Carbonate Polymorphs Research Articles

Improvement of microstructure of cementitious composites by microbially-induced calcite precipitation.

In this study, microstructural improvement of cementitious composites was achieved by bacterial CaCO3 precipitation using three bacterial species, namely Sporosarcina pasteurii, Bacillus cereus, and Actinobacteria sp. M135-3, respectively. The final product was comparatively investigated regarding the physical effects of urease activity of different cells on the mortar in the long term.Microstructural improvement was determined by evaluating the pore structure by determining the increase in strength, decrease in water absorption, and capillary water absorption rate of the cement mortars having different microorganism concentrations (106-109 bacteria/ml). These measurements were taken on bacteria-containing and control samples on the 2nd, 7th, 28th, and 56th days, respectively. In addition, calcite and vaterite as calcium carbonate polymorphs formed by the precipitation of calcium carbonate by three types of bacteria were identified by Scanning electron microscopy and energy dispersive X-ray spectroscopy(SEM/EDS), X-ray diffraction (XRD)and Thermogravimetric analysis - Differential scanning calorimetry (TGA-DSC) analyzes.The bacteria-containing mortar samples showed that bacterial species and concentrations directly affect cementitious composites' mechanical and physical properties. Composite samples containing bacteria resulted in statistically significant microstructural improvements measured by higher mechanical strength, lower water absorption value, and capillary water absorption rate compared to control samples, especially at early ages. However, the effect of microbial calcite formation diminishes at later ages, especially at 56-days, attributed to the bacteria cells losing their vitality and integrity and forming spaces inside the mortars.

The Influence of Acidic Oxygen Containing Groups Located on the Surface of Graphene Oxide (GO) on the Carbonation of Tricalcium Silicate (C3S) Based on Boehm's‐Theorem

AbstractIn various cementitious materials, the carbonation of tricalcium silicate (C3S) by the acidic oxygen‐containing groups located on the surface of graphene oxide (GO) can support cutting down the CO2 emissions, in addition to the formation of different crystalline CaCO3. The current work investigates the direct chemical reaction of dry‐C3S with 0.4 % GO solution and the mechanism of CH and CSH carbonation depending on the concept of Boehme's‐theorem. FTIR‐spectroscopy has been utilized to demonstrate and identify the effective transitions in the formulation of portlandite (Ca(OH)2), calcium‐silicate‐hydrate (CaO ⋅ SiO2 ⋅ H2O), and calcium carbonate (CaCO3) polymorphs during the reaction. This paper clarifies the relationship between XRD peak intensity and morphologies of CaCO3 crystals resulting from using various weights of dry‐C3S. Thus, the XRD peak intensity of CaCO3 varies according to their morphologies. XRD‐Rietveld Refinement has examined the quantity percentages of the crystalline phases. The differences in the dissociation temperature (TGA) illustrate the possible variation in the structure and properties of CaCO3 crystals formed during the carbonation of CH and CSH. SEM with different magnifications was selected to observe the prevalent morphology of vaterite, aragonite, and calcite crystalline phases during the transformation process.

Effect of acidic microbial polysaccharides on calcium carbonate polymorph formation in hot water at 40-80 °C

Microbial organic molecules are widely involved in the formation of calcium carbonate (CaCO3) minerals in various environments on the earth’s surface including hot springs. To evaluate the effect of acidic microbial polysaccharides on the CaCO3 polymorph formation in hot water environments, batch experiments on the CaCO3 formation were performed in the systems containing alginic acid (A system) or gellan gum (G system) at 40, 60, and 80 oC for 24 h. Each system contained 5.0 mmol/L Ca2+ and 20.0 mmol/L HCO3- ions with 0.0, 1.0, 5.0, 10, 50, and 100 mg/L alginic acid or gellan gum. Results showed that needle- or rod-like shaped aragonite crystals were formed as the predominant polymorph in the absence of polysaccharides at 40 - 80 oC. In the presence of polysaccharides, alginic acid greatly inhibited the aragonite formation and favored the rhombohedral calcite formation as the predominant polymorph with increasing alginic acid concentration at 40 oC. The effect of alginic acid on the polymorphs slightly decreased as temperature increased but was maintained up to 80 oC. Gellan gum also exhibited a similar effect to a lesser extent than alginic acid at the same concentrations and temperatures. Thus, acidic microbial polysaccharides exhibited significant inhibitory effect on the aragonite formation and favored the calcite formation depending on their molecular structures in hot water environments. This effect of polysaccharides on the CaCO3 polymorphs is attributed to the high adsorption affinity of the polymer molecules for the aragonite surface.

