CN107176798A - A kind of production method and application that biological cement is prepared based on low price calcium ion - Google Patents

Abstract

The invention discloses a production method and application for preparing biocement based on low-priced calcium ions, that is, using limestone powder in mining waste to react with acetic acid, a by-product of rapid pyrolysis of agricultural waste to produce biomass oil, to generate soluble calcium Ions are used as the key raw material for the preparation of biocement-calcium source to replace the high-cost industrial grade CaCl ₂ in the traditional method, and then mixed with Bacillus and urea solution that can secrete urease to decompose urea to make biocement. The biocement prepared by the invention has high strength, low cost and wide source of raw materials, realizes the concept of sustainable and environment-friendly development, and is beneficial to promote the application and popularization of the microorganism-induced calcite precipitation technology in actual engineering.

Description

A production method and application of biocement based on low-priced calcium ions

technical field

The invention relates to a production method and application of bio-cement based on low-priced calcium ions, that is, on the basis of traditional microorganism-induced calcite precipitation technology, agricultural and mining wastes are used as raw materials to produce bio-cement-based materials, specifically belonging to bio-building material technology field.

Background technique

In recent years, an environmentally friendly green building material - biocement has been widely used in civil engineering. Biocement is a building material produced by mixing calcium salt, urea, and microorganisms (such as urease bacteria) in a certain proportion. The mechanism is called microorganism-induced calcite precipitation. The effect of biocement is similar to that of conventional cement, that is, to reduce hydraulic conductivity and increase ground strength, and the grouting method is roughly the same as that of traditional cement. At present, there have been a lot of research on the use of biocement to replace conventional cement, such as the construction of solid waste landfills, the stabilization of dams, and the construction of groundwater biological ponds. In addition, biocement has the following advantages compared with traditional Portland cement: (1) less energy consumption in the production process; (2) low viscosity, easy to inject into the ground; (3) small particle size, can repair narrower gaps and cracks, etc. .

However, there are great challenges in the practical promotion and application of biocement. The commonly used microbial-induced calcite precipitation process usually requires a large amount of industrial-grade calcium chloride as a calcium source, but calcium chloride is expensive and the large amount of calcium chloride will pollute the environment. Therefore, researchers have been working on finding alternative calcium sources. For example, Park et al. reported the process of plant-induced calcite precipitation, using the active urease of the sheep bean and the mixed reaction of calcium hydroxide or calcium nitrate to generate the reactant for sand cementation, but the content of the active urease of the sheep bean is low, requiring a large amount of Planting, occupying agricultural fields, and its extraction and processing costs are high. Zhang et al. used calcium nitrate and calcium acetate as calcium sources instead of calcium chloride. Choi et al. used eggshells and vinegar to make calcium sources. Although eggshells are rich in calcium, a large number of eggshells need to be collected for promotion. There are many obstacles in the process of eggshell collection. A lot of manpower and time to collect. Therefore, there are certain limitations in the large-scale application of the above methods.

Qian Chunxiang of Southeast University applied for a patent "Method for preparing calcium carbonate by microbial deposition" (CN200510094744.5), proposing to inoculate Bacillus pasteurianus on the medium containing urea substrate, mix it with CaCl ₂ and react under certain conditions to generate carbonic acid Preparation method of calcium precipitate. The patent proposes to use industrial-grade calcium chloride as a calcium source. According to the survey, the cost price of industrial-grade calcium chloride is about 950 yuan per ton, while the cost of traditional cement is about 400 yuan per ton. Therefore, using calcium chloride as a raw material makes biocement There is a costly defect in mass promotion and use. In 2015, Jia Qiang and others applied for a patent "A Microbial Grouting Method to Increase the Early Deposition of Calcium Carbonate" (CN201510113200.2) and publicly proposed to optimize the preparation method of biocement by controlling different reaction factors, which mentioned that acetic acid can be used Calcium is used as a calcium source for traditional biocement production, which provides an improved idea for the present invention in terms of raw material preparation.

As a large agricultural country, my country produces a huge amount of agricultural waste. Agricultural waste in my country mainly comes from planting and breeding. It is estimated that the total output of crop straws in China is about 6.5×10 ⁸ t/a, and most of the crop straws in China are used for one-time use such as burning. Moreover, a large amount of nitrogen oxides, sulfur dioxide, hydrocarbons and smoke will be produced during the combustion process, directly polluting the atmosphere, and harmful substances produced by sunlight will further cause secondary pollution. The present invention utilizes the by-product acetic acid of agricultural straw waste to rapidly pyrolyze biomass oil as a raw material in the traditional biocement technology. On the one hand, the agricultural waste has a wide source, a large quantity, easy acquisition and low cost; on the other hand, the invention can be used Carry out recycling of waste resources, reduce the amount of agricultural waste used for combustion and reduce environmental pollution during combustion, and achieve the purpose of resource recycling and sustainable environmental protection development.

