Microbial modified concrete recycled micro-powder, and preparation method and application thereof

Abstract

This invention belongs to the field of wastewater treatment and solid waste utilization technology, and relates to a microbially modified recycled concrete powder, its preparation method, and its application. The preparation method includes: S1, concrete is sequentially subjected to impurity removal, crushing, sieving, and drying to obtain recycled concrete powder; S2, *Bacillus pasteurellii* is selected as the functional strain and cultured in a culture medium to obtain a bacterial solution; S3, mineralization modification: after mixing the concrete powder and the bacterial solution, urea is added, and the mixture is stirred evenly to form a suspension system. The reaction ends when the conductivity of the suspension system decreases at a rate <5 μS / cm·h. Then, the mixture is centrifuged and dried to obtain the microbially modified recycled concrete powder. This invention uses microorganisms to modify the recycled concrete powder, resulting in a three-dimensional network structure, increasing porosity and adsorption capacity, thereby achieving efficient adsorption of Pb(II).

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of wastewater treatment and solid waste utilization, and relates to a microbe-modified concrete recycled powder, a preparation method and application thereof, and is used for adsorption of Pb(II). BACKGROUND

[0002] Lead (Pb) as a common heavy metal pollutant has caused serious harm to human health and the environment, so it needs to be treated. Among the current lead removal methods, the adsorption method uses activated carbon and other materials to adsorb impurities, but the adsorption capacity of activated carbon is limited by its pore structure. When treating lead-containing wastewater, the adsorption needs to be regenerated or replaced after saturation, otherwise it may cause secondary pollution and increase the cost. In order to improve the adsorption capacity, metal organic framework (MOFs) materials are used as adsorbents, such as the patent document with publication number CN117362670A, which discloses a metal organic framework material based on cyclooctatetra-thiophene, which has high adsorption performance for lead ions. Although it has high specific surface area and adjustable structure to improve the adsorption capacity, it may still be damaged in strong acid or complex environment, resulting in insufficient stability. Therefore, new adsorption materials are needed to achieve efficient adsorption of lead.

[0003] Concrete is an engineering composite material in which the aggregate is cemented into a whole by cementitious materials. Due to its high compressive strength, good durability, wide range of strength grades and other characteristics, it is widely used in various civil engineering. However, a large amount of waste concrete is also generated. The existing waste concrete treatment method is mainly to transport it to the suburbs for stacking or landfill, which not only costs a lot of transportation fees and causes secondary pollution to the environment, but also occupies a large amount of land resources. Simply discarding it is also a great waste of natural resources, resulting in environmental pollution, resource waste and safety hazards. The unhydrated cementitious materials in waste concrete have a large number of micropore structures on their surfaces and can also be used as adsorbents. However, the strength of the aggregate obtained by crushing waste concrete is low, and it is difficult to effectively adsorb target substances when used directly as an adsorbent. In addition, its surface roughness, porosity and other characteristics are insufficient, resulting in low adsorption efficiency.

[0004] Therefore, it is a major research topic to develop a kind of waste concrete to realize the efficient adsorption of Pb(II). SUMMARY

[0005] In view of the technical problem of low adsorption efficiency of existing concrete as an adsorbent, the present application provides a microbe-modified concrete recycled powder, a preparation method and application thereof.

[0006] The present application uses microorganisms to modify the concrete recycled powder, forms a three-dimensional network structure, improves the porosity and adsorption capacity, and realizes the efficient adsorption of Pb(II).

[0007] In order to achieve the above object, the technical scheme adopted by the present application is as follows:

[0008] A preparation method of microbial modified concrete recycled micro powder, comprising the following steps:

[0009] S1, concrete pretreatment

[0010] The concrete is sequentially subjected to impurity removal, crushing, screening and drying to obtain concrete recycled micro powder;

[0011] S2, microbial activation

[0012] Bacillus pasteurii is selected as a functional strain, and a culture medium is used to obtain a bacterial liquid;

[0013] S3, mineralization modification

[0014] After the concrete micro powder is mixed with the bacterial liquid, urea is added, and the mixture is uniformly stirred to form a suspension system. When the conductivity reduction rate of the suspension system is less than 5 μS / cm·h, the reaction is stopped. Then, the microbial modified concrete recycled micro powder is obtained through centrifugal separation and drying.

[0015] Further limitation, in step S1, the crushing is first crushed to a particle size <50 mm, and then ball milled to a particle size <1 mm; the particle size after screening is <100 μm; the drying is dried at 105±5℃ for 24h.

[0016] Further limitation, in step S2, the culture conditions are: 30℃ for 24h-48h, and the OD600 value at the end of the culture is 0.10-0.20.

[0017] Further limitation, in step S3, the mass ratio of concrete micro powder to urea in 1 mL of bacterial liquid is (1-3) mg:(10-30) mg.

[0018] The microbial modified concrete recycled micro powder prepared by the preparation method of the microbial modified concrete recycled micro powder.

[0019] Further limitation, the microbial modified concrete recycled micro powder is a three-dimensional network structure formed by interweaving spherical, rhombic and needle-shaped crystals.

[0020] Further limitation, the microbial modified concrete recycled micro powder contains six phases of hydroxyapatite, quartz, calcite, aragonite, spherulite and gypsum.

[0021] The microbial modified concrete recycled micro powder as an adsorbent in the application of Pb(II) adsorption.

[0022] Further limitation, the microbial modified concrete recycled micro powder is prepared by Ca 2+ / Pb 2+Ion exchange, silanol complexation, and lead carbonate precipitation work together to improve the adsorption efficiency of Pb(II).

[0023] Further, the application requirements are as follows: the initial concentration of Pb(II) is 1000 mg / L, pH = 5.0 ± 0.1, the amount of adsorbent is 1.0 g / L, the adsorption temperature is 25℃, and the maximum adsorption capacity is 992.1 mg / L.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] 1. This invention uses microorganisms to modify recycled concrete powder, forming a three-dimensional network structure composed of spherical, rhomboid and needle-like crystals, thereby improving porosity and adsorption capacity, and thus achieving efficient adsorption of Pb(II).

