Biological cement sand-fixing and water-retaining material with synergistic effect of calcium ammonium nitrate and soybean urease as well as preparation method and application of biological cement sand-fixing and water-retaining material

Abstract

The invention discloses a biological cement sand-fixing and water-retaining material with synergistic effect of calcium ammonium nitrate and soybean urease as well as a preparation method and application of the biological cement sand-fixing and water-retaining material, and belongs to the technical field of environmental restoration and biological materials. The invention discloses a biological cement sand-fixing and water-retaining material with synergistic effect of calcium ammonium nitrate and soybean urease. The biological cement sand-fixing and water-retaining material is prepared from soybeans, deionized water, calcium ammonium nitrate and urea. The method comprises the following steps: 1, preparing a soybean urease solution; 2, preparing a calcium ammonium nitrate-urea salt solution; and 3, mixing. The biological cement sand-fixing and water-retaining material with the synergistic effect of calcium ammonium nitrate and soybean urease is applied to desertification control, coast dune fixation or soil ecological restoration. After the biological cement sand-fixing and water-retaining material with the synergistic effect of the calcium ammonium nitrate, the soybean urease and the polymer is solidified, the water content of sandy soil is nearly 80%, the biological cement sand-fixing and water-retaining material has a certain water supplementing effect on growth of crops planted in desertified or severely weathered soil, chloride ion residues are avoided, the strain culture problem is avoided, the cost is reduced by 40%, and the effect is obvious. Meanwhile, nitrogen nutrition is provided to promote vegetation recovery.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental restoration and biomaterials, and particularly relates to a biocement sand-fixing and water-retaining material with synergistic effects of calcium ammonium nitrate and soybean urease, as well as a preparation method and application thereof. Background Art

[0002] Desertification is one of the most serious ecological and environmental problems in the world today. Desertified land is mostly caused by wind erosion and water erosion. Current methods for sand control include biological sand control, engineering sand control, and chemical sand fixation.

[0003] Chemical sand fixation technology offers the advantages of low cost, rapid results, and simple construction. In areas susceptible to sandstorms, chemical sand fixation uses chemical materials and processes to create a consolidation layer on sand dunes or sandy surfaces. This layer prevents windblown sand, retains moisture, and improves the sand's properties. The goal is to control and improve the sand-damaged environment and enhance sand productivity. It can be considered a special case of mechanical sand fixation. This method is fast-acting and easily mechanized, and is often used to protect development and construction projects in areas severely affected by sandstorms, such as railways, highways, airports, national defense facilities, and oil fields. When selecting a chemical binder, the permeability of the sand should be considered, and it should be combined with plant-based measures whenever possible.

[0004] However, the existing chemical sand fixation technology still has the following technical defects:

[0005] (1) Traditional chemical sand fixation agents (such as asphalt emulsions and synthetic polymers) are costly and pose environmental pollution risks;

[0006] (2) Microbial induced carbonate precipitation (MICP) technology relies on living bacteria (such as Bacillus pasteurianus), which has the problems of long culture cycle and poor environmental adaptability;

[0007] (3) The existing urease extraction process is complex, and the enzyme activity is easily affected by environmental factors (temperature, pH). Summary of the Invention

[0008] In order to solve the above technical defects of the prior art, a biocement sand-fixing and water-retaining material with synergistic effects of calcium ammonium nitrate and soybean urease, as well as a preparation method and application thereof are provided.

[0009] A biocement sand-fixing and water-retaining material with synergistic effects of calcium ammonium nitrate and soybean urease is prepared from soybeans, deionized water, calcium ammonium nitrate and urea; the mass ratio of the deionized water, soybeans, calcium ammonium nitrate and urea is 2000:(10-100):(200-1200):(12-120).

[0010] A method for preparing a biocement sand-fixing and water-retaining material with synergistic effects of calcium ammonium nitrate and soybean urease is specifically completed by the following steps:

[0011] 1. Preparation of soybean urease solution:

[0012] ①. Crush the dried soybeans, add deionized water, stir, and refrigerate for a period of time to obtain a mixed solution;

[0013] ② Centrifuge the mixed solution and filter out the dregs. The resulting solution is the soybean urease solution and store in a refrigerator.

