Calcite Structure Research Articles

Coupled dissolution-precipitation and growth processes on calcite, aragonite, and Carrara marble exposed to cadmium-rich aqueous solutions

Calcium carbonate and cadmium-rich fluid interactions have been studied at the nano and microscale with fluid flow and static fluid conditions for three forms of CaCO3: calcite in single crystals of Iceland Spar, calcite in a polycrystalline Carrara marble, and aragonite single crystals. Atomic Force Microscopy (AFM) showed the nanoscale effect of cadmium on CaCO3 dissolution and growth under flow-through conditions at ambient temperature, with the modification of calcite dissolution behaviour and simultaneous precipitation of a Cd-rich phase on all the different samples. Hydrothermal experiments at 200 °C revealed that the reactivity of single calcite crystals is passivated by epitaxial growth of the less soluble Cd-rich endmember of the (Ca,Cd)CO3 solid-solution on the sample surface due to the similar crystallographic structures of calcite and otavite (CdCO3). Conversely, the presence of grain boundaries in Carrara marble or the change of crystallographic structure and reaction-induced fracturing in aragonite allowed, to some extent, the pseudomorphic replacement of Carrara marble and aragonite samples by a porous (Ca,Cd)CO3 solid-solution phase of variable composition. These phenomena have been observed in solutions undersaturated with respect to all solid phases and are the result of an interface-coupled dissolution-precipitation mechanism where the dissolving CaCO3 provides ions to supersaturate the mineral-fluid interfacial layer, leading to the precipitation of a Cd-containing phase on the samples' surfaces. This coupled dissolution-precipitation mechanism could potentially be used as a remediation process to sequester cadmium from contaminated effluents.

Nanoscale Analysis of the Structure and Composition of Biogenic Calcite Reveals the Biomineral Growth Pattern.

The vast majority of calcium carbonate biocrystals differ from inorganic crystals in that they display a patent nanoroughness consisting of lumps of crystalline material (calcite/aragonite) surrounded by amorphous pellicles. Scanning transmission electron microscopy coupled with electron energy loss spectroscopy (STEM-EELS) was used to map the calcite secreted by a barnacle chemically and structurally with ultrahigh resolution (down to 1 nm). The material is composed of irregular lumps of calcite (up to two hundred nm in diameter) surrounded by relatively continuous cortexes (up to 20 nm thick) of amorphous calcium carbonate (ACC) and/or nanocalcite plus biomolecules, with a surplus of calcium relative to carbonate. We develop a model by which the separation of the crystalline and amorphous phases takes place upon crystallization of the calcite from a precursor ACC. The organic biomolecules are expelled from the crystal lattice and concentrate in the form of pellicles, where they stabilize minor amounts of ACC/nanocalcite. In this way, we change the previously established conception of biomineral structure and growth.

Evolution of Structural and Spectral Characteristics of Lu-=SUB=-0.99-x-=/SUB=-Sm-=SUB=-x-=/SUB=-Eu-=SUB=-0.01-=/SUB=-BO-=SUB=-3-=/SUB=- orthoborates

The structure, IR absorption and luminescence spectra, and morphology of Lu0.99-xSmxEu0.01BO3 (0≤ x≤0.99) orthoborates synthesized at 970oC were studied. With an increase in the Sm3+ concentration, a successive change of five structural states is observed: calcite (0≤ x≤ 0.1)-> calcite + vaterite (0.1<x<0.3)-> vaterite (0.3≤ x≤ 0.95)-> vaterite + a triclinic phase (0.95<x≤ 0.98)-> a triclinic phase (0.98<x≤1). A wide range of Sm3+, concentrations at which the vaterite phase (0.3≤ x≤ 0.95) exists and a very narrow region of triclinic phase formation (0.98<x≤1) are important distinctive features of this system. Correspondence between the structure and spectral characteristics of these compounds was established. It is shown that the vaterite phase appears in the bulk of the microcrystals of the samples that have a calcite structure. Keywords: rare earth orthoborates, crystal structure, X-ray diffraction analysis, IR-spectroscopy, luminescence spectra.

