Preparation method of asphalt warm mixing agent

Abstract

The invention discloses a preparation method of an asphalt warm mixing agent, artificial zeolite is used as a raw material, and the asphalt warm mixing agent is obtained through S1, calcination, S2, internal modification and S3, coating. S2, internal modification: immersing the calcined artificial zeolite in a mixed solution of sodium carboxymethyl cellulose and chitosan, stirring for 30-50 minutes at normal temperature, and filtering and drying to obtain the modified artificial zeolite; s3, coating: immersing the modified artificial zeolite in a sodium alginate mixture containing iron powder, stirring, filtering, and drying to obtain the warm mixing agent; according to the invention, the mixing temperature and the paving temperature can be reduced, paving in a low-temperature environment is realized, and the anti-aging performance of the asphalt mixture can also be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of asphalt additives, relates to asphalt warm mix additives, and particularly relates to a preparation method of an asphalt warm mix additive. Background Art

[0002] According to the different temperatures required by asphalt during mixing and construction, asphalt mixtures can be divided into cold mix asphalt mixtures, warm mix asphalt mixtures, and hot mix asphalt mixtures. SBS asphalt has excellent high-temperature rutting resistance, low-temperature cracking resistance, fatigue resistance, and excellent elastic recovery ability. However, the mixing temperature of SBS asphalt mixture is 175°C to 185°C, which is a commonly used hot mix asphalt. During the mixing process, due to high temperature, thermal aging will occur rapidly in a short time, which has a greater impact on the comprehensive performance of the asphalt mixture. In addition, the paving and compaction temperatures of hot mix asphalt are usually not lower than 140°C. At high temperatures, asphalt is very easy to be ignited, and a large amount of thick smoke and heat will be generated during combustion, which is extremely dangerous and brings inconvenience to our actual operation.

[0003] In the prior art, the goal of reducing the mixing temperature, paving and compaction temperatures of asphalt can be achieved by adding warm mix additives. Zeolite, due to its porous structure, can improve the water release period and make asphalt foam continuously, and is a commonly used asphalt foaming warm mix additive. However, existing zeolite warm mix additives often have problems such as non-connected internal pores, low water content, uneven water release rate, and short water release period, and their warm mix effect needs to be improved. Moreover, for some cold regions, the temperature of asphalt mixtures will drop too fast during transportation and paving, resulting in hardening problems.

[0004] In order to improve the warm mix effect of zeolite and avoid the hardening problem caused by too fast temperature drop when applied in cold regions, the present invention conducts research on asphalt warm mix additives with zeolite as the raw material. Summary of the Invention

[0005] The purpose of the present invention is to improve the warm mix effect of zeolite and avoid the hardening problem caused by too fast temperature drop when applied in cold regions. The present invention uses zeolite as the main raw material of the warm mix additive and conducts research and development on the preparation process of the warm mix additive.

[0006] The technical solution adopted by the present invention provides a preparation method of an asphalt warm mix additive. The key lies in that the above warm mix additive is made from synthetic zeolite as the raw material and obtained through S1, calcination, S2, internal modification, and S3, coating; the above S2, internal modification is to immerse the calcined synthetic zeolite in a mixed solution of sodium carboxymethylcellulose and chitosan, stir at room temperature for 30 min to 50 min, and obtain the modified synthetic zeolite through filtration and drying; the above S3, coating is to first immerse the modified synthetic zeolite in a sodium alginate mixture containing iron powder, stir, and obtain the above warm mix additive through filtration and drying.

[0007] Further, in the above-mentioned S2, internal modification, the stirring speed at room temperature is 10 r / min to 20 r / min; the volume ratio of the synthetic zeolite to the mixed solution of the above-mentioned sodium carboxymethyl cellulose and chitosan is 1:2 to 4.

[0008] Specifically, in the above-mentioned S2, internal modification, the preparation method of the mixed solution of sodium carboxymethyl cellulose and chitosan is as follows: dissolve chitosan in a citric acid buffer solution with a pH of 5.5 to 6.5 to obtain a chitosan solution with a concentration of 5 g / L to 10 g / L; mix it with an equal volume of an aqueous solution of sodium carboxymethyl cellulose with a concentration of 5 g / L to 10 g / L, and stir evenly to obtain the above-mentioned mixed solution of sodium carboxymethyl cellulose and chitosan.