[0014] 2. Preparation of calcium ammonium nitrate-urea salt solution:

[0015] Dissolve calcium ammonium nitrate and urea in deionized water and stir evenly to obtain a calcium ammonium nitrate-urea salt solution;

[0016] 3. Mixing the soybean urease solution and the calcium ammonium nitrate-urea salt solution, then adding the polymer and stirring at room temperature to obtain a biocement sand-fixing and water-retaining material with the synergistic effect of calcium ammonium nitrate and soybean urease.

[0017] A biocement sand-fixing and water-retaining material with synergistic effects of calcium ammonium nitrate and soybean urease is used in desertification control, coastal sand dune fixation or soil ecological restoration.

[0018] Principle of the Invention

[0019] The present invention uses calcium ammonium nitrate (5Ca(NO3)2·NH4NO3·10H2O) to provide dual calcium and nitrogen sources, uses urea as a substrate, and uses soybean urease to catalyze the decomposition of calcium ammonium nitrate, releasing calcium ions and inducing the formation of calcium carbonate crystals, thereby achieving efficient cementation of sand particles.

[0020] Advantages of the present invention:

[0021] 1. Synergy of dual-functional raw materials: Calcium ammonium nitrate (5Ca(NO3)2·NH4NO3·10H2O) is used in the present invention: it provides Ca 2+ (forming CaCO3) and NH4 + / NO3 - (source of nitrogen fertilizer), provides dual calcium and nitrogen sources, promotes calcium carbonate precipitation and enhances sandy soil fertility;

[0022] Second, the present invention uses soybean urease: soybean urease is a plant-derived enzyme with high stability (activity loss ≤ 5% / month when stored at room temperature), the cost is only 1 / 3 of microbial agents, and there is no genetic engineering biosafety risk;

[0023] 3. Ecological compatibility: The residual nitrate in the present invention can be used as plant nutrients, and the porosity of the solidified layer is 30-40%, which is conducive to water penetration and root growth;

[0024] 4. No chloride ions or heavy metals are added during the entire process of this invention, which complies with GB / T 33891-2017 "Environmental Protection Standards for Desert Ecological Restoration Materials";

[0025] 5. The present invention optimizes the formula, achieves rapid curing (≤24 hours), and the product is eco-friendly;

[0026] 6. The biocement sand-fixing and water-retaining material using the synergistic effect of calcium ammonium nitrate, soybean urease and polymer of the present invention has a residual moisture content of nearly 80% in the sand after solidification, which indirectly reflects the good water retention. It has a certain water replenishment effect for the growth of crops planted in desertified or severely weathered soils, and there is no residual chloride ion. The present invention replaces traditional microbial agents with plant-derived urease, avoids the problem of strain cultivation, reduces costs by 40%, shortens the curing cycle to 5-7 days, and provides nitrogen nutrition to promote vegetation recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is the water evaporation rate;

[0028] Figure 2 Surface image of the cementing layer for the water retention experiment. DETAILED DESCRIPTION

[0029] Specific embodiment 1: This embodiment provides a biocement sand-fixing and water-retaining material with synergistic effects of calcium ammonium nitrate and soybean urease, which is prepared from soybeans, deionized water, calcium ammonium nitrate and urea; the mass ratio of the deionized water, soybeans, calcium ammonium nitrate and urea is 2000:(10~100):(200~1200):(12~120).

[0030] Specific embodiment 2: This embodiment differs from the specific embodiment 1 in that: a method for preparing a biocement sand-fixing and water-retaining material with the synergistic effect of calcium ammonium nitrate and soybean urease is specifically completed in the following steps:

[0031] 1. Preparation of soybean urease solution:

[0032] ①. Crush the dried soybeans, add deionized water, stir, and refrigerate for a period of time to obtain a mixed solution;

[0033] ② Centrifuge the mixed solution and filter out the dregs. The resulting solution is the soybean urease solution and store in a refrigerator.

