Search Results (15)

Calcium–magnesium (Ca–Mg) carbonates are among the most widely distributed carbonates in the Earth’s surface environment, and their formation mechanisms are of great significance for revealing geological environmental changes and carbon sequestration processes. In this study, the gas diffusion method was employed with L-glutamic acid, L-glycine, and L-lysine as nucleation templates for carbonate minerals to systematically investigate their regulatory effects on the mineralization of Ca–Mg carbonates. The results demonstrated that L-glycine, with the shortest length, was more conducive to forming aragonite, whereas acidic L-glutamic acid, which contains more carboxyl groups, was more beneficial for the structural stability of aragonite. The morphology of the Ca-Mg carbonate minerals became more diverse and promoted the formation of spherical and massive mineral aggregates under the action of amino acids. Moreover, the amino acids significantly increased the MgCO₃ content in Mg calcite (L-glutamic acid: 10.86% > L-glycine: 7.91% > L-lysine: 6.63%). The acidic L-glutamic acid likely promotes the dehydration and incorporation of Mg²⁺ into the Mg calcite lattice through the preferential adsorption of Mg²⁺ via its side-chain carboxyl groups. This study shows how amino acid functional groups influence Ca–Mg carbonate mineralization and provides insights into biogenic Mg-rich mineral origins and advanced mineral material synthesis. Full article

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

Microbially induced calcium carbonate precipitation (MICP) by the urease-producing bacteria has wide applications in the field of geology and environmental engineering. Compared to bacteria, fungi usually possess more tolerance to high salts and heavy metals, enabling MICP induced by the urease-producing fungi to be applied to harsh environments. In this study, the carbonate minerals, induced by the urease-producing fungi isolated from marine sediments, were investigated. One of the urease-producing fungi, designated as YPLJS-14, was identified with the high efficiency of precipitating calcium carbonate. The ITS sequence of YPLJS-14 revealed that it belongs to the genus of Cladosporium. The precipitates induced by this strain were characterized by XRD, SEM, TEM, SAED, and FTIR, respectively. The results show that the mineral phase of fungal precipitates is composed of calcite and vaterite. SEM, TEM, and SAED confirm that the minerals in rhombohedral morphology are calcite and the spherical minerals are vaterite. Thermogravimetric and derivative thermogravimetric (TG/DTG) analyses show that vaterite is a thermodynamically unstable mineral phase compared to calcite and easily decomposes at lower temperatures. These findings provide a foundation for understanding the mineralization mechanism of the urease-producing fungi and the potential applications in environmental engineering. Full article

The non-natural mineralization of CaCO₃ with special structures or morphologies is generated during the migration of crude oil and is the main form of scale in alkaline/surfactant/polymer (ASP) flooding in oilfields, adversely affecting oil recovery and causing environmental pollution. To date, the mineralization of aragonite superstructures and the role of heavy alkyl-benzene sulfonate (HABS) in mineralization are still unclear. In this work, aragonite-based superstructures of CaCO₃ crystals were obtained in an O/W emulsion with HABS to help deepen the understanding of the diversified growth of CaCO₃ scaling in oilfields. As a result, rosette-like, bouquet-like, and dumbbell-shaped CaCO₃ crystals with vaterite–aragonite, aragonite, and calcite–aragonite phases were formed with 200 mg/L HABS concentration at 45 °C for 60 min and spherical vaterite phase stabilized at a high HABS concentration (800 mg/L and 1000 mg/L). Rhombohedral calcite content experienced a fluctuation of about 40% as the HABS concentration varied. Needle-like and bundle-like aragonite precipitates were generated with increasing temperatures from 65 °C to 85 °C. Thus, HABS affects the nucleation and growth of the precipitated CaCO₃ solid, leading to modifications in the structure and morphology of the crystals. The synergistic effect between HABS and temperature can regulate ion pairs with the calcium ions and block sites that are essential to the incorporation of new solutes into the crystal lattice, which leads to the heterogeneous nucleation of vaterite and aragonite on calcite, forming aragonite-based superstructures in kerosene emulsion. This work may enrich the understanding of CaCO₃ mineralization in oilfields, and also provide a novel strategy for manufacturing organic–inorganic composites. Full article

