Precipitation Of Amorphous Calcium Carbonate Research Articles

Interaction and Stability of Nanobubbles and Prenucleation Calcium Clusters during Ultrasonic Treatment of Hard Water.

To investigate the stability of nanobubbles in natural hard water, a series of eight samples ranging in hardness from 0 to 332 mg/L CaCO3 were sonicated for periods of 5-45 min with an ultrasonic horn. Conductivity, temperature, ζ-potential, composition, and pH of the water were analyzed, together with the crystal structure of any calcium carbonate precipitate. Quasi-stable populations of bulk nanobubbles in Millipore and soft water are characterized by a ζ-potential of -35 to -20 mV, decaying over 60 h or more. After sonicating the hardest waters for about 10 min, they turn cloudy due to precipitation of amorphous calcium carbonate when the water temperature reaches 40 °C; the ζ-potential then jumps from -10 to +20 mV and remains positive for several days. From an analysis of the change of conductivity of the hard water before and after sonication, it is estimated that 37 ± 5% of calcium was not originally in solution but existed in nanoscale prenucleation clusters, which decorate the nanobubbles formed in the early stages of sonication. Heating and charge screening in the nanobubble colloid cause the decorated bubbles to collapse or disperse, leaving an amorphous precursor of aragonite. Sonicating the soft supernatant increases its conductivity and pH and restores the negative ζ-potential associated with bulk nanobubbles, but there is no further precipitation. Our study of the correlation between nanobubble production and calcium agglomeration spanning the hardness and composition ranges of natural waters shows that the sonication method for introducing nanobubbles is viable only for hard water if it is kept cold; the stability of the nanobubble colloid will be reduced in any case by the presence of dissolved calcium and magnesium.

Carbonate diagenesis: A celebration of the work of John Anthony Dawson (Tony) Dickson

Carbonate diagenesis: A celebration of the work of John Anthony Dawson (Tony) Dickson

Protection of Historical Mortars through Treatment with Suspensions of Nanoparticles

Mortars, which are very important elements for the integrity of historic monuments, consist mainly of calcium carbonate and silicates in different proportions. Chemical dissolution due to exposure in open air is very important for the degradation of mortars. Inorganic nanoparticles with chemical and crystallographic affinity with mortar components are expected to be effective structure stabilizers and agents offering resistance to chemical dissolution. In the present work, we have developed and applied suspensions of amorphous calcium carbonate (ACC), silicon oxide (am-SiO2) and composite nanoparticles by the precipitation of ACC on am-SiO2 and vice versa. The application of suspensions of the synthesized nanoparticles on three different historical mortars of Roman times (1st century AD), retarded their dissolution rate in solutions undersaturated with respect to calcite, in acid pH (6.50, 25 °C). All three test historic mortars, treated with suspensions of the nanoparticles prepared, showed high resistance towards dissolution at pH 6.50. The ability of the nanoparticles’ suspension to consolidate the damaged mortar was the key factor in deciding the corresponding effectiveness in the retardation of the rate of dissolution. The combination of ACC with am-SiO2 nanoparticles showed high efficiency for protection from the dissolution of calcite rich mortars.

Small‐Molecular‐Weight Additives Modulate Calcification by Interacting with Prenucleation Clusters on the Molecular Level**

AbstractSmall‐molecular‐weight (MW) additives can strongly impact amorphous calcium carbonate (ACC), playing an elusive role in biogenic, geologic, and industrial calcification. Here, we present molecular mechanisms by which these additives regulate stability and composition of both CaCO3 solutions and solid ACC. Potent antiscalants inhibit ACC precipitation by interacting with prenucleation clusters (PNCs); they specifically trigger and integrate into PNCs or feed PNC growth actively. Only PNC‐interacting additives are traceable in ACC, considerably stabilizing it against crystallization. The selective incorporation of potent additives in PNCs is a reliable chemical label that provides conclusive chemical evidence that ACC is a molecular PNC‐derived precipitate. Our results reveal additive‐cluster interactions beyond established mechanistic conceptions. They reassess the role of small‐MW molecules in crystallization and biomineralization while breaking grounds for new sustainable antiscalants.