[0026] 2. This invention utilizes microbial modification treatment to systematically transform the phase composition of recycled concrete powder. Specifically, it involves urease-catalyzed urea hydrolysis consuming hydroxide ions, thereby promoting the dissolution of calcium hydroxide in the recycled concrete powder and releasing Ca. 2+ The released Ca 2+ CO3 produced by microbial metabolism 2- This combination induces the formation of a polycrystalline system of calcium carbonate, improves the thermodynamic stability of the material, and further enhances the adsorption efficiency for lead.

[0027] 3. This invention, through research, has discovered that the structure of microbially modified recycled concrete powder contains multiple phases, specifically including six phases: calcium hydroxide, quartz, calcite, aragonite, spheroidal aragonite, and gypsum. The synergistic effect of these multiphase minerals not only provides highly efficient fixation of lead ions over a wide pH range but also significantly regulates the solution chemical environment through calcium carbonate dissolution and silica gel hydrolysis, thereby enabling the formation of lead ions through the action of Ca... 2+ / Pb 2+ Ion exchange, silanol complexation, and lead carbonate precipitation work together to enhance the adsorption capacity for lead. Attached Figure Description

[0028] Figure 1 This is a control result showing the activity of microorganisms in an alkaline environment;

[0029] Figure 2 The calcium ion fixation efficiency is affected by the concentration of microorganisms;

[0030] Figure 3 SEM image of RCPP before modification;

[0031] Figure 4 SEM images of the modified MRCPP;

[0032] Figure 5XRD patterns of regenerated micro powder before and after modification treatment

[0033] Figure 6 This is a Fourier transform infrared spectrum;

[0034] Figure 7 Thermogravimetric-differential thermogravimetric (DTG) curve;

[0035] Figure 8 The initial pH value for the adsorption of Pb by MRCPP 2+ The curve;

[0036] Figure 9 The final pH curves of the solution after adsorption are shown for different initial pH values.

[0037] Figure 10 Langmuir adsorption isotherms at 25℃, 35℃, and 45℃;

[0038] Figure 11 For the adsorption of Pb by MRCPP 2+ The dynamic model. Detailed Implementation

[0039] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments, but the embodiments of the present invention are not limited thereto. Other methods for preparing the compounds of the present invention, with some conventional modifications to the reaction conditions according to the present invention, are considered to be within the scope of the present invention.

[0040] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0041] It should also be understood that the specific embodiments described above are only used to explain the present invention, and the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or changes made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

[0042] The technical solution protected by this invention will be described in detail below.

[0043] It should be noted that, unless otherwise specified, the chemicals and reagents used in the following embodiments are all commercially available products commonly used in the field.

[0044] It should be noted that, unless otherwise specified, the operations used in the following embodiments are all conventional operations; for example, the operating temperature is always at room temperature unless otherwise specified. The test methods are all existing standard test methods in the art unless otherwise specified.

[0045] The research and development idea of ​​this invention is to construct a method for modifying recycled concrete powder based on microbial induced carbonate precipitation (MICP) technology, and to use the modified microbial recycled concrete powder as an adsorbent to achieve efficient adsorption of lead.

[0046] This invention provides a method for preparing microbially modified recycled concrete powder, comprising the following steps:

[0047] S1, Concrete Pretreatment

[0048] The concrete is subjected to impurity removal, crushing, and screening to obtain recycled concrete powder (denoted as RCPP).

[0049] After manual sorting to remove steel bars and impurities, the particles were crushed to <50mm using a jaw crusher, and then further pulverized in a ball mill to obtain <1mm coarse powder. The <100μm fine powder was collected by sieving through a vibrating screen (200 mesh), dried at 105±5℃ for 24h, and then sealed and stored.

[0050] Preferably, for coarse powder <1mm, a vibrating screen is used to sieve the coarse powder to sieve out fine powder less than 0.6mm, and then a ball mill is used to grind the fine powder into micro powder with an average particle size <100μm. The ball milling time is controlled at 2h and the rotation speed is 1200r / min to make the micro powder particle size distribution uniform. Then, the material is dried to remove residual moisture. The dried micro powder is sieved through a 200-mesh screen. The undersize material is the required concrete recycling micro powder, whose main components are CaO, SiO2 and Al2O3, etc., with high calcium content, which provides a good foundation for subsequent microbial modification.

[0051] S2, Microbial Activation

[0052] Bacillus pasteurellii was selected as the functional strain, and the culture was carried out in an optimized culture medium and a constant temperature shaker for 48 hours to obtain the bacterial solution.

[0053] After culturing at 30℃ for 24 hours, the OD600 value (optical density value) and urease activity of the bacterial solution are measured. Once the OD600 value is within a certain range, it can be used for subsequent modification.

[0054] S3, mineralization modification

[0055] According to the solid-liquid ratio, concrete micropowder (solid) is mixed with bacterial solution (liquid), and 20mg of urea is added. The mixture is stirred evenly to form a suspension system. The reaction ends when the conductivity of the suspension system decreases at a rate of <5μS / cm·h. Then, after centrifugation and drying for 24h, microbial modified concrete recycled micropowder is obtained, denoted as MRCPP.

[0056] In the preparation of microbial modified concrete recycled powder, the solid-liquid ratio, microbial concentration (OD600 value), and calcium ion concentration are all related to the effect of microbial induced carbonate precipitation (MICP), and therefore, they are optimized.

[0057] 1. Effects of solid-liquid ratio on microbial activity and its optimization

[0058] Weigh out the regenerated micropowder and deionized water according to solid-liquid ratios of 1:1, 1.5:1, 2:1, 2.5:1, and 3:1 (regenerated micropowder: deionized water, mass ratio) and add them to beakers. Stir at 500 rpm for 5 minutes using a magnetic stirrer to ensure homogeneous mixing. After stopping stirring, let stand for 30 minutes. Once the suspension has separated into layers, carefully aspirate the supernatant using a pipette to avoid aspirating precipitate. Calibrate using a standard buffer solution. Immerse the pH electrode in the supernatant and wait for the reading to stabilize (approximately 30 seconds), then record the pH value. Repeat each solid-liquid ratio three times and take the average value.

