Induced Carbonate Precipitation Research Articles

CT image-based simulation of microbially induced carbonate precipitation

Soil improvement efforts occasionally negatively impact the delicate balance of the natural environment and disrupt ecosystems. Thus, adopting ecologically sensitive techniques that can harmoniously safeguard the Earth is imperative. Recently, researchers have focused on microbially induced carbonate precipitation (MICP), an eco-friendly soil enhancement method that fosters increased interparticle cohesion and augments the mechanical strength of soil. The spatial distribution of calcium carbonate precipitation in MICP-treated soil can be observed using scanning electron microscopy and X-ray computed tomography (CT). However, since this precipitation occurs in the microscopic region, it cannot be directly observed over time. Therefore, in this study, we propose a simulation technique to replicate the MICP process using a voxel dataset obtained via X-ray CT analysis. The calculated patterns of calcium carbonate were distributed on the soil particles in the same manner as the spatial precipitation observed in the experiments. Notably, some precipitates bridged the soil particles, indicating that the proposed technique could morphologically estimate the calcium carbonate distribution through MICP. Evidently, the proposed technique could accurately simulate MICP phenomena. Furthermore, the results showed that the proposed technique can effectively express a multidiscliplinary phenomenon. Therefore, the study can inspire further studies that employ such techniques to investigate MICP.

Microscale insights into enzyme-induced carbonate precipitation in rock-based microfluidic chips

Biomineralization technology shows promise for sealing subsurface fractures, but understanding its microscale mechanisms in real rock fractures remains incomplete. This study utilized a microfluidic chip incorporating real rock slices to conduct enzymatically induced carbonate precipitation (EICP) experiments using one-phase continuous injection strategy. Real-time observations revealed gray flocs forming and clustering into aggregates susceptible to transport by flow. CaCO₃ crystals formed on rock and PDMS surfaces effectively filled and bridged fractures, leading to a significant pressure drop. Rough surfaces can provide additional sites for solute attachment and CaCO3 heterogeneous nucleation. High velocities and small apertures generally promoted floc formation and reduced crystal growth. Precipitation content gradually increased with a decreasing rate. Lower estimated precipitation efficiency was obtained in smaller, high-flow fractures. Precipitates on rock interfaces induced eddies and significant pressure drops within narrow pore throats. Crystal growth displayed a two-stage development: an initial increase followed by a decrease, varying across different facets (the surfaces or orientations of the growing crystals). Growth competition will occur when two or more neighboring crystals come into contact with diverse grain orientations. The findings provide valuable microscale insights into microscale processes governing EICP within real-rock fractures, contributing to evaluate its efficacy in subsurface fracture sealing applications.

Enhanced steel corrosion inhibition through microbially induced carbonate precipitation with facultative anaerobic denitrifying bacterium

Denitrification processes are increasingly studied as a promising alternative to ureolytic microbially induced carbonate precipitation (MICP). This study investigates the capabilities of the newly isolated denitrifying bacterium, Stutzerimonas stutzeri CF3, in promoting calcium carbonate precipitation and enhancing steel corrosion resistance under both aerobic and anaerobic conditions. The facultative anaerobe was tested across a range of environmental parameters including pH levels (7.5–11.5), C/N ratios (5−15), NaCl salinity (0–5 %), and Ca²⁺ concentrations (0–30 mmol), to determine its adaptability and effectiveness in precipitating calcium carbonate. Our findings reveal that S. stutzeri CF3 not only survives but thrives under extreme conditions, demonstrating significant nitrate removal and robust calcium carbonate precipitation, particularly in high salinity and variable pH environments. Furthermore, the study examines the implications of S. stutzeri CF3 on steel corrosion, particularly Q235 steel, using Tafel polarization techniques, demonstrating enhanced corrosion resistance. These results underscore the dual utility of S. stutzeri CF3 in microbial self-healing concrete applications, pointing to its potential to improve the durability and integrity of construction materials by leveraging its versatile metabolic pathways.

