Microorganism and waste concrete sand soil improvement liquid, preparation method and improvement method

Abstract

The application discloses a sand soil improvement liquid combined with microorganisms and waste concrete, a preparation method and an improvement method. The preparation method of the sand soil improvement liquid comprises the following steps: preparing RCF leaching solution, preparing bacterial solution, preparing cementing solution and preparing sand soil improvement liquid. The application adopts RCF as a main raw material, uses ammonium chloride solution to improve calcium solution, replaces traditional calcium sources, reduces cost, and realizes waste recycling. The method fully utilizes the calcium-rich advantage of waste concrete, reduces the dependence on traditional calcium sources such as calcium chloride or calcium nitrate. Through microbial urea hydrolysis, the pH value is naturally improved, the functional groups on the surface of the microorganisms provide nucleation sites for calcium ions, promote calcium carbonate precipitation, and realize waste resource utilization. The process is non-toxic and harmless, and does not need corrosive chemical reagents. Compared with traditional reinforcement methods, the process has small environmental impact, no harmful waste or secondary pollution, simple operation, low energy consumption, and significantly improved economic efficiency and environmental protection.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering and bio-building materials, specifically relating to a sand amendment liquid combining microorganisms and waste concrete, its preparation method and amendment procedure. Background Technology

[0002] Microbially induced calcium carbonate precipitation (MICP) is a naturally occurring biomineralization process with broad application potential in geotechnical engineering. Urease catalyzes the hydrolysis of urea to produce CO3. 2- Under the influence of a calcium source, CaCO3 crystals gradually grow using bacteria as nucleation sites, filling loose voids and forming an effective bonding structure between sand grains. In recent years, MICP technology has been increasingly applied in various fields such as cultural relic preservation, soil stabilization, liquefaction prevention, permeability control, heavy metal solidification, and concrete repair. However, with further research, microbial-induced calcium carbonate precipitation technology faces challenges in practical engineering applications, including high technical costs, low resource utilization efficiency, and significant environmental burden.

[0003] Traditionally, the calcium sources used in MCP research have primarily been reagent-grade calcium such as calcium chloride, calcium nitrate, and calcium acetate, which are considered expensive and have environmentally burdensome manufacturing processes. To reduce costs and achieve efficient waste utilization, numerous researchers have explored methods to extract usable materials from waste to replace traditional chemicals. Among these, the recycling and reuse of abundant calcium-based waste has shown great potential in MCP processes. For example, researchers have proposed a method to extract calcium from eggshells using vinegar or hydrochloric acid, but several problems remain. For instance, the supply of raw materials such as eggshells is limited and unstable, and the calcium extraction process is time-consuming, posing significant challenges to large-scale application. Furthermore, industrial reagent hydrochloric acid is not only expensive but may also have adverse environmental impacts, further limiting the large-scale promotion and application of this method.

[0004] With the rapid advancement of urbanization and industrialization, the demolition and replacement of old buildings and infrastructure have accelerated significantly. This trend generates a large amount of construction and demolition waste, the main component of which is waste concrete. How to achieve sustainable management of this waste has become a major challenge that the construction industry urgently needs to address. During the recycling process, waste concrete is typically processed into recycled concrete aggregate (RCA) and recycled concrete fines (RCF), with RCF accounting for approximately 20-30% of the total mass of waste concrete. Compared to RCA, RCF faces more limitations due to its unique physical and chemical properties. Its particle size is smaller (<150μm), its structure is porous, and its water absorption rate is significantly higher. Furthermore, RCF contains a large amount of residual cement paste, resulting in a rough surface, low activity, and strong water absorption. These characteristics lead to poor workability of RCF and a tendency to undergo significant shrinkage deformation, becoming a major obstacle to its widespread application in concrete production. Nevertheless, some studies have shown that using RCF powder as an inert filler can partially replace stone powder or cement raw materials in concrete products, thereby achieving resource reuse. However, due to the aforementioned performance limitations, RCF is generally not suitable for direct use in the production of new concrete, but is instead used in landfills or for less efficient applications. It is worth noting that RCF exhibits good adaptability to carbonation reactions, which is closely related to the cement hydration products it contains, such as calcium hydroxide, calcium silicate hydrate gel, and unhydrated clinker. These characteristics offer new possibilities for further research and high-value utilization of RCF.

