Formation Of Aragonite Research Articles

Influence of Temperature on Calcium Carbonate Polymorph formed from Ammonium Carbonate and Calcium Acetate

This research used ammonium carbonate and calcium acetate in the preparation of various calcium carbonate polymorphs for biomimetic composite applications. Biominerals were synthesized at temperatures ranging from 25 to 80°C to investigate the effect of synthesis temperature on the abundance of vaterite, aragonite, and calcite, delineating regions that are favorable for the formation of these different calcium carbonate polymorphs. In particular, it was observed that lower temperatures of 25-30°C were favorable for vaterite formation with increasing crystallite size at the higher temperature. Calcite was the preferred polymorph formed at temperatures of approximately 50°C. Although a trace of aragonite was observed at 70°C, it was not observed at the highest temperature investigated (80°C). The absence of aragonite formation at elevated temperatures may be a function of the lower pH (~8.4) in the ammonium carbonate/calcium acetate system compared to ~9.9 for the sodium carbonate/calcium acetate system that promotes the formation of vaterite over aragonite. These results are important when developing biomimetic materials incorporating calcium carbonate with different polymorphs and crystal sizes.

Rapid discrimination of china sponges by Tri-step infrared spectroscopy: A preliminary study

Trip-step infrared spectroscopy, Fourier transform infrared spectroscopy combined with second derivative infrared spectroscopy (SD-IR) and two-dimensional correlation infrared spectroscopy (2DCOS-IR), was employed to characterize and discriminate nine China sponges. Sponges from different classes and different orders had respective unique IR macro-fingerprints. Their IR spectra suggested that the prime ingredient of calcareous sponges was calcium carbonate in calcite and/or aragonite forms, but that of demosponges was protein. Particularly, the sponges from the same genus which could not be identified by traditional spicule identification have been definitely discriminated. For sponges having highly similar chemical profile (IR spectral profile), SD-IR and 2DCOS-IR have been applied to enhance the spectral resolution to distinguish the sponges convincingly.

Sodium Lignosulfonate Induced Vaterite Calcium Carbonate with Multilayered Structure

AbstractSodium lignosulfonate (SL), a byproduct of the pulping industry, was used as a stabilizer for the mineralization of CaCO3. In a calcium acetate–urea–water system, the direct aging of the aqueous solution of calcium acetate and urea resulted in the formation of mixed aragonite and vaterite phases or a pure aragonite phase depending on the aging time. However, SL was introduced into the calcium acetate–urea–water system to markedly stabilize the formation of a thermodynamically unstable vaterite phase. Various morphologies of vaterite structures were observed by adjusting the concentration of urea and SL as well as the aging time. Based on these results, ion exchange, carbonate attacking the calcium(II) ions, aggregations of SL‐stabilized primary CaCO3 particles through oriented attachment and Ostwald ripening, as well as mesoscale self‐assembly were proposed as mechanisms to elucidate the formation of various morphologies.

The Application of Ammonium Hydroxide and Sodium Hydroxide for Reagent Softening of Water

The calcium carbonate crystallization from aqueous solutions in the presence of alkali additives such as sodium hydroxide and ammonium hydroxide has been researched. It is found CaCO3 crystallizes predominantly in the modification of aragonite in the presence of ammonium hydroxide. The calcium carbonate formation rate in an alkaline medium and the gaseous reaction products due to sorption of gas bubbles on crystal surfaces, affect the aragonite structure formation. It is shown use of ammonium hydroxide for water treatment can solve two urgent tasks such as water softening and exclusion sediment of deposits on the equipment surfaces by a calcium carbonate crystallization in the form of aragonite.