Effects of urease and cementing solution concentrations on micro-scale enzymatic mineralisation characteristics

Enzymatically induced carbonate precipitation holds significant promise in geotechnical engineering. The concentrations of urease enzyme and cementing solution play vital roles in precipitation behaviours under distinct injection strategies. In situ microscale experiments, conducted in S-shaped microchips, were aimed at exploring precipitation distribution characteristics and micro-clogging effects due to biological precipitation. In the one-phase continuous injection methods, elevated urease concentrations correlated with increased amorphous calcium carbonate formation and more heterogeneous distributions. Conversely, lower cementing solution concentrations produced larger, fewer crystals and more uniform distributions. Higher urease improved efficiency but increased cost, while lower cementing solution concentrations displayed efficient performance. Permeability reduction exhibited a power-law relationship with the precipitation area fraction. In the two-phase staged injection method, elevated urease concentrations fostered more regularly shaped crystals. Higher calcium ion concentrations could inhibit ureolysis rate, reducing precipitates. Higher urease concentrations proved beneficial in improving efficiencies. Permeability exhibited a marginal decrease initially, followed by a significant decline as the precipitation area fraction increased. The results offer microscale insights into concentration effects, aiding the understanding of upscaling mechanisms and numerical simulations.

A pore-scale study of fracture sealing through enzymatically-induced carbonate precipitation (EICP) method demonstrates its potential for CO2 storage management

Geological fractures are mechanical breaks in subsurface rock volumes that provide important subsurface flow pathways. However, the presence of fractures can cause unwanted challenges, such as gas leakage through fractured caprocks, which must be addressed. In this study, the dynamics of enzymatically induced carbonate precipitation in rock fractures and their subsequent influence on CO2 leakage were investigated from a pore-scale perspective for the first time. This was achieved through real-time monitoring of the injection of the solution into a rock-microfluidic flow cell using optical and scanning electron microscopy. It was revealed that the main growth dynamics occur during the first three injection cycles, with growth continuing until the fracture aperture is fully closed in the 6th cycle. Based on the flow simulation, a significant reduction of up to 25% in the CO2 conductivity of the original fracture is expected even after the first treatment cycle. Future studies are suggested to explore different resolutions, testing conditions, and to conduct 3-dimensional investigations of the growth dynamics.

Mechanical properties and stability of zinc-contaminated red clay cured by MICP synergistically activated MgO

Microbially Induced Carbonate Precipitation (MICP) technology offers an innovative approach for the solidification and stabilization of heavy metal-contaminated soils; However, the mechanical strength and long-term stability of this remediation method have not been thoroughly investigated. This study introduces an innovative curing and stabilization technique using MICP-activated MgO to address the geotechnical challenges posed by zinc ion-contaminated soils. To investigate the effect of zinc ions on soil and the optimal efficacy of MICP-activated MgO in curing zinc contamination, experiments were conducted on zinc-contaminated soils with varying zinc ion concentrations (0.05%, 0.1%, 0.5%, 1.0%), dry densities (1.35, 1.4, 1.45, 1.5g/cm³), and activated MgO admixtures (1%, 2%, 5%, 10%). The effectiveness of MICP-activated MgO was evaluated through macroscopic analysis and stability tests, including unconfined compressive strength tests, direct shear tests, and the Toxicity Characteristic Leaching Procedure (TCLP). The results indicated that zinc ions disrupted soil particle cementation, enlarged inter-particle pores, and significantly reduced both unconfined compressive strength and shear strength. The optimal dosage of MICP-activated MgO for curing zinc-contaminated soil was determined to be 10%, resulting in an unconfined compressive strength of 1.196MPa and a Zn2+ leaching concentration of 0.1414mg/L. The combined actions of MICP-activated MgO facilitated the formation of alkaline magnesium carbonate, calcium carbonate, and magnesium hydroxide. These compounds filled the inter-particle pores of zinc-contaminated soil, encapsulating and co-precipitating zinc ions, thereby enhancing the soil's strength and stability. These findings establish a theoretical foundation for the engineering application of MICP-activated MgO in the remediation of zinc-contaminated soils.

Effects of different Mg/Ca molar ratio on the formation of carbonate minerals in microbially induced carbonate precipitation (MICP) process

Traditional MICP technology has been extensively applied to improve soil properties and solidify heavy metal contaminated soil. However, the traditional product performance of calcite is far less than that of huntite, dolomite, and other carbonate minerals. Therefore, the soil strength and environmental safety after curing cannot reach the safety index. This study has examined the distribution of carbonate minerals induced by microorganisms under different Mg/Ca ratio. Compared with the sample with 0 Mg/Ca content, the unconfined compressive strength (UCS) can be increased by 1–5 times by increasing the content. By X-ray diffraction (XRD) and thermogravimetric analysis (TGA), the contents of different carbonate minerals under different Mg/Ca content were determined semi-quantitatively. The microscopic results have also shown that the introduction of microorganisms can provide nucleation sites for the synthesis of dolomite and huntite. MICP experiment coupled with Quantum ESPRESSO calculations revealed the mechanism of microbial influence on the formation of carbonate minerals under different Mg/Ca conditions through first principles calculations and nucleation kinetics. These findings advance our understanding of the reaction mechanisms and pathways of biogenic precipitation of carbonate minerals, and provide insights into the artificial quantitative synthesis of dolomite.

