Formation Of Calcium Carbonate Research Articles

Development of high-volume steel slag as cementitious material by ethylenediamine tetraacetic acid induced accelerated carbonation

Steel slag, a by-product of primary steel production, is produced in large quantities and is primarily used as landfill or aggregate. Due to its high reactivity with CO2, steel slag can form calcium carbonate at room temperature and pressure, making it an ideal material for CO2 capture in the development of sustainable construction materials. Due to the transport properties of CO2 and carbonation kinetics, carbonation of steel slag is frequently carried out using pure gas under high pressure. In this study, ethylenediamine tetraacetic acid (EDTA)-induced accelerated carbonation was used to produce cement paste mixes consisting of up to 100% steel slag powder. Combination of cement and EDTA with steel slag proved to be effective in accelerating the carbonation reaction. EDTA increased the leaching of Ca from the steel slag, thereby enhancing the carbonation reaction, which was more obvious in longer durations (up to 28 days). The optimum cement paste mix (80% steel slag and 20% cement, with 0.1 mol/L EDTA solution) achieved maximum compressive strength of 14 MPa and CO2 uptake of 8.7% after 28 days of accelerated carbonation. Results demonstrated that the use of high-volume steel slag as a cementitious material has great potential in non-structural building applications.

Crystallinity assessment of anthropogenic calcites using Raman micro-spectroscopy

Anthropogenic calcite is a form of calcium carbonate produced through pyrotechnological activities, and it is the main component of materials such as lime binders and wood ash. This type of calcite is characterized by a significantly lower degree of crystallinity compared with its geogenic counterparts, as a result of different formation processes. The crystallinity of calcite can be determined using infrared spectroscopy in transmission mode, which allows decoupling particle size effect from atomic order and thus effectively distinguish anthropogenic and geogenic calcites. On the contrary, Raman micro-spectroscopy is still in the process of developing a reference framework for the assessment of crystallinity in calcite. Band broadening has been identified as one of the proxies for crystallinity in the Raman spectra of geogenic and anthropogenic calcites. Here we analyze the full width at half maximum of calcite bands in various geogenic and anthropogenic materials, backed against an independent crystallinity reference based on infrared spectroscopy. Results are then used to assess the crystallinity of anthropogenic calcite in archaeological lime binders characterized by different states of preservation, including samples affected by the formation of secondary calcite, and tested on micromorphology thin sections in which lime binders are embedded in sediments.

A study on the mechanical and durability properties of bacterial culture with Ground Granulated Blast Furnace Slag (GGBS) as partial replacement for cement

In concrete structures, the formation of cracks leads to reduction in the strength of the structures. Bioconcrete is an environmentally friendly material used for healing of cracks. In this study, the indigenous bacteria Bacillus cereus KOV15 obtained from the soil is used in bioconcrete with Ground Granulated Blast Furnace Slag (GGBS) as partial replacement for cement. Five different mixes of concrete such as conventional concrete and various mixes of concrete with bacterial broth culture (30% GGBS + 5% bacterial broth culture), (30% GGBS +10% bacterial broth culture), (40% GGBS + 5% bacterial broth culture) and (40% GGBS + 10% bacterial broth culture) were used to find the mechanical and durability properties and to study the microstructure of bioconcrete. The maximum percentage increase in the cube compressive strength, the split tensile strength and the flexural strength of bioconcrete was 26.79%, 11.69% and 21.3% respectively for concrete with 30% cement replaced with GGBS and 10% bacterial broth culture in comparison with the control concrete at the 28th day. The XRD, SEM and EDX analyses were performed to identify the calcium carbonate formation in bioconcrete. The SEM images of the bioconcrete with GGBS as replacement for cement have better hydrated form and have lesser pores than the conventional concrete. The EDX results exhibited a significant increase in the amount of calcium in the bioconcretewith 30% GGBS and 10% bacterial broth culture by 103.82% than that of the conventional concrete.The permeability of chloride ion was very low (903.2 Coulombs) in concrete with 10% bacterial broth culture and 30% GGBS as partial replacement for cement. The water absorption was maximum (3.03%) in the conventional concrete specimens when compared to other bioconcrete specimens with bacterial broth culture and GGBS as partial replacement for cement. Bioconcrete showed very low permeability and higher acid resistance than the conventional concrete. The Load deflection studies exhibited higher ultimate load and ductility factor for bioconcrete and the failure pattern of bioconcrete indicated lesser number of cracks, minimum crack width and no shear failure pattern. The indigenous Bacillicus Cereus KOV15 strains can be used for the synthesis of green construction materials like calcite-based biocement.