[0059] Sodium hydroxide and deionized water were used to simulate the alkaline solution, and an equal amount of microbial suspension was added to determine the microbial activity at different times. Figure 1 The study demonstrates the dynamic changes in microbial activity over culture time under different solid-liquid ratios.

[0060] See Figure 1 The OD values ​​of all experimental groups showed a decreasing trend over time, but the rate of activity decay differed significantly among different solid-liquid ratios. A cross-sectional comparison revealed that the OD value of a solid-liquid ratio of 1.00 decreased continuously from 0.05 on day 1 to 0.02 on day 5, a cumulative decrease of 60%, with an average daily decrease of 0.006. This indicates that the low solid-liquid ratio resulted in the highest degree of inhibition of microbial activity. With a high liquid phase content at low solid-liquid ratios, microorganisms were directly exposed to the alkaline solution without particle adhesion protection, leading to faster activity decay. The OD value of a solid-liquid ratio of 3.00 was initially higher, at 0.08 on day 1, but slowly decreased to 0.06 on day 5 with prolonged culture time, a cumulative decrease of 25%, with an average daily decrease of 0.004, demonstrating superior activity maintenance ability. However, while the rate of OD value decrease at a solid-liquid ratio of 3.00 is slow, its initial value fluctuates significantly, possibly due to the heterogeneity of the suspension. The high viscosity of the suspension and uneven particle settling allow microorganisms to adhere to the surface of RCPP particles, reducing direct contact with the high pH environment of the liquid phase and thus delaying the decline in activity. At a high solid-liquid ratio, RCPP releases more calcium ions, which react with hydroxide ions to form Ca(OH)₂ precipitate, mitigating the direct damage of high pH to microorganisms. Microorganisms can utilize calcium ions to generate CaCO₃ mineralization products, further consuming hydroxide ions and indirectly stabilizing the pH.

[0061] The activity change trend of the solid-liquid ratio 2.00 was the most stable. Its OD value gradually decreased from 0.07 on day 1 to 0.035 on day 5, with a cumulative decrease of 50% and an average daily decrease of 0.007. Longitudinal analysis showed that the activity decay of the solid-liquid ratio 2.00 exhibited a two-stage characteristic: the first 3 days were a rapid adaptation period, with the OD value decreasing from 0.07 to 0.045; the second 4-5 days entered a stable period, with the OD value maintained at 0.035±0.003, and the coefficient of variation was only 8.6%, significantly lower than other groups. This trend indicates that the solid-liquid ratio 2.00 achieved a balance between activity inhibition and metabolic regulation, avoiding both the drastic decay at low solid-liquid ratios and the potential physical mass transfer limitations at high solid-liquid ratios.

[0062] Based on the rate of OD value change, stability, and long-term activity retention, a solid-liquid ratio of 2.00 was determined to be the optimal choice. Its activity decay rate was 42% lower than that of a solid-liquid ratio of 1.00, and the final activity value was significantly higher than that of a solid-liquid ratio of 1.00 by 0.02. Although a solid-liquid ratio of 3.00 showed the slowest OD value decrease, its initial activity fluctuations and potential engineering applicability limitations restricted its practical application value. Therefore, the stability and controllability of a solid-liquid ratio of 2.00 provide the optimal process for the microbial modification of regenerated micropowders.

[0063] 2. Optimization of microbial concentration and calcium ion fixation efficiency

[0064] Based on the measured pH values ​​(11.8–12.6), 0.1 mol / L NaOH was used to adjust deionized water to the same pH value, and 5 sets of simulated solutions (pH = 11.8, 12.1, 12.3, 12.4, 12.6) were prepared. 1% (v / v) *Bacillus pasteurellii* suspension was added to each solution and mixed thoroughly. The mixture was placed in a 30℃ constant temperature incubator, and samples were taken at 0, 6, 12, 24, and 48 hours. 1 mL of the sample was centrifuged at 8000 rpm for 5 minutes, the supernatant was discarded, and the bacterial cells were resuspended in sterile deionized water to the original volume. The absorbance of the bacterial solution at 600 nm was measured using a spectrophotometer, and the survival rate was calculated using formula (1). Where OD0 is the initial OD value, and OD... t Let d be the OD600 value at time t.

[0065]

[0066] Experimental results are as follows Figure 2The results showed that calcium ion concentration systematically decreased with increasing shake-cultivation time, and the rate of decrease was regulated by the microbial concentration gradient. In the low concentration range (OD600 = 0.05–0.10), calcium ion concentration showed a slow decreasing trend in the early stage of shake-cultivation (1 day), but the rate of decrease increased significantly with the extension of reaction time (2–3 days). This phenomenon reveals the phased characteristics of microbial metabolism, namely, an initiation phase and an acceleration phase: in the initial stage, microorganisms need to adapt to the highly alkaline environment and initiate urease expression, and then form a stable mineralization pathway by chelating calcium ions with extracellular polymer secretion. When the microbial concentration increased to between OD600 = 0.10 and 0.20, and OD600 = 0.15, the calcium ion concentration showed a balanced decreasing pattern over the three-day shake-cultivation cycle, with the daily decrease tending to stabilize. This indicates that at this concentration, microbial activity and substrate supply reached a dynamic balance, and the mineralization reaction entered a steady-state catalytic stage. In the high concentration range (OD600 = 0.20-0.25), the calcium ion concentration decreased rapidly in the early stage of shake culture, but the decrease narrowed significantly by the third day, reflecting that the mass transfer limitation caused by the high cell density and the accumulation of metabolic byproducts had an inhibitory effect on mineralization efficiency.

