CaCO3 Nucleation Research Articles

Interfacial energies for heterogeneous nucleation of calcium carbonate on mica and quartz.

Interfacial free energies often control heterogeneous nucleation of calcium carbonate (CaCO3) on mineral surfaces. Here we report an in situ experimental study of CaCO3 nucleation on mica (muscovite) and quartz, which allows us to obtain the interfacial energies governing heterogeneous nucleation. In situ grazing incidence small-angle X-ray scattering (GISAXS) was used to measure nucleation rates at different supersaturations. The rates were incorporated into classical nucleation theory to calculate the effective interfacial energies (α'). Ex situ Raman spectroscopy identified both calcite and vaterite as CaCO3 polymorphs; however, vaterite is the most probable heterogeneous nuclei mineral phase. The α' was 24 mJ/m(2) for the vaterite-mica system and 32 mJ/m(2) for the vaterite-quartz system. The smaller α' of the CaCO3-mica system led to smaller particles and often higher particle densities on mica. A contributing factor affecting α' in our system was the smaller structural mismatch between CaCO3 and mica compared to that between CaCO3 and quartz. The extent of hydrophilicity and the surface charge could not explain the observed CaCO3 nucleation trend on mica and quartz. The findings of this study provide new thermodynamic parameters for subsurface reactive transport modeling and contribute to our understanding of mechanisms where CaCO3 formation on surfaces is of concern.

Role of crystal structure on [formula omitted] capture by limestone derived CaO subjected to carbonation/recarbonation/calcination cycles at Ca-looping conditions

Large scale pilot plants are currently demonstrating the feasibility of the Calcium-looping (CaL) technology built on the multicyclic calcination/carbonation of natural limestone for post-combustion and pre-combustion CO2 capture. Yet, limestone derived CaO exhibits a drop of conversion when subjected to multiple carbonation/calcination cycles, which lessens the efficiency of the technology. In this paper we analyze a novel CaL concept recently proposed to mitigate this drawback based on the introduction of an intermediate stage wherein carbonation is intensified at high temperature and high CO2 partial pressure. It is shown that carbonation in this stage is mainly driven by solid-state diffusion, which is determined by the solid’s crystal structure. Accordingly, a reduction of crystallinity by ball milling, which favors diffusion, serves to promote recarbonation. Conversely, thermal annealing, which enhances crystallinity, hinders recarbonation. An initial fast phase has been identified in the recarbonation stage along which the rate of carbonation is also a function of the crystal structure indicating a relevant role of surface diffusion. This is consistent with a recently proposed mechanism for nucleation of CaCO3 on the CaO surface in islands with a critical size determined by surface diffusion. A further issue analyzed has been the effects of pretreatment and cycling on the mechanical strength of the material, whose fragility hampers the CaL process efficiency. Particle size distribution of samples dispersed in a liquid and subjected to high energy ultrasonic irradiation indicate that milling promotes friability whereas thermal annealing enhances the resistance of the particles to fragmentation even though pretreatment effects become blurred after cycling. Our study demonstrates that recarbonation conditions and crystal-structure controlled diffusion are important parameters to be considered in order to assess the efficiency of CO2 capture in the novel CaL concept.

Investigating Processes of Nanocrystal Formation and Transformation via Liquid Cell TEM

Recent ex situ observations of crystallization in both natural and synthetic systems indicate that the classical models of nucleation and growth are inaccurate. However, in situ observations that can provide direct evidence for alternative models have been lacking due to the limited temporal and spatial resolution of experimental techniques that can observe dynamic processes in a bulk solution. Here we report results from liquid cell transmission electron microscopy studies of nucleation and growth of Au, CaCO3, and iron oxide nanoparticles. We show how these in situ data can be used to obtain direct evidence for the mechanisms underlying nanoparticle crystallization as well as dynamic information that provide constraints on important energetic parameters not available through ex situ methods.

