Preparation method and application of micro-pore calcite based on microbial mineralization

Abstract

The invention discloses a preparation method and application of micro-pore calcite based on microbial mineralization, and relates to the technical field of preparation of calcite. The method comprises the following steps: separating and purifying a batch of bacteria from a natural environment in which carbonate minerals are precipitated, screening strains with a calcium ion sedimentation rate of more than 95% and a magnesium ion sedimentation rate of more than 50%, and then selecting one strain to prepare a seed solution; preparing a mineral ion culture medium, wherein the mineral ion culture medium contains calcium ions, magnesium ions and lithium ions; inoculating the seed solution into a mineral ion culture medium and culturing for a period of time; and taking out all sediments at the bottom of the cultured mineral ion culture medium, washing and drying. According to the method, bacteria are used for biomineralization in a water environment containing calcium, magnesium and lithium ions to produce the porous calcite, product particles are loose and porous, the specific surface area is large, the method is environmentally friendly and low in cost, no waste gas and dust are discharged in the preparation process, and ecological damage caused by natural environment exploitation is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of calcite preparation, and in particular to a preparation method and application of microporous calcite based on microbial mineralization. Background Art

[0002] Calcium carbonate is an inexpensive, readily available, and widely used inorganic material. As science and technology mature, calcium carbonate products are increasingly developing towards diversified crystal forms, ultrafine particle sizes, and surface modifications. Calcite (CaCO3) is an important mineral material, widely used for adsorption of various inorganic pollutants (cadmium, lead, copper, chromium, zinc, cobalt, etc.) and organic pollutants (oils, dyes, and benzene) in soil and water due to its remarkable surface adsorption properties. Currently, the primary source of industrial calcite is the mining of natural limestone and marble. However, this process inevitably causes irreversible damage to the natural geographical environment and is relatively costly. Furthermore, the adsorption capacity of naturally mined calcite is significantly inferior to that of porous calcite, a potentially important industrial material.

[0003] In recent years, many scholars have done a lot of research on the preparation of porous calcium carbonate. Chen Yanmeng, Mo Huiling and others studied the carbonization process for preparing porous calcium carbonate, which consists of calcination, digestion, carbonization, filtration, drying and other processes. CaO and CO2 are obtained by calcining limestone, and then the Ca(OH)2 emulsion generated by the digestion of CaO with water is carbonized with CO2 gas to obtain porous calcium carbonate; CN110589865A discloses a method for preparing loose porous calcite using steel slag. The method is based on obtaining a leaching solution of CaCl2-NH4Cl-NH3-H2O system from steel slag, then adding sucrose, and then passing CO2 into the leaching solution. At the same time, ultrasonic treatment is turned on, and then the porous calcite is obtained by vacuum filtration, rinsing and drying. At present, the carbonization method is mainly used in China. The porous calcium carbonate produced by this method has the advantages of large specific surface area, low oil absorption value, and stable product performance. Although the above methods can obtain porous calcium carbonate, from the perspective of the preparation route, there are also problems such as high process energy consumption, high wastewater discharge, uneven product pore size distribution and irregular structural morphology. Therefore, it is very necessary to carry out research on the preparation of porous calcium carbonate using other process routes.

[0004] Biomineralization involves the mineralization of metal ions into biominerals through the physiological and biochemical metabolism of organisms. This method has been used to precipitate and remove metal ions from contaminated water and soil. Due to the advantages of rapid bacterial reproduction and efficient biochemical metabolism, different types of bacteria have been used to treat water pollution and repair concrete. Currently, the industrial production of calcium carbonate mainly involves direct mining from the natural environment. This not only damages the ecological environment but also inevitably generates a large amount of wastewater, waste gas, and waste materials during the mining process. Furthermore, the dense structure of naturally mined calcium carbonate has poor adsorption capacity for wastewater. Microbial mineralization is a new clean production method, and this more economical and environmentally friendly method for preparing microporous calcite remains to be explored. Summary of the Invention

[0005] One of the purposes of the present invention is to provide a method for preparing microporous calcite based on microbial mineralization, which solves the technical problems of high energy consumption and high sewage and waste gas emissions of porous calcium carbonate in the prior art. The microporous calcite prepared by microbial mineralization in the present invention has high porosity and uniform pores, well-controlled morphology and structure, and a more environmentally friendly preparation process.

