrogen, heated to 800 °C for 1 h at a rate of 5 °C/min, and then cooled to 25 °C with the furnace. ℃, at 80 ℃, 30kHz, ultrasonic cleaning for 20min, repeated washing and suction filtration 3 times until the pH value of the washing solution is neutral, drying to constant weight, to obtain sludge straw-based activated carbon;

(4) According to the weight parts of each raw material in Example 1 in Table 1, to the sludge straw-based activated carbon obtained in step (3), add an aqueous solution of 1 mol/L iron salt (prepared from 7 parts by weight of ferric nitrate and deionized water) , at a rate of 120r/min, after shaking and immersing for 6h, and drying at 80°C for 15h, the magnetic sludge straw-based activated carbon precursor was obtained;

(5) The magnetic sludge straw-based activated carbon precursor obtained in step (4) was placed in a ceramic crucible in a box-type atmosphere furnace, and heated to 250 °C for 1.0 h under high-purity nitrogen at a rate of 5 °C/min. Cooled to 25°C with the furnace, ultrasonically cleaned for 20min at 80°C and 30kHz, repeated washing and suction filtration 3 times until the pH value of the washing solution was neutral, and dried to constant weight to obtain magnetic sludge straw-based activated carbon.

Through observation, the magnetic sludge straw-based activated carbon obtained in this example is granular, with good wear resistance, uniform size, high compressive strength and good water resistance.

As shown in Figures 1 and 2, the magnetic sludge straw-based activated carbon obtained in this example is characterized by BET, and its isotherm adsorption/desorption curve belongs to the combination of type I and type IV isotherms, and has an obvious H4-type hysteresis loop , which shows that the magnetic sludge straw-based activated carbon obtained in this example is mainly mesoporous and microporous; the specific surface area of the magnetic sludge straw-based activated carbon obtained in this example is 596.78 m ² /g, the average pore diameter is 2.467 nm, and the total pore size is 2.467 nm. The pore volume was 0.389 cm ³ /g, and the micropore volume accounted for 75.96% of the total pore volume.

The saturation magnetization test shows that the magnetic sludge straw-based activated carbon obtained in this example has a specific saturation magnetization of 8.5139 emu/g.

A kind of preparation method of magnetic sludge straw-based activated carbon Example 2

(1) According to the weight parts of each raw material in Example 2 in Table 1, crush the dry sludge and dry straw, dry to constant weight at 110°C, pulverize with a high-speed universal pulverizer, and pass through a 40-mesh sieve to obtain sludge. mixed powder with straw;

(2) According to the weight parts of each raw material in Example 2 in Table 1, in the mixed powder of sludge and straw obtained in step (1), add a foaming agent, mix evenly, and then add an aqueous solution of carbonate with a mass fraction of 5% (consisting of 5 parts by weight of potassium carbonate and 95 parts of carbon dioxide-free deionized water), at a rate of 120 r/min, after oscillating activation for 4 hours, and drying at 110 °C for 10 hours to obtain a sludge straw-based activated carbon precursor;

(3) The sludge straw-based activated carbon precursor obtained in step (2) was placed in the furnace of the box-type atmosphere electric furnace, heated to 750 °C for 1 h at a rate of 4 °C/min under high-purity nitrogen, and then cooled to 25 °C with the furnace. ℃, at 70℃, 40kHz, ultrasonic cleaning for 15min, repeated washing and suction filtration 2 times until the pH value of the washing solution is neutral, drying to constant weight, to obtain sludge straw-based activated carbon;

(4) According to the weight parts of each raw material in Example 2 in Table 1, to the sludge straw-based activated carbon obtained in step (3), add an aqueous solution of 1.2 mol/L iron salt (prepared from 5 parts by weight of ferric nitrate and deionized water) ), at a rate of 100 r/min, after shaking and immersing for 8 hours, drying at 90 °C for 10 hours to obtain the magnetic sludge straw-based activated carbon precursor;

(5) The magnetic sludge straw-based activated carbon precursor obtained in step (4) was placed in a ceramic crucible in a box-type atmosphere furnace, and heated to 200°C for 1.5h under high-purity nitrogen at a rate of 4°C/min. Cool to 25°C with the furnace, ultrasonically clean for 15 minutes at 70°C and 40 kHz, repeat water washing and suction filtration 3 times until the pH value of the washing solution is neutral, and dry to constant weight to obtain magnetic sludge straw-based activated carbon.