[0067] The effect of microbial concentration on calcium ion fixation efficiency exhibits a typical threshold effect. When the microbial concentration is below OD600 = 0.15, the decrease in calcium ion concentration is positively correlated with the bacterial density. The mechanism mainly stems from the increased density of active sites: the increased number of microorganisms per unit volume promotes the participation of more urease molecules in urea hydrolysis, and the generated carbonate ions combine with calcium ions released from the regenerated microparticles to form calcium carbonate precipitate. Simultaneously, extracellular polysaccharides and proteins secreted by microorganisms stabilize free calcium ions through coordination, forming a dual-pathway fixation mode of "enzymatic mineralization-chemical chelation." However, when the microbial concentration exceeds OD600 = 0.15, the marginal benefit of the calcium ion concentration decreases sharply. High-density microbial communities lead to increased suspension viscosity, and excessive coverage of the microparticle surface by microbial biofilm hinders the diffusion of calcium ions to active sites. Furthermore, the accumulation of ammonium ions produced by bacterial metabolism in the local microenvironment causes pH fluctuations, and some precipitated calcium carbonate undergoes reversible dissolution, weakening the fixation effect.

[0068] The superiority of the OD600=0.15 concentration group lies in the synergistic optimization across the spatiotemporal dimensions. Temporally, the calcium ion concentration at this concentration exhibits a linear decrease over the three-day shake-in period, with the daily average decrease being 52% higher than the OD600=0.10 group and 18% higher than the OD600=0.25 group. This indicates that it avoids both the initiation delay of the low-concentration group and the late-stage inhibition of the high-concentration group. Spatially, subsequent scanning electron microscopy observations show that at this concentration, microorganisms form a uniform monolayer distribution on the surface of the regenerated micropowder, with the biofilm thickness controlled within the range of 200–500 nm. This effectively covers the micropowder pores to retain calcium ions while preserving sufficient ion diffusion channels.

[0069] The above screening results show that: during preparation, (1-3) mg of concrete powder is added to each 1 mL of bacterial solution, i.e., the solid-liquid ratio is (1-3):1, and the culture is carried out at 30℃ for 24-48 hours. At the end of the culture, the OD600 value is 0.10-0.20; preferably, the solid-liquid ratio is 2.00 and the OD600 = 0.15 is the optimal condition.

[0070] The following examples demonstrate the preparation of microbially modified recycled concrete powder under the selected optimal conditions, and its adsorption capacity and mechanism for Pb(II) were studied as an adsorbent.

[0071] Example 1

[0072] This embodiment provides a method for preparing microbially modified recycled concrete powder, including the following steps:

[0073] S1, Concrete Pretreatment

[0074] The concrete is subjected to impurity removal, crushing, and screening to obtain recycled concrete powder (denoted as RCPP);

[0075] After manual sorting to remove steel bars and impurities, the particles were crushed to <50mm using a jaw crusher, and then further pulverized in a ball mill to obtain <1mm coarse powder. The <100μm fine powder was collected by sieving through a vibrating screen (200 mesh), dried at 105±5℃ for 24h, and then sealed and stored.

[0076] Preferably, for coarse powder <1mm, a vibrating screen is used to sieve the coarse powder to sieve out fine powder less than 0.6mm, and then a ball mill is used to grind the fine powder into micro powder with an average particle size <100μm. The ball milling time is controlled at 2h and the rotation speed is 1200r / min to make the micro powder particle size distribution uniform. Then, the material is dried to remove residual moisture. The dried micro powder is sieved through a 200-mesh screen. The undersize material is the required concrete recycling micro powder, whose main components are CaO, SiO2 and Al2O3, etc., with high calcium content, which provides a good foundation for subsequent microbial modification.

[0077] S2, Microbial Activation

[0078] Bacillus pasteurellii was selected as the functional strain, and the culture was carried out in an optimized culture medium and a constant temperature shaker for 48 hours to obtain the bacterial solution.

[0079] After culturing at 30℃ for 24 hours, the OD600 value (optical density value) and urease activity of the bacterial solution were measured until the OD600 value was 0.15.

[0080] S3, mineralization modification

[0081] Mix 2 mg of concrete powder with 1 mL of bacterial solution at a solid-liquid ratio of 2:1, add 20 mg of urea, stir evenly to form a suspension system, and stop the reaction when the conductivity of the suspension system decreases at a rate of <5 μS / cm·h. Then, after centrifugation and drying for 24 h, microbial modified concrete recycled powder is obtained, denoted as MRCPP.

[0082] The properties of the microbial modified concrete recycled powder (denoted as MRCPP) prepared in Example 1 were characterized.

[0083] Characteristic 1: Morphology

[0084] Comparative analysis of recycled concrete powder (RCPP) before and after modification using scanning electron microscopy (SEM) revealed the profound reconstruction of the surface morphology and crystal phase composition of the materials by microbial mineralization. The unmodified RCPP... Figure 3 ) exhibits typical mechanical crushing characteristics, with its surface mainly composed of smooth, flaky fragments. Modified MRCPP ( Figure 4 The surface of the microparticles is covered with a large number of calcium carbonate crystals of various shapes, forming a multi-level porous network, which verifies the directional regulation mechanism of microbial metabolism on the active sites on the surface of the microparticles.

[0085] Unmodified recycled concrete powder ( Figure 3 The microstructure exhibits a single, disordered stacked structure, primarily composed of plate-like or blocky particles with diameters of 5–50 μm. The surface is smooth and flat, with sharp edges formed by mechanical fracture. The particles are loosely bound together by physical interlocking and van der Waals forces, and the pore structure is dominated by submicron-sized gaps. High-magnification SEM images show that the plate-like particles lack traces of crystal growth, exhibiting typical amorphous characteristics. XRD full-spectrum fitting indicates a high amorphous phase content, primarily composed of calcium silicate hydrate (CSH) gel and unhydrated cement clinker. This low-roughness, low-specific-surface-area surface characteristic stems from the mechanical energy input during the original concrete crushing process, resulting in the failure to form a secondary mineralization layer after the surface silica-oxygen network fractures, thus limiting the surface chemical activity of the material.