[0006] In order to achieve the above-mentioned objectives, the present invention adopts the following technical scheme: a method for preparing microporous calcite based on microbial mineralization, comprising the following steps in sequence: step 1, isolating and purifying a batch of bacteria from a natural environment where carbonate minerals are being precipitated, selecting strains with a calcium ion sedimentation rate greater than 95% and a magnesium ion sedimentation rate greater than 50%, and then selecting one of the strains to prepare a seed liquid.

[0007] Step 2: prepare a mineral ion culture medium, which includes: 5 g / L beef extract, 10 g / L tryptone, 10 g / L sodium chloride, 0.02 mol / L calcium ions, 0.02 mol / L magnesium ions, and 0-0.05 mol / L lithium ions.

[0008] Step 3: Add NaHCO3 solution and Na2CO3 solution to the mineral ion culture medium to make the NaHCO3 concentration be 0.021 mol / L and the Na2CO3 concentration be 0.01 mol / L, and adjust the pH to 7.0 with hydrochloric acid solution.

[0009] Step 4: Add the seed solution described in step 1 to the mineral ion culture medium obtained in step 3 and culture for a period of time.

[0010] Step 5: Take out all the precipitates at the bottom of the mineral ion culture medium obtained by culture, rinse and dry them.

[0011] In the above-mentioned method for preparing microporous calcite based on microbial mineralization, in step 1, the selected strain has been deposited in the General Microbiology Center of the China Culture Collection Administration of Microorganisms with the deposit number: CGMCC No. 34171, and the classification name of the strain is: Bacillus licheniformis.

[0012] In the above-mentioned method for preparing microporous calcite based on microbial mineralization, in step 1, the preparation steps of the seed liquid are: first, the purified bacterial water sample is smeared on the solid culture medium; then the colonies in the solid culture medium are inoculated into the liquid culture medium to obtain the seed liquid.

[0013] The above-mentioned method for preparing microporous calcite based on microbial mineralization has a solid culture medium formula of: 5 g / L beef extract, 10 g / L tryptone, 10 g / L sodium chloride, 20 g / L agar, and NaOH solution to adjust the pH to 7.0.

[0014] The above-mentioned method for preparing microporous calcite based on microbial mineralization has a liquid culture medium formula of: 5 g / L beef extract, 10 g / L tryptone, 10 g / L sodium chloride, and NaOH solution to adjust the pH to 7.0.

[0015] In the above-mentioned method for preparing microporous calcite based on microbial mineralization, the sources of the calcium ions, magnesium ions, and lithium ions all come from their chlorides. Microporous calcite with different porosities is obtained by adjusting the concentration of lithium ions. The particle size distribution of the microporous calcite is 5~30μm.

[0016] In the above-mentioned method for preparing microporous calcite based on microbial mineralization, the chloride containing calcium ions is anhydrous calcium chloride, the chloride containing magnesium ions is magnesium chloride hexahydrate, and the chloride containing lithium ions is anhydrous lithium chloride; the concentration of the anhydrous lithium chloride is 0.005 mol / L.

[0017] In the above-mentioned method for preparing microporous calcite based on microbial mineralization, in step 4, the inoculation volume of the seed liquid is 1% of the volume of the mineral ion culture medium, and the culture is carried out for 4 to 5 days in a constant temperature shaker set at a temperature of 36°C and a rotation speed of 100 rpm.

[0018] In the above-mentioned method for preparing microporous calcite based on microbial mineralization, in step 5, distilled water and anhydrous ethanol are used for washing in turn, and the number of washing times is 4.

[0019] Another object of the present invention is to provide an application of microporous calcite based on microbial mineralization, wherein the application is to use the microporous calcite to adsorb heavy metal ions in wastewater.

[0020] The preparation mechanism of microporous calcite based on microbial mineralization in the present invention is mainly as follows: the growth and metabolic activities of microorganisms can change various physical and chemical parameters of the water chemical environment. During the growth process, bacteria release ammonia (NH3) and carbonic anhydrase (CA), which work together to increase the pH of the surrounding water environment. At the same time, ammonia and carbonic anhydrase also increase HCO3 - 、CO3 2- and OH - The role of NH3 and CA can be illustrated by the following chemical reaction.

[0021] .

[0022] .

[0023] .

[0024] .