Microbial EPS‐mediated amorphous calcium carbonate–monohydrocalcite–calcite transformations during early tufa deposition

AbstractThe Holocene Wolfenden tufa deposit in south‐eastern British Columbia, western Canada, preserves a unique record of the earliest stages of calcium carbonate deposition resulting from microbial extracellular polymeric substances‐mediated precipitation of amorphous calcium carbonate (ACC) with partial transformation to monohydrocalcite (MHC) and subsequently to nanocrystalline calcite. This is the first documentation of tufa mineralogy involving ACC transformation to MHC. Progressive dehydration triggered ACC–MHC–nanocrystalline calcite transformations on bryophytes, algae and cyanobacteria sheaths. The adsorption of extracellular polymeric substances matrix molecules into the ACC and ACC–MHC structures preserved polymorph mineralogy of incomplete transformation. Unusual concentrations of biofilm extracellular polymeric substances filaments provided nucleation sites for the ACC precipitation. The ACC nucleation calcified extracellular polymeric substances filaments and resulted in partially coalesced arrays of nanoscale ACC spheroids. Mesocrystalline structures of MHC reconfigured the concentric growth layers of ACC precipitate with bulbous ACC–MHC protuberances. Nanocrystalline rhombic faces of calcite developed within and on the surfaces of the ACC–MHC protuberances. Dehydration of these concentric growth layers of ACC–MHC resulted in the transformation into nanocrystalline calcite with substrates coalesced into micrite fabrics. Recrystallisation obliterated evidence of the calcified extracellular polymeric substances filaments and resulted in microcrystalline calcite spar domains as the widespread encrustation fabric. Localised magnesium adsorption during nucleation of the ACC within the biofilms resulted in needle calcite crystals without the precursor ACC–MHC transformation process. Microbial extracellular polymeric substances‐mediated precipitation of ACC as a necessarily critical step in the earliest phase of the tufa deposition process, leading to the nucleation of calcite has been underappreciated and generally not considered. These earliest stages of calcium carbonate precipitation are proposed as a possible template for other tufa deposits, where the evidence of microbial extracellular polymeric substances‐mediated precipitation of ACC with transformation to MHC and subsequently to nanocrystalline calcite has been obscured by recrystallisation into micrite and spar fabrics.

The Impact of Ambient Atmospheric Mineral-Dust Particles on the Calcification of Lungs

For the first time, it is shown that inhaled ambient air-dust particles settled in the human lower respiratory tract induce lung calcification. Chemical and mineral compositions of pulmonary calcium precipitates in the lung right lower-lobe (RLL) tissues of 12 individuals who lived in the Upper Silesia conurbation in Poland and who had died from causes not related to a lung disorder were determined by transmission and scanning electron microscopy. Whereas calcium salts in lungs are usually reported as phosphates, calcium salts precipitated in the studied RLL tissue were almost exclusively carbonates, specifically Mg-calcite and calcite. These constituted 37% of the 1652 mineral particles examined. Mg-calcite predominated in the submicrometer size range, with a MgCO3 content up to 50 mol %. Magnesium plays a significant role in lung mineralization, a fact so far overlooked. The calcium phosphate (hydroxyapatite) content in the studied RLL tissue was negligible. The predominance of carbonates is explained by the increased CO2 fugacity in the RLL. Carbonates enveloped inhaled mineral-dust particles, including uranium-bearing oxides, quartz, aluminosilicates, and metal sulfides. Three possible pathways for the carbonates precipitation on the dust particles are postulated: (1) precipitation of amorphous calcium carbonate (ACC), followed by its transformation to calcite; (2) precipitation of Mg-ACC, followed by its transformation to Mg-calcite; (3) precipitation of Mg-free ACC, causing a localized relative enrichment in Mg ions and subsequent heterogeneous nucleation and crystal growth of Mg-calcite. The actual number of inhaled dust particles may be significantly greater than was observed because of the masking effect of the carbonate coatings. There is no simple correlation between smoking habit and lung calcification.

Cellular bicarbonate accumulation and vesicular proton transport promote calcification in the sea urchin larva.

