Aragonite Polymorph Research Articles

Preparation and Characterization of Calcium Hydroxide from Cockle Shell Waste via Sol-Gel Method: Effect of HCl Concentration

Continuous cockle shell dumping in open areas has become a global problem which generate major environmental issues. The conversion of the wastes into value-added products is highly desirable and economic. This work aimed to investigate the influence of sol-gel processing parameter on the properties of the synthesized calcium hydroxide (Ca(OH)2). In this study, cockle shell waste was used as calcium carbonate (CaCO3) precursor in the preparation of Ca(OH)2 via sol-gel method and the processing parameter varied was hydrochloric acid (HCl) concentration (0.5, 1.0 and 2.0 M). The cockle shell based CaCO3 and the prepared Ca(OH)2 powders were characterized by X-ray diffraction (XRD), Fourier transform infra-Red (FTIR), field emission scanning electron microscopy with energy dispersive X-ray (FESEM-EDX), X-ray fluorescent (XRF) and particle size analyzer (PSA). The XRD analysis indicates that the calcium carbonate obtained from cockle shell was mainly in the form of aragonite polymorph. Upon sol-gel processing, the analysis of the sample shows the presence of portlandite and small traces of aragonite in all samples suggesting an incomplete reaction of the hydrolysis process. Ca(OH)2 powder prepared using 1M HCl yields the smallest particle size.

Optimising a method for aragonite precipitation in simulated biogenic calcification media.

Resolving how factors such as temperature, pH, biomolecules and mineral growth rate influence the geochemistry and structure of biogenic CaCO3, is essential to the effective development of palaeoproxies. Here we optimise a method to precipitate the CaCO3 polymorph aragonite from seawater, under tightly controlled conditions that simulate the saturation state (Ω) of coral calcification fluids. We then use the method to explore the influence of aspartic acid (one of the most abundant amino acids in coral skeletons) on aragonite structure and morphology. Using ≥200 mg of aragonite seed (surface area 0.84 m2), to provide a surface for mineral growth, in a 330 mL seawater volume, generates reproducible estimates of precipitation rate over Ωaragonite = 6.9-19.2. However, unseeded precipitations are highly variable in duration and do not provide consistent estimates of precipitation rate. Low concentrations of aspartic acid (1-10 μM) promote aragonite formation, but high concentrations (≥ 1 mM) inhibit precipitation. The Raman spectra of aragonite precipitated in vitro can be separated from the signature of the starting seed by ensuring that at least 60% of the analysed aragonite is precipitated in vitro (equivalent to using a seed of 200 mg and precipitating 300 mg aragonite in vitro). Aspartic acid concentrations ≥ 1mM caused a significant increase in the full width half maxima of the Raman aragonite v1 peak, reflective of increased rotational disorder in the aragonite structure. Changes in the organic content of coral skeletons can drive variations in the FWHM of the Raman aragonite ν1 peak, and if not accounted for, may confuse the interpretation of calcification fluid saturation state from this parameter.

Mixture of CaCO 3 Polymorphs Serves as Best Adsorbent of Heavy Metals in Quadruple System

This study compares and analyzes removal of Pb (II), Cu (II), Mn (II), and Zn (II) from aqueous solution as individual ions (monometal system) or as mixed ions (quadruple system) by commercial laboratory-grade calcium carbonate (C–CaCO3) and as-synthesized CaCO3 (S–CaCO3) as adsorbents. This was performed to determine whether heavy metal ion adsorption can be influenced by the polymorphic phases of CaCO3. C–CaCO3 and S–CaCO3 were equally efficient in the removal of Pb (II) and Cu (II) from a monometal system. However, S–CaCO3 exhibited only 49.3% ± 0.14 heavy metal removal when compared with 96.7% ± 0.08 by C–CaCO3 in a quadruple system. FTIR and HR-SEM analysis revealed C–CaCO3 consisted of a mixture of calcite and aragonite polymorphs, whereas S–CaCO3 was pure calcite polymorph. These results indicated the importance of identification of the polymorphic phase and phase transformation in any experiment while utilizing CaCO3 as adsorbent.