[0025] In the presence of bacteria, The ions can be easily precipitated according to the following chemical reactions.

[0026] .

[0027] In addition, extracellular polymeric substances (EPS) as nucleation sites also play a key role in the biomineralization of calcium carbonate. EPS provide nucleation sites for minerals because they contain a large number of amino acids, polysaccharides and other substances, and the free hydroxyl ions have a large amount of negative charge in an alkaline environment, which is conducive to the absorption of calcium ions. The added magnesium ions and CO3 2- The formation of soluble complexes locally increases supersaturation and accelerates nucleation. In addition, the adsorption of magnesium ions partially blocks the crystal growth sites, generating finer micron particles.

[0028] Compared with the prior art, the present invention brings the following beneficial technical effects: (1) The particle size distribution of the porous calcite produced by microbial action is roughly between 5 and 30 μm. The surface and interior of these calcite particles are covered with micron-sized pores. Microporous calcite with different porosities can be prepared by changing the concentration of lithium ions. Compared with directly mined calcite, this microporous calcite has a larger specific surface area and large pores, which is conducive to the adsorption of heavy metal ions and other pollutants in wastewater.

[0029] (2) Compared with chemical precipitation of calcium carbonate, biomineralization precipitation of microporous calcite mainly relies on bacterial growth to increase pH, produce ammonia, and change HCO3 - 、CO3 2- and OH -Ion concentration can be reduced, enabling the precipitation of minerals under low metal ion concentration conditions, reducing the consumption of chemicals and energy. Using bacteria to biomineralize water environments containing calcium, magnesium, and lithium ions to produce microporous calcite simplifies the preparation process and contributes to sustainable environmental remediation strategies. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 X-ray diffraction (XRD) characterization of microporous calcite.

[0031] Figure 2 This is a dot-line graph showing the change in lithium ion concentration and calcite surface porosity. The calcite surface porosity was calculated using imageJ software.

[0032] Figure 3 This is a curve diagram of bacterial concentration (OD) and pH value changes in liquid culture medium.

[0033] Figure 4 The mineralized calcite and natural calcite have a great influence on Cu 2+ Variation of removal rate over time.

[0034] Figure 5 To adsorb Cu 2+ After the experiment, scanning electron microscopy (SEM) was performed on the microporous calcite at certain points.

[0035] Figure 6 This is the energy dispersive X-ray spectrum (EDS) of point 1.

[0036] Figure 7 This is a scanning electron microscope image of the microporous calcite produced by mineralization when the lithium ion concentration is 0 mol / L.

[0037] Figure 8 This is a scanning electron microscope image of microporous calcite produced by mineralization when the lithium ion concentration is 0.005 mol / L.

[0038] Figure 9 This is a scanning electron microscope image of microporous calcite produced by mineralization when the lithium ion concentration is 0.01 mol / L.

[0039] Figure 10 This is a scanning electron microscope image of microporous calcite produced by mineralization when the lithium ion concentration is 0.02 mol / L.

[0040] Figure 11 This is a scanning electron microscope image of microporous calcite produced by mineralization when the lithium ion concentration is 0.03 mol / L.

[0041] Figure 12 This is a scanning electron microscope image of microporous calcite produced by mineralization when the lithium ion concentration is 0.04 mol / L.

[0042] Figure 13 This is a scanning electron microscope image of microporous calcite produced by mineralization when the lithium ion concentration is 0.05 mol / L.

[0043] Figure 14 This is a scanning electron micrograph of calcite prepared without inoculation of seed solution. DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application.

[0045] In the description of this application, unless otherwise specified, " / " means "or". For example, A / B can mean A or B. "And / or" in this document is simply a description of the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone.

[0046] The technical solution of the present application is further described in detail below with reference to the accompanying drawings.

[0047] The magnesium ions, calcium ions, and lithium ions mentioned in the present invention are all derived from their chlorides, such as magnesium ions from magnesium chloride hexahydrate, calcium ions from anhydrous calcium chloride, and lithium ions from anhydrous lithium chloride, and all of them can be purchased through commercial channels.

[0048] The main technical concept of the present invention is to use bacteria to biomineralize an aqueous environment containing calcium, magnesium and lithium ions to prepare microporous calcite, which is a new method different from the existing physical and chemical methods.

