Carbonate Polymorphs Research Articles

Influence of proteinoids on calcium carbonate polymorphs precipitation in supersaturated solutions

Influence of proteinoids on calcium carbonate polymorphs precipitation in supersaturated solutions

Experimental formation of carbonates from perchlorate and sulphate brines: Implications for Jezero crater, Mars.

Extensive carbonate precipitation has occurred on Mars. To gain insight into the carbonation mechanisms and formation processes under ancient Martian aqueous conditions, we examine the precipitation of carbonates resulting from atmospheric carbon fixation, focusing on interactions between various brines and silicate and perchlorate solutions in alkaline environments. The micro-scale morphology and composition of the resulting precipitates are analysed using ESEM micrographs, EDX chemical compositional analysis, X-ray diffraction, and micro-Raman spectroscopy. Our findings indicate a significant atmospheric carbonation process involving chlorate and sulphate brines reacting with alkaline perchlorate solutions, leading to the precipitation of calcium carbonate polymorphs, including vaterite, aragonite, and calcite, as well as other carbonates like siderite (iron carbonate) and zaratite (nickel carbonate). Some precipitates exhibit biomorphic structures (such as globular spherical aggregates, fine branched tubes, and flower-like morphologies) that should not be mistaken for fossils. These experiments demonstrate that various precipitates can form simultaneously in a single reaction vessel while being exposed to different micro-scale pH conditions. We propose that systematic laboratory studies of such precipitate reactions should be conducted in preparation for the analysis of the Mars Sample Return collection on Earth, aiding in the interpretation of carbonate presence in natural brine-rock carbonation processes under Martian conditions while also helping to distinguish potential biosignatures from purely geochemical processes.

Melting Behavior and Ionic Conduction of Multicomponent Carbonates Coexisting with Porous Oxides

Multicomponent systems of alkali carbonates indicate high electrical conductivity, high chemical and thermal conductivity, and low viscosity in the medium temperature range around 500°C, and are used as high temperature reaction media, thermocouples, and sensing materials for CO However, in electrochemical reactions, the high reactivity of carbonates is accompanied by the problem of corrosion of electrodes and reaction systems. We have studied ceria-based oxides and zirconia, which have high reactivity through surface treatment of CO2 absorbing media, and have examined the electrical and thermal properties of the composite materials with molten carbonate. Ceria-based oxides have been considered for application in solid oxide fuel cells as solid electrolytes, whereas γ-LiAlO2 has insulating properties and is used as an electrolyte in molten carbonate fuel cells. In this study, lithium carbonate, sodium carbonate, and potassium carbonate are used as the liquid phase, and mono-, binary-, and ternary complex carbonates or carbonates with eutectic compositions are used. The results are summarized on the effect of salt complexation on the improvement of electrical conductivity at low temperature ranges and the lowering of melting points.The solid phase was obtained by drying three types of γ-LiAlO2 (24.0 m2/g, 10.3 m2/g, 5.4 m2/g) and other various oxides such as α-Al2O3, MgO, ZrO2 etc. at 500°C for 2 hours under nitrogen. Li2CO3, Na2CO3, and K2CO3 were used for the carbonate phase and dried at 200°C for 48 hours under a carbon dioxide atmosphere. Eutectic carbonates were prepared by mixing them to form a eutectic composition. Each oxide powder was mixed thoroughly in a mortar to form carbonate at a given volume ratio. The sample was formed by pressurization and sintered at 500°C for 1 hour to obtain a tablet for the measurements of ionic conduction and thermal analysis.As shown in Figure 1, the activation energy of electrical conductivity increased near the solid phase in all cases. The range of influence from the solid phase decreased significantly with increasing carbonate polymorphism: 40 nm for the mono-salt system, 10 nm for the binary system, and about 2 nm for the ternary system. These melting point drops are also affected by the solid phase, but the effect of the distance from the solid phase is not so great. In the vicinity of the solid phase, the effect of the solid phase on ionic conduction is not as strong as that on the phase change, and the more numerous ions move, the less affected by the solid phase the system is. In this presentation, we will discuss the influence of the solid phase from a viewpoint of thermodynamics.Fig.1 Variation of ΔE a with apparent average thickness for various carbonates /inorganic powders coexisting systems. Carbonates: (a)Li2CO3, (b) (Li0.52Na0.48)2CO3, and (c) (Li0.435Na0.315K0.25)2CO3. Figure 1

