Preparation method of biological soil dust inhibitor based on sword beans

Abstract

The invention discloses a preparation method of a biological soil dust inhibitor based on sword beans, the biological soil dust inhibitor comprises a urease solution and a cementing solution, the urease solution and the cementing solution are respectively prepared by adopting a reasonable preparation method, and the biological soil dust inhibitor which is strong in external force interference resistance, good in dust suppression effect and high in soil dust suppression efficiency can be prepared. The soil dust inhibitor has good ecological compatibility, and the problem that an existing soil dust inhibitor is difficult to have dust suppression application performance and environmental protection performance at the same time is solved.

Description

Technical Field

[0001] The invention relates to the technical field of soil dust inhibitors, and in particular to a method for preparing a bio-type soil dust inhibitor based on sword beans. Background Art

[0002] Soil dust generated by construction is the main source of dust in urban construction sites. During the construction process, large areas of exposed construction surfaces, loose soil piles formed by earth excavation, construction waste piles, and unhardened temporary roads and other bare soil surfaces will generate a large amount of soil dust under the action of wind, forming a diffuse dust environment, affecting the local environment and personnel health. The contribution rate of dust to total suspended particulate matter (TSP) in the air exceeds 50%, and TSP has a significant correlation with population mortality. When 1 square meter of air contains 100μg TSP, the population mortality rate increases by 6%, the mortality rate of respiratory diseases increases by 32%, the mortality rate of asthma increases by 12%, and the mortality rate of cardiovascular diseases also increases by 9%. The problem of wind erosion and dust from bare soil in construction sites seriously endangers the environmental air quality and human health. Effective control of construction dust pollution is crucial to improving air quality.

[0003] At present, the measures taken by China and abroad to prevent and control dust at infrastructure construction sites mainly include laying dust nets, sprinkling water, spraying dust suppressants, etc. The cost of suppressing dust by laying dust nets or plastic sheets is high, and the installation and removal time is long. Especially when using plastic sheets to prevent dust, this disposable plastic product is not easy to recycle and degrade, and it is easy to cause soil pollution when it flows into the soil or runoff. Dust suppression by spraying water has limited dust suppression effect due to the poor viscosity, durability and consolidation ability of water. Therefore, the most effective way to reduce soil dust in infrastructure construction is to spray dust suppressants, and with the continuous increase in the protection of the ecological environment, the research on dust suppressants is gradually moving towards a green and environmentally friendly direction.

[0004] At present, the raw materials for preparing dust suppressants include solid wastes such as bagasse, straw, and discarded shrimp shells. These raw materials need to be prepared by chemical reactions, or use chemicals to increase their dust suppression performance. The dust suppressants synthesized using the above materials do not deviate from the category of chemical dust suppressants, which will affect the environmental protection and degradability of the products. Therefore, in order to ensure the application performance of the dust suppressant while having both environmental protection and degradability, the present invention proposes a preparation method of a biological soil dust suppressant based on sword beans. Summary of the invention

[0005] In order to overcome the deficiencies of the prior art, the object of the present invention is to provide a method for preparing a bio-type soil dust inhibitor based on sword bean to achieve better environmental protection performance and application effect.

[0006] The technical solution adopted by the present invention is as follows: A method for preparing a bio-type soil dust inhibitor based on sword bean, wherein the bio-type soil dust inhibitor comprises urease solution and a cementing solution, and the preparation method comprises: Urease solution preparation: S1, select sword beans and crush them; S2, taking sword bean powder and adding citric acid-sodium citrate extract in a solid-liquid ratio of 1:2 to 4; S3, the material is fully stirred in a constant temperature water bath at a temperature of 25°C to 35°C, and centrifuged at 4000 rpm for 40 minutes, and the supernatant is taken to obtain urease solution; S4, adjusting the pH of the urease solution to 5-9 for standby use; Preparation of cementing fluid: Take urea and calcium chloride of the same concentration and mix them in a mass ratio of 1:1 to prepare a cementing liquid with a concentration of 0.5 mol / L to 0.7 mol / L for use.

[0007] As a preferred embodiment of the present invention, eggshell powder is added to the binder at a mass volume ratio of 20-30%.

[0008] The present invention adds eggshell powder in a mass volume ratio of 20-30%. On the one hand, since the eggshell powder has adsorption properties for calcium ions, nucleation sites can be provided in the process of generating calcium carbonate by reaction, so that the generated calcium carbonate is more stable; on the other hand, the crystal type and distribution of the generated calcium carbonate can be improved, thereby forming a solidified layer to maintain good integrity and hardness of the soil.

[0009] As a preferred embodiment of the present invention, eggshell powder is added to the binder at a mass volume ratio of 24%. As a preferred embodiment of the present invention, in S2, sword beans and citric acid-sodium citrate extract are mixed at a solid-liquid ratio of 1:2.8-3.

[0010] As a preferred embodiment of the present invention, in S3, the materials are fully stirred in a constant temperature water bath at a temperature of 30°C.

