Mixture Of Vaterite Research Articles

Valorization of Crocus Sativus L waste extracts as efficient, eco-friendly and economical inhibitors of scaling: Experimental and computational investigations

The valorization of biomass and the use of plant extracts as new green inhibitors of scaling are amongthe most innovative research topics. In this light, this study aims to evaluate the effectiveness of two extracts of Crocus Sativus L (CSL) wastes towards the formation of calcareous scale, namely the Aqueous Extract of Leaf (ALE) and the Aqueous Extract of Petal and Stamen (AEPS). Folin-Ciocalteau and colorimetric methods are used to determine thetotal polyphenols and flavonoids contents, respectively. Then, the anti-scaling property of the investigated extracts is determined using a conductivity test and the Laboratory of Chemistry and Genie of the Environment (LCGE) technique at a temperature of 25 °C. After that, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) analysesare employed to examine the formed scale during the LCGE tests. To support the experimental findings, Molecular Dynamic (MD) simulations and Density Functional Theory (DFT) calculations are carried out. The data obtained revealed that AEPS has a higher concentration of total polyphenol and flavonoids than ALE. Total inhibition occurs after the addition of 60 mg‧L-1 of AEPS to the calco-carbonic solution with a hardness of 40°F. Whereas an amount of 82 mg‧L-1 of ALE was the optimal concentration to completely inhibit CaCO3 formation. This allows us to conclude that the anti-scaling effectiveness is correlated with polyphenols and flavonoids contents in CSL extracts. SEM and FTIR analyses reveal that the crystallization of CaCO3 without inhibitor was a stable variety of calcite with a rhombohedral form. However, the presence of a low concentration of AEPS (20 mg‧L-1) resulted in a significant modification on the morphology of CaCO3 and a mixture of vaterite with calcite phases. The theoretical outcomes agree with the anti-scaling efficiencies reported experimentally. Based on these results, the CSL biomass could be an interesting renewable source of eco-friendly and inexpensive inhibitors of scaling.

Experimental investigation and molecular dynamic simulation of Tannic acid as an eco-friendly inhibitor for calcium carbonate scale

The present study aims to assess the performance of Tannic acid (TA), a natural polyphenol, as a new eco-friendly inhibitor on the deposition scale of calcium carbonate. The conductivity test and the Laboratory of Chemistry and Genie of the Environment (LCGE) technique are used to evaluate the anti-scaling property of TA. The dispersion property of CaCO3 is also investigated using UV–visible method. To characterize the morphology and crystal structure of the formed scale during the LCGE tests, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses are utilized. Then, Molecular dynamic simulations are carried out to prove theoretically the ability of TA molecule to inhibit CaCO3 scaling. Results show that the addition of a low concentration of TA (7.8 mg L −1) inhibits completely the precipitation of calcium carbonate of calco-carbonic solution with a hardness of TH = 40 ° F (1 ° F = 4 mg L −1 of calcium ions) at 25 °C. We recorded also that TA has a good dispersion property of CaCO3. It was observed that the scales formed in the absence of TA are regular rhombohedral forms. However, in the presence of a low concentration of TA (2 mg L −1) the significant modification in the crystal morphology and the crystal sizes are noted. XRD diffractogram reveals that CaCO3-calcite is the main polymorph formed during the tests without inhibitor. Nevertheless, in the presence of inhibitor, a mixture of vaterite and calcite was obtained. The geometrical and energetic analyses of the interfacial interactions of TA inhibitor with calcite (110) and (104) surfaces proved its enhanced capacity to interact with calcite crystals. These findings explain the good obtained scale inhibition efficiency of TA. Consequently, we suggest the use of TA as a new eco-friendly inhibitor for calcareous scaling.

Ultrasonic-assisted production of precipitated calcium carbonate particles from desulfurization gypsum

This study aimed to investigate the effect of ultrasonic application on the production of precipitated calcium carbonate (PCC) particles from desulfurization gypsum via direct mineral carbonation method using conventional and venturi tube reactors in the presence of different alkali sources (NaOH, KOH and NH4OH). The venturi tube was designed to determine the effect of ultrasonication on PCC production. Ultrasonic application was performed three times (before, during, and after PCC production) to evaluate its exact effect on the properties of the PCC particles. Scanning electron microscope (SEM), X-ray diffraction (XRD), Atomic force microscope (AFM), specific surface area (SSA), Fourier transform infrared spectrometry (FTIR), and particle size analyses were performed. Results revealed the strong influence of the reactor types on the nucleation rate of PCC particles. The presence of Na+ or K+ ions in the production resulted in producing PCC particles containing only calcite crystals, while a mixture of vaterite and calcite crystals was observed if NH4+ ions were present. The use of ultrasonic power during PCC production resulted in producing cubic calcite rather than vaterite crystals in the presence of all ions. It was determined that ultrasonic power should be conducted in the venturi tube before PCC production to obtain PCC particles with superior properties (uniform particle size, nanosized crystals, and high SSA value). The resulting PCC particles in this study can be suitably used in paint, paper, and plastic industries according to the ASTM standards.