Different calcium sources affect the products and sites of mineralized Cr(VI) by microbially induced carbonate precipitation

Microbially induced carbonate precipitation (MICP) is a common biomineralization method, which is often used for remediation of heavy metal pollution such as hexavalent chromium (Cr(VI)) in recent years. Calcium sources are essential for the MICP process. This study investigated the potential of MICP technology for Cr(VI) remediation under the influence of three calcium sources (CaCl2, Ca(CH3COO)2, Ca(C6H11O7)2). The results indicated that CaCl2 was the most efficient in the mineralization of Cr(VI), and Ca(C6H11O7)2 could significantly promote Cr(VI) reduction. The addition of different calcium sources all promoted the urease activity of Sporosarcina saromensis W5, in which the CaCl2 group showed higher urease activity at the same Ca2+ concentration. Besides, with CaCl2, Ca(CH3COO)2 and Ca(C6H11O7)2 treatments, the final fraction of Cr species (Cr(VI), reduced Cr(III) and organic Cr(III)-complexes) were mainly converted to the carbonate-bound, cytoplasm and cell membrane state, respectively. Furthermore, the characterization results revealed that three calcium sources could co-precipitate with Cr species to produce Ca10Cr6O24(CO3), and calcite and vaterite were present in the CaCl2 and Ca(CH3COO)2 groups, while only calcite was present in the Ca(C6H11O7)2 group. Overall, this study contributes to the optimization of MICP-mediated remediation of heavy metal contaminated soil. CaCl2 was the more suitable calcium source than the other two for the application of MICP technology in the Cr(VI) reduction and mineralization.

Montmorillonite-coupled microbially induced carbonate precipitation (MICP) enhanced contaminant removal and carbon capture in cyanide tailings

Microbial induced carbonate precipitation (MICP) technology is an effective method for immobilization of heavy metals in tailings. However, how to sustainably improve the removal of contaminants and the carbon capture capacity of tailings is a current concern. In this study, montmorillonite-coupled MICP (Mt-MICP) process is proposed to solidify cyanide tailings by improving mineralization properties, heavy metal and cyanide removal, and carbon capture. The results showed that Mt -MICP increased the amount of mineralized precipitation by 0.16–1.33 times; Total cyanide (T-CN) and free cyanide (F-CN) concentrations were reduced by 82.00 and 97.14 %, respectively; Cr, Zn, Cu and Pb leaching concentrations were reduced by 87.18, 42.85, 60.56 and 88.79 %, respectively. Characterizations results such as X-computed tomography (X-CT) confirmed that Mt enhanced the uniformity of the bio-cementation. Furthermore, the Mt-MICP process increased CO2 capture from tailings by 27.15∼34.55 %. Density Functional Theory (DFT) and thermogravimetry (TG) showed that Mt increased the adsorption energy of tailings for CO2 and was converted to CaCO3 by urea catalysis. This work provided new insights into the harmless treatment of CT and microbial carbon capture.

Effects of biochar and magnesium oxide on cadmium immobilized by microbially induced carbonate: Mobilization or immobilization in alkaline agricultural soils?