[0011] As a preferred embodiment of the present invention, in S4, the pH of the urease solution is adjusted to 6 to 8.5.

[0012] As a preferred embodiment of the present invention, in S4, the pH of the urease solution is adjusted to 8.

[0013] As a preferred embodiment of the present invention, the concentration of the binder is 0.6 mol / L.

[0014] As a preferred embodiment of the present invention, the pretreatment in S1 is: after washing the sword beans with distilled water, drying them in an electric heated blast drying oven, crushing the dried sword beans, and passing them through a 100-mesh sieve.

[0015] The use principle of the present invention: The soil dust suppressant of the present invention is used by uniformly spraying equal volumes of the cementing liquid and the urease solution on the soil in sequence. After the soil is sprayed, the dust on the soil surface is wrapped by the formed mineralized products, and the fine particles on the surface are agglomerated to effectively consolidate the dust, which can fully improve the soil's ability to resist dispersion. Since the urease in the urease solution can promote the hydrolysis of urea in the cementing liquid, the hydrolysis product can react with the calcium ions in the calcium chloride, and then generate calcium carbonate precipitation to fill the pores between the soil particles and cement them. In the process of cementing the soil, the soil particles are combined together to change the particle size of the soil particles, thereby effectively inhibiting the generation of dust.

[0016] Beneficial effects of the present invention: 1. The present invention uses citric acid-sodium citrate with a solid-liquid ratio of 1:2-4 as the extracting solution. Citric acid-sodium citrate has a good extraction effect on urease, and the inventors have found that under the content of the specific solid-liquid mass volume ratio of 1:2-4 in the present invention, the activity of urease in the urease solution can be ensured to be optimal, thereby maximizing the dust suppression effect. If a citric acid-sodium citrate extracting solution with a solid-liquid ratio lower than 1:2-4 is used, the obtained solution is too viscous during the process of dissolving the sword bean powder in the extracting solution, which is not conducive to uniform stirring, and the urease contained in the sword bean cannot be fully extracted by the extracting solution, resulting in a reduction in the extraction amount, resulting in the urease not being completely extracted, resulting in a decrease in activity. If a citric acid-sodium citrate extracting solution with a solid-liquid ratio higher than 1:2-4 is used, although urease can be effectively extracted, so that the amount of extracted urease increases, the applicant has found that adding an extracting solution exceeding the above ratio range will reduce the concentration of the solution formed by the sword bean and the extracting solution, resulting in a decrease in urease activity. The inventors found in their research that the selection, ratio and effective content of the extract are critical to ensuring both the extraction of urease and the control of activity. Therefore, the present invention selects citric acid-sodium citrate with a solid-liquid ratio of 1:2 to 4 as the extract, and the concentration of citric acid-sodium citrate is further preferably 0.1 mol / L.

[0017] 2. The present invention adjusts the pH of the urease solution to 5-9. When the urease solution is in an environment with a pH of 5-9, the activity of the urease in the urease solution can reach the optimum. In an alkaline environment with a pH higher than 9, the urease structure will be destroyed due to excessive alkalinity, which will inhibit the activity of the urease. In an acidic environment with a pH lower than 5, the concentration of hydrogen ions (H⁺) is too high, which may cause the molecular structure of the enzyme protein to change or even denature, thereby reducing the activity. Therefore, the present invention chooses to adjust the pH of the urease solution to 5-9 to ensure that the urease has a higher activity, so as to greatly improve the catalytic efficiency, hydrolyze urea more quickly and effectively, thereby generating calcium carbonate precipitation to absorb dust, improve dust suppression efficiency, quickly improve air quality, and improve the stability and durability of the enzyme in application.

[0018] 3. The urease solution of the present invention is extracted from sword beans and is a natural material. The binder uses urea and calcium chloride. Urea is a naturally occurring organic compound, and calcium chloride is an inorganic salt. Both are environmentally friendly materials, which are easily degraded in the natural environment and will not cause adverse effects on the ecosystem. Compared with traditional chemical preparations, the soil dust suppressant prepared by the present invention has good ecological compatibility under reasonable application, and can effectively suppress the generation of dust, and has the advantages of both environmental protection performance and good dust suppression effect.