[0086] Microbially modified recycled concrete powder Figure 4 Its surface is covered with a large number of calcium carbonate crystals, forming a three-dimensional network structure composed of spherical, rhombic, and needle-like crystals. The crystals are tightly connected to the surface through edge interlocking and surface bridging, resulting in reduced pore size and increased porosity. Analysis shows that the modified product contains two calcium carbonate crystal forms: calcite and acicular aragonite. The preferential formation of calcite is closely related to the alkaline microenvironment produced by microbial metabolism: urease secreted by Bacillus pasteurellium catalyzes the hydrolysis of urea to produce CO3. 2- Ca dissolved from RCPP 2+ They combine to form thermodynamically stable calcite crystal nuclei.

[0087] Characterization 2, XRD

[0088] This study mainly investigates the phase evolution and crystal form regulation mechanism of recycled concrete powder (i.e., RCPP and MRCPP) before and after microbial modification.

[0089] Phase analysis of recycled concrete powder (RCPP and MRCPP) before and after microbial modification using X-ray diffraction (XRD) revealed the deep reconstruction of the material's crystal structure by microbial metabolism. Figure 5 As shown, the XRD pattern of unmodified recycled concrete powder (RCPP) exhibits broad diffuse peaks and low strength characteristics, while the modified recycled concrete powder (MRCPP) after soaking in a bacterial solution and incubating on a shaker for 3 days shows sharp diffraction peaks in the 30°–40° range, with its strength being more than 2.5 times higher than that of SP, indicating that microbial activity significantly induced crystal rearrangement and the formation of new phases. Based on phase assignment, six phases were detected in MRCPP: Portlandite, Quartz, Calcite, Aragonite, Vaterite, and Gypsum.

[0090] The XRD pattern of unmodified recycled concrete powder (RCPP) exhibits broad peaks in the 2θ = 20°–40° range, indicating that the material is mainly composed of amorphous calcium silicate hydrate gel, with small amounts of β-dicalcium silicate and free calcium hydroxide residues. The characteristic peak intensity of calcium hydroxide reflects the enrichment of alkaline minerals due to incomplete hydration of the original concrete. The weak signal of the quartz phase originates from incompletely reacted siliceous components during aggregate crushing. Overall, the low crystallinity and multiphase hybridity of RCPP stem from the disruption of the long-range ordered structure of the crystals during mechanical crushing, resulting in low density of surface active sites and low chemical stability.

[0091] Microbial modification treatment led to a systematic transformation of the phase composition of recycled concrete powder. The sharp drop in the intensity of the original calcium hydroxide main peak indicates that microorganisms, through urease-catalyzed urea hydrolysis, consumed hydroxide ions, promoting the dissolution of calcium hydroxide (Ca(OH)2) and releasing Ca. 2+ Released Ca 2+ CO3 produced by microbial metabolism 2- The combination induces the formation of a polymorphic calcium carbonate system; as a thermodynamically stable phase, the preferential formation of calcite is directly related to the weakly alkaline environment of the modified system, and the acidic polysaccharides secreted by microorganisms react with Ca through carboxyl groups. 2+Coordination lowers the nucleation energy barrier of calcite crystal faces, promoting preferential crystal growth. The increased intensity of the quartz peak reflects the partial recrystallization of the silicate network caused by microbial activity; the formation of gypsum originates from the bio-oxidation of sulfate impurities in the micronized powder by sulfate-reducing bacteria.

[0092] Characterization 3: Fourier transform infrared spectroscopy

[0093] Fourier transform infrared (FTIR) spectroscopy tests of recycled concrete powders (RCPP and MRCPP) before and after microbial modification, such as... Figure 6 As shown. The unmodified sample (RCPP) at 3402 cm⁻¹ -1 The peak exhibits a broad OH stretching vibration absorption peak, which is attributed to the association of hydroxyl groups in physically adsorbed water molecules and silicate gel. In the microbially modified sample (MRCPP), the peak shifts to lower frequencies, the peak width decreases, and shoulder peak splitting occurs, indicating that the modification process weakens the hydrogen bond association strength of hydroxyl groups through the grafting effect of microbial metabolites.

[0094] The modification process has a particularly significant effect on the regulation of oxygen-containing functional groups. The unmodified sample (RCPP) at 1632 cm⁻¹... -1 The absorption peak at this location corresponds to the HOH bending vibration of adsorbed water and the antisymmetric stretching vibration of the carboxylate group -COO-. However, the absorption peak intensity and peak shape of the microbially modified sample decrease at this position, indicating that the microbial mineralization products partially cover the carboxylate groups. Meanwhile, the microbially modified sample (MRCPP) shows a peak intensity at 1725 cm⁻¹. -1 A new characteristic peak appeared, attributed to the C=O stretching vibration of the ester group -COO-R or amide I band in the extracellular polymeric microorganism. The peak position and intensity confirmed the successful loading of protein-like substances. The most significant modification characteristic was observed in the fingerprint region: the unmodified sample showed a peak at 1048 cm⁻¹. -1 The weak absorption peak at this point corresponds to the Si-O-Si antisymmetric stretching vibration of the silicate framework; after microbial modification, this peak shifts to a lower frequency, reaching 1037 cm⁻¹. -1 Furthermore, the increased strength indicates that the acidic polysaccharides produced by microbial metabolism chemically bond with the silicate surface via etheric COC bonds, forming a stable organic-inorganic hybrid interface. In addition, the microbially modified sample showed improved strength at 1456 cm⁻¹. -1 The weak absorption shoulder peaks observed can be attributed to the in-plane bending vibrations of carbonate groups, which are directly related to the calcium carbonate mineral phase induced by microorganisms. The above comparative analysis revealed that microbial modification significantly altered the surface functional group composition and distribution characteristics of regenerated RCPP powder.

[0095] Characterization 4, Thermogravimetric Analysis

[0096] Thermogravimetric-differential thermogravimetric (DTG) curves are as follows: Figure 7Analysis revealed the differences in thermal decomposition behavior between deionized water treatment (refer to Example 1, but with the bacterial solution replaced by deionized water) and microbial-modified concrete powder in different temperature ranges. By comparing the mass loss rate and decomposition peak characteristics of the materials under the two treatment conditions, the composition evolution and thermal stability regulation mechanism can be systematically analyzed.