Performance augmentation of fiber reinforced concrete through in situ mineralization of polycrystalline calcium carbonate on fiber surfaces

Enhancing the performance of fiber-reinforced concrete through the meticulous regulation of interfacial microstructure and interaction mode stands as a pivotal area of research. Notably, there are significant differences in the microstructure of several polycrystalline forms of calcium carbonate, which can profoundly influence the interaction behavior between them and the matrix. However, the tailored modulation of calcium carbonate polymorphism for the purpose of fiber surface modification remains unreported. In this paper, polycrystalline mineralization was induced by polydopamine on the surface of polyvinyl alcohol fiber by biomimetic method, and the fiber surface was modified by calcite and aragonite. The cubic calcite and acicular aragonite minerals notably roughened the fiber surface, enhancing interfacial properties between PVA fibers and cement matrix. The damaged form of the interface changed from adhesion failure to cohesive failure. Quantitative assessment of fiber-matrix interfacial interactions via single-fiber pullout tests revealed aragonite's unique morphology and exceptional mechanical attributes yielding higher frictional resistance against pullout loads. The good bonding between calcite and the cement matrix improves the strain-hardening behavior of fiber pullout and significantly enhances energy dissipation. In addition, enhanced interfacial properties bolster composites' mechanical strength. The acicular and cubic mineralized layers increased the flexural strength of the fiber cementitious materials by 35 % and 41 %, respectively. The energy absorbed in resisting the impact of a falling ball increased by 25 % and 36 %, respectively. Analysis reveals calcite promotes hydration more significantly at comparable particle sizes, bolstering interfacial bond strength with cement, and offering superior reinforcement over aragonite for fiber matrix bridging. This research provides a theoretical basis for promoting the application of polycrystalline CaCO3 and the sustainable development of high-performance fiber-reinforced concrete.

Stabilization of metastable calcium carbonate polymorphs on the surface of recycled cement paste particles: A two-step carbonation approach without chemical additives

In this study, a two-step carbonation method is developed to control the formation of calcium carbonate (Cc) polymorphs on the surface of recycled hardened cement paste (RHCP) without the use of chemical additives. In the first step, RHCP undergoes semi-dry carbonation under controlled humidity conditions, followed by wet carbonation at various temperatures in the second step. The results show that vaterite and aragonite are stabilized during the wet carbonation process, forming primarily on the surface of RHCP particles. The stabilization of the metastable Cc phases is driven by the synergistic effect of existing Cc seeds in the RHCP and the reaction temperature. A temperature range of 9–48 °C promotes the formation of vaterite, while higher temperatures (60–90 °C) lead to its dissolution. The calcite seeds present in RHCP do not enhance the formation of vaterite and aragonite during wet carbonation. This method offers a potential practical approach for valorizing concrete waste while capturing CO₂ from the atmosphere.

Effects of hexagonal boron nitride nanosheets on the biostabilization of recycled sands for geotechnical fill applications

Biostabilization techniques including plant enzyme induced calcite precipitation (EICP) and microbially induced calcite precipitation (MICP) represent promising and environmentally friendly methods for improving the engineering properties of recycled geomaterials for geotechnical fill applications. In this study, hexagonal boron nitride (h-BN) nanosheets were dispersed and utilized as nano-additives in the EICP and MICP reaction processes to facilitate the precipitation of calcium carbonate polymorphs (CaCO3) in washed recycled sands (RS) derived from construction and demolition (C&D) wastes for geotechnical fill applications. The investigation comprised a systematic range of biological and chemical microscopic and macroscopic experiments intending to stabilize the RS for geotechnical fill applications. The study results suggested that using h-BN nanosheets did not have a notable impact on bacterial growth or the functioning of bacterial and plant enzyme activity. In addition, it was observed that the optimal addition of h-BN nanosheet additives substantially increased CaCO3 precipitation by up to 34 % and 28 % in the EICP and MICP reaction processes respectively, which can be postulated to be due to the nanosheets acting as nucleation sites throughout the high surface area and negatively surface charge. Furthermore, the introduction of h-BN nanosheets led to a significant enhancement in the performance of unconfined compressive strength (UCS) of the stabilized RS through nanofillers and reinforcements, with improvements of up to 20 % and 13 % in the biostabilization of RS using the EICP and MICP after 10 treatment cycles. Detailed analyses, including Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) imaging, revealed that h-BN nanosheets, with a substantial surface area and effective chemical functional groups, interconnected with the CaCO3 mineral surface. Overall, the study suggests that integrating effective additives can improve the utilization of EICP and MICP in geotechnical fill applications, namely in road embankments and pavements, whilst providing both commercial viability and enhanced performance.