[0019] 4. The soil dust suppressant of the present invention has a small calcium carbonate crystal formed with urease as the core. In the process of soil consolidation, it is easier to adhere to soil particles and fill the gaps between particles. In this process, a part of the calcium carbonate will act as a bridge to cement adjacent soil particles, causing changes in the internal structure of the soil, making it more stable and the soil body more compact. It can not only significantly improve the dust suppression effect, but also effectively resist external interference, thereby prolonging the effective dust suppression period. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the effect of the volume and pH of the extract on the urease activity in an embodiment of the present invention; Figure 2 Schematic diagram of the effect of calcium chloride-urea concentration on the amount and rate of calcium carbonate precipitation in an embodiment of the present invention; Figure 3 It is a schematic diagram of the wind erosion resistance of the dust sample treated with soil dust inhibitor and water after 6 erosions in an embodiment of the present invention; Figure 4 is a schematic diagram comparing the initial and final surface morphologies of dust samples treated with soil dust inhibitor and water under wind erosion in an embodiment of the present invention; Figure 5 is a schematic diagram of the water holding rate of a dust sample treated with a soil dust inhibitor and water after being dried six times in an embodiment of the present invention; Figure 6 is a schematic diagram of the hardness of the consolidation layer at different positions on the surface of the dust sample treated with soil dust inhibitor and water in an embodiment of the present invention; Figure 7 is a schematic diagram comparing the degradation rates of dust samples treated with soil dust suppressants and water after one week in an embodiment of the present invention; Figure 8 1 is a schematic diagram of a dust sample sprayed with (a) a soil dust suppressant and (b) water at a SEM image of 10000× magnification in an embodiment of the present invention, and a dust sample sprayed with (c) a soil dust suppressant and (d) water at a SEM image of 1000× magnification; Fig. 9 Schematic diagram of the XRD spectrum of the mineralized product formed by EICP in the embodiment of the present invention; Fig.10 is a schematic diagram of the FTIR spectrum of a dust sample treated with soil dust inhibitor and water in an embodiment of the present invention; Fig.11 is a schematic diagram comparing the surface morphologies of dust samples treated with soil dust inhibitor and water in an embodiment of the present invention; Fig.12 is a schematic diagram of the change in TSP concentration after treatment with soil dust inhibitor and water in an embodiment of the present invention; Fig.13 Schematic diagram of the change in TSP concentration on days 1, 7, 14 and 30 after treatment with soil dust inhibitor and water in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] Typical embodiments that embody the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention can have various changes in different embodiments without departing from the scope of the present invention, and the descriptions and illustrations therein are essentially used for illustration purposes rather than for limiting the present invention.

[0022] The citric acid-sodium citrate extract used in the present invention is a purchased citric acid-sodium citrate extract with a concentration of 0.1 mol / L.

[0023] Example 1 This embodiment discloses a method for preparing a bio-type soil dust inhibitor based on sword bean, wherein the bio-type soil dust inhibitor comprises urease solution and a cementing solution, and the preparation method comprises: Urease solution preparation: S1, select sword beans, wash the sword beans with distilled water, dry them in an electric hot air drying oven, use a crushing device to crush the dried sword beans, and pass them through a 100-mesh sieve to obtain sword bean powder.

[0024] S2. Weigh the sword bean powder, and add citric acid-sodium citrate extract with a pH of 6 and a concentration of 0.1 mol / L into the sword bean powder at a solid-liquid ratio of 1:2.

[0025] S3, fully stirring the material in S2 in a constant temperature water bath at 30°C, centrifuging at 4000 rpm for 40 min, taking the supernatant to obtain urease solution; S4, adjusting the pH of the urease solution to 5 for later use; Preparation of cementing fluid: Take 0.5 mol / L urea and 0.5 mol / L calcium chloride in a mass ratio of 1:1 and mix them to prepare a 0.5 mol / L cementing liquid for use.

[0026] The soil dust inhibitor of the present invention is used by uniformly spraying equal volumes of the binder solution and the urease solution on the soil in sequence.

[0027] Example 2 The difference between this embodiment and embodiment 1 is that in the preparation of urease solution, the sword bean powder and citric acid-sodium citrate extract in S2 are mixed at a solid-liquid ratio of 1:2.8. In S4, the pH of the urease solution is adjusted to 8. In the preparation of the cementing solution, 0.6 mol / L urea and 0.6 mol / L calcium chloride are mixed at a mass ratio of 1:1 to obtain a cementing solution with a concentration of 0.6 mol / L for standby use.

[0028] Example 3 The difference between this embodiment and embodiment 1 is that in the preparation of urease solution, the sword bean powder and citric acid-sodium citrate extract in S2 are mixed at a solid-liquid ratio of 1:4. In S4, the pH of the urease solution is adjusted to 9. In the preparation of the cementing solution, 0.7 mol / L urea and 0.7 mol / L calcium chloride are mixed at a mass ratio of 1:1 to obtain a cementing solution with a concentration of 0.7 mol / L for standby use.

[0029] Example 4 The difference between this embodiment and embodiment 2 is that eggshell powder is added to the binder at a mass volume ratio of 20%.

[0030] Example 5 The difference between this embodiment and embodiment 4 is that eggshell powder is added to the binder at a mass volume ratio of 24%.

[0031] Example 6 The difference between this embodiment and embodiment 4 is that eggshell powder is added to the binder at a mass volume ratio of 30%.

[0032] Urease extraction test The commonly used extraction solution for urease is water. Take 10g of each portion of sword bean powder and dissolve it in different volumes of water and citric acid-sodium citrate extraction solution respectively. Use the above urease extraction method to prepare urease solution, and take 3ml of each portion of urease solution and add it to 27mL of 1.1mol / L urea solution.