[0005] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the present invention provides a sand amendment liquid combining microorganisms and waste concrete, its preparation method and improvement method, aiming to solve the problems of high cost, low resource utilization efficiency and large environmental burden of current microbial induced calcium carbonate precipitation technology.

[0007] This invention combines microbial mineralization with the resource utilization of waste concrete. It uses RCF as the main raw material and prepares RCF leachate with ammonium chloride solution to obtain a solution with high calcium content, which is used to replace traditional chemical calcium sources (such as reagent-grade calcium chloride, calcium nitrate, and calcium acetate). Then, it combines microorganisms to prepare a sand amendment solution. The obtained sand amendment solution is used to treat sand materials, which can promote the precipitation of calcium carbonate, thereby realizing the solidification and reinforcement of sand materials.

[0008] This invention is achieved through the following technical solution:

[0009] Option 1)

[0010] The method for preparing a soil amendment solution combining microorganisms and waste concrete includes the following steps:

[0011] Step 1: Mix the recycled concrete fines and ammonium chloride solution and filter to prepare RCF leachate;

[0012] Step 2: Cultivate urease-producing bacteria to obtain a bacterial solution;

[0013] Step 3: Add urea to the RCF leachate obtained in Step 1 and mix to prepare a cementing solution;

[0014] Step 4: Adjust the pH of the cementing solution to neutral, and then mix the bacterial solution and the cementing solution to obtain the sand and soil amendment solution.

[0015] Option 2)

[0016] The sand amendment solution is obtained by the method of preparing the sand amendment solution combining microorganisms and waste concrete.

[0017] Option 3)

[0018] The method for improving sandy soil involves soaking, grouting, or spraying the sandy soil to be improved with the aforementioned sandy soil improvement solution at room temperature for at least one time, and allowing it to stand for 24-48 hours each time.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] This invention uses recycled concrete fines as the main raw material and utilizes ammonium chloride solution to leach a high-calcium solution, replacing traditional chemical calcium sources, significantly reducing production costs and achieving efficient recycling of waste. This method fully leverages the calcium-rich properties of waste concrete powder while reducing reliance on traditional calcium sources (such as calcium chloride or calcium nitrate). In this way, calcium resources in waste can be effectively converted into calcium carbonate precipitate, achieving the goal of "turning waste into resources." By utilizing the natural metabolic process of urea hydrolysis by microorganisms, urea is hydrolyzed by bacteria to generate ammonia and carbon dioxide, leading to a local pH increase. Simultaneously, microorganisms provide nucleation sites for calcium ions through their cell surface functional groups (such as amino and carboxyl groups), further promoting calcium precipitation. This process does not require the use of toxic or corrosive chemical reagents, and compared to traditional chemical reinforcement methods (such as lime, cement, or the use of polymers), it has less environmental impact and does not produce harmful waste or secondary pollution. The method of this invention is simple to operate, has low energy consumption, and produces no secondary pollution, significantly improving the economic and environmental benefits of this invention. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the sand improvement method in an embodiment of the present invention;

[0022] Figure 2This is a schematic diagram of the preparation method of sand and soil amendment liquid in an embodiment of the present invention;

[0023] Figure 3 This describes the calcium ion leaching concentration and leaching efficiency under different solid-liquid ratios in the embodiments of the present invention.

[0024] Figure 4 This relates the calcium carbonate content and unconfined compressive strength in biocemented sand treated with different calcium sources.

