Formation Of Calcium Carbonate Research Articles

Aragonite and its composites: preparations, properties and applications.

Aragonite, a metastable crystal form of calcium carbonate, exhibits the highest density and hardness among all species. Diversified forms of aragonite composites can be produced through different preparation processes, forming a relatively complete system in various application fields. Their properties and applications are determined by their multiple levels of structures and shapes. However, research information for aragonite‐related fields is currently lacking integration and clarification. This review provides a comprehensive overview on the preparation methods, properties, and potential applications of three main aragonite‐based materials: aragonite particles, nacre‐inspired mineralized aragonite composites (NMACs), and shell‐derived aragonite nanoparticles (SANPs). The formation mechanisms and versatile applications of these materials are thoroughly surveyed based on their initial precursor, reaction conditions, product forms including filler of aragonite whiskers synthesized by carbonation reaction; functional materials of NMACs fabricated by amorphous calcium carbonate‐organic matter (ACC‐OM) mediated process; biomedical materials of SANPs derived from aragonite cockle shells. Overall, this review aims to provide assistance for customized production of aragonite‐based materials as well as new research directions for both pure aragonites and its composites.

Effects of hydrotalcites with different laminate element composition on the properties of sulfoaluminate cement-based materials

Sulfoaluminate cement-based materials (SCBMs) are widely used for grout reinforcement. It is common to use a large water-to-binder ratio in the construction of sulfoaluminate cement-based materials (SAGMs) to obtain good workability and permeability, which results in poor early strength. Nanotechnology has been increasingly employed to enhance the mechanical properties of cementitious materials. Nano Zn-Mg-Al hydrotalcite-like (LDHs) and nano Mg-Al LDHs increased the early compressive strength, while nano Zn-Al LDHs had the opposite effect. However, the reason for this observation remains unclear. In this study, the influence of LDHs structures with different laminar element compositions on the hydration and hardening processes of SCBMs was analysed. The results showed that nano-ZnAl-LDHs, ZnAl-LDHs, and MgAl-LDHs could provide nucleation sites for ettringites. The three hydrotalcite-like materials slowly released different concentrations of zinc and/or magnesium ions and carbonate ions in the cement paste. Zinc ions entered the hydration product of ettringite and aluminum gel and promoted the transformation of amorphous aluminum gel to bayerite, which inhibited the hydration reaction of SCBMs. Magnesium ions could also enter the ettringite, and carbonate ions promoted the formation of calcium carbonate, which facilitated the hydration reaction of SCBMs. The nucleation effect and the release of zinc and/or magnesium ions and carbonate ions acted synergically to influence the hydration rate, pore size distribution, and compressive strength of SCBMs.

Preparation of nanocellulose-based flexible calcium carbonate to improve filler retention and combustion performance of cigarette paper

The addition of calcium carbonate to cigarette paper can enhance its combustion performance and apparent properties. However, it does come at the cost of reduced paper strength. In this study, a flexible calcium carbonate (FCC) was developed through the in-situ formation of calcium carbonate on nanocellulose surfaces. The incorporation of FCC into cigarette paper offered the potential to improve filler retention and combustion performance while maintaining high paper strength. The results of the study demonstrated that when compared to the addition of 30% precipitated calcium carbonate (PCC), the filler retention rate in cigarette paper increased by 31.5% when 30% FCC was used. Scanning electron microscopy images showed that only a minimal number of inorganic particles were observed between the fibers in the FCC-containing paper, indicating appropriate air permeability and fiber-fiber bond strength. Furthermore, when compared to PCC-containing paper, the FCC-containing paper exhibited an 8.8% increase in tensile strength and a 7.5% increase in folding resistance. Additionally, thermogravimetric analysis of the cigarette paper revealed that the incorporation of flexible calcium carbonate effectively lowered the thermal decomposition temperature, leading to a 10.3% increase in the combustion rate of FCC-containing paper. The inclusion of FCC into paper fibers has the potential to enhance air permeability and regulate cigarette burning performance. Consequently, the FCC developed in this study holds promise as a substitute for traditional calcium carbonate fillers in cigarette paper applications.