[0033] Through testing, when water is used as the extracting liquid and the solid-liquid ratio is 1:3.5, the maximum activity of urease extracted is 33.2mMurea hydrolysed / min. When citric acid is used as the extracting liquid and the ratio is 1:3, the maximum activity of urease extracted is 37.4mM ureahydrolysed / min. By comparison, it can be seen that the urease activity extracted by using citric acid-sodium citrate as the extracting liquid is higher than that extracted by using water. Therefore, the extraction effect of using citric acid-sodium citrate as the extracting liquid is better.

[0034] Test on factors affecting urease activity (1) Effect of extraction volume on urease activity Considering the reason of solubility, the volume of extract has an impact on urease activity. Weigh 8 parts of sword bean powder 10g and dissolve them in 22mL, 24mL, 26mL, 28mL, 30mL, 35mL, 40mL, 50mL of citric acid-sodium citrate solution respectively. Except that the volume of extract is different, other steps are the same as the urease extraction method of Example 2, and 8 parts of urease liquid are obtained. Each part of urease liquid takes 3ml and is added to 27mL of 1.1mol / L urea solution. Due to the hydrolysis of urea to produce ammonia ions and carbonate ions, urease can accelerate the hydrolysis of urea so that the conductivity of the solution changes, and it is proved that the conductivity change of the solution system is proportional to the amount of urea hydrolysis, so the urease activity is indirectly characterized by the change value of conductivity, so the urease activity is measured by adopting conductivity method.

[0035] Test results, such as Figure 1 As shown in the figure on the left, it can be seen that when the volume is 22ml to 28ml, the urease activity rises slowly. When 10g of soybean powder is dissolved in 28mL of citric acid-sodium citrate extract, the prepared urease activity is the highest. At this time, the citric acid-sodium citrate solution completely extracts the urease contained in the soybean powder, that is, it reaches the optimal extraction degree. As the volume of the extract continues to increase, the urease activity shows a clear downward trend. It can be concluded that the more extract, the better. It may be because excessive extract will reduce the concentration and affect the mixing efficiency, thereby causing a decrease in urease activity. In summary, when the volume of the extract is 28mL, the catalytic efficiency of urease can be maximized.

[0036] (2) Effect of pH on urease activity Urease is composed of protein and is an amphoteric electrolyte. pH has a great influence on urease activity. Take 8 equal amounts of urease of equal concentration, add equal amounts of urea of ​​equal concentration to 8 urease solutions, and adjust the pH of the mixed solution to 4, 5, 6, 7, 8, 9, 10, and 11 respectively. Insert the pH meter into the mixed solution of urease and urea, and take the average of the three valid results of the pH meter measurement as the final result.

[0037] Test results, such as Figure 1As shown in the figure on the right, it can be seen that the urease activity is higher when the pH value is in the range of 4.0 to 8.0, especially when the pH is 8, the urease activity reaches the highest. With the increase of pH, the urease activity is significantly inhibited in the pH range of 8.0 to 11.0. The reason may be that the structure of urease is destroyed under alkaline conditions. If the solution environment is too alkaline, it will have a significant inhibitory effect on the urease activity. This is because the pH value of the enzyme reaction medium will affect the enzyme molecules, especially the degree of dissociation of the essential groups on the active center and the ionization state required by the proton donor and acceptor in the catalytic group center. Only at the optimal pH, the dissociation of the enzyme and the substrate reaches the optimal binding state, and the reaction rate can be maximized. In summary, the urease extracted from the sword bean has higher activity under weakly acidic and weakly alkaline conditions, and the urease activity is significantly inhibited under strong alkaline conditions. The urease activity reaches the highest when pH=8.

[0038] Effect of eggshell powder on dust suppression Take 7 portions of 20 ml of cementing liquid of equal concentration, and add 0 g, 1.2 g, 2.4 g, 3.6 g, 4.8 g, 6.0 g, and 7.2 g of eggshell powder to the 7 portions of cementing liquid, respectively. Weigh 7 portions of 200 g of soil dust samples and place them in an iron plate of 29.5 cm × 19.5 cm × 2 cm, spray the 7 portions of cementing liquid evenly on the 7 portions of soil dust samples, and then spray the urease solution of Example 2, and after wind erosion for 120 min, and drying for 2 h at 105 ° C in an electric blast drying oven, the performance data are measured, as shown in Table 1.

[0039] Table 1 Eggshell powder dosage 0g 1.2g 2.4g 3.6g 4.8g 6.0g 7.2g Wind erosion resistance 98.58% 98.87% 99.26% 99.33% 99.64% 99.58% 98.92% Water retention rate 32.67% 34.72% 36.54% 38.24% 38.57% 37.46% 33.54% Hardness value 60.1HA 61.8HA 63.3HA 64.9HA 64.1HA 63.8HA 62.3HA As shown in Table 1, after a long period of erosion, the wind erosion resistance rate of the soil dust inhibitor sprayed with eggshell powder is higher than that of the soil dust inhibitor without protein powder. This shows that the soil dust inhibitor with eggshell powder can make the generated calcium carbonate more stable. Moreover, from the measured water retention rate and hardness values, the soil water retention effect and soil hardness of the soil dust inhibitor sprayed with eggshell powder are also better than those of the soil dust inhibitor without protein powder. In summary, it can be fully explained that by adding eggshell powder to the soil dust inhibitor, not only can the dust be combined more stably, but also a good solidification layer can be formed, so that the soil maintains good integrity and hardness, and reduces the generation of dust.