[0097] The DTG curves of concrete micropowder treated with deionized water show a significant negative peak in the 0–100℃ range, corresponding to the rapid removal of adsorbed water from the micropowder surface. The mass loss rate is highest during this stage, indicating that physically adsorbed water and weakly bound water molecules within the micropores preferentially escape within this temperature range. When the temperature rises to 100–300℃, the DTG value rebounds and forms a plateau, reflecting the slow release of internal crystalline water or structural water from the silicate gel. Notably, a second sharp negative peak appears at 400℃, its position coinciding with the characteristic decomposition temperature of lead carbonate and its mixture, indicating that residual lead compounds in the original micropowder undergo thermal decomposition during this stage, releasing carbon dioxide gas. Furthermore, the DTG value tends to level off in the 500–700℃ range, suggesting that phase transformation of inorganic minerals or slow oxidation of residual organic matter dominates; the weak negative peak at 700–800℃ may originate from calcium carbonate decomposition or silicate lattice reconstruction. The overall curve did not show a significant oxidation peak, confirming that deionized water treatment effectively inhibited the combustion reaction of carbonaceous components, and the thermal decomposition process was mainly characterized by physical dehydration and chemical bond breaking.

[0098] The DTG curves of microbially modified regenerated micropowder exhibit a more complex multi-stage decomposition characteristic. In the 0–100℃ range, the DTG value is significantly lower than the red line, indicating that the introduction of microbial metabolites significantly increases the mass loss rate in the low-temperature range. In the 100–200℃ range, the DTG value rebounds and tends to stabilize, indicating that the release rate of bound water after modification decreases, possibly related to the blocking effect of microbial mineralization products on the pore structure. Unlike the red line, the blue line does not show a significant metathesis peak in the 200–400℃ range, and its DTG value only fluctuates slightly, indicating that microbial treatment effectively removes residual lead compounds in the regenerated micropowder or transforms them into a form with higher thermal stability. The small negative peak in the 400–500℃ range may correspond to the decomposition of residual organic matter from microbial metabolism, while the significant negative peak in the 600–700℃ range is directly related to the vigorous decomposition of calcium carbonate, and its intensity is stronger than that of the red line, confirming that microbial mineralization significantly increases the relative content of calcium carbonate in the material. The DTG value in the high-temperature region of 700–800℃ rises rapidly, suggesting an accelerated lattice reconstruction rate of the silicate framework. This may be related to the thermal response characteristics of the microbially induced silicate-calcium carbonate interlocking structure.

[0099] The above comparison and mechanism analysis show that microbial modification reconstructs the thermal behavior of microbially modified recycled concrete powder through the following pathways:

[0100] (1) The introduction of microbial metabolites increases mass loss in the low-temperature range, but the pore structure generated by its thermal decomposition optimizes the mass transfer efficiency of subsequent high-temperature reactions.

[0101] (2) The disappearance of the metathesis peak at 200–400℃ indicates that microorganisms convert lead compounds into stable phases through biomineralization, or reduce their thermosensitivity through adsorption-precipitation mechanisms.

[0102] (3) The enhancement of the decomposition peak at 600-700℃ confirms that the amount of calcium carbonate produced by microorganisms is significantly increased, and its thermal decomposition behavior dominates the mass loss in the high-temperature region.

[0103] (4) The rapid change in the mass loss rate at 700–800℃ reflects that the interfacial bonding between microbial mineralization products and silicate matrix enhances the lattice energy, requiring higher thermal energy to trigger structural reconstruction.

[0104] The evolution of the aforementioned thermal decomposition characteristics is highly consistent with the XRD analysis results. No calcium hydroxide decomposition peak was detected in the 400–500℃ range, verifying the conclusion that microbial metabolism consumes hydroxide ions and inhibits the formation of free calcium hydroxide. The intensity difference of the calcium carbonate decomposition peak directly points to the directional regulation of material components by microbial mineralization. The results indicate that microbial modification not only improves the thermal stability of microbially modified recycled concrete powder through component transformation but also optimizes the decomposition pathway through multi-scale structural design, providing a theoretical basis for selecting thermal processing parameters for building solid waste resource products.

[0105] Example 2

[0106] The microbial modified concrete recycled powder (MRCPP) prepared in Example 1 was used as an adsorbent to adsorb Pb(II).

[0107] 2.1 Effect of pH value

[0108] To investigate the effect of initial solution pH on the adsorption performance of microbially modified regenerated powder MRCPP for lead ions.

[0109] This study systematically investigated the regulatory effect of pH value in the range of 2.0–7.0 on the adsorption process under the conditions of fixed initial lead ion concentration of 1000 mg / L, adsorbent dosage of 1000 mg / L, reaction temperature of 25℃ and contact time of 1440 min.

[0110] Experimental results show that the removal efficiency of lead ions by MRCPP exhibits a significant pH-dependent characteristic, but its mechanism of action differs fundamentally from that of conventional adsorbents. When the initial solution pH increases from 2.0 to 5.0, the lead ion removal rate rapidly increases and remains stable at pH ≥ 5.0. This result demonstrates the highly efficient immobilization capacity of MRCPP for lead ions over a wide pH range, with its core driving force stemming from the synergistic effect of multiple mechanisms induced by microbial modification.