Through observation, the magnetic sludge straw-based activated carbon obtained in this example is granular, with good wear resistance, uniform size, high compressive strength and good water resistance.

After testing, the magnetic sludge straw-based activated carbon obtained in this example is characterized by BET, and its isotherm adsorption/desorption curve belongs to the combination of type I and type IV isotherms, and there is an obvious H4 type hysteresis loop, which shows that this implementation The magnetic sludge straw-based activated carbon obtained in Example contains mesoporous and microporous structures, and the mesoporous structure is dominant; the magnetic sludge straw-based activated carbon obtained in this example has a specific surface area of 567.46 m ² /g, an average pore diameter of 5.892 nm, and a total of 567.46 m 2 /g. The pore volume was 0.354 cm ³ /g, and the micropore volume accounted for 41.56% of the total pore volume.

The saturation magnetization test shows that the magnetic sludge straw-based activated carbon obtained in this example has a specific saturation magnetization of 7.7328 emu/g.

A kind of preparation method of magnetic sludge straw-based activated carbon Example 3

(1) According to the weight parts of each raw material in Example 3 in Table 1, crush the dry sludge and dry straw, dry at 100°C to constant weight, pulverize with a high-speed universal pulverizer, and pass through an 80-mesh sieve to obtain sludge mixed powder with straw;

(2) According to the weight parts of each raw material in Example 3 in Table 1, in the mixed powder of sludge and straw obtained in step (1), add a foaming agent, mix evenly, and then add an aqueous solution of carbonate with a mass fraction of 15% (configured by 15 parts by weight of sodium carbonate and 85 parts of carbon dioxide-free deionized water), at a rate of 80 r/min, after shaking and activating for 8 hours, and drying at 100 ° C for 14 hours, the sludge straw-based activated carbon precursor was obtained;

(3) The sludge straw-based activated carbon precursor obtained in step (2) was placed in the furnace of a box-type atmosphere electric furnace, heated to 850 °C for 1.5 h at a rate of 6 °C/min under high-purity argon, and then cooled with the furnace. to 25℃, at 90℃, 20kHz, ultrasonic cleaning for 25min, repeated washing and suction filtration 3 times until the pH value of the washing solution is neutral, drying to constant weight, to obtain sludge straw-based activated carbon;

(4) According to the weight parts of each raw material in Example 3 in Table 1, to the sludge straw-based activated carbon obtained in step (3), add 0.8 mol/L iron salt aqueous solution (prepared by 10 weight parts of iron sulfate with deionized water) ), at a rate of 140 r/min, after shaking and dipping for 4 h, and drying at 70 °C for 20 h, the magnetic sludge straw-based activated carbon precursor was obtained;

(5) The magnetic sludge straw-based activated carbon precursor obtained in step (4) was placed in a ceramic crucible in a box-type atmosphere furnace, and heated to 300 °C at a rate of 6 °C/min under high-purity argon for 0.5 h after carbonization. , cooled to 25 °C with the furnace, ultrasonically cleaned at 90 °C and 20 kHz for 25 min, repeated washing and suction filtration twice until the pH value of the washing solution was neutral, and dried to constant weight to obtain magnetic sludge straw-based activated carbon.

Through observation, the magnetic sludge straw-based activated carbon obtained in this example is granular, with good wear resistance, uniform size, high compressive strength and good water resistance.

After testing, the magnetic sludge straw-based activated carbon obtained in this example is characterized by BET, and its isotherm adsorption/desorption curve belongs to the combination of type I and type IV isotherms, and there is an obvious H4 type hysteresis loop, which shows that this implementation The magnetic sludge straw-based activated carbon obtained in Example contains mesoporous and microporous structures; the magnetic sludge straw-based activated carbon obtained in this example has a specific surface area of 571.25 m ² /g, an average pore diameter of 6.042 nm, and a total pore volume of 0.365 cm ² / g, The micropore volume accounts for 48.92% of the total pore volume.

The saturation magnetization test shows that the specific saturation magnetization of the magnetic sludge straw-based activated carbon obtained in this example is 7.4327 emu/g.