[0040] In addition, it can be seen from Table 1 that when 4.8g of eggshell powder is added, the calcium ion conversion rate of the eggshell powder is the best, and the wind erosion resistance rate and water retention rate can reach the maximum value. Therefore, when 4.8g of eggshell powder is added to the binder, the dust suppression effect can be maximized.

[0041] Effect of cementing fluid concentration on cementing effect Different concentrations of cementing liquid have an effect on the precipitation amount and precipitation rate of calcium carbonate. Take 12 equal portions of cementing liquids with concentrations of 0.1mol / L, 0.2mol / L, 0.3mol / L, 0.4mol / L, 0.5mol / L, 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L, 1.0mol / L, 1.1mol / L, and 1.2mol / L, add an equal volume of urease solution (the urease solution is selected from the urease solution in Example 2) to each portion of cementing liquid, react for 24 hours under the same environment, filter out the supernatant, obtain a precipitate, dry the precipitate to constant weight, and weigh it as m. Calculate the mineralization yield, calculated by the following formula: Where: is the precipitation rate of mineralization products; The weight of the glass dish before the precipitate dissolves; is the weight of the glass dish after the precipitate is dissolved; is the theoretical value of calcium carbonate precipitation; C is the concentration of cementing fluid; V is the volume of cementing fluid; M is the molar mass of calcium carbonate.

[0042] Test results, such as Figure 2 As shown in the figure, when the concentration is between 0.1mol / L and 0.6mol / L, the amount of mineralized products precipitated increases significantly, and the precipitation rate also increases significantly. When the concentration is 0.6mol / L, the precipitation rate of mineralized products reaches its maximum value. As the concentration continues to increase, the rising trend of precipitation slows down, and the precipitation rate continues to decrease. The precipitation rate in the figure shows a trend of first increasing and then decreasing. This may be because as the concentration of the cementing fluid increases, there are too many urea molecules in the solution, resulting in a hydration shell formed around the ions produced by the hydrolysis of urea, thereby reducing the mobility of calcium ions, resulting in a decrease in the precipitation rate.

[0043] In summary, the selection of a cementing liquid with a concentration of 0.6 mol / L can maximize the precipitation rate of mineralized products. The mineralized products are used to adsorb cementitious dust, thereby maximizing the dust suppression effect.

[0044] Biological Soil Dust Suppressant Performance Test (1) Wind erosion resistance test Weigh 200g of soil dust samples and place them in an iron pan of 29.5cm×19.5cm×2cm, and use an electric hot air drying oven to dry at 105℃ for 2h. Spray water on one of the soil dust samples, and evenly spray 115ml of cementing liquid and 115ml of urease solution on the other soil dust sample (spraying volume is about 2L / cm). , using the urease solution and cementing solution in Example 2). After natural drying at room temperature, the mass is weighed as follows: Use a blower to blow away the dust at a distance of 15 cm from the iron plate, and keep the central air outlet of the blower level with the upper end of the iron plate, so that the wind speed level on the surface of the dust sample is level 7 (13.9-17.2 m / s). Blow away the dust for 120 minutes, and weigh the iron plate every 20 minutes. The wind erosion resistance is calculated according to the formula: Where: is the wind erosion resistance rate; is the weight of the iron plate every 20 minutes after erosion; M is the weight of the iron plate after spraying soil dust inhibitor or water.

[0045] After testing, Figure 3 The wind erosion resistance rate changes with time after the soil dust sample is sprayed with soil dust inhibitor and water. It can be seen from the figure that the wind erosion resistance rate decreases with the increase of time. After 2 hours, the wind erosion resistance rate of spraying water is only 81.95%, and the wind erosion resistance rate of spraying soil dust inhibitor is 98.58%, which is 20.29% higher than water. Figure 4 The soil dust samples before and after erosion are shown. It can be seen that there is a large area of ​​dust loss on the surface of the soil dust sample sprayed with water, which indicates that a large amount of dust will be generated during the erosion process. The surface of the soil dust sample sprayed with soil dust inhibitor is effectively solidified by the white part. After a long period of erosion, it is not blown away, which fully demonstrates that the formed solidified layer maintains good integrity and hardness. In summary, it can be concluded that the soil dust inhibitor has good wind erosion resistance, can effectively consolidate dust and reduce the generation of dust.