Microbially induced carbonate precipitation (MICP) is a promising technique for remediating heavy metal-contaminated soils. However, the effectiveness of MICP in immobilizing Cd in alkaline calcareous soils, especially when applied in agricultural soils, remains unclear. Biochar and magnesium oxide are two environmentally friendly passivating materials, and there are few reports on the combined application of MICP with passivating materials for remediating heavy metal-contaminated soils. Additionally, the number of treatments with MICP cement and the concentration of calcium chloride during the MICP process can both affect the effectiveness of heavy metal immobilization by MICP. Therefore, we conducted MICP and MICP-biochar-magnesium oxide treatments on agricultural soils collected from Baiyin, Gansu Province (pH = 8.62), and analyzed the effects of the number of treatments with cement and the concentration of calcium chloride on the immobilization of Cd by MICP and combined treatments. The results showed that early-stage MICP could immobilize exchangeable cadmium and increase the residual cadmium content, especially with high-concentration calcium chloride MICP treatment. However, in the later stage, soil nitrification and exchange processes led to the dissolution of carbonate-bound cadmium and cadmium activation. The fixing effect of MICP influence whether the MICP-MgO-biochar is superior to the MgO-biochar. Four treatments with cement were more effective than single treatment in MICP-biochar-magnesium oxide treatment, and the MICP-biochar-magnesium oxide treatment with four treatments was the most effective, with passivation rates of 40.7% and 46.6% for exchangeable cadmium and bioavailable cadmium, respectively. However, attention should be paid to the increase in soil salinity. The main mechanism of MICP-magnesium oxide-biochar treatment in immobilizing cadmium was the formation of Cd(OH)2, followed by the formation of cadmium carbonate.

Mechanical properties and repairing mechanism of recycled cement stabilized macadam for road base based on microbial induced carbonate precipitation technology

The utilization of recycled coarse aggregate derived from construction and demolition waste (CDW) in the construction of road cement stabilized macadam base could effectively alleviate the shortage of natural sand and aggregate resources. To explore the repairing effect of microbial induced carbonate precipitation (MICP) on recycled cement stabilized macadam (RCSM), the physical, mechanical, and microscopic properties of recycled concrete aggregate under different precipitation precursor concentrations were researched in this paper. The mechanical properties of RCSM with varying contents of recycled concrete aggregate were analyzed before and after repairing. Based on scanning electron microscopy (SEM) and mercury intrusion porosimeter (MIP) tests, the microstructure and pore structure parameters of recycled concrete aggregate were explored, and the repair mechanism of MICP on RCSM was revealed via the performance analysis of recycled concrete aggregate and RCSM. The results show that MICP could effectively reduce the water absorption of recycled concrete aggregates, while simultaneously enhancing its apparent density and crushing resistance. In a certain range, the higher the concentration of the precipitation precursor, the better the repairing effect on the performances of recycled concrete aggregates. However, while the concentration of urea or calcium source concentration exceeding 1.0 mol/L, the activity of urease would start to be inhibited. The unconfined compressive strength of RCSM after MICP repairing could be increased by 22.7 % with a maximum extent compared with that before repair, while the maximum increase of indirect tension strength and flexural tensile strength was 15 % and 8.2 %, respectively. The biological CaCO3 generated by MICP reaction could fill the micro-cracks and pores of the recycled concrete aggregate efficaciously. Besides, it could also optimize the pore parameters and pore size distribution parameters, and enhance the adhesive strength of interfacial transition zone (ITZ) between cement and recycled concrete aggregates, which could improve the mechanical properties of RCSM.

Synergistic enhancement of cadmium immobilization and soil fertility through biochar and artificial humic acid-assisted microbial-induced calcium carbonate precipitation

Microbially induced carbonate precipitation (MICP) is emerging as a favorable alternative to traditional soil remediation techniques for heavy metals, primarily due to its environmental friendliness. However, a significant challenge in using MICP for farmland is not only to immobilize heavy metals but also to concurrently enhance soil fertility. This study explores the innovative combination of artificial humic acid (A-HA), biochar (BC), and Sporosarcina pasteurii (S. pasteurii) to mitigate the bioavailability of cadmium (Cd) in contaminated agricultural soils through MICP. X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses revealed that the integration of BC and A-HA significantly enhances Cd immobilization efficiency by co-precipitating with CaCO3. Moreover, this treatment also improved soil fertility and ecological functions, as evidenced by increases in total nitrogen (TN, 9.0–78.2 %), alkaline hydrolysis nitrogen (AN, 259.7–635.5 %), soil organic matter (SOM, 18.1–27.9 %), total organic carbon (TOC, 43.8–48.8 %), dissolved organic carbon (DOC, 36.0–88.4 %) and available potassium (AK, 176.2–193.3 %). Additionally, the relative abundance of dominant phyla such as Proteobacteria and Firmicutes significantly increased with the introduction of BC and A-HA in MICP. Consequently, the integration of BC and A-HA with MICP offers a promising solution for remediating Cd-contaminated agricultural soil and synergistically enhancing soil fertility.