[0111] like Figure 8 Analysis shows that under strongly acidic conditions, the adsorption performance of MRCPP for lead ions is significantly limited by the protonation effect and ion competition. At pH 2.0, the high concentration of H+ in the solution... + The adsorption process is suppressed through two pathways: firstly, H... + Secondly, H competes with lead ions for adsorption at active sites on the MRCPP surface, such as carbonate groups and hydroxyl groups, resulting in the occupation of effective adsorption sites; + The erosion of the calcium carbonate mineral phases (calcite and aragonite) on the surface of MRCPP induces partial dissolution of CaCO3, weakening its ability to fix lead ions through ion exchange and surface precipitation. Nevertheless, MRCPP still exhibits a high lead ion removal rate at pH 2.0, significantly higher than unmodified RCPP, attributed to the unique stability of microbially mineralized aragonite under acidic conditions. The high-density suspended oxygen atoms on the surface of aragonite nanoparticles can still capture lead ions through complexation reactions at low pH. As the pH increases to 3.0–5.0, the H+ in the solution… + As the concentration decreases, the competition for adsorption sites due to the protonation effect weakens, and the lead ion removal rate of MRCPP rapidly increases. The dominant mechanism at this stage gradually shifts from surface complexation to ion exchange and chemical precipitation. Simultaneously, when the solution pH approaches the critical point of the solubility product of Pb(OH)₂, some lead ions undergo hydroxylation reactions on the MRCPP surface to generate Pb(OH). + The binding energy of MRCPP to carbonate groups is significantly higher than that of free lead ions, thus enhancing the adsorption driving force. At pH 5.0, the adsorption capacity of MRCPP for lead ions reaches its peak. At this point, the complexation of aragonite, the ion exchange of calcite, and the precipitation of trace amounts of PbCO3 form a multi-level fixed network, maximizing the adsorption efficiency. When the solution pH > 5.0, although thermodynamically favorable for the hydrolysis and precipitation of lead ions, the lead ion removal rate of MRCPP does not increase significantly. Based on the above analysis, this study selected pH 5.0 as the optimization condition for subsequent experiments.

[0112] 2.2 Adsorption Mechanism

[0113] Figure 9 Pb was displayed 2+The final pH of the solution changed from acidic and neutral to alkaline, which can be attributed to the hydrolysis of calcium carbonate and silica gel in MRCPP. When the initial pH was 2.0, the final pH rose to 5.24; as the initial pH increased from 3.0 to 7.0, the final pH stabilized in the range of 6.35–6.40. This indicates that MRCPP significantly regulates the chemical environment of the solution through calcium carbonate dissolution and silica gel hydrolysis. This buffering effect originates from the synergistic effect of multiphase minerals in MRCPP: calcite (CaCO3) continuously dissolves under acidic conditions, releasing carbonate ions, neutralizing H+, and generating HCO3-. - Buffer pairs; silicate gel Si-O-Si consumes protons through surface hydroxylation, and its hydrolysis product Si-OH is further deprotonated to form negatively charged Si-O- groups, jointly driving the solution pH towards neutral. Under low initial pH conditions of 2.0–3.0, the hydroxylation reaction of silica gel is dominant. At this time, the Si-O-Si groups on the MRCPP surface react with H... + The formation of Si-OH groups imparts a positive charge to the material surface, creating electrostatic repulsion with lead ions and inhibiting ion exchange and surface complexation reactions. However, the nanoscale protrusions of aragonite in MRCPP weaken electrostatic repulsion through steric hindrance, and the suspended oxygen atoms on its surface form strong coordination bonds with lead ions, resulting in a relatively high lead ion removal rate even at low pH. The simultaneous dissolution of calcium carbonate not only alleviates the protonation effect's occupation of adsorption sites but also releases Ca... 2+ It participates in ion exchange, further enhancing the adsorption process. When the initial pH is >5.0, the buffering capacity of MRCPP tends to saturate, and eventually the pH stabilizes, and the silica gel is completely deprotonated.

[0114] 2.3 Effect of Adsorption Temperature

[0115] Analysis of the effect of temperature on Pb using the Langmuir model 2+ The effect of adsorption performance.

[0116] Langmuir adsorption isotherms at 25℃, 35℃ and 45℃ were constructed according to formula (2), as follows: Figure 10 As shown, the regulation of temperature gradient on the thermodynamic behavior of lead ion adsorption in microbially modified regenerated powder MRCPP is revealed.

[0117]

[0118] In the above formula: Q e Q represents the actual adsorption amount. m K represents the maximum adsorption capacity of metal ions. L The Langmuir constant related to the binding energy (L / mg); C e This represents the initial lead ion concentration.

[0119] Within the initial lead nitrate concentration range of 50–2000 mg / L, all three isotherms exhibited typical monolayer adsorption characteristics, but the saturation adsorption capacity and adsorption intensity decreased significantly with increasing temperature. The saturation adsorption capacity of the 25℃ isotherm was higher than that of the 35℃ and 45℃ isotherms, and C… e The actual adsorption capacity Q at 2000 mg / L e The concentration stabilized at 992.1 mg / L, indicating that the adsorption site utilization efficiency and mass transfer kinetics were optimally matched at this temperature. This temperature dependence stems from the dual effects of microbial activity regulation and mineral phase stability: at 25°C, the urease activity produced by Bacillus pasteurization maintained its peak value, and the carbonate ions generated by its catalytic urea hydrolysis formed nanoscale aragonite with the calcium ions released from the regenerated micropowder, strengthening lead ion fixation through an "ion bridging-lattice substitution" mechanism; however, when the temperature rose above 35°C, the thermal denaturation of the extracellular polymeric substances of the microorganisms led to a decrease in the density of CaCO3 nucleation sites, while the urease activity decreased, weakening the gain effect of biomineralization on adsorption capacity.

[0120] The Langmuir model parameters further quantified the influence mechanism of temperature on the adsorption process. The adsorption strength coefficient at 25℃ was significantly higher than that at 35℃ and 45℃, indicating that lower temperatures are more conducive to the specific binding of lead ions to adsorption sites. The selection of 25℃ as the optimal temperature was based not only on maximizing adsorption capacity but also on its comprehensive advantages in engineering applicability and stability. In dynamic adsorption experiments, when the MRCPP dosage increased from 50 mg / L to 2000 mg / L, the unit adsorption capacity increase rate of the 25℃ group was significantly higher than that of the 35℃ and 45℃ groups, indicating higher adsorbent utilization at this temperature. Furthermore, after five adsorption-desorption cycles, the capacity retention rate of the 25℃-modified MRCPP remained high, while the 35℃ and 45℃ samples showed a slight decrease. This is related to the difference in mineral phase crystallinity; the crystallinity index of the spheroidal aragonite generated at 25℃ was higher than that at 45℃, and the reduction in lattice defects enhanced the intercalation stability of lead ions. Finally, calculations showed that at 25℃, Pb... 2+ The maximum adsorption capacity is 992.1 mg / L.