[0009] Further, in the above-mentioned S3, coating, the volume ratio of the modified synthetic zeolite to the sodium alginate mixture containing iron powder is 1:2 to 4.

[0010] Specifically, in the above-mentioned S3, coating, the preparation method of the above-mentioned sodium alginate mixture containing iron powder is to add iron powder to an aqueous solution of sodium alginate with a concentration of 20 g / L to 30 g / L, and the amount of iron powder added to each liter of the aqueous solution of sodium alginate is 30 g to 40 g.

[0011] More specifically, in the above-mentioned S3, coating, before the synthetic zeolite is immersed in the mixed solution of sodium carboxymethyl cellulose and chitosan, it can be first immersed in a cetyltrimethylammonium bromide solution with a volume 2 to 4 times that of the synthetic zeolite, and stirred at 40 °C to 50 °C for 4 h to 8 h.

[0012] Preferably, the concentration of the above-mentioned cetyltrimethylammonium bromide solution is 15 g / L to 20 g / L, and the stirring speed at 40 °C to 50 °C is 100 r / min to 200 r / min.

[0013] Optimally, the above-mentioned S1, calcination means calcining the synthetic zeolite in a muffle furnace at 540 °C to 580 °C for 30 min to 50 min.

[0014] It should be noted that the particle size of the above-mentioned synthetic zeolite is 1 mm to 3 mm; the particle size of the above-mentioned iron powder is 50 μm to 500 μm.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The present invention prepares a modified zeolite warm mix additive with iron powder coated on the surface, and its preparation method is simple and the production cost is not high. In the preparation method of the present invention, the crystal structure of the synthetic zeolite is changed by calcination, so that the crystal framework arrangement of the zeolite is more compact and orderly, the pore diameter of the internal pore channels becomes larger, and the impurities inside the pore channels are removed, thereby making the channels smoother.

[0017] The mixed solution of sodium carboxymethylcellulose and chitosan is mixed with the calcined zeolite in a slightly acidic environment, which can form a carboxymethylcellulose-chitosan-zeolite community with a grid-like internal structure, increase the water retention rate of the zeolite, control the water release rate of the zeolite, extend the water release period, and make the water release rate of the zeolite more uniform, manifested as an extended foaming time.

[0018] The sodium alginate mixture containing iron powder can coat a uniform layer of iron powder on the outside of the carboxymethylcellulose-chitosan-zeolite community. The iron powder is distributed on the zeolite surface by the binding action of sodium alginate, and a new type of warm mix additive is prepared. When mixed with asphalt, the iron powder is oxidized by oxygen or moisture, releasing heat energy, avoiding problems such as early hardening and difficult paving due to the too rapid decrease in the temperature of the mixture when used in a low-temperature environment. In addition, the present invention has low requirements for the particle size of the iron powder, which reduces the production cost to a certain extent.

[0019] Sodium alginate itself has a certain water retention capacity and can also be used as a thickener for asphalt. However, in the research on the application of the warm mix additive in low-temperature conditions in the present invention, it is not expected that the warm mix additive will increase the viscosity of the asphalt. Therefore, it is particularly necessary to control the concentration and dosage of sodium alginate, and its dosage should not be too high. Thus, in order to ensure the coating effect of the iron powder, before coating the iron powder, the present invention can also use cetyltrimethylammonium bromide solution to improve the adsorption capacity of the zeolite surface. At the same time, in the grid structure formed inside the zeolite, the carboxymethylcellulose-chitosan-zeolite community contains a large number of hydrogen bonds and amide bonds, further improving the binding ability between the zeolite and the iron powder.

[0020] In addition, the warm mix additive prepared by the present invention can not only reduce the mixing temperature and paving temperature and achieve paving in a low-temperature environment, but also improve the anti-aging performance of the asphalt mixture. This is because some of the iron powder with relatively tight binding, or the iron powder located in deeper pores, and the citric acid buffer salt used to dissolve chitosan during the preparation process remain inside the pores of the zeolite, and its release process is more persistent. Also, because its properties are more likely to age than asphalt, it plays a protective role for the asphalt. Specific Embodiments

[0021] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0022] For those without specific conditions indicated in the examples, they can be carried out according to conventional conditions; for the reagents or instruments without the manufacturer indicated, they are all conventional products that can be obtained by purchasing in the market; the normal temperature in the examples is 18°C to 35°C.

