Search Results (291)

This study presents a comprehensive characterization of Argopecten purpuratus (AP) shells—a marine-derived natural bioceramic composed predominantly of calcium carbonate (CaCO₃)—to evaluate their potential as biomaterials for regenerative medicine. Structural and compositional analyses were performed using micro-computed tomography (MicroCT), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and X-ray diffraction (XRD). These techniques confirmed a high CaCO₃ content (>96 wt%) and revealed distinct microstructural features: the outer surface showed irregular grooves and rough textures, while the inner surface exhibited smoother, foliated morphologies with mixed calcite and aragonite phases. To assess biocompatibility, human gingival mesenchymal stem cells (hGMSCs) were cultured on both shell surfaces. Viability and adhesion were evaluated via MTS assays and fluorescence microscopy at time points ranging from 30 min to four weeks. Both surfaces supported robust early metabolic activity and long-term proliferation, with cells covering the entire surface area after four weeks. Morphometric analysis indicated time-dependent changes in cell shape, transitioning from rounded to elongated morphologies, with minor differences linked to surface topography. The integration of structural, compositional, and biological data demonstrates that AP shells provide a cytocompatible and sustainable natural material platform capable of supporting cell adhesion and proliferation. Their inherent micro- and nanoscale surface features may facilitate protein adsorption and cell–material interactions. These findings highlight the importance of correlating microstructural material properties with cellular responses and support the future exploration of marine-derived bioceramics for regenerative medicine applications. Full article

This study examines the carbonation behavior and CO₂ storage potential of a Ca-rich alkali-activated binder produced entirely from industrial residues-ladle furnace slag (LFS), coal ash (CA), and cement kiln dust (CKD). The system was designed as a one-part alkali-activated material (AAM), with CKD acting as an internal activator, and subjected to ambient curing, water curing, and accelerated CO₂ curing at ambient pressure. Phase evolution, microstructural development, and pore-structure characteristics were investigated using X-ray diffraction, FTIR spectroscopy, DSC–TG analysis, scanning electron microscopy, and X-ray micro-computed tomography, together with measurements of density, water absorption, and compressive strength. Loss-on-ignition measurements combined with chemical analysis were further used to quantify CO₂ uptake and evaluate the degree of carbonation of the binder system. CO₂ curing fundamentally altered the reaction pathway of the binder, shifting it from hydration-dominated to carbonation-controlled phase evolution, leading to the decomposition of calcium-bearing hydrates and complete carbonation of non-hydraulic γ-belite with the formation of vaterite, aragonite, and calcite. These transformations induced pronounced microstructural densification, reflected in a near-doubling of compressive strength (>48 MPa), increased apparent density, reduced water absorption, and simplified pore-network topology. A preliminary carbon footprint assessment indicates that the production of 1 m³ of the developed LFS–CA–CKD concrete generates about 14.36 kg CO₂-eq, while the carbonation process enables significant CO₂ sequestration, resulting in a net negative carbon balance. The results demonstrate that controlled carbonation is an effective post-treatment strategy for waste-derived alkali-activated binders, enabling simultaneous performance enhancement and permanent CO₂ sequestration. Full article

Limestone corrosion and coastal karst cave (flank margin cave) enlargement are closely related by the mixing zone between meteoric and seawater, yet quantitative data on corrosion rates in these environments remain scarce. Recent speleodiving exploration in flanking margin caves in Mallorca revealed numerous submerged cavities with different haloclines between 0 and 25 m below m.s.l. To investigate rock-decay mechanisms along these haloclines, exposure trials were conducted in Cova de sa Gleda. Three sets of water-loss rock tablets (WLRT), composed of bioclastic calcarenite limestone and crystalline aragonite (aragonite crystal aggregates), were deployed along a water-column depth profile ranging from 5 to 16 m. After 749 exposure days, tablets were explored by SEM and XRD. Differences in mass show that calcarenite tablets lost an average of 1.89% of their initial mass, while aragonite tablets have lost 8.05%. Corrosion rates varied along haloclines: at 5 m depth (10 to 16 PSU), rates were 3.10% for calcarenites and 11.08% for aragonite; at 10 m (19 to 29 PSU), corrosion increased respectively to 10.8% and 17.93%; at 16 m (>35 PSU, seawater), corrosion decreased to 1.97% and 3.48%, respectively. These haloclines coincide with the height position of notches and other observable corrosion features within the cave. Consequently, these corrosion features present along the cave can be interpreted as proxies of the former position of the groundwater mixing zone. Full article