Cadmium isotopes in Bahamas platform carbonates: A base for reconstruction of past surface water bioproductivity and their link with chromium isotopes

The distribution of cadmium (Cd) within the oceans strongly suggests that it is used as a nutrient by marine phytoplankton. Biologically induced removal of Cd from modern surface waters is accompanied by an isotopic fractionation leaving surface-waters enriched in isotopically heavy Cd. This first study focusses on tying the Cd isotopic record preserved in modern shallow platform carbonates of the Great Bahama Bank (GBB) to conditions in the upper water column, and provides a base for future studies aiming at reconstructing past bioproductivity levels in ancient ocean/basin surface waters. In addition, we compare δ114Cd values with previously published chromium (Cr) isotope values and link signals of bioproductivity with redox conditions in the surface waters. The GBB core samples yield [Cd] (21–188 μg/kg), which increases with depth alongside changes in carbonate mineralogy related to sediment supply and diagenesis. The δ114Cd values of these carbonates are mainly positively fractionated with an average of 0.11‰ ± 0.17 (2σ; n = 17) relative to the NIST 3108 reference standard. Unlike previously observed for Cr isotopes, there is no control of δ114Cd values by relative abundances of the carbonate polymorphs aragonite and calcite in the studied profile. Likewise, δ114Cd values are not correlated to major and trace element (e.g. Ca, Mg, Mn and Sr) contents. We postulate that the burial and diagenetic processes of carbonate cannot modify the Cd isotope signals. Using the experimental fractionation factor for Cd into calcite (−0.45‰), calculated seawater δ114Cd of +0.56 ± 0.17‰ is in agreement with values for modern North Atlantic Surface Seawater. This study's results suggest that δ114Cd values in carbonates are a reliable tool for reconstruction of bioproductivity levels in past surface seawaters, and open new possibilities in combination with Cr isotopes to link these with past ocean redox.

Sclerites of the soft coral Ovabunda macrospiculata (Xeniidae) are predominantly the metastable CaCO3 polymorph vaterite

Soft corals (Cnidaria, Anthozoa, Octocorallia, Alcyonacea) produce internal sclerites of calcium carbonate previously shown to be composed of calcite, the most stable calcium carbonate polymorph. Here we apply multiple imaging and physical chemistry analyses to extracted and in-vivo sclerites of the abundant Red Sea soft coral, Ovabunda macrospiculata, to detail their mineralogy. We show that this species’ sclerites are comprised predominantly of the less stable calcium carbonate polymorph vaterite (> 95%), with much smaller components of aragonite and calcite. Use of this mineral, which is typically considered to be metastable, by these soft corals has implications for how it is formed as well as how it will persist during the anticipated anthropogenic climate change in the coming decades. This first documentation of vaterite dominating the mineral composition of O. macrospiculata sclerites is likely just the beginning of establishing its presence in other soft corals. Statement of significanceVaterite is typically considered to be a metastable polymorph of calcium carbonate. While calcium carbonate structures formed within the tissues of octocorals (phylum Cnidaria), have previously been reported to be composed of the more stable polymorphs aragonite and calcite, we observed that vaterite dominates the mineralogy of sclerites of Ovabunda macrospiculata from the Red Sea. Based on electron microscopy, Raman spectroscopy, and X-ray diffraction analysis, vaterite appears to be the dominant polymorph in sclerites both in the tissue and after extraction and preservation. Although this is the first documentation of vaterite in soft coral sclerites, it likely will be found in sclerites of other related taxa as well.

Influence of ontogenetic development, temperature, and pCO2 on otolith calcium carbonate polymorph composition in sturgeons

Changes to calcium carbonate (CaCO3) biomineralization in aquatic organisms is among the many predicted effects of climate change. Because otolith (hearing/orientation structures in fish) CaCO3 precipitation and polymorph composition are controlled by genetic and environmental factors, climate change may be predicted to affect the phenotypic plasticity of otoliths. We examined precipitation of otolith polymorphs (aragonite, vaterite, calcite) during early life history in two species of sturgeon, Lake Sturgeon, (Acipenser fulvescens) and White Sturgeon (A. transmontanus), using quantitative X-ray microdiffraction. Both species showed similar fluctuations in otolith polymorphs with a significant shift in the proportions of vaterite and aragonite in sagittal otoliths coinciding with the transition to fully exogenous feeding. We also examined the effect of the environment on otolith morphology and polymorph composition during early life history in Lake Sturgeon larvae reared in varying temperature (16/22 °C) and pCO2 (1000/2500 µatm) environments for 5 months. Fish raised in elevated temperature had significantly increased otolith size and precipitation of large single calcite crystals. Interestingly, pCO2 had no statistically significant effect on size or polymorph composition of otoliths despite blood pH exhibiting a mild alkalosis, which is contrary to what has been observed in several studies on marine fishes. These results suggest climate change may influence otolith polymorph composition during early life history in Lake Sturgeon.

