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1
Yaxley, Gregory M., Bruce A. Kjarsgaard e A. Lynton Jaques. "Evolution of Carbonatite Magmas in the Upper Mantle and Crust". Elements 17, n. 5 (1 ottobre 2021): 315–20. http://dx.doi.org/10.2138/gselements.17.5.315.
Testo completoAbstract (sommario):
Carbonatites are the most silica-poor magmas known and are amongst Earth’s most enigmatic igneous rocks. They crystallise to rocks dominated by the carbonate minerals calcite and dolomite. We review models for carbonatite petrogenesis, including direct partial melting of mantle lithologies, exsolution from silica-undersaturated alkali silicate melts, or direct fractionation of carbonated silicate melts to carbonate-rich residual melts. We also briefly discuss carbonatite–mantle wall-rock reactions and other processes at mid-to upper crustal depths, including fenitisation, overprinting by carbohydrothermal fluids, and reaction between carbonatite melt and crustal lithologies.
2
Korinevsky, V. G., e E. V. Korinevsky. "Isotopic evidences of magmatic nature of the dolomite-calcite bodies of the Ilmeny Mountains and the Plastovsky district of the South Urals". Vestnik of Geosciences 11 (2020): 3–19. http://dx.doi.org/10.19110/geov.2020.11.1.
Testo completoAbstract (sommario):
The data obtained for the first time on the isotopic composition of oxygen and carbon of calcites and graphites of dolomitecalcite rocks of the Ilmeny Mountains and dykes of a similar composition in the Plastovsky district have confirmed their magmatic genesis. The temperature of formation of carbonate bodies (590—1000 °Ñ), determined from the isotopic ratios of C and O in calcite and graphite, corresponds to the temperature range (600—900 °Ñ) of the formation of carbonatite associations. According to the same ratios of isotopes in calcites, the protoliths of carbonate rocks are located within the carbonatite fields of the folded regions and in the transition zone to carbonates of marine origin. This is probably due to the fact that these rocks are a product of carbonate magma during remelting of sedimentary carbonate rocks in subduction zones, or under the influence of the heat of granite intrusions.
3
Tang, Guowang, Feng Huang, Guihe Wang, Zhengyang Song, Cangqin Jia, Peizhi Yu e Yongshuai Sun. "Valorization of Water-Based Drill Cuttings through the Bio-Carbonation Approach". Advances in Materials Science and Engineering 2022 (6 maggio 2022): 1–10. http://dx.doi.org/10.1155/2022/3836863.
Testo completoAbstract (sommario):
This study proposed a novel bio-carbonation method to recycle water-based drill cutting (WDC) to prepare samples, which contains reactive magnesia (MgO) cement (RMC), ground granulated blast furnace slag (GGBS), and fly ash (FA), with the adoption of microbially induced carbonate precipitation (MICP). Through the investigation of some parameters (i.e., GGBS content, FA content, and curing time), the microstructures and strength development of bio-carbonated RMC-based WDC samples were evaluated. The preliminary results revealed that bio-carbonated RMC-based WDC samples outperformed the control group (i.e., without bio-carbonation) in terms of the 28-day strength (i.e., 9.8 MPa versus 4.4 MPa), which can be assigned to formation of the carbonates, that is, hydrated magnesium carbonates (HMCs). Further, in addition to the identification of HMCs, the microstructural analysis also revealed a continuous carbonate network due to the presence of HMCs, which accounts for the strength boost of samples.
4
Nikiforov, Anatoly V., Elena O. Dubinina, Nikolay A. Polyakov, Amina M. Sugorakova e Aylan K. Khertek. "Influence of Host Marble Rocks on the Formation of Intrusive Alkaline Rocks and Carbonatites of Sangilen (E. Siberia, Russia)". Minerals 11, n. 7 (22 giugno 2021): 666. http://dx.doi.org/10.3390/min11070666.
