Method for co-solidifying soft clay with activated magnesium oxide microbial slurry and CO2

Abstract

This invention relates to the field of biomass cement technology and discloses a method for solidifying soft clay using activated magnesium oxide microbial slurry in synergistic CO2 co-solidification. The method includes: mixing a bacterial solution with urea to obtain a pre-hydrolyzed mixture; the bacterial solution containing urease-producing microorganisms; mixing and stirring the pre-hydrolyzed mixture, activated magnesium oxide, and soft clay sediment, while simultaneously introducing carbon dioxide gas during the mixing and stirring process; and curing after stirring is completed. This invention effectively overcomes the limitations of single biological carbonization or single gas carbonization by introducing a dual carbonization mechanism of urea pre-hydrolysis and short-term CO2 gas carbonization, synergistically improving reaction efficiency and ultimately enhancing the solidification effect of soft clay sediments.

Description

Technical Field

[0001] This invention relates to the field of biomass cement technology, and in particular to a method for co-solidifying soft clay with active magnesium oxide microbial slurry and CO2. Background Technology

[0002] Urea pre-hydrolysis-microbial activated magnesium oxide carbonization technology is an emerging green solidification method. It utilizes urease-producing microorganisms to pre-hydrolyze urea, releasing a large amount of carbonate ions, which react with magnesium hydroxide produced during the hydration of activated magnesium oxide to form basic magnesium carbonate. This mineral possesses excellent cementing properties, effectively solidifying various aggregates to form materials with good mechanical properties. Compared to traditional cement, the magnesium oxide in this technology has significant carbon emission reduction potential and shows promising application prospects in areas such as crack repair and tailings solidification. However, this technology currently suffers from low utilization rates of activated magnesium oxide and urea, leading to material waste and hindering its further promotion.

[0003] Carbon dioxide (CO2), as a gas that promotes the carbonization of cementitious materials, has been used to improve the early strength of materials and achieve carbon sequestration. Compared with traditional cement, active magnesium oxide (MgO) exhibits superior reaction efficiency and low carbon characteristics during carbonization: its hydration product Mg(OH)2 can react with CO2 to generate basic magnesium carbonate with strong cementing properties, significantly enhancing the matrix density and mechanical properties. However, in practical applications, systems relying solely on MgO or CO2 still suffer from problems such as uneven carbonization, insufficient reaction depth, and slow early strength development, especially in soft clays with high moisture content, where the limited diffusion capacity of CO2 further restricts the solidification effect.

[0004] Therefore, the existing technology still needs further research and improvement. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method for solidifying soft clay using activated magnesium oxide microbial slurry in synergy with CO2, and a clay solidification slurry using activated magnesium oxide microorganisms in synergy with carbon dioxide. This aims to solve the problem of uneven carbonization in existing single-reaction systems relying on MgO or CO2 gas, especially in high-moisture-content soft clay where CO2 gas diffusion is limited. Specifically: In a first aspect, embodiments of the present invention provide a method for solidifying soft clay using activated magnesium oxide microbial slurry in conjunction with CO2, comprising: The bacterial solution is mixed with urea to obtain a pre-hydrolyzed mixture; the bacterial solution contains urease-producing microorganisms. The pre-hydrolyzed mixture, active magnesium oxide, and soft clay sediment are mixed, and carbon dioxide gas is introduced simultaneously during the mixing and stirring process. After the mixing is completed, the mixture is cured.

[0006] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0007] As a preferred technical solution, the method for co-solidifying soft clay with active magnesium oxide microbial slurry and CO2, wherein the bacterial solution concentration has an OD600 value of 0.8 to 3 and a urease activity of 5 to 30 U.

[0008] As a preferred technical solution, in the method of co-solidifying soft clay with active magnesium oxide microbial slurry and CO2, the concentration of urea is 1.5-3.5 mol / L.

[0009] As a preferred technical solution, in the method of co-solidifying soft clay with active magnesium oxide microbial slurry and CO2, the amount of active magnesium oxide added is 5% to 25% of the mass of the soft clay deposit.