Effect of impure components in flue gas desulfurization (FGD) gypsum on the generation of polymorph CaCO3 during carbonation reaction.

As one of the typical solid-wastes, FGD gypsum usually occupies land and causes resource waste and environmental pollution. Its high content of CaSO4·2H2O shows highly potential in synthesizing CaCO3 by incorporating CO2. Nevertheless, the impurities in FGD gypsum have significant effects on polymorph of CaCO3 and the formation mechanism of CaCO3 polymorph during FGD gypsum carbonation was still unclear. Here, we selected CaSO4·2H2O as model to explore the effects of impurities of muscovite and dolomite in FGD gypsum on polymorph of CaCO3 during carbonation. Results showed that the carbonation products of FGD gypsum are a mixture of vaterite (˜60%) and calcite (˜40%), while only pure vaterite was obtained in CaSO4·2H2O carbonation reaction. Muscovite has negligible effects on obtaining pure vaterite during CaSO4·2H2O carbonation. Interestingly, the content of calcite increases to the maximum value (˜27%) at 1.0 wt% dolomite and then decreases with the increment of dolomite in CaSO4·2H2O carbonation reaction. Correspondingly, vaterite declines first and then increases. Mechanism study shows that hydrophilicity and negative surface charge of dolomite might be the key factors to selectively form calcite during the carbonation of FGD gypsum. These findings might contribute to further utilization of FGD gypsum.

Growing Innovative Calcium Carbonate Morphologies by Utilizing the Colloidal Gas Aphron System as a Surfactant-Based Template Method

Many studies have been conducted to study the various polymorphs and morphologies of calcium carbonate crystals in nature and living organisms. In this experimental work, a novel method has been employed to crystallize calcium carbonate by using colloidal gas aphron dispersion. The polymorph and morphology of prepared particles were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectrometry techniques. SEM and XRD analyses demonstrated that the morphology of synthesized CaCO3 can be changed from spherical (vaterite phase) to novel rod and plate-like shapes (mixture of vaterite and calcite phases) with changes in the surfactant concentration. The quantitative examination results of different calcium carbonate polymorph orientations showed that the precursor concentrations had no significant effect on the orientation of calcite phase, but rather they affected the orientation development of vaterite phase at a higher surfactant concentration.

Precipitation of calcium carbonate from a calcium acetate and ammonium carbamate batch system

In this paper, we report a novel approach for preparing precipitated calcium carbonate using solutions of ammonium carbamate and calcium acetate as the sources of calcium and carbon dioxide, respectively. Two different concentrations of the starting solutions at three different temperatures (15, 25 and 50 °C) were used for the reaction. The influence of temperature and concentration on the polymorphism and the resulting morphology of calcium carbonate are discussed. The most important parameter for controlling a particular crystal structure and precipitate morphology were the concentrations of the initial solutions. When initial solutions with lower concentrations were used, the crystal form of the precipitate changed with time. Regardless the different polymorphism at different temperatures, after one day only the calcite form was detected in all samples, regardless of at which temperature the samples were prepared. At higher concentrations, pure vaterite or a mixture of vaterite and calcite were present at the beginning of the experiment. After one day, pure vaterite was found in the samples that were prepared at 15 and 25 °C. If calcium carbonate precipitated at 50 °C, the XRD results showed a mixture of calcite and vaterite regardless of the time at which the sample was taken. The morphology of calcium carbonate particles prepared at various conditions changed from calcite cubes to spherical particles of vaterite and aragonite needles. When a low starting concentration was used, the morphology at the initial stage was strongly affected by the temperature at which the experiments were conducted. However, after one day only, cubes were present in all cases at low initial concentrations. In contrast, at high concentrations spherical particles precipitated at all three temperatures at the beginning of the reaction. Spherical particles were made up from smaller particles. Over time, the size of the particles was diminishing due to their disintegration into primary particles; after one day, particles of 30–50 nm were obtained. The lower the temperature was during the experiment, the faster the larger particles fell apart. To our knowledge, this behavior has thus far not yet been reported. Moreover, for the first time ammonium carbamate and calcium acetate are used together to prepare calcium carbonate.