[0046] (2) Water retention test Dry an empty round aluminum box with a diameter of 75 mm at 105 °C for 2 h and weigh it. Weigh 2 10g dried soil dust samples and spread them flat in a round empty aluminum box. Spray water on one of the soil dust samples, and evenly spray 13ml of cementing liquid and 13ml of urease solution on the other soil dust sample (the spraying volume is about 2L / , the urease solution and the cementing solution in Example 2 are selected), weighed and recorded as . Cover the box tightly and place it in a blast drying oven preheated to 105℃ for 6 hours. Weigh the aluminum box every hour. The water retention rate is calculated as follows: Where: Wc is soil water retention rate; is the weight of the aluminum box after every 1 hour; is the weight of the aluminum box after spraying; It is the weight of the aluminum box before spraying.

[0047] After testing, Figure 5 The following is a graph showing the changes in water retention rate after spraying soil dust inhibitor and water at different time periods. Compared with spraying soil dust inhibitor, the water retention rate of spraying water shows a faster downward trend with the increase of time. After 6 hours, the water retention rate of soil dust samples sprayed with water was 2.29%, while the water retention rate of soil dust samples sprayed with soil dust inhibitor was 32.67%, which was 13.27% higher than that of soil dust samples sprayed with water. In summary, the water retention effect of soil dust samples sprayed with soil dust inhibitor is significantly better than that of spraying with water. This shows that under high temperature conditions, compared with water treatment, soil dust samples treated with soil dust inhibitor have better water retention, and their surface is effectively solidified by white precipitation, thereby slowing down the evaporation rate of soil moisture and prolonging the effective dust suppression period.

[0048] (3) Hardness test of cured layer Weigh 200g of dried soil dust samples and place them in an iron pan of 29.5cm×19.5cm×2cm. Spray water on one of the soil dust samples and evenly spray 115ml of cementing liquid and 115ml of urease solution on the other soil dust sample (spraying volume is about 2L / cm). , the urease solution and the cementing solution in Example 2 are selected), and the soil dust sample is dried at room temperature. The hardness of the solidified layer is measured using a HA hardness meter (0-100HAACD). The hardness values ​​are measured at five random points on the sample surface, and the average value is taken as the final hardness value.

[0049] It has been found through experiments that after spraying soil dust suppressant and water on soil dust samples, a solidified layer with a certain strength will be formed on the surface. Figure 6 The results show that the hardness of the solidified layer on the surface of the soil dust sample after spraying the soil dust inhibitor is significantly higher than that of the one sprayed with water. Among them, the average hardness of the surface solidified layer formed by spraying the soil dust inhibitor is 60.1HA, while the hardness of the solidified layer formed by spraying water is only 36.02HA, a difference of 24.08HA. The reason why the surface hardness of the soil dust sample after the soil dust inhibitor treatment is higher may be that the calcium carbonate generated by the urease soil dust inhibitor adheres to the surface of the soil dust sample, making its hardness value larger.

[0050] (4) Degradability test Take appropriate amounts of soil dust inhibitor (the soil dust inhibitor of Example 2) and the soil solidification layer after water spraying. In high-quality fertile soil 5 cm away from the soil surface, bury the solidification layer underground for comparative testing. The degradation rate is calculated as follows: Where: is the degradation rate; is the initial mass of the cured layer before the degradation experiment; This is the quality of the cured layer after one week.

[0051] After testing, it can be found that Figure 7 The degradation rate of the solidified layer formed by spraying soil dust suppressant and water under natural conditions in the soil environment is shown. In a 7-day period, the degradation rate of the solidified layer formed by spraying water is 6.60%, while the degradation rate of the solidified layer formed by spraying soil dust suppressant is 4.65%, which is 29.55% lower than that of water. Figure 7 It can be seen that the solidified layer formed by spraying water has split under the degradation conditions of the soil, while the one treated with soil dust suppressant remains as a whole, and the white part on the surface of the solidified layer continues to exist, which indicates that the solidified layer formed by spraying soil dust suppressant can slow down the natural degradation to a certain extent and prolong the dust suppression period.

[0052] Microscopic Analysis of Soil Dust Consolidation (1) Scanning electron microscopy (SEM) The surface morphology of the soil dust sample sprayed with soil dust inhibitor (the soil dust inhibitor of Example 2) and water was observed using a scanning electron microscope at a magnification of 1000-10000. Figure 8 As shown, compared Figure 8 (a) (b) It can be seen that there are many irregularly shaped calcium carbonate deposits on the surface of the soil dust sample after being treated with soil dust inhibitor, and the accumulation is dense. Compared with the soil dust sample after water treatment, the calcium carbonate precipitation effectively solidifies the soil particles to form a complete block. Figure 8 As can be seen in (a), there are obvious clustered particles condensed on the surface of the soil dust sample, and the coverage is high. Clustered particles are a process of formation-accumulation-growth, that is, the calcium carbonate crystal clusters will gradually increase with the continuous accumulation of newly generated calcium carbonate crystals until the urease is wrapped by the precipitated calcium carbonate, and the size of the crystal clusters depends largely on the size of the urease.