[0034] 2. Preparation of calcium ammonium nitrate-urea salt solution:

[0035] Dissolve calcium ammonium nitrate and urea in deionized water and stir evenly to obtain a calcium ammonium nitrate-urea salt solution;

[0036] 3. Mix the soybean urease solution and the calcium ammonium nitrate-urea salt solution, then add the polymer and stir at room temperature to obtain a biocement sand-fixing and water-retaining material with the synergistic effect of calcium ammonium nitrate and soybean urease. The other steps are the same as those in the first embodiment.

[0037] Specific embodiment 3: This embodiment differs from specific embodiments 1 or 2 in that the mass ratio of deionized water to soybeans in step 1 (1) is 1000:(10-100); the stirring time in step 1 (1) is 4-6 hours; and the refrigeration temperature in step 1 (1) is 3°C-5°C, and the refrigeration time is 20-24 hours. Other steps are the same as those in specific embodiments 1 or 2.

[0038] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the centrifugation temperature in step 1 (2) is 3°C to 5°C, the centrifugation speed is 3000 rpm, and the centrifugation time is 10 to 20 minutes. In step 1 (2), the mixed solution is centrifuged and then filtered through a 100-200 mesh filter to remove the soybean dregs. The resulting solution is the soybean urease solution. The other steps are the same as those in specific embodiments 1 to 3.

[0039] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the soybean urease solution in step 1 ② has an enzyme activity of ≥ 200 U / g and the refrigeration temperature in step 1 ② is 3° C. to 5° C. The other steps are the same as those in specific embodiments 1 to 4.

[0040] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that the mass ratio of calcium ammonium nitrate, urea, and deionized water in step 2 is (200-1200):(12-120):1000. The other steps are the same as specific embodiments 1 to 5.

[0041] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that the polymer in step 3 is polyglutamic acid or xanthan gum. The other steps are the same as those in specific embodiments 1 to 6.

[0042] Specific embodiment 8: This embodiment differs from Specific embodiments 1 to 7 in that the mass ratio of deionized water, soybeans, calcium ammonium nitrate, and urea in the biocement sand-fixing and water-retaining material synergistically produced by calcium ammonium nitrate and soybean urease described in step 3 is 2000:(10-100):(200-1200):(12-120). The other steps are the same as Specific embodiments 1 to 7.

[0043] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that the mass fraction of the polymer in the biocement sand-fixing and water-retaining material synergistically produced by calcium ammonium nitrate and soybean urease in step 3 is 0% to 2%. The other steps are the same as specific embodiments 1 to 8.

[0044] Specific embodiment ten: This embodiment is a biocement sand-fixing and water-retaining material with synergistic effects of calcium ammonium nitrate and soybean urease, which is used in desertification control, coastal dune fixation or soil ecological restoration.

[0045] The following examples are used to verify the beneficial effects of the present invention:

[0046] Example 1: A method for preparing a biocement sand-fixing and water-retaining material with the synergistic effect of calcium ammonium nitrate and soybean urease is specifically completed by the following steps:

[0047] 1. Preparation of soybean urease solution:

[0048] ① Grind the dried soybeans, add deionized water, and stir at room temperature for 5 hours to obtain a mixed solution;

[0049] The mass ratio of deionized water to soybeans described in step 1① is 1000:70;

[0050] ② Centrifuge the mixed solution and filter the dregs through a 200-mesh filter. The resulting solution is the soybean urease solution.