Long‐Term Performance on Drought Mitigation of Soil Slope Through Bio‐Approach of MICP: Evidence and Insight from Both Field and Laboratory Tests

AbstractDrought is a serious global environmental issue that causes water resource scarcity and threatens agriculture and food supplements. This study aims to investigate the long‐term performance of an eco‐friendly technique‐microbial induced carbonate precipitation (MICP) on drought mitigation at field and laboratory scales. Seven in‐situ slopes treated with different MICP rounds and cementation solution concentrations were subjected to 16‐month weathering. Tests were conducted to evaluate the evaporation characteristics, water retention capacity, and CaCO3 distribution. Laboratory soil samples were further prepared to provide evidence related to underlying weathering mechanisms. The results show that MICP has a time‐dependent performance on drought mitigation. After MICP treatment, soil performs a remarkable evaporation suppression ability and the evaporation rate can decrease by 50%. This is attributed to the soluble salts which increase soil water retention capability and dense hard crust which inhibits water vapor migration into the atmosphere. However, the soluble salts and crust are sensitive to weathering thus leading to degradation of MICP. Suffering 16‐month weathering, the MICP‐induced CaCO3 decreases by more than 60%. The evaporation rate of soil increases with MICP rounds and cementation solution concentrations and can reach nearly two times of untreated soil. MICP‐treated field soil exhibits weaker water retention capacity than untreated soil because MICP alters soil microstructure which expands macropores and decreases volume of micropores. Connected macropores act as favorable evaporation channels and accelerate evaporation. To ensure MICP long‐term effects, periodical treatments are necessary. The most effective MICP treatment scheme is four to six treatment rounds and 1.0 M cementation solution.

Effect of sand minerals on microbially induced carbonate precipitation by denitrification

Soil improvement techniques utilizing the metabolic functions of microorganisms, including microbially induced carbonate precipitation (MICP), have been extensively researched over the past few decades as part of bio-inspired geotechnical engineering research. Given that metabolic reactions in microorganisms produce carbonate minerals, an enhanced understanding of microbial interaction with soils could improve the effectiveness of MICP as a soil improvement technique. Therefore, this study investigated the effects of sands on MICP by denitrification to employ MICP for geotechnical soil improvement. Under the coexistence of natural sand and artificial silica sand, nitrate-reducing bacteria were cultured in a mixed liquid medium with nitrate, acetate, and calcium ions at 37 °C. Nitrate reduction occurred only in the presence of natural sand. However, the lack of chemical weathering of the composed minerals likely prevented the progress of bacterial growth and nitrate reduction in artificial silica sands. For natural sand, artificial chemical weathering by acid wash and ferrihydrite coating of the sand improved bacterial growth and accelerated nitrate reduction. The calcium carbonate formation induced by denitrification was also influenced by the state of the minerals in the soil and the nitrate reduction rate. The observed MICP enhancement is due to the involvement of coexisting secondary minerals like ferrihydrite with large specific surface areas and surface charges, which may improve the reaction efficiency by serving as adsorbents for bacteria and electron donors and acceptors in the solid phases, thereby promoting the precipitation and crystallization of calcium carbonate on the surfaces. This crystal formation in the minerals provides valuable insights for improving sand solidification via MICP. Considering the interactions between the target soil and microorganisms is essential to improving MICP processes for ground improvement.

Bacterial activity and cementation pattern in biostimulated MICP-treated sand-bentonite mixtures

The application of microbially induced carbonate precipitation (MICP) in clayey soils has attracted much attention, and many studies used clay as an additive to enhance microbial mineralization efficiency in sandy soils. Within the sand-clay-bacteria-calcite system, the property and content of clay play crucial roles in affecting bacterial growth and calcite formation. More important, bentonite is particularly sensitive to changes in the geochemical environment. In this study, the sand-bentonite mixtures were treated by biostimulated MICP, aiming to provide insights into the behavior of this system. The bacterial activity and cementation pattern at different bentonite contents were evaluated through a series of tests such as enrichment tests, unconfined compressive strength (UCS) tests, cementation content measurements, mercury intrusion porosimetry (MIP) tests, scanning electron microscopy (SEM) observations, and energy dispersive X-ray spectroscopy (EDS) analyses. The findings showed that the bentonite presence promoted the enrichment of indigenous ureolytic bacteria, with lower bentonite levels enhancing ureolytic activity. Macroscopic and microscopic characterization indicated that the bentonite-coating sand structure was more conducive to the formation of large-sized calcite crystals capable of cementing soil particles compared to sand-supported and bentonite-supported structures. Additionally, excessive calcium ions (Ca2+) concentrations in the cementitious solution would lead to predominant calcite deposition on soil particle surfaces, contributing minimally to strength improvement.