Testo completoAbstract (sommario):
The study of the O and C isotope composition of calcite from nepheline syenites, ijolites and carbonatites of the Chik intrusion and the intrusions of the Erzin–Tarbagatay group of Sangilen (Eastern Siberia, Russia) showed derivation from alkaline melts enriched with a carbonate component from the host marbleized sedimentary rocks. The calculations showed that about 40% of the initial mass of carbonates involved in the interaction with silicate melts have remained after decarbonation. During the assimilation of the carbonate, an oxygen isotope exchange took place between the residual carbonate material and the silicate phase. Crystallization products of such hybrid magmas are carbonatite veins, calcite-rich nepheline rocks and their pegmatites with a calcite core.
5
El Howayek, Alain, Antonio Bobet e Marika Santagata. "Microstructure and cementation of two carbonatic fine-grained soils". Canadian Geotechnical Journal 56, n. 3 (marzo 2019): 320–34. http://dx.doi.org/10.1139/cgj-2018-0059.
Testo completoAbstract (sommario):
This paper presents an investigation of the microstructure and cementation of two carbonatic fine-grained soils obtained from a deposit of lacustrine origin formed during the Wisconsin glaciation. The two soils differ in the degree of cementation (with average total carbonate contents of ∼55% and ∼38%), the dominating carbonate mineral (calcite versus dolomite), and the forms of carbonates present. The study is founded on observations of the microstructure using scanning electron microscopy (SEM) equipped with energy-dispersive X-ray (EDX) spectrometry, and examination of the effects of carbonate dissolution on Atterberg limits and particle-size distribution. In both soils, the majority of the carbonate is in the form of a coating layer on the clay and silt particles, with a thickness less than 2–3 μm, and decreasing in the sample with lower carbonate content. This coating layer “networks” particles and groups of particles. Carbonate cementation impacts the engineering properties of both soils, and the site’s overconsolidation ratio (OCR) profile clearly reflects changes in carbonate content and microstructure. One-dimensional compression tests show that cementation is associated with a moderate degree of structuring, and that the resulting structure is stable, with no complete destructuration occurring even after the effective stress exceeds 10 times the preconsolidation stress.
6
Casola, Valentin, Lydéric France, Albert Galy, Nordine Bouden e Johan Villeneuve. "No evidence for carbon enrichment in the mantle source of carbonatites in eastern Africa". Geology 48, n. 10 (25 giugno 2020): 971–75. http://dx.doi.org/10.1130/g47629.1.
Testo completoAbstract (sommario):
Abstract Carbonatites are unusual, carbon-rich magmas thought to form either by the melting of a carbon-rich mantle source or by low-degree partial melting of a carbon-poor (<80 ppm C) mantle followed by protracted differentiation and/or immiscibility. Carbonate-bearing mantle xenoliths from Oldoinyo Lengai (East African Rift), the only active volcano erupting carbonatites, have provided key support for a C-rich mantle source. Here, we report unique microscale O and C isotopic analyses of those carbonates, which are present as interstitial grains in the silicate host lava, veins in the xenoliths, and pseudo-inclusions in olivine xenoliths. The δ18O values vary little, from 19‰ to 29‰, whereas δ13C values are more variable, ranging from –23‰ to +0.5‰. We show that such carbonate δ18O values result from the low-temperature precipitation of carbonate in equilibrium with meteoric water, rather than under mantle conditions. In this framework, the observed δ13C values can be reproduced by Rayleigh distillation driven by carbonate precipitation and associated degassing. Together with petrological evidence of a physical connection between the three types of carbonates, our isotopic data support the pedogenic formation of carbonates in the studied xenoliths by soil-water percolation and protracted crystallization along xenolith cracks. Our results refute a mechanism of C enrichment in the form of mantle carbonates in the mantle beneath the Natron Lake magmatic province and instead support carbonatite formation by low-degree partial melting of a C-poor mantle and subsequent protracted differentiation of alkaline magmas.
7
Clarke, M. G. C., e B. Roberts. "Carbonated melilitites and calcitized alkalicarbonatites from Homa Mountain, western Kenya: a reinterpretation". Geological Magazine 123, n. 6 (novembre 1986): 683–92. http://dx.doi.org/10.1017/s0016756800024195.