[0025] Figure 5 This describes the relationship between the hydraulic conductivity of samples treated with different calcium sources and the number of treatments in the embodiments of the present invention.

[0026] Figure 6 This is a cost analysis of different calcium sources in the embodiments of the present invention;

[0027] Figure 7 This is a life cycle evaluation analysis of different calcium source costs in the embodiments of the present invention. Detailed Implementation

[0028] This invention provides a soil amendment liquid combining microorganisms and waste concrete, its preparation method, and amendment procedure. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0029] Recovering calcium ions from RCF via leaching-carbonation is a promising value-added utilization method. This process not only efficiently extracts calcium resources from RCF but also allows for further use in the production of high-value-added products. Ammonium chloride plays a crucial role in the high-value utilization of calcium-based waste, particularly in the preparation of high-purity calcium carbonate. In the leaching-carbonation process, ammonium chloride acts as an auxiliary agent, converting insoluble calcium in calcium-based waste into soluble calcium chloride. Subsequently, calcium carbonate is generated by introducing carbon dioxide into the calcium solution. Calcium carbonate, as an important industrial raw material, is widely used in construction, papermaking, plastics, and coatings. Currently, this process typically generates calcium carbonate by introducing carbon dioxide, but the acquisition and treatment costs of carbon dioxide are high, especially in large-scale industrial applications. Furthermore, carbon dioxide emissions put pressure on the environment, failing to fully achieve low-carbon production. Moreover, due to the complexity of soil and unsuitable pH environments, solubility, and diffusivity, directly introducing carbon dioxide into the soil does not directly react with calcium ions to generate calcium carbonate, thus failing to effectively promote calcium carbonate precipitation and failing to produce the expected cementing effect.

[0030] The method for preparing the sand amendment liquid combining microorganisms and waste concrete of the present invention includes the following steps:

[0031] Step 1: Mix the recycled concrete fines and ammonium chloride solution and filter to prepare RCF leachate;

[0032] Step 2: Cultivate urease-producing bacteria to obtain a bacterial solution;

[0033] Step 3: Add urea to the RCF leachate obtained in Step 1 and mix to prepare a cementing solution;

[0034] Step 4: Adjust the pH of the cementing solution to neutral, and then mix the bacterial solution and the cementing solution to obtain the sand and soil amendment solution.

[0035] Step one involves leaching the fine aggregates from recycled concrete; step three involves preparing the cementing solution; and step four involves preparing the sand and soil amendment solution. In this embodiment, microbial mineralization and waste concrete resource utilization are combined. RCF is used as the main raw material, and a high-calcium-content solution is leached using ammonium chloride solution to replace the traditional chemical calcium source. Then, microbial action promotes calcium carbonate precipitation, which can be used to solidify and strengthen sand and soil materials.

[0036] In one embodiment, the mixing temperature in step one is 25℃-85℃, the solid-liquid ratio of the recycled concrete aggregate and the ammonium chloride solution is 0.2-1g / mL, and the concentration of ammonium chloride in the ammonium chloride solution is 1-4mol / L.

[0037] The reaction rate between ammonium chloride solution and soluble components in recycled concrete aggregates increases with temperature. 25°C is room temperature, ensuring low energy consumption and ease of operation; 85°C is close to the solution's operating limit temperature, significantly accelerating the dissolution reaction. Too low a reaction rate leads to prolonged dissolution time, affecting leaching efficiency. In practice, longer soaking times are required to achieve the same dissolution effect, increasing cost and time investment. Excessively high temperatures may cause ammonium chloride volatilization loss, reducing the actual effective concentration of the solution. This places higher demands on equipment heat resistance, increasing operational complexity and cost.

