Biochar-based alkali-activated containment material, preparation method therefor and use thereof

Abstract

Disclosed in the present invention are a biochar-based alkali-activated containment material, a preparation method therefor, and the use thereof. The biochar-based alkali-activated containment material comprises 50-70% by mass of in-situ soil and 30-50% by mass of a cementitious material, wherein the cementitious material comprises an ash material and a composite alkali activator, and the composite alkali activator is obtained by ball milling activated magnesium oxide and biochar together. The biochar-based alkali-activated containment material of the present invention has better early compressive strength under a low cement-to-sand ratio and the 7d compressive strength thereof can reach 9.33 MPa; in addition, because of the presence of biochar, the containment material can better adsorb and trap soil contaminants and has better anti-seepage performance, and the permeability coefficient can reach 2.4×10-10 m / s. When being applied to rapid emergent containment for contaminated sites, the containment material can be quickly spread and quickly shape and achieve a lower seepage concentration of contaminants, thereby having a great application prospect.

Description

Biochar-based alkali-activated blocking and controlling material, and preparation method and application thereof TECHNICAL FIELD

[0001] The present application relates to an alkali-activated blocking and controlling material, in particular to a biochar-based alkali-activated blocking and controlling material, and also relates to a preparation method and application of the biochar-based alkali-activated blocking and controlling material. BACKGROUND

[0002] The current stage of industrialization and urbanization brings about sudden environmental events and frequent environmental risks, and the environmental safety situation is facing serious challenges. Sudden pollution often has the characteristics of high instantaneous concentration, difficulty in control, and complex composition, and the pollutants will spread in a short time, causing great harm to the environment and human health. Therefore, it is necessary to quickly block and control the sudden pollution to cut off the source of infection.

[0003] In order to avoid the seepage and diffusion of pollutants, the blocking and controlling material needs to be formed within a certain time, and also has good anti-seepage performance. Traditional cement blocking walls are widely used in the process of pollution site remediation, but they are not suitable for rapid blocking and controlling due to their slow hydration process, high energy consumption in production process, poor anti-seepage performance and other shortcomings. Bentonite and solid waste cementitious materials have good anti-seepage performance, and although they have low cost and relatively green production, they are also relatively slow in forming under normal circumstances.

[0004] Currently, NaOH, Na2SiO3 and their different proportions are commonly used as alkali activators, but they are highly dependent on alkalinity, have poor environmental friendliness, and have unstable material performance development, and also have the disadvantages of needing to calculate water quantity according to modulus, and the effect being greatly affected by alkali equivalent, which limits large-scale application. At the same time, in the demand for using biochar to intercept pollutants, liquid activators cannot achieve uniform distribution of biochar. Therefore, it is necessary to develop an environmentally friendly, stable and biochar-introducing-demand-satisfying alkali-activated blocking and controlling material suitable for rapid blocking and controlling scenarios. SUMMARY

[0005] The purpose of the present application is to provide a biochar-based alkali-activated blocking and controlling material, and also to provide a preparation method and application of the biochar-based alkali-activated blocking and controlling material.

[0006] Technical scheme: The biochar-based alkali-activated blocking and controlling material of the present application comprises 50-70% of in-situ soil and 30-50% of colloidal material by mass percentage; wherein the colloidal material comprises 90-80% of ash material and 10-20% of composite alkali activator by mass percentage, the composite alkali activator is obtained by co-milling of active magnesium oxide and biochar, the mass ratio of biochar to magnesium oxide is 0.5-6:100, and the water-solid mass ratio is 22-28%.

[0007] The mass ratio of the biochar to the magnesium oxide is preferably 1-4:100.

[0008] The ash body material is one or more of blast furnace slag, fly ash, coal gangue, steel slag, etc., preferably a combination of blast furnace slag and fly ash in a mass ratio of 1:1.

[0009] The preparation method of the composite alkali activator is as follows: screening and crushing of biochar raw materials, pyrolysis at 500-700°C for 1-3h to obtain biochar, and grinding and sieving; drying the active magnesium oxide and biochar at 60-70°C for 4-6h to obtain dry mixture; grinding the dry mixture in a ball mill for 2-3h to obtain the composite alkali activator.

[0010] The ball mill rotates at a speed of 100-300r / min, and the ball-to-material ratio is 4:1-8:1.

[0011] The sand has a particle size of ≤630μm, the magnesium oxide has an activity of 55-70%, and the biochar has a particle size of ≤50μm.