[0121] 2.4 Adsorption Kinetics Analysis

[0122] The adsorption process of lead ions was quantitatively analyzed using the kinetic model formula (3). Figure 11 The study revealed the synergistic regulation of adsorption time and initial concentration on the adsorption rate of MRCPP in microbially modified regenerated powder.

[0123]

[0124] In the above formula: t is the adsorption time; Q t K is the adsorption amount at time t; k2 is the rate constant of the second-order kinetic model; Qe The equilibrium adsorption amount is the amount of Pb(II) adsorbed per unit mass of adsorbent when adsorption reaches equilibrium.

[0125] The equilibrium adsorption capacities of lead nitrate solutions with initial concentrations of 1000 mg / L, 500 mg / L, and 250 mg / L were 982 mg / L, 480 mg / L, and 220 mg / L, respectively. The adsorption times required to reach 90% equilibrium adsorption capacity were 125 min, 210 min, and 315 min, respectively, exhibiting a significant positive correlation between concentration and rate. The fitting results showed that the rate constant was highest in the 1000 mg / L group, followed by the 500 mg / L group, and lowest in the 250 mg / L group, indicating that high concentration systems significantly improved the chemisorption kinetic efficiency by enhancing the competition effect of surface sites.

[0126] The kinetic behavior during the mid-to-late adsorption stage (20-200 min) exhibited significant heterogeneity. For the 1000 mg / L group, the adsorption rate decreased compared to the initial stage, but the fitted curve still showed a high degree of agreement with the experimental data, indicating that the dominant mechanism in this stage was the gradual occupancy of chemisorption sites rather than physical diffusion. In contrast, the 250 mg / L group showed that most of the adsorption increment in this stage came from intraparticle diffusion, and its kinetic curve deviated significantly from the model compared to the 1000 mg / L group, reflecting the coupling effect of physical and chemisorption in the low-concentration system. The adsorption behavior in the equilibrium stage showed a concentration-dependent hysteresis effect. In the equilibrium state, the interplanar spacing of aragonite crystals in MRCPP expanded, and its lattice distortion energy provided energy compensation for the lattice solid solution of lead ions, giving the chemisorption process thermodynamic spontaneity. In addition, the hydroxylation network of the silica gel maintained the surface negative charge density through dynamic proton exchange equilibrium, providing electrostatic driving force for continuous adsorption. This kinetic model is based on the theory of chemisorption and correlates the adsorption rate with the square of the number of unoccupied active sites, which is closer to the synergistic effect of multi-step reactions in the actual adsorption process. Its theoretical framework is more in line with the chemical nature of MRCPP adsorption of lead ions.

[0127] The above results show that the adsorption capacity of MRCPP for Pb(II) increases with increasing pH, reaching the optimal effect at pH = 5.0; the theoretical maximum adsorption capacity of MRCPP at 25℃ is 992.1 mg / L, significantly higher than that of unmodified RCPP. This also indicates that the adsorption of Pb(II) by the microbially modified recycled concrete powder of this invention is related to Ca... 2+ / Pb 2+ Ion exchange, silanol complexation, and lead carbonate precipitation work together.

[0128] It should be noted that the above performance tests were conducted on the microbial modified concrete recycled micropowder prepared in Example 1 (i.e., prepared under the preferred process). When the raw material ratio (the mass ratio of concrete micropowder to urea in 1 mL of bacterial solution is (1-3) mg: (10-30) mg) and preparation parameters in Example 1 were replaced, the microbial modified concrete recycled micropowder prepared also showed the same or similar performance and was used for the efficient adsorption of Pb(II).

[0129] The above are several preferred embodiments of the preparation method of the present invention, but they should not be regarded as limitations on the technical solutions protected by the present invention. Any alternative solutions obtained by those skilled in the art based on the technical ideas of the present invention without creative labor should fall within the protection scope of the present invention.

Claims

1. The application of microbially modified recycled concrete powder as an adsorbent in Pb(II) adsorption, characterized in that, The preparation method of microbially modified recycled concrete powder includes the following steps: S1, Concrete Pretreatment The concrete is sequentially processed through impurity removal, crushing, screening, and drying to obtain recycled concrete powder. S2, Microbial Activation Bacillus pasteurellii was selected as the functional strain, and bacterial culture was obtained by culturing in a culture medium. S3, mineralization modification After mixing concrete micropowder with bacterial solution, urea is added and stirred evenly to form a suspension system. The reaction ends when the conductivity of the suspension system decreases at a rate of <5μS / cm·h. Then, the microbial modified concrete recycled micropowder is obtained by centrifugation and drying. In step S3, the mass ratio of concrete powder to urea in each 1 mL of bacterial solution is (1~3) mg: (10~30) mg; Microbial modified concrete recycled powder is a three-dimensional network structure composed of spherical crystals, rhombic crystals and needle-like crystals; the microbial modified concrete recycled powder contains six phases: calcium hydroxide, quartz, calcite, aragonite, spheroidal aragonite and gypsum. Microbial modified concrete recycled powder through Ca 2+ / Pb 2+ Ion exchange, silanol complexation, and lead carbonate precipitation work together to improve the adsorption efficiency of Pb(II).

2. The application according to claim 1, characterized in that, In step S1, crushing is performed by first crushing to a particle size <50mm, then ball milling to a particle size <1mm; the particle size after sieving is <100μm; and drying is performed at 105±5℃ for 24h.

3. The application according to claim 1, characterized in that, In step S2, the cultivation conditions are: 24-48 hours at 30°C, and the OD600 value at the end of the cultivation is 0.10-0.

20.

4. The application according to claim 1, characterized in that, When used, the initial concentration of Pb(II) was 1000 mg / L, pH=5.0±0.1, the amount of adsorbent was 1.0 g / L, the adsorption temperature was 25℃, and the maximum adsorption capacity was 992.1 mg / L.

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