[0038] A solid-liquid ratio within the range of 0.2-1 g / mL ensures sufficient contact between the solid material and the solution during leaching, while avoiding excessive solution waste or uneven mixing caused by excessive solids. An appropriate solid-liquid ratio ensures that the ammonium chloride solution concentration does not decrease rapidly during the reaction, thus maintaining continuous leaching capacity. A solid-liquid ratio that is too low leads to insufficient effective contact of the solid phase, significantly increasing solution consumption and reducing treatment efficiency. An excessively high solid-liquid ratio may cause solution saturation or incomplete local reactions, thus reducing overall leaching efficiency; furthermore, an overly viscous slurry can affect mixing uniformity and mass transfer efficiency.

[0039] An ammonium chloride concentration in the range of 1-4 mol / L provides sufficient ammonium chloride ion concentration to react with and dissolve the target components in recycled concrete. Low-concentration ammonium chloride solutions may not adequately dissolve the target components, resulting in low leaching efficiency. High-concentration solutions do not significantly improve leaching efficiency but increase the cost of chemical usage.

[0040] In one embodiment, the first leaching process is carried out in a conical flask equipped with an ammonia collection device. To ensure temperature stability during the leaching process, the conical flask is placed in a temperature-controlled water bath. After filtration, the filter residue is removed, and the resulting leachate is the RCF leachate.

[0041] In one embodiment, the urease-producing bacteria in step two are selected from *Sporosarcina pasteurii*, with the Chinese name *Sporosarcina pasteurii* and the preservation number ATCC 11859. Step two specifically includes: placing the urease-producing bacteria in a culture medium containing 10.00 g / L ammonium sulfate, 15.73 g / L Tris buffer, and 20.00 g / L yeast extract and shaking for 24-48 hours until the bacteria reach the required activity; then storing the cultured bacterial solution for later use; the shaking culture temperature is 28-32℃. This invention utilizes *Sporosarcina pasteurii*, which exhibits significant advantages in microbial-induced calcium carbonate precipitation (MICP), mainly due to its highly efficient urease activity, which can rapidly decompose urea, increase the solution pH, and thus promote calcium carbonate precipitation. The calcium carbonate precipitate produced by this bacterium has high purity and stability (mainly calcite), making it particularly suitable for engineering applications such as foundation reinforcement and crack self-repair. Meanwhile, *Pasteurella multocida* exhibits strong adaptability, growing across a wide range of pH, temperature, and salinity levels, and is non-pathogenic, making it environmentally and health-friendly. Furthermore, its sustained bioactivity reduces the frequency of cell replenishment, improving engineering feasibility. With its wide range of applications in foundation improvement, concrete crack repair, heavy metal pollution remediation, and carbon dioxide capture, *Pasteurella multocida* is considered one of the most promising strains for MICP technology.

[0042] In one embodiment, the initial urease activity of the urease-producing bacterial solution obtained in step two is 4-10 U / mL.

[0043] In one embodiment, the stored bacterial solution is activated for a certain period of time before use to reactivate its enzyme activity.

[0044] In one embodiment, the concentrations of calcium ions and urea in the cementing solution of step three are identical, with the calcium ion concentration before mixing being 0.5-2 mol / L. Too low a calcium ion concentration will significantly reduce the precipitation efficiency of calcium carbonate, failing to meet engineering requirements. Insufficient precipitation may lead to unsatisfactory cementing results, thus requiring a longer reaction time to achieve the target precipitation amount, thereby increasing the construction cycle and cost. Conversely, too high a calcium ion concentration may inhibit microorganisms (such as Pasteurella multocida), reducing urease activity and consequently affecting the calcium carbonate precipitation efficiency.

[0045] In one embodiment, the concentration of calcium ions before mixing is obtained based on the analysis results of the RCF leachate, and then urea with the same concentration of calcium ions is added.

[0046] In one embodiment, the volume ratio of the bacterial solution to the cementing solution in step four is 1-2:1.