Crystallization of vaterite and aragonite on chitin whiskers

The need for the possibility of producing calcium carbonate crystals by the evaporation method within five minutes and the growth of different calcium carbonate polymorphs on chitin whiskers within the same time frame at room temperature necessitated these report. Chitin whiskers (CHWs) were used as insoluble substrates, while poly (acrylic) acid (PAA) is used as soluble additive. The crystals were grown in chitin whiskers, Poly (acrylic) acid and CHW/PAA composites. The volume fractions for aragonite, vaterite, and calcite are 0.10, 0.25, and 0.65, respectively, in the absence of chitin whiskers or Poly (acrylic) acid. Calcite and aragonite volume fractions decrease in favour of vaterite when PAA and or CHWs were added. SEM images in the absence of CHWs and PAA shows rhombohedral calcites that display steady and step like plane appearances with an average edge of between 1.3 and 1.4 μm. In the presence of only CHWs, the SEM images show a mixture of ellipsoidal and spherical shape vaterites. The spherical vaterites have smooth, rough, and some irregular surfaces. Rod-like aragonite polymorphs were seen when only PAA was used as the template. In the presence of both PAA and CHWs, the rhombohedral shape showed roughness with irregular faces.
 Keywords: Chitin whisker, Calcium carbonate, Calcium, vaterite aragonite, Polymorph, Mole fraction

Application of µ-Raman spectroscopy to the study of the corrosion products of archaeological coins

<p>In this paper, a study of the corrosion products formed on archaeological bronze artefacts excavated in Tharros (Sardinia, Italy) is presented. The investigation was carried out by means of the combination of different analytical techniques, including optical microscopy, micro-Raman spectroscopy (µ-RS), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and X-ray diffraction. The artefacts under study are three bronze coins from the Phoenician–Punic period that are deeply corroded due to the chloride-rich soil of the Tharros excavation site. µ-Raman spectroscopy was chosen to investigate the corroded surfaces of the artefacts because it is a non-destructive technique, it has high spatial resolution, and it makes it possible to discriminate between polymorphs and correlate colour and chemical composition. Through µ-RS, it was possible to identify different mineralogical phases and different polymorphs, such as cuprite (Cu<sub>2</sub>O), copper trihydroxychloride [Cu<sub>2</sub>Cl(OH)<sub>3</sub>] polymorphs, hydroxy lead chloride laurionite [PbCl(OH)] and calcium carbonate polymorph aragonite. The experimental findings highlight that micro-Raman spectroscopy can be used to provide further knowledge regarding the environmental factors that may cause the degradation of archaeological bronzes in soil.</p>

Low cost and eco-friendly nanoparticles from cockle shells as a potential matrix for the immobilisation of urease enzyme

Cockle shells (a marine mollusc) are by-products or waste from the seafood industry, primarily made up of calcium carbonate (CaCO3) and are beneficial for the immobilisation of urease (Urs). In this study, a composition of 99.5% CaCO3 nanoparticles (NPs) from cockle shells was synthesised using a simple and environmentally friendly method involving the grinding and milling of cockle shells. Findings showed that the production of the pure NPs resulted in CaCO3 aragonite polymorphs approximately 78 nm in size and primarily functionalised with acrylic acid N-hydroxysuccinimide ester, which had a succinimide group that bound to the amine group of Urs. Fourier Transform Infrared Spectroscopy (FTIR) spectra confirmed peaks at 1120 cm−1 and 1016.63 cm−1, which were due to the presence of aliphatic amine C-N and amide bonds, revealing the immobilisation of Urs on functionalised NPs. Moreover, X-ray photoelectron spectroscopy (XPS) analysis showed changes in binding energy (eV) before and after immobilisation with Urs, with peaks at 131 eV and 170 eV representing phosphate and sulphur, respectively, from the Urs enzyme. Approximately 85.8% of Urs were successfully immobilised covalently on the larges surface areas of the NPs, enabling greater enzyme loading for the potential development of urea biosensors.