[0023] Example 1

[0024] The warm mix agent is prepared according to the following steps, specifically including:

[0025] S1. Calcination: The synthetic zeolite is calcined in a muffle furnace at 560°C for 40 min to obtain the calcined zeolite; the particle size of the synthetic zeolite used is 2 mm.

[0026] S2. Internal modification:

[0027] S2-1. Preparation of the mixed solution of sodium carboxymethyl cellulose and chitosan:

[0028] Chitosan is dissolved in a citric acid buffer solution with a pH of 6.0 to prepare a chitosan solution with a concentration of 8 g / L; it is mixed with an equal volume of an aqueous solution of sodium carboxymethyl cellulose with a concentration of 8 g / L and stirred evenly to prepare the mixed solution of sodium carboxymethyl cellulose and chitosan;

[0029] S2-2. The calcined synthetic zeolite is immersed in a mixed solution of sodium carboxymethyl cellulose and chitosan with a volume 3 times that of the synthetic zeolite, and stirred at a rotation speed of 15 r / min for 40 min under normal temperature conditions, and then obtained the modified synthetic zeolite after filtration and drying.

[0030] S3. Coating:

[0031] S3-1. Preparation of the sodium alginate mixture containing iron powder:

[0032] Iron powder with a particle size of 250 μm is added to an aqueous solution of sodium alginate with a concentration of 25 g / L, and the amount of iron powder added to each liter of the aqueous solution of sodium alginate is 35 g;

[0033] S3-2. The modified synthetic zeolite is first immersed in a cetyltrimethylammonium bromide solution with a volume 3 times that of the zeolite, and the concentration of the cetyltrimethylammonium bromide solution is 18 g / L, and stirred at 45°C for 6 h;

[0034] S3-3. The modified synthetic zeolite is then immersed in a sodium alginate mixture containing iron powder with a volume 3 times that of the zeolite, and after stirring, it is obtained the warm mix agent sample after filtration and drying, denoted as warm mix agent sample 1.

[0035] Example 2

[0036] The warm mix agent is prepared according to the following steps, specifically including:

[0037] S1. Calcination: The synthetic zeolite is calcined in a muffle furnace at 580 °C for 30 min to obtain the calcined zeolite. The particle size of the synthetic zeolite used is 3 mm.

[0038] S2. Internal modification:

[0039] S2-1. Preparation of the mixed solution of sodium carboxymethyl cellulose and chitosan:

[0040] Chitosan is dissolved in a citric acid buffer solution with a pH of 6.5 to prepare a chitosan solution with a concentration of 5 g / L; it is mixed with an equal volume of an aqueous solution of sodium carboxymethyl cellulose with a concentration of 5 g / L and stirred evenly to prepare the mixed solution of sodium carboxymethyl cellulose and chitosan.

[0041] S2-2. The calcined synthetic zeolite is immersed in a mixed solution of sodium carboxymethyl cellulose and chitosan with a volume twice that of the synthetic zeolite, and stirred at a speed of 10 r / min for 50 min at room temperature, and then obtained the modified synthetic zeolite after filtration and drying.

[0042] S3. Coating:

[0043] S3-1. Preparation of the sodium alginate mixture containing iron powder:

[0044] Iron powder with a particle size of 50 μm is added to an aqueous solution of sodium alginate with a concentration of 20 g / L, and the amount of iron powder added to each liter of the aqueous solution of sodium alginate is 40 g.

[0045] S3-2. The modified synthetic zeolite is first immersed in a cetyltrimethylammonium bromide solution with a volume twice that of the zeolite, and the concentration of the cetyltrimethylammonium bromide solution is 15 g / L, and stirred at 40 °C for 8 h.

[0046] S3-3. The modified synthetic zeolite is then immersed in a sodium alginate mixture containing iron powder with a volume four times that of the zeolite, and after stirring, it is filtered and dried to obtain the warm mix additive sample, denoted as warm mix additive sample 2.