Testo completoAbstract (sommario):
AbstractHoma Mountain is a well developed ijolite/carbonatite complex of Miocene to Quaternary age. Late stage olivine melilitite occurs as a satellite plug, parts of which show strong deuteric alteration to carbonate resulting in complete pseudomorphing of the melilite.A second satellite centre exposes a grey carbonate tuff and accompanying dykes, all of which exhibit relic textures after an elongate, rectangular mineral also formerly believed to be melilite. Comparison with other recently described occurrences indicates however that the second centre erupted alkali-carbonatite and that the chief mineral originally present was nyerereite (Na2Ca(CO3)2). The field relationships and petrographic characters of both rock types are described and criteria are given which permit distinction between carbonated melilite and calcitized nyerereite. It is concluded that olivine melilitite and alkalicarbonatite are closely related in space and time.
8
Thaler, Caroline, Amandine Katz, Magali Bonifacie, Bénédicte Ménez e Magali Ader. "Oxygen isotope composition of waters recorded in carbonates in strong clumped and oxygen isotopic disequilibrium". Biogeosciences 17, n. 7 (3 aprile 2020): 1731–44. http://dx.doi.org/10.5194/bg-17-1731-2020.
Testo completoAbstract (sommario):
Abstract. Paleoenvironmental reconstructions, which are mainly retrieved from oxygen isotope (δ18O) and clumped isotope (Δ47) compositions of carbonate minerals, are compromised when carbonate precipitation occurs in isotopic disequilibrium. To date, knowledge of these common isotopic disequilibria, known as vital effects in biogenic carbonates, remains limited, and the potential information recorded by δ18O and Δ47 offsets from isotopic equilibrium values is largely overlooked. Additionally, in carbonates formed in isotopic equilibrium, the use of the carbonate δ18O signature as a paleothermometer relies on our knowledge of the paleowaters' δ18O value, which is often assumed. Here, we report the largest Δ47 offsets observed to date (as much as −0.270 ‰), measured on microbial carbonates that are strongly linked to carbonate δ18O offsets (−25 ‰) from equilibrium. These offsets are likely both related to the microorganism metabolic activity and yield identical erroneous temperature reconstructions. Unexpectedly, we show that the δ18O value of the water in which carbonates precipitated, as well as the water–carbonate δ18O fractionation dependence on temperature at equilibrium, can be retrieved from these paired δ18O and Δ47 disequilibrium values measured in carbonates. The possibility to retrieve the δ18O value of paleowaters, sediments' interstitial waters or organisms' body water at the carbonate precipitation loci, even from carbonates formed in isotopic disequilibrium, opens long-awaited research avenues for both paleoenvironmental reconstructions and biomineralization studies.
9
Алиев, А. Р., И. Р. Ахмедов, М. Г. Какагасанов e З. А. Алиев. "Колебательные спектры ионно-молекулярных кристаллов карбонатов в предпереходной области вблизи структурных фазовых переходов". Журнал технической физики 127, n. 9 (2019): 429. http://dx.doi.org/10.21883/os.2019.09.48196.104-19.
Testo completoAbstract (sommario):
Molecular relaxation processes in lithium carbonate (Li2CO3), sodium carbonate (Na2CO3) and potassium carbonate (K2CO3) were studied by Raman spectroscopy. It has been established that in crystalline carbonates Li2CO3, Na2CO3 and K2CO3, the structural phase transition of the first kind is stretched (diffuse phase transition). The existence of the pretransition region in the studied carbonates Li2CO3, Na2CO3 and K2CO3 was found.
10
Kamgaing, Théophile. "Précipitation de carbonates de cations divalents dans les systèmes lacustres : intérêt, état des connaissances des mécanismes et suggestions (Revue critique de la littérature)". Revue des sciences de l’eau 28, n. 2 (7 luglio 2015): 81–102. http://dx.doi.org/10.7202/1032292ar.