A Novel Acidic Matrix Protein, PfN44, Stabilizes Magnesium Calcite to Inhibit the Crystallization of Aragonite

Magnesium is widely used to control calcium carbonate deposition in the shell of pearl oysters. Matrix proteins in the shell are responsible for nucleation and growth of calcium carbonate crystals. However, there is no direct evidence supporting a connection between matrix proteins and magnesium. Here, we identified a novel acidic matrix protein named PfN44 that affected aragonite formation in the shell of the pearl oyster Pinctada fucata. Using immunogold labeling assays, we found PfN44 in both the nacreous and prismatic layers. In shell repair, PfN44 was repressed, whereas other matrix proteins were up-regulated. Disturbing the function of PfN44 by RNAi led to the deposition of porous nacreous tablets with overgrowth of crystals in the nacreous layer. By in vitro circular dichroism spectra and fluorescence quenching, we found that PfN44 bound to both calcium and magnesium with a stronger affinity for magnesium. During in vitro calcium carbonate crystallization and calcification of amorphous calcium carbonate, PfN44 regulated the magnesium content of crystalline carbonate polymorphs and stabilized magnesium calcite to inhibit aragonite deposition. Taken together, our results suggested that by stabilizing magnesium calcite to inhibit aragonite deposition, PfN44 participated in P. fucata shell formation. These observations extend our understanding of the connections between matrix proteins and magnesium.

Susceptibility of mineral phases of steel slags towards carbonation: mineralogical, morphological and chemical assessment

Process limitations have thus far prevented mineral carbonation of alkaline wastes from been widely applied. These barriers are caused by inefficient processing, but also by mineralogical aspects inherent to the materials. Better understanding and predictability of the effects of mineral carbonation on alkaline materials could be obtained by studying the carbonation susceptibility of constituent minerals separately, allowing for detailed and accurate analysis of their reaction kinetics and maximal conversions and of the carbonate products formed. For this purpose, this paper presents the synthesis and carbonation of the seven most abundant alkaline minerals found in AOD, CC and BOF slags, namely: akermanite (Ca 2 MgSi 2 O 7 ), bredigite (Ca 7 Mg(SiO 4 ) 4 ), cuspidine (Ca 4 Si 2 O 7 F 2 ), β– and γ–C 2 S (Ca 2 SiO 4 ), merwinite (Ca 3 Mg(SiO 4 ) 2 ), and srebrodolskite (Ca 2 Fe 2 O 5 ). Two experimental approaches to mineral carbonation of increasing levels of process severity are utilized: (mild) incubator carbonation, and (accelerated) pressurized slurry carbonation. In addition, the slags and two free oxides (CaO and MgO) are equally carbonated and evaluated. Data regarding CO 2 uptake, mineral conversion and formed carbonate and non-carbonate products in the samples were obtained through TGA, QXRD (Rietveld refinement) and SEM techniques. Reduction in material basicity and evolution of particle morphology were also assessed. The synthesized mineral purities (>70 wt% target mineral phase) were found sufficient for more accurate assessment of carbonation behaviour of the individual minerals. Bredigite was found to be the most reactive mineral under all processing conditions; C 2 S and wollastonite were more reactive under slurry carbonation, while srebrodolskite and calcium monoferrite were found to be more reactive under moist carbonation. Merwinite and diopside had the slowest carbonation conversions. Calcite and aragonite were the dominant carbonate products formed, whereby aragonite formation was promoted in Mg-containing materials. The morphology of aragonite crystals and the packing density of its product layer were found to vary depending on the parent mineral. Characteristic slag carbonation products, not observed as extensively from synthetic mineral samples, were magnesian calcite from slurry carbonation, and monohydrocalcite and vaterite from moist carbonation. Wollastonite was the main crystalline non-carbonate product, occurring predominantly from slag carbonation, while silica-rich amorphous matter formed in all samples proportionally to CO 2 uptake. Free lime, when present, controlled material basicity above pH 12, while silicates were found to typically possess pH in the range of 11.3–11.9, and Ca-carbonates eventually controlled the pH of well carbonated samples to values under 10.