[0010] As a preferred technical solution, the method for solidifying soft clay with active magnesium oxide microbial slurry and CO2 is wherein the water content of the soft clay sediment is 60% to 150%.

[0011] As a preferred technical solution, the method for solidifying soft clay with activated magnesium oxide microbial slurry and CO2 is wherein the concentration of carbon dioxide gas introduced is 20-70%, and the introduction time is 1-40 min.

[0012] As a preferred technical solution, the method for co-solidifying soft clay with active magnesium oxide microbial slurry and CO2 includes mixing the bacterial solution with urea to obtain a pre-hydrolyzed mixture, wherein the pre-hydrolyzation time is 6 to 24 hours and the pre-hydrolyzation temperature is 25 to 35°C.

[0013] As a preferred technical solution, the method for co-solidifying soft clay with active magnesium oxide microbial slurry and CO2, wherein the water content of the soft clay sediment is 80% to 120%; the organic matter content of the soft clay sediment is 0% to 10%, and the clay content is 0% to 40%.

[0014] As a preferred technical solution, the method for co-solidifying soft clay with active magnesium oxide microbial slurry and CO2, wherein the urease-producing microorganisms include: Bacillus pasteurellii and Bacillus pasteurellii.

[0015] Beneficial effects: Compared with the prior art, the embodiments of the present invention have the following advantages: This invention provides a method for solidifying soft clay using activated magnesium oxide microbial slurry in synergistic CO2 co-processing. Through the synergistic effect of urea pre-hydrolysis and CO2 gas carbonization, it significantly improves the utilization efficiency of activated magnesium oxide and the amount of cementing products generated, achieving an organic combination of microbial-induced carbonization and gas carbonization, effectively enhancing the early strength and overall performance of the solidified body. This method is suitable for soft clay sediments with high water content, overcoming the problems of uneven reaction and insufficient carbonization depth under high water content conditions in traditional solidification technologies, and expanding its application prospects in complex engineering projects such as deep seabed mixing piles and hydraulic fill. While improving the mechanical properties of the solidified body, it achieves efficient carbon dioxide sequestration and resource utilization, resulting in significant environmental benefits. Employing short-time carbonization reaction and conventional temperature and pressure conditions, the process is simple, easy to implement on-site, and applicable to various engineering scenarios such as roadbed filling and foundation treatment. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the process for solidifying soft clay with active magnesium oxide microbial slurry and CO2, as provided by the present invention.

[0018] Figure 2 The present invention provides a conceptual process for sample preparation and practical application.

[0019] Figure 3 The bar chart shows the change in unconfined compressive strength (UCS) of the examples and comparative examples as a function of carbonization time.

[0020] Figure 4 Secant modulus (E) for examples and comparative examples 50 (Bar chart showing the change with carbonization time)

[0021] Figure 5 Unconfined compressive strength (UCS) and secant modulus (E) for examples and comparative examples 50 The correlation scatter plot of ).

[0022] Figure 6 The bar chart shows the changes in carbonization degree (DC) for the examples and comparative examples.

[0023] Figure 7 The X-ray diffraction patterns of the carbonized products of the examples and comparative examples are shown. Detailed Implementation

[0024] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] like Figure 1 As shown in the figure, an embodiment of the present invention provides a method for solidifying soft clay with activated magnesium oxide microbial slurry and CO2, comprising the following steps: Step S10: Mix the bacterial solution with urea to obtain a pre-hydrolyzed mixture; the bacterial solution contains urease-producing microorganisms.