Kinetics of calcium carbonate precipitation through CO2 absorption from flue gas into distiller waste of soda ash plant

Kinetics of CaCO3 precipitation by CO2 absorption from flue gas into distiller waste of soda ash plant was investigated by minimizing the differences between the model predictions and experimental data through a method of genetic algorithm. A population balance equation coupled with a mass balance equation was used to model CaCO3 precipitation. These model equations were solved using the numerical method of Crank–Nicolson. Impurities in distiller waste and different concentrations of CO2 in synthetic flue gas were found to be influential in mechanisms of nucleation, growth and agglomeration of CaCO3 precipitates. The impurities increased the agglomeration but reduced the nucleation and growth rates.

Effect of surface properties of calcium carbonate on aggregation process investigated by molecular dynamics simulation

The control of the morphology and polymorphs of CaCO3 has been required, since their capabilities are dependent on particle characteristics of CaCO3. It is difficult to clarify the formation mechanism only by the experimental approaches because the nucleation and crystal growth of CaCO3 occurred at nanoscale. The objective of the present work is to investigate the effect of surface properties including in the charge density and the dielectric constant of water on the aggregation process of primary particles by means of molecular dynamics simulations. The grain boundary energy was also calculated by molecular dynamics simulation to investigate the change of energy in the aggregation process of primary particles. From the results of molecular dynamics simulation, we found that the interface of (001)Ca and (001)CO3 contacted with water charged positively and negatively and the interface of (100) and (104) contacted with water charged neutrally. When the distance of interfaces between CaCO3 particles came close to colliding, the dielectric constant of water became small except the interface of (001)CO3. The boundary energy of interface between (001)Ca and (001)CO3 was the lowest among five types of interfaces. It indicates that the aggregation of (001)Ca and (001)CO surface is the easiest among all types of interfaces.

Biomineralized polypropylene/CaCO3 composite nonwoven meshes for oil/water separation

ABSTRACTPolypropylene/calcium carbonate (CaCO3) composite nonwoven meshes were prepared on the basic principle of biomineralization by using a facile alternate soaking process (ASP) within 20 min. Negatively charged poly(acrylic acid) brushes, which can induce CaCO3 nucleation, were first tethered onto the fiber surface of polypropylene nonwoven meshes via UV‐induced graft polymerization. ASP procedure was followed to mineralize CaCO3 particles on the fiber surface and to form the composite nonwoven meshes. Fourier transform infrared spectroscopy/attenuated total reflectance, field emission scanning electron microscope, equipped X‐ray spectroscope, and X‐ray diffraction were used to characterize the prepared composite meshes. The mineral cover density increased with the ASP cycles, and it progressively increased for the relative content of calcite in the crystalline part of the mineral layer as well. Contact angle measurements indicate that the as‐prepared composite nonwoven meshes were endowed with superhydrophilicity and underwater superoleophobicity, thus they showed prominent application prospects in wastewater treatment and oil/water separation. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39897.

Kinetics, energy characteristics, and intensification of crystallization processes in chemical precipitation of hardness ions

An analysis of the literature data on the solubility and kinetics of the chemical (reagent) precipitation of calcium carbonate and magnesium hydroxide is performed. The possible causes of the significant discrepancy in the available data are considered. The kinetics of the homogeneous and heterogeneous crystallization of calcium carbonate and magnesium hydroxide in reagent precipitation is studied using different methods. It is shown that the use of heterogeneous crystallization on seed particles pretreated in an ultrasonic field raises the rate of crystallization by an order of magnitude. The kinetics of nucleation is studied; the effect of supersaturation and temperature on the induction period in the homogeneous and heterogeneous nucleation of CaCO3 and Mg(OH)2 crystals is investigated. The energy characteristics of nucleation, namely, the interfacial tension (surface energy) and activation energy, are determined. The use of fine-dispersed particles activated by ultrasound makes it possible to considerably reduce the energy barrier for nucleation.