Characterisation and expression of the biomineralising gene Lustrin A during shell formation of the European abalone Haliotis tuberculata

The molluscan shell is a remarkable product of a highly coordinated biomineralisation process, and is composed of calcium carbonate most commonly in the form of calcite or aragonite. The exceptional mechanical properties of this biomaterial are imparted by the embedded organic matrix which is secreted by the underlying mantle tissue. While many shell-matrix proteins have already been identified within adult molluscan shell, their presence and role in the early developmental stages of larval shell formation are not well understood. In the European abalone Haliotis tuberculata, the shell first forms in the early trochophore larva and develops into a mineralised protoconch in the veliger. Following metamorphosis, the juvenile shell rapidly changes as it becomes flattened and develops a more complex crystallographic profile including an external granular layer and an internal nacreous layer. Amongst the matrix proteins involved in abalone shell formation, Lustrin A is thought to participate in the formation of the nacreous layer. Here we have identified a partial cDNA coding for the Lustrin A gene in H. tuberculata and have analysed its spatial and temporal expression during abalone development. RT-PCR experiments indicate that Lustrin A is first expressed in juvenile (post-metamorphosis) stages, suggesting that Lustrin A is a component of the juvenile shell, but not of the larval shell. We also detect Lustrin A mRNAs in non-nacre forming cells at the distal-most edge of the juvenile mantle as well as in the nacre-forming region of the mantle. Lustrin A was also expressed in 7-day-old post-larvae, prior to the formation of nacre. These results suggest that Lustrin A plays multiple roles in the shell-forming process and further highlight the dynamic ontogenic nature of molluscan shell formation.

Effects of amine, amine salt and amide on the behaviour of carbon dioxide absorption into calcium hydroxide suspension to precipitate calcium carbonate

The amount of carbon dioxide (CO2) absorption and calcium ion (Ca2+) concentration besides the pH of aqueous solution were observed during the CO2 absorption to precipitate calcium carbonate (CaCO3) from calcium hydroxide (Ca(OH)2). A reaction rate-limiting effect of an amount of CO2 absorption without any organic additives in the early stage of the precipitation was observed, which was attributed to an interruption effect of bicarbonate ion (HCO−3) on the precipitation of CaCO3. The improvement for the reaction rate was achieved not only by amine additives but also by neutral additives such as ε-caprolactam or amine salt. When the hexamethylene diamine was dissolved in the solution, successive change of crystal forms of CaCO3 aragonite to calcite in aqueous suspensions, confirmed by Ca2+ concentration change and X-ray diffraction, was concluded that a local environment around the amine group in aqueous solution and an interaction of the diamine with precipitated CaCO3 particles were important factors for these reactions.

Crystallographic Orientation of Cuttlebone Shield Determined by Electron Backscatter Diffraction

In common with many cephalopod mollusks, cuttlefish produce an internal biomineral buoyancy device. This cuttlebone is analogous to a surf board in shape and structure, providing rigidity and a means of controlling buoyancy. The cuttlebone is composed of calcium carbonate in the form of aragonite and comprises an upper dorsal shield and a lower lamellar matrix. The lamellar matrix comprises layers of chambers with highly corrugated walls. The dorsal shield comprises bundles of aragonite needles stacked on top of each other. Electron backscatter diffraction analyses of the dorsal shield reveal that the c-axis of aragonite is parallel with the long axis of the needles in the bundles such that any spread in crystallographic orientation is consistent with the spread in orientation of the fibers as they radiate to form the overall structure of the dorsal shield. This arrangement of c-axis coincident with the long axis of the biomineral structure is similar to the arrangement in corals and in contrast to the situation in the molluskan aragonite nacre of brachiopod calcite where the c-axis is perpendicular to the aragonite tablet or calcite fiber, respectively.

Magnesium chloride as a leaching and aragonite-promoting self-regenerative additive for the mineral carbonation of calcium-rich materials