The effect of amorphous calcium carbonate as a culture media supplement on embryonic development of murine sibling embryos.

The aim of this study was to compare the addition in culture media of stabilized amorphous calcium carbonate (ACC) versus calcium chloride (CaCl2) or calcium carbonate in crystalline form (CCC) on growth rates among sibling mouse embryos. We evaluated the effect of different ACC concentrations on the rates of embryo compaction at 60 h, blastocyst rate at 84 h and percentage of fully hatched at 108 h following hCG injection. As ACC is stabilized by tripolyphosphate (TPP), we also evaluated the addition of TPP alone to the culture media. Finally, we compared supplemented ACC culture media to one-step SAGE and Irvine cleavage media. The results revealed that ACC accelerates the compaction and blastocyst rates, as well as the percentage of fully hatched embryos in a dose-dependent manner, with an increased positive effect at 2.5 mM. The magnitude of the effect for ACC-supplemented media on the embryo developmental rate was between 30 to 40% (p < 0.01) faster for each stage, compared to both SAGE and Irvine one-step standard media. Embryos cultured with SAGE or Irvine media with or without supplementation of CaCl2 or CCC, did not produce the same improvements as observed with ACC. In conclusion, the ACC demonstrates a rapid modulation effect for restoring media optimal pH. ACC can inhibit cathepsin B activity during in vitro culture of fibroblast cells. The beneficial impact of ACC on cleavage mouse embryos is likely due to an improved buffering effect causing slower pH media variations, which may enhance quality and implantation potential of embryos following in vitro culture.

Self-healing properties of cement-based materials in different matrix based on microbial mineralization coupled with bimetallic hydroxide

Self-healing properties of cement-based materials in different matrix based on microbial mineralization coupled with bimetallic hydroxide were systematically studied. Firstly, the self-healing macroscopic properties of cement-based materials in different matrix were studied. The area repair rate of cement paste early crack was better than that of mortar and concrete, which showed that self-repairing agent also had excellent repair properties in the early stage. With the extension of the curing time, the repair effect was significantly enhanced; The repair effect was basically the same when the curing time was 28 d. After curing for 28 d, the resistance of the three matrix to water permeability were basically restored to intact. At each curing time, the ultrasonic propagation velocity in concrete was the largest, and that in cement paste was the smallest. Secondly, the composition and microstructure of the mineralized products were analyzed by XRD, SEM, EDS and TGA. Additionally, the pore size of the product was also tested. The characteristic peaks of XRD were consistent with the products of the target design, corresponding to the formation of calcium-aluminum bimetallic hydroxide and calcium carbonate. Mineralized products were mainly composed of two forms of inorganic minerals, one was bimetallic hydroxide with lamellar structure, and the other was CaCO3; Moreover, the quantity of calcite was much higher than that of bimetallic hydroxide. Finally, the principle that ultrasonic velocity differently after repair in different matrix was explained, and the mechanism of microbial mineralization coupled with bimetallic hydroxide to repair crack was revealed. The bimetallic hydroxide could fix the hydroxide ion, chloride ion and sulfate ion, which not only improved the repair efficiency, but also reduced the corrosion.

Amorphous Calcium Carbonate Shows Anti-Cancer Properties That are Attributed to Its Buffering Capacity.