Biomimetic nucleation and growth of CaCO3 in bacterial cellulose produced by Gluconacetobacter xylinus (Acetobacter xylinus)

Biomimetic nucleation and growth of CaCO3 in bacterial cellulose produced by Gluconacetobacter xylinus (Acetobacter xylinus)

Amphiphilic Polypeptides as a Bifunctional Template in the Mineralization of Calcium Carbonate at the Air/Water Interface

A well-defined amphiphilic polypeptide, poly(glutamic acid)22 -block-poly(alanine)8 (PGlu22 -b-PAla8 ), which plays the roles of both soluble (functional) additive and insoluble (structural) matrix, is employed to mediate the mineralization of CaCO3 at the air/water interface. X-ray diffraction (XRD) and Raman spectroscopy, for example, show that the polymorph of CaCO3 particles obtained is calcite. The observations from SEM and TEM suggest that PGlu22 -b-PAla8 initiates the amorphous precursor phase and heterogeneous nucleation of CaCO3 at the air/water interface, while temporarily stabilizes the gelatinous precursors as a process-directing agent; nevertheless, the initial concentration of Ca(2+) controls the procedure of crystallization and the final morphology of CaCO3 particles. Such "bifunctional" amphiphilic-polypeptide-regulated mineralization at the air/water interface may be applied to the synthesis of many kinds of symmetrical inorganic/organic hybrids.

Study of calcium carbonate and sulfate co-precipitation

Co-precipitation of mineral based salts in scaling is still not well understood and/or thermodynamically well defined in the water industry. This study focuses on investigating calcium carbonate (CaCO3) and sulfate mixed precipitation in scaling which is commonly observed in industrial water treatment processes including seawater desalination either by thermal-based or membrane-based processes. Co-precipitation kinetics were studied carefully by monitoring several parameters simultaneously measured, including: pH, calcium and alkalinity concentrations as well as quartz microbalance responses. The CaCO3 germination in mixed precipitation was found to be different than that of simple precipitation. Indeed, the co-precipitation of CaCO3 germination time was not anymore related to supersaturation as in a simple homogenous precipitation, but was significantly reduced when the gypsum crystals appeared first. On the other hand, the calcium sulfate crystals appear to reduce the energetic barrier of CaCO3 nucleation and lead to its precipitation by activating heterogeneous germination. However, the presence of CaCO3 crystals does not seem to have any significant effect on gypsum precipitation. IR spectroscopy and the Scanning Electronic Microscopy (SEM) were used to identify the nature of scales structures. Gypsum was found to be the dominant precipitate while calcite and especially vaterite were found at lower proportions. These analyses showed also that gypsum crystals promote calcite crystallization to the detriment of other forms.

Impacts of aqueous carbonate accumulation rate, magnesium and polyaspartic acid on calcium carbonate formation (6–40 °C)

The formation of anhydrous CaCO3 polymorphs is very common and widespread in low-temperature inorganic and biogenic environments. An increase in aqueous carbonate concentration frequently induces CaCO3 formation in nature. Nevertheless, no systematic experiment has assessed the impact of the continuous accumulation of aqueous carbonate ions on CaCO3 formation. Also, the coupled influences of temperature, inorganic and organic additives, and rates of aqueous carbonate accumulation and supersaturation to induce CaCO3 polymorph formation have been poorly investigated. The latter two factors comprise reaction times that are required for nucleation and subsequently affect the precipitation kinetics through ongoing CaCO3 formation. To address these issues, CaCO3 formation was experimentally studied at a variety of aqueous carbonate accumulation rates (10−1.5≤ACAR≤101.8μmolh−1l−1) between 6 and 40°C using a CO2 diffusion technique at conditions that were analogous to sea water (pH8.3; [Ca2+]=10mmoll−1). The impacts of an inorganic and organic constituent on CaCO3 formation were investigated using Mg2+ and polyaspartic acid (Pasp) at concentrations up to 55mmoll−1 and 3.4mgl−1, respectively.The experimental data clearly reveal that the time for CaCO3 nucleation depends strongly on ACAR, T, [Mg2+] (>0.5mmoll−1), and [Pasp] (>0.1mgl−1) but not on the formation of different CaCO3 polymorphs. Elevated ACAR results in earlier CaCO3 formation and causes Mg2+ to have less of an impact on the retardation of nucleation. The ion activity product (IAP) required for CaCO3 nucleation is positively correlated to the subsequent CaCO3 precipitation rates but is independent of whether aragonite or calcite formation is induced. The type of CaCO3 polymorph from the primary nuclei is controlled by the influences of Mg2+ and Pasp, which are coupled to ACAR and T. Elevated ACAR, T, and [Mg2+] promote the formation of aragonite, and high [Mg2+] levels suppress the formation of vaterite. In contrast, [Pasp]>0.02mgl−1 inhibits aragonite and favours vaterite formation. Thus, if both Mg2+ and Pasp are present, the formation of calcite is favoured. The precipitation rates for ongoing calcite and aragonite formation are nearly the same at analogous conditions and particularly for a given IAP. According to our experimental results, the combined impacts of ACAR, T, [Mg2+], and [Pasp] must be considered to identify distinct conditions of CaCO3 polymorph formation and precipitation kinetics.