Two approaches for the intensification of the mineral carbonation reaction are combined and studied in this work, namely: (i) the calcium leaching and aragonite promoting effects of magnesium chloride (MgCl2), and (ii) the passivating layer abrasion effect of sonication. The alkaline materials subjected to leaching and carbonation tests included lime, wollastonite, steel slags, and air pollution control (APC) residue. Batch leaching tests were conducted with varying concentrations of additives to determine extraction efficiency, and with varying solids-to-liquid ratios to determine solubility limitations. Aqueous mineral carbonation tests, with and without the use of ultrasound, were conducted applying varying concentrations of magnesium chloride and varying durations to assess CO2 uptake improvement and characterize the formed carbonate phases. The leaching of calcium from lime with the use of MgCl2 was found to be atom-efficient (1mol Ca extracted for every mole Mg added), but the extraction efficiency from slags and APC residue was limited to 26–35% due to mineralogical and microstructural constraints. The addition of MgCl2 notably improved argon oxygen decarburization (AOD) slag carbonation extent under sonication, where higher additive dosage resulted in higher CO2 uptake. Without ultrasound, however, carbonation extent was reduced with MgCl2 addition. The benefit of MgCl2 under sonication can be linked to the preferential formation of aragonite (85wt% of formed carbonates), which precipitates on the slag particles in the form of acicular crystals with low packing density, thus becoming more susceptible to the surface erosion effect of sonication, as evidenced by the significantly reduced carbonated slag particle size.

A Pearl Protein Self-Assembles To Form Protein Complexes That Amplify Mineralization

The formation of the nacre pearl in marine invertebrates represents an on-demand production of mineralization in response to an irritant or parasite threat to the mantle organ. In the Japanese pearl oyster (Pinctada fucata), this process is mediated by a 12-member protein family known as PFMG (Pinctada fucata mantle gene). One of these proteins, PFGM1, has been implicated in modulating calcium carbonate crystal growth and has been reported to possess an EF-hand-like domain. In this report, we establish that the recombinant PFMG1 (rPFMG1) is an intrinsically disordered "imitator" EF-hand protein that increases the number of calcium carbonate mineral crystals that form relative to control scenarios and does not induce aragonite formation. This protein possesses a modified pseudo-EF-hand sequence at the C-terminal end which exhibits low homology (30-40%) to the pseudo-EF-hand mitochondrial SCaMCs buffering/solute transport proteins. This low sequence homology is the result of the inclusion of disorder-promoting amino acids and short amyloid-like aggregation-prone cross-β-strand sequences within the putative PFMG1 pseudo-EF-hand sequence region. Similar to other nacre proteins, rPFMG1 oligomerizes to form amorphous, heterogeneously sized protein oligomers and films in vitro, and this process is enhanced by Ca(2+), which promotes the formation of aggregation-prone extended β-strand structure within rPFMG1. From these results, we conclude that PFMG1 forms supramolecular assemblies that play an important role in amplifying the nucleation process that is crucial for coating or neutralizing invasive threats to the mantle organ.

Characterization of the Zhikong Scallop (Chlamys farreri) Mantle Transcriptome and Identification of Biomineralization-Related Genes

Chlamys farreri is a significant species in aquaculture and fishery in East Asia. A deep understanding of its shell formation by studying the transcriptome of the mantle, a key organ in shell formation, could provide important guidance for its culture. Thus, we sequenced and analyzed the mantle transcriptome of C. farreri. The 77,975 unigenes were generated after Illumina sequencing and de novo assembly. The unigenes were annotated using authoritative databases (non-redundant (NR), COG, Gene Ontology (GO), and KEGG) to obtain functional information. BLASTX alignment was performed between unigenes and reported proteins related to biomineralization. The results identified 53 homologous genes representing 17 matrix proteins, most of which are involved in calcite formation, and 171 homologies with 26 proteins related to general processes of biomineralization. The discovery and unusually high expression of MSP-1 suggested its importance in scallops. Homologous unigenes with aragonite-formation-related matrix proteins were much fewer compared with those related to calcite formation. The results implied that, in C. farreri, the number and proportion of matrix proteins related to aragonite formation is much lower than those related to calcite formation, which was consistent with the proportions of aragonite and calcite in C. farreri shells. Thus, the formation of different polymorphs of calcium carbonate (calcite and aragonite) in molluskan shells is regulated by different groups of proteins. Moreover, 17 candidate unigenes, which are probably involved in biomineralization, were predicted by screening for gene products with secreted domains and tandem-arranged repeat units. Our results contribute to the understanding of biomineralization processes and the evolution of shell formation.