Calcium carbonate formation mechanism in MSHC revealed by molecular simulation

ABSTRACT Microbial self-healing concrete (MSHC) is an eco-friendly material that supports low-carbon development. However, the formation mechanism of calcium carbonate (CaCO3) in MSHC remains unclear. This study investigated the formation process of CaCO3 clusters in MSHC using molecular simulation. The hydroxide ion and carbonate ion (CO3 2−) would compete for association with calcium ion in MSHC. The formation process of CaCO3 clusters could be summarised as follows: free ions first associated to form ion pairs, then ion pairs aggregated into small clusters through ion-dipole interactions, and finally, small clusters overcame the surface charge effect by high-frequency aggregation-separation behaviour to transform into large clusters and further densify themselves. The reaction rate of CaCO3 cluster formation decreased significantly with the decrease of CO3 2− concentration, and the association between calcium ion and hydroxide ion would dominate when the CO3 2− concentration was low.

Carbonation curing of belite-rich cement: The role of fly ash and strengthening mechanism

Belite-rich cement (BRC) has gained increased attention in recent years due to its low energy consumption and high long-term performance. However, the carbonation behavior of the binder formed by its combination with fly ash (FA) has been scarcely revealed. This study investigated the influence of carbonation curing and FA replacement level on the carbon capture and mechanical properties of BRC. The carbon uptake, phase composition, microstructure, and micromorphology of BRC-FA composites after carbonation curing were characterized through quantitative XRD, TG, FT-IR, MIP, and SEM-EDS. The results indicated that carbonation curing significantly increased the compressive strength by up to 81.6% of BRC compared to standard curing due to the high reactivity of belite phase with CO2, whilst the hydration products of BRC gradually disappeared, and calcite and amorphous silica became the main phase accompanied with pore refinement behavior. Moderate addition of FA increased the degree of carbonation and compressive strength of BRC-FA composites, however excessive addition (45%) of FA results in adverse effect. Additionally, FA accelerated the phase recombination but coarsened the pore structure. The rapidly formed calcium carbonate crystals stacked and squeezed together, its blend with amorphous silica gel, and the pore structure rapidly densified explain the carbonation strength growth of BRC-FA composites.

Study on Carbonation of Porcine Blood Hydrogel in the Composite Mortar of Ancient Chinese Architectural Painting.

In the ancient Chinese recipe for composite mortar used in the construction of ground layers for architectural painting, the mixture of porcine blood and lime water is one of the constituent materials. Herein, according to the traditional recipe, the interaction between porcine blood and lime water was systematically and deeply investigated. The experimental investigation demonstrated that porcine blood mixed with lime water at the ratio found in the recipe can form a hydrogel with a hydrophobic surface. During air-drying, the lime water in porcine blood hydrogel can react with CO2 to form calcium carbonate. The crystal morphology of the formed calcium carbonate depends on the surrounding micro-environment of calcium ions in the porcine blood hydrogel. The formed morphology of calcium carbonate includes small calcite crystallites, small graininess calcite crystals with round features, calcite aggregates with layered ladder-like structures, and amorphous calcium carbonate (ACC). Interestingly, the calcium carbonate formed in the inner part of the porcine blood hydrogel exhibits lamellar distribution due to a Liesegang pattern formation. Based on the findings that the porcine blood hydrogel has surface hydrophobicity and brittleness, it can be predicted that in the preparation process of composite mortar for ancient building color painting base course, porcine blood used in the form of a hydrogel is not only easier to be dispersed in hydrophobic tung oil than in liquid porcine blood but also the affinity between porcine blood gel and tung oil is enhanced. As constituent material dispersed in the composite mortar, the layered distribution of calcium carbonate in the porcine blood hydrogel may presumably be beneficial to reduce the internal stress of the composite mortar material.

Effect of Heating/Cooling Rate on the Local Electronic Structure of Amorphous Calcium Carbonate

Here, in the impact of heating/cooling rate was investigated on the formation of amorphous calcium carbonate (calcite) during sol-gel synthesis by probing local electronic structure. The amorphous calcium carbonate was synthesized by annealing precursor at 400oC at different heating/cooling rates i.e., 1.5 and 3oC /min. X-ray diffraction studies revealed amorphous nature at both heating/cooling rates. Fourier transformed infrared spectroscopic measurements characteristics bands in the spectra of both materials. Near edge X-ray absorption fine structure measurements at Ca L-edge, C K-edge and O K-edge were utilized to reveal the associated changes in the local electronic structure during synthesis. Local electronic structure investigation using near edge X-ray absorption fine structure measurements shows onset of moisture absorption on the surface particles when kept in the open environment.