[0026] Combination Figure 2 As shown, specifically, the urea here is a urea solution with a concentration of 1.5–3.5 mol / L. The urea solution is mixed with a highly active bacterial solution, uniformly stirred, and pre-hydrolyzed in situ under controlled conditions to obtain a pre-hydrolyzed mixture. The pre-hydrolyzation time is 6–24 hours; for example, 6–12 hours. The material strength reaches its peak within the 6–12 hour range, and the strength increase can exceed 400%. The pre-hydrolyzation is carried out at 25–35°C. *Bacillus pasteurellii* and *Bacillus pasteurellii* are used, with a bacterial solution concentration of OD600 value of 0.8–3 and urease activity of 5–30 U. Excessively high urea concentrations will cause dehydration of the bacterial cells in the solution, rapidly killing the cells, and urea hydrolysis will also produce a large amount of NH4. + And NH3 (ammonia). Excessive ammonia is toxic to microorganisms and can inhibit or terminate their activity. Urea hydrolysis can cause the environmental pH to rise sharply to above 9. Although magnesium carbonate precipitation requires an alkaline environment, excessively high pH (e.g., >10) will also be unsuitable for the survival of the strains used. At excessively high pH, ​​urea byproducts or other ions dissolved in the soil will preferentially form precipitates. These precipitates will coat the surface of bacteria or soil particles, blocking the channels for ion transport and gas diffusion, causing the reaction to stop locally and resulting in extremely uneven solidification.

[0027] Step S20: Mix the pre-hydrolyzed mixture, active magnesium oxide and soft clay sediment, and simultaneously introduce carbon dioxide gas during the mixing and stirring process. After the mixing is completed, perform curing.

[0028] Specifically, soft clay sediments with a moisture content of 60–150% are uniformly mixed with activated magnesium oxide to form a solid mixture. The amount of activated magnesium oxide added can be 5%–25% of the mass of the soft clay sediments. The organic matter content of the soft clay sediments is 2–10%. If it is too low (<1.5%), the soil may be too infertile, which is not conducive to the initial colonization and survival of microorganisms. If the organic matter content is too high, it will coat soil particles, competitively adsorb metal ions, seriously interfere with the formation of cementation products, and lead to excessive settlement.

[0029] The clay content (particle size <0.002 mm) is 15%–40%. Soft clay sediments serve as the reaction matrix and physical framework, providing habitats and reaction sites for bacteria. The original particles constitute the basic framework of the final solidified body. The clay particles carry a negative charge on their surface, attracting positively charged Mg2+. 2+ Plasma promotes the precipitation and cementation of magnesium carbonate minerals on and between soil particles. The clay particles provide a large specific surface area, optimizing the reaction interface. However, excessive content can lead to excessively small porosity, severely hindering the uniformity of grouting and reaction.

[0030] Further, the pre-hydrolyzed mixture is uniformly mixed with the solid mixture at a stirring speed of 50–150 r / min, while simultaneously introducing CO2 gas at a concentration of 20–70% for a short-term carbonization reaction lasting 1–40 minutes. To ensure dual carbonization, multiple gas inlets can be used for the carbonization reaction. The short-term carbonization reaction is carried out under ambient temperature and normal pressure conditions. A carbon dioxide concentration below 20% will result in insufficient carbonization kinetics, a slow reaction rate, and low solidified body strength, while a concentration above 70% can easily lead to acidification of the reaction environment, strongly inhibiting or completely terminating the urea hydrolysis activity of microorganisms.

[0031] This invention significantly improves the utilization efficiency of active magnesium oxide, carbon sequestration efficiency, amount of cementing products generated, and overall strength of the sample through a dual carbonization mechanism of urea pre-hydrolysis and CO2 gas, effectively promoting the resource utilization of carbon dioxide.

[0032] Based on the same inventive concept, the present invention also provides an active magnesium oxide microbial clay solidification slurry comprising: a pre-hydrolyzed solution of bacterial solution and urea, active magnesium oxide, and soft clay sediment; wherein the bacterial solution contains urease-producing microorganisms.

[0033] The active magnesium oxide microbial clay solidification slurry prepared by this invention can be used for deep seabed mixing pile construction, roadbed fill material preparation, or dredged fill solidification projects. It shows great promise for applications in deep seabed mixing piles, roadbed fill materials, and dredged fill solidification, providing an innovative solution to the problem of treating soft clay with high water content.

[0034] The technical solutions provided by the present invention will be further explained and illustrated below through specific embodiments.