[0012] The preparation method of the biochar-based alkali-activated control material includes the following steps:

[0013] (1) preparing ash body material and composite alkali activator according to mass percentage, uniformly stirring and mixing for 3-5min to obtain premix;

[0014] (2) taking 60-70% of the premix obtained in step (1), adding water to the premix according to a water-to-solid mass ratio of 22-28%, low-speed stirring for 4-5min to form a slurry-like slurry, adding in-situ soil according to a clay-to-soil ratio of 3:7-5:5, high-speed stirring for 2-3min, and finally adding the remaining premix, high-speed stirring for 2-3min to obtain the biochar-based alkali-activated control material.

[0015] The curing conditions of the preparation method are 25±2°C and humidity ≥75%.

[0016] In step (2), the low-speed stirring is at a speed of 700-900r / min, and the high-speed stirring is at a speed of 1500-1800r / min.

[0017] The biochar-based alkali-activated control material can also be applied in emergency pollution site rapid control and soil pollution control or remediation.

[0018] The application includes the following steps: excavating a groove at the planned blocking position by a trencher; configuring the biochar-based alkali-activated control material, fully mixing, and then pumping the slurry made of the biochar-based alkali-activated control material back to the groove; and covering a layer of in-situ soil on the top of the control material after pouring to prevent top shrinkage cracking.

[0019] Invention principle: the biochar-based alkali-activated control material of the application selects active magnesium oxide as the alkali source on the material, and compared with the traditional hydroxide-activated slag, the alkali is lower, and the environmental friendliness is higher; the powdery active magnesium oxide is more conducive to the introduction of biochar, so that it is uniformly dispersed; the solid waste-based component replaces the conventional cement-based material with blast furnace slag or fly ash, accounting for 30-50% of the material system, improving the waste utilization rate, which is conducive to resource saving and environmental protection; and further doping biochar in the composite alkali activator not only improves the activity of magnesium oxide to promote the activation effect and improves the slow hydration rate caused by low alkalinity, and when 2% of corn straw biochar is added, the improvement effect is most obvious.

[0020] The composite alkali activator in the above raw materials is a hydrotalcite-like substance generated by the reaction of active magnesium oxide and slag, which can better fill the voids of hydration products; biochar can also play a role in void filling, further improving the impermeability effect, and the permeability coefficient meets the impermeability requirement (10 -9 m / s). And the active magnesium oxide and biochar achieve a synergistic effect, biochar promotes the hydration rate, and the alkaline environment provided by magnesium oxide can also modify the biochar during the ball milling process, promoting the formation of its porous structure and forming good interception effect on pollutants, which is very suitable for application in emergency control scenarios. In the preparation method, dry mixing is performed first, and then batch mixing is performed, so that the materials are fully mixed and uniform, and the performance of the materials is further improved.

[0021] Advantages: compared with the prior art, the application has the following obvious advantages:

[0022] (1) The biochar-based alkali-activated control material of the application has the advantages of easy availability of raw materials, low cost, low carbon emissions, and high economic benefits; application is convenient and does not need to adjust the alkali equivalent and water glass modulus of traditional alkali-activated materials, and application is relatively convenient;

[0023] (2) The application in the rapid control of emergency pollution sites can be quickly formed, and the initial setting time can be as short as 34 min, which is about 20 min shorter than that of unmodified materials. Compared with traditional alkali-activated materials, the early strength is improved, and the compressive strength can reach 9.33 MPa under standard curing for 7d, and it is suitable for low cement mortar ratio, and has good engineering application prospect;

[0024] (3) The biochar-based alkali-activated control material of the application better introduces biochar and magnesium oxide through ball milling, which improves the impermeability effect compared with traditional cement walls and unmodified materials, and has better chemical compatibility, and can meet the impermeability requirement under the action of pollutants while achieving blocking. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is the activity change of the composite alkali activator prepared in Examples 1-4 measured by hydration method;

[0026] Figure 2 is the 0.5d and 1d unconfined compressive strength change of the biochar-based alkali activation control material of different mortar ratios obtained in Example 2, Examples 5-6;

[0027] Figure 3 is the unconfined compressive strength change of the control material described in Examples 1-4, Comparative Examples 1-5 with curing time;

[0028] Figure 4 is the barrier performance test results of the barrier material described in Examples 1-4, Comparative Examples 6-8. Embodiment of the present application

[0029] The technical solutions of the present application are further described below in combination with examples. The test materials used in the examples can be purchased through conventional channels.