Claims (9)

1. A magnetic sludge straw-based activated carbon, characterized in that it is mainly made from the following raw materials: dry sludge, dry straw, foaming agent, carbonate and iron salt. 2 . The magnetic sludge straw-based activated carbon according to claim 1 , wherein the weight parts of each raw material are: 20-40 parts of dry sludge, 60-80 parts of dry straw, and 5-10 parts of foaming agent. 3 . , 5 to 15 parts of carbonate and 5 to 10 parts of iron salt. 3. The magnetic sludge straw-based activated carbon according to claim 1 or 2, wherein the dry sludge has a moisture content of 50-60% and a carbon content of 15-30%, wherein the fixed carbon content is 5-10%; the sludge is one or more of municipal sludge, papermaking sludge or farm wastewater sludge; the moisture content of the dried straw is 50-60%, and the carbon content is 30- 50%, wherein the fixed carbon content is 5-10%; the straw is one or more of corn straw, rice straw or sorghum straw; the foaming agent is azodicarbonamide, azodicarbonamide Or one or more in p-toluenesulfonyl hydrazide; Described carbonate is one or more in potassium carbonate, calcium carbonate or sodium carbonate; Described iron salt is ferric nitrate, ferric chloride or ferric sulfate , and one or more of its hydrates. 4. A preparation method of magnetic sludge straw-based activated carbon according to one of claims 1 to 3, characterized in that, comprising the following steps: (1) Crushing the dry sludge and dry straw, drying to constant weight, pulverizing and sieving to obtain the mixed powder of sludge and straw; (2) adding a foaming agent to the mixed powder of sludge and straw obtained in step (1), mixing evenly, then adding an aqueous solution of carbonate, shaking and activating, and drying to obtain a precursor of sludge and straw-based activated carbon; (3) The sludge straw-based activated carbon precursor obtained in step (2) is heated and carbonized in an inert atmosphere, cooled to room temperature with the furnace, ultrasonically cleaned, washed with water, suction filtered, and dried to constant weight to obtain the sludge straw-based activated carbon precursor. activated carbon; (4) adding an aqueous solution of iron salt to the sludge straw-based activated carbon obtained in step (3), oscillating and dipping, and drying to obtain a magnetic sludge straw-based activated carbon precursor; (5) The magnetic sludge straw-based activated carbon precursor obtained in step (4) is heated and carbonized in an inert atmosphere, cooled to room temperature with the furnace, ultrasonically cleaned, washed with water, suction filtered, and dried to constant weight to obtain magnetic sludge. Straw-based activated carbon. The preparation method of magnetic sludge straw-based activated carbon according to claim 4, characterized in that: in step (1), the drying temperature is 90-110°C; the mesh number of the sieving is 40- 80 mesh. The preparation method of magnetic sludge straw-based activated carbon according to claim 4 or 5, characterized in that: in step (2), the mass fraction of the carbonate aqueous solution is 5-15%; the vibration activation The drying rate is 80-120r/min, and the time is 4-8h; the drying temperature is 100-110°C, and the time is 10-14h. 7 . The method for preparing magnetic sludge straw-based activated carbon according to claim 4 , wherein in step (3), the inert atmosphere is one or more of nitrogen, argon or helium. 8 . The heating rate is 2-8 ℃/min, and the temperature is raised to 750-900 ℃; the heating and carbonization time is 0.5-2.0 h; the temperature of the ultrasonic cleaning is 60-100 ℃, and the ultrasonic frequency is 20 ～40 kHz, the time is 15～25min; repeat the water washing and suction filtration ≥1 times, until the pH value of the washing solution is neutral. 8 . The method for preparing magnetic sludge straw-based activated carbon according to claim 4 , wherein in step (4), the concentration of the iron salt aqueous solution is 0.5-1.5 mol/L; the The oscillating impregnation rate is 100-140 r/min, and the time is 4-8h; the drying temperature is 70-90°C, and the time is 10-20h. 9 . The method for preparing magnetic sludge straw-based activated carbon according to claim 4 , wherein in step (5), the inert atmosphere is one or more of nitrogen, argon or helium. 10 . The heating rate is 2-8 ℃/min, and the temperature is raised to 150-300 ℃; the heating and carbonization time is 0.5-2.0 h; the temperature of the ultrasonic cleaning is 60-100 ℃, and the ultrasonic frequency is 20 ～40 kHz, the time is 15～25min; repeat the water washing and suction filtration ≥1 times, until the pH value of the washing solution is neutral.