Polyamines Promote Aragonite Nucleation and Generate Biomimetic Structures.

Calcium carbonate biomineralization is remarkable for the ability of organisms to produce calcite or aragonite with perfect fidelity, where this is commonly attributed to specific anionic biomacromolecules. However, it is proven difficult to mimic this behavior using synthetic or biogenic anionic organic molecules. Here, it is shown that cationic polyamines ranging from small molecules to large polyelectrolytes can exert exceptional control over calcium carbonate polymorph, promoting aragonite nucleation at extremely low concentrations but suppressing its growth at high concentrations, such that calcite or vaterite form. The aragonite crystals form via particle assembly, giving nanoparticulate structures analogous to biogenic aragonite, and subsequent growth yields stacked aragonite platelets comparable to structures seen in developing nacre. This mechanism of polymorph selectivity is captured in a theoretical model based on these competing nucleation and growth effects and is completely distinct from the activity of magnesium ions, which generate aragonite by inhibiting calcite. Profiting from these contrasting mechanisms, it is then demonstrated that polyamines and magnesium ions can be combined to give unprecedented control over aragonite formation. These results give insight into calcite/aragonite polymorphism and raise the possibility that organisms may exploit both amine-rich organic molecules and magnesium ions in controlling calcium carbonate polymorph.

Calcitic shells in the aragonite sea of the earliest Cambrian

Abstract The initial acquisition of calcium carbonate polymorphs (aragonite and calcite) at the onset of skeletal biomineralization by disparate metazoans across the Ediacaran-Cambrian transition is thought to be directly influenced by Earth's seawater chemistry. It has been presumed that animal clades that first acquired mineralized skeletons during the so-called “aragonite sea” of the latest Ediacaran and earliest Cambrian (Terreneuvian) possessed aragonite or high-Mg calcite skeletons, while clades that arose in the subsequent “calcite sea” of Cambrian Series 2 acquired low-Mg calcite skeletons. Here, contrary to previous expectations, we document shells of one of the earliest helcionelloid molluscs from the basal Cambrian of southwestern Mongolia that are composed entirely of low-Mg calcite and formed during the Terreneuvian aragonite sea. The extraordinarily well-preserved Postacanthella shells have a simple prismatic microstructure identical to that of their modern low-Mg calcite molluscan relatives. High-resolution scanning electron microscope observations show that calcitic crystallites were originally encased within an intra- and interprismatic organic matrix scaffold preserved by aggregates of apatite during early diagenesis. This indicates that not all molluscan taxa during the early Cambrian produced aragonitic shells, weakening the direct link between carbonate skeletal mineralogy and ambient seawater chemistry during the early evolution of the phylum. Rather, our study suggests that skeletal mineralogy in Postacanthella was biologically controlled, possibly exerted by the associated prismatic organic matrix. The presence of calcite or aragonite mineralogy in different early Cambrian molluscan taxa indicates that the construction of calcium carbonate polymorphs at the time when skeletons first emerged may have been species dependent.

Meta-analysis of vaterite secondary data revealed the synthesis conditions for polymorphic control

The synthesis of vaterite was investigated from a statistical point of view to identify sets of optimal experimental conditions to obtain pure anhydrous calcium carbonate polymorph. Relevant research papers in the field of the precipitation of calcium carbonate were compiled in a secondary dataset using a statistical mixed method described in another of our publications. This statistical mixed method consisted of three distinctive stages: a systematic literature review (Stage 1), followed by a meta-analysis of the acquired secondary data (Stage 2) and the validation in the laboratory (Stage 3).In this work we present the results of Stages 2 and 3 of the mentioned method. A decision tree was built with the vaterite dataset and obtained good classification performance. A number of if-then decision rules were created covering the occurrence and absence of vaterite. The oven drying temperature, the pH and the concentration of the salt were used to control polymorphism. The best result corresponded to a vaterite polymorphic abundance of 93.6 ± 0.3 %. It was possible to carry out a different investigation and arrive at new insights as a result of the unique size and characteristics of the mined data from Web of Science scientific articles.