The sea urchin embryo develops a calcitic endoskeleton through intracellular formation of amorphous calcium carbonate (ACC). Intracellular precipitation of ACC, requires [Formula: see text] concentrating as well as proton export mechanisms to promote calcification. These processes are of fundamental importance in biological mineralization, but remain largely unexplored. Here, we demonstrate that the calcifying primary mesenchyme cells (PMCs) use Na+/H+-exchange (NHE) mechanisms to control cellular pH homeostasis during maintenance of the skeleton. During skeleton re-calcification, pHi of PMCs is increased accompanied by substantial elevation in intracellular [Formula: see text] mediated by the [Formula: see text] cotransporter Sp_Slc4a10. However, PMCs lower their pHi regulatory capacities associated with a reduction in NHE activity. Live-cell imaging using green fluorescent protein reporter constructs in combination with intravesicular pH measurements demonstrated alkaline and acidic populations of vesicles in PMCs and extensive trafficking of large V-type H+-ATPase (VHA)-rich acidic vesicles in blastocoelar filopodial cells. Pharmacological and gene expression analyses underline a central role of the VHA isoforms Sp_ATP6V0a1, Sp_ATP6V01_1 and Sp_ATPa1-4 for the process of skeleton re-calcification. These results highlight novel pH regulatory strategies in calcifying cells of a marine species with important implications for our understanding of the mineralization process in times of rapid changes in oceanic pH.

Effect of relative humidity on the carbonation rate of portlandite, calcium silicate hydrates and ettringite

The carbonation of portlandite, calcium silicate hydrate (C-S-H), and ettringite was investigated at 57% RH and 91% RH using X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, and the phenolphthalein spray test. The experiments show that the carbonation of portlandite, ettringite, and C-S-H with Ca/Si = 0.7 is significantly faster at 91% RH than at 57% RH. Little effect of RH is observed for C-S-H with higher Ca/Si. Portlandite and C-S-H with Ca/Si = 0.7 carbonate only partially at 57% RH; complete carbonation is observed if the relative humidity is increased to 91% RH. In contrast, the carbonation of C-S-H with Ca/Si = 1.2 and 1.5 is complete at both relative humidities. The carbonation rate of C-S-H decreases with decreasing Ca/Si ratio, both at 57% and 91%RH. Carbonation at 57% RH promotes the formation of vaterite and aragonite over calcite; the precipitation of amorphous calcium carbonate is observed for C-S-H with Ca/Si = 0.7.

Co-incorporation of alkali metal ions during amorphous calcium carbonate precipitation and their stabilizing effect

Calcium carbonate formation has been studied extensively due to its central role in biomineralization and geochemistry. Specifically, the effect of additives incorporated during the formation process has been described in several works related to inorganic, small organic, molecular or macromolecular additives. However, in these previous experiments the presence of counter ions and their possible role has been mostly disregarded. Co-incorporation of counter ions into calcite at low supersaturations has been studied in detail but their incorporation in and effect on the formation and stability of the amorphous phase, which precedes the formation of the crystalline phase at high supersaturations, has not been studied. To address this, we have investigated the incorporation of alkali metal ions into the amorphous phase using various carbonate salts as a carbonate source. We show that the incorporation is the highest for Rb+ with the highest measured value being 5.8 at% Rb+/(Rb+ + Ca2+). The extent of ion incorporation follows the ion size of Rb+ > K+ > Na+ > Li+ which is opposite to that observed in calcite formed at low supersaturation. The presence of these ions in the amorphous phase increases the crystallization temperature, which can be shifted by as much as 200 °C depending on the concentration of alkali metal ions incorporated. However, the lifetime of ACC in solution was similar for all the different carbonate sources.

Crystallization kinetics of amorphous calcium carbonate in confinement.

Phase transformations of carbonates are relevant to a wide range of biological, environmental, and industrial processes. Over the past decade, it emerged that crystallization pathways in these systems can be quite complex. Metastable intermediates such as amorphous calcium carbonate (ACC) were found to greatly impact composition, structure, and properties of more stable phases. However, it has been challenging to create predictive models. Rapid transformation of ACC in bulk has been one obstacle in the determination of nucleation rates. Herein, it is reported that confinement in microfluidic droplets allows separating in time the precipitation of ACC and subsequent nucleation and growth of crystalline CaCO3. An upper limit of 1.2 cm-3 s-1 was determined for the steady-state crystal nucleation rate in the presence of ACC at ambient conditions. This rate has implications for the formation of calcium carbonate in biomineralization, bio-inspired syntheses, and carbon sequestration.