[0047] Example 3

[0048] The warm mix additive is prepared according to the following steps, specifically including:

[0049] S1. Calcination: The synthetic zeolite is calcined in a muffle furnace at 540 °C for 50 min to obtain the calcined zeolite. The particle size of the synthetic zeolite used is 1 mm.

[0050] S2. Internal modification:

[0051] S2-1. Preparation of the mixed solution of sodium carboxymethyl cellulose and chitosan:

[0052] Dissolve chitosan in a citric acid buffer solution with a pH of 5.5 to prepare a chitosan solution with a concentration of 10 g / L; mix it with an equal volume of an aqueous sodium carboxymethyl cellulose solution with a concentration of 10 g / L, and stir evenly to prepare a mixed solution of sodium carboxymethyl cellulose and chitosan.

[0053] S2-2: Immerse the calcined synthetic zeolite in a mixed solution of sodium carboxymethyl cellulose and chitosan with a volume 4 times that of the synthetic zeolite. Under normal temperature conditions, stir at a rotation speed of 20 r / min for 30 min, and obtain the modified synthetic zeolite after filtration and drying.

[0054] S3: Coating

[0055] S3-1: Preparation of a sodium alginate mixture containing iron powder

[0056] Add iron powder with a particle size of 500 μm to an aqueous sodium alginate solution with a concentration of 30 g / L, and the amount of iron powder added to each liter of the aqueous sodium alginate solution is 30 g.

[0057] S3-2: First immerse the modified synthetic zeolite in a cetyltrimethylammonium bromide solution with a volume 4 times that of the zeolite. The concentration of the cetyltrimethylammonium bromide solution is 20 g / L, and stir at 50 °C for 4 h.

[0058] S3-3: Then immerse the modified synthetic zeolite in a sodium alginate mixture containing iron powder with a volume 2 times that of the zeolite. After stirring, obtain the warm mix additive sample through filtration and drying, denoted as warm mix additive sample 3.

[0059] Example 4

[0060] The implementation process of this example is the same as that of Example 1, except that in this example, step S3-2 is omitted, that is, the modified synthetic zeolite is not immersed in the cetyltrimethylammonium bromide solution, but directly immersed in the sodium alginate mixture containing iron powder. After stirring, obtain the warm mix additive sample through filtration and drying, denoted as warm mix additive sample 4.

[0061] Comparative Example 1

[0062] The implementation method of this comparative example is the same as that of Example 1. The difference is that in the S3 coating process, the mixture used is not a sodium alginate mixture containing iron powder, but a gelatin mixture containing iron powder. That is, add iron powder with a particle size of 250 μm to a gelatin solution with a mass concentration of 6%, and the amount of iron powder added to each liter of the gelatin solution is 35 g. The subsequent S3-2 step is the same as that of Example 1. Since the gelatin solution with a mass concentration of 6% is a gel at normal temperature, heating is required during the stirring process in step S3-3 to dissolve the gelatin. After filtration and drying, the warm mix additive control sample 1 is prepared.

[0063] Comparative Example 2

[0064] The implementation method of this comparative example is the same as that of Example 1, with the difference in S3, the coating process. The mixture used is not the sodium alginate mixture containing iron powder, but the sodium sulfate mixture containing iron powder. That is, iron powder with a particle size of 250 μm is added to an aqueous sodium sulfate solution with a concentration of 25 g / L, and the amount of iron powder added to each liter of the aqueous sodium sulfate solution is 35 g. The subsequent steps are the same as those in Example 1, and the warm mix additive control sample 2 is prepared.

[0065] Comparative Example 3

[0066] The implementation method of this comparative example is the same as that of Example 1, except that S2, internal modification, is omitted, and the calcined artificial zeolite is directly coated. The subsequent steps are the same as those in Example 1, and the warm mix additive control sample 3 is prepared.

[0067] Application test

[0068] In this invention, the common SBS modified asphalt in the field is selected as the test object. The SBS modified asphalt used meets the quality requirements of SBS type I-B level for polymer modified asphalt technology requirements in the "Technical Specification for Construction of Highway Asphalt Pavement"; the coarse aggregate, fine aggregate, and filler meet the quality requirements of the corresponding mixture for expressways and first-class highways in the "Technical Specification for Construction of Highway Asphalt Pavement"; the test conditions meet the construction requirements of hot mix asphalt mixture pavement in the "Technical Specification for Construction of Highway Asphalt Pavement".