Calcium isotope fractionation by intracellular amorphous calcium carbonate (ACC) forming cyanobacteria.

The formation of intracellular amorphous calcium carbonate (ACC) by various cyanobacteria is a widespread biomineralization process, yet its mechanism and importance in past and modern environments remain to be fully comprehended. This study explores whether calcium (Ca) isotope fractionation, linked to ACC-forming cyanobacteria, can serve as a reliable tracer for detecting these microorganisms in modern and ancient settings. Accordingly, we measured stable Ca isotope fractionation during Ca uptake by the intracellular ACC-forming cyanobacterium Cyanothece sp. PCC 7425. Our results show that Cyanothece sp. PCC 7425 cells are enriched in lighter Ca isotopes relative to the solution. This finding is consistent with the kinetic isotope effects observed in the Ca isotope fractionation during biogenic carbonate formation by marine calcifying organisms. The Ca isotope composition of Cyanothece sp. PCC 7425 was accurately modeled using a Rayleigh fractionation model, resulting in a Ca isotope fractionation factor (Δ44Ca) equal to -0.72 ± 0.05‰. Numerical modeling suggests that Ca uptake by these cyanobacteria is primarily unidirectional, with minimal back reaction observed over the duration of the experiment. Finally, we compared our Δ44Ca values with those of other biotic and abiotic carbonates, revealing similarities with organisms that form biogenic calcite. These similarities raise questions about the effectiveness of using the Ca isotope fractionation factor as a univocal tracer of ACC-forming cyanobacteria in the environment. We propose that the use of Δ44Ca in combination with other proposed tracers of ACC-forming cyanobacteria such as Ba and Sr isotope fractionation factors and/or elevated Ba/Ca and Sr/Ca ratios may provide a more reliable approach.

Field implementation to resist coastal erosion of sandy slope by eco-friendly methods

Coastal erosion is a global issue that not only compresses land space but also undermines offshore structures. In this study, two eco-friendly technologies (microbially and enzyme induced calcium carbonate precipitation) were implemented at a sandy slope field site to enhance erosion resistance. Improvement of the treated sandy slope against erosion was assessed by penetration resistance, calcium carbonate content, cone penetration testing (CPT) results, terrain data and microscopic morphology. Results indicated that the penetration resistance and calcium carbonate content of treated slopes increased first and then decreased over time because of the gradual formation of calcium carbonate and the erosion caused by the marine environment. Calcium carbonate content and penetration resistance presents an obvious linear relationship. The existence of the superficial cemented crust layer increased the water retention capacity of the sand in the atmosphere region. The calcium carbonate content and CPT results in the tidal region shows the characteristics of layered cement. The spherical calcium carbonate cementation improves the roughness and integrity of the terrain, enhances the particle size of the sand, gradually changing the topography from pre-treatment dynamic erosion to depositional patterns. The treated slope still maintained a certain penetration resistance and calcium carbonate content for 60 days until being eroded by the wind in the atmosphere region. However, the effective protection duration in the tidal zone which encounters wind, wave, tide and reflow was about 24 days, and would thus need to be reinforced periodically over time to obtain long-term protection.

Preparation and Mechanism of Calcium Carbonate Whiskers from DoLOMITE Refined Solution

AbstractThe preparation of calcium carbonate whiskers by gas‐liquid contact method using low‐grade dolomite refining solution and CO2 as raw materials has attracted widespread attention. The effects of reaction temperature, Mg2+ concentration and pH value on the morphology, particle size, aspect ratio and crystal form of CaCO3（Calcium carbonate） whiskers are investigated in detail. SEM (Scanning Electron Microscope) and XRD (X‐ray powder diffraction) are combined to analyze the calcium carbonate whiskers. The results demonstrated that under the conditions such as 100 °C, Mg2+ concentration of 0.05 mol L−1 and pH value of 9.5, calcium carbonate whiskers with uniform distribution, aspect ratio of 15–20, and purity of 99.38% can be prepared. Through Material Studios simulation software and critical nucleation energy analysis, it is confirmed that the morphology of calcium carbonate whiskers emerged to be a long hexagonal prism. Mg2+ in the refined solution would adhere to the surface of calcium carbonate during carbonization, inhibit the formation of calcite phase, and promote the growth of face clusters connected by vertex angles between CaCO3 crystals. The initial pH condition determines the solubility of CO32− and the supersaturation of the solution, which in turn affected the formed calcium carbonate crystal form.