From Palaeolithic ornaments to modern biomimetics, the use of nacre and shells has evolved. Initially utilised for jewellery and tools, they now inspire the development of advanced materials. This paper reviews the current knowledge on nacre’s composition, focusing on the highly regulated biomineralisation process wherein amorphous calcium carbonate (ACC) transforms into crystalline aragonite. It examines the important role of the organic matrix (specifically soluble, insoluble, and acidic proteins) in controlling crystal nucleation, growth, and polymorph selection. Scientists study natural nacre formation to create nacre-inspired composites for various applications. Charles Hatchett’s in 1799 shell categorisation, Sorby and Sowerby’s 19th-century microscopy, Taylor, Beedham, Bøggild, and Currey’s mid-20th-century research on bivalve structures, and mechanical property investigations in the 1970s are some of the major developments. The hierarchical structure, cooperative plastic deformation, surface asperities, organic–inorganic interactions, and interphase in such complex composite materials give rise to impressive mechanical properties. In the early 2000s, with the emergence of biomimetics, inspired by nacre, several macroscopic structural materials with uniform micro- and nanoscale architectures have been synthesised in recent decades, and their mechanical properties and potential applications have been explored. Modern nacre-inspired fabrication utilises 3D printing for precision, freeze casting for sustainability, and mineralisation for scalability. Techniques like layer-by-layer assembly and nanomaterial integration enhance mechanical performance through advanced interfacial engineering. Full article

Conventional production methods of aragonite production utilize chemical inducers to promote the evolution of the calcite crystalline phase to the aragonite phase of calcium carbonate. The chemical inducers used require a considerable amount of magnesium chloride (MgCl₂) to induce crystallization, which is a major operational cost. Application of such materials in large amounts can be a deterrent to achieving a sustainable and economically feasible end-product derived from carbon dioxide (CO₂) molecules. A number of previous research works focused mainly on optimizing the usage of MgCl₂ or introducing alternative chemical inducers for aragonite production. In this work, we are proposing the usage of natural seawater as it is a naturally available and abundant resource to induce the synthesis and continuous production of aragonite compounds. Due to inconsistent quality and salinity of the natural seawater sampled, harvested, and dried, Red Sea Salt is utilized, blended at 33 g/L throughout the laboratory experiments for better statistical control, and is referred to as blended or artificial seawater. A methodology of utilizing seawater, which has a considerable concentration of MgCl₂ compound, can be utilized as a sustainable, natural, and economically feasible natural inducer to synthesize aragonite has been developed by utilizing artificial seawater for laboratory proof of concept. The main effects identified for the optimization of aragonite synthesis are lime (CaO) feedstock concentration in seawater, reaction temperature, and reaction duration. The experiment results indicated that only by increasing temperature and reaction duration, or both, can the aragonite yield be increased. It is suggested that the range of operation to obtain > 80% aragonite purity has been identified with the reaction temperature at 90 °C, reaction duration of 10 min, and CaO concentration in seawater at 1 g/L. The quality of the aragonite synthesized via seawater is characterized using XRD, ICP, FESEM, and TGA, and compared with aragonite particles synthesized using MgCl₂ inducers. In comparison, seawater aragonite has lower residual alkalinity compared to both calcite and aragonite via MgCl₂ and has a mixture of predominantly needle-shaped crystalline structure and remnants of cubic-shaped particles, presumably calcite, suitable for application in food, beverages, and pharmaceuticals (calcium antacids, nutritional supplements, chewable, lozenges). Full article