[0047] To adapt to permeable soils and the target precipitation density, a 1:1 volume ratio is preferred in this invention. During the MIP process, a 1:1 volume ratio of bacterial solution to cementing solution is an optimized choice, achieving a good balance between microbial activity and calcium carbonate precipitation efficiency. This 1:1 volume ratio ensures that both bacterial and calcium ion concentrations are within suitable ranges, maximizing the efficiency of microbial-induced precipitation. This ratio maintains a suitable pH and chemical environment in the reaction medium, which is beneficial for generating high-quality calcium carbonate precipitates. Insufficient bacterial concentration leads to limited urease activity, resulting in a reduced urea hydrolysis rate and consequently lower calcium carbonate precipitation efficiency. Excessive bacterial solution may exceed the effective concentration required for the reaction, wasting the bacterial solution and increasing costs. Insufficient calcium ion concentration in the cementing solution, even with a sufficient number of bacteria, may result in insufficient calcium carbonate precipitation to meet engineering requirements.

[0048] In one embodiment, before mixing the bacterial solution and the cementing solution in step four, acid is added dropwise to the bacterial solution until the pH of the bacterial solution is adjusted to 4.5-6.5.

[0049] Specifically, the acid mentioned can be hydrochloric acid.

[0050] The present invention also provides an embodiment of the sand improvement method, wherein the sand to be improved is treated with the sand improvement liquid (the treatment method includes soaking, grouting or spraying) once or more at room temperature, and each time it is left to stand for a certain period of time.

[0051] In one embodiment, the sand to be improved is dry sand. The sand is first compacted in layers to a target relative density of 60%-90%, and then grouting is selected for treatment, followed by a certain period of time.

[0052] To facilitate later testing, such as Figure 1 As shown, in this embodiment, the example uses a vertically arranged PVC pipe of appropriate size as a mold. First, the sand to be improved is compacted to the target relative density. Then, a specific grouting method is selected for treatment. After a certain period of time, the bio-cemented sand sample to be tested is formed.

[0053] Dry sand is compacted to the target relative density using a layered compaction method, where the initial relative density is set to a specific value and the porosity is maintained within a predetermined range. Subsequently, a prepared amendment solution is uniformly injected into the top surface of the sample (in this embodiment, grouting is used; under other conditions, wetting and spraying may also be used), allowing it to penetrate into the voids between the sand particles under gravity. The sample is then left to stand at room temperature until the microbial-induced calcium carbonate precipitation process is fully completed. This process is repeated until the predetermined number of treatments is reached (generally more than two). Finally, the sample is dried and removed from the mold to obtain the bio-cemented sand sample.

[0054] Example 1

[0055] The method for improving sandy soil by combining microorganisms and waste concrete in this embodiment includes the following steps:

[0056] Step 1: Mix the recycled concrete fines and ammonium chloride solution and filter to prepare RCF leachate;

[0057] Step 2: Cultivate urease-producing bacteria to obtain a bacterial solution;

[0058] Step 3: Add urea to the RCF leachate obtained in Step 1 and mix to prepare a cementing solution;

[0059] Step 4: Adjust the pH of the cementing solution to neutral, and then mix the bacterial solution and the cementing solution to obtain the sand amendment solution;

[0060] Step 5: Then, compact the sand in layers to the target relative density of 84%. Next, grout the sand to be improved 12 times with the obtained sand improvement liquid. The number of treatments can be adjusted according to the specific requirements of the project for permeability coefficient and strength to ensure that the expected results are achieved. Each treatment should be allowed to stand for 36 hours.

[0061] The first four steps describe the preparation method of the sand amendment solution, and the preparation process is as follows: Figure 2 As shown.

[0062] In step one, the mixing temperature was 85℃, and the solid-liquid ratio of the recycled concrete aggregate to the ammonium chloride solution was 0.2 g / mL; the concentration of ammonium chloride in the solution was 2 mol / L. This step was carried out in a conical flask equipped with an ammonia collection device, and the temperature was maintained stable using a temperature-controlled water bath with a thermostatic magnetic stirrer. The entire process was conducted at a relatively high temperature and stirred for a certain period of time to ensure the leaching reaction proceeded fully.