Experimental study on macro-micro effectiveness of Yellow River silt solidified by using soybean-induced carbonate precipitation (SICP) technology

For a long time, the sediment problem has been regarded as the most concerning issue for the Yellow River in China. Meanwhile, the research on the resource utilization of Yellow River silt has been highly valued. In this paper, soybean-induced carbonate precipitation (SICP) technology was adopted to catalyze the formation of calcium carbonate with the view of solidifying the Yellow River silt. The sensitivity of unconfined compressive strength (UCS) of solidified Yellow River silt sample to various factors such as cementation solution concentration C, grouting times N, and relative density D r was analyzed. The influence of different bio-treatment plans considering cementation solution concentration C, grouting times N on the calcium carbonate content of Yellow River silt sample with a certain relative density was characterized. Furthermore, loading failure modes of Yellow River silt cured with different cementation solution concentration C were demonstrated. Scanning electron microscope (SEM) images were used to illustrate the microscopic mechanism of biomineralization technology. The results of this study show that soybean-induced carbonate precipitation method can provide a technical guarantee for the resource utilization of the Yellow River silt.

Engineering whiting events in culture: A microalgae-driven calcium carbonate and biomass production process at high pH and alkalinity with the marine microalga Nannochloropsis oceanica IMET1

The impact of whiting events on global inorganic carbon cycle and climate change is debatable at the current ocean pH. This work engineered whiting events in a high pH, high alkalinity microalgal culture for carbon dioxide capture and storage. When growing the marine microalga Nannochloropsis oceanica IMET1 in photobioreactors, culture alkalinity more than doubled, increasing from 72.5 mg L-1 to a maximum level of 159.6 mg L-1. At the same time, culture pH increased from 7.9 to 10.1 with concomitant calcium carbonate production. X-ray diffraction analysis revealed the precipitated calcium carbonate was primarily monohydrocalcite. The lab culture was scaled up to a 340-L bioreactor, in which Nannochloropsis ash-free dry weight productivities ranged from 25.1 to 51.4 g m-2 d-1 and a maximum monohydrocalcite productivity of 133.4 g m2 d-1 was recorded. In this system, Nannochloropsis biomass contained about 23.9 % lipids and the eicosapentaenoic acid content was about 1.8 %. Together, these results suggest the microalgae-driven calcium carbonate and biomass production process efficiently captures and stores atmospheric carbon dioxide in the form of calcium carbonate while producing valuable bioproducts. Study of the bacterial communities associated with the Nannochloropsis culture identified four dominant species Maricaulis maris, Marinisubtilis pacificus, Gracilimonas sp., and an uncultured bacterium in the OD1 phylum with interesting features that warrant further investigation.

Effect of carbonation of soil-slag mixtures on the resilient behaviour and structural response of an asphalt pavement

In the face of rapid population growth and industrialisation, mitigating the harmful effects of CO2 emissions becomes an important issue to be studied. The objective of this study was to perform a structural analysis evaluating the influence of carbonation of soil-electric arc furnace slag (EAFS) mixtures used in the subgrade layer of an asphalt pavement. Resilient modulus tests (RM) were performed on the soil-EAFS mixtures subjected to two curing processes. The structural analysis was performed using the AEMC software, being evaluated: (i) the deflection at the top of the asphalt layer, (ii) the horizontal tensile strain at the bottom of the same layer, and (iii) the vertical strain at the top of the subgrade layer. Carbonation increased the values of RM due to the formation of calcium carbonate, which led to a reduction in the analysed deflection and strains, resulting in a more durable asphalt pavement.