Testo completoAbstract (sommario):
Les carbonates de fer, de manganèse, de calcium et de magnésium précipités en solution des lacs sont documentés. Indicateurs de climat et de variation des caractéristiques chimiques des lacs, ils sont de plus en plus recherchés dans les sédiments. Souvent incomplets, les mécanismes de leur précipitation dans la colonne d’eau du lac et dans les eaux interstitielles sont reprécisés dans cette étude. D’après la littérature, la sidérite et la rhodochrosite précipitent en milieu réducteur saturé de carbonate de fer et de carbonate de manganèse respectivement. Ces prévisions sont confirmées dans cette étude, le potentiel redox étant un paramètre déterminant pour la précipitation du carbonate de fer. Toutefois, la littérature ne décrit pas suffisamment l’origine (géochimique ou biologique) des éléments constitutifs des solides carbonatés lacustres, encore moins les phénomènes qui stabilisent ces derniers ou les rendent vulnérables (dissolution). Cette étude apporte plus de précisions à l’endogènèse de ces carbonates, l’origine de leurs éléments constitutifs étant prise en compte. Elle montre que le caractère de l’eau (agressif ou incrustant) pourrait avoir un impact considérable sur le devenir de ces carbonates. Ainsi un dégazage forcé d’un lac rendrait ses eaux incrustantes, caractère idéal pour la précipitation des carbonates, mais néfaste à la stabilité des strates qui changent de composition après précipitation d’espèces chimiques. Par conséquent, tout projet de dégazage de lac devrait prendre en considération ce paramètre (caractère de l’eau) dans sa conception, sa mise en oeuvre et son exploitation.
11
Weidner, Victoria L., Molly C. Carney, Demetra V. Schermerhorn, Jill D. Pasteris e Claude H. Yoder. "A-type substitution in carbonated strontium fluor-, chlor- and hydroxylapatites". Mineralogical Magazine 79, n. 2 (aprile 2015): 399–412. http://dx.doi.org/10.1180/minmag.2015.079.2.17.
Testo completoAbstract (sommario):
AbstractCarbonated strontium fluor-, hydroxyl- and chlorapatites (carbonated Sr10(PO4)6X2 = CSrApX, where X= OH, Cl and F) were synthesized in aqueous solution. The substitution mode of carbonate was determined from infrared (IR) stretching frequencies for carbonate and from the variation in unit-cell axial lengths as a function of carbonate content. The a-axis lengths of CSrApF and CSrApCl decrease, whereas the a-axis length of CSrApOH increases slightly with increasing carbonate substitution. The carbonate IR stretching region from ∼1390 to 1590 cm–1 contains two doublets for both CSrApOH and CSrApCl, indicating the presence of both A- and B-type carbonate. The carbonate spectral region for CSrApF is reminiscent of that for CCaApF, which contains one doublet for B-type carbonate with a small shoulder attributable to A-type carbonate. Activity-based Ksp values (assuming B-type substitution) were determined for all three series of carbonated Sr apatites and show that the solubilities of CSrApOH and CSrApCl increase at higher carbonate values, whereas those of CSrApF stay constant. The Ksp values for uncarbonated SrApOH, SrApCl and SrApF were determined by extrapolation to zero percent carbonate (10–120, 10–112 and 10–113 for SrApOH, SrApCl and SrApF, respectively).
12
Chandra, Jyoti, Debajyoti Paul, Andreas Stracke, François Chabaux e Mathieu Granet. "The Origin of Carbonatites from Amba Dongar within the Deccan Large Igneous Province". Journal of Petrology 60, n. 6 (3 maggio 2019): 1119–34. http://dx.doi.org/10.1093/petrology/egz026.