Эволюция спектральных и структурных характеристик боратов, образующихся при взаимодействии оксидов лантана и скандия с расплавом тетрабората калия

The structure, morphology, IR spectra, as well as luminescence spectra and luminescence excitation spectra of europium-doped borates formed during the interaction of lanthanum and scandium oxides with a potassium tetraborate melt at 970°С with the general formula La0.99-xScxEu0.01BO3 were studied. It is shown that with an increase in the Sc3+ concentration, three compounds are successively formed: LaBO3, LaSc3(BO3)4, and ScBO3. At 0 ≤ x ≤ 0.26, the samples are single-phase and have the structure of LaBO3 aragonite. Within the range of 0.26 < x < 0.75, the samples are two-phase and contain the structures of LaBO3 aragonite and LaSc3(BO3)4 huntite. At 0.75 ≤ x ≤ 0.85, LaSc3(BO3)4 is observed. Within the range of 0.85 < x ≤ 0.97, the samples are two-phase and consist of LaSc3(BO3)4 huntite and ScBO3 calcite. At 0.97 < x ≤ 0.99, the ScBO3 samples have a calcite structure. Correspondence between the structure and spectral characteristics of these compounds was established.

Evolution of the spectral and structural characteristics of borates formed during the interaction of lanthanum and scandium oxides with a potassium tetraborate melt

The structure, morphology, IR spectra, as well as luminescence spectra and luminescence excitation spectra of europium-doped borates formed during the interaction of lanthanum and scandium oxides with a potassium tetraborate melt at 970oC with the general formula La0.99-xScxEu0.01BO3 were studied. It is shown that with an increase in the Sc3+ concentration, three compounds are successively formed: LaBO3, LaSc3(BO3)4, and ScBO3. At 0≤ x≤ 0.26, the samples are single-phase and have the structure of LaBO3 aragonite. Within the range of 0.26<x<0.75, the samples are two-phase and contain the structures of LaBO3 aragonite and LaSc3(BO3)4 huntite. At 0.75≤ x≤0.85, LaSc3(BO3)4 is observed. Within the range of 0.85<x≤0.97, the samples are two-phase and consist of LaSc3(BO3)4 huntite and ScBO3 calcite. At 0.97<x≤0.99, the ScBO3 samples have a calcite structure. Correspondence between the structure and spectral characteristics of these compounds was established. Keywords: phosphors for LEDs, rare earth orthoborates, X-ray diffraction analysis, IR spectroscopy, luminescence spectra.

Эволюция структурных и спектральных характеристик ортоборатов Lu-=SUB=-0.99-x-=/SUB=-Sm-=SUB=-x-=/SUB=-Eu-=SUB=-0.01-=/SUB=-BO-=SUB=-3-=/SUB=-

The structure, IR absorption and luminescence spectra, and morphology of Lu0.99xSmxEu0.01BO3 (0 ≤ x ≤ 0.99) orthoborates synthesized at 970°С were studied. With an increase in the Sm3+ concentration, a successive change of five structural states is observed: calcite (0 ≤ x ≤ 0.1) → calcite + vaterite (0.1 < x < 0.3) → vaterite (0.3 ≤ x ≤ 0.95) → vaterite + a triclinic phase (0.95 < x ≤ 0.98) → a triclinic phase (0.98 < x ≤ 1). A wide range of Sm3+ concentrations at which the vaterite phase (0.3 ≤ x ≤ 0.95) exists and a very narrow region of triclinic phase formation (0.98 < x ≤ 1) are important distinctive features of this system. Correspondence between the structure and spectral characteristics of these compounds was established. It is shown that the vaterite phase appears in the bulk of the microcrystals of the samples that have a calcite structure.