PHYSICAL AND CHEMICAL RESEARCH OF PROCESSES OF SALT FORMATION IN THE WATER OF BALKHASH LAKE

In recent years about 5.04 million tons of salts a year arrive down the River Ili to Balkhash Lake. Using water of the Ili River for filling the Kapchagaisky reservoirreduced volume of arriving water from the river to 2/3 and decreased level of the lake. It causes mineralization, which advances forecasts. Complex research of influence of the IliRiver on the current state of salt formation in Balkhash Lake is needed as well as hydrochemical research of the water area of Balkhash Lake and the Ili River. In our study the chemical analysis of the qualitative and quantitative characteristics of water with use of classical and physical and chemical methods of the analysis, such as, nuclear and absorbing, roentgen fluоrescence spectrometry and crystal and optical analysis was realized. It is established that crystallization of salts begins with calcium carbonate in the form of aragonite, crystals of nesquehonite join this process, and in deposit the main carbonate of magnesium drops out. Processes of metamorfization with participation of ions of carbonate, hydro carbonate and calcium, are bringing calcite sedimentation. They occur everywhere, but processes with participation of magnesium ions are bringing magnesite or dolomite sedimentation only in extreme east stretch of the lake. In saturated solutions of carbonates there is an increase in ions of potassium in sediment. Thus, their quantities increase a little. It is especially sharp for sulfate and sodium chloride in the direction from the west to the east. The calcium carbonate in the firm phase possesses more absorbing ability, than magnesium carbonate, and the presence of ions of potassium at sediment doesn't change structure of the last. At isothermal evaporation of mix of solutions of potassium carbonate with saturated solution of calcium carbonate, and also potassium sulfate with saturated solution of calcium sulfate and the joint sedimentation of potassium is noticed.

Effects of temperature on precipitation kinetics and microstructure of calcium carbonate in the presence of magnesium and sulphate ions

In the present work, the effects of the temperature on the kinetics and microstructure of CaCO3, precipitated in the presence of magnesium and sulphate ions, were studied using degassing dissolved CO2 method. The precipitates were identified by X-ray diffraction, atomic absorption spectroscopy and scanning electron microscopy. It was shown that at fixed temperature and ionic strength, the presence of sulphate and magnesium ions increased the induction time, decreased the crystal growth rate and reduced the amount of the CaCO3 precipitates obtained. Magnesium induced the formation of aragonite form rather than the calcite and vaterite form. The increase of temperature in presence of magnesium and sulphate ions lead to a change on the effect of magnesium on kinetics of CaCO3 precipitation and caused the Mg2+ ions incorporation in the CaCO3 lattice. The increase of temperature favoured the aragonite phase in magnesium solutions and both aragonite and vaterite in presence of sulphate ions.

Patterns of Expression in the Matrix Proteins Responsible for Nucleation and Growth of Aragonite Crystals in Flat Pearls of Pinctada fucata

The initial growth of the nacreous layer is crucial for comprehending the formation of nacreous aragonite. A flat pearl method in the presence of the inner-shell film was conducted to evaluate the role of matrix proteins in the initial stages of nacre biomineralization in vivo. We examined the crystals deposited on a substrate and the expression patterns of the matrix proteins in the mantle facing the substrate. In this study, the aragonite crystals nucleated on the surface at 5 days in the inner-shell film system. In the film-free system, the calcite crystals nucleated at 5 days, a new organic film covered the calcite, and the aragonite nucleated at 10 days. This meant that the nacre lamellae appeared in the inner-shell film system 5 days earlier than that in the film-free system, timing that was consistent with the maximum level of matrix proteins during the first 20 days. In addition, matrix proteins (Nacrein, MSI60, N19, N16 and Pif80) had similar expression patterns in controlling the sequential morphologies of the nacre growth in the inner-film system, while these proteins in the film-free system also had similar patterns of expression. These results suggest that matrix proteins regulate aragonite nucleation and growth with the inner-shell film in vivo.