Targeted Crystallization of Rare Earth Carbonate Polymorphs at Hydrothermal Conditions via Mineral Replacement Reactions.

The interaction between rare earth element (REE)-rich (La, Pr, Nd, Dy) aqueous solutions, dolomite (CaMg(CO3)2), and aragonite (CaCO3) at low temperature hydrothermal conditions (25-220°C) is studied. The experiments result in the solvent-mediated surface precipitation and subsequent pseudomorphic mineral replacement of the dolomite and aragonite seeds by newly formed REE-carbonates. The host grains are replaced from periphery inward. The newly formed REE-bearing carbonates in La-, Pr-, and Nd-doped systems follow the crystallization sequence: lanthanite [REE2(CO3)3·8H2O] → kozoite [orthorhombic REECO3(OH)] → hydroxylbastnasite [hexagonal REECO3(OH)]. The interaction of Dy-bearing solutions with dolomite results only in the crystallization of kozoite [orthorhombic DyCO3(OH)]. However, experiments with aragonite reveal a two-step crystallization pathway: tengerite [Dy2(CO3)3·2-3(H2O)] → kozoite [orthorhombic DyCO3(OH)]. The temperature, the dissolution rate of the host mineral, and the ionic radii of the REE3+ in question are found to control the kinetics of the replacement reaction, the polymorph selection, and the crystallization pathways toward bastnasite. The findings allow to gain a more in-depth understanding of the formation REE-bearing carbonates, particularly the mineral bastnasite, which is the main source of REEs for industry. This knowledge can be used to improve REE separation, exploration, exploitation methods, as well to produce carbonate minerals with tailored structures.

Activation of Neutrophils by Mucin–Vaterite Microparticles

Nano- and microparticles enter the body through the respiratory airways and the digestive system, or form as biominerals in the gall bladder, salivary glands, urinary bladder, kidney, or diabetic pancreas. Calcium, magnesium, and phosphate ions can precipitate from biological fluids in the presence of mucin as hybrid nanoparticles. Calcium carbonate nanocrystallites also trap mucin and are assembled into hybrid microparticles. Both mucin and calcium carbonate polymorphs (calcite, aragonite, and vaterite) are known to be components of such biominerals as gallstones which provoke inflammatory reactions. Our study was aimed at evaluation of neutrophil activation by hybrid vaterite–mucin microparticles (CCM). Vaterite microparticles (CC) and CCM were prepared under standard conditions. The diameter of CC and CCM was 3.3 ± 0.8 µm and 5.8 ± 0.7 µm, with ƺ-potentials of −1 ± 1 mV and −7 ± 1 mV, respectively. CC microparticles injured less than 2% of erythrocytes in 2 h at 1.5 mg mL−1, and no hemolysis was detected with CCM; this let us exclude direct damage of cellular membranes by microparticles. Activation of neutrophils was analyzed by luminol- and lucigenin-dependent chemiluminescence (Lum-CL and Luc-CL), by cytokine gene expression (IL-6, IL-8, IL-10) and release (IL-1β, IL-6, IL-8, IL-10, TNF-α), and by light microscopy of stained smears. There was a 10-fold and higher increase in the amplitude of Lum-CL and Luc-CL after stimulation of neutrophils with CCM relative to CC. Adsorption of mucin onto prefabricated CC microparticles also contributed to activation of neutrophil CL, unlike mucin adsorption onto yeast cell walls (zymosan); adsorbed mucin partially suppressed zymosan-stimulated production of oxidants by neutrophils. Preliminary treatment of CCM with 0.1–10 mM NaOCl decreased subsequent activation of Lum-CL and Luc-CL of neutrophils depending on the used NaOCl concentration, presumably because of the surface mucin oxidation. Based on the results of ELISA, incubation of neutrophils with CCM downregulated IL-6 production but upregulated that of IL-8. IL-6 and IL-8 gene expression in neutrophils was not affected by CC or CCM according to RT2-PCR data, which means that post-translational regulation was involved. Light microscopy revealed adhesion of CC and CCM microparticles onto the neutrophils; CCM increased neutrophil aggregation with a tendency to form neutrophil extracellular traps (NETs). We came to the conclusion that the main features of neutrophil reaction to mucin–vaterite hybrid microparticles are increased oxidant production, cell aggregation, and NET-like structure formation, but without significant cytokine release (except for IL-8). This effect of mucin is not anion-specific since particles of powdered kidney stone (mainly calcium oxalate) in the present study or calcium phosphate nanowires in our previous report also activated Lum-CL and Luc-CL response of neutrophils after mucin sorption.