[0051] The centrifugation temperature in step 1 (2) is 15°C to 25°C, the centrifugation speed is 3000 rpm, and the centrifugation time is 15 min;

[0052] The enzyme activity of the soybean urease solution described in step 1 (2) is ≥ 200 U / g;

[0053] 2. Preparation of calcium ammonium nitrate-urea salt solution:

[0054] Dissolve calcium ammonium nitrate and urea in deionized water and stir evenly to obtain a calcium ammonium nitrate-urea salt solution;

[0055] The mass ratio of calcium ammonium nitrate, urea and deionized water described in step 2 is 1081:60:1000;

[0056] 3. Mixing the soybean urease solution and the calcium ammonium nitrate-urea salt solution, stirring at room temperature for 5 minutes, and obtaining a biocement sand-fixing and water-retaining material with synergistic effects of calcium ammonium nitrate and soybean urease (referred to as calcium ammonium nitrate-urea cementing solution);

[0057] The mass ratio of deionized water, soybeans, calcium ammonium nitrate and urea in the biocement sand-fixing and water-retaining material with synergistic effect of calcium ammonium nitrate and soybean urease described in step three is 2000:70:1081:60.

[0058] Determination of soybean urease activity in the soybean urease solution obtained in step 1② of Example 1:

[0059] The change in solution conductivity is linearly positively correlated with urease activity, so soybean urease activity can be expressed as the amount of urea hydrolyzed per unit time. The bacterial activity used in MICP soil stabilization studies both domestically and internationally generally ranges from 3.3 to 20 mmol / min. Therefore, the present invention determines the appropriate soybean powder concentration within this range.

[0060] At room temperature, 1 mL of soybean urease solution was mixed with 4 mL of deionized water and poured into 5 mL of 3 mol / L urea solution. The conductivity change of the mixed solution within five minutes was measured using a conductivity meter (the conductivity change values at 0, 5, 10, and 15 minutes were recorded respectively). According to the research results of Whiffin et al., in a solution containing 1.5 mol / L urea concentration, a change in conductivity of 1 mS / cm reflects the amount of 11.11 mmol of urea hydrolyzed. This method is used in the present invention to calculate the activity index of liquid soybean crude urease:

[0061]

[0062] Where: U is the activity of urease solution per unit volume (mmol / min), ΔE is the change in solution conductivity within time t (mS / cm), and m is the dilution factor of the urease solution.

[0063] Example 2: A method for preparing a biocement sand-fixing and water-retaining material with synergistic effects of calcium ammonium nitrate and soybean urease, which is specifically completed by the following steps:

[0064] 1. Preparation of soybean urease solution:

[0065] ① Grind the dried soybeans, add deionized water, and stir at room temperature for 5 hours to obtain a mixed solution;

[0066] The mass ratio of deionized water to soybeans described in step 1① is 1000:70;

[0067] ② Centrifuge the mixed solution and filter out the dregs. The resulting solution is the soybean urease solution.

[0068] The centrifugation temperature in step 1 (2) is 15°C to 25°C, the centrifugation speed is 3000 rpm, and the centrifugation time is 15 min;

[0069] In step 1②, the mixed solution is centrifuged, and then the dregs are filtered through a 200-mesh filter. The resulting solution is the soybean urease solution;

[0070] The enzyme activity of the soybean urease solution described in step 1 (2) is ≥ 200 U / g;

[0071] 2. Preparation of calcium ammonium nitrate-urea salt solution:

[0072] Dissolve calcium ammonium nitrate and urea in deionized water and stir evenly to obtain a calcium ammonium nitrate-urea salt solution;

[0073] The mass ratio of calcium ammonium nitrate, urea and deionized water described in step 2 is 1081:60:1000;

[0074] 3. Mixing the soybean urease solution and the calcium ammonium nitrate-urea salt solution, then adding the polymer, and stirring at room temperature for 5 minutes to obtain a biocement sand fixation and water retention material with the synergistic effect of calcium ammonium nitrate and soybean urease (denoted as calcium ammonium nitrate-urea binder-xanthan gum);

[0075] The polymer described in step 3 is xanthan gum;

[0076] The mass ratio of deionized water, soybean, calcium ammonium nitrate and urea in the biocement sand-fixing and water-retaining material with synergistic effect of calcium ammonium nitrate and soybean urease described in step 3 is 2000:70:1081:60;

[0077] The mass fraction of the polymer in the biocement sand-fixing and water-retaining material with the synergistic effect of calcium ammonium nitrate and soybean urease described in step three is 0.3%.