To sum up, the currently used microbial-induced calcite precipitation technology is not only costly to produce raw materials for biocement in large-scale applications, but also causes environmental pollution when used in large quantities. Therefore, it is urgent to find a new low-cost, sustainable calcium source to replace industrial-grade calcium chloride, so as to achieve large-scale application. Based on the traditional microorganism-induced calcite precipitation technology, the present invention uses quarry waste and agricultural waste to rapidly pyrolyze the by-product acetic acid to produce bio-crude oil to produce soluble calcium salt instead of industrial-grade CaCl ₂ to produce a new type of environmentally friendly bio-cement , realizing the sustainable development of resource recycling, and greatly promoting the application and promotion of calcite precipitation technology based on microbial induction in practical engineering.

Contents of the invention

The object of the present invention is to provide a novel production method for preparing biocement based on low-priced calcium ions aiming at the defects in the prior art. The soluble calcium salt produced by the acetic acid reaction of the by-product of the rapid pyrolysis of quarry waste and agricultural waste to produce biomass oil replaces the traditional calcium chloride as the calcium source, and then mixes it with urea and urease bacillus to utilize urea decomposition. Microbial-induced calcite precipitation technology for the production of biocement.

The present invention provides a kind of production method and application based on low-priced calcium ion preparation biological cement, and described production method is as follows:

Step (1): the cultivation of urease bacillus bacterial liquid

According to the volume ratio of 1:0.1~1:1000, inoculate the strain of Bacillus urease in the culture medium, culture it with shaking at 15~35°C for 24~72 hours, and obtain the Bacillus urease bacteria liquid; measure its cell concentration by optical density method .

The formula of the culture solution is: 20 g/L of yeast extract, 10 g/L of ammonium sulfate, 0.13 g/L of Tris buffer, and the pH of the culture solution is 9.0.

The optical density method refers to the absorbance of the bacterial liquid measured at a wavelength of 600 nm with pure culture liquid as a reference, and the cell concentration _OD600 value ranges from 0.1 to 3.0;

Step (2): Pyrolysis of agricultural waste

Under the condition of nitrogen atmosphere, the agricultural waste is pulverized and then pyrolyzed at 200-900° C. for 1-60 minutes to obtain a liquid phase product rich in acetic acid.

Step (3): Preparation of Calcium Solution

Limestone powder and the liquid phase product rich in acetic acid in step (2) are mixed at a mass ratio of 1:2~1:12, reacted at 4~40°C for 36~120h, the pH is controlled at 0.1~10, and centrifuged to obtain a mass concentration of 0.1 %-99% calcium acetate solution.

Step (4): Preparation of cementing liquid

The calcium acetate solution in step (3) and the urea solution are mixed in equal volumes at the same molar concentration of 0.1-1 mol/L, and the pH is adjusted to obtain a cementing solution.

Step (5): Preparation of biocement in free solution

Combine the urease bacillus liquid of step (1) with the step The cementing liquid is mixed according to the volume ratio of 1:1~1:100, and after reacting at room temperature for 12h~72h, the obtained sediment is biocement.

The applications described are as follows:

will step The urease bacillus solution was circulated into a sand column device at room temperature of 20-25°C for 1-10 hours, and the urease bacillus solution, urea solution with a mass concentration of 0.1-10 mol/L and calcium with an equal mass concentration were added. The cementing liquid made by mixing the solutions is mixed and passed into the sand column device, and recirculated for 3 to 12 hours; repeat the above operation 1 to 2 times a day, and after 7 to 28 days, wash the cemented sand column with distilled water and remove the outer cylinder of the sand column device. layer, the form-bonded biocement can be obtained.

The sand column device is a PVC cylinder with a diameter of 1-100 cm and a height of 1-300 cm, the sand grains in which are raw materials for preparing molding cemented biocement, and the particle size ranges from 100 to 275 μm.

The limestone powder is more than one kind of limestone or waste materials from dolomite quarries, and the particle size of the powder is 0.1-1000 μm.

The agricultural waste includes at least one of corn stalks, corn cobs, wheat straw, rice stalks, rice husks, bagasse, cotton stalks, wood chips and fruit shells.

The urease bacillus includes bacillus pasteurianus and bacillus sarcina.