Exploring the secondary mineral products generated by microbial iron respiration in Archean ocean simulations.

Marine chemical sedimentary deposits known as Banded Iron Formations (BIFs) archive Archean ocean chemistry and, potentially, signs of ancient microbial life. BIFs contain a diversity of iron- and silica-rich minerals in disequilibrium, and thus many interpretations of these phases suggest they formed secondarily during early diagenetic processes. One such hypothesis posits that the early diagenetic microbial respiration of primary iron(III) oxides in BIFs resulted in the formation of other iron phases, including the iron-rich silicates, carbonates, and magnetite common in BIF assemblages. Here, we simulated this proposed pathway in laboratory incubations combining a model dissimilatory iron-reducing (DIR) bacterium, Shewanella putrefaciens CN32, and the ferric oxyhydroxide mineral ferrihydrite under conditions mimicking the predicted Archean seawater geochemistry. We assessed the impact of dissolved silica, calcium, and magnesium on the bioreduced precipitates. After harvesting the solid products from these experiments, we analyzed the reduced mineral phases using Raman spectroscopy, electron microscopy, powder x-ray diffraction, and spectrophotometric techniques to identify mineral precipitates and track the bulk distributions of Fe(II) and Fe(III). These techniques detected a diverse range of calcium carbonate morphologies and polymorphism in incubations with calcium, as well as secondary ferric oxide phases like goethite in silica-free experiments. We also identified aggregates of curling, iron- and silica-rich amorphous precipitates in all incubations amended with silica. Although ferric oxides persist even in our electron acceptor-limited incubations, our observations indicate that microbial iron reduction of ferrihydrite is a viable pathway for the formation of early iron silicate phases. This finding allows us to draw parallels between our experimental proto-silicates and the recently characterized iron silicate nanoinclusions in BIF chert deposits, suggesting that early iron silicates could possibly be signatures of iron-reducing metabolisms on early Earth.

Acorn worm ossicle ultrastructure and composition and the origin of the echinoderm skeleton.

Here, we describe the shape and mineral composition of ossicles from eight acorn worm species, bringing the total known biomineralizing enteropneusts to 10 and confirming that ossicles are widespread in Enteropneusta. Three general forms were identified including a globular form that occurs in all three major enteropneust families. The biomineral compositions included all three polymorphs of calcium carbonate; calcite, aragonite and vaterite, and low to high magnesium concentrations. Calcite was the most common and characteristic of echinoderm ossicles. Based on these findings we hypothesize that an enteropneust-like ancestor to the Ambulacraria had ectodermal ossicles, formed in an extracellular occluded space bordered by a sheath of sclerocyte cells. The ossicles were microscopic, monotypic globular shaped, calcite ossicles with low to high Mg content and MSP130 proteins. The ossicles lacked intercalation with other ossicles. The function of acorn worm ossicles is unknown, but the position of ossicles in the trunk epithelia and near to the surface suggests predator deterrence, to provide grip on the walls of a burrow or tube, as storage of metabolic waste, or to regulate blood pH, rather than as an endoskeleton function seen in fossil and crown group Echinodermata.

The Impact of Water on the Tribological Behavior of Lubricating Grease Based on Calcium Carbonate Polymorphs

In this article, calcium sulfonate complex grease with different polymorphs was acquired. With reference to the improved rolling stability test method, 5% and 10% water were added to the calcium sulfonate composite grease respectively. The influence of water on the flow and deformation characteristics of grease under external force was characterized by rheological analysis. Moreover, the influence of water on the tribological behaviors of grease was evaluated at 30 and 80 °C. The results indicate that water could affect the flow and deformation characteristics of calcium sulfonate complex grease in vaterite polymorph (CSCG-V) more than calcium sulfonate complex grease in calcite polymorph (CSCG-C), and CSCG-V could combine with water to form a more stable grease under external force. Tribological results also clearly show that CSCG-C with water shows better tribological properties than CSCG-V with water under harsh conditions. There was no significant difference in the components of the films that consisted of CaCO3 and CaO regardless of grease within or without water. The improvement of tribological properties of CSCG-C with 5% and 10% water benefited from the influence of water on the film forming capacity of calcium carbonate on the steel surface.