[0078] Example 3: A method for preparing a biocement sand-fixing and water-retaining material with synergistic effects of calcium ammonium nitrate and soybean urease, which is specifically completed by the following steps:

[0079] 1. Preparation of soybean urease solution:

[0080] ① Grind the dried soybeans, add deionized water, and stir at room temperature for 5 hours to obtain a mixed solution;

[0081] The mass ratio of deionized water to soybeans described in step 1① is 1000:70;

[0082] ② Centrifuge the mixed solution and filter out the dregs. The resulting solution is the soybean urease solution.

[0083] The centrifugation temperature in step 1 (2) is 15°C to 25°C, the centrifugation speed is 3000 rpm, and the centrifugation time is 15 min;

[0084] In step 1②, the mixed solution is centrifuged, and then the dregs are filtered through a 200-mesh filter. The resulting solution is the soybean urease solution;

[0085] The enzyme activity of the soybean urease solution described in step 1 (2) is ≥ 200 U / g;

[0086] 2. Preparation of calcium ammonium nitrate-urea salt solution:

[0087] Dissolve calcium ammonium nitrate and urea in deionized water and stir evenly to obtain a calcium ammonium nitrate-urea salt solution;

[0088] The mass ratio of calcium ammonium nitrate, urea and deionized water described in step 2 is 1081:60:1000;

[0089] 3. Mixing the soybean urease solution and the calcium ammonium nitrate-urea salt solution, then adding the polymer and stirring evenly to obtain a biocement sand-fixing and water-retaining material with synergistic effects of calcium ammonium nitrate and soybean urease (denoted as calcium ammonium nitrate-urea binder-polyglutamic acid);

[0090] The polymer described in step 3 is polyglutamic acid;

[0091] The mass ratio of deionized water, soybeans, calcium ammonium nitrate and urea in the biocement sand-fixing and water-retaining material with synergistic effect of calcium ammonium nitrate and soybean urease described in step three is 2000:70:1081:60.

[0092] The mass fraction of the polymer in the biocement sand-fixing and water-retaining material with synergistic effect of calcium ammonium nitrate and soybean urease described in step three is 2%.

[0093] Comparative Example 1: The preparation method of CaCl2-urea cementing fluid is specifically completed according to the following steps:

[0094] 1. Preparation of soybean urease solution:

[0095] ① Grind the dried soybeans, add deionized water, and stir at room temperature for 5 hours to obtain a mixed solution;

[0096] The mass ratio of deionized water to soybeans described in step 1① is 1000:70;

[0097] ② Centrifuge the mixed solution and filter out the dregs. The resulting solution is the soybean urease solution.

[0098] The centrifugation temperature in step 1 (2) is 15°C to 25°C, the centrifugation speed is 3000 rpm, and the centrifugation time is 10 min to 20 min;

[0099] In step 1②, the mixed solution is centrifuged, and then the dregs are filtered through a 200-mesh filter. The resulting solution is the soybean urease solution;

[0100] The enzyme activity of the soybean urease solution described in step 1 (2) is ≥ 200 U / g;

[0101] 2. Preparation of CaCl2-urea salt solution:

[0102] Dissolve CaCl2 and urea in deionized water and stir evenly to obtain a CaCl2-urea salt solution;

[0103] The mass ratio of CaCl2, urea and deionized water described in step 2 is 111:60:1000;

[0104] 3. Mix the soybean urease solution and the CaCl2-urea salt solution and stir at room temperature for 5 minutes to obtain a CaCl2-urea cement solution;

[0105] The mass ratio of deionized water, soybean, CaCl2 and urea in the CaCl2-urea binder described in step three is 2000:70:111:60.