Testo completoAbstract (sommario):
Abstract There are disparate views about the origin of global rift- or plume-related carbonatites. The Amba Dongar carbonatite complex, Gujarat, India, which intruded into the basalts of the Deccan Large Igneous Province (LIP), is a typical example. On the basis of new comprehensive major and trace element and Sr–Nd–Pb isotope data, we propose that low-degree primary carbonated melts from off-center of the Deccan–Réunion mantle plume migrate upwards and metasomatize part of the subcontinental lithospheric mantle (SCLM). Low-degree partial melting (∼2%) of this metasomatized SCLM source generates a parental carbonated silicate magma, which becomes contaminated with the local Archean basement during its ascent. Calcite globules in a nephelinite from Amba Dongar provide evidence that the carbonatites originated by liquid immiscibility from a parental carbonated silicate magma. Liquid immiscibility at crustal depths produces two chemically distinct, but isotopically similar magmas: the carbonatites (20% by volume) and nephelinites (80% by volume). Owing to their low heat capacity, the carbonatite melts solidified as thin carbonate veins at crustal depths. Secondary melting of these carbonate-rich veins during subsequent rifting generated the carbonatites and ferrocarbonatites now exposed at Amba Dongar. Carbonatites, if formed by liquid immiscibility from carbonated silicate magmas, can inherit a wide range of isotopic signatures that result from crustal contamination of their parental carbonated silicate magmas. In rift or plume-related settings, they can, therefore, display a much larger range of isotope signatures than their original asthenosphere or mantle plume source.
13
Sieber, Melanie J., Max Wilke, Oona Appelt, Marcus Oelze e Monika Koch-Müller. "Melting relations of Ca–Mg carbonates and trace element signature of carbonate melts up to 9 GPa – a proxy for melting of carbonated mantle lithologies". European Journal of Mineralogy 34, n. 5 (6 ottobre 2022): 411–24. http://dx.doi.org/10.5194/ejm-34-411-2022.
Testo completoAbstract (sommario):
Abstract. The most profound consequences of the presence of Ca–Mg carbonates (CaCO3–MgCO3) in the Earth's upper mantle may be to lower the melting temperatures of the mantle and control the melt composition. Low-degree partial melting of a carbonate-bearing mantle produces CO2-rich, silica-poor melts compositionally imposed by the melting relations of carbonates. Thus, understanding the melting relations in the CaCO3–MgCO3 system facilitates the interpretation of natural carbonate-bearing silicate systems. We report the melting relations of the CaCO3–MgCO3 system and the partition coefficient of trace elements between carbonates and carbonate melt from experiments at high pressure (6 and 9 GPa) and temperature (1300–1800 ∘C) using a rocking multi-anvil press. In the absence of water, Ca–Mg carbonates are stable along geothermal gradients typical of subducting slabs. Ca–Mg carbonates (∼ Mg0.1–0.9Ca0.9–0.1CO3) partially melt beneath mid-ocean ridges and in plume settings. Ca–Mg carbonates melt incongruently, forming periclase crystals and carbonate melt between 4 and 9 GPa. Furthermore, we show that the rare earth element (REE) signature of Group-I kimberlites, namely strong REE fractionation and depletion of heavy REE relative to the primitive mantle, is resembled by carbonate melt in equilibrium with Ca-bearing magnesite and periclase at 6 and 9 GPa. This suggests that the dolomite–magnesite join of the CaCO3–MgCO3 system might be useful to approximate the REE signature of carbonate-rich melts parental to kimberlites.
14
Demény, Attila, László Rinyu, Péter Németh, György Czuppon, Nóra Enyedi, Judit Makk, Szabolcs Leél-Őssy, Dóra Kesjár e Ivett Kovács. "Bacterial and abiogenic carbonates formed in caves–no vital effect on clumped isotope compositions". PLOS ONE 16, n. 1 (25 gennaio 2021): e0245621. http://dx.doi.org/10.1371/journal.pone.0245621.