Effect of nanoparticle-enhanced biocementation in kaolinite clay by microbially induced calcium carbonate precipitation

Microbially induced calcium carbonate precipitation (MICP) is a nature-based technique that has been developed over the past two decades for soil stabilization. However, the use of MICP for clay stabilization has received limited attention in the literature. On the other hand, the utilization of nanomaterials, such as nano-silica (nano-SiO2), for soil stabilization has been explored in numerous studies in the literature. This paper investigates the effect of nano-CaCO3 and nano-SiO2 on MICP stabilization in kaolinite clay. Nanoparticle-enhanced bio-cementation is introduced to effectively improve the strength of kaolinite clay at high water contents. Unconfined compressive strength (UCS) tests were conducted to evaluate the impact of the nano-bio-treatment (mixture of nano-additives and MICP) on soil strength. Additionally, the microstructure of the treated soils was examined using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Raman spectroscopy, and X-ray diffraction (XRD) analyses. The results indicate that the MICP stabilization method is effective in enhancing the strength of kaolinite soil through a mixing approach. The study of UCS in the treated samples revealed that the use of nano-CaCO3 and nano-SiO2 can have either detrimental or beneficial effects on the MICP method, depending on the degree of saturation of the treated samples. The highest UCS observed for the MICP method at a target water content of 0.25 was more than three times that of untreated soil at the same moisture content. Furthermore, the increase in UCS for the samples treated with MICP was 2.5 times that of the untreated soil at a 30% target water content. The most significant finding, however, is that, at a 30% target water content, the samples improved with MICP+ 1.5% nano − SiO2 exhibited UCS values that were six and fifteen times greater than those of the untreated and MIC-treated samples, respectively. SEM images illustrated that the addition of nano-SiO2 with the MICP method led to an agglomerated soil texture, and the formation of calcium carbonate attached to the clay minerals. This results in an increase in soil strength.

Carbon storage in mollusk shells: An overlooked yet significant carbon sink in terrestrial ecosystems

Mollusks, the second largest animal family, are found in a variety of ecosystems. As they grow, their shells absorb carbon and form calcium carbonate, making them an important storage place for carbon. However, the amount of carbon deposited in the carbonate shells of terrestrial mollusks throughout modern and geological history has not been quantified. In this study, we first conducted an investigation of carbon deposits in shells from various mollusk species at 470 modern surface soil sample sites across diverse terrestrial ecosystems in China. The deciduous broadleaf forest and shrublands exhibited a higher carbon deposition rate of ∼1.37 ± 2.15 and ∼1.56 ± 2.92 g C m−2/yr−1, while croplands and grasslands displayed a rate of ∼1.11 ± 1.95 and 1.07 ± 1.78 g C m−2/yr−1, respectively. Using geostatistical methods, we estimated the total shell carbon deposition of grassland, forest, shrublands, and croplands in China to be ∼3.39–5.45 × 106 t C yr−1, constituting ∼1.68–2.71 % of China's terrestrial carbon sink, an overlooked portion in previous studies. Additionally, we provided quantitative data on shell carbon fluxes spanning a remarkable 20,000-year period through over ten fossil sequences from loess deposits. The results underscore the continuous and abundant carbon deposition in mollusk shells across various locations for at least 20,000 years, highlighting the persistence and substantial accumulation of shell carbon deposits over time. Remarkably, we estimated that the total shell carbon deposition of loess sediments in China and the world over the past 20,000 years may reach 1.10 × 108 t C and 1.29 × 109 t C, roughly equivalent to an afforestation area of 2.32 × 106 km2 and 2.72 × 107 km2, respectively.

Colloidal pathways of amorphous calcium carbonate formation lead to distinct water environments and conductivity.

CaCO3 is the most abundant biomineral and a major constituent of incrustations arising from water hardness. Polycarboxylates play key roles in controlling mineralization. Herein, we present an analytical and spectroscopic study of polycarboxylate-stabilized amorphous CaCO3 (ACC) and its formation via a dense liquid precursor phase (DLP). Polycarboxylates facilitate pronounced, kinetic bicarbonate entrapment in the DLP. Since bicarbonate is destabilized in the solid state, DLP dehydration towards solid ACC necessitates the formation of locally calcium deficient sites, thereby inhibiting nucleation. Magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy of poly-aspartate-stabilized ACC reveals the presence of two distinct environments. The first contains immobile calcium and carbonate ions and structural water molecules, undergoing restricted, anisotropic motion. In the second environment, water molecules undergo slow, but isotropic motion. Indeed, conductive atomic force microscopy (C-AFM) reveals that ACC conducts electrical current, strongly suggesting that the mobile environment pervades the bulk of ACC, with dissolved hydroxide ions constituting the charge carriers. We propose that the distinct environments arise from colloidally stabilized interfaces of DLP nanodroplets, consistent with the pre-nucleation cluster (PNC) pathway.