Dynamics of calcium carbonate formation: Geochemical modeling of a two-step mechanism

A new kinetic model was developed based on a transition-state-theory (TST)/surface-complexation-model (SCM) coupling. It aims to describe the successive precipitation of amorphous calcium carbonate (ACC) and calcite, taking account of their mutual influence: ACC precipitates according to the standard TST and creates surface complexation sites from which calcite can form and create new surface complexation sites. When the kinetics of calcite precipitation are fast enough, the consumption of dissolved matter leads to the re-dissolution of ACC. This model is first compared to batch experiments (Gebauer et al., 2008) and then applied with a reactive transport calculation code to a dynamic experiment carried out on a microfluidic device composed of a single straight channel (Beuvier et al., 2015). The results show a good match between experiments and reactive transport modeling. This suggests that the combination of simple experimental microfluidic devices and reactive transport modeling could be a promising integrated methodology to study the dynamics of geochemical reactivity at the pore scale, as a first step before application to more complex and larger systems.

A comparison of amorphous calcium carbonate crystallization in aqueous solutions of MgCl2 and MgSO4: implications for paleo-ocean chemistry

Based on the terminology of “aragonite seas” and “calcite seas”, whether different Mg sources could affect the mineralogy of carbonate sediments at the same Mg/Ca ratio was explored, which was expected to provide a qualitative assessment of the chemistry of the paleo-ocean. In this work, amorphous calcium carbonate (ACC) was prepared by direct precipitation in anhydrous ethanol and used as a precursor to study crystallization processes in MgSO4 and MgCl2 solutions having different concentrations at 60 °C (reaction times 240 and 2880 min). Based on the morphology of the aragonite crystals, as well as mineral saturation indices and kinetic analysis of geochemical processes, it was found that these crystals formed with a spherulitic texture in 4 steps. First, ACC crystallized into columnar Mg calcite by nearly oriented attachment. Second, the Mg calcite changed from columnar shapes into smooth dumbbell forms. Third, the Mg calcite transformed into rough dumbbell or cauliflower-shaped aragonite forms by local dissolution and precipitation. Finally, the aragonite transformed further into spherulitic radial and irregular aggregate forms. The increase in Ca2+ in the MgSO4 solutions compared with the MgCl2 solutions indicates the fast dissolution and slow precipitation of ACC in the former solutions. The phase transition was more complete in the 0.005 M MgCl2 solution, whereas Mg calcite crystallized from the 0.005 M MgSO4 solution, indicating that Mg calcite could be formed more easily in an MgSO4 solution. Based on these findings, aragonite and Mg calcite relative to ACC could be used to provide a qualitative assessment of the chemistry of the paleo-ocean. Therefore, calcite seas relative to high-Mg calcite could reflect a low concentration MgSO4 paleo-ocean, while aragonite seas could be related to an MgCl2 or high concentration of MgSO4 paleo-ocean.

Thermodynamic-Kinetic Precipitation Modeling. A Case Study: The Amorphous Calcium Carbonate (ACC) Precipitation Pathway Unravelled

Nine accurate experimental data sets on amorphous calcium carbonate (ACC) formation in dilute solution were collected varying temperature and pH. The entire precipitation process is described using a complete thermodynamic-kinetic model. The thermodynamic model includes two new complex chemical interactions whereas the kinetic model is based on the discretized population balance approach. Saturation, primary particles size distribution, average secondary particles size, nucleation, and growth rates, as well as a number of additional parameters on the ACC precipitation reaction, are reported. The excellent agreement among experiments, calculated results, and literature data demonstrates that a complete thermodynamic-kinetic model can significantly contribute toward the understanding of a plausible pathway for precipitating systems. In this case study, the classical nucleation theory, which includes homogeneous nucleation, “true” secondary nucleation, and diffusion limited growth events, is able to completely describe the entire precipitation process. The calculated surface (γ) and cohesion (β) energies range from 28 to 35 and 30 to 42 mJ m–2, respectively, as a function of pH and temperature. Clusters or prenucleation entities act as spectators and are not directly involved in the solid formation pathway. The general methodological approach presented can be readily applied to other solid phase formation processes.