An insight into the microstructures and composition of 2,700 m-depth deep-sea limpet shells

Structural and physiochemical properties contribute to the biological adaptation of deep-sea animals to their harsh living environment but have hardly been investigated systematically. In the present study, we for the first time applied various material characterization techniques including transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Fourier-transform infrared (FT-IR) spectroscopy to investigate the shell microstructures and chemical composition of a deep-sea limpet Eulepetopsis crystallina collected from the Tiancheng hydrothermal vent field at a depth of around 2,700 m in the Southwest Indian Ocean. Analyses of shell microstructural morphology and diffraction patterns of E. crystallina explicitly revealed the layered structures, exfoliation characteristics, and crystallographic orientation of each layer’s unit cell which was tilted at a small angle sequentially. In comparison with ordinary shallow-water limpet Cellana toreuma shells, E. crystallina shells showed a unique chemical composition and contained pure calcite of calcium carbonate polymorph and the trace of phosphate originated from regional phosphatic sediments of the Southwest Indian Ocean. The further microscopic analyses indicated that the shell of the deep-sea limpet E. crystallina features integrated and untruncated layer structures with a compressed width, possibly owning to the ultra-high hydrostatic pressure, which confirmed the effects of the living environment on the shell microstructure of deep-sea animals.

The ikaite to calcite transformation: Implications for palaeoclimate studies

Marine sedimentary ikaite is the parent mineral to glendonite, stellate pseudomorphs found throughout the geological record which are most usually composed of calcite. Ikaite is known to be metastable at earth surface temperatures and pressures, readily breaking down to more stable carbonate polymorphs when exposed to warm (ambient) conditions. Yet the process of transformation of ikaite to calcite is not well understood, and there is an ongoing debate as to the palaeoclimatic significance of glendonites in the geological record. This study uses a combination of techniques to examine the breakdown of ikaite to calcite, outside of the ikaite growth medium, and to assess the palaeoclimatic and palaeoenvironmental significance of stable and clumped isotope compositions of ikaite-derived calcite. Powder X-ray diffraction shows that ikaite undergoes a quasi- solid-state transformation to calcite during heating of samples in air, yet when ikaite transforms under a high temperature differential, minor dissolution-recrystallisation may also occur with the ikaite structural waters. No significant isotopic equilibration to transformation temperature is observed in the resulting calcite. Therefore, in cases of transformation of ikaite in air, clumped and stable isotope thermometry can be used to reconstruct ikaite growth temperatures. In the case of ancient glendonites, where transformation of the ikaite occurred in contact with the interstitial waters of the host sediments over unknown timescales, it is uncertain whether the reconstructed clumped isotope temperatures reflect ikaite crystallisation or its transformation temperatures. Yet clumped and stable isotope thermometry may still be used conservatively to estimate an upper limit for bottom water temperatures.Furthermore, stable isotope along with element/Ca ratios shed light on the chemical environment of ikaite growth. Our data indicate that a range of (bio)geochemical processes may act to promote ikaite formation at different marine sedimentary sites, including bacterial sulphate reduction and anaerobic oxidation of methane. The colours of the ikaites, from light brown to dark brown, indicate a high organic matter content, favouring high rates of bacterial sulphate reduction as the main driver of ikaite precipitation. Highest Mg/Ca ratios are found in the most unstable ikaites, indicating that Mg acts to destabilise ikaite structure.