[0035] Example 1 Highly active bacterial solution was uniformly mixed with urea and pre-hydrolyzed in situ at 30°C for 24 hours. The urea concentration was 2 mol / L; the bacterial solution concentration had an OD600 value of 1.5 and a urease activity of 15 U. Soft clay sediment with 100% water content was uniformly mixed with activated magnesium oxide to form a solid mixture. The amount of activated magnesium oxide added was 15% of the soft clay sediment mass. The organic matter content of the soft clay sediment was approximately 5%, and the clay content was approximately 30%. The pre-hydrolyzed mixture and the solid mixture were uniformly mixed at a stirring speed of 100 r / min, while a short-term carbonization reaction was carried out using CO2 gas at a concentration of 40%. The carbonization reaction was conducted under ambient temperature and normal pressure conditions.

[0036] The slurry was injected into the mold and saturated for 7 days at 30°C and 95% relative humidity, followed by various performance tests.

[0037] Example 2 Highly active bacterial solution was uniformly mixed with urea and pre-hydrolyzed in situ at 35°C for 20 hours. The urea concentration was 1.5 mol / L; the bacterial solution concentration had an OD600 value of 0.8 and a urease activity of 5 U. Soft clay sediment with a water content of 60% was uniformly mixed with activated magnesium oxide to form a solid mixture. The amount of activated magnesium oxide added was 5% of the mass of the soft clay sediment. The organic matter content of the soft clay sediment was approximately 5%, and the clay content was approximately 30%. The pre-hydrolyzed mixture and the solid mixture were uniformly mixed at a stirring speed of 100 r / min, while a short-time carbonization reaction was carried out by introducing CO2 gas at a concentration of 20%. The carbonization reaction was conducted under ambient temperature and normal pressure conditions.

[0038] Example 3 Highly active bacterial solution was uniformly mixed with urea and pre-hydrolyzed in situ at 25°C for 6 hours. The urea concentration was 3.5 mol / L; the bacterial solution concentration had an OD600 value of 3 and a urease activity of 30 U. Soft clay sediment with a water content of 120% was uniformly mixed with activated magnesium oxide to form a solid mixture. The amount of activated magnesium oxide added was 25% of the soft clay sediment mass. The organic matter content of the soft clay sediment was approximately 10%, and the clay content was approximately 40%. The pre-hydrolyzed mixture and the solid mixture were uniformly mixed at a stirring speed of 100 r / min, while a short-term carbonization reaction was carried out by introducing CO2 gas at a concentration of 70%. The carbonization reaction was conducted under ambient temperature and normal pressure conditions.

[0039] Comparative Example 1 The difference between this comparative example and Example 1 is that no pre-hydrolysis is performed (i.e., the pre-hydrolysis time is 0 hours), while the remaining steps and parameters are exactly the same as in Example 1.

[0040] Comparative Example 2 The difference between this comparative example and Example 1 is that no highly active bacteria or urea hydrolysis (i.e., pure CO2 gas carbonization absorption) are added; the remaining steps and parameters are exactly the same as in Example 1.

[0041] The performance of the samples obtained in Example 1 and Comparative Examples 1-2 was tested, and the results are as follows: See Figure 3 The bar chart shows the unconfined compressive strength (UCS) of the samples at different carbonization times. Example 1 (pre-hydrolysis for 24 hours followed by CO2 carbonization) achieved the highest unconfined compressive strength after 5 minutes of carbonization, significantly higher than all comparative examples. Comparative Example 1 (no pre-hydrolysis but CO2 gas purging) and Comparative Example 2 (pure CO2 gas carbonization absorption) both had lower strengths than Example 1, while Comparative Example 2 (pure CO2 gas carbonization absorption) had the lowest strength. This indicates that urea pre-hydrolysis and CO2 carbonization have a synergistic enhancing effect.

[0042] See Figure 4 It is the secant modulus (E) of the samples at different carbonization times. 50 (Bar chart) Example 1 (pre-hydrolysis for 24 hours followed by CO2 carbonization) and Comparative Example 1 (no pre-hydrolysis but CO2 passed through) achieved the highest stiffness after 10 minutes of carbonization, which was significantly higher than that of Comparative Example 2 (pure CO2 gas carbonization absorption).