[0106] Comparative Example 2: The preparation method of CaCl2-urea cementing fluid-xanthan gum is specifically completed according to the following steps:

[0107] 1. Preparation of soybean urease solution:

[0108] ① Grind the dried soybeans, add deionized water, and stir at room temperature for 5 hours to obtain a mixed solution;

[0109] The mass ratio of deionized water to soybeans described in step 1① is 1000:70;

[0110] ② Centrifuge the mixed solution and filter out the dregs. The resulting solution is the soybean urease solution.

[0111] The centrifugation temperature in step 1 (2) is 15°C to 25°C, the centrifugation speed is 3000 rpm, and the centrifugation time is 10 min to 20 min;

[0112] In step 1②, the mixed solution is centrifuged, and then the dregs are filtered through a 200-mesh filter. The resulting solution is the soybean urease solution;

[0113] The enzyme activity of the soybean urease solution described in step 1 (2) is ≥ 200 U / g;

[0114] 2. Preparation of CaCl2-urea salt solution:

[0115] Dissolve CaCl2 and urea in deionized water and stir evenly to obtain a CaCl2-urea salt solution;

[0116] The mass ratio of CaCl2, urea and deionized water described in step 2 is 111:60:1000;

[0117] 3. Mix the soybean urease solution and the CaCl2-urea salt solution, then add the polymer and stir at room temperature for 5 minutes to obtain the CaCl2-urea binder-xanthan gum;

[0118] The polymer described in step 3 is xanthan gum;

[0119] In step 3, the mass ratio of deionized water, soybean, CaCl2 and urea in the CaCl2-urea binder is 2000:70:111:60;

[0120] The mass fraction of the polymer in the CaCl2-urea binder-xanthan gum described in step 3 is 0.3%.

[0121] Comparative Example 3: The preparation method of CaCl2 urea cementing liquid-polyglutamic acid is specifically completed according to the following steps:

[0122] 1. Preparation of soybean urease solution:

[0123] ① Grind the dried soybeans, add deionized water, and stir at room temperature for 5 hours to obtain a mixed solution;

[0124] The mass ratio of deionized water to soybeans described in step 1① is 1000:70;

[0125] ② Centrifuge the mixed solution and filter out the dregs. The resulting solution is the soybean urease solution.

[0126] The centrifugation temperature in step 1 (2) is 15°C to 25°C, the centrifugation speed is 3000 rpm, and the centrifugation time is 10 min to 20 min;

[0127] In step 1②, the mixed solution is centrifuged, and then the dregs are filtered through a 200-mesh filter. The resulting solution is the soybean urease solution;

[0128] The enzyme activity of the soybean urease solution described in step 1 (2) is ≥ 200 U / g;

[0129] 2. Preparation of CaCl2-urea salt solution:

[0130] Dissolve CaCl2 and urea in deionized water and stir evenly to obtain a CaCl2-urea salt solution;

[0131] The mass ratio of CaCl2, urea and deionized water described in step 2 is 111:60:1000;

[0132] 3. Mix the soybean urease solution and the CaCl2-urea salt solution, then add the polymer and stir at room temperature for 5 minutes to obtain the CaCl2-urea binder-polyglutamic acid;

[0133] The polymer described in step 3 is polyglutamic acid;

[0134] In step 3, the mass ratio of deionized water, soybean, CaCl2 and urea in the CaCl2 urea binder-polyglutamic acid is 2000:70:111:60;

[0135] The mass fraction of the polymer in the CaCl2 urea binder-polyglutamic acid described in step 3 is 0.3%.

[0136] Comparative Example 4: The preparation method of calcium ammonium nitrate-black water binder-polyglutamic acid is completed according to the following steps:

[0137] 1. Preparation of soybean urease solution:

[0138] ① Grind the dried soybeans, add deionized water, and stir at room temperature for 5 hours to obtain a mixed solution;

[0139] The mass ratio of deionized water to soybeans described in step 1① is 1000:70;

[0140] ② Centrifuge the mixed solution and filter out the dregs. The resulting solution is the soybean urease solution.