Reversed crystal growth of rhombohedral calcite in the presence of chitosan and gum arabic

Calcite crystals with a rhombohedral morphology were synthesized using a biomimetic method in the presence of organic structure-directing agents (chitosan and gum arabic). Analysis of the microstructures of these crystals by scanning electron microscopy, high resolution transmission electron microscopy and powder X-ray diffraction revealed a non-classical growth mechanism. Initially, the biomaterials and inorganic precursor molecules aggregated into large particles. Multiple nucleation of CaCO3 took place either on the surface of the aggregates (in the chitosan system) or inside the aggregates (in the gum arabic system). These nanocrystallites aggregated again to form some large polycrystalline rhombohedral or spherical particles. Surface recrystallization then occurred, forming small single-crystal islands, which joined together as the reaction time increased leading to a core–shell structure where a polycrystalline core was encased in a thin single-crystal shell. The crystallization then extended from the surface to the core, ultimately resulting in true single crystals.

Writing on Superhydrophobic Nanopost Arrays: Topographic Design for Bottom-up Assembly

A well-known property of superhydrophobic surfaces, such as an array of hydrophobic nanoposts, is to allow only limited surface contact of a liquid to the tips of the nanoposts. Herein we demonstrate that material deposition from solution, whether solid precipitation, surface adsorption or colloidal adhesion in static system, or dynamic "writing", can be limited to these specific areas of the surface when in this nonwetting state. As an example of solid precipitation, we show that nucleation of CaCO(3) results in the growth of small, uniform, amorphous deposits (which can merge and recrystallize) instead of disordered, large crystals due to the abundance of identical, small heterogeneous nucleation sites. The growth of amorphous CaCO(3) can be used to trap molecules from solution, as a potential application for controlled drug release. To demonstrate the localized surface adsorption, we show that chemical functionalization of the post tips can make them "sticky" for specific attachment of species (such as colloidal particles) from solution. The electrostatic charge and relative size ratio of the particle/post diameters control the attachment of particles to the post tips with great specificity. Dynamic conditions have also been shown for writing using droplets translated across the nonwetting surface at controlled speeds during deposition. These methods offer unprecedented control over the heterogeneous nucleation and localized growth of crystals from solution and avoid nonspecific adsorption. There is selective control of colloidal or molecular attachment to the nanopost tips, whereby the contact area, time of contact, and tip surface chemistry for reaction are all independently tunable parameters.

Influence of the Mole Ratio of the Interacting to the Stabilizing Portion (RI/S) in Hyperbranched Polymers on CaCO3Crystallization: Synthesis of Highly Monodisperse Microspheres

This work investigates the influence of the mole ratio of the interacting to the stabilizing portion (RI/S) in hyperbranched polymers on the morphology and the polymorph evolution of CaCO3. The RI/S is defined as the mole ratio of the carboxyl units (interacting portion) to the glycerol units (stabilizing portion) in carboxyl-terminated hyperbranched polyglycerol (HPG-COOH) and can be changed systematically from 0.1 to 0.9. Especially, when it is above 0.5, highly monodisperse CaCO3 microspheres are first prepared by direct mixing of Ca2+ and CO32– in the presence of HPG-COOH. Our results demonstrate the topology effect of the hyperbranched polymers on the crystallization of CaCO3 and suggest that both the conformation of the stabilizing portion and the density and the distribution of the interacting portion determine the roles of HPG-COOH in CaCO3 crystallization, such as the calcium-binding ability, the face-selective interaction with crystals, and the inhibition of CaCO3 nucleation and growth.