Lime kiln dust (LKD), a by-product of the paper industry, generates about 100 tonnes of waste per 400,000 tonnes of kraft paper produced, while global aquaculture yields more than 16 million tonnes of oysters annually, 65–90% of which is made up of shells. This study explores their valorisation in the production of more eco-friendly mortars by partially replacing hydrated lime with LKD and oyster shell powder (OSP). In addition, a vinegar solution (VS), prepared by reacting oyster shells with white vinegar (~5% acetic acid), was used as an alternative mixing liquid instead of water. The LKD and OSP were tested at different substitution levels, showing promising mechanical performance, supporting their use as sustainable alternatives in mortar production. Replacement levels of 25%, 50% and 90% achieved compressive strengths ≥ 0.4 MPa at 28 days. At 28 days, the reference lime mortar prepared with water reached 0.83 MPa, while the use of the vinegar solution increased the compressive strength to 1.86 MPa, representing an improvement of approximately 124%. Regarding binder replacement by wastes, the most efficient mechanical performance was obtained for mixtures with 50% LKD substitution, reaching 2.04 MPa at 28 days and 3.11 MPa at 60 days, increasing by 10% and 43%, respectively, while mixtures incorporating oyster shell powder showed more stable mechanical behaviour across substitution levels. Using a hot-mixing process with quicklime in the presence of the vinegar-based solution and sand may account for the higher strengths, due to the heat/steam generated during lime hydration prior to moulding and verified by microscopy. In addition, VS-containing mixes showed higher aragonite contents and detectable phosphorus-bearing compounds, which may further contribute to matrix densification and strengthening. Overall, the results indicate that the combined use of uncalcined calcium-based wastes and a vinegar-based solution can contribute to the development of calcium-based mortars with good mechanical performance, supporting circular economy strategies and the reduction in calcined-binder use in construction materials. Full article

The Cambrian Period represents a critical yet debated interval in the global transition from “Aragonite Seas” to “Calcite Seas”. This study reconstructs the physicochemical evolution of paleoseawater through microstructural analysis and trace element geochemistry of Cambrian oolitic rocks in the northern Sichuan Basin, South China. Our results demonstrate that micrite envelopes on ooid margins and early submarine cements (Stage 1) effectively least-altered signals, resisting diagenetic alteration. Consequently, the maximum values of trace element in these fabrics serve as reliable proxies for paleoseawater reconstruction. Ooids from the upper Canglangpu Formation to the Longwangmiao Formation (Lower Cambrian, Series 2) are characterized by concentric laminations with tangential ultrastructures, high Sr contents (up to 1536 ppm), and high seawater molar Mg/Ca ratios (hereafter mMg/Ca, up to 5.02). These features contrast sharply with the radial fabrics, low Sr contents (<400 ppm), and low seawater mMg/Ca ratios (<0.4) observed in the Xixiangchi Formation (Upper Cambrian, Furongian). Integrating regional data with global correlations, this study confirms that Aragonite Sea conditions persisted on the northern margin of the Yangtze Block until at least the late Early Cambrian (Stage 4). The Middle Cambrian (Miaolingian) represents a pivotal transitional interval, leading to a complete shift to a stable Calcite Sea by the Late Cambrian (Furongian). These findings provide crucial regional constraints for refining the Phanerozoic model of seawater chemical evolution. Full article

To overcome the high cost, marine ecological risks of traditional coral sand reinforcement, and the insufficient mechanical performance of standalone Enzyme-Induced Carbonate Precipitation (EICP), this study proposes a novel soil improvement method integrating EICP with aluminum chloride hexahydrate (AlCl₃·6H₂O). The objectives are to identify optimal EICP curing parameters, evaluate AlCl₃·6H₂O’s enhancement effect, and reveal the synergistic micro-mechanism. Through aqueous solution, unconfined compressive strength, permeability, X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and Scanning Electron Microscope (SEM) tests, this study systematically investigated the reaction conditions, mechanical properties, anti-seepage performance, mineral composition, and pore structure. The results demonstrate that EICP achieves the best curing effect under specific conditions: temperature of 30 °C, pH of 8, and cementing solution concentration of 1 mol/L. Under these optimal conditions, the unconfined compressive strength of EICP-solidified coral sand columns reaches 761.6 kPa, and the permeability coefficient is reduced by one order of magnitude compared to unsolidified samples. Notably, AlCl₃·6H₂O incorporation yields a significant synergistic effect, boosting the UCS to 2389.1 kPa (3.14 times standalone EICP) and further reducing permeability by 26%. Micro-mechanism analysis reveals that AlCl₃·6H₂O acts both by generating cementitious aggregates that provide nucleation sites for uniform calcite deposition and by accelerating the transformation of metastable aragonite and vaterite to stable calcite, thereby enhancing cementation stability. This study delivers a cost-effective, eco-friendly solution for coral sand reinforcement, providing practical technical support for marine engineering in environments like the South China Sea. By addressing the core limitations of conventional bio-cementation, it opens new avenues for advancing soil improvement science and applications. Full article