[0141] The centrifugation temperature in step 1 (2) is 15°C to 25°C, the centrifugation speed is 3000 rpm, and the centrifugation time is 10 min to 20 min;

[0142] In step 1②, the mixed solution is centrifuged, and then the dregs are filtered through a 200-mesh filter. The resulting solution is the soybean urease solution;

[0143] The enzyme activity of the soybean urease solution described in step 1 (2) is ≥ 200 U / g;

[0144] 2. Dissolve 360.3 g of calcium ammonium nitrate in 1000 mL of black water to form a calcium ammonium nitrate-black water salt solution;

[0145] 3. Mixing the calcium ammonium nitrate-black water salt solution and the soybean urease solution in a volume ratio of 1:1, and then adding polyglutamic acid to obtain a calcium ammonium nitrate-black water binder-polyglutamic acid;

[0146] The mass fraction of polyglutamic acid in the calcium ammonium nitrate-black water binder-polyglutamic acid described in step three is 2%.

[0147] The disposable paper cups (or plastic cups) used in the test were of the same specifications. When preparing the sample, first fill the sand sample to a level above the top of the cup. Gently compact the cup to slightly compact the sand sample. Then, use a steel ruler to level the surface, ensuring that the dry density of each sample group is roughly the same.

[0148] According to 4L / m 2 The amount of water, the water-retaining materials prepared in Examples 1 to 3, and Comparative Examples 1 to 3 were evenly added to the surface of the cup using a disposable dropper. When adding drops, it should be noted that the dropper mouth should not be too close to the sample surface to prevent the impact of water drops from damaging the surface flatness of the sample; then placed in an incubator at a temperature of 30°C and a humidity of 40% for natural evaporation for 20 days, and the water evaporation rate was shown in FIG. Figure 1 As shown, after 20 days of evaporation, the cementation layer was photographed. Figure 2 As shown;

[0149] Figure 1 is the water evaporation rate;

[0150] from Figure 1 It can be seen that after the formed cementing layer solidifies the surface of the sand, the maximum residual moisture in its interior is nearly 80%, which directly reflects the effect of the sand-fixing layer in preventing the evaporation of moisture inside the sand, and indirectly reflects that the formed cementing layer has good water retention, and calcium ammonium nitrate will not cause residual chloride ions.

[0151] Table 1 is Figure 1 The test was conducted after stabilization, with a time difference of 45 days between the first and second tests;

[0152] Table 1

[0153] formula First moisture content% Second moisture content% water 0.26 0.78 <![CDATA[CaCl2-Urea Cementing Liquid (Control Example 1)]]> 0.41 0.58 Calcium ammonium nitrate-urea cementing fluid (Example 1) 0.98 0.97 <![CDATA[CaCl2-Urea Cementing Liquid - Xanthan Gum (Comparative Example 2)]]> 0.40 0.48 <![CDATA[CaCl2 Urea Cementing Liquid - Polyglutamic Acid (Comparative Example 3)]]> 0.40 0.54 Calcium ammonium nitrate-urea cementing fluid-polyglutamic acid (Example 3) 1.16 1.65 Calcium ammonium nitrate-black water binder-polyglutamic acid (Comparative Example 4) 1.17 1.22 Calcium ammonium nitrate-urea cementing fluid-xanthan gum (Example 2) 1.11 1.00

[0154] As can be seen from Table 1, when the single variables are only calcium chloride and calcium ammonium nitrate, the binder containing calcium ammonium nitrate has better water retention; the addition of black water or polymer (i.e., polyglutamic acid) has a certain effect of enhancing water retention and can be used as an auxiliary water retention measure.

[0155] Figure 2 Surface image of the cementing layer from the water retention experiment;

[0156] from Figure 2 It can be seen that: considering the water evaporation rate, the white solid layer (i.e. calcium carbonate) formed by the cementing layer containing calcium ammonium nitrate is more significant, and the formed calcium carbonate layer enhances the water retention.

[0157] The water retention test shows that calcium ammonium nitrate binder has less water evaporation and the water retention inside the sand is more advantageous.