Amorphous calcium carbonate (ACC) is a non-crystalline form of calcium carbonate, and it is composed of aggregated nano-size primary particles. Here, we evaluated its anti-cancer effect postulated relative to its buffering capabilities in lung cancer. Tumors were evaluated in vivo using the Lewis lung carcinoma (LLC) mouse cell line and A549 human lung cancer carcinoma cell line. LLC and A549 cells were injected subcutaneously into the right hind leg of mice. Treatments (ACC, cisplatin, vehicle, and ACC with cisplatin, all given via daily IP injections) started once tumors reached a measurable size. Treatments were carried out for 14 days in the LLC model and for 22 and 24 days in the xenograft model (two experiments). LLC tumors were resected from ACC at the end of the study, and vehicle groups were evaluated for cathepsin B activity. Differential gene expression was carried out on A549 cells following 8 weeks of in vitro culture in the presence or absence of ACC in a culture medium. The ACC treatment decelerated tumor growth rates in both models. When tumor volumes were compared on the last day of each study, the ACC-treated animal tumor volume was reduced by 44.83% compared to vehicle-treated animals in the LLC model. In the xenograft model, the tumor volume was reduced by 51.6% in ACC-treated animals compared to vehicle-treated animals. A more substantial reduction of 74.75% occurred in the combined treatment of ACC and cisplatin compared to the vehicle (carried out only in the LLC model). Cathepsin B activity was significantly reduced in ACC-treated LLC tumors compared to control tumors. Differential gene expression results showed a shift towards anti-tumorigenic pathways in the ACC-treated A549 cells. This study supports the ACC anti-malignant buffering hypothesis by demonstrating decelerated tumor growth, reduced cathepsin B activity, and altered gene expressions to produce anti-cancerous effects.

Steerable artificial magnetic bacteria with target delivery ability of calcium carbonate for soil improvement.

The microbial-induced carbonate precipitation (MICP) has acquired significant attention due to its immense potential in sustainable engineering applications, particularly in soil improvement. However, the precise control of microbial-induced calcium carbonate precipitation remains a formidable challenge in engineering practices, owing to the uncertain movement paths of bacteria and the nonuniform distribution of soil pores. Taking inspiration from targeted therapy in medicine, this paper presents novel research on the development and validation of magnetically responsive bacteria. These bacteria demonstrate the ability to target calcium carbonate precipitation in a microfluidic chip, thereby promoting an environmentally friendly and ecologically sustainable biomineralization paradigm. The study focuses on investigating the migration of magnetite nanoparticles (MNPs) in aqueous solutions and enhancing the stability of MNP culture liquids. A specially designed microfluidic chip is utilized to simulate natural sand particles and their pores, while an external magnetic field is applied to precisely control the movement path of the artificial magnetic bacteria, enabling targeted precipitation of calcium carbonate at the micron-scale. Verification of the engineered artificial magnetic bacteria and their ability to induce calcium carbonate precipitation is conducted through SEM-EDS analysis, microfluidic chip observations, and the application of the K-means algorithm and ImageJ software to analyze calcium carbonate formation. The influence of the concentration of magnetic nanoparticles on the calcium carbonate production rate was also studied. The results confirm the potential of the artificial magnetic bacteria for future engineering applications. KEY POINTS: • Sporosarcina pasteurii is first time successfully engineered into artificial magnetic bacteria. • The artificial magnetic bacteria show excellent performance of targeted transportation and directional deposition of CaCO3 in microfluidic chip. • The emergence of artificial magnetic bacteria promotes paradigm shift of next generation environmentally friendly biomineralization.

CRACK REPAIR IN CONCRETE USING CHEMICAL PROCESSES AND BACTERIA

The article describes technological processes of concrete self-restoration with the help of basic bio-additives: calcium concentration, concentration of soluble inorganic carbon, pH value, presence of crystallization center. In transportation construction, there are many building structures in harsh operating conditions that require strengthening or restoration of their physical and mechanical properties for stability, reliability and safety. A number of bacteria, which can be found in soil, sand and natural minerals, have the ability to release calcium carbonate, both in natural and laboratory conditions, are capable of restoring these properties. The laboratory method of self-remediation of concrete used in the construction of transportation structures is considered. Calcium lactate (CaC6H10O6) was used as a starting substance for calcium carbonate formation. In addition, urea required by the bacteria as a source of urease enzyme and yeast extract as a source of carbon and nitrogen were added. This study showed that this simplified representation of the processes occurring during carbonate deposition induced by biomicrobes has a positive effect on the physical and mechanical properties affecting the safety, reliability and sustainability of transportation infrastructure building structures.