Testo completoAbstract (sommario):
Speleothems (dominated by cave-hosted carbonate deposits) are valuable archives of paleoclimate conditions. As such, they are potential targets of clumped isotope analyses that may yield quantified data about past temperature variations. Clumped isotope analyses of stalagmites, however, seldom provide useful temperature values due to various isotope fractionation processes. This study focuses on the determination of the microbially induced vital effect, i.e., the isotope fractionation processes related to bacterial carbonate production. A cave site with biologically mediated amorphous calcium carbonate precitation was selected as a natural laboratory. Calcite deposits were farmed under a UV lamp to prevent bacterial activity, as well as under control conditions. Microbiological analyses and morphological investigations using scanning electron microscopy showed that the UV lamp treatment effectively reduced the number of bacterial cells, and that bacterial carbonate production strongly influenced the carbonate’s morphology. Stable oxygen isotope analyses of calcite and drip waters, as well as clumped isotope measurements revealed that, although most of the studied carbonates formed close to oxygen isotope equilibrium, clumped isotope Δ47 values varied widely from equilibrium to strongly fractionated data. Site-specific kinetic fractionations played a dominant role in the distribution of Δ47 values, whereas bacterial carbonate production did not result in a detectable clumped isotope effect.
15
Karrow, P. F., e R. S. Geddes. "Drift carbonate on the Canadian Shield". Canadian Journal of Earth Sciences 24, n. 2 (1 febbraio 1987): 365–69. http://dx.doi.org/10.1139/e87-036.
Testo completoAbstract (sommario):
Carbonates occur in the drift over large areas of the Precambrian Shield in Ontario. Paleozoic carbonates were transported by glaciers from the Hudson Bay Lowland and from Manitoba. Local sources in Precambrian rocks also contribute carbonate. A carbonate line corresponding approximately to the Nipigon and Chapleau moraines delimits high–carbonate drift to the north and may represent a significant ice marginal position or readvance about 9500 BP.Shield drift carbonates suggest that there are potential errors in radiocarbon dating of fine organic sediment (old carbon error); that there is a relationship between the occurrence of fossil molluscs in glacial and postglacial lake deposits and drift carbonate distribution; that long-distance transport will affect drift prospecting; and that susceptibility to acidification of lakes is affected by both drift and bedrock composition.
16
Kovaleva, Elena, Maxim Shabanov, Valery Putlyaev, Yury Tretyakov, Vladimir Ivanov e Nikolay Silkin. "Bioresorbable carbonated hydroxyapatite Ca10−xNax(PO4)6−x(CO3)x(OH)2 powders for bioactive materials preparation". Open Chemistry 7, n. 2 (1 giugno 2009): 168–74. http://dx.doi.org/10.2478/s11532-009-0018-y.
Testo completoAbstract (sommario):
AbstractThe purpose of this work was to find and investigate a correlation between the carbonate ion content in crystalline lattice and defect structure, and solubility of the materials; finally, to prepare the materials under study for in vitro tests. Various techniques, such as XRD, FTIR, TEM, FESEM/EDX, TG/DTA, AES (ICP), wet chemical analysis, Ca-ionometry, microvolumetric analysis of evolved CO2, BET adsorption, were applied to determine the efficiency of carbonate substitution, and to quantify the elemental composition, as well as to characterize the structure of the carbonated hydroxyapatite and the site(s) of carbonate substitution,. It was shown that AB-type substitution prevails over other types with the carbonate content increase. According to in vitro tests, the bioactivity of the samples is correlated with the carbonate content in carbonate-doped hydroxyapatite due to accumulation of defects in carbonated hydroxyapatite nanocrystals.
17
Shaikh, Abbas Alli G., e Swaminathan Sivaram. "Dialkyl and diaryl carbonates by carbonate interchange reaction with dimethyl carbonate". Industrial & Engineering Chemistry Research 31, n. 4 (aprile 1992): 1167–70. http://dx.doi.org/10.1021/ie00004a028.
Testo completo
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Sønju Clasen, A. B., e I. E. Ruyter. "Quantitative Determination of Type A and Type B Carbonate in Human Deciduous and Permanent Enamel by Means of Fourier Transform Infrared Spectrometry". Advances in Dental Research 11, n. 4 (novembre 1997): 523–27. http://dx.doi.org/10.1177/08959374970110042101.