An anomalous otolith of Engraulis australis (Clupeiformes, Engraulidae) from the food of the Australasian gannet Morus serrator, New Zealand

ABSTRACT Saccular otoliths are hearing and balance structures in teleost fish and usually consist of the aragonite form of calcium carbonate but may contain varying amounts of the vaterite polymorph in abnormal cases. Environmental impacts, nutritional problems, pollution, stress, and changes in water parameters, or a combination of these factors, may cause deformities in saccular otoliths. In this study, we examined the morphologies and calcium carbonate polymorphs within abnormal and normal saccular otoliths in the anchovies Engraulis australis, retrieved from regurgitated stomach contents of the Australasian gannet Morus serrator, Hauraki Gulf, New Zealand. Scanning electron microscopy (SEM) and Raman microscopy revealed several prominences in numerous areas on the surfaces of abnormal otoliths. This is the first study to report on the morphology and compositional differences in abnormal otoliths retrieved from the food of a piscivorous bird in New Zealand. Abnormalities in the structure and composition of otoliths may impact balance and hearing functions in fish and have implications on their fitness. Further studies should explore whether such fish are preferentially targeted by their avian predators.

Lab scale evaluation of biomineralization-assisted decolourization of reactive blue 4 and toxicity analysis

The process of microbial mineral precipitation has proven to be highly effective in addressing a wide range of pollutants in different environments. The objective of this study is to utilize the mineralization abilities of microbial strains found in the Noyyal River basin, which is home to a significant textile center in India, in order to both remove the color from reactive blue 4 and promote biomineralization. Promising results were obtained from the microbial isolates Streptomyces sp., Rhodococcus ruber, and Bacillus sp., and their consortium which demonstrated the ability to induce biomineralization and decolorize reactive blue 4. Characterization of the obtained biominerals through X-ray diffraction and FT-IR analysis showed the presence of well-crystallized polymorphs of calcium carbonate, along with other organic compounds. SEM-EDX analysis of biominerals formed during biomineralization-assisted decolourization of RB4 revealed distinct morphologies and elemental composition of the biominerals produced by microbial interactions with dye molecules. Further, to assess the safety and efficacy of these biominerals, zebrafish embryo toxicity tests were conducted by comparing biominerals produced during dye decolourization with the pure reactive blue 4 dye. Zebrafish embryos treated with biominerals exhibited normal developmental patterns, whereas those exposed to reactive blue 4 displayed mortality and abnormal hatching rates. The heart rates of the Zebrafish embryos were normal for controls and biomineral groups, but lower for RB4-exposed embryos. In conclusion, this study underscores the potential of biomineralization in remediating dye-contaminated wastewater, offering circular solutions for waste reduction and resource utilization.

In Situ Monitoring the Nucleation and Growth of Nanoscale CaCO3 at the Oil-Water Interface.

Interfaces can actively control the nucleation kinetics, orientations, and polymorphs of calcium carbonate (CaCO3). Prior studies have revealed that CaCO3 formation can be affected by the interplay between chemical functional moieties on solid-liquid or air-liquid interfaces as well as CaCO3's precursors and facets. Yet little is known about the roles of a liquid-liquid interface, specifically an oil-liquid interface, in directing CaCO3 mineralization which are common in natural and engineered systems. Here, by using in situ X-ray scattering techniques to locate a meniscus formed between water and a representative oil, isooctane, we successfully monitored CaCO3 formation at the pliable isooctane-water interface and systematically investigated the pivotal roles of the interface in the formation of CaCO3 (i.e., particle size, its spatial distribution with respect to the interface, and its mineral phase). Different from bulk solution, ∼5 nm CaCO3 nanoparticles form at the isooctane-water interface. They stably exist for a long time (36 h), which can result from interface-stabilized dehydrated prenucleation clusters of CaCO3. There is a clear tendency for enhanced amounts and faster crystallization of CaCO3 at locations closer to isooctane, which is attributed to a higher pH and an easier dehydration environment created by the interface and oil. Our study provides insights into CaCO3 nucleation at an oil-water interface, which can deepen our understanding of pliable interfaces interacting with CaCO3 and benefit mineral scaling control during energy-related subsurface operation.