Molecular and geochemical basis of microbially induced carbonate precipitation for treating acid mine drainage: The case of a novel Sporosarcina genomospecies from mine tailings

Microbially induced carbonate precipitation (MICP) immobilizes toxic metals and reduces their bioavailability in aqueous systems. However, its application in the treatment of acid mine drainage (AMD) is poorly understood. In this study, the genomes of Sporosarcina sp. UB5 and UB10 were sequenced. Urease, carbonic anhydrases, and metal resistance genes were identified and enzymatic assays were performed for their validation. The geochemical mechanism of precipitation in AMD was elucidated through geo-mineralogical analysis. Sporosarcina sp. UB5 was shown to be a new genomospecies, with an average nucleotide identity < 95 % (ANI) and DNA-DNA hybridization < 70 % (DDH) whereas UB10 is close to S. pasteurii. UB5 contained two urease operons, whereas only one was identified in UB10. The ureolytic activities of UB5 and UB10 were 122.67 ± 15.74 and 131.70 ± 14.35 mM NH4+ min−1, respectively. Both strains feature several carbonic anhydrases of the α, β, or γ families, which catalyzed the precipitation of CaCO3. Only Sporosarcina sp. UB5 was able to immobilize metals and neutralize AMD. Geo-mineralogical analyses revealed that UB5 directly immobilized Fe (1–23 %), Mn (0.65–1.33 %) and Zn (0.8–3 %) in AMD via MICP and indirectly through adsorption to calcite and binding to bacterial cell walls. The MICP-treated AMD exhibited high removal rates (>67 %) for Ag, Al, As, Ca, Cd, Co, Cu, Fe, Mn, Pb, and Zn, and a removal rate of 15 % for Mg. This study provides new insights into the MICP process and its applications to AMD treatment using autochthonous strains.

Comparative study on the effect of SRB and Sporosarcina pasteurii on the MICP cementation and solidification of lead–zinc tailings

The production of tailings sand due to mining and smelting activities is one of the reasons for the accelerated environmental pollution caused by heavy metals, drawing social attention to the management of tailings sand. Microbially induced carbonate precipitation (MICP) is an environmentally friendly soil remediation technique that is gradually becoming the preferred method for soil stabilisation and heavy metal pollution control. To address the issues of heavy metal pollution release and the loose particle structure of lead–zinc tailings sand (LZTS), this study employs a layered MICP approach. The solidification effects of two typical mineralising bacteria, sulfate-reducing bacteria (SRB) and Sporosarcina pasteurii, on LZTS, were compared for the first time. The results show that the maximum unconfined compressive strength (UCS) of SRB cemented solidified lead–zinc tailings sand (SRB-CS-LZTS) specimens is 0.22 MPa, while that of S. pasteurii cemented solidified lead–zinc tailings sand (SP-CS-LZTS) specimens is 0.95 MPa. Compared with the UCS of SRB-CS-LZTS, the UCS of SP-CS-LZTS increased by 3.32 times. The effect of S. pasteurii on the improvement of UCS and immobilisation of heavy metal ions was greater than that of SRB. The immobilisation effect of SRB on SO42- in the LZTS was better than that of S. pasteurii. Compared with SRB, the biological CaCO3 formed by S. pasteurii exhibited stronger adhesion and was more suitable for the cementation and solidification of LZTS. This study uses MICP technology to treat LZTS, aligning with the green environmental concept and providing a reference for the bioremediation of multiple heavy metals in tailing areas.