[0030] Example 1

[0031] The biochar-based alkali activation control material of the present application comprises 70% in mass percentage of in-situ soil and 30% of colloidal material; wherein the colloidal material comprises 85% in mass percentage of ash material and 15% of composite alkali activator, the composite alkali activator is obtained by co-milling of active magnesium oxide and biochar, the mass ratio of biochar to magnesium oxide is 1:100; and the water-solid mass ratio is 24%.

[0032] The preparation method of the composite alkali activator is as follows: the biochar raw material is screened and crushed, the biochar is prepared by pyrolysis in a tubular furnace at 500-700℃ for 2h and ground through a sieve; the active magnesium oxide and the biochar are dried at 60℃ for 5h to obtain dry mixture; the dry mixture is put into a maroon jar and ground in a planetary ball mill at a rotation speed of 210r / min and a ball-to-material ratio of 5:1 for 3h to obtain magnesium oxide@biochar composite alkali activator.

[0033] The preparation method of the above-mentioned biochar-based alkali activation control material is as follows:

[0034] (1) mixing of raw materials: 42.5% of slag, 42.5% of fly ash and 15% of composite alkali activator are mixed in a concrete mixer at a mass percentage ratio for 5min to obtain premix;

[0035] (2) 60% of the premix is put into a concrete mixer, water is added to the dry mixture according to a water-solid mass ratio of 24%, low-speed stirring for 5min to form a mud-like slurry, 3:7 of in-situ soil is added according to the mortar-soil ratio, fast stirring for 3min, and finally the remaining 40% of the premix is added, fast stirring for 2min to obtain the biochar-based alkali activation control material, which is recorded as MgO@1BC.

[0036] Example 2

[0037] The biochar-based alkali-activated control material of the present application, compared with Example 1, changes the mass ratio of biochar to magnesium oxide: contains 70% in-situ soil and 30% of colloidal material by mass percentage; wherein the colloidal material contains 85% of ash body material and 15% of composite alkali activator by mass percentage, the composite alkali activator is obtained by co-milling of active magnesium oxide and biochar, the mass ratio of biochar to magnesium oxide is 2:100; the water-solid mass ratio is 24%.

[0038] The preparation method of the composite alkali activator is: screening and crushing biochar raw materials, pyrolyzing the biochar in a tubular furnace at 500-700 DEG C for 2h to obtain biochar and grinding it through a sieve; drying the active magnesium oxide and biochar at 60 DEG C for 5h to obtain dry mixture; putting the dry mixture into a maroon jar, putting it into a planetary ball mill under the condition of a rotation speed of 210r / min and a ball-material ratio of 5:1 for 3h to obtain magnesium oxide@biochar composite alkali activator.

[0039] The above-mentioned biochar-based alkali-activated control material has the following preparation method:

[0040] (1) mixing raw materials: putting 42.5% of slag, 42.5% of fly ash and 15% of composite alkali activator by mass percentage into a concrete mixer and uniformly mixing for 5min to obtain premix;

[0041] (2) putting 60% of the premix into a concrete mixer, adding water to the dry mixture according to a water-solid mass ratio of 24%, low-speed stirring for 5min to form a mud-like slurry, adding 3:7 of in-situ soil according to a glue-soil ratio, fast stirring for 3min, finally adding the remaining 40% of the premix, fast stirring for 2min to obtain the biochar-based alkali-activated control material, which is recorded as MgO@2BC.

[0042] Example 3

[0043] The biochar-based alkali-activated control material of the present application, compared with Example 1, changes the mass ratio of biochar to magnesium oxide: contains 70% in-situ soil and 30% of colloidal material by mass percentage; wherein the colloidal material contains 85% of ash body material and 15% of composite alkali activator by mass percentage, the composite alkali activator is obtained by co-milling of active magnesium oxide and biochar, the mass ratio of biochar to magnesium oxide is 3:100; the water-solid mass ratio is 24%.

[0044] The preparation method of the composite alkali activator is: screening and crushing biochar raw materials, pyrolyzing the biochar in a tubular furnace at 500-700 DEG C for 2h to obtain biochar and grinding it through a sieve; drying the active magnesium oxide and biochar at 60 DEG C for 5h to obtain dry mixture; putting the dry mixture into a maroon jar, putting it into a planetary ball mill under the condition of a rotation speed of 210r / min and a ball-material ratio of 5:1 for 3h to obtain magnesium oxide@biochar composite alkali activator.