A modern scleractinian coral with a two-component calcite–aragonite skeleton

One of the most conserved traits in the evolution of biomineralizing organisms is the taxon-specific selection of skeletal minerals. All modern scleractinian corals are thought to produce skeletons exclusively of the calcium-carbonate polymorph aragonite. Despite strong fluctuations in ocean chemistry (notably the Mg/Ca ratio), this feature is believed to be conserved throughout the coral fossil record, spanning more than 240 million years. Only one example, the Cretaceous scleractinian coral Coelosmilia (ca. 70 to 65 Ma), is thought to have produced a calcitic skeleton. Here, we report that the modern asymbiotic scleractinian coral Paraconotrochus antarcticus living in the Southern Ocean forms a two-component carbonate skeleton, with an inner structure made of high-Mg calcite and an outer structure composed of aragonite. P. antarcticus and Cretaceous Coelosmilia skeletons share a unique microstructure indicating a close phylogenetic relationship, consistent with the early divergence of P. antarcticus within the Vacatina (i.e., Robusta) clade, estimated to have occurred in the Mesozoic (ca. 116 Mya). Scleractinian corals thus join the group of marine organisms capable of forming bimineralic structures, which requires a highly controlled biomineralization mechanism; this capability dates back at least 100 My. Due to its relatively prolonged isolation, the Southern Ocean stands out as a repository for extant marine organisms with ancient traits.

Carbonation of high-calcium lime mortars containing cactus mucilage as additive: a spectroscopic approach

Lime mortar is one of the oldest building materials. In Mexico, ingredients added to it to enhance its properties may include cactus mucilage, among others. We have evaluated the effect of adding, at two different concentrations, mucilage from Opuntia ficus-indica (prickly pear), Acanthocereous tetragonus (fairy castle cactus), and Hylocereus undatus (pitahaya or dragon fruit) in the accelerated carbonation of hydrated lime. The carbonation kinetics were followed by spectroscopic techniques such as Fourier transform mid-infrared (FTIR) spectroscopy, X-ray diffraction (XRD) spectroscopy, energy-dispersive X-ray (EDX) spectroscopy, and scanning electron microscopy (SEM). The results showed that mucilage promoted carbonation, functioning as a positive catalyst. Analysis of the infrared (IR) absorption corresponding to the in-plane asymmetric stretching $${v}_{3}$$ of the $${\text{C}}{\text{O}}_{3}^{2-}$$ anion indicated that the carbonation rate increased with the percentage of mucilage, being directly dependent on the concentration of Opuntia and Acanthocereous mucilage at both concentration levels tested. SEM observations confirmed that the inclusion of mucilage promoted the creation of the aragonite polymorph of calcium carbonate (CaCO3).

Structural evaluation of chitosan-modified precipitated calcium carbonate composite fillers for papermaking applications

Industries from different business sectors are facing challenges against global competitions for the development of sustainable and renewable products in the twenty-first century. Likewise, constant effort from pulp and paper manufacturers in minimizing paper cost with better quality in the active field of filler modification technology is much appreciated. In the present study, chitosan has been explored as a surface modifier alternative to conventional starch for precipitated calcium carbonate (PCC) to design chitosan/PCC composite filler. Two different dissolution mediums, hydrochloric and acetic acid, for chitosan have been seen to affect PCC crystals. Commercial PCC comprises mostly aragonite polymorphs along with some calcite crystals as implied by FTIR, XRD and FE-SEM images. It is interesting to note that surface treatment of PCC with 4.5% chitosan can successfully induce crystal transformation of PCC from aragonite to calcite polymorphs. Further, the deposition of chitosan was estimated from TOC measurements and the presence of deposited amount was validated from TGA analysis. Moreover, the introduction of chitosan (dissolved in HCl) to PCC dispersion was found to raise the zeta potential from − 14.43 to − 11.3 mv. Finally, the tensile strength of handsheets increased by 8.2% with 20% enhancement in ash with chitosan/PCC composite filler compared to the unmodified PCC. Therefore, bio-based PCC composites which proved to be promising for the development of high ash paper without compromising essential properties may result in saving wood pulp and production cost. Thus, implementing such seafood waste as a value-added additive is beneficial both to the industries and the environment because of its biodegradability and eco-friendliness.

Collaborative disposal of problematic calcium ions in seawater and carbon and sulfur pollutants in flue gas by bipolar membrane electrodialysis

The scale pollution caused by calcium ions (Ca2+) in seawater limits the development of seawater desalination. Emissions of CO2 and SO2 in flue gas can cause environmental problems. Under alkaline conditions, Ca2+ in seawater and CO2 in flue gas are precipitated while SO2 in flue gas is ionized. Based on the removal of calcium and carbon sequestration by bipolar membrane method, this study explored the feasibility of flue gas carbon fixation and desulfurization by seawater in the electrodialysis device. The effects of current density, aeration, CO2 content and the crystal form of seeds on pollutant treatment were investigated. The results indicated that the lower energy consumption can be obtained when the current density was 12.5 A/m2, the flue gas flow rate was 40 L/h and the CO2 content was 10% in flue gas, which established an operating conditions to obtain the decalcification rate greater than 90%, the carbon fixation rate up to 30% and the desulfurization rate close to 100%. Aragonite polymorph of calcium carbonate can be obtained regardless of polymorph of seeds in flue gas. Therefore, bipolar membrane electrodialysis integrated gas absorption and ionic reaction in order to overcome the pollution caused by the addition of traditional chemical reagents.