H+/K+ ATPase activity is required for biomineralization in sea urchin embryos

The bioelectrical signatures associated with regeneration, wound healing, development, and cancer are changes in the polarization state of the cell that persist over long durations, and are mediated by ion channel activity. To identify physiologically relevant bioelectrical changes that occur during normal development of the sea urchin Lytechinus variegatus, we tested a range of ion channel inhibitors, and thereby identified SCH28080, a chemical inhibitor of the H+/K+ ATPase (HKA), as an inhibitor of skeletogenesis. In sea urchin embryos, the primary mesodermal lineage, the PMCs, produce biomineral in response to signals from the ectoderm. However, in SCH28080-treated embryos, aside from randomization of the left-right axis, the ectoderm is normally specified and differentiated, indicating that the block to skeletogenesis observed in SCH28080-treated embryos is PMC-specific. HKA inhibition did not interfere with PMC specification, and was sufficient to block continuing biomineralization when embryos were treated with SCH28080 after the initiation of skeletogenesis, indicating that HKA activity is continuously required during biomineralization. Ion concentrations and voltage potential were abnormal in the PMCs in SCH28080-treated embryos, suggesting that these bioelectrical abnormalities prevent biomineralization. Our results indicate that this effect is due to the inhibition of amorphous calcium carbonate precipitation within PMC vesicles.

Correction: Amorphous Calcium Carbonate Precipitation by Cellular Biomineralization in Mantle Cell Cultures of Pinctada fucata

Correction: Amorphous Calcium Carbonate Precipitation by Cellular Biomineralization in Mantle Cell Cultures of Pinctada fucata

Amorphous calcium carbonate precipitation by cellular biomineralization in mantle cell cultures of Pinctada fucata.

The growth of molluscan shell crystals is generally thought to be initiated from the extrapallial fluid by matrix proteins, however, the cellular mechanisms of shell formation pathway remain unknown. Here, we first report amorphous calcium carbonate (ACC) precipitation by cellular biomineralization in primary mantle cell cultures of Pinctada fucata. Through real-time PCR and western blot analyses, we demonstrate that mantle cells retain the ability to synthesize and secrete ACCBP, Pif80 and nacrein in vitro. In addition, the cells also maintained high levels of alkaline phosphatase and carbonic anhydrase activity, enzymes responsible for shell formation. On the basis of polarized light microscopy and scanning electron microscopy, we observed intracellular crystals production by mantle cells in vitro. Fourier transform infrared spectroscopy and X-ray diffraction analyses revealed the crystals to be ACC, and de novo biomineralization was confirmed by following the incorporation of Sr into calcium carbonate. Our results demonstrate the ability of mantle cells to perform fundamental biomineralization processes via amorphous calcium carbonate, and these cells may be directly involved in pearl oyster shell formation.

Phase and morphology evolution of calcium carbonate precipitated by carbonation of hydrated lime

Phase and morphology evolution of CaCO3 precipitated during carbonation of lime pastes via the reaction Ca(OH)2 + CO2 → CaCO3 + H2O has been investigated under different conditions (pCO2 ≈ 10−3.5 atm at 60 % RH and 93 % RH; pCO2 = 1 atm at 93 % RH) using XRD, FTIR, TGA, and SEM. Simulations of the pore solution chemistry for different stages and conditions of carbonation were performed using the PHREEQC code to investigate the evolution of the chemistry of the system. Results indicate initial precipitation of amorphous calcium carbonate (ACC) which in turn transforms into scalenohedral calcite under excess Ca2+ ions. Because of their polar character, $$ \left\{ {21\bar{3}4} \right\} $$ scalenohedral faces (type S) interact more strongly with excess Ca2+ than non-polar $$ \left\{ {10\bar{1}4} \right\} $$ rhombohedral faces (type F), an effect that ultimately favors the stabilization of $$ \left\{ {21\bar{3}4} \right\} $$ faces. Following the full consumption of Ca2+ ions and further dissolution of CO2 leading to a pH drop of the pore solution, $$ \left\{ {21\bar{3}4} \right\} $$ scalenohedra are subjected to dissolution. This eventually results in re-precipitation of $$ \left\{ {10\bar{1}4} \right\} $$ rhombohedra at close-to-neutral pH. This crystallization sequence progresses through the carbonated depth with a strong dependence on the degree of exposure to CO2, which is controlled by the carbonated pore structure governing the diffusion of CO2. Both the carbonation process and the scalenohedral-to-rhombohedral transformation are kinetically favored under high RH and high pCO2. Supersaturation plays a critical role on the nucleation density and size of CaCO3 crystals. These results have important implications in understanding the behavior of ancient and modern lime mortars for applications in architectural heritage conservation.