Testo completoAbstract (sommario):
Caries progression has been shown to be faster in the deciduous than in the permanent dentition. Several factors influence caries progression. Among these are variations in the chemical composition of the two enamel types. The carbonate ion is known to occupy two different positions in the hydroxyapatite structure of the enamel, the hydroxide position (A) and the phosphate position (B). Carbonate may be of different chemical importance in the two lattice positions. In the present study, a quantitative determination of the carbonate in the two different positions (type A and type B) in deciduous and permanent enamel was performed by FTIR spectrometry. Calibration curves, made with synthesized hydroxyapatites with carbonates in either position, were used to determine the quantity of type A and type B carbonates in both enamel types. The deciduous enamel contained significantly more type A carbonate than permanent enamel. The total carbonate content (sum of type A and type B carbonates) was also significantly higher in deciduous than in permanent enamel. TG analysis of enamel samples confirmed the quantitative carbonate determinations by FTIR spectrometry. The difference in carbonate content between deciduous and permanent enamel may be one of several factors contributing to faster caries progression in deciduous teeth.
19
Harbar, Vladyslav, e Andriy Lisovskiy. "Carbonations and carbonate profile forming processes of rendzinas of the Podilski Tovtry". Visnyk of the Lviv University. Series Geography, n. 51 (27 dicembre 2017): 88–97. http://dx.doi.org/10.30970/vgg.2017.51.8741.
Testo completoAbstract (sommario):
The peculiarities of content and profile distribution of carbonates in rendzinas and soil-forming rocks of the Podilski Tovtry are investigated. It has been determined that the predominant process of weathering of carbonate rocks is a chemical dissolution, in which carbonates are converted into bicarbonates and, in the case of washing water regime, are applied from the soil (the process of decarbonization) and mechanical grinding and destruction of the remaining carbonate inclusions in the process of soil cultivation. The dissolution of carbonate rocks causes accumulation in the soil profile of an insoluble residue, the intensity of which depends on the composition of carbonate rocks, the rate of filtration of aqueous solutions, their aggressiveness and the concentration of destructive substances. The most intensive such accumulation occurs in acidic medium, at a low rate of infiltration of solutions and at high concentrations of CO2. It was established that the highest proportion of CaCO3 is characterized by lithotamium limestone (up to 90–93 %), and the lowest – carbonate polygenetic loams (up to 35–40 %). The feature of the profile distribution of the content of carbonates in rendzinas is its gradual growth in the upper part of the soil profile and rapid in the middle and lower parts. It is determined that the rendzinas of the Podilski Tovtry carbonates are represented predominantly in the form of wreckage of initial soil-forming rocks of different sizes and shapes, as well as amorphous solid-phase crude and finely dispersed products of weathering in the form of powdery and powdery carbonate dusting. It is established that in dense crystallized lithotamium limestones of the main strand, the carbonate mass weakly passes moisture, and the main process of weathering occurs due to surface corrosion. The accumulation of secondary carbonates in the form of mycelium and veins is characteristic on the slopes of the Tovtry (mostly in brown rendzinas and pararendzinas), due to the vertical and lateral migration flows of the dissolved forms of CaCO3. Key words: rendzinas, Podilski Tovtry, carbonates, carbonate profile.
20
Yin, Gongming, Chunru Liu, Renmao Yuan, Fei Han, Rui Ding e Jean-Jacques Bahain. "ESR Chronology of Bedrock Fault Activity in Carbonate Area: Preliminary Results from the Study of the Lijiang-Xiaojinhe Fault, Southeastern Tibet, China". Geochronometria 48, n. 1 (1 gennaio 2021): 215–21. http://dx.doi.org/10.2478/geochr-2020-0033.
Testo completoAbstract (sommario):
Abstract Carbonated rocks constitute one of the main lithologies of the southeastern Tibet area, China, a tectonically very active zone. However, due to the lack of suitable dating materials, it is difficult to carry out chronological studies of the local tectonic evolution in such carbonate areas. In the present study, electron spin resonance (ESR) method had been applied on the dating of carbonates heated during fault activity of the Lijiang-Xiaojinhe (LX) Fault, an important active fault located in the northwest of Yunnan Province. Clear displaced landforms show that the fault has undergone strong late-Quaternary activity. During the fault activity, the heat produced by friction lead to the melting of the frictional surface of the rocks, and the melting can attenuate or zero the ESR dating signal of carbonate. The aim of the present paper was to check the ability of carbonate use to chronologically identify fault activity using electron spin resonance (ESR) method. The results showed the last fault activity of the LX fault was dated by ESR about 2.0±0.2 ka ago, in agreement with historical and radiocarbon data. Hence ESR can be if necessary a practicable dating alternative method for the study of fault activity chronology in carbonate rock area.