Rate Equation Theory for the Carbonation Reaction of CaO with CO2

Rate equation theory for CaO carbonation reaction was developed to replace the assumption of critical product layer thickness with a complete calculation of the rates of CaCO3 nucleation and growth. The model includes rate expressions for the island size distribution function with time evolution, and the surface reaction, surface diffusion, grain boundary and lattice diffusion, and Ostwald ripening were considered in this theory to describe CaCO3 product islands growing on the CaO surface. The macroscopic behavior of a gas–solid reaction can be calculated with the island size distribution. The carbonation reaction of CaO with CO2 including both early islands growth stage and later product layer diffusion stage was calculated with the developed theory and was validated with experimental data, and the relative importance of some elementary steps was discussed. This rate equation theory provides a link between the macroscopic behavior of a gas–solid reaction with the microscopic mechanisms from the molecular...

In Situ Determination of Interfacial Energies between Heterogeneously Nucleated CaCO3 and Quartz Substrates: Thermodynamics of CO2 Mineral Trapping

The precipitation of carbonate minerals--mineral trapping--is considered one of the safest sequestration mechanisms ensuring long-term geologic storage of CO(2). However, little is known about the thermodynamic factors controlling the extent of heterogeneous nucleation at mineral surfaces exposed to the fluids in porous reservoirs. The goal of this study is to determine the thermodynamic factors controlling heterogeneous nucleation of carbonate minerals on pristine quartz (100) surfaces, which are assumed representative of sandstone reservoirs. To probe CaCO(3) nucleation on quartz (100) in solution and with nanoscale resolution, an in situ grazing incidence small-angle X-ray scattering technique has been utilized. With this method, a value of α' = 36 ± 5 mJ/m(2) for the effective interfacial free energy governing heterogeneous nucleation of CaCO(3) has been obtained by measuring nucleation rates at different solution supersaturations. This value is lower than the interfacial energy governing calcite homogeneous nucleation (α ≈ 120 mJ/m(2)), suggesting that heterogeneous nucleation of calcium carbonate is favored on quartz (100) at ambient pressure and temperature conditions, with nucleation barriers between 2.5% and 15% lower than those expected for homogeneous nucleation. These observations yield important quantitative parameters readily usable in reactive transport models of nucleation at the reservoir scale.

CaCO3Mineralization under β-Sheet Forming Peptide Monolayers

In biominerals, proteins are key elements in the controlled nucleation and growth of the mineral phase. We report here on the coupled evolution of the organic and inorganic structures during the nucleation and growth of CaCO3 under a monolayer of acidic β-sheet forming peptides that mimic the natural proteins found in nacre. The investigation is carried out using in situ analytical techniques (X-ray diffraction and IR spectroscopy) to provide molecular scale structural information over the whole course of the mineralization process. Mineralization is shown to coexist with β-sheet order while inducing other conformational changes to the peptide assembly. Peptides promote the growth of unoriented vaterite crystals; no templating effect of the β-sheet order is observed.