[0063] The urease-producing bacteria selected for step two is *Sporosarcina pasteurii*, with the Chinese name *Sporosarcina pasteurii* and the preservation number ATCC 11859.

[0064] Step two specifically includes: placing the bacteria in a culture medium containing 10.00 g / L ammonium sulfate, 15.73 g / L Tris buffer, and 20.00 g / L yeast extract and shaking for 24 hours until the bacteria reach the required activity. The cultured bacterial solution is then stored for later use; it is stored at low temperature to enter a dormant state to maintain its activity. The shaking culture temperature is 30°C.

[0065] The initial urease activity of the urease-producing bacterial solution obtained in step two was 8 U / mL.

[0066] In step three, the concentrations of calcium ions and urea in the cementing solution are the same, and the concentration of calcium ions before mixing is 0.8 mol / L.

[0067] The volume ratio of the bacterial solution to the cementing solution in step four is 1:1.

[0068] Before mixing the bacterial solution obtained in step two and the cemented solution obtained in step three in step four, hydrochloric acid is added dropwise to the bacterial solution until the pH of the bacterial solution is adjusted to 5.0.

[0069] Example 2

[0070] The difference from Example 1 is that the solid-liquid ratio of the recycled concrete aggregate and ammonium chloride solution in step one is 0.5 g / mL.

[0071] Example 3

[0072] The difference from Example 1 is that the solid-liquid ratio of the recycled concrete aggregate and ammonium chloride solution in step one is 1 g / mL.

[0073] Comparative Example 1

[0074] The difference from Example 1 is that in step one, the solid-liquid ratio of raw concrete aggregate to hydrochloric acid is 1 g / mL, and the concentration of hydrochloric acid is 2 mol / L. This comparative example uses hydrochloric acid (HCl) as the leaching solvent for RCF. Specifically, a certain mass of RCF is mixed with a hydrochloric acid solution of appropriate concentration, stirred under a set solid-liquid ratio, and kept at room temperature for a certain period of time to complete the leaching process.

[0075] Comparative Example 2

[0076] The difference from Example 1 is that chemical calcium (calcium chloride) with the same molar concentration as the recycled concrete aggregate in Example 1 is used as the calcium source for MICP.

[0077] To evaluate the permeability of the biocemented sand samples after different treatment cycles, deionized water was injected into the bottom of the water supply pipe connected to the bottom of the PVC pipe, while maintaining overflow at the top of the sample to keep the liquid level constant; the riser was pre-filled with water, and the permeability of the sample was calculated by measuring the time required for the water head change.

[0078] The UC test was performed on the cylindrical bio-cemented samples modified with the modified solution using a VJ-Tech Tri-Scan 50 triaxial testing machine.

[0079] A method for determining the calcium carbonate (CCC) content in biocemented samples includes the following steps: A certain amount of dried biocemented sample is mixed with an equimolar concentration of hydrochloric acid solution and allowed to react fully to dissolve the calcium carbonate in the sample. Subsequently, the solid residue is filtered through filter paper and washed with distilled water, with the filtration time controlled within an appropriate range. Finally, the solid residue on the filter paper is dried and weighed, and the calcium carbonate content is calculated based on the difference between the initial dry mass of the sample and the residual dry mass after the reaction.

[0080] This invention analyzes the environmental impact of different calcium sources on microbially induced calcium carbonate (MICP) deposition based on life cycle assessment (LCA). The method constructs a full life cycle model of the MICP process to systematically analyze the energy consumption and carbon emission characteristics of different calcium sources during preparation and application, quantifying their environmental impact. This invention focuses on evaluating the impact of calcium source selection on the sustainability of MICP, providing a scientific basis for optimizing process design and reducing environmental load, and is applicable to the fields of green building materials technology and environmental engineering.