[0049] This study uses bacteria isolated from a well at Lanhai Xinyuan, a mining facility in the Dongying Economic and Technological Development Zone, Dongying City. The bacteria have been deposited with the General Microbiology Center of the China National Committee for Microbiological Culture Collection (CGMCC), located at No. 3, Yard 1, Beichen West Road, Chaoyang District, Beijing, on April 11, 2025. The deposit number is CGMCC No. 34171, and the classification name is Bacillus licheniformis. This strain was used for biomineralization to produce microporous calcite. The biomineralization mechanism and mineral properties of the strain were explored, and the results were compared with the ability of natural calcite to adsorb heavy metal ions.

[0050] First, a preliminary assessment of the bacteria and mineralization capacity is given. The following sections provide detailed descriptions of bacterial isolation and purification, evaluation of bacterial mineralization capacity, bacterial preservation, growth of Bacillus licheniformis, changes in water pH, and ammonia detection.

[0051] (1) Bacterial isolation and purification: The liquid culture medium consists of 5 g / L beef extract, 10 g / L trypsin, 10 g / L sodium chloride, and a pH of 7.0. The solid culture medium is the same as above, with the addition of 20 g / L agar powder.

[0052] A 100 mL sample of well water from the Lanhai Xinyuan well was added to 500 mL of sterile liquid culture medium, sealed, and incubated in a constant temperature shaker until the liquid became turbid. In a clean bench, 20 μL of the turbid liquid culture medium was spread on the surface of a sterile solid culture medium, sealed, and incubated in a 37°C incubator until colonies were visible on the plate. A single colony was selected and inoculated into the liquid culture medium until the liquid became turbid, then inoculated into the solid culture medium. This process was repeated until a single colony was present on the solid culture medium.

[0053] (2) Evaluation of bacteria with mineralization ability: After separation and purification, each bacterial strain was subjected to a microbial mineralization experiment in a mineral ion culture medium (5 g / L beef extract, 10 g / L trypsin, 10 g / L sodium chloride, pH = 7.0) containing calcium ions (0.01 mol / L) and magnesium ions (0.01 mol / L). This method can be applied to strains with a calcium ion sedimentation rate greater than 95% and a magnesium ion sedimentation rate greater than 50%.

[0054] (3) Deposit of bacteria: The strain has been deposited and named Bacillus licheniformis with the deposit number CGMCC No.34171.

[0055] (4) Growth, pH changes, and ammonia detection of Bacillus licheniformis: To investigate bacterial growth and pH changes, the seed solution was inoculated into a liquid culture medium (initial pH 7.0) at an inoculation volume of 1% of the volume of the liquid culture medium. The culture medium was placed in a constant temperature incubator (37°C, 100 rpm) and the cell concentration was measured at a wavelength of 600 nm using a spectrophotometer at different time periods.

[0056] Figure 3 A graph shows the changes in bacterial concentration (OD) and pH in an inoculated liquid culture. Bacterial growth occurs in three phases: lag phase (0-5 hours), logarithmic growth phase (5-20 hours), and stationary phase (20-130 hours). The pH value rises rapidly from 7.0 to 7.83, then continues to rise to 9.03 before finally stabilizing at around 9. This indicates that the presence of bacteria increases the pH of the water environment, which promotes mineral precipitation.

[0057] To investigate the cause of the increased pH, the ammonia production ability of Bacillus licheniformis was tested. The composition of 100 mL of liquid culture medium for the ammonia test was as follows: 0.5 g tryptone, 0.05 g K₂HPO₄, and 0.05 g MgSO₄. The pH was adjusted to 7.0-7.2. Nessler reagent was prepared by adding 16.0 g NaOH, 7.0 g KI, and 10.0 g HgI₂ to 100 mL of distilled water. The seed solution was inoculated into 10 mL of liquid culture medium at an inoculum volume of 1% (the experimental group). Another group of samples was inoculated with the same volume of sterile distilled water (the control group). After 24 hours of incubation, 3-5 drops of Nessler reagent were added to each of the experimental and control groups, and the color changes were observed. The experimental group exhibited a dark yellow color, indicating ammonia production, while the control group exhibited a light yellow color, indicating the absence of ammonia. The presence of ammonia is a key factor in the increase in pH in the culture medium.