[0045] The biochar-based alkali-activated blocking and controlling material is prepared by the following method:

[0046] (1) Raw material mixing: 42.5% of slag, 42.5% of fly ash and 15% of composite alkali activator are proportioned by mass percentage, and are uniformly mixed in a concrete mixer for 5 min to obtain a premix;

[0047] (2) 60% of the premix is taken into the concrete mixer, water is added to the dry mix according to a water-solid mass ratio of 24%, low-speed stirring is performed for 5 min to form a mud-like slurry, 3:7 of clay soil is added according to a clay-soil ratio, fast stirring is performed for 3 min, finally, the remaining 40% of the premix is added, and fast stirring is performed for 2 min to obtain the biochar-based alkali-activated blocking and controlling material, which is recorded as MgO@3BC.

[0048] Example 4

[0049] The biochar-based alkali-activated blocking and controlling material of the application is compared with Example 1, and the mass ratio of biochar to magnesium oxide is changed: 70% of in-situ soil and 30% of colloidal material are contained by mass percentage; wherein the colloidal material contains 85% of ash material and 15% of composite alkali activator by mass percentage, the composite alkali activator is obtained by co-milling of active magnesium oxide and biochar, the mass ratio of biochar to magnesium oxide is 4:100, and the water-solid mass ratio is 24%.

[0050] The preparation method of the composite alkali activator is as follows: biochar raw materials are screened and crushed, biochar is prepared by pyrolysis in a tubular furnace at 500-700 DEG C for 2 h and is ground and sieved; the active magnesium oxide and the biochar are dried at 60 DEG C for 5 h to obtain a dry mix; the dry mix is put into a maroon jar, and is ground in a planetary ball mill at a rotation speed of 210 r / min and a ball-material ratio of 5:1 for 3 h to obtain the magnesium oxide@biochar composite alkali activator.

[0051] The biochar-based alkali-activated blocking and controlling material is prepared by the following method:

[0052] (1) Raw material mixing: 42.5% of slag, 42.5% of fly ash and 15% of composite alkali activator are proportioned by mass percentage, and are uniformly mixed in a concrete mixer for 5 min to obtain a premix;

[0053] (2) 60% of the premix is taken into the concrete mixer, water is added to the dry mix according to a water-solid mass ratio of 24%, low-speed stirring is performed for 5 min to form a mud-like slurry, 3:7 of clay soil is added according to a clay-soil ratio, fast stirring is performed for 3 min, finally, the remaining 40% of the premix is added, and fast stirring is performed for 2 min to obtain the biochar-based alkali-activated blocking and controlling material, which is recorded as MgO@4BC.

[0054] Example 5

[0055] The biochar-based alkali-activated control material of the present application, compared with Example 2, changes the ratio of glue to soil: contains 40% in-situ soil and 60% of colloidal material by mass percentage; wherein the colloidal material contains 85% of ash body material and 15% of composite alkali activator by mass percentage, the composite alkali activator is obtained by co-milling of active magnesium oxide and biochar, the mass ratio of biochar to magnesium oxide is 2:100; the water-solid mass ratio is 24%.

[0056] Example 6

[0057] The biochar-based alkali-activated control material of the present application, compared with Example 2, changes the ratio of glue to soil: contains 40% in-situ soil and 60% of colloidal material by mass percentage; wherein the colloidal material contains 85% of ash body material and 15% of composite alkali activator by mass percentage, the composite alkali activator is obtained by co-milling of active magnesium oxide and biochar, the mass ratio of biochar to magnesium oxide is 2:100; the water-solid mass ratio is 24%.

[0058] Comparative Example 1

[0059] An alkali-activated control material, which uses an equal amount of ordinary active magnesium oxide to replace the composite alkali activator compared with Example 1, and the rest of the preparation method is the same, the product is recorded as MgO.

[0060] Comparative Example 2

[0061] An alkali-activated control material, which only mixes biochar and active magnesium oxide without ball milling compared with Example 1; the rest of the preparation method is the same, and the obtained product is recorded as MgO+1BC.

[0062] Comparative Example 3

[0063] An alkali-activated control material, which only mixes biochar and active magnesium oxide without ball milling compared with Example 2; the rest of the preparation method is the same, and the obtained product is recorded as MgO+2BC.