[0081] The calcium ion leaching concentration and leaching efficiency of Examples 1 and Comparative Example 1 under different solid-liquid ratios are shown in the figure. Figure 3 ;Depend on Figure 3It can be seen that as the amount of RCF increases, the concentration of calcium ions in the leachate rises, but the leaching efficiency decreases. A higher RCF dosage may alter the pH of the solution, thereby reducing the solubility of calcium ions and consequently affecting the extraction efficiency. Under the same solid-liquid ratio, ammonium chloride exhibits slightly higher leaching concentration and efficiency than hydrochloric acid. This provides a theoretical basis for selecting an appropriate leaching agent, especially in terms of improving leaching efficiency and optimizing leaching conditions; ammonium chloride may be a more suitable choice.

[0082] Ammonium chloride has demonstrated significant advantages in the leaching process of RCF. Compared with hydrochloric acid, ammonium chloride can achieve higher calcium ion leaching efficiency at the same solid-liquid ratio. Overall, ammonium chloride, with its high efficiency, shows broad application prospects in the RCF leaching-carbonation process. Ammonium chloride leachate exhibits significant advantages in the MIP process, effectively increasing calcium carbonate content, significantly reducing sample permeability, and ensuring high unconfined compressive strength, demonstrating its feasibility and environmental friendliness as a substitute for traditional calcium sources. As a substitute for traditional calcium sources, ammonium chloride leachate is comparable in performance while reducing environmental impact, providing a more economical and environmentally friendly option for MIP technology.

[0083] The relationship between calcium carbonate content and unconfined compressive strength in the biocemented sands provided in Example 1, Comparative Example 1, and Comparative Example 2 is shown in the figure. Figure 4 Different treatment cycles yield different calcium carbonate contents. The appropriate number of treatment cycles can be performed based on the specific requirements of the project regarding permeability and strength to ensure the desired effect is achieved. The relationship between the hydraulic conductivity of MIP samples treated with different calcium sources and the number of treatment cycles is shown in [reference needed]. Figure 5 .like Figure 4 As shown, the bio-cemented sand samples treated with different calcium sources exhibited an increase in calcium carbonate content in all treated samples. The unconfined compressive strength of samples treated with different MIP methods varied significantly, and the calcium carbonate content also changed accordingly. For example... Figure 5 As shown, the permeability of the samples decreased significantly with increasing MIP treatment cycles. Samples treated with different calcium sources generally showed a decrease in permeability, while the unconfined compressive strength showed relatively little change. This indicates that calcium source alternatives such as ammonium chloride have good application prospects in the MIP process, effectively improving permeability while maintaining high strength.

[0084] Based on the analysis of Example 1, Comparative Example 1, and Comparative Example 2, and considering the different calcium source costs and life cycle assessment results required to produce 1000 kg of calcium carbonate (see Example 2), Figure 6 and Figure 7Ammonium chloride leachate exhibits superior performance in terms of energy demand and carbon emissions, thanks to its highly efficient production process based on the Hou's process. Cost analysis shows that the cost of ammonium chloride leachate is only about one-third that of calcium chloride and significantly lower than that of hydrochloric acid leachate, which costs less than one-ninth. As a substitute for calcium chloride, ammonium chloride leachate is not only more economical but also significantly reduces carbon emissions and energy consumption, thereby improving the sustainability and practical application value of MICP technology.

[0085] This invention demonstrates significant environmental and economic advantages in life cycle analysis. Compared to other calcium sources, ammonium chloride leachate exhibits superior performance in terms of energy demand and carbon emissions, thanks to its highly efficient production process based on the Hou's process. Furthermore, cost analysis shows that the cost of ammonium chloride leachate is only about one-third that of calcium chloride, and significantly lower than that of hydrochloric acid leachate, less than one-ninth of its cost. As a substitute for calcium chloride, ammonium chloride leachate not only offers greater economic efficiency but also significantly reduces carbon emissions and energy consumption, further enhancing the sustainability and practical application value of MICP technology.