[0058] The following is a detailed description of the present invention's method for preparing microporous calcite based on microbial mineralization. In order to increase the purity of bacteria seeded into a mineral ion culture medium and improve mineralization efficiency, the present invention first inoculates a purified bacterial water sample into a solid culture medium. The bacterial colonies in the solid culture medium are then inoculated into a liquid culture medium to obtain a seed solution. Finally, the seed solution is inoculated into the mineral ion culture medium.

[0059] Specifically, the steps include: step 1, taking a water sample of a bacterial strain after separation and purification and smearing it on the surface of a solid culture medium; the solid culture medium formula is: beef extract 5g / L, tryptone 10g / L, sodium chloride 10g / L, agar 20g / L, and NaOH solution is used to adjust the pH to 7.0; the solid culture medium is sterilized in a high-pressure sterilizer at a temperature of 121°C for 20 minutes; in a clean bench, the bacterial water sample is diluted 10 with sterile distilled water; 0 times, 10 -1 times, 10 -2 times, 10 -3 times, 10 -4 times, 10 -5 times, apply them on the surface of the condensed solid culture medium, seal them and then place them in a static incubator (temperature close to 37°C) for culture.

[0060] Step 2: Transfer the bacteria from the solid culture medium to the liquid culture medium; wait for colonies to grow on the solid culture medium (it will grow in 2-4 days), prepare the liquid culture medium in a conical flask, the liquid culture medium formula is: 5g / L beef extract, 10g / L tryptone, 10g / L sodium chloride, and adjust the pH to 7.0 with NaOH solution; sterilize the liquid culture medium in a high pressure sterilizer at 121°C for 20 minutes; use a pipette equipped with a sterile tip in a clean bench, dip a small amount of colonies on the solid culture medium, inject it into the liquid culture medium cooled to room temperature, seal it, and culture it in a shaker for 2-3 days to obtain the seed solution; set the shaker temperature to 36°C and the oscillation frequency to 100rpm.

[0061] Step 3: Preserve the bacterial strain; use a spectrophotometer to measure the cell concentration of the seed liquid cultured on a shaker at a wavelength of 600 nm. When the OD value is greater than or equal to 1, prepare a 30% glycerol solution made of glycerol and distilled water and place it in a high-pressure sterilizer for sterilization. Mix the sterilized glycerol solution and seed liquid in a 1:1 volume ratio in a sterile centrifuge tube, seal it with a sterile sealing film, and store it in the freezer layer of the refrigerator (temperature below -20°C). The preserved bacterial strain can be directly taken for experiments later.

[0062] Step 4. Inoculate the seed liquid into the mineral ion culture medium; prepare the mineral ion culture medium with the following formula: 5 g / L beef extract, 10 g / L tryptone, 10 g / L sodium chloride, 0.02 mol / L magnesium ion concentration, 0.02 mol / L calcium ion concentration, and lithium ion concentration controlled at 0~0.05 mol / L, wherein the lithium ion concentration can be set in multiple gradients to regulate the porosity of calcite, and then place the mineral ion culture medium in a high pressure sterilizer for sterilization; in an ultra-clean workbench, use sterile distilled water to prepare 0.8 mol / L NaHCO3 solution and 0.8 mol / L Na2CO3 solution, and filter the NaHCO3 solution and Na2CO3 solution into sterile conical flasks using sterile needle filters; add 4 ml of filtered NaHCO3 solution and 2 ml of filtered Na2CO3 solution to every 150 ml of mineral ion culture medium, and adjust the pH to 7.0 with hydrochloric acid; in the ultra-clean workbench, inoculate the mineral ion culture medium with a seed liquid with an inoculation volume of 1% of the culture medium volume.

[0063] Step 5: Seal the inoculated mineral ion culture medium and place it in a constant temperature shaker for 5 days.

[0064] Step 6: Take out the mineral ion culture medium cultured in the shaker, remove all the sediment at the bottom of the culture medium, rinse it three times in turn with distilled water and anhydrous ethanol, and then place it in a drying oven at a constant temperature of 43°C to dry it to obtain the product microporous calcite.

[0065] The present invention will be further described below with reference to specific embodiments.

[0066] Example 1: The present invention provides a method for preparing microporous calcite based on microbial mineralization, comprising the following steps: Step 1: selecting a water sample of Bacillus licheniformis, diluting 10% with sterile distilled water in a clean bench, 0 times, 10 -1 times, 10 -2 times, 10 -3 times, 10 -4 times, 10 -5 The mixture was divided into 6 gradients and smeared on the surface of the sterilized and condensed solid culture medium, sealed and placed in a static incubator for 2 days.