[0069] I. Measuring the temperature during the construction process

[0070] The surface temperature of the underlying layer in this test is 25 °C, and the paving layer thickness is 100 mm.

[0071] In this test, 2 wt% of the warm mix additive samples 1-4 or the warm mix additive control samples 1-3 are respectively incorporated into the SBS modified asphalt. The SBS asphalt with 2 wt% of commercially available artificial zeolite added is used as Control Group 1, and the SBS asphalt without any warm mix additive is used as Control Group 2. The mixing temperature and compaction temperature of the asphalt mixture during the construction process are measured, and the test is repeated 3 times, and the average value is taken as the result. The results are shown in Table 1.

[0072] Table 1: Summary table of test results of the temperature during the construction process

[0073] Group Warm Mix Agent Number Mixing Temperature (°C) Compaction Temperature (°C) Test Group 1 Warm Mix Agent Sample 1 143.6 133.4 Test Group 2 Warm Mix Agent Sample 2 144.5 134.6 Test Group 3 Warm Mix Agent Sample 3 145.3 134.8 Test Group 4 Warm Mix Agent Sample 4 148.1 140.2 Test Group 5 Warm Mix Agent Reference 1 146.3 135.3 Test Group 6 Warm Mix Agent Reference 2 153.1 148.2 Test Group 7 Warm Mix Agent Reference 3 163.5 153.2 Control Group 1 Commercially Available Synthetic Zeolite 164.5 155.4 Control Group 2 —— 179.8 172.6

[0074] As can be seen from the results in Table 1, adding different warm mix additives can all achieve the effect of reducing the mixing temperature and compaction temperature. Among them, the effects of experimental groups 1 - 6 are significantly better than those of experimental group 7 and control group 1, and the mixing temperature is reduced by more than 30°C. It can be seen that ordinary zeolite has a certain warm mix effect. However, the modification step of the present invention changes the internal structure of the zeolite, forming a cross-linked composite structure of sodium carboxymethylcellulose - chitosan - zeolite inside the zeolite, increasing the water content of the zeolite, and thus improving the warm mix effect. During application, the temperature of the mixer can be controlled by controlling the addition amount of the warm mix additive.

[0075] II. Performance Testing

[0076] In this experiment, warm mix additive samples 1 - 4 or warm mix control products 1 - 3 were respectively incorporated into SBS modified asphalt at 2wt%. SBS asphalt with 2wt% of commercially available natural zeolite added was used as control group 1, and SBS asphalt without any warm mix additive was used as control group 2.

[0077] During the experiment, after heating the SBS modified asphalt, a certain proportion of cold water, air, and surfactant were injected to prepare foamed asphalt. According to the "Test Regulations for Asphalt and Asphalt Mixtures in Highway Engineering", the foaming time and viscosity (180°C rotational viscosity) of the foamed asphalt under the same process treatment were measured. The prepared foamed asphalt was mixed with the mixture and paved, and the stability, freeze - thaw splitting strength ratio, and dynamic stability under the same process treatment were measured according to the "Test Regulations for Asphalt and Asphalt Mixtures in Highway Engineering". The results are shown in Table 2. The surface temperature of the subgrade in this experiment was 10°C, and the paving layer thickness was 100mm.

[0078] Table 2: Summary Table of Performance Test Results

[0079]

[0080]

[0081] As can be seen from the results in Table 2, experimental groups 1 - 4 can significantly increase the foaming time of asphalt, reduce the viscosity of asphalt, and improve the fluidity of asphalt. According to the "Technical Specifications for Construction of Highway Asphalt Pavements", when the surface temperature of the subgrade is 10°C, it is not allowed to pave the modified asphalt mixture because in areas with relatively low temperatures, the asphalt mixture will harden due to rapid temperature drop during paving, affecting construction operations and even reducing the performance of the mixture. Under the paving conditions of this experiment, the stability, splitting strength ratio, and dynamic stability of experimental groups 1 - 4 were not affected by the too - low surface temperature of the subgrade, and the effects of some warm mix additive samples even exceeded those of control group 2.

[0082] Based on the results of Table 1 and Table 2, the warm mix agent samples of the present invention can not only reduce the mixing and paving temperatures, but also lower the viscosity of asphalt, and are also suitable for construction under low temperature conditions.