Abnormal Crystallization Sequence of Calcium Carbonate in the Presence of Synechococcus sp. PCC 7942

Studying the crystallization sequence of calcium carbonate (CaCO3) polymorphs provides great insights into bacterial mineralization mechanisms, and carbonate rock genesis in recent geological history. CaCO3 biomineralization studies were conducted using Synechococcus sp. PCC 7942. Changes in bacterial optical density, polysaccharide content, carbonic anhydrase activity, pH, Ca2+, Mg2+, phosphate, and bicarbonate concentrations in medium, and precipitation levels were recorded, while precipitate morphology and polymorphisms were characterized. We identified an abnormal crystallization sequence order of carbonate polymorphs: calcite, aragonite, and vaterite, which failed to obey Ostwald’s rule. We investigated saturation indices (SI) and calculated calcite, aragonite, and vaterite quantities. Also, two mineralization studies were performed using PCC 7942 in the medium-plus different phosphates levels and extracellular polymeric substances (EPS) secreted by PCC 7942. Calcite was precipitated due to phosphate levels >7 µmol·L−1 and SIvaterite values <2.1. SIaragonite values >2.3 and phosphate levels <7 µmol·L−1 exerted crucial roles in aragonite formation. Finally, decreased phosphate and Mg2+ levels promoted vaterite crystallization. We suggest this unique crystallization order may be attributed to changes in bacterial density and PO4 3− levels. Our study provides new insights into bacterial mineralization mechanisms. HIGHLIGHTS Show that calcite, aragonite, and vaterite crystallized in order in MICP. The abnormal crystallization sequence of CaCO3 polymorphs does not follow Ostward’s theory. The metabolic activity of Synechococcus sp. PCC 7942 and phosphate levels should be responsible for this unique crystallization order.

Long-term sulfate resistance of synthesized cement systems with variable C3A/C4AF ratio at low temperature or ambient conditions: Insights into the crystalline and amorphous phase assemblage

Synthesized cement systems made with variable C3A/C4AF ratios, containing C3S, gypsum and, optionally, calcite, were stored long-term at humid conditions at 5 or 20 °C, without any protection against atmospheric carbonation. Analytical techniques able to assess both the crystalline and amorphous phases were used. Experimental results were compared with thermodynamic simulations. The systems with C3A/C4AF < 1 better preserved the soundness of the CSH phase, which hosted iron, and prevented thaumasite formation. The addition of calcite in these systems inhibited carbonation. When occurred (mixtures without calcite), the carbonation was significantly more intense at ambient temperature. In the systems that underwent extensive deterioration, cross-linking of silicate structures, AFt decomposition, and iron release from the deteriorating CSH, occurred, while Al-incorporating amorphous silica, calcium carbonate polymorphs and hydrous iron oxide formed. The presence of unreacted C3A in the systems with C3A/C4AF = 1, suggested that CSH decomposition was contributed by available sulfates.

Behavior of cementitious mixtures with filler carbonate subjected to accelerated carbonation

Calcium carbonate limestone filler is used as a partial replacement for clinker in cements to reduce carbon dioxide emissions and fill the voids in the cement paste. However, concrete durability conditions depend on the composition and the water/cement ratio, one of the major origin of concrete´s porosity. The objective of this study was to evaluate physical and chemical effects of calcium carbonate limestone filler in mortar pastes subjected to accelerated carbonation. Composite formulations were elaborated with three proportions of filler substitution (15%, 25% and 35%) and three water/cement ratios (0.42, 0.50 and 0.58). Physical, chemical and mineral characterizations were performed on Portland cement PC V and calcium carbonate limestone. The resulting mortar paste formulations were evaluated with respect to mechanical strength and capillary water absorption both for samples without carbonation and with accelerated exposure conditions. In the latter, carbonation depth penetration was also ascertained. Carbonation effects were determined from X-ray diffraction and thermogravimetric analysis. Results on compression strength and water absorption determined that a 25% filler substitution achieved the best performance with 40.72 MPa and an absorption of up to 7% for the water/cement ratio of 0.42. The carbonation coefficient was primarily affected by the water/cement ratio rather than substitution level. Thermal and mineral analysis indicated that carbonation consumed portlandite and formed calcite. Further calcium carbonate polymorphs were identified after 28 days of accelerated carbonation as a result so far unreported in studies of Portland cement.

Marine Biofilm effect on mortar surface layer.