[0067] Step 2: Prepare liquid culture medium in a conical flask and sterilize it in a high-pressure sterilizer; use a pipette equipped with a sterile tip in a clean bench to dip a small amount of colonies on the solid culture medium, inject it into the liquid culture medium cooled to room temperature, seal it and culture it in a shaker for 3 days to obtain seed liquid.

[0068] Step 3. Prepare mineral ion culture medium, set the calcium ion concentration to 0.02 mol / L, the magnesium ion concentration to 0.02 mol / L, and the lithium ion concentration to 0 mol / L, and place the mineral ion culture medium in a high-pressure sterilizer for sterilization; in an ultra-clean workbench, use sterile distilled water to prepare 0.8 mol / L NaHCO3 solution and 0.8 mol / L Na2CO3 solution, and filter the NaHCO3 solution and Na2CO3 solution into sterile conical flasks with needle filters; add 4 ml of filtered NaHCO3 solution and 2 ml of Na2CO3 solution to every 150 ml of mineral ion culture medium, and adjust the pH to 7.0 with hydrochloric acid; in the ultra-clean workbench, inoculate each mineral ion culture medium with a seed solution with an inoculation volume of 1% of the culture medium volume.

[0069] Step 4: Seal the inoculated mineral ion culture medium and place it in a shaker for 5 days.

[0070] Step 5. Take out the mineral ion culture medium cultured in the shaker, tilt the mineral ion culture medium 30 degrees, use a pipette to install a pipette tip without a pointed tip, and take out all the sediment at the bottom of the mineral ion culture medium into a centrifuge tube. Use distilled water and anhydrous ethanol to rinse the centrifuge tube three times in turn, and then put it into a drying oven at a constant temperature of 43°C to dry it to obtain a micron-pore calcite product.

[0071] The electron microscope image of the microporous calcite prepared in this example is as follows: Figure 7 shown.

[0072] Example 2: The difference from Example 1 is that the lithium ion concentration in the mineral ion culture medium in step 3 is 0.005 mol / L; the electron microscope image of the microporous calcite prepared in this example is as follows: Figure 8 shown.

[0073] Example 3: The difference from Example 1 is that the lithium ion concentration in the mineral ion culture medium in step 3 is 0.01 mol / L; the electron microscope image of the microporous calcite prepared in this example is as follows: Figure 9 shown.

[0074] Example 4: The difference from Example 1 is that the lithium ion concentration in the mineral ion culture medium in step 3 is 0.02 mol / L; the electron microscope image of the microporous calcite prepared in this example is as follows: Figure 10 shown.

[0075] Example 5: The difference from Example 1 is that the lithium ion concentration in the mineral ion culture medium in step 3 is 0.03 mol / L; the electron microscope image of the microporous calcite prepared in this example is as follows: Figure 11 shown.

[0076] Example 6: The difference from Example 1 is that the lithium ion concentration in the mineral ion culture medium in step 3 is 0.04 mol / L; the electron microscope image of the microporous calcite prepared in this example is as follows: Figure 12 shown.

[0077] Example 7: The difference from Example 1 is that the lithium ion concentration in the mineral ion culture medium in step 3 is 0.05 mol / L; the electron microscope image of the microporous calcite prepared in this example is as follows: Figure 13 shown.

[0078] Comparative Example 1: The difference from Example 1 is that the mineral ion culture medium is not inoculated with seed solution. The electron microscope image of the calcite prepared in this comparative example is as follows: Figure 14 shown.

[0079] XRD characterization of microporous calcite Figure 1 The measurement range (2θ) is 20° to 60°. According to the MDI Jade 6 phase search software, the peak positions (2θ) in the figure: 23.117°, 29.499°, 36.055°, 39.516°, 43.268°, 47.702°, and 48.668° are characteristic diffraction peaks of Magnesium calcite, syn (magnesium-containing calcite). The magnesium content is relatively low, and syn indicates that the mineral is laboratory-synthesized, rather than naturally occurring.