Assessing the antibacterial properties of eggshell-titanium powder

The global distribution of oral diseases caused by bacterial and the severity of their consequences constitute a pandemic condition.The present paper reports on the antibacterial properties of a modified eggshell and titanium dioxide using the mechanochemical method. EB@TiO2 was modified and characterized using X-raydiffraction (XRD) while the degradation condition was studied using Thermogravimetric analysis (TGA).The inhibitory properties of EB@TiO2at differentconcentrations (2:1; 3:1 and 4: 1) against both Grampositive (E. coli) and negative bacterial (B. Cereus)strain were studied the using disk diffusion method.The XRD result confirmed the presence of a thermodynamically stable calcite structure, which is indicative of calcium carbonate. The diffraction peak of the XRD at 2θ = 29.5o suggests the deposition of TiO2 on the surface of CaCo3. TGA curves shows the decomposition of anatase form of titanium dioxide and calcium carbonate. The study evidently shows the antibacterial activities of EB@TiO2 against Escherichia coli and B. Cereus. The salient feature of the study finding is that modifying eggshells with titanium dioxide improves the antibacterial properties, and thus offers a promising role for the development of potent d

25 years of continuous sewage sludge application vs. mineral fertilizers on a calcareous soil affected pH but not soil carbonates

Inorganic and organic fertilizers have been widely used to maintain crop yields. However, several studies have demonstrated that the dissolution of carbonates in agricultural soils by the acidification induced by N-fertilizers can result in their total or partial loss in the tilled layer of some agricultural soils. The effect of inorganic and organic fertilization on carbonates in calcareous semiarid Mediterranean soils has been less studied and is still unclear. Based on a 25-year field experiment, we investigated the effects of different fertilization strategies on the soil pH, inorganic C content, and in the proportion of pedogenic carbonates in the topsoil (0-30 cm) of a carbonate-rich soil in Navarre (N Spain). Five treatments were compared: no amendments as a control (SC), mineral fertilization (MF), and the application of sewage sludge at different doses (80 Mg ha-1 every year (80-1), 40 Mg ha-1 every year (40-1) and 40 Mg ha-1 every four years (40-4). Results showed a decrease in soil pH values by increasing the amount of sewage sludge and a small alteration in the calcite structure particularly in 40-4. However, no significant differences between treatments were found in the total content of carbonates nor in the proportion of pedogenic carbonates. The high concentration of total carbonates in the soil (16.09 ± 0.48%), and of the proportion of pedogenic carbonates (40.21 ± 1.29%, assuming a δ13C of primary carbonates = 0 ‰) seemed elevated enough to compensate for the observed acidification in the studied soil. In the case of MF, no changes were observed in the pH values, nor in the carbonate content (total and pedogenic). This suggests that the use of sewage sludge could induce changes in the future at a faster rate and of greater dimension than the use of mineral fertilizers such as the ones used in this field (46% urea, superphosphate and ClK).

Synthesis of White Mineral Trioxide Aggregate (WMTA) Using Silica from Rice Husk Ash and CaCO<sub>3</sub> from Limestone

White mineral trioxide aggregate (WMTA) was successfully synthesized using silica from rice husk ash (RHA) and precipitate calcium carbonate (PCC) from limestone. Silica was synthesized from rice husk ash by the sol-gel method with the help of a strong base NaOH to obtain sodium silicate solution. In contrast, PCC in the calcite structure was extracted from limestone by a carbonation method. The limestone powder sample was calcined at 900 °C for 3 hours, dissolved in 0.8 M nitric acid solution, and was followed by carbonation for 60 minutes. The synthesis of WMTA was carried out by mixing silica, PCC, bismuth oxide, aluminum oxide, NH3 solution catalysts and treating the mixture thermally at 950 °C for 3 hours. Products were characterized by Fourtier-Transform Infrared (FTIR) spectroscopy, X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). The results showed that the RHA silica had an amorphous phase that peaked at 2θ= 22°, but the background intensity was irregular. The PCC obtained through isolation from limestone is predominantly calcite structure. WMTA has been successfully synthesized by thermal treatment at 950 °C using NH3 solution catalyst, as evidenced by the presence of tricalcium silicate (C3S), dicalcium silicate (C2S), tricalcium aluminate (C3A), and Bi2O3.