The co-effect of organic matrix from carp otolith and microenvironment on calcium carbonate mineralization

In vitro mineralization experiment is an effective way to study the effect of organic matrix on calcium carbonate crystallization, and to reveal the relationship between organic matrix and inorganic crystal in natural biominerals. In natural biominerals, organic matrix plays an important role in crystal formation and stability, together with microenvironment changes, they can affect crystal polymorph, morphology, density, size, orientation etc.In this work, we systematically studied the effects of different organic matrices in fish otoliths, the organic matrix concentration changes, as well as the co-effect of organic matrices with temperature, pH value and Mg ion changes in the in vitro CaCO3 mineralization experiments.The organic matrix and concentration change experiments prove that water soluble matrix (WSM) plays an important role in crystal form transition. It can induce CaCO3 crystals with same crystal polymorph as the otolith from which organic matrix was extracted. The temperature change experiment proves that CaCO3 has a tendency to form calcite, vaterite, and then aragonite in priority as temperature goes up. Under different temperature, WSM from lapillus/asteriscus still has the effect to mediate different CaCO3 crystals. The pH change experiment shows that, near the neutral environment, as pH value goes up, calcites have a tendency to form crystal aggregates with more faces exposed, the organic matrix still keeps crystal mediation effect. The Mg2+ experiment shows that, Mg ion can promote aragonite formation, together with lapillus organic matrix, aragonites with different shapes are formed.

Ecostratigraphy of benthic foraminifera for interpreting Arctic record of Early Toarcian biotic crisis (Northern Siberia, Russia)

The present contribution focusses on ecostratigraphic fluctuations of foraminiferal assemblages occurring during the benthic biotic crisis corresponding to the Early Toarcian anoxic event. We aim at understanding the response of benthic biota to the environmental changes that occurred during the crisis in a high latitude setting and compare with previous data from total organic carbon (TOC) and δ13C from previous works. The Kelimyar River section exposes a Lower Jurassic marine succession made up of siltstones, sandy siltstones (uppermost Pliensbachian) and black shales (Lower Toarcian) deposited close to the Early Jurassic North Pole in a relatively deep continental shelf. The Pliensbachian sediments are represented by a foraminiferal assemblage dominated by epifauna, mainly Trochammina, but showing a progressive diminution in diversity. This suggests an unfavourable microhabitat for infaunal forms, probably involving salinity fluctuations. Although the opportunist Trochammina tolerated salinity fluctuations, the decreasing proportions of aragonitic and calcitic hyaline foraminifera indicate the progressive deterioration of the benthic environment. A context of relative sea-level fall in the Arctic palaeobasin during the margaritatus Zone and the beginning of the viligaensis ammonite Zone related to an abrupt climatic cooling would explain these environmental changes (including salinity fluctuations) that lead to decreased diversity and even the disappearance of calcitic and aragonitic forms. The debut of the falciferum Zone (Lower Toarcian) is characterised by laminated black shales, high total organic carbon, a negative carbon isotopic excursion, and an abrupt decrease in the foraminiferal abundance and diversity. These features indicate oxygen-restricted conditions in the sea-bottom. Only opportunist Trochammina shows a rapid increase in abundance after the debut of the black shales, congruent with the relation of this genus with high TOC and a poorly oxygenated sediment water interface. Trochammina was able to colonise the sea-bottom after the development of hypoxic conditions in the Kelimyar River section. These adverse conditions occurred just after the negative carbon isotopic excursion and maximum values of TOC and correlate with the climatic warming that occurred in the Arctic palaeobasins referred to by previous authors. Detailed analysis of the sea-bottom recolonisation points to a foraminiferal replacement in which distinct foraminiferal morphogroups reach their optimum values. Finally, despite certain differences, the benthic foraminiferal assemblages from Kelimyar River section are comparable with those from the North African palaeomargin in the Ratnek El Kahla section (Algeria), thus illustrating an equivalent response of benthic foraminiferal assemblages to the Early Toarcian biotic crisis. In both cases the composition of assemblages, diversity and abundance of foraminifera were sensitive to restricted oxygen conditions, and opportunist species did colonize the sea bottom after this biotic crisis.