The South Sakhalin mud volcano (Sakhalin Island, Russia) emits HCO₃-Cl/Na-Mg water, emanates CO₂ prevailing over CH₄ in the gas phase, and extrudes mud bearing five carbonate mineral species. The study focuses on the distribution, diversity, and origin of the carbonate minerals from the mud volcano (MV) ejecta, in terms of carbon cycle processes. The data presented include a synthesis of field observations, compositions of MV gases and waters, chemistry of carbonate minerals, as well as stable isotope geochemistry of MV waters (δ¹³C, δD, and δ¹⁸O) and carbonates (δ¹³C and δ¹⁸O). The sampled MV waters are isotopically heavy, with δ¹⁸O = +5.7‰ to +7.5‰ VSMOW, δD = −18.0‰ to −11.0‰ VSMOW, and ¹³C (δ¹³C_DIC = +6.9‰ to +8.1‰ VPDB). This composition may be due to the dilution of basinal water with dehydration water released during the diagenetic illitization of smectite. Carbonates in the sampled mud masses belong to three genetically different groups. Mg-rich siderite, (Fe_0.54–0.81Mg_0.04–0.30Ca_0.05–0.23Mn_0.00–0.08)CO₃, disseminated in abundance throughout the mud masses, coexists with common calcite and sporadic ankerite. The trace-element chemistry of Mg-siderite, as well as the oxygen (δ¹⁸O = +34.4‰ to +36.8‰ VSMOW) and carbon (δ¹³C = −1.3‰ to +0.6‰ VPDB) isotopic signatures, confirms its authigenic origin. Siderite formed during early diagenesis of the Upper Cretaceous sandy and clayey marine sediments mobilized by mud volcanism in the area. Another assemblage, composed of dawsonite, siderite, and vein calcite (±kaolinite), represents altered arkose sandstones found as few fragments in the mud. This assemblage may be a marker of later CO₂ flooding into the sandstone aquifer in the geological past. The trace-element chemistry, particular morphology, and heavy C (δ¹³C = +5.5‰ to +7.0‰ VPDB) and O (δ¹⁸O = +39.1‰ to +39.5‰ VSMOW) isotope compositions indicate that aragonite is the only carbonate species that is related to the current MV activity. It crystallized in a shallow reservoir and was maintained by CO₂ released from rapidly ascending liquefied mud and HCO₃-Cl/Na-Mg-type of MV waters. Full article

Lake sediments on the Tibetan Plateau serve as crucial carbon sinks in the regional carbon cycles. In recent decades, climate change has triggered significant hydrological changes in many lakes across this region, potentially impacting their carbon-sink functions. Previous studies have predominantly focused on the dynamics of organic carbon burial, largely overlooking the contribution of inorganic carbon sinks, and particularly lacking systematic investigation into the carbon burial processes in lakes experiencing water level decline. Therefore, this study examines a sediment core from Lake Yamzhog Yumco, a lake in the southern Tibetan Plateau with a gradually declining water level. The mineralogical and geochemical analyses of both lake and catchment sediments show that the inorganic carbon (carbonates are dominated by aragonite) and organic carbon are primarily authigenic origin. Over the past four decades, the inorganic carbon burial rate (ICBR) in Lake Yamzhog Yumco has been primarily controlled by water level fluctuations and is closely related to hydrochemical processes regulated by regional climate change. In contrast, the increase in the organic carbon burial rate (OCBR) has been co-influenced by both water level changes and regional temperature. During this period, the ICBR reached as high as 186 g m⁻² yr⁻¹, approximately five times the OCBR. This demonstrates that in lakes in semi-arid regions, the sink potential of inorganic carbon significantly exceeds that of organic carbon, highlighting the necessity of incorporating inorganic carbon burial into carbon-sink assessments. This study provides novel perspectives for a deeper understanding of the driving mechanisms behind carbon burial in Tibetan Plateau lakes and offers a scientific basis for accurately assessing and predicting regional carbon-sink potential. Full article