Spectral induced polarization monitoring of induced calcite precipitation in subsurface sediments

SUMMARY Co-precipitation of contaminants within the crystalline structure of calcite is a promising natural attenuation or remedial technology being considered at contaminated sites. We explore the sensitivity of the spectral induced polarization (SIP) method to induced calcite precipitation in natural sediments as a path forward to non-invasively monitor these sites. We performed time-lapse column experiments using phased (I–IV) injections over 40 d on natural sediments from the Hanford Site (WA, USA). In the phased injections, abiotic calcite precipitation was induced and confirmed to have occurred. Previous work on glass beads and homogeneous sand was limited to high frequency detection of calcite, however in this work we observed the development of two polarization mechanisms, one at high frequency (>100 Hz) and one at low frequency (<100 Hz). Based on the characteristic frequencies from the SIP high and low frequency regimes, characteristic length scales (L) were computed where the adsorption mode of Na+ versus Ca2+ was compared by using diffusion coefficients corresponding to Na+ versus an arithmetically averaged value for Na+ and Ca2+. Using the diffusion coefficient of Na+, the high frequency L was found to correlate well with the size of the calcite crystals. The low frequency L correlated well with the individual natural sediment grain sizes within the columns. During late experimental times (day 36 and 40), the characteristic low frequency in two of the experimental columns shifted to lower frequencies (<0.001 Hz) which may signify SIP sensitivity of the formed calcite with the sediment grains. In field applications, the development of a low frequency polarization length scale to monitor calcite precipitation is promising for field monitoring applications, however further laboratory work needs to be performed to examine the SIP sensitivity of calcite formation in the presence of natural sediments.

Construction of porous calcite structure using microbially induced calcite precipitation

Sporosarcina pasteurii is a well-known ureolytic bacteria that promotes the microbially induced calcite precipitation (MICP) process for several environmental and engineering purposes. In our work, for the first time, MICP has been implemented to form pure, porous calcite structures. The maximum urease activity of S. pasteurii was 1.91 mM urea hydrolyzed min−1 at the late-exponentially phase. A reactor has been designed to achieve semi-continuous treatments, and reagents were introduced to it by a peristaltic pump. A new alternating injection pattern was adopted to obtain well-distributed precipitation. SEM images of treated structures indicated the shapes of CaCO3 crystals at a microscale level and revealed the successful formation of calcite-calcite bonds, which has contributed to achieving a consolidated porous structure. Such synthetic pure, porous calcite structure has found growing industrial interest where chemically intrusive procedures (e.g., acidizing, fracturing) should be performed on expensively excavated core samples.

Effect of Mg(II), Mn(II), and Fe(II) doping on the mechanical properties and electronic structure of calcite

Calcite is one of the most important rock-forming minerals in the earth's crust, it is a very common mineral in nature and is widely used. Metal ions, such as Mg(II), Mn(II) and Fe(II), are often introduced into calcite as defects, which have a great influence on the crystal structure, mechanical properties and electronic structure of calcite. In order to understand the mechanism of the Mg(II), Mn(II), and Fe(II) doping of calcite, first-principles calculations are used to comprehensively study the various properties of calcite doped with different ions from an atomic-scale perspective. The calculation results show that the bonding characteristics of adjacent carbonate ions and layer spacing change after Mg-, Mn-, and Fe-doping, and the influence of Fe(II) on the calcite properties is the greatest, followed by those of Mn(II) and Mg(II). The influence of Fe(II) on the calcite properties is related to the ion radius and distribution of extra nuclear electrons. The elastic modulus of doped calcite decreases substantially, but the hardness of the material increases. The distribution of the density of states, energy band structure, and electrical conductivity of calcite doped with different ions also change significantly, which result in a variation in the electrical properties of calcite.

Photocatalytic mineralization of phenol by Sn-modified calcites

Calcium-based photocatalysts represent an economic and available alternative for the photodegradation of distinct pollutants such as pesticides, pigments, colorants, and drugs, among others. In the following paper, the morphological, structural, optical, and textural properties of a series of materials based on calcium carbonate (calcite) modified with Tin and their evaluation in phenol photodegradation were studied. The synthesized materials were characterized by several techniques, including X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), N2 adsorption–desorption at 196 °C, Diffuse Reflectance Spectroscopy (DRS), Scanning Electron Microscopy (SEM), and X-ray Photoelectron Spectroscopy (XPS). The characterization information indicated that a portion of Sn4+ was incorporated into calcite structure and the rest crystallized as SnO2. The effect of tin incorporation was also evidenced by the calculated bandgap values whereas the tin amount increased the values got close to SnO2 value. Neither the bare sample SnO2 nor CaCO3 presented photoactivity for phenol mineralization. Nevertheless, it was demonstrated that the modified calcites presented a photocatalytic activity comparable to P25-TiO2, carrying out phenol mineralization in 3 h. Tin-modified calcite compounds were obtained by a controlled coprecipitation method. The photocatalytic evaluations presented a photocatalytic activity comparable to P25-TiO2, which was assigned to tin presence in a low-value material such as calcite.