Gas-seep related carbonate and barite authigenic mineralization in the northern Gulf of California

Authigenic barite and carbonates (dolomite, high-Mg calcite and aragonite) have been recovered from active gas seep sites of the pull-apart Consag and Wagner basins, the northernmost and shallowest (∼225 m deep) active basins in the Gulf of California. This gulf encompasses a transform–spreading ridge transitional plate boundary; while seafloor spreading is known to take place in a few basins of the central and southern gulf, in the northern basins mantle upwelling is only suspected. Despite of their tectonic framework, the studied authigenic deposits show fabrics, minerals and isotope compositions similar to those reported for common gas seeps in passive continental margins and in accretionary active margins, and suggest that methane accompanied by Ba- and Sr-rich basinal cold fluids is released to the seafloor. Authigenic carbonates occur as centimeter-sized concretions scattered within silty sands. These concretions consist of cryptocrystalline carbonate pervasive cement (high-Mg calcite to dolomite) containing bioclasts in variable amounts. Aragonite forms crack-fill fibrous cement in association to barite. In addition, well-sorted, sandy sediments largely constituted by barite spheroids with subordinate pyrite have been recovered. The δ13CPDB from carbonates (cements and skeletal grains) has an overall variation of −45.5 to +1.7‰. The δ18OPDB of carbonates varies from −3.1 to +4.0‰. The cryptocrystalline cement yielded the lowest δ13C, indicating that it formed through the anaerobic oxidation of methane. The highest δ18OPDB values (>+3.0‰) correspond to this cement. The range of δ18OSMOW calculated for water (+1.3 to +2.1‰) is compatible with pore fluid compositions of typical deep-water methane seeps. Barite yielded δ34S from +38.2 to +44.8‰, well above that of sulfate from pore- and seawater (+14.8 to +23.6‰). Barite precipitates within the sediments through mixing of (a) reducing, Ba-rich seep fluids, with (b) pore-water, containing sulfate residual from microbial reduction. The reaction of sulfate reduction is coupled to the oxidation of methane. Skeletal carbonates (coral and bivalves) yielded the lowest 87Sr/86Sr ratios (0.709133–0.709177), so they do not show further influence than that of seawater. Barite from sandy deposits yielded high 87Sr/86Sr values (0.709477–0.709698). The source of radiogenic strontium could be the clastic infill of the basins, while an oceanic crust isotopic signature is absent.

Characterization of calcium phosphate powders originating from Phyllacanthus imperialis and Trochidae Infundibulum concavus marine shells

The study reports the preparation and characterization of powders consisting of the different phases of calcium phosphates that were obtained from the naturally derived raw materials of sea-shell origins reacted with H3PO4. Species of sea origin, such as corals and nacres, attracted a special interest in bone tissue engineering area. Nacre shells are built up of calcium carbonate in aragonite form crystallized in an organic matrix. In this work two natural marine origin materials (shells of echinoderm Sputnik sea urchin — Phyllacanthus imperialis and Trochidae Infundibulum concavus mollusk) were involved in the developing powders of calcium phosphate based biomaterials (as raw materials for bone-scaffolds) by hotplate and ultrasound methods. Thermal analyses of the as-prepared materials were made for an assessment of the thermal behavior and heat treatment temperatures. Samples from both sea shells each of them prepared by the above mentioned methods were subjected to thermal treatments at 450°C and 850°C in order to evaluate the crystalline transformations of the calcium phosphate structures in the heating process. By X-ray diffraction analyses various calcium phosphate phases were identified. In Sputnik sea urchins originated samples were found predominantly brushite and calcite as a small secondary phase, while in Trochidae I. concavus samples mainly monetite and HA phases were identified. Thermal treatment at 850°C resulted flat-plate whitlockite crystals — β-MgTCP [(Ca, Mg)3 (PO4)2] for both samples regardless the preparation method (ultrasound or hotplate) or the targeted Ca/P molar ratio according with XRD patterns. Scanning electron microscopy and Fourier transformed infrared spectroscopy were involved more in the characterization of these materials and the good correlations of the results of these methods were made.

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.