Impact of New Combined Treatment Method on the Mechanical Properties and Microstructure of MICP-Improved Sand

Microbially induced calcite precipitation (MICP) is a green bio-inspired soil solidification technique that depends on the ability of urease-producing bacteria to form calcium carbonate that bonds soil grains and, consequently, improves soil mechanical properties. Meanwhile, different treatment methods have been adopted to tackle the key challenges in achieving effective MICP treatment. This paper proposes the combined method as a new MICP treatment approach, aiming to develop the efficiency of MICP treatment methods and simulate naturally cemented soil. This method combines the premixing, percolation, and submerging MICP methods. The strength outcomes of Portland-cemented and MICP-cemented sand using the percolation and combined methods were compared. For Portland-cemented sand, the UCS values varied from 0.6 MPa to 17.2 MPa, corresponding to cementation levels ranging from 5% to 30%. For MICP-cemented sand, the percolation method yielded UCS values ranging from 0.5 to 0.9 MPa, while the combined method achieved 3.7 MPa. The strength obtained by the combined method is around 3.7 times higher than that of the percolation method. The stiffness of bio-cemented samples varied between 20 and 470 MPa, while for Portland-cemented sand, it ranged from 130 to 1200 MPa. In terms of calcium carbonate distribution, the percolation method exhibited higher concentration at the top of the sample, while the combined method exhibited more precipitation at the top and perimeter, with less concentration in the central bottom region, equivalent to 10% of a half section’s area.

Assembly of the Intraskeletal Coral Organic Matrix during Calcium Carbonate Formation.

Scleractinia coral skeleton formation occurs by a heterogeneous process of nucleation and growth of aragonite in which intraskeletal soluble organic matrix molecules, usually referred to as SOM, play a key role. Several studies have demonstrated that they influence the shape and polymorphic precipitation of calcium carbonate. However, the structural aspects that occur during the growth of aragonite have received less attention. In this research, we study the deposition of calcium carbonate on a model substrate, silicon, in the presence of SOM extracted from the skeleton of two coral species representative of different living habitats and colonization strategies, which we previously characterized. The study is performed mainly by grazing incidence X-ray diffraction with the support of Raman spectroscopy and electron and optical microscopies. The results show that SOM macromolecules once adsorbed on the substrate self-assembled in a layered structure and induced the oriented growth of calcite, inhibiting the formation of vaterite. Differently, when SOM macromolecules were dispersed in solution, they induced the deposition of amorphous calcium carbonate (ACC), still preserving a layered structure. The entity of these effects was species-dependent, in agreement with previous studies. In conclusion, we observed that in the setup required by the experimental procedure, the SOM from corals appears to present a 2D lamellar structure. This structure is preserved when the SOM interacts with ACC but is lost when the interaction occurs with calcite. This knowledge not only is completely new for coral biomineralization but also has strong relevance in the study of biomineralization on other organisms.

Insights into the precipitation kinetics of CaCO3 particles in the presence of polystyrene sulfonate using in situ small-angle X-ray scattering.

The formation of calcium carbonate (CaCO3) nanoparticles (NPs) in the presence of polystyrene sulfonate (PSS) as an additive was examined by time-resolved small-angle X-ray scattering (SAXS) in a flow system that mimics experimental conditions used at home facilities where the precipitation can be achieved in a beaker. The experiments were carried out at low concentrations to remain in the dilute regime. A model-independent analysis was performed using the Porod invariant which defines the scale factor, leaving only the distribution of radii as the adjustable parameter. The presence of the PSS additive strongly retards the precipitation of CaCO3 NPs. The formation of NPs reaches a state of equilibrium after a few minutes. Here, it is shown that the concentration of precursors at a fixed PSS concentration plays a key role in determining the size of the NPs obtained. A full analysis of the SAXS patterns was carried out using the Hurd-Flower model to account for the weaker intensity decay than the classical Porod behaviour. The temporal evolution of the particle radii was determined. Wide-angle X-ray scattering experiments carried out simultaneously show that the particles formed have the structure of vaterite with growth consistent with the evolution of the Porod invariant.