Access to quantitative analysis of carbonates using a portable LIBS instrument: First applications to single minerals and mineral mixtures

Natural carbonate standards of calcite structure were analysed using a handheld Laser-Induced Breakdown Spectroscopy (LIBS) device to investigate the spectral applicability for quantitative analysis in the Ca-Mg-Fe-Mn carbonate system. To obtain an initial understanding of the relationship between the elemental concentrations and LIBS signals, the determination coefficient (R2), root mean square error (RMSE) and mean arctangent absolute percentage error (MAAPE) for cross-validation and forecast accuracy were used, respectively. To relate the changes in spectral characteristics to the mineral content of carbonate mixtures, different spectral ratios were compared with mixture ratios between the two carbonate minerals. We found that spectral information from LIBS emission lines showed high correlations to their elemental concentration (Ca, Mg, Fe, and Mn), and their spectral ratios in carbonate mixtures showed a linear correlation with mineral content. Principal component analysis (PCA) was investigated the chemometric capability of the discrimination for carbonate minerals. This study demonstrates that handheld LIBS can be effectively applied in the field for the discrimination and identification of carbonate endmembers and their quantification for the case of mixtures.

First-principle studies of the pressure effect on metal carbonates elastic properties

Using the ab initio methods of the density functional theory, the influence of hydrostatic pressure on the elastic properties of magnesium, zinc, cadmium, calcium carbonates with the structure of calcite, double calcium-magnesium carbonates, cadmium-magnesium, calcium-zinc with the structure of dolomite and calcium, strontium, lead, barium carbonates with the structure of aragonite is studied. Derivatives with respect to pressure for elastic constants and linear moduli, polycrystalline compression and shear moduli, transverse and longitudinal velocities of acoustic waves are obtained. Dependences on the cation radius for the ratio of the elastic constant to its pressure derivative, the velocity of longitudinal waves to its pressure derivative, the pressure derivative of the bulk modulus, the pressure derivative of the shear modulus, and other parameters of a number of metal carbonates have been established.

Mesocrystalline structure and mechanical properties of biogenic calcite from sea urchin spine.

Using X-ray scattering, we measured detailed maps of the diffuse scattering intensity distribution and a number of phonon dispersion branches for a single crystal of inorganically formed natural calcite and for high-quality mesocrystals of biogenic calcite from a Mediterranean sea urchin spine. A comparison shows that the known differences in the mechanical properties between the `strong' biogenic and `brittle' abiotic material should be attributed to the mesoscopic architecture of the crystal rather than to a modification of the calcite crystal structure. The data are rationalized by comparing them to the results of ab initio model calculations of lattice dynamics. For the mesocrystal, they are augmented by the evaluation of the faceting of the constituent nanocrystals.

The evolution of the spectral and structural characteristics of La-=SUB=-0.98-x-=/SUB=-Lu-=SUB=-x-=/SUB=-Eu-=SUB=-0.02-=/SUB=-BO-=SUB=-3-=/SUB=- orthoborates

The structure, IR absorption, luminescence, and luminescence excitation spectra of La0.98-xLuxEu0.02BO3 orthoborates synthesized at 970oC were studied at 0≤ x≤0.98. An increase in x leads to a sequential change of the structural state of the orthoborates. At first, the compound has the aragonite structure. Then, it becomes two-phase and contains the aragonite and vaterite phases. With a further increase in x, the compounds have the vaterite structure, then the vaterite and calcite structure, and, finally, the calcite structure. Correspondence between the structure and spectral characteristics of these compounds was established. Luminescence spectra were investigated at different wavelengths of exciting light. This allowed obtaining information on the structure of a near-surface layer and the bulk of microcrystals of the investigated samples. It is shown that the vaterite phase arises in the bulk of microcrystals of samples that have the aragonite structure. Keywords: phosphors for LEDs, rare earth orthoborates, X-ray diffraction analysis, IR spectroscopy, luminescence spectra.