A Non-destructive Method for the determination of Carbonation Time for Nominal Concrete Cover Depth Using Non-Linear En-semble Prediction

Carbonation, a process involving the reaction of carbon dioxide and moisture, results in the for-mation of powdery calcium carbonate, a critical durability issue causing reinforcement corrosion. The study analyzed carbonation data from coastal and inland buildings in the Turkish Republic of Northern Cyprus, re-vealing higher carbonation rates than anticipated within their lifespan. An artificial intelligence model named Support Vector Machine (SVM) was applied to predict carbonation time (T) to penetrate concrete cover of 25mm in the TRNC. Subsequently used two ensemble techniques, namely Neural Network Ensembles (NNE) and Support Vector Machine Ensembles (SVME) to enhance the performance of the prediction of T. Four performance criteria namely Correlation Coefficient (CC), Root Mean Square Error (RMSE), Correlation Co-efficient (R2), Mean Absolute Error (MAE) was applied to verify the modelling accuracy. The Values of R2 of Ensemble techniques indicated significant increase in the performance, greater than the SVM model. This shows that using ensemble techniques is promising in getting better predictions of carbonation time (T) to penetrate concrete cover. The results obtained showed that NNE and SVME combination demonstrated the best performance under the evaluation criteria of R2 = 0.8721 and R2 = 0.8644 in testing phases respectively in comparison SVM-M1 to SVM-M3.

Effects of bacterial consortium enhanced recycled coarse aggregates on self‐healing concrete immobilized with Bacillus megaterium MTCC 1684 and Bacillus subtilis NCIM 2193

AbstractThe strength and durability properties of the recycled aggregate concrete (RAC) have been affected by the cracks and the weak interfacial transition zone (ITZ) of the recycled coarse aggregates (RCA). However, the mechanical and physical features of RCA can be improved by microbially induced calcite precipitation (MICP). Therefore, immobilization techniques were used to protect and maintain the high efficiency of Bacillus bacteria for the formation and precipitation of calcium carbonates in self‐healing concrete over a period of time. The objective of the present study was to show the viability of the immobilized bacterial consortium‐enhanced RCA to form self‐healing cracks. Further, the self‐healing capability of enhanced RCA was investigated along with two other immobilization methods, that is, RCA and hydrated lime and brick powder (HBr)‐immobilized bacteria. The experimental results show that the increase in the bio‐deposition time improved the physical and mechanical properties of the RCA. Further, subsequently 56 days of the healing incubation period, the immobilized consortium‐enhanced RCA concrete specimens completely healed the cracks of width 0.58 mm. However, the equivalent cracks of width 0.56 mm were also recovered by the HBr immobilized bacterial cultures. Furthermore, the field emission scanning electron microscope (FESEM), energy dispersive spectroscopy (EDS) and X‐ray diffraction (XRD) analysis revealed that the existence of precipitation at the crack surface was calcium carbonate with a regular cubic‐shaped and lamellar layer morphology. The outcomes of the current study show that consortium‐enhanced RCA has promising potential to develop self‐healing concrete with self‐repaired and improved durability properties in the concrete construction field.

TYPOMORPHISM OF THE CHEMICAL COMPOSITION OF BIOGENIC CARBONATES WITHIN THE PRADNIPROV METHANE ANOMALY ON THE BLACK SEA SHELF