Resistance to acid, alkali, chloride, and carbonation in ternary blended high-volume mineral admixed concrete

The World Bank study predicts that 4 °C warming will bring high temperatures, sea-level rise, and saltwater intrusion to coastal areas, damaging coastal concrete structures. Increased CO2 from industrialization exacerbates this, necessitating durable, low-carbon concrete. Combined use of fly ash (FA) and ground granulated blast furnace slag (GGBFS) as high-volume OPC replacements boosts performance while reducing concrete’s carbon footprint. In this perspective current study examines the durability of concrete against aggressive agents (H2SO4, MgSO4, NaCl, and CO2) causing premature deterioration of concrete structures. Initially, three cost-effective sustainable concrete mix designs were developed, incorporating 50% replacement of OPC with locally available supplementary cementitious materials, specifically FA and GGBFS. These mixes were then evaluated for their mechanical and durability performances. The impact of aggressive ions (SO4 2−, Cl−, and CO3 2−) was studied by examining the changes in mechanical performance and phase assemblages. Thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) techniques were used to estimate the phase compositions. Ternary blended concrete having 50% OPC+ 30% GGBFS + 20% FA exhibited optimal synergistic performance, enhancing pozzolanic and hydraulic reactions for better resistance to harmful ions. The sorptivity test confirmed that as the GGBFS content increased, the sorption rate decreased, indicating the higher reactive nature of GGBFS to that of FA. Deleterious compounds formed due to the action of SO4 2-, Cl-, and CO3 2- were identified to be ettringite (Ca6Al2(SO4)3(OH)12.32H2O, AFt) and gypsum (CaSO4.2H2O, Gy), Friedel’s salt (Ca4Al2(OH)12Cl2.4H2O, Fs) and polymorphs of calcium carbonate (CaCO3), respectively through TG mass loss curve. These results were corroborated by FTIR analysis, which showed predominant characteristic bands at 662 cm−1 for SO4 2−, 459 cm−1 for Mg–O stretching, 790 cm−1 for Al–OH bending, and 1431-1443 cm−1 for C–O, confirming the presence of the deleterious compounds.

Evaluation of long-term aging of low-carbon cementitious materials under severe H2S impact in sewerage systems

The durability of cementitious materials in harsh environments, like marine or sulfate-rich soils, is influenced by various factors, with bacteria playing a significant role alongside environmental chemistry. To address sustainability concerns, research focuses on developing cement mixes that reduce emissions and withstand aggressive conditions. New standards require testing these mixes. This study developed and tested low-carbon cement mixes (CEM III, CEM V, CAC, and CSS) under real sewer conditions enriched with H2S and bacteria for four years. The specimens underwent SEM-EDS, XRD, TGA-DTA, and µRaman analysis to enhance understanding of degradation processes by conducting detailed and localized characterization of both initial and newly formed phases. Through this analysis, the work offers a precise description of the effects of bio-alteration on various cement matrices, elucidating their reactions under such conditions. The analysis of mortar specimens has revealed the presence of expansive products such as gypsum besides various polymorphs of calcium carbonate.

Evaluating carbonation resistance and microstructural behaviors of calcium sulfoaluminate cement concrete incorporating fly ash and limestone powder

This study investigates the effects of accelerated carbonation on calcium sulfoaluminate (CSA) cement concrete, focusing on mixtures enhanced with 20 % fly ash (FA), 20 % remediated fly ash (RF), 15 % limestone powder (LP), and a combination of 20 % FA with 15 % LP (35 %). The study further evaluates the mechanical properties including compressive strength, splitting tensile strength, elastic modulus, along with drying shrinkage and bulk resistivity. To delve into the microstructural characteristics of moist curing versus carbonation exposure on the CSA cement system, X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were employed, particularly analyzing phase assemblage changes. The results show that the addition of FA reduced the carbonation depth in concrete mixtures over time (105 days). However, LP and the combination of FA and LP presented mixed effects. The microstructural analysis highlighted ettringite as the predominant phase in samples moist cured for 3 days. In contrast, carbonation-cured samples were characterized by different calcium carbonate (CaCO3) polymorphs alongside aluminum hydroxide (Al(OH)3) and residual ye'elimite, with the formation of low-pH carbonic acid facilitating the conversion of ettringite into CaCO3. This study highlights the impact of different SCMs on the durability and microstructural characteristics of CSA cement concrete, underscoring the interplay between curing methods, effects of SCM, and carbonation processes.