Структурные и спектральные характеристики ортоборатов Pr-=SUB=-1-x-=/SUB=-Lu-=SUB=-x-=/SUB=-BO-=SUB=-3-=/SUB=-

The structure, IR absorption and luminescence spectra of Pr0.99xLuxEu0.01BO3 orthoborates synthesized at 970°C were studied at 0 ≤ x ≤ 0.99. An increase in the concentration of lutetium leads to a sequential change of the structural state of the orthoborates. At first, the orthoborates are single-phase and have an aragonite structure (0 ≤ x ≤ 0.1). Then, they become two-phase and contain the aragonite and vaterite phases (0.1 < x < 0.6). With a further increase in х (0.6 < x ≤ 0.8), the compounds are single-phase with a vaterite structure, then they contain the vaterite and calcite phases (0.8 < x ≤ 0.95), and, finally, they become single-phase with a calcite structure (0.95 < x ≤ 0.99). An unambiguous correspondence between the structural modification and IR spectra of these compounds was established. It is shown that the emission of Eu3 + ions is observed in samples where the concentration of europium exceeds that of praseodymium.

Structural and spectral characteristics of Pr-=SUB=-1-x-=/SUB=-Lu-=SUB=-x-=/SUB=-BO-=SUB=-3-=/SUB=- orthoborates

The structure, IR absorption and luminescence spectra of Pr0.99-xLuxEu0.01BO3 orthoborates synthesized at 970oC were studied at 0≤ x≤0.99. An increase in the concentration of lutetium leads to a sequential change of the structural state of the orthoborates. At first, the orthoborates are single-phase and have an aragonite structure (0≤ x≤0.1). Then, they become two-phase and contain the aragonite and vaterite phases (0.1<x<0.6). With a further increase in x (0.6<x≤0.8), the compounds are single-phase with a vaterite structure, then they contain the vaterite and calcite phases (0.8<x≤0.95), and, finally, they become single-phase with a calcite structure (0.95<x≤0.99). An unambiguous correspondence between the structural modification and IR spectra of these compounds was established. It is shown that the emission of Eu3+ ions is observed in samples where the concentration of europium exceeds that of praseodymium. Keywords: rare earth orthoborates, X-ray diffraction analysis, crystal structure, IR spectroscopy, luminescence spectra.

Low-Temperature Synthesis of Disordered Dolomite and High-Magnesium Calcite in Ethanol–Water Solutions: The Solvation Effect and Implications

How dolomite [CaMg(CO3)2] forms is still underdetermined, despite over a century of efforts. Challenges to synthesizing dolomite at low temperatures have hindered our understanding of sedimentary dolomite formation. Unlike calcium, magnesium’s high affinity toward water results in kinetic barriers from hydration shells that prevent anhydrous Ca–Mg carbonate growth. Previous synthesis studies show that adding low-dielectric-constant materials, such as dioxane, dissolved sulfide, and dissolved silica, can catalyze the formation of disordered dolomite. Also, polar hydrophilic amino acids and polysaccharides, which are very common in biomineralizing organisms, could have a positive role in stimulating Mg-rich carbonate precipitation. Here, we show that disordered dolomite and high-magnesium calcite can be precipitated at room temperature by partially replacing water with ethanol (which has a lower dielectric constant) and bypassing the hydration barrier. Increasing the ethanol volume percentage of ethanol results in higher Mg incorporation into the calcite structure. When the ethanol volume percentage increases to 75 vol %, disordered dolomite (>60 mol % MgCO3) can rapidly precipitate from a solution with [Mg2+] and [Ca2+] mimicking seawater. Thus, our results suggest that the hydration barrier is the critical kinetic inhibitor to primary dolomite precipitation. Ethanol synthesis experiments may provide insights into other materials that share similar properties to promote high-Mg calcite precipitation in sedimentary and biomineral environments.