[0053] contrast Figure 8 (c) (d) It can be concluded that after the soil dust suppressant treatment, the fine soil particles are condensed together by calcium carbonate precipitation. Nano-sized urease can penetrate deeply into the soil dust sample and induce calcium carbonate precipitation in situ in a narrow space, partially filling the holes between particles, forming bridges at the connection points of soil particles, and introducing cementation into the soil dust sample, which greatly improves the anti-dispersion ability of the soil dust sample. It can resist external interference for a certain period of time, thereby significantly improving the dust suppression effect.

[0054] (2) X-ray diffractometer (XRD) An X-ray diffractometer was used to characterize the crystal structure of the dust samples before and after curing. By analyzing the diffraction pattern, information such as the composition of the material was obtained, so as to qualitatively determine whether the phase existed in the sample. The soil dust sample after spraying the soil dust inhibitor was dried, fully ground and passed through a 200-mesh sieve to ensure uniform particle size. The scanning range was set to 10° to 90°, and the scanning rate was set to 10° / min.

[0055] The three common crystal forms of calcium carbonate are calcite, vaterite and aragonite, and calcite is the most thermodynamically stable crystal form with better mechanical properties such as elastic modulus, hardness and ductility. Fig. 9 The XRD pattern of the soil dust sample after being treated with soil dust inhibitor. In the soil dust sample treated with soil dust inhibitor, the diffraction peak of calcite calcium carbonate is =23.07°, 29.41°, 35.98°, 39.42°, 43.17°, 47.53° and 48.52°, and the corresponding crystal planes are (012), (104), (110), (113), (202), (018) and (116), respectively, which indicates that the mineralized products exist in the soil dust sample in the form of stable crystalline calcite. In addition, except for the diffraction peak of calcite, the diffraction peak intensity of other impurities can be ignored, indicating that the mineralized products are of high purity. The sharp diffraction peaks in the figure indicate that the sample has good crystallinity. These mineralized products can fill the pores between the soil dust samples, thereby solidifying them into a whole. Active calcium carbonate crystals (precipitates) bind soil particles together and gather at soil contact points, increasing the cementation between soil particles.

[0056] (3) Fourier transform infrared spectrometer (FTIR) Infrared spectroscopy is widely used in the study of molecular structure and chemical composition of substances. The spatial configuration of the molecule can be determined based on the relationship between the position, intensity and shape of the spectral band frequency obtained after the molecule absorbs infrared light. Take an appropriate amount of dry dust sample and potassium bromide powder and add them to the mortar, grind them thoroughly, and then put them into the tablet press to make tablets. The FTIR spectrometer (Nicolet iS50, Thermo Fisher Scientific, USA) has a wave number range of 4000 to 400 .

[0057] The position and shape of the absorption peak in the infrared spectrum can be observed by FTIR to determine the chemical bonds and functional groups of the soil dust sample. The spectrum is shown in Figure 10. The absorption peak wave number is 3440 is the stretching vibration region of free OH, 1629 The absorption peak belongs to the vibration of carboxyl v (-COOH). Carboxyl groups exist in biomacromolecules such as polysaccharides, sugars and glycoproteins, and can serve as the main binding site in the mineralization process. The absorption peak is attributed to the stretching vibration of the CO bond in CO32-. The absorption peak of 875 and 712 New absorption peak wavenumbers appeared, which correspond to the characteristic absorption peaks of calcite, which is consistent with the XRD analysis results. Corresponding to the v3 vibration mode of the carbonate ion in calcium carbonate, 875 Corresponding to v2 vibration mode, 712 corresponds to the v4 vibration mode, and 745 The characteristic absorption peak corresponding to vaterite was not found in the FTIR spectrum, indicating that the calcium carbonate crystal in the soil dust sample was mainly calcite. These findings indicate that the soil dust inhibitor successfully acted on the soil dust sample after spraying and formed calcite-type calcium carbonate, and the mineralized precipitate was formed through biosorption and EICP process.

[0058] Field experiment The field test selected an earthwork construction section of a construction site, opened up two test areas of about 1 square meter, and separated different areas with white thin lines, and sprayed soil dust inhibitor (the soil dust inhibitor of Example 2) and water respectively. During the spraying stage, according to the standard (DB / T 3804-2021), for test sites with an area of ​​less than 1,000 square meters, a gasoline-powered sprayer was used to spray the test area at 2L / Spraying was carried out manually with a spraying amount of . During the monitoring stage, after air-drying for 24 hours under natural conditions, a hardness tester was used to detect the hardness of the soil surface in the test area. In addition, a dust detector was used to monitor the TSP concentration in the air in the experimental area during construction. The monitoring time was from 8:00 to 18:00, and data was recorded every 2 hours, for a total of 6 times. Three monitoring points were selected in each experimental area, and a dust detector was set up in each. The average value of the monitoring data was used as the TSP concentration in the air of the experimental area to reduce errors. The same method was used to monitor the experimental area for a long time, and the TSP emissions were recorded after 1, 7, 15, and 30 days.