Differentiating the Bonding States in Calcium Carbonate Polymorphs by Low-Loss Electron-Energy-Loss Spectroscopy

Differentiating the Bonding States in Calcium Carbonate Polymorphs by Low-Loss Electron-Energy-Loss Spectroscopy

Carbonate chimneys at the highly productive point Dume methane seep: Fine-scale mineralogical, geochemical, and microbiological heterogeneity reflects dynamic and long-lived methane-metabolizing habitats.

Methane is a potent greenhouse gas that enters the marine system in large quantities at seafloor methane seeps. At a newly discovered seep site off the coast of Point Dume, CA, ~ meter-scale carbonate chimneys host microbial communities that exhibit the highest methane-oxidizing potential recorded to date. Here, we provide a detailed assessment of chimney geobiology through correlative mineralogical, geochemical, and microbiological studies of seven chimney samples in order to clarify the longevity and heterogeneity of these highly productive systems. U-Th dating indicated that a methane-driven carbonate precipitating system at Point Dume has existed for ~20 Kyr, while millimeter-scale variations in carbon and calcium isotopic values, elemental abundances, and carbonate polymorphs revealed changes in carbon source, precipitation rates, and diagenetic processes throughout the chimneys' lifespan. Microbial community analyses revealed diverse modern communities with prominent anaerobic methanotrophs, sulfate-reducing bacteria, and Anaerolineaceae; communities were more similar within a given chimney wall transect than in similar horizons of distinct structures. The chimneys represent long-lived repositories of methane-oxidizing communities and provide a window into how carbon can be transformed, sequestered, and altered over millennia at the Point Dume methane seep.

Effect of temperature on binding process of calcium carbonate concrete through aragonite crystals precipitation

This study investigated the impact of temperature on the strength development of calcium carbonate concrete (CCC) comprising calcium carbonate and concrete waste. CCC exhibited its highest compressive strength when manufactured at temperatures between 60 and 70 °C, thereby demonstrating strengths 1.5 and 2.7 times greater than those achieved at 40 and 90 °C, respectively. At this temperature range (60–70 °C), CCC showed the highest amount of precipitated aragonite with large acicular aragonite crystals, which decreased the porosity of CCC. This temperature range governed the homogeneous distribution of calcium carbonate deposition within the CCC specimen. Moreover, the carbonated cement paste particles within the CCC continuously underwent aqueous carbonation, thereby providing an additional Ca source for calcium carbonate precipitation in CCC. At high temperatures, this process promotes the precipitation of Ca ions as needle-like aragonite crystals during reprecipitation with accelerating the transformation of calcium carbonate polymorphs. The CCC strength arose from the deposition of calcium carbonate from input calcium bicarbonate solution and the reprecipitation of calcium carbonate during aqueous carbonation. The calcium carbonate precipitation from aqueous carbonation accounts for 30 % of the total calcium carbonate precipitation of CCC. Needle-like aragonite crystals functioned as interlocking bridges between the particles and frame connections, effectively strengthening the CCC composite.

The Formation of Calcium–Magnesium Carbonate Minerals Induced by Curvibacter sp. HJ-1 under Different Mg/Ca Molar Ratios

Microbial mineralization of calcium–magnesium carbonate has been a hot research topic in the fields of geomicrobiology and engineering geology in the past decades. However, the formation and phase transition mechanism of calcium–magnesium carbonate polymorphs at different Mg/Ca ratios still need to be explored. In this study, microbial induced carbonate mineralization experiments were carried out for 50 days in culture medium with Mg/Ca molar ratios of 0, 1.5, and 3 under the action of Curvibacter sp. HJ-1. The roles of bacteria and the Mg/Ca ratio on the mineral formation and phase transition were investigated. Experimental results show that (1) strain HJ-1 could induce vaterite, aragonite, and magnesium calcite formation in culture media with different Mg/Ca molar ratios. The increased stability of the metastable phase suggests that bacterial extracellular secretions and Mg2+ ions inhibit the carbonate phase-transition process. (2) The morphology of bacteriological carbonate minerals and the formation mechanism of spherical minerals were different in Mg-free and Mg-containing media. (3) The increased Mg/Ca ratio in the culture medium has an influence on the formation and transformation of calcium–magnesium carbonate by controlling the metabolism of Curvibacter sp. HJ-1 and the activity of bacterial secretion.