Galvanic corrosion of Ni–Cu–Al composite coating and its anti-fouling property for metal pipeline in simulated geothermal water

A novel anti-fouling epoxy-silicone composite coating containing Ni–Cu–Al alloy powder for metal pipeline in geothermal water was fabricated based on the basic principles of galvanic corrosion. Fouling behaviors of the surface of composite coating in the simulated geothermal water were studied in comparison with stainless steel and epoxy-silicone resin coating. The results indicated that composite coating possessed a good anti-fouling performance. In the geothermal water, Ni2+, Cu2+ and Al3+ ions, originated from interface electrochemical corrosion, were released into bulk solution. These metal ions intensively inhibited nucleation and crystal growth rate of CaCO3 fouling on the surface of composite coating, and promoted precipitation of CaCO3 fouling in the bulk-solution, which could be easily washed away by flowing water. But for 304 stainless-steel and epoxy-silicone resin coating, CaCO3 fouling grew easily and adhered firmly to their surfaces, and influenced the transport efficiency of geothermal water for pipelines.

Structural evolution, formation pathways and energetic controls during template-directed nucleation of CaCO3

Through the process of biomineralization living organisms use macromolecules to direct nucleation and growth of nanophases of a variety of inorganic materials. Evidence shows this is a widespread strategy for controlling the timing, polymorphism, morphology, and crystallographic orientation of CaCO3 nuclei. In the past decade, self-assembled monolayers (SAMs) of alkanethiols have been used as a simple model to reproduce the controls of organic substrates. However, despite the importance of nucleation phenomena in the crystallization of inorganic materials our understanding of the reaction dynamics is extremely limited because, until recently, there was no experimental tool that possessed the spatial and temporal resolution needed to capture the formative events in the process. Issues such as the formation of amorphous precursors, and polymorph selection during the initial stages of nucleation, as well as the structural relationships and energetic controls of the inorganic matrix on the emerging nucleus have not been fully explored. To address these gaps in our understanding we have developed a suite of in situ methods and applied them, along with synchrotron-based X-ray spectroscopies, to CaCO3 nucleation. We used these methods to observe CaCO3 nucleation rates on alkanethiol SAMs. We found that for two carboxyl-terminated alkanethiol SAMs with odd (mercaptoundecanoic acid) and even (mercaptohexadecanoic acid) carbon chains, the effective interfacial energy is reduced from about 109 mJ m−2 in solution to 81 mJ m−2 and 72 mJ m−2, respectively, showing that templating is driven by a reduction in the thermodynamic barrier to nucleation. We also report in situ transmission electron microscopy (TEM) observations of crystal nucleation and growth in solution at the nanometre scale and video rates. This capability is enabled by the combination of a custom designed TEM stage and fluid cell. Significantly, the design of the cell and holder ensures temperature and electrochemical control over the reaction environment, allowing for direct investigation of nucleation. Our first results show that CaCO3 nucleates via nanoparticles of an apparent metastable precursor— most likely ACC—followed by consolidation and faceting. Finally, we report insights from the use of synchrotron-based near-edge X-ray absorption fine structure spectroscopy (NEXAFS) into the evolution of the SAM during the nucleation process. Based on measurements of SAM monomer orientation, we argue that the ability of the SAM to reorganize during the nucleation process is a key feature of an organic matrix that successfully directs mineralization.

Bio-inspired CaCO3 coating for superhydrophilic hybrid membranes with high water permeability

Surface hydrophilicity is a prerequisite of polymer membranes used for clean water regeneration, although commercial membranes are generally manufactured from hydrophobic polymers. Here, we report a promising approach to hydrophilize hydrophobic membranes using a CaCO3-based mineral coating inspired by biomineralization. Poly(acrylic acid) (PAA) brushes, which are negatively charged and can induce nucleation of CaCO3, were tethered on the pore surface of microporous polypropylene membranes (MPPMs) via photoinitiated graft polymerization. The CaCO3-based coating was then fabricated on the pore surface by an alternate soaking process. The resulting mineral coating is composed of CaCO3 nanoparticles which are much smaller than the pore diameter and distributed evenly on the pore surface throughout the membrane, ensuring the separation performance of membranes. Due to the intrinsic superhydrophilicity of CaCO3, the hybrid membranes are superhydrophilic, and show excellent water permeability with high water flux and ultralow operational pressure. As such, this work provides a generally applicable and cost-effective chemical route to improve the surface hydrophilicity of membranes or other porous materials which have potential in chemical separation, microfluidics, catalysis and other applications.