In Situ Study of the Precipitation and Crystallization of Amorphous Calcium Carbonate (ACC)

The precipitation and crystallization of amorphous calcium carbonate (ACC) from metastable calcium carbonate solutions in the concentration range 2–10 mM have been investigated in situ in solution in the absence of additives, and in the presence of Mg2+ and poly(acrylic acid). We demonstrate that measurement of the intensity of transmitted light provides an effective method for monitoring the early stages of precipitation of calcium carbonate in solution, where the nature of the scattering particles was confirmed with transmission electron microscopy. The recorded changes in light transmission with time and concentration can be related to the precipitation and aggregation of ACC, its subsequent crystallization to calcite (or vaterite), and the gravitational sedimentation of the growing crystals. Addition of Mg2+ or poly(acrylic acid) is shown to retard the process, delaying the precipitation of ACC and increasing the lifetime of this phase. These results show that measurement of turbidity provides an effe...

Precipitation of ACC in liposomes—a model for biomineralization in confined volumes

Biomineralizing organisms frequently precipitate minerals in small phospholipid bilayer-delineated compartments. We have established an in vitro model system to investigate the effect of confinement in attoliter to femtoliter volumes on the precipitation of calcium carbonate. In particular, we analyze the growth and stabilization of liposome-encapsulated amorphous calcium carbonate (ACC) nanoparticles using a combination of in situ techniques, cryo-transmission electron microscopy (Cryo-TEM), and small angle X-ray scattering (SAXS). Herein, we discuss ACC nanoparticle growth rate as a function of liposome size, carbon dioxide flux across the liposome membrane, pH, and osmotic pressure. Based on these experiments, we argue that the stabilization of ACC nanoparticles in liposomes is a consequence of a low nucleation rate (high activation barrier) of crystalline polymorphs of calcium carbonate.

Revisiting geochemical controls on patterns of carbonate deposition through the lens of multiple pathways to mineralization

The carbonate sedimentary record contains diverse compositions and textures that reflect the evolution of oceans and atmospheres through geological time. Efforts to reconstruct paleoenvironmental conditions from these deposits continue to be hindered by the need for process-based models that can explain observed shifts in carbonate chemistry and form. Traditional interpretations assume minerals precipitate and grow by classical ion-by-ion addition processes but are unable to reconcile a number of unusual features contained in Proterozoic carbonates. The realization that diverse organisms produce high Mg carbonate skeletal structures by non-classical pathways involving amorphous intermediates raises the question of whether similar processes are also active in sedimentary environments. This study examines the hypothesis that non-classical pathways to mineralization are the physical basis for some of the carbonate morphologies and compositions observed in natural and laboratory settings. We designed experiments with a series of different solution Mg : Ca ratios and saturation environments to investigate the effects on carbonate phase, Mg content, and morphology. Our observations of diverse carbonate mineral compositions and textures suggest geochemical conditions bias the mineralization pathway by a systematic relationship to Mg : Ca ratio and the abundance of carbonate ions. Environments with low Mg levels produce calcite crystallites with 0–12 mol% MgCO3. In contrast, the combination of high initial Mg : Ca and rapidly increasing saturation opens a non-classical pathway that begins with extensive precipitation of an amorphous calcium carbonate (ACC). This phase slowly transforms to aggregates of very high Mg calcite nanoparticles whose structures and compositions are similar to natural disordered dolomites. The non-classical pathways are favored when the local environment contains sufficient Mg to inhibit calcite growth through increased solubility—a thermodynamic factor, and achieves saturation with respect to ACC on a timescale that is shorter than the rate of aragonite nucleation—a kinetic factor. Aragonite is produced when Mg levels are high but saturation is insufficient for ACC precipitation. The findings provide a physical basis for anecdotal claims that the interplay of kinetic and thermodynamic factors underlies patterns of carbonate precipitation and suggest the need to expand traditional interpretations of geological carbonate formation to include non-classical pathways to mineralization.