Influence of relative humidity on carbon sequestration and crystal morphology of air lime: A sustainable building material

This study investigated the carbon sequestration potential of air lime by carbonation in two different relative humidity conditions. The carbonation rate and amount of carbon dioxide captured were quantified using weight gain and various analytical techniques. Samples cured in high relative humidity showed almost complete carbon capture by sequestering 94.8 % of carbon dioxide from atmospheric air within 56 days, with calcite crystal formation and a high crystallinity index. Similarly, samples cured in low relative humidity conditions showed slightly less carbonation around 83.8 % with different calcium carbonate polymorphs like aragonite and vaterite, along with amorphous calcium carbonate. Results demonstrated that carbonation of lime is a promising technology for carbon capture and utilization in buildings as non-load bearing mortars or plasters and could be used to reduce carbon dioxide levels in the atmosphere.

Synergistic biocementation: harnessing Comamonas and Bacillus ureolytic bacteria for enhanced sand stabilization

Biocementation, driven by ureolytic bacteria and their biochemical activities, has evolved as a powerful technology for soil stabilization, crack repair, and bioremediation. Ureolytic bacteria play a crucial role in calcium carbonate precipitation through their enzymatic activity, hydrolyzing urea to produce carbonate ions and elevate pH, thus creating favorable conditions for the precipitation of calcium carbonate. While extensive research has explored the ability of ureolytic bacteria isolated from natural environments or culture conditions, bacterial synergy is often unexplored or under-reported. In this study, we isolated bacterial strains from the local eutrophic river canal and evaluated their suitability for precipitating calcium carbonate polymorphs. We identified two distinct bacterial isolates with superior urea degradation ability (conductivity method) using partial 16 S rRNA gene sequencing. Molecular identification revealed that they belong to the Comamonas and Bacillus genera. Urea degradation analysis was performed under diverse pH (6,7 and 8) and temperature (15 °C,20 °C,25 °C and 30 °C) ranges, indicating that their ideal pH is 7 and temperature is 30 °C since 95% of the urea was degraded within 96 h. In addition, we investigated these strains individually and in combination, assessing their microbially induced carbonate precipitation (MICP) in silicate fine sand under low (14 ± 0.6 °C) and ideal temperature 30 °C conditions, aiming to optimize bio-mediated soil enhancement. Results indicated that 30 °C was the ideal temperature, and combining bacteria resulted in significant (p ≤ 0.001) superior carbonate precipitation (14–16%) and permeability (> 10− 6 m/s) in comparison to the average range of individual strains. These findings provide valuable insights into the potential of combining ureolytic bacteria for future MICP research on field applications including soil erosion mitigation, soil stabilization, ground improvement, and heavy metal remediation.

Effect of Temperature on Calcium‐Based Chemical Garden Growth

AbstractHydrothermal vents maintain far‐from equilibrium conditions that may have provided the necessary settings for the origin of life. To understand reactions under these physicochemical conditions, scientists have turned to the classic demonstration experiment, chemical gardens. The self‐organization of precipitate tubes separates high and low pH environments similarly to the naturally occurring geological structures. Here, we report calcium‐based chemical gardens forming in solutions containing anions of silicate, carbonate, or a mixture of the two in 100 °C and 23 °C environments. Under high temperature conditions, chemical gardens tend to have faster average growth velocities and form taller structures. We measure the composition of the precipitate tubes using Fourier transform infrared spectroscopy and find the formation of all polymorphs of calcium carbonate along with calcium silicates.

Comparison of calcium carbonate production by bacterial isolates from recycled aggregates.

The new technology of microbially induced calcium carbonate precipitation (MICP) has been applied in construction materials as a strategy to enhance their properties. In pursuit of solutions that are more localized and tailored to the study's target, this work focused on isolating and selecting bacteria capable of producing CaCO3 for posterior application in concrete aggregates. First, eleven bacterial isolates were obtained from aggregates and identified as genera Bacillus, Lysinibacillus, Exiguobacterium, and Micrococcus. Then, the strains were compared based on the quantity and nature of calcium carbonate they produced using thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy with energy dispersive spectroscopy. Bacillus sp. dominated the cultured isolates and, along with Lysinibacillus sp., exhibited the highest CaCO3 conversion (up to 80%). On the other hand, Exiguobacterium and Micrococcus genera showed the poor ability to MICP (21.3 and 20.3%, respectively). Calcite and vaterite were the dominant carbonate polymorphs, with varying proportions. Concrete aggregates have proven to be a source of microorganisms capable of producing stable calcium carbonates with a high conversion rate. This indicates the feasibility of using microorganisms derived from local sources for application in construction materials as a sustainable way to enhance their characteristics.