Marine deposits in western Europe provide insight into the interplay between the warm Tethys and cooler Boreal domains, offering a climatic context for the radiation of Early Jurassic species. Reconstructions of temperature for the Hettangian and Sinemurian periods are scarce, with inferred marine temperatures of 15–20 °C based on δ¹⁸O values, which are lower than those of subsequent Jurassic stages. This emphasizes the necessity for supplementary data in order to enhance our comprehension of the climatic dynamics that characterized the Early Jurassic period. This study analyses 75 invertebrate samples, including 53 specimens of Gryphaea arcuata, from Early Sinemurian marine sediments in the Fresville quarry, Normandy, France. The present study employs a multi-proxy approach, utilizing δ¹³C and δ¹⁸O values in conjunction with Sr and Mg contents, to assess the processes of fossil diagenesis, marine productivity, and seawater temperatures. Significant post-depositional alteration was observed in the geochemical compositions of 22 bivalve shells assigned to the genera Pseudolimea, Plagiostoma, and Chlamys, which were originally composed of aragonite, except for the outer layer, which is made of calcite. However, the low-Mg calcite shells of Gryphaea arcuata, which are renowned for their diagenetic resistance, retained the majority of their isotopic integrity. The results of the statistical analyses indicate that there was minimal late pervasive diagenesis involving meteoric waters at Fresville. This is in accordance with the typical decrease in δ¹³C, δ¹⁸O values, and Sr and Mg contents that such processes would otherwise cause. Published isotopic data from Sinemurian marine fossils (plesiosaur and shark teeth) were used to estimate seawater δ¹⁸O (~−1‰ VSMOW) and surface temperatures (~24 °C). The calculated benthic temperatures of Gryphaea (17 °C) correspond to habitats at depths of about 50 m. These findings suggest a positive hydrological balance and euhaline conditions in a humid tropical climate context. Full article

Natural fillers have been widely explored to enhance the mechanical and barrier properties of biodegradable films. In this study, a mineral-rich powder obtained from the solid components of Ucides cordatus crab shells was processed (washing, drying, milling, and sieving at 75 µm) and extensively characterized using SEM, FTIR XRD, EDX, mineral analysis, hygroscopicity, density, and particle size distribution. The powder exhibited heterogeneous morphology and contained 22.52 g·kg⁻¹ of calcium carbonate, along with other trace minerals; its crystalline profile indicated the presence of both calcite and aragonite. Low hygroscopicity (1.76%) and a true density of 2.11 g/cm³ were also observed. When incorporated into pectin-based films at 1–5%, the filler promoted a reduction in film thickness, indicating enhanced structural compaction. Solubility increased linearly with filler content, whereas water vapor permeability (WVP) decreased at 1% and 2% but rose again at 4% and 5%, correlating positively with solubility (r = 0.895). Films containing 4% and 5% exhibited higher tensile strength and elastic modulus, confirming increased rigidity. At elevated concentrations, the films also became less luminous and more chromatic. Overall, the findings demonstrate that crab-shell mineral powder is a viable and sustainable reinforcement capable of tailoring the structural, mechanical, and barrier performance of biodegradable films. Full article