[0086] As demonstrated by the results of the above embodiments, this invention utilizes waste concrete fine powder as the main raw material, fully leveraging its high calcium content, and employs ammonium chloride as the leaching solvent, effectively reducing the high cost associated with traditional calcium source preparation processes. This method is simple, energy-efficient, and produces no secondary pollution, fully embodying the concepts of resource recycling and sustainable development. Furthermore, this invention significantly improves the utilization efficiency of waste resources, possessing both significant environmental and social benefits, and providing an efficient and economical technical solution for green development and ecological protection.

[0087] In summary, this invention demonstrates significant environmental friendliness by combining urease-producing bacteria with microorganisms to promote carbonate precipitation. The invention operates at ambient temperature and pressure, resulting in low energy consumption, minimal carbon emissions, and no toxic byproducts. Through microbial metabolic activity, calcium carbonate precipitation is promoted, producing a natural and harmless mineral. Furthermore, it avoids secondary pollution or waste accumulation that may occur with traditional methods, thus minimizing its environmental impact. In addition, this invention effectively recovers calcium resources from waste, achieving resource recycling. Unlike traditional chemical reinforcement methods (such as lime, cement, or polymers), this invention eliminates the need for toxic chemical additives or solvents, reducing potential harm to ecosystems. Therefore, this invention is not only a sustainable reinforcement technology but also possesses significant environmental advantages.

[0088] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a soil amendment solution combining microorganisms and waste concrete, characterized in that: Includes the following steps: Step 1: Mix the recycled concrete fines and ammonium chloride solution and filter to prepare RCF leachate; Step 2: Cultivate urease-producing bacteria to obtain a bacterial solution; Step 3: Add urea to the RCF leachate obtained in Step 1 and mix to prepare a cementing solution; Step 4: Adjust the pH of the cementing solution to neutral, and then mix the bacterial solution and the cementing solution to obtain the sand amendment solution; The mixing temperature in step one is 25℃-85℃, the solid-liquid ratio of the recycled concrete aggregate and the ammonium chloride solution is 0.2-1g / mL, and the concentration of ammonium chloride in the ammonium chloride solution is 1-4 mol / L. The urease-producing bacteria selected in step two is *Pasteurella multocida*, scientifically known as *Pasteurella spp.* Sporosarcina pasteurii And the bacteria with accession number ATCC 11859; Step two specifically includes: placing urease-producing bacteria in a culture medium containing 10.00 g / L ammonium sulfate, 15.73 g / L Tris buffer and 20.00 g / L yeast extract and shaking culture for 24-48 hours until the bacteria reach the required activity, and then storing the cultured bacterial solution for later use; the shaking culture temperature is 28-32℃. The concentrations of calcium ions and urea in the cementing solution in step three are the same, and the concentration of calcium ions in the RCF leachate before mixing in step three is 0.5-2 mol / L. The volume ratio of the bacterial solution to the cementing solution in step four is 1-2:1; Before mixing the bacterial solution and the cementing solution in step four, acid is added dropwise to the bacterial solution until the pH of the bacterial solution is adjusted to 4.5-6.

5.

2. The method for preparing the sand amendment liquid combining microorganisms and waste concrete according to claim 1, characterized in that: The initial urease activity of the bacterial solution obtained in step two was 4-10 U / mL.

3. A soil amendment solution, characterized in that: Obtained by the method described in claim 1 or 2.

4. A method for improving sandy soil, characterized in that: The steps include: at room temperature, soaking, grouting or spraying the sand to be improved with the sand improvement liquid of claim 3 once or more, and letting it stand for 24-48 hours each time.

5. The method for improving sandy soil according to claim 4, characterized in that: The sand to be improved is dry sand. Before soaking, grouting or spraying, the sand should be compacted in layers to the target relative density of 60%-90%.

Images