Study on the carbonation degree of lime-activated low carbon cementitious materials: Based on the CO2 binding capacity of hydrates

To investigate the CO2 uptake capacity of lime-activated low carbon cementitious materials (LCM), this work focused on the evaluation of the carbonation degree of LCM based on the phase assemblage, and Portland cement (PC) as a reference was compared in this work. According to the composition of carbonation products quantified by QXRD and TGA, an improved method to calculate the carbonation degree of LCM based on the CO2 binding capacity of hydrates was applied. Moreover, the origin of calcium carbonate of LCM after carbonation was analyzed, and the different carbonation zones of LCM were determined and compared based on the carbonation degree. The results showed that the calculation of the carbonation degree based on the CO2 binding capacity could better evaluate the carbonation degree of LCM compared to other method. For LCM, the calcium carbonate in the carbonation zone was primarily attributed to the carbonation of C-(A)-S-H rather than the carbonation of portlandite, and the calcium carbonate in the surface sample originating from the carbonation of C-(A)-S-H accounted for 74% of the total formed calcium carbonate. After accelerated carbonation for 28 d, the partial carbonation zone of LCM could be divided into two parts: the partial carbonation zones without calcium hydroxide (CH) and with CH.

DECOMPOSITION MECHANISM AND DISSOCIATION CONSTANTS OF BICARBONATE IONS

Using carbonic acid to explain pH changes in aqueous solutions is invalid due to its undetectability under normal temperature and pressure conditions. Instead, two reversible reactions involving the decomposition of HCO3- ions into OH- and CO2 or H+ and CO32- should be employed. The second reaction (H-mechanism) is well known as the basis for the second dissociation constant of “carbonic acid”. For the first reaction (OH-mechanism), the formula has been derived from the first imaginary constant of the same acid. That is, the researchers experimentally determined the proposed constant based on the results of pH value, CO2 and HCO3- concentrations, but calculated the imaginary constant from these values. The pH increase observed following filtration on the cationic resin in Na+ form is attributed to the weakened HCO3- decomposition via the H-mechanism, resulting in decreased H+ and CO32- concentrations. A significant decrease in Ca2+ concentration (from 5.0 to 0.05 mmol/dm3) is the main reason for the observed phenomenon, as it leads to a decrease in the driving force of calcium carbonate formation. The mechanism of bicarbonate ions decomposition based on two reactions has been confirmed experimentally. An increase in the pH of the mixture of CaCl2 and NaHCO3 solutions (both with the same pH and concentration) indicates the H-mechanism, while a decrease in the pH indicates the OH-mechanism decomposition of bicarbonate ions. The pH value at which the pH does not change indicates a change in the decomposition mechanism. The change in the HCO3- dissociation mechanism depends on hardness and alkalinity, and the pH of this change decreases from softened water (pH 8.30) to seawater (pH 7.5).

Degradation of alkali-activated slag subjected to water immersion

In this study, the impacts of tap water immersion on the pore solution, phase assemblages, gel chemistry and structure, and pore structure of alkali-activated slag (AAS) pastes were studied. AAS degrades under such condition and the potential mechanisms can be concluded as lower reaction rates, gel decomposition and carbonation. The leaching of Na+ and OH− at early stages hinders the reaction of slag, which leads to a slower formation of reaction products. Long-term leaching can result in gel decomposition after 90 d. Coarsened gel pores and capillary pores are both identified in water-immersed samples. Additionally, the leached Ca2+ can react with the dissolved CO2 in tap water to form calcium carbonate. A calcium carbonate layer is observed surrounding the paste while the inner matrix is free of carbonation. The insights provided by this paper contribute to understanding the behaviors and durability of AAS in underwater conditions.