The appearance of cracks is one of the reasons that affect the performance of asphalt pavement, and traditional repair methods have the potential problem of causing adverse effects on the environment. In this paper, an environmentally friendly method for asphalt concrete crack repair was investigated using microbially induced calcite precipitation (MICP) for asphalt concrete cracks of different widths (0.5 mm, 1.0 mm, 1.5 mm, and 3 mm), and the effectiveness of repair was evaluated using nondestructive and destructive experiments. A varied ultrasonic pulse velocity was used to evaluate the healing process, and it was found that the samples with an initial crack width of 0.5 mm showed the most significant increase in wave velocity of 18.06% after repair. The results also showed that the uniaxial compressive strength and indirect tensile strength of the MICP-repaired samples recovered up to 47.02% and 34.68%. Static creep test results showed that MICP-repaired samples with smaller width cracks had greater resistance to permanent deformation. The results of uniaxial compressive strength tests on larger width (3 mm) cracks repaired by MICP combined with fibers showed that the strength of the samples was significantly increased by the addition of fibers. In addition, the SEM/EDS results showed that the MICP products were spherical calcite particles with a particle size distribution from 0 to 10 μm. This study shows that MICP has some potential for repairing cracks in asphalt concrete of different widths within the range investigated. Full article

Currently, approximately 70% of paintings in museum collections are affected by the presence of metallic soaps, evidenced by spherical globules visible on the surface of the paintings. They are responsible for altering the paintings’ surface through processes such as exfoliation and cracking, or even in the form of surface “skins” that appear in the pictorial layers. The objective of this study is the investigation of the icon paintings from Saint Mary Monastery, Techirghiol, Romania, which underwent some restoration procedures. This study is so important/significant, due to the presence of efflorescence that is correlated with the conversion of some fatty acids, as palmitic acid, stearic acid and azelaic acid, in the so-called metallic soaps through the reaction of the metals contained in the pigments from the painting layer and the binder. The investigated paintings are strongly affected by zinc carboxylate aggregation, and for this, the sample was embedded in polyester resin and the obtained cross-section, after polishing, was investigated by microscopic techniques (optical microscopy (OM), stereomicroscopy, and scanning electron microscopy with electronic dispersion spectroscopy (SEM-EDS), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and gas-chromatography with mass spectrometry (GC-MS) in good agreement with data from the literature. The potential result of this study is the identification and quantification of the metallic soap generated as a white deposit (probably salts, a kind of white efflorescence), from the binding medium of the metal carboxylate ionomer, by the crystallization of saturated fatty acids, through polymerization in oil. Six pigments (calcite, lithopone, carbon black, red ochre, vermilion, and ultramarine), present in the sublayers of the samples were identified. Full article

In this study, calcium carbonate nanoparticles (CCNPs) and calcium oxide nanoparticles (CONPs) are synthesized by the carbonization/calcination of calcium oleate. CONPs are an essential inorganic material, and they are used as catalysts and as effective chemisorbents for toxic gases. CCNPs are widely used in plastics, printing ink, and medicines. Here, calcium oleate is used as a starting material for the preparation of CCNPs and CONPs. This calcium oleate is prepared from calcium hydroxide and oleic acid in ethanol under mild reflux conditions. The effect of the calcination temperature of calcium oleate is examined during the synthesis of CCNPs and CONPs. By simple carbonization/calcination, calcite-type CCNPs and CONPs are prepared at <550 °C and >600 °C, respectively. The synthesized nanomaterials are analyzed by various physicochemical characterization techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy, thermogravimetric analysis (TGA) with derivative thermogravimetry (DTG), and scanning electron microscopy (SEM) with energy dispersive X-ray analysis. An X-ray diffractometer and the Scherrer formula are used to analyze the crystalline phase and crystallite size of prepared nanoparticles. TGA techniques confirm the thermal stability of the calcium oleate, CCNPs, and CONPs. The SEM analysis illustrates the dispersive behavior and cubic/spherical morphologies of CCNPs/CONPs. Furthermore, the obtained results are compared to the CCNP and CONP samples prepared using calcium hydroxide. As a result, the carbonization/calcination of calcium oleate produces monodispersed CONPs, which are then compared to the CONPs from calcium hydroxide. Additionally, from calcium oleate, CONPs can be prepared on a large scale in a cheap, convenient way, using simple equipment which can be applied in various applications. Full article