[0083] III. Aging Resistance Test

[0084] In this test, warm mix agent samples 1-4 or warm mix agent reference samples 1-3 were respectively incorporated into SBS modified asphalt at 2 wt%. SBS asphalt incorporated with 2 wt% of commercially available synthetic zeolite was used as Control Group 1. They were respectively mixed with asphalt mixtures. According to the accelerated aging method for hot mix asphalt mixtures recorded in the "Test Procedures for Bitumen and Bituminous Mixtures for Highway Engineering", the asphalt mixtures were subjected to long-term aging treatment, the ductility before and after aging was measured, and a low-temperature bending test was carried out to evaluate the low-temperature crack resistance of the asphalt mixtures. The results are shown in Table 3.

[0085] Table 3: Summary Table of Aging Resistance Test Results

[0086]

[0087]

[0088] As can be seen from the results of Table 3, the warm mix agent samples in this test can improve the aging resistance of asphalt mixtures, reduce the influence of aging on ductility, flexural tensile strength and failure strain, and contribute to improving the low-temperature stability of asphalt mixtures.

Claims

1. A method for preparing a warm mix asphalt agent, characterized in that: The warm-mix agent is prepared by taking artificial zeolite as raw material through S1, calcination, S2, internal modification and S3, coating; the S2, internal modification is to immerse the calcined artificial zeolite in a mixed solution of sodium carboxymethyl cellulose and chitosan, stir for 30 to 50 minutes at room temperature, filter and dry to obtain the modified artificial zeolite; the S3, coating is to immerse the modified artificial zeolite in a sodium alginate mixture containing iron powder, stir, filter and dry to obtain the warm-mix agent.

2. The method for preparing a warm mix asphalt agent according to claim 1, characterized in that: In the S2, internal modification, the stirring speed at room temperature is 10 r / min to 20 r / min; the volume ratio of the artificial zeolite to the mixed solution of sodium carboxymethyl cellulose and chitosan is 1:2 to 4.

3. The method for preparing a warm mix asphalt agent according to claim 1, characterized in that: In the S2, internal modification, the mixed solution of sodium carboxymethyl cellulose and chitosan is prepared by: dissolving chitosan in a citric acid buffer solution with a pH of 5.5 to 6.5 to obtain a chitosan solution with a concentration of 5 g / L to 10 g / L; mixing the solution with an equal volume of a sodium carboxymethyl cellulose aqueous solution with a concentration of 5 g / L to 10 g / L, stirring the mixture evenly, to obtain the mixed solution of sodium carboxymethyl cellulose and chitosan.

4. The method for preparing a warm mix asphalt agent according to claim 1, characterized in that: In the S3 coating, the volume ratio of the modified artificial zeolite to the sodium alginate mixture containing iron powder is 1:2-4.

5. The method for preparing a warm mix asphalt agent according to claim 1, characterized in that: In the S3, coating, the preparation method of the sodium alginate mixture containing iron powder is to add the iron powder to a sodium alginate aqueous solution with a concentration of 20g / L to 30g / L, and the amount of iron powder added to each liter of sodium alginate aqueous solution is 30g to 40g.

6. The method for preparing a warm mix asphalt agent according to claim 1, characterized in that: In the above-mentioned S3, coating, the artificial zeolite can be immersed in a 2-4 times volume of hexadecyltrimethylammonium bromide solution before being immersed in the mixed solution of sodium carboxymethylcellulose and chitosan, and stirred at 40°C to 50°C for 4h to 8h.

7. The method for preparing a warm mix asphalt agent according to claim 6, characterized in that: The concentration of the hexadecyltrimethylammonium bromide solution is 15 g / L to 20 g / L, and the stirring speed is 100 r / min to 200 r / min at 40° C. to 50° C.

8. The method for preparing a warm mix asphalt agent according to claim 1, characterized in that: The S1, calcination, refers to calcining the artificial zeolite in a muffle furnace at 540° C. to 580° C. for 30 min to 50 min.

9. The method for preparing a warm mix asphalt agent according to claim 1, characterized in that: The particle size of the artificial zeolite is 1 mm to 3 mm; the particle size of the iron powder is 50 μm to 500 μm.

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