Calcium carbonate (CaCO₃) whiskers are promising materials for the high-value utilization of calcium-based resources. Here, aragonite whiskers were synthesized at a carbonation temperature of 90 °C using carbide slag ammonium leachate as the calcium source and CO₂ as the precipitant. The effects of control agents, carbonation temperature, Ca²⁺ solution feeding rate, CO₂ flow rate, and stirring speed on whisker morphology and aspect ratio were systematically investigated. Characterization via SEM and XRD revealed that the optimal conditions—carbonation temperature of 90 °C, Ca²⁺ feeding rate of 1.2 mL∙min⁻¹, ethanol addition of 2 mL, CO₂ flow rate of 150 mL∙min⁻¹, and stirring speed of 300 rpm—yielded uniform CaCO₃ whiskers with an average length of ~10 μm, an aspect ratio of ~24, and an aragonite purity of 99.42%. TEM confirmed that the whiskers are single crystals growing preferentially along the [001] direction. Hydroxyl groups were found to suppress lateral growth on the (200) facet, favoring elongation along the c-axis and enabling high-aspect-ratio whisker formation. These findings provide useful guidance for the scalable synthesis and industrial application of aragonite whiskers. Full article

The Muji carbonic springs on the northeastern margin of the Pamir Plateau provide a natural window into tectonically controlled CO₂ degassing within a continental collision zone. Through mineralogical and geochemical analyses, this study constrains the formation mechanisms and regional geological significance of carbonic spring systems. The formed deposits are dominated by calcite and aragonite, with minor dolomite, quartz, and gypsum. The compositions of major elements are consistent with the observed mineral assemblages, reflecting that the carbonate deposition was mainly governed by CO₂ degassing intensity and associated kinetic effects under cold-spring conditions. Carbon isotopes of the deposits are consistently enriched in heavy carbon with δ¹³C values of +3.5‰ to +9.1‰, indicating a persistent contribution of deep-sourced CO₂, most likely derived from metamorphic decarbonation of the crustal carbonates. Calcite exhibits moderate δ¹³C values due to rapid precipitation limiting isotope enrichment, whereas aragonite records higher δ¹³C signatures under subdued degassing and stable hydrodynamic regimes. The narrow δ¹⁸O range (−10.7‰ to −12.6‰), closely matching that of the spring waters, indicates that the tufas record the δ¹⁸O of the spring waters through DIC-water oxygen exchange. Trace element distributions (Sr–Ba–U) reveal systematic enrichment in deep-sourced fluids and progressive downstream geochemical alteration driven by spring–river mixing. The HD springs show high Sr and δ¹³C values, indicating minimal dilution of ascending CO₂-rich fluids, while MJX and MJXSP groups record variable degrees of shallow mixing. Collectively, the Muji system exemplifies a coupled process of “deep fluid input–shallow mixing–precipitation kinetics.” Its persistent heavy δ¹³C and trace-element enrichments demonstrate persistent metamorphic CO₂ release through fault conduits under ongoing compression. These findings establish the Muji springs as a key non-volcanic analogue for deep CO₂ degassing in continental collision zones and provides new insights into crustal carbon recycling and tectonic–hydrochemical coupling at plateau margins. Full article

Seafood-derived carbonate waste, primarily calcium carbonate (CaCO₃), has attracted growing interest for sustainable reuse, yet the unique potential of aged biogenic sources remains underexplored. Blue crab (Callinectes sapidus) shells are particularly distinctive: they consist of Mg-calcite with an intrinsic 3D-porous structure and naturally embedded astaxanthin, a potent antioxidant not found in other calcite- or aragonite-based residues. While organic degradation over time is often assumed to compromise functionality, this study demonstrates that five-years-aged crustacean shell waste retains both its crystallinity and bioactive carotenoids after calibrated ball milling. Across four powder batches produced under distinct milling conditions by varying frequencies and durations, dynamic light scattering confirmed only subtle particle size variation, while Raman spectroscopy, XRD, FT-IR, and SEM-EDX confirmed structural and chemical integrity and highlighted the subtle amorphization induced by slightly different milling parameters, which, in turn, driven to slightly different conversion efficiency into phosphate mineral. Strikingly, all powders underwent rapid transformation into dicalcium phosphate dihydrate (brushite) enriched with carotenoids upon reaction with phosphoric acid. This work reveals, for the first time, that years-aged biogenic Mg-calcite waste not only preserves its naturally embedded carotenoids but also offers a direct route to functional phosphate composites, establishing its untapped value in environmental and biomedical applications. Full article