Improving the thermal-mechanical performance of bio-treated backfill materials by addition of magnetic iron oxide nanoparticles (nano-Fe3O4)

The thermal conductivity of backfill materials directly affects the heat transfer efficiency between energy geo-structures and the surrounding stratum. Microbially induced carbonate precipitation (MICP) possesses great potential for improving the thermal conductivity of backfill materials. Magnetic iron oxide nanoparticles (i.e., nano-Fe3O4) have been proven to enhance bacterial biochemical activity by altering the permeability of bacterial biofilms, thus potentially improving the MICP process. It was supposed to enhance the thermal conductivity of backfill materials, allowing for applying energy geo-structures in arid environments. In this study, MICP in a solution environment was conducted to analyze bacterial urease activity and morphology of precipitation at varying nano-Fe3O4 contents. Additionally, sand columns treated with MICP and different nano-Fe3O4 contents were performed to obtain the thermal conductivity and unconfined compressive strength (UCS) through the transient plane source (TPS) method and uniaxial compression (UC) experiment. The mineral type, precipitation morphology, and microstructure were identified using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The mechanism of the effect of nano-Fe3O4 on bacterial urease activity and thermal-mechanical behaviors was also discussed. The results indicated that the nano-Fe3O4 could enhance bacterial urease activity and promote vaterite precipitation in the solution environment. Conversely, when applied to MICP-treated sand, nano-Fe3O4 could facilitate calcite formation. Increasing the nano-Fe3O4 content showed a positive correlation with increased thermal conductivity and UCS. Specifically, the optimal values of thermal conductivity and UCS increased by 2.42 times and 2.39 times, respectively, compared to MICP-treated specimens without nano-Fe3O4. Microstructure analysis revealed that calcite precipitation at the particle contact served a dual function: cementing particles, thereby improving the mechanical strength and simultaneously acting as a "thermal bridge" to enhance the thermal conductivity. Furthermore, this study provides a new perspective on utilizing magnetized bacteria to reinforce specific locations within rocks and soils in the presence of an external magnetic field.

Evaluation of mechanical properties and potential environmental applications of biomimetic mineralized composites

With the growing emphasis on environmental protection, there has been extensive research on new green cementitious materials suitable for different conditions. This study focuses on the influence of key environmental factors on proposed biomimetic mineralized composites (BMC) using polyacrylic acid (PAA) as a modifier, based on the biomimetic chemistry induced carbonate precipitation (BCICP) method. The environmental factors examined include the cementing matrices type, the magnesium ions concentration, and the cementing solution pH. The samples treated under various conditions were evaluated for their unconfined compressive strength (UCS) and calcium carbonate content, and their microstructure was characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results demonstrate that the BMC treatment could achieve high-strength cementation for both Toyoura sand and Fujian quartz sand, with a more pronounced enhancement observed for Toyoura sand. Magnesium ions reduce the cementation effect, and they cannot fully replace calcium ions in participating in the cementation process. Moreover, the cementing solution pH significantly influences the cementation effect, with the best acid-base condition for PAA to modify BMC sand samples found at a pH of 11.5. Overall, the BMC exhibits high performance under various environmental conditions. These findings could provide valuable insights into the influence of environmental factors and the potential applications of BMC in diverse environments.

Enhancing alkali resistance of recycled GFRP fibers and mechanical performances of cement mortars with microbial induced carbonate precipitation

Applying the recycled glass fiber reinforced plastic (rGFRP) fiber to reinforce cement-based materials is a promising way to reuse this massively waste material. However, rGFRP fiber is prone to be corroded in the alkali environment of cement. To solve this problem, the rGFRP fiber was treated with microbial induced CaCO3 precipitation (MICP) technique. The effects of MICP treatment on the rGFRP fiber and the reinforced mortar were investigated. It was revealed that the alkali resistance of the rGFRP fiber was significantly modified by CaCO3 deposition, which was increased with the concentration of mineralizing solution and treating time. The tensile strength and aging resistance of the rGFRP fiber reinforced mortar were all improved by MICP treatment, since fiber-cement friction, fiber-cement compatibility, microstructural compactness and cement hydration degree were enhanced by the properly precipitated CaCO3 crystals on fiber surface. However, excessive MICP treating process was detrimental for effective CaCO3 precipitation. The rGFRP fiber treated in the mineralizing solution of 1.0 mol/L for 3 times with 24 h/time (1−24−3) had the most promising modification effect on the rGFRP fiber and the reinforced mortar in this study. The 1–24–3 rGFRP fiber had similar alkali resistance to the alkali resistance glass fiber, which increased the tensile strength of mortar by 34.1 % and improved the bending strength of mortar by 10.8 % after accelerated aging. The MICP technique was used on modifying rGFRP fiber and the reinforced mortar for the first time, which would benefit the durability of rGFRP fiber and its wider application in cement-based materials, while the long-term performance of rGFRP fiber reinforced mortar should be studied in the future.