Study on MICP dust suppression technology in open pit coal mine: Preparation and mechanism of microbial dust suppression material

With the recent increases in energy demands, the dust hazards of coal mining caused by transportation, loading and unloading and other processes are becoming increasingly serious. To control dust in open pit coal mines more environmentally friendly and efficiently, and to promote the use and development of non-in situ high-yield urease microorganisms for dust suppression in coal mines, Bacillus pasteurii was selected for dust suppression experiments in this article. Additionally, the growth of microorganisms in the coal dust microenvironment was simulated, and the effect of microbial mineralization products on the calorific value of upper coal dust was further studied. Our findings indicated that Bacillus pasteurii induced dust suppression by forming a calcite precipitate with non-uniform particle size to coal dust cementation. Moreover, after a single spray, the wind erosion resistance efficiency was 84% when the wind speed was set at 10 m/s. The growth of microorganisms and urease activity in the coal dust leachate were largely equal to those in the control group, reaching a peak at approximately 24 h, that the maximum growth quantity of OD600 was about 1.5, and the maximum urease activity was 11 mmol·L−1·min−1. The difference between the peak heat release rate of mixed coal dust and pure coal was only 4.82 kW/m2, which would not affect the value of coal products. Non in-situ Bacillus pasteurii can be growth metabolized normally in the microenvironment of coal dust. Finally, the mechanism of coal dust suppression by mineralization of microbial bacterial solution to form calcium carbonate was described by a reaction equation, which is important for further application and development of microbial dust suppressants.

Effect of ion and protein concentration of Ps19, a shell protein from Pteria sterna, on calcium carbonate polymorph

Calcium carbonate is present in many biological structures such as bivalve shell, which is composed mainly of two CaCO3 polymorphs: calcite and aragonite. However, exist other forms of calcium carbonate like vaterite and amorphous calcium carbonate (ACC) that are not commonly reported. Polymorph selection is influenced by salt concentration, cofactor ions, and the presence of shell matrix proteins (SMPs) which regulates calcium carbonate deposition, among other factors. In this study, calcium carbonate crystallization in vitro of four different saline solutions at two molarities was evaluated with increased concentrations of the Ps19 protein, an insoluble extracted protein from the shell of Pteria sterna, previously described as a promotor of aragonite platelet crystallization. In vitro crystallizations showed that Ps19 is capable to induce aragonite and calcite deposition in a dose-dependent manner, but also vaterite under ciertan conditions, acting as a promoter and inhibitor of crystallization. The results contribute to understand how Ps19 control precipitation of calcium polymorphs in the growth of the prismatic and nacre layer of the shell of P. sterna.

Microbial Induced Calcite Precipitation (MICP) Potential of Ureolytic Bacillus sp. Isolated from the Soil of Eroded Ecosystems for Stabilizing and Improving the Fertility of Eroded Soils

The loss of soil from lands due to erosion has a negative effect on ecosystems and food security. Bacillus due to high catabolic capability is an appropriate candidate for application in biocementation process. The aim of this study is isolate and characterize Bacillus sp. with biocementation capability from various ecosystems. The isolates were separated from 400 samples, and characterized by biochemical and molecular methods include the amplification and sequencing analysis of gyrA and 16S rRNA genes. Growth in presence of urea, in different salinity, pH, and temperature, also scanning electron microscope (SEM), X-ray diffraction (XRD), and wind tunnel analysis were applied to determine biocementation ability. A total number of 195 isolates were recovered from environmental samples, of which 25 isolates (12.82%) were identified as urease-positive Bacillus which belonged to 10 species consisting of Bacillus subtilis five strains (20%), Bacillus vallismortis and Bacillus seohaeanensis four strains (16%) each, Bacillus mobilis, Bacillus pseudofirmus, Bacillus cohnii, Bacillus cereus, Bacillus alkalinitrilicus two strains (8%) each, and Bacillus sphaericus and Bacillus megaterium one strain (4%) each. Moreover, 15 urease-positive isolates (7.7%) belonging to Ralostenia, Actinomycete, and Halomonas genera were identified. Optimum conditions for microbial induced calcite precipitation (MICP) by isolates are 30 °C, pH 9, and 6% salinity. The highest rate of calcium carbonate formation and urease activity recorded in B. subtilis with 24.15 mg/mL of calcium carbonate and 4.40 × 103 unit/L of urease, followed by B. mobilis and B. alkalinitrilicus with 22.85 mg/mL of calcium carbonate and 3.93 × 103 unit/L of urease. After MICP the lowest soil loss ratio at a flow rate of 90 km/h, was observed in B. subtilis 100-fold reduction, followed by B. seohaeanensis, B. cereus, B. vallismortis, with 90, 85, 80-folds reduction, respectively. Results indicate that the diversity of Bacillus sp. offers the potential ability for adaptation to harsh and untapped environments, also showed that the use of MICP on the soil surface can have a very significant role in reducing soil losses due to wind erosion.