The objective of this study is to evaluate the effect of biofilm development on the surface layer of a mortar. This work aims at understanding the modifications occurred within the cementitious matrix such as its composition as its microstructure following the bio-colonization. These properties were studied after 360 days of immersion in two immersion media (Artificial Seawater (AS) and Natural Seawater (NS)) using ATG/DTG, XRD analyses and SEM observations. It was found that the biofilm caused the dissolution of the portlandite deeper than when the mortar was not colonized (AS medium). Moreover, a strong carbonation was observed in the first millimeters of the matrix. Two polymorphs of calcium carbonate were particularly identified. Aragonite is the dominant form present on the surface of the mortar immersed in NS. Calcite and magnesian calcite were also observed but after bio-colonization of the mortar. Thus, the development and the biological activity of the biofilm seems to modify the properties of the mortar and could control the precipitation of calcium carbonates on its surface.

Effect of temperature on the carbonation behavior of γ-C2S compacts

This study presents experimental results on the carbonation behavior of γ-C2S cured under different temperatures ranging from 0 to 80 °C, including the development in compressive strength and carbonation reactivity, characterization of carbonation products and microstructure. Results indicate the dominant polymorphs of calcium carbonate in the carbonated γ-C2S compacts are found to be calcite at lower temperatures and aragonite at higher temperatures, respectively. Higher temperatures increase early carbonation reactivity and compressive strength while a lower temperature leads to a more sustained development in the two metrics which eventually exceeds those at higher temperatures. This can be accounted for by the premature densification of surface region and the depletion of pore moisture associated with the excessively exothermic carbonation reaction at high temperatures. An improved kinetic model is developed for the simultaneous incorporation of temperature effects on the intrinsic reactivity and the moisture retainment. The obtainment of two parameters ks and kp enables an improved understanding the carbonation behavior of γ-C2S under different temperatures, which will benefit its application as a carbon sink for industrial flue gases.

Analogue Application of Behaviour and Transport of Naturally Occurring Strontium in Cold-Region Aquatic Environments to 90Sr

Quantification and scientific observations of the fate and transport of dissolved strontium in water systems, particularly cold climate water systems, are severely lacking. In this work, in an experiment conducted at a temperature of 6 °C, the observation of strontium precipitation along with calcium carbonate minerals from cold wastewater is investigated. ICP-MS is used for metal analyses where the distribution of the species and saturation state of minerals along with a surface complexation model was performed using the public-use USGS geochemical modeling software, PHREEQC (PH Redox Equilibrium (in C language)). Sample media were analyzed using XPS and Raman spectroscopy. The results suggest that the loss of strontium from natural waters is via the process of co-precipitation with calcite, a calcium carbonate polymorph. The observations and findings are intended to be useful to quantify the loss of 90Sr from the water, in the case of an unplanned release from a nuclear reactor-operated facility. The results indicate that the precipitation model is a robust and reliable approach to predicting and monitoring the behaviour and transport of strontium that may occur in natural environments as a result of an accidental nuclear release.

Parental exposure of Eastern oysters (Crassostrea virginica) to elevated pCO2 mitigates its negative effects on early larval shell growth and morphology

AbstractLarvae of marine calcifying organisms are particularly vulnerable to the adverse effects of elevated pCO2 on shell formation because of their rapid calcification rates, reduced capacity to isolate calcifying fluid from seawater, and use of more soluble polymorphs of calcium carbonate. However, parental exposure to elevated pCO2 could benefit larval shell formation through transgenerational plastic responses. We examined the capacity of intergenerational exposure to mitigate the adverse effects of elevated pCO2 on Eastern oyster (Crassostrea virginica) early larval shell growth, shell morphology, and survival. Adult oysters were exposed to control (572 ppm pCO2) or elevated pCO2 (2827 ppm pCO2) conditions for 30 d during reproductive conditioning. Offspring from each parental treatment were produced using a partial North Carolina II cross design and grown under control and elevated pCO2 conditions for 3 d. We found evidence of transgenerational plasticity in early larval shell growth and morphology, but not in survival, in response to the parental pCO2 exposure. Larvae from parents exposed to elevated pCO2 exhibited faster shell growth rates than larvae from control parents, with this effect being significantly larger when larvae were grown under elevated pCO2 compared to control conditions. Parental exposure to elevated pCO2, however, was insufficient to completely counteract the adverse effects of the prescribed elevated pCO2 on early larval shell formation and survival. Nevertheless, these results suggest that oysters have some capacity to acclimate intergenerationally to ocean acidification.