[0064] Comparative Example 4

[0065] An alkali-activated control material, which only mixes biochar and active magnesium oxide without ball milling compared with Example 3; the rest of the preparation method is the same, and the obtained product is recorded as MgO+3BC.

[0066] Comparative Example 5

[0067] An alkali-activated control material, which only mixes biochar and active magnesium oxide without ball milling compared with Example 4; the rest of the preparation method is the same, and the obtained product is recorded as MgO+4BC.

[0068] Comparative Example 6

[0069] An alkali-activated barrier material, which is prepared by replacing the composite alkali activator in Example 1 with an equal amount of ball-milled active magnesium oxide, and the rest of the preparation method is the same as Example 1. The product is recorded as MgO*.

[0070] Comparative Example 7

[0071] A traditional cement barrier wall material, which is prepared by replacing the colloidal material in Example 1 with ordinary portland cement, i.e. cement: in-situ soil = 3:7, and the rest of the preparation method is the same as Example 1.

[0072] Comparative Example 8

[0073] An alkali-activated barrier material, which is prepared by replacing the alkali activator in Example 1 with sodium hydroxide, configured to a solution close to the pH of Example 1, added according to the water-solid ratio, and the rest of the preparation method is the same as Example 1. The product is recorded as NaOH.

[0074] The materials prepared in the above examples and comparative examples are tested for performance:

[0075] The performance of the barrier material is tested according to the Highway Geotechnical Test Code (JTG 3430-2020) and ASTM D4972. The basic physical properties are shown in Tables 1-2:

[0076] Table 1, Performance of barrier materials of Examples 1-4 and Comparative Examples 1-8

[0077]

[0078] Table 2, Unconfined compressive strength (MPa) of barrier materials of Examples 1-4 and Comparative Examples 1-8

[0079] As can be seen from Tables 1-2 and Figures 2-3, the composite alkali-activated agent prepared by ball milling of active magnesium oxide and biochar has the characteristics of high early strength, shorter initial setting time, better workability and meets the demand for rapid forming. The initial setting time can be as short as 34 min, and the 7d compressive strength can be as high as 9.33 MPa. As can be seen from Comparative Examples 1-5, the biochar cannot be directly mixed without ball milling to improve the early strength of the blocking and controlling material, and the initial setting time and compressive strength are far worse than those of the biochar-based alkali-activated blocking and controlling material. As can be seen from Examples 1-4 and Comparative Example 6, single ball milling can slightly increase the activation effect of magnesium oxide, and the early strength is increased compared with that of unball-milled magnesium oxide, but this increase is not as obvious as that of co-ball-milled magnesium oxide and biochar. Comparative Example 8 provides a traditional NaOH-activated slag blocking and controlling material. Under the condition of ensuring the same pH and cement mortar ratio as the present application, the traditional blocking and controlling material has poorer workability and fluidity, and the construction is relatively difficult. At the same time, the traditional blocking and controlling material is strictly limited by the alkali equivalent, and the strength development is relatively slow compared with that of the ball-milled blocking and controlling material.

[0080] The blocking and controlling ability of the materials prepared in the above examples and Comparative Examples 1-8 was tested.

[0081] The test site was a chemical pollution site in Jiangsu with an area of 700m 2 The average content of heavy metal lead in the site was 7000mg / kg, which was 7.75 times higher than the screening value (800mg / kg) of the second type of construction land in the "Soil Environmental Quality Control Standard for Construction Land" (GB 36600-2018). The biochar-based alkali-activated blocking and controlling material mentioned in the examples was used for rapid forming in a 5x5m area in the chemical pollution site. The specific construction included the following steps:

[0082] (1) A trench was excavated at the proposed blocking position by a trenching machine;

[0083] (2) The cement material and the composite alkali-activated agent were prepared according to the mass percentage, and were uniformly mixed in a concrete mixer for 5min to obtain a premix. 60% of the premix was put into the concrete mixer, and water was added to the dry mix at a water-solid mass ratio of 24%, and was stirred at low speed for 5min to form a slurry. Then, the in-situ soil excavated from the trench was added, and was quickly stirred for 3min. Finally, the remaining 30-40% of the premix was added, and was quickly stirred for 2min to fully mix and form a slurry, which was pumped back into the trench;

[0084] (3) After pouring, a layer of in-situ soil was covered on the top of the blocking and controlling material to prevent top shrinkage cracking and to be leveled.