[0059] (1) Soil surface morphology After spraying soil dust suppressant and water on the surface of earthwork construction soil in the experimental area, it was found that the average hardness value of the soil surface in the experimental area sprayed with water was 36.9HA, while that in the experimental area sprayed with soil dust suppressant was 61.2HA, which was 65.86% higher than that of water. The average hardness value of the field test was slightly higher than that of the performance test, which may be attributed to the fact that during the laboratory experiment, the soil dust was sieved through a 100-mesh sieve to obtain a uniform and fine soil, while the soil particles were unevenly distributed in the field experiment. The comparison of the two dust suppression methods sprayed on the surface of earthwork construction soil is shown in the figure. Fig.11 As shown in (a) and (b), it is obvious that white precipitation is produced on the soil surface after being treated with soil dust inhibitor. This indicates that after spraying, the EICP process successfully acts on the soil and produces calcium carbonate, which can effectively agglomerate fine particles on the surface of the soil dust sample, thereby forming a solidified layer with a certain hardness, which can cement the dust on the soil surface.

[0060] (2) TSP concentration In field experiments, the dust suppression effect can be indirectly characterized by TSP concentration. Fig.12 The figure shows the change of TSP concentration in the air of the experimental area with different dust suppression methods over time. It can be concluded that the TSP concentration in the air in the experimental area sprayed with soil dust suppressants has a smaller change range, and at any time period, it is lower than the TSP concentration in the experimental area sprayed with water. The average daily TSP concentration in the experimental area sprayed with soil dust suppressants is 49.83μg / , while the average daily concentration of spray water was 67.92 μg / , the difference between the two is 18.09μg / The TSP concentration reached two peaks at 10:00 a.m. and 16:00 p.m. At 10:00 a.m. and 16:00 p.m., the TSP concentration in the experimental area sprayed with soil dust inhibitor was 25.01% and 30.02% lower than that in the experimental area sprayed with water, respectively.

[0061] Fig.13 The TSP concentration changes after 1 day, 7 days, 15 days and 30 days were monitored for the experimental areas with different dust suppression methods. The TSP concentration in the experimental areas of the two dust suppression methods increased with time. Since the soil dust inhibitor has a good solidification effect, the TSP concentration in the experimental area sprayed with soil dust inhibitor is still lower than that of the experimental area sprayed with water. After 30 days, the average TSP concentration in the experimental area of ​​soil dust inhibitor was 60.8μg / , while the water experimental area is 99.1μg / , the soil dust suppressant is 38.65% lower than water. Water cannot effectively solidify soil particles, thus reducing the dust suppression effect, so the TSP concentration in the experimental area sprayed with water has a larger increase. From the above, it can be concluded that the soil dust suppressant has an excellent dust suppression effect and can exert a dust suppression effect for a long time, thereby reducing the harm of soil dust to workers and the pollution to the construction environment.

[0062] The above-mentioned embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and substitutions made by technicians in this field on the basis of the present invention shall fall within the scope of protection required by the present invention.

Claims

1. A method for preparing a bio-type soil dust inhibitor based on sword bean, characterized in that: The biological soil dust suppressant comprises urease solution and cementing solution, and the preparation method comprises: Urease solution preparation: S1, select sword beans and crush them; S2, taking sword bean powder and adding citric acid-sodium citrate extract at a solid-liquid ratio of 1:2-4; S3, the material is fully stirred in a constant temperature water bath at a temperature of 25°C to 35°C, and centrifuged at 4000 rpm for 40 minutes, and the supernatant is taken to obtain urease solution; S4, adjusting the pH of the urease solution to 5-9 for standby use; Preparation of cementing fluid: Take urea and calcium chloride of the same concentration and mix them in a mass ratio of 1:1 to prepare a cementing liquid with a concentration of 0.5 mol / L to 0.7 mol / L for use.

2. The method for preparing the biological soil dust suppressant according to claim 1, characterized in that: Eggshell powder is added to the binder at a mass volume ratio of 20-30%.

3. The method for preparing the biological soil dust suppressant according to claim 2, characterized in that: Eggshell powder is added to the binder at a mass volume ratio of 24%.

4. The method for preparing the biological soil dust suppressant according to claim 1, characterized in that: In S2, sword beans and citric acid-sodium citrate extract are mixed in a solid-liquid ratio of 1:2.8-3.

5. The method for preparing the biological soil dust suppressant according to claim 1, characterized in that: In S3, the materials are fully stirred in a constant temperature water bath at 30°C.

6. The method for preparing the biological soil dust suppressant according to claim 1, characterized in that: In the step S4, the pH of the urease solution is adjusted to 6 to 8.

5.

7. The method for preparing the biological soil dust suppressant according to claim 1, characterized in that: In S4, the pH of the urease solution is adjusted to 8.

8. The method for preparing the biological soil dust suppressant according to claim 1, characterized in that: The concentration of the binder is 0.6 mol / L.

9. The method for preparing the biological soil dust suppressant according to claim 1, characterized in that: The pretreatment in S1 is as follows: washing the sword beans with distilled water, drying them in an electric heated air drying oven, crushing the dried sword beans, and passing them through a 100-mesh sieve.

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