Biomineralization, a well-known natural phenomenon associated with various microbial species, is being studied to protect and strengthen building materials such as concrete. We characterized Rhodococcus erythreus S26, a novel urease-producing bacterium exhibiting CaCO₃-forming activity, and investigated its ability in repairing concrete cracks for the development of environment-friendly sealants. Strain S26 grown in solid medium formed spherical and polygonal CaCO₃ crystals. The S26 cells grown in a urea-containing liquid medium caused culture fluid alkalinization and increased CaCO₃ levels, indicating that ureolysis was responsible for CaCO₃ formation. Urease activity and CaCO₃ formation increased with incubation time, reaching a maximum of 2054 U/min/mL and 3.83 g/L, respectively, at day four. The maximum CaCO₃ formation was achieved when calcium lactate was used as the calcium source, followed by calcium gluconate. Although cell growth was observed after the induction period at pH 10.5, strain S26 could grow at a wide range of pH 4–10.5, showing its high alkali tolerance. FESEM showed rhombohedral crystals of 20–60 µm in size. EDX analysis indicated the presence of calcium, carbon, and oxygen in the crystals. XRD confirmed these crystals as CaCO₃ containing calcite and vaterite. Furthermore, R. erythreus S26 successfully repaired the artificially induced large cracks of 0.4–0.6 mm width. Full article

Monohydrocalcite (CaCO₃·H₂O) is a mineral rarely found in natural environments. Here, we report finding of this mineral in the composition of the microbialites in Laguna de los Cisnes (Isla Grande, Chile), a saline alkaline lake with high Mg/Ca ratio. We have made a detailed structural and mineralogical description of these microbialites with the use of light and scanning electron microscopy, infrared spectroscopy and X-ray analysis. The predominantly carbonate composition of microbialites was revealed. Carbonates were represented mainly by high-magnesium calcites and monohydrocalcite. Calcite and aragonite were found in minor quantities. In addition, a small amount of silicates and amorphous hydromagnesite were found. The yellowish-brown surface layer of microbialites consists of numerous crystals within a mineralized exopolysaccharide (EPS) matrix. A large number of unicellular and filamentous algae, as well as areas of released EPS, are also seen here. Below is a slimy green layer. This layer is not mineralized; it represents an "algal-bacterial mat" consisting of algae, cyanobacteria, and diatoms developed in EPS. Chisel-shaped crystals of monohydrocalcite and its amorphous spherical precursors are numerous in these upper layers. The deeper layers are mineralized; they predominantly consist of Mg-carbonates with varying degrees of Mg. Algae and cyanobacteria are decomposed or fossilized there. Thus, monohydrocalcite occurs in the composition of the microbialites, being one of the main mineral components. As in other lacustrine localities, it is formed in the presence of algae and cyanobacteria. To our knowledge, this is the first report on the discovery of monohydrocalcite in South America. This research was funded by the Ministry of Science and Higher Education of the Russian Federation. Full article