Claims

1. A biocement sand-fixing and water-retaining material with synergistic effects of calcium ammonium nitrate and soybean urease, characterized in that The biocement sand-fixing and water-retaining material is prepared from soybeans, deionized water, calcium ammonium nitrate and urea; the mass ratio of the deionized water, soybeans, calcium ammonium nitrate and urea is 2000:(10-100):(200-1200):(12-120).

2. The method for preparing a biocement sand-fixing and water-retaining material with synergistic action of calcium ammonium nitrate and soybean urease according to claim 1, characterized in that The preparation method is specifically completed according to the following steps:

1. Preparation of soybean urease solution: ①. Crush the dried soybeans, add deionized water, stir, and refrigerate for a period of time to obtain a mixed solution; ② Centrifuge the mixed solution and filter out the dregs. The resulting solution is the soybean urease solution and store in a refrigerator.

2. Preparation of calcium ammonium nitrate-urea salt solution: Dissolve calcium ammonium nitrate and urea in deionized water and stir evenly to obtain a calcium ammonium nitrate-urea salt solution; 3. Mixing the soybean urease solution and the calcium ammonium nitrate-urea salt solution, then adding the polymer and stirring at room temperature to obtain a biocement sand-fixing and water-retaining material with the synergistic effect of calcium ammonium nitrate and soybean urease.

3. The method for preparing a biocement sand-fixing and water-retaining material with synergistic action of calcium ammonium nitrate and soybean urease according to claim 2, characterized in that The mass ratio of deionized water to soybeans in step 1① is 1000:(10-100); the stirring time in step 1① is 4h-6h; the refrigeration temperature in step 1① is 3°C-5°C, and the refrigeration time is 20h-24h.

4. The method for preparing a biocement sand-fixing and water-retaining material with synergistic action of calcium ammonium nitrate and soybean urease according to claim 2, characterized in that The centrifugation temperature in step 1 ② is 3°C to 5°C, the centrifugation speed is 3000 rpm, and the centrifugation time is 10 min to 20 min; in step 1 ②, the mixed solution is centrifuged, and then the bean dregs are filtered using a 100-200 mesh filter, and the resulting solution is the soybean urease solution.

5. The method for preparing a biocement sand-fixing and water-retaining material with synergistic effects of calcium ammonium nitrate and soybean urease according to claim 2, characterized in that The enzyme activity of the soybean urease solution in step 1② is ≥200U / g; the refrigeration temperature in step 1② is 3°C to 5°C.

6. The method for preparing a biocement sand-fixing and water-retaining material with synergistic effects of calcium ammonium nitrate and soybean urease according to claim 2, characterized in that The mass ratio of calcium ammonium nitrate, urea and deionized water described in step 2 is (200-1200):(12-120):1000.

7. The method for preparing a biocement sand-fixing and water-retaining material with synergistic effects of calcium ammonium nitrate and soybean urease according to claim 2, characterized in that The polymer described in step 3 is polyglutamic acid or xanthan gum.

8. The method for preparing a biocement sand-fixing and water-retaining material with synergistic effects of calcium ammonium nitrate and soybean urease according to claim 2, characterized in that The mass ratio of deionized water, soybean, calcium ammonium nitrate and urea in the biocement sand-fixing and water-retaining material with synergistic effect of calcium ammonium nitrate and soybean urease described in step three is 2000:(10-100):(200-1200):(12-120).

9. The method for preparing a biocement sand-fixing and water-retaining material with synergistic effects of calcium ammonium nitrate and soybean urease according to claim 2, characterized in that The mass fraction of the polymer in the biocement sand-fixing and water-retaining material with synergistic effect of calcium ammonium nitrate and soybean urease described in step three is 0% to 2%; the stirring time at room temperature in step three is 3 minutes to 5 minutes.

10. The use of a biocement sand-fixing and water-retaining material with synergistic action of calcium ammonium nitrate and soybean urease as claimed in claim 1, characterized in that A biocement sand-fixing and water-retaining material with synergistic effects of calcium ammonium nitrate and soybean urease is used in desertification control, coastal sand dune fixation or soil ecological restoration.

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