Problem Statement and Purpose. The aim of the article is to study the typomorphism of the chemical composition of biogenic calcium carbonates within methane anomalies formed by deep fluids in the bottom sediments of the Black Sea shelf. Gas chromatography was performed at the «Pradniprovska» study area. The results of the site`s bottom sediments analysis confirmed the content of pure methane and its homologues in the samples. Due to the presence of methane homologues, oxygen and carbon isotope analysis of the sediment shells was performed (it is known that the most stable information about the chemical composition of the mineral formation environment can be stored in biogenic carbonates of benthic organisms’ shells). The values obtained from the analysis had a small spread and did not show any visible variability. Data & Methods. Data on the chemical composition of benthic organisms’ shells can be obtained using inductively coupled plasma atomic emission spectrometry. This method requires large samples by weight, so only the shells of the Mytilus mollusks were taken for the study due to their relatively large size. The gas-geochemical studies were based on the methodology of the NDL‑3 laboratory. The extracted gas was stored in glass tubes under a saturated saline solution, which ensured minimal losses from gas dissolution in the seal fluid, followed by studying it using a «Tsvet‑400» gas chromatograph. The separation of hydrocarbon gases was carried out on a chromatographic column filled with aluminum oxide. The detector is flame ionization. Calibration was carried out before the start of each cycle with calibration gas mixtures of standard composition. The spectrometric analysis was performed on a Thermo Scientific inductively coupled plasma atomic emission spectrometer with a CID or CMOS detector operating in the range of 167–820 nm. The method is based on the dissolution of substances in a mixture of nitric, hydrochloric and hydrofluoric acids at a temperature of at least 125 °C, followed by the determination of elements in solutions by inductively coupled plasma atomic emission. To consider matrix effects and improve measurement accuracy, calibration using internal standard lines is used. Results. The analysis of the obtained material allowed the author to draw the following conclusions: a) chemical elements in shells are unevenly distributed, and this unevenness is determined by two main reasons – the peculiarity of the formation of biogenic carbonate of shells and the ability of the carbonate to isomorphically capture a number of elements from the mineral-forming environment; b) according to the quantitative characteristics, three groups of elements can be distinguished: macroelements, mesoelements and trace elements. The first group of elements (macroelements) includes Na, S, Mg, Sr, Fe, Si, Mn, P, K. Among them, one can clearly distinguish elements that are isomorphically included in the structure of calcite or aragonite (Na, Mg, Sr, Fe, Mn, K) and elements captured as non-structural impurities in the agglutination process during the growth of biogenic carbonate (Si, S and P). The second group (mesoelements) includes Ba, Al, As, Zn, Cu, Ti, among which two groups can also be distinguished. One is associated with the formation of sulfide minerals paragenetic to biogenic calcite (As, Zn, Cu), and the other with agglutination of clay minerals in sediments (Al, Ti), or a feature of isomorphism in the biogenic formation of calcium carbonate (Ba). The third group (trace elements) is associated with elements of low content and uneven distribution (Ni, Mo, Pb, Se). The main group here is Ni, Cr, Co, V. These groups, taking into account the fact that they were found in the areas of penetration of deep-sea fluids into the sedimentary strata, allows to consider them as typomorphic signs of biogenic carbonate formation in the areas of fluid influence, and, consequently, as a search sign of such areas on the Black Sea shelf.

Unlocking the mysteries: Investigating the kinetic mechanism of calcium carbonate formation from phosphogypsum

Apparent inconsistencies exist in the comprehensive utilization of sulfate, indicating a lack of systematic investigation into the relationships between reacting conditions and the structures of materials. This study quantifies the coprecipitation and transformation process during dissolution-carbonation from phosphogypsum (PG) to polymorphs of calcium carbonates (CaCO3) in the presence of NaOH, NH3, and CO2 through a two-step process. The research establishes a framework for characterizing resulting solutions and achieving products. Additionally, the kinetic mechanism of CaCO3 preparation and PG carbonation was established using a new atomistic KMC model, which reconciles discrepancies and predicts dissolution modes approaching equilibrium. Particularly, it predicts the structures and stability of CaSO4 hydrates by leveraging differential solubilities at a molecular level. Subsequent carbonation with CO2 and the calculation of equilibrium relationships under controlled conditions resulted in the production of CaCO3 from CaSO4·2 H2O. Model simulations and parameter optimization for precursors, intermediates, and generators were monitored and compared over time using RS and powder EPR experiments, yielding optical information for investigating the kinetic mechanism. The findings highlight that PG-involved pathways play a role in purification and mineralization, emphasizing the need to reevaluate traditional concepts of utilizing calcium-rich waste and capturing CO2.