Influence of ageing conditions on the mineralogical micro-character of natural hydraulic lime mortars

The investigation of the chemical composition and physical and mechanical properties of old building materials is relevant for planning restoration interventions and designing compatible restoration materials. The quality of the binders used in mortars determines their durability, and consequently, influences the durability of the building structures in which they are applied. Lime binders continuously undergo chemical alterations as they age. Moreover, weathering agents cumulatively affect their properties, which adds to the difficulty in identifying their original composition. The mineralogy and microstructure of the binders of three historic mortar specimens collected from medieval bridges in the Czech Republic and a mortar designed in the laboratory to mimic the composition of the historic specimens were characterised using thermogravimetry analysis with mass spectrometry, x-ray powder diffraction and scanning electron microscopy coupled with energy dispersive spectroscopy. Two specimens showed binder decalcification and the presence of metastable CaCO3 vaterite and aragonite polymorphs. A mortar of comparable age, which was not exposed to elevated moisture, contained no CaCO3 modification other than calcite.

A novel matrix protein PfX regulates shell ultrastructure by binding to specific calcium carbonate crystal faces

Here, we have identified a novel matrix protein, named PfX, from the pearl oyster Pinctada fucada, and investigated the effects of recombinant PfX protein on calcium carbonate crystallization. The expression of PfX was spatially concentrated in the mantle tissue and gill, the former of which is responsible for the formation of shell structures. The shell notching assay showed a PfX expression response during injured shell repair and regeneration, suggesting the potential involvement of this matrix protein in shell biomineralization. Further, an in vitro crystallization assay showed that PfX could alter the CaCO3 morphologies of both calcite and aragonite polymorphs. Correspondingly, a binding assay indicated that PfX has strong binding affinity for CaCO3 crystals, especially aragonite. Further, the protein's calcite binding capacity increased obviously when particular crystal faces were induced. In addition, PfX conjugated with fluorescent dye cyanine-5 (cy5) was preferentially distributed on rough crystal faces instead of the smooth and common (1 0 4) faces of calcite during the crystallization. These results suggest that matrix protein PfX might regulate CaCO3 morphology via selective binding and inhibit the growth of certain crystal faces, providing new clues for understanding biomineralization mechanisms in mollusk.

Coral acid rich protein selects vaterite polymorph in vitro

Corals and other biomineralizing organisms use proteins and other molecules to form different crystalline polymorphs and biomineral structures. In corals, it’s been suggested that proteins such as Coral Acid Rich Proteins (CARPs) play a major role in the polymorph selection of their calcium carbonate (CaCO3) aragonite exoskeleton. To date, four CARPs (1–4) have been characterized: each with a different amino acid composition and different temporal and spatial expression patterns during coral developmental stages. Interestingly, CARP3 is able to alter crystallization pathways in vitro, yet its function in this process remains enigmatic. To better understand the CARP3 function, we performed two independent in vitro CaCO3 polymorph selection experiments using purified recombinant CARP3 at different concentrations and at low or zero Mg2+ concentration. Our results show that, in the absence of Mg2+, CARP3 selects for the vaterite polymorph and inhibits calcite. However, in the presence of a low concentration of Mg2+ and CARP3 both Mg-calcite and vaterite are formed, with the relative amount of Mg-calcite increasing with CARP3 concentration. In all conditions, CARP3 did not select for the aragonite polymorph, which is the polymorph associated to CARP3 in vivo, even in the presence of Mg2+ (Mg:Ca molar ratio equal to 1). These results further emphasize the importance of Mg:Ca molar ratios similar to that in seawater (Mg:Ca equal to 5) and the activity of the biological system in a aragonite polymorph selection in coral skeleton formation.