[0080] Morphological analysis of the products prepared in Examples 1 to 7 and Comparative Example 1 was performed. Scanning electron micrographs (SEM) of the products obtained in the corresponding examples show that the calcite produced using microorganisms contains numerous pores. This is because carbonate and calcium ions accumulate and precipitate around them under the action of bacteria. The pores in the calcite are traces of bacterial growth activity. The morphology of the calcite gradually changes with increasing lithium ion concentration, which may indicate that changes in lithium ion concentration affect bacterial growth and metabolism. Figure 14 These are minerals produced without inoculation of bacterial culture fluid. It can be observed that the minerals do not have any pores and have a flaky or spherical morphology.

[0081] Figure 2 The change of surface porosity corresponding to lithium ion concentration is shown in Origin 2021 software. The surface porosity in Table 1 is the average porosity. It can be seen from the figure that the higher the lithium ion concentration, the surface pores of micron calcite first increase and then decrease. + The porosity is highest when the concentration is 0.005mol / L. Figures 7 to 13 It can also be observed that as the lithium ion concentration increases, the pores rich in calcite first increase and then decrease, but its surface becomes rough with a large number of tiny protrusions, and the morphology of calcite changes significantly.

[0082] Table 1 is the correspondence between lithium ion concentration and calcite surface porosity Lithium ion concentration (mol / L) Surface porosity (%) 0 42.46 0.005 46.01 0.01 39.92 0.02 35.87 0.03 34.48 0.04 32.04 0.05 29.7

[0083] The application of the microporous calcite prepared in Examples 1 to 7 is described in detail below.

[0084] The mineralized calcite of the present invention and natural mineral calcite were put into simulated wastewater to conduct performance tests on adsorbing copper in the wastewater, and the adsorption equilibrium time, removal rate and adsorption amount of the two were examined.

[0085] Specific experimental steps: Weigh a certain mass of copper nitrate trihydrate and dissolve it in distilled water to make a 24 mg / L copper ion solution as a simulated wastewater solution. Take 50 ml of the simulated wastewater solution in a polyethylene bottle and add 0.2 g of mineralized calcite and natural calcite with different lithium ion concentrations. The experiments were placed in a constant temperature oscillator, oscillated at 100 rpm, and the temperature was set to 25 ° C. 1 mL of the supernatant after the reaction was extracted at different time intervals and injected into distilled water to dilute 10 times, and then filtered through a 0. 22 μm hydrophilic microporous filter membrane. The filtered solution was detected by flame atomic absorption spectrophotometer for Cu 2+ concentration.

[0086] Removal rate = (1).

[0087] Adsorption amount qe = (2).

[0088] In formula (1): is the initial concentration, mg / L; is the equilibrium concentration, mg / L.

[0089] In formula (2): is the volume of the solution, L; is the mass of the basic material, g; is the adsorption amount, mg / g.

[0090] Conclusion: Figure 4 It can be seen that with the increase of time, the 2+ The removal rate of Cu2+ increased gradually; in the initial stage of adsorption, the removal rate of Cu2+ was significantly increased by mineralized calcite and natural calcite. 2+ The adsorption rate of ions is very fast. Within 15 minutes, all mineralized calcites adsorb Cu 2 + The removal rate of Cu increased from 0% to more than 60%, while the natural calcite could only reach 25% at this time, with poor adsorption performance. The adsorption efficiency of calcite regulated by different lithium ions was slightly different 30 minutes before the reaction. As time went on, the adsorption efficiency of each mineralized calcite on Cu 2 + The removal rates of mineralized calcite and Cu are similar, with a removal rate of up to 85%, an average adsorption capacity of 5.1 mg / g, and an adsorption capacity of natural calcite of 1.8 mg / g. 2 + The adsorption rate of ions becomes slow as time goes by, and the reaction reaches equilibrium after 30 minutes. Figure 5 To adsorb Cu 2+ The subsequent scanning electron microscope images of mineralized calcite were scanned at 5 points. Figure 6 The energy spectrum of point 1 shows the elemental composition and distribution of the sample. Among them, Cu (copper) has a clear peak, representing the adsorbed copper ions or copper compounds (such as CuO, CuCO3), which is important evidence that copper ions are adsorbed by calcite. Tables 2 and 3 show the weight and atomic percentage of point 1. It can be concluded that the main phase is calcite (CaCO3). The Cu content also proves that Cu 2+ Adsorbed by calcite.