Cockle shells are a natural reservoir of calcium carbonate (CaCO₃), which is widely used in bone repair, tissue scaffolds, and the development of advanced drug delivery systems. Although many studies report on the preparation of CaCO₃, the development of a nanosized spherical CaCO₃ precursor for calcium oxide (CaO) that is suitable to be incorporated in dental material was scarce. Therefore, this study aimed to synthesize a nanosized spherical CaCO₃ precursor for CaO derived from cockle shells using a sol–gel method. Cockle shells were crushed to powder form and mixed with hydrochloric acid, forming calcium chloride (CaCl₂). Potassium carbonate (K₂CO₃) was then fed to the diluted CaCl₂ to obtain CaCO₃. The effect of experimental parameters on the morphology of CaCO₃, such as volume of water, type of solvents, feeding rate of K₂CO₃, and drying method, were investigated using field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffractometry (XRD), Brunauer–Emmett–Teller surface area analysis, and thermogravimetric analysis. Optimized CaCO₃ was then calcined to form CaO. XRD analysis of CaCO₃ nanoparticles was indicative of the formation of a calcite phase. The well-structured spherical shape of CaCO₃ was obtained by the optimum condition of the addition of 50 mL of water into CaCl₂ in ethanolic solution with a 1 h feeding rate of K₂CO₃. Less agglomeration of CaCO₃ was obtained using a freeze-drying technique with the surface area of 26 m²/g and average particle size of 39 nm. Spherical shaped nanosized CaO (22–70 nm) was also synthesized. The reproducibility, low cost, and simplicity of the method suggest its potential applications in the large-scale synthesis of the nanoparticles, with spherical morphology in an industrial setting. Full article

The goal of this work is to study the influence of coccolithophore blooms on the underwater light field and albedo of the water column. A coccolithophore is a single-celled alga with spherical cells surrounded by disk-shaped calcite plates (coccolites), which produce strong light scattering. Because of that, we can observe coccolithophore blooms on satellite ocean color images. We calculated the angular underwater radiance distributions and their integral parameters by the exact numerical method with the input parameters, corresponding to real conditions observed in the Barents Sea and Black Sea. Using the results of the exact calculations, we estimated, for various situations, the accuracy of the approximating formulas applied to the assessment of the water radiance reflectance and the diffuse attenuation coefficients and we make recommendations for their application. As a finding of practical importance, we can note the estimate of the accuracy of the widely used Gordon’s formula for the diffuse attenuation coefficient; this formula results in large errors under strong coccolithophore blooms. We also mention the interesting and important results concerning the features of the asymptotic regime under such conditions. Full article

Valentinite forms through the alteration of stibnite in sulphide deposits. Colloform sphalerite is a widespread mineral in low-temperature deposits, particularly those of the Mississippi-Valley type. We identified valentinite and colloform sphalerite in hydrothermal deposits occurring in the Baia Mare area. The Baia Mare metallogenic district of Neogene age occurs in the northwestern part of the Neogene volcanic chain within the Eastern Carpathians. The Neogene volcanism from Baia Mare area is related to the subduction processes of the East European plate under two microplates, Alcapa and Tisza-Dacia/Tisia, in the post-collisional compressive phase. We have identified valentinite in the Dealul Crucii and Baia Sprie deposits, associated with other epithermal minerals, in the absence of the stibnite. Valentinite is deposited in the final phase of the epithermal process after calcite and manganese-bearing calcite. Micro-Raman and microprobe determinations indicate the presence of valentinite. The formula of valentinite is close to stoichiometric Me₂O₃ and contains small amounts of tin as an antimony substituent. Colloform sphalerite was identified in the Baia Sprie ore deposit associated with minerals formed in the final epithermal phase. It was deposited on idiomorphic crystals of stibnite, which it corrodes. Its structure and an alternate banding, exhibited on the nano-/microscale, were identified by optical microscopy, SEM (scanning electron microscopy), and BSE (backscattered electron microscopy) imaging. These structures are typical for colloform sphalerite and suggest a genesis due to episodic precipitation. The spherical nano/micro-particles (nodules) are characteristic of the colloform sphalerite from Baia Sprie. Raman analysis indicates the presence of a colloform sphalerite with low iron content. The typical diffraction lines for sphalerite were identified in X-ray diffraction: 3.118 Å (111), 1.907 Å (220), 1.627 Å (311). Microprobe analysis certifies the presence of sphalerite with the stoichiometric formula close to ZnS. Iron content is low (0%–0.0613%), but Sb (0.7726%–2.6813%), Pb (0.56%–1.1718%), Bi (0%–0.1227%) are also present. The negative correlation between Zn and Sb suggests the simultaneous deposition from the same epithermal fluids. Valentinite and colloform sphalerite were formed at low temperatures (100–150 °C) at the end of the epithermal process. Full article