Aragonite bias exhibits systematic spatial variation in the Late Cretaceous Western Interior Seaway, North America

AbstractPreferential dissolution of the biogenic carbonate polymorph aragonite promotes preservational bias in shelly marine faunas. While field studies have documented the impact of preferential aragonite dissolution on fossil molluscan diversity, its impact on regional and global biodiversity metrics is debated. Epicontinental seas are especially prone to conditions that both promote and inhibit preferential dissolution, which may result in spatially extensive zones with variable preservation. Here we present a multifaceted evaluation of aragonite dissolution within the Late Cretaceous Western Interior Seaway of North America. Occurrence data of mollusks from two time intervals (Cenomanian/Turonian boundary, early Campanian) are plotted on new high-resolution paleogeographies to assess aragonite preservation within the seaway. Fossil occurrences, diversity estimates, and sampling probabilities for calcitic and aragonitic fauna were compared in zones defined by depth and distance from the seaway margins. Apparent range sizes, which could be influenced by differential preservation potential of aragonite between separate localities, were also compared. Our results are consistent with exacerbated aragonite dissolution within specific depth zones for both time slices, with aragonitic bivalves additionally showing a statistically significant decrease in range size compared with calcitic fauna within carbonate-dominated Cenomanian–Turonian strata. However, we are unable to conclusively show that aragonite dissolution impacted diversity estimates. Therefore, while aragonite dissolution is likely to have affected the preservation of fauna in specific localities, time averaging and instantaneous preservation events preserve regional biodiversity. Our results suggest that the spatial expression of taphonomic biases should be an important consideration for paleontologists working on paleobiogeographic problems.

Trash or treasure? Use of sagittal otoliths partially composed of vaterite for hatchery stock discrimination in steelhead

Sagittal otoliths are normally deposited as the CaCO3 polymorph aragonite; however, a proportion of otoliths transitions to vaterite during growth. This transition can complicate otolith chemistry analyses, as differences in the crystalline structure (aragonite or vaterite) of otoliths causes variation in otolith chemistry signatures. To address this issue, we introduce a method to utilize sagittal otoliths partially composed of vaterite for stock discrimination. Using this method, we determined the hatchery origins of yearlings from five Lake Erie hatcheries by using Ba, Mg, Mn, and Sr concentrations in vaterite sections of steelhead (Oncorhynchus mykiss) otoliths. We then compared the classification accuracy of our vaterite method with a method in which otoliths composed entirely of aragonite were used. Overall, quadratic discriminant function analyses revealed similar classification success when elemental concentrations from vaterite (95% accuracy) and aragonite (94% accuracy) otolith regions were used. The methods introduced here could likely be used for other fish species that have otoliths that transition to vaterite as long as an adequate number of juvenile fish are available to develop vaterite otolith chemistry signatures.

Enhanced Vaterite And Aragonite Crystallization At Controlled Ethylene Glycol Concentrations

Calcium carbonate (CaCO3) has three distinct anhydrous polymorphs, namely vaterite, aragonite and calcite. Although there is a high demand for aragonite and vaterite polymorphs for biomedical use, their unstable nature makes it challenging to synthesize them compared to calcite, which is the most stable form of CaCO3. Despite the remarkable effort on stabilizing vaterite and aragonite polymorphs in aqueous solutions, phase-pure vaterite and aragonite polymorphs have not been synthesized yet, without referring to the use of additives, surfactants or elevated temperatures. Herein, the effect of ethylene glycol (EG) concentration and temperature on the formation of vaterite and aragonite particles were investigated at 25 °C and 70 °C. Results showed that 60% EG containing precursor solution -without any other additive- can prevent vaterite/aragonite-to-calcite transformation regardless of the synthesis temperature. Furthermore, the size of CaCO3 particles decreased as EG concentration increased and it reached its minimum average values at 80% EG. The results of this study revealed the potential use of the proposed synthesis route to stabilize vaterite and aragonite polymorphs, tailor their content, morphology and size without using any additives, surfactants and elevated temperatures.

Calcium extraction and synthesis of precipitated calcium carbonate from Mg-rich dolomite

Abstract A green-reaction assisted synthesis using a natural occurring dolomite is reported for precipitated calcium carbonate production over aloe barbadensis miller extract template under ambient condition. Uniform, hierarchical aragonite precipitated calcium carbonate stacked from nanoparticles was synthesized. The tainted Mg influence on resultant PCC purity was averted via D-glucose extraction of dolomite constituent calcium and subsequent precipitation using CO2. The as-synthesized PCC was characterized using SEM, XRD, PSD, and FTIR spectroscopy. Under ambient conditions using carbonation route and 1 L/min CO2 flowrate, aragonite polymorph with hierarchical flower-like structure was produced. Energy is conserved as heat is not required for phase transformation. Minerals & Environment (RAMM) 2018.