The present invention uses urease bacillus to metabolize or decompose urea to generate carbonate under certain conditions, and reacts with agricultural waste by-product acetic acid to dissolve mining waste to generate a large amount of soluble calcium ions in calcium acetate solution to generate a binder that is biocement based material.

Beneficial effects of the present invention: Compared with the traditional biocement preparation method, its advantages are: (1) The present invention solves the problem of high raw material cost in the traditional method, and fully utilizes the calcium source required for the production of agricultural waste and mining waste, In line with the concept of resource utilization of waste and sustainable development, it provides a new method for sustainable production of low-cost biocement; (2) Make full use of agricultural waste, reduce waste of resources and reduce environmental pollution caused by burning agricultural waste, to achieve Resource recycling, the purpose of environment-friendly development.

Description of drawings

Fig. 1: Process flow chart of biocement preparation by free solution of the present invention;

Figure 2: XRD pattern of biocement;

Figure 3: XRD pattern of pure reagent calcium carbonate;

Figure 4: Schematic diagram of the sand column device;

Figure 5: Schematic diagram of the formed cemented biocement;

Figure 6: Unconfined compressive strength versus axial strain of the formed cemented biocement;

Figure 7: The relationship between splitting compressive strength and axial strain of formed cemented biocement;

Figure 8: SEM image of sand treated by MICP;

Figure 9: SEM images of the gaps between sand grains bridged by CaCO ₃ ;

Figure 10: SEM images of the size of CaCO3 crystals covering the surface of sand grains.

detailed description

The present invention is described in detail below in conjunction with example.

Example 1

Preparation of a low-valent calcium ion-based biocement in free solution

(1) Preparation of NH ₄ -YE culture medium: Weigh 15.75g of Tris salt, dilute it to 1L with deionized water, adjust the pH to 9 with 1+9HCl, add 20g of yeast extract and 10g of ammonium sulfate, and stir well to obtain NH4-YE ₄ -YE culture medium;

(2) Preparation of Bacillus urease bacteria solution: After activating Bacillus urease ATCC 11859 (Sporosarcina Pasteurii) seed bacteria, inoculate an appropriate amount into 100ml of the culture solution prepared in step (1), and place it in a shaking box (130rpm ) cultured at 30°C for 48 hours (to make the bacterial cell concentration OD ₆₀₀ =0.8~1.2) to obtain the bacterial liquid;

(3) Preparation of acetic acid: pulverized agricultural waste such as corn stalks at 470°C under nitrogen atmosphere. Pyrolysis under temperature conditions for 20 minutes, the obtained liquid phase product is rich in acetic acid;

(4) Preparation of calcium solution: Mix and react 800ml of acetic acid obtained in step (2) with 100g of mining waste for 5 days, add distilled water to adjust the calcium ion concentration of the mixture to 0.3mol/L, and use 1mol/L of NaOH Further adjust the pH of the mixture to 7.0~7.5. Then the solution is centrifuged at 4000rpm for 20 minutes, and the supernatant obtained is the calcium source required for the preparation of biocement;

(5) Dissolve 18.02g of urea and add water to 1L, stir until fully mixed, and prepare 0.3mol/L;

(6) Prepare biocement-based materials in free solution: Mix 30ml of the urea bacillus liquid obtained in step (2) and urea obtained in step 4 at a ratio of 1:1, and adjust the pH of the mixture to 7.0 with NaOH ~7.5, keep it in a beaker for one day, and then add 30ml of the calcium solution prepared in step 3 (see Figure 1 for the specific operation process).

(7) The resulting precipitate was filtered with FG/C filter paper, and dried at 115° C. for 1 day, and then the dried precipitate was analyzed using X-ray diffraction (XRD). The XRD pattern of this precipitate (see Figure 2) perfectly matched the XRD pattern of pure reagent grade calcium carbonate (Figure 3), and the results confirmed that the precipitate was calcium carbonate.

Example 2

Preparation of a biocement based on low-valent calcium ions in a sand column device

The sand column device is shown in Figure 4. A PVC cylinder with a diameter of 5 cm and a length of 10 cm is placed in the cylinder with a density of 1.20 g/cm sand, and a piece of scouring pad is placed at the upper and lower ends of the cylinder as a filter, and then the A PVC cylinder is placed on a funnel filled with gravel, and a beaker is used to collect the solution seeping through the sand column, which is then circulated to the top of the column through a pump;

(2) Preparation of cementing liquid: cementing liquid prepared by mixing equal volumes of urea solution (0.3mol/L) and calcium solution (0.3mol/L) prepared in step (3) of Example 1;