The Kovdor phoscorite-carbonatite ore-pipe rocks form a natural series, where apatite and magnetite first gradually increase due to the presence of earlier crystallizing forsterite in the pipe marginal zone and then decrease as a result of carbonate development in the axial zone. In all lithologies, magnetite grains contain (oxy)exsolution inclusions of comparatively earlier ilmenite group minerals and/or later spinel, and their relationship reflects the concentric zonation of the pipe. The temperature and oxygen fugacity of titanomagnetite oxy-exsolution decreases in the natural rock sequence from about 500 °C to about 300 °C and from NNO + 1 to NNO − 3 (NNO is Ni-NiO oxygen fugacity buffer), with a secondary positive maximum for vein calcite carbonatite. Exsolution spinel forms spherical grains, octahedral crystals, six-beam and eight-beam skeletal crystals co-oriented with host magnetite. The ilmenite group minerals occur as lamellae oriented along {111} and {100} planes of oxy-exsolved magnetite. The kinetics of inclusion growth depends mainly on the diffusivity of cations in magnetite: their comparatively low diffusivities in phoscorite and carbonatites of the ore-pipe internal part cause size-independent growth of exsolution inclusions; while higher diffusivities of cations in surrounding rocks, marginal forsterite-rich phoscorite and vein calcite carbonatite result in size-dependent growth of inclusions. Full article

An important component of phosphorite (phosphate rock) is carbonate apatite, as it is required for phosphorous fertilizer production due to its increased phosphate solubility caused by carbonate substitution in the apatite mineral lattice. High phosphate concentrations in municipal wastewater treatment plants are commonly reduced by precipitating iron phosphate by addition of iron chloride. We investigated the possibility of precipitating carbonate apatite from a potential range of phosphate concentrations that could be available from municipal wastewater treatment plants with anaerobic digestion reactors (5 mM–30 mM). Synthetic phosphate solutions at neutral pH were mixed in batch experiments with a calcium carbonate solution produced by dissolving calcite in contact with carbon dioxide gas, with and without carbonate apatite seed. Batch experiments were used to identify the carbonate apatite supersaturation ranges for homogeneous and heterogeneous nucleation, and the precipitates analyzed with Raman spectroscopy, powder X-ray diffraction, inorganic carbon coulometry, and scanning electron microscopy. Some precipitates contained carbonate weight fractions within the range reported for geological phosphate rock (1.4–6.3 wt %). The precipitates were spherical, poorly crystalline carbonate apatite, suggesting an amorphous precursor transformed to a poorly crystalline carbonate apatite without changing morphology. Full article

In this paper, we report a facile, rapid, and green strategy for the synthesis of cellulose/hydroxyapatite (HA) nanocomposites using an inorganic phosphorus source (sodium dihydrogen phosphate dihydrate (NaH₂PO₄·2H₂O)), or organic phosphorus sources (adenosine 5′-triphosphate disodium salt (ATP), creatine phosphate disodium salt tetrahydrate (CP), or D-fructose 1,6-bisphosphate trisodium salt octahydrate (FBP)) through the microwave-assisted hydrothermal method. The effects of the phosphorus sources, heating time, and heating temperature on the phase, size, and morphology of the products were systematically investigated. The experimental results revealed that the phosphate sources played a critical role on the phase, size, and morphology of the minerals in the nanocomposites. For example, the pure HA was obtained by using NaH₂PO₄·2H₂O as phosphorus source, while all the ATP, CP, and FBP led to the byproduct, calcite. The HA nanostructures with various morphologies (including nanorods, pseudo-cubic, pseudo-spherical, and nano-spherical particles) were obtained by varying the phosphorus sources or adjusting the reaction parameters. In addition, this strategy is surfactant-free, avoiding the post-treatment procedure and cost for the surfactant removal from the product. We believe that this work can be a guidance for the green synthesis of cellulose/HA nanocomposites in the future. Full article