[0043] See Figure 5 It is the unconfined compressive strength (UCS) and the secant modulus (E). 50 A scatter plot showing the correlation between the two. The data shows a significant linear positive correlation (E). 50 = 73.1 * UCS, R² = 0.96), indicating that the material's strength and stiffness develop in tandem.

[0044] See Figure 6 The figure shows a bar chart of the degree of carbonization (DC) of the samples at different carbonization times. Example 1 showed the highest degree of carbonization at almost every carbonization time point, with the highest degree of carbonization observed at 10 minutes of carbonization, indicating that the method of the present invention can most effectively promote the carbonization reaction of active magnesium oxide.

[0045] See Figure 7The figures show the X-ray diffraction patterns of samples under different treatment conditions and carbonization times. In Example 1, after carbonization for 10 and 40 minutes, the intensity of the characteristic peak of brucite decreased most significantly, while the intensity of the characteristic peaks of carbonate products such as dipinite and hydromagnesite increased most rapidly and significantly. The carbonization product formation rate and total amount in Comparative Example 1 were lower than those in Example 1. This indicates that the carbonization treatment of the present invention can effectively accelerate the dissolution and reaction of active components, significantly promote the rapid formation and crystallization of carbonization products, and reveal the intrinsic mechanism by which its intensity and degree of carbonization are superior to those of the comparative example from the perspective of phase evolution.

[0046] In summary, this invention provides a method for solidifying soft clay deposits using a synergistic combination of activated magnesium oxide microbial slurry and carbon dioxide gas. The solidification method includes: mixing a bacterial solution with urea to obtain a pre-hydrolyzed mixture; the bacterial solution containing urease-producing microorganisms; mixing the pre-hydrolyzed mixture, activated magnesium oxide, and soft clay deposits; simultaneously introducing carbon dioxide gas during mixing and stirring; and curing after stirring. This invention effectively overcomes the limitations of single biological carbonization or single gas carbonization by introducing a dual carbonization mechanism of urea pre-hydrolysis and short-term CO2 gas carbonization, synergistically improving reaction efficiency and ultimately significantly enhancing the solidification effect of soft clay deposits.

[0047] It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for co-solidifying soft clay with activated magnesium oxide microbial slurry and CO2, characterized in that, include: The bacterial solution is mixed with urea to obtain a pre-hydrolyzed mixture; the bacterial solution contains urease-producing microorganisms. The pre-hydrolyzed mixture, active magnesium oxide, and soft clay sediment are mixed, and carbon dioxide gas is introduced simultaneously during the mixing and stirring process. After the mixing is completed, the mixture is cured.

2. The method for co-solidifying soft clay with activated magnesium oxide microbial slurry and CO2 according to claim 1, characterized in that, The bacterial culture concentration has an OD600 value of 0.8–3 and a urease activity of 5–30 U.

3. The method for co-solidifying soft clay with activated magnesium oxide microbial slurry and CO2 according to claim 1, characterized in that, The concentration of urea is 1.5–3.5 mol / L.

4. The method for co-solidifying soft clay with activated magnesium oxide microbial slurry and CO2 according to claim 1, characterized in that, The amount of active magnesium oxide added is 5% to 25% of the mass of the soft clay sediment.

5. The method for co-solidifying soft clay with activated magnesium oxide microbial slurry and CO2 according to claim 1, characterized in that, The concentration of carbon dioxide gas introduced is 20-70%, and the introduction time is 1-40 minutes.

6. The method for co-solidifying soft clay with activated magnesium oxide microbial slurry and CO2 according to claim 1, characterized in that, The bacterial solution was mixed with urea to obtain a pre-hydrolyzed mixture, wherein the pre-hydrolyzation time was 6 to 24 hours and the pre-hydrolyzation temperature was 25 to 35°C.

7. The method for co-solidifying soft clay with activated magnesium oxide microbial slurry and CO2 according to claim 1, characterized in that, The organic matter content of soft clay sediments is 0-10%, and the clay content is 0%-40%.

8. The method for co-solidifying soft clay with activated magnesium oxide microbial slurry and CO2 according to claim 1, characterized in that, The urease-producing microorganisms include: Bacillus pasteurellii and Bacillus pasteurellii.

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