[0085] Another 5*5m range is taken for the preparation of the control material of the comparative example, and the permeability difference is compared.

[0086] After construction, samples in the range are taken for flexible wall permeability test, and the test standard is referred to ASTM D5084 specification. The sample is permeability under the action of Pb 2+ , and the change of permeability coefficient is compared with that of the original soil without pollution, and the chemical compatibility is compared. The results are shown in Table 3

[0087] Table 3, permeability of the control material of the comparative example in the original soil without pollution and the original soil polluted by 7000mg / kg Pb 2+

[0088]

[0089] As shown in Table 3, the permeability coefficient of each control material of the example in the original soil without pollution is reduced by about one order of magnitude compared with the comparative example, and the permeability coefficient of the example under the action of the polluted liquid is nearly 5-7 times lower than that of the comparative example; at the same time, according to the requirements in the “Technical Specification for Vertical Barrier of Industrial Contaminated Site” (HG / T 20715-2020), the permeability coefficient of the barrier material under the action of tap water should be less than 10 - 9 m / s, and the permeability coefficient under the action of the pollutant should be less than 10 - 8 m / s, it can be seen that the comparative example cannot meet the specification requirements, and the experimental examples can meet the specification requirements. This may be because the fine particles caused by ball milling increase the contact reaction area, and the reaction is more thorough; the introduction of biochar fills the large pores and makes the material more dense, so the impermeability effect is good.

[0090] The reduction of the permeability coefficient in the flexible wall permeability test and the better chemical compatibility under the action of the polluted liquid indicate that the control material proposed in the application has improved impermeability compared with the traditional control material. In terms of chemical compatibility, the chemical compatibility of each control material of the example is less than 11, while the chemical compatibility of the comparative example is more than 40, and the impermeability effect and chemical compatibility of the traditional cement wall are the worst. The chemical compatibility of the biochar-based alkali-activated control material prepared by rapid forming in the application is obviously better than that of the comparative example. The smaller the chemical compatibility, the more the diffusion of the pollution is reduced, the better the impermeability is, and the stronger the adaptability to the environment is.

[0091] In Examples 1-4, the effects caused by different contents of biochar are different. In order to ensure that the rapid forming and excellent impermeability are taken into account, the effect is the best when the mass ratio of biochar to magnesium oxide is 2:100. The biochar content should not be too high. Although the biochar content is too high, it can improve the barrier of the pollutant to some extent, but it will slow down the forming speed and reduce the strength, and it is not easy to stay under the action of water flow.

[0092] ​The blocking control ability test was carried out on the materials prepared according to the above examples and comparative examples 6-8:

[0093] The test site was a coking plant in the north of Anhui Province. The site was contaminated with volatile organic compounds such as 1,2-dichloroethane and benzene series. The 1,2-dichloroethane pollution was the most serious, with a maximum pollution of 102 mg / kg, which was 11.33 times the screening value (9 mg / kg) of the second type of construction land in the "Soil Environmental Quality for Construction Land Soil Pollution Risk Control Standard" (GB 36600-2018). The rapid forming of the biochar-based alkali-activated blocking control material mentioned in examples 1-4 was used in this site, and the specific construction included the following steps:

[0094] (1) Excavate a trench at the proposed blocking position by a trenching machine;

[0095] (2) Prepare the ash material and the composite alkali activator according to the mass percentage, and put them into a concrete mixer for uniform mixing for 5 min to obtain a premix. Take 60% of the premix and put it into a concrete mixer, add water to the dry mix according to a water-solid mass ratio of 24%, and stir at low speed for 5 min to form a slurry-like slurry. Then add the in-situ soil excavated from the trench, and quickly stir for 3 min. Finally, add the remaining 30-40% of the premix, and quickly stir for 2 min to fully mix and make a slurry. Pump the slurry back into the trench;

[0096] (3) After pouring, cover the top of the blocking material with a layer of uncontaminated soil to prevent top shrinkage cracking and leveling.

[0097] At the same time, the blocking control materials mentioned in comparative examples 6-8 were also tested to compare the blocking performance.

[0098] From the beginning of soil leveling, the 1,2-dichloroethane concentration in the uncontaminated soil above the blocking control material was tested at regular intervals, and the blocking effect was evaluated according to the change trend. The test results are shown in Table 5.