Calcium carbonate crystallization process from the mineralization of calcium chloride waste

The distillation waste stream from the ammonia-alkali process contains 90–120 g/L of calcium chloride. Using calcium chloride as raw material to mineralize carbon dioxide can achieve efficient utilization of calcium chloride waste and CO2 emission reduction. This article is based on a two-step synthesis method, using ammonium carbonate and calcium chloride as raw materials to synthesize calcium carbonate. The changes in pH of the mineralized solution with time were investigated under factors such as temperature, ammonium carbonate concentration, feeding method, and retention time. The crystallization mechanism of carbonation process shows that the pH of solution will affect the degree of supersaturation of calcium carbonate, and high supersaturation is conducive to the precipitation of metastable aragonite and vaterite phases. The experimental results showed that when ammonium carbonate was passed into calcium chloride at a rate of 10 mL/min at different temperatures and different ammonium carbonate concentrations, the pH change of the mineralized solution could be divided into three stages: a rapid pH decrease stage (9.5–7), a pH stabilization stage (∼7) and a pH rebound stage (7–8.5). Increasing the temperature is conducive to the formation of submicron calcite type calcium carbonate, changing the concentration of ammonium carbonate, and the crystal phase and size of the product are almost unaffected. If calcium chloride is added to ammonium carbonate, under low calcium ion concentration conditions, calcium carbonate tends to form aragonite phase.

Influence on the magnetic field on the scale formation in a microfluidic channel under a low Reynolds number flow

This study presents an external magnetic array to rapidly investigate the calcium carbonate formation in a microfluidic channel. The system comprises a copper coil capillary serving as the heat exchanger, a high-precision thermostatic water tank, a magnetic drive pump, and an external magnetic array. Various factors were considered during the experiment, including different concentrations (3 mM and 10 mM) of the test solution, magnetic treatment efficiency (magnet length 4.0 cm and 14.0 cm, treatment time 24 h and 72 h), and temperatures ranging from 25 ℃ to 50 ℃. The concentration of calcium ions, electrical conductivity, and pH value were measured to monitor subtle changes during water treatment. Additionally, particle size distribution and morphology of calcium carbonate were analyzed using SEM and XRD under various magnetic treatments. The experimental results revealed that (1) applying a magnetic field to the solution in a microfluidic channel under low Reynolds number flow led to a decrease in the particle size of calcium carbonate, (2) aragonite did not form in the microfluidic channel, and (3) the physicochemical properties of the solution remained unaltered by the magnetic treatment. Consequently, the reduction in particle size can prevent blockage in microchannels, providing an alternative solution to mitigate scaling issues in micro-heat exchangers.

Calcium Carbonate Prenucleation Cluster Pathway Observed via In Situ Small-Angle X-ray Scattering.

For more than 150 years, our understanding of solid-phase mineral formation from dissolved constituent ions in aqueous environments has been dominated by classical nucleation theory (CNT). However, an alternative paradigm known as non-classical nucleation theory (NCNT), characterized by the existence of thermodynamically stable and highly hydrated ionic "prenucleation clusters" (PNCs), is increasingly invoked to explain mineral nucleation, including the formation of calcium carbonate (CaCO3) minerals in aqueous conditions, which is important in a wide range of geological and biological systems. While the existence and role of PNCs in aqueous nucleation processes remain hotly debated, we show, using in situ small-angle X-ray scattering (SAXS), that nanometer-sized clusters are present in aqueous CaCO3 solutions ranging from thermodynamically under- to supersaturated conditions regarding all known mineral phases, thus demonstrating that CaCO3 mineral formation cannot be explained solely by CNT under the conditions examined.