(3) Take 80ml of the urease bacillus bacteria solution in step (2) of Example 1, put it in a beaker and circulate it to the top of the sand column through a pump for 3 hours. Then change fresh 30ml of bacterial solution and mix with 300ml of cementing liquid prepared in step 2 and circulate through the sand column device for 9h. The above cycle steps were repeated twice a day for 7 days, calcium carbonate started to precipitate in the column, and the above steps were recirculated for 3 days. A total of 10 days were processed. Wash the cemented sand column with distilled water, and remove the outer layer of the cylinder to obtain the formed cemented biocement sand column as shown in Figure 5;

(4) Test the unconfined compressive strength (USC) and splitting compressive strength (TS) of the formed cemented biocement sand column obtained in step (3). The USC and TS strengths of the formed cemented biocement vary with the The calcium content increases (as shown in Figure 6 and Figure 7. The USC/US strength ratio is known to indicate the brittleness of the biocement sand column, and the higher the ratio, the more brittle the material. The biocement sand column prepared in step (3) The strength ratio increases with increasing calcium carbonate content.

(5) Observing the microstructure image of the formed cemented biocement through SEM scanning electron microscope, it can be seen that the sand particles are covered with CaCO ₃ (Fig. 8), and the gaps between the sand particles are bridged by CaCO ₃ as shown in Fig. 9. And the size of CaCO ₃ crystals covering the surface of sand grains is about 5-20um (Figure 10), which is almost the same size as the size of calcite crystals induced by CaCl ₂ as carbon source reported previously.

Claims (4)

1. A production method and application for preparing biocement based on low-priced calcium ions, characterized in that: the production method is as follows: Step (1): the cultivation of urease bacillus bacterial liquid According to the volume ratio of 1:0.1~1:1000, inoculate the strain of Bacillus urease in the culture medium, culture it with shaking at 15~35°C for 24~72 hours, and obtain the Bacillus urease bacteria liquid; measure its cell concentration by optical density method ; The formula of the culture solution is: yeast extract 20g/L, ammonium sulfate 10g/L, Tris buffer 0.13g/L, culture solution pH=9.0; The optical density method refers to the absorbance of the bacterial liquid measured at a wavelength of 600 nm with pure culture liquid as a reference, and the cell concentration _OD600 value ranges from 0.1 to 3.0; Step (2): Pyrolysis of agricultural waste Under the condition of nitrogen atmosphere, the agricultural waste is pulverized and then pyrolyzed at 200-900°C for 1-60 minutes to obtain a liquid phase product rich in acetic acid; Step (3): Preparation of Calcium Solution Limestone powder and the liquid phase product rich in acetic acid in step (2) are mixed at a mass percentage of 1:2~1:12, reacted at 4~40°C for 36~120h, the pH is controlled at 0.1~10, and centrifuged to obtain a mass concentration of 0.1 %-99% calcium acetate solution; Step (4): Preparation of cementing liquid Mixing the calcium acetate solution in step (3) with the urea solution in equal volumes at the same molar concentration of 0.1 to 1 mol/L, and adjusting the pH to obtain a cementing solution; Step (5): Preparation of biocement in free solution Combine the urease bacillus liquid of step (1) with the step The cementing liquid is mixed according to the volume ratio of 1:1~1:100, and after reacting at room temperature for 12h~72h, the obtained sediment is biocement; The applications described are as follows: Circulate the Bacillus urea solution in step (1) into a sand column device at a room temperature of 20-25°C for 1-10 hours, then add the Bacillus urea solution and urea solution with a mass concentration of 0.1-10 mol/L and The cementing liquid prepared by mixing calcium solutions with equal mass concentrations is mixed and passed into the sand column device, and then circulated for 3 to 12 hours; repeat the above operation 1 to 2 times a day, and after 7 to 28 days, wash the cemented sand column with distilled water and remove the sand column The outer layer of the cylinder of the device can be formed and cemented biocement; The sand column device is a PVC cylinder with a diameter of 1-100 cm and a height of 1-300 cm, the sand grains in which are raw materials for preparing molding cemented biocement, and the particle size ranges from 100 to 275 μm. 2. a kind of production method and the application that prepare biocement based on low-priced calcium ion according to claim 1, it is characterized in that: described limestone powder is more than one in the waste material of limestone or dolomite quarry, The particle size of the powder is 0.1-1000 μm. 3. A production method and application for preparing biocement based on low-priced calcium ions according to claim 1, characterized in that: said agricultural wastes include corn stalks, corncobs, wheat straw, rice straw, rice husk, At least one of bagasse, cotton stalks, wood chips and fruit shells. 4. The production method and application of preparing biocement based on low-priced calcium ions according to claim 1, characterized in that: the urease bacillus comprises bacillus pasteurianus and bacillus sarcina.