[0099] Table 4, Blocking performance test results (in terms of 1,2-dichloroethane concentration, mg / kg)

[0100]

[0101] As shown in Table 4 and Fig. 4, the rapid forming biochar-based alkali-activated barrier and control material proposed in the application can achieve barrier in about 150 min, and compared with the traditional alkali-activated barrier material and cement barrier wall material, the magnesium oxide provides an alkaline ball milling environment, promotes the modification of biochar, the pores are more abundant, the adsorption and retention of pollutants can make the leaching concentration of pollutants lower, the barrier effect is better, and the rapid forming demand can be met. Although the traditional material can also achieve barrier, it is basically applied to long-term maintenance and development situation, and is limited by time, pH and mortar ratio, the leaching concentration of barrier is higher, and the pollution concentration is still increasing within the detection time.

[0102] Therefore, the rapid forming biochar-based alkali-activated barrier and control material of the application has better early compressive strength than the untreated magnesium oxide activated cementitious material under low mortar ratio, and the 7d compressive strength can reach 9.33MPa; at the same time, the presence of biochar and slag can better adsorb and retain soil pollutants, and the impermeability is better, and the permeability coefficient can reach 2.4x10 -10 m / s. In application, the barrier is relatively rapid, and the leaching concentration of pollutants is lower. Compared with the cement barrier wall, the production process is low in cost, rapid in forming, low in carbon emission, and belongs to low-carbon green material.

Claims

1. A biochar-based alkali-activated barrier and control material, characterized in that, The biochar-based alkali-activated blocking and controlling material comprises 50-70% of in-situ soil and 30-50% of colloidal material in mass percentage; wherein the colloidal material comprises 90-80% of ash body material and 10-20% of composite alkali activator in mass percentage, the composite alkali activator is obtained by co-milling of active magnesium oxide and biochar, the mass ratio of biochar to magnesium oxide is 0.5-6:100; the water-solid mass ratio is 22-28%; the preparation method of the composite alkali activator is as follows: screening and crushing biochar raw materials, pyrolyzing at 500-700℃ for 1-3h to obtain biochar and grinding and sieving; drying the active magnesium oxide and biochar at 60-70℃ for 4-6h to obtain dry mixture; grinding the dry mixture in a ball mill for 2-3h to obtain the composite alkali activator.

2. The biochar-based alkali-activated barrier control material of claim 1, wherein, The ash body material is one or more combinations of blast furnace slag, fly ash, coal gangue and steel slag.

3. The biochar-based alkali-activated barrier control material of claim 1, wherein, In the preparation method of the composite alkali activator, the rotation speed of the ball mill is 100-300r / min, and the ball-material ratio is 4:1-8:

1.

4. The biochar-based alkali-activated barrier control material of claim 1, wherein, The activity of the magnesium oxide is 55-70%, and the particle size of the biochar is ≤50μm.

5. A method for preparing the biochar-based base activation and inhibition control material according to claim 1, characterized in that, The method comprises the following steps: (1) preparing ash body material and composite alkali activator according to mass percentage, uniformly stirring and mixing for 3-5min to obtain premix; (2) taking 60-70% of the premix obtained in step (1), adding water to the premix according to a water-solid mass ratio of 22-28%, stirring at low speed for 4-5min to form a slurry-like slurry, then adding in-situ soil according to a clay-soil ratio of 3:7-5:5, stirring at high speed for 2-3min, finally adding in the remaining premix, and stirring at high speed for 2-3min to obtain the biochar-based alkali-activated blocking and controlling material.

6. The method of claim 5, wherein, The curing condition of the preparation method is 25±2℃ and humidity ≥75%.

7. The manufacturing method according to claim 5, characterized in that, In step (2), the stirring speed at low speed is 700-900r / min, and the stirring speed at high speed is 1500-1800r / min.

8. Application of the biochar-based alkali-activated blocking and controlling material of claim 1 in emergency pollution site rapid blocking and controlling and soil pollution control or remediation.

9. Use according to claim 8, characterized in that, The application comprises the following steps: excavating a trench at a planned blocking position by a trenching machine; configuring the biochar-based alkali-activated blocking and controlling material, fully mixing the biochar-based alkali-activated blocking and controlling material, pumping the slurry prepared from the biochar-based alkali-activated blocking and controlling material back to the trench, and covering a layer of in-situ soil on the top of the blocking material after pouring.

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