[0091] Table 2: Quantitative analysis of elemental composition by weight C O Mg Ca Cu 8.35 55.50 2.30 30.62 2.36

[0092] Table 3: Quantitative analysis of elemental composition in atomic percentages C O Mg Ca Cu 13.66 68.16 1.86 15.01 0.73

[0093] It should be noted that ordinary technicians in this technical field should realize that the above implementation methods are only used to illustrate the present application and are not used to limit the present application. As long as they are within the essential spirit of the present application, appropriate changes and modifications to the above embodiments fall within the scope of protection required by the present application.

Claims

1. A method for preparing microporous calcite based on microbial mineralization, characterized in that: The following steps are included in sequence: Step 1: Isolate and purify a batch of bacteria from a natural environment where carbonate minerals are being precipitated, select strains with a calcium ion sedimentation rate greater than 95% and a magnesium ion sedimentation rate greater than 50%, and then select one of the strains to prepare a seed solution; Step 2: preparing a mineral ion culture medium, wherein the mineral ion culture medium comprises: 5 g / L beef extract, 10 g / L tryptone, 10 g / L sodium chloride, 0.02 mol / L calcium ion, 0.02 mol / L magnesium ion, and 0-0.05 mol / L lithium ion; Step 3: adding sodium bicarbonate solution and sodium carbonate solution to the mineral ion culture medium to make the sodium bicarbonate concentration of the culture medium 0.021 mol / L and the sodium carbonate concentration 0.01 mol / L, and adjusting the pH to 7.0 with hydrochloric acid solution; Step 4: inoculating the seed solution described in step 1 into the mineral ion culture medium obtained in step 3 and culturing for a period of time; Step 5: Take out all the precipitates at the bottom of the mineral ion culture medium obtained by culture, rinse and dry them.

2. The method for preparing microporous calcite based on microbial mineralization according to claim 1, characterized in that: In step 1, the selected strain has been deposited in the General Microbiology Center of China Microorganism Culture Collection Administration, with the deposit number: CGMCC No.34171, and the classification name: Bacillus licheniformis Bacillus licheniformis .

3. The method for preparing microporous calcite based on microbial mineralization according to claim 1, characterized in that: In step 1, the preparation steps of the seed solution are: first, the purified bacterial water sample is smeared on the solid culture medium; then the colonies on the surface of the solid culture medium are inoculated into the liquid culture medium to obtain the seed solution.

4. The method for preparing microporous calcite based on microbial mineralization according to claim 3, characterized in that: The formula of solid culture medium is: beef extract 5g / L, tryptone 10g / L, sodium chloride 10g / L, agar 20g / L, and sodium hydroxide solution is used to adjust the pH to 7.

0.

5. The method for preparing microporous calcite based on microbial mineralization according to claim 3, characterized in that: The formula of the liquid culture medium is: beef extract 5g / L, tryptone 10g / L, sodium chloride 10g / L, and sodium hydroxide solution is used to adjust the pH to 7.

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6. The method for preparing microporous calcite based on microbial mineralization according to claim 1, characterized in that: The sources of the calcium ions, magnesium ions and lithium ions are all from their chlorides. By adjusting the concentration of lithium ions, micron-porous calcite with different porosities is obtained. The particle size distribution of the micron-porous calcite is 5-30 μm.

7. The method for preparing microporous calcite based on microbial mineralization according to claim 6, characterized in that: The chloride containing calcium ions is anhydrous calcium chloride, the chloride containing magnesium ions is magnesium chloride hexahydrate, and the chloride containing lithium ions is anhydrous lithium chloride; the concentration of the anhydrous lithium chloride is 0.005 mol / L.

8. The method for preparing microporous calcite based on microbial mineralization according to claim 1, characterized in that: In step 4, the inoculation volume of the seed solution is 1% of the volume of the mineral ion culture medium, and the culture is carried out in a constant temperature shaker at a temperature of 36° C. and a rotation speed of 100 rpm for 4 to 5 days.

9. The method for preparing microporous calcite based on microbial mineralization according to claim 1, characterized in that: In step 5, distilled water and anhydrous ethanol are used for rinsing in turn, and the number of rinses is 4 times.

10. An application of microporous calcite based on microbial mineralization, characterized in that: The microporous calcite is prepared by the preparation method according to any one of claims 1 to 9, and the application is to use the microporous calcite to adsorb heavy metal ions in wastewater.

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