Interaction between dissolved silica and calcium carbonate: 1. Spontaneous precipitation of calcium carbonate in the presence of dissolved silica

The kinetics of spontaneous precipitation of CaCO 3 from aqueous solution in the presence of dissolved silica was investigated by recording pH as a function of time. The presence of dissolved silica, at concentrations below saturation with respect to the amorphous phase, decreases induction time for CaCO 3 nucleation, but does not affect CaCO 3 polymorphism. For a “pure” system without silica, the surface free energy, σ, determined from classical nucleation theory is 42 mJ m −2. This agrees well with values reported in the literature for vaterite and indicates some degree of heterogeneous nucleation, which can occur because of the relatively low degree of supersaturation used for the experiments. In the presence of 1 and 2 mM silica, σ is 37 and 34 mJ m −2, indicating an increasing degree of heterogeneous nucleation as the amount of polymeric silica increases. The ratio of Ca 2+ to CO 3 2− activity was a governing parameter for determining which CaCO 3 polymorph precipitated. At high Ca 2+ to CO 3 2− activity ratios, almost all initial solid was vaterite, whereas at low ratios, a mixture of vaterite and calcite was observed. In solutions with low Ca 2+ to CO 3 2− activity ratios, the presence of silica at concentrations above saturation with respect to amorphous silica led to formation of only calcite and strongly influenced the crystalline structure and morphology of the precipitates. At high Ca 2+ to CO 3 2− ratios, system behaviour did not differ from that without silica.

Rock hyraces: a cause of San rock art deterioration?

AbstractSan rock art sites are found throughout southern Africa, many showing signs of deterioration. In order to conserve this invaluable heritage, a long‐term multidisciplinary project has been launched to monitor the rate of their deterioration and determine the various chemical processes that are possibly contributing to the decay. This study was initiated to establish if Raman spectroscopy could contribute to this project and since rock hyrax colonies live in close proximity to many of these archaeological sites, the possible influence of their metabolic products on the deterioration process was investigated.The precipitates from the urine of rock hyraces were analysed with Raman and Fourier‐transform infrared (FTIR) spectroscopy. Where the urine was in contact with the faeces, the precipitates are a mixture of vaterite (a rare polymorph of CaCO3) and the hydrated salt calcium monohydrocalcite (also rarely found in nature). On areas where this contact is at a minimum the common and stable polymorph of CaCO3, calcite, is the main component. SEM micrographs and XRD analysis support the Raman and FTIR results.XRD, FTIR and preliminary GC‐MS analyses of hyraceum, the fossilised mixture of faeces and urine, identified an inorganic phase (potassium chloride, with small concentrations of other salts, e.g. vaterite and weddelite) and an organic phase, which is a cocktail of various aromatic compounds, mainly amides, alcohols and acids. These compounds could contribute to the crystallisation of these rare carbonates, as well as other uncommon salts detected on the cave walls, such as syngenite. The presence of phosphates in the urine may further act as a stabilizing agent. Copyright © 2007 John Wiley & Sons, Ltd.

Transformation of Vaterite into Cubic Calcite in the Presence of Copper(II) Species

By a simple washing of vaterite with ultrapure water, it transforms rapidly into cubic calcite. When the solid is washed with Cu2+ solutions, the transformation depends on the concentrations of the copper solutions applied in the process. For concentrations of 10-4 mol dm-3, a certain delay in the transformation process is detected, and the obtained cubic calcite seems to be in the form of CuxCa1-xCO3. For concentrations of 10-3 mol dm-3, the vaterite structure remains stable with time, and this stability seems to be correlated with the saturation of the surface by Cu2+ in place of Ca2+. For concentrations of 10-2 mol dm-3, a mixture of vaterite, aragonite, cubic calcite, and malachite is obtained during the transformation process.

ChemInform Abstract: FORMATION OF VATERITE BY THE REACTION OF CALCIUM METHOXIDE WITH AQUEOUS SODIUM CARBONATE SOLUTION

AbstractReaktion von Ca(OMe)2 mit wäßrigen Na2CO3‐Lösungen (0.25‐1 N) führt zwischen 30 und 90°C zur Bildung von CaCO3 in den beiden polymorphen Modifikationen Vaterit und Calcit, wobei das Produktverhältnis in erster Linie von der Reaktionstemp abhängt.