21
Arefiev, Anton V., Anton Shatskiy, Altyna Bekhtenova e Konstantin D. Litasov. "Phonolite-Carbonatite Liquid Immiscibility at 3–6 GPa". Minerals 13, n. 3 (20 marzo 2023): 443. http://dx.doi.org/10.3390/min13030443.
Testo completoAbstract (sommario):
Liquid immiscibility plays an important role in the formation of carbonatites and associated alkaline Si-undersaturated magmas. Experiments in the sodium carbonate-aluminosilicate systems suggest that the carbonate-silicate miscibility gap is limited by crustal and shallow mantle pressures (up to 2.5 GPa). Unlike in the potassium-rich carbonate-aluminosilicate systems, the carbonate-silicate miscibility gap was established at pressures of 3.5–6 GPa. It is therefore interesting to elucidate the immiscibility range under intermediate pressures, corresponding to 100–200 km depths. Here we conducted experiments over 3–6 GPa and 1050–1500 °C in the systems corresponding to immiscible melts obtained by partial melting of carbonated pelite (DG2) at 6 GPa and 1200 °C. We found that partial melting begins with the alkali-rich carbonatite melt, while immiscible phonolite melt appears over 1050–1200 °C at 3 GPa, 1200 °C at 4.5 GPa, and 1200–1500 °C at 6 GPa. As pressure decreases from 6 to 3 GPa, Na becomes less compatible, and the concentration of the jadeite component in clinopyroxene decreases by a factor of 1.5–6. As a result, the compositions of the immiscible phonolite and carbonatite melts evolve from ultrapotassic (K2O/Na2O weight ratio = 10–14) resembling silicic and carbonatitic micro-inclusions in diamonds from kimberlites and placers worldwide to moderately potassic (K2O/Na2O = 1–2), which may correspond to phonolitic and associated carbonatitic melts of the spinel facies of the shallow mantle.
22
Wöckel, L., A. Seifert, C. Mende, I. Roth-Panke, L. Kroll e S. Spange. "Resin and carbon foam production by cationic step-growth polymerization of organic carbonates". Polymer Chemistry 8, n. 2 (2017): 404–13. http://dx.doi.org/10.1039/c6py01572g.
Testo completoAbstract (sommario):
Acid induced step-growth polymerizations of bis(p-methoxybenzyl) carbonate (pMBC), bis(m-methoxybenzyl) carbonate (mMBC) and difurfuryl carbonate (DFC) have been performed to produce resin-foams, because controlled release of carbon dioxide takes place during polymerization of those organic carbonates.
23
Indran, Vidhyaa Paroo, Anisah Sajidah Haji Saud, Gaanty Pragas Maniam, Mashitah Mohd Yusoff, Yun Hin Taufiq-Yap e Mohd Hasbi Ab. Rahim. "Versatile boiler ash containing potassium silicate for the synthesis of organic carbonates". RSC Advances 6, n. 41 (2016): 34877–84. http://dx.doi.org/10.1039/c5ra26286k.
Testo completoAbstract (sommario):
Boiler ash containing potassium silicate (BA 900) and potassium silicate (K2SiO3) were proven to be feasible Lewis acid catalysts for the synthesis of different organic carbonates (glycerol carbonate, ethylene carbonate, and propylene carbonate).
24
Wang, Dunling, e Darwin W. Anderson. "Pedogenic carbonate in Chernozemic soils and landscapes of southeastern Saskatchewan". Canadian Journal of Soil Science 80, n. 2 (1 maggio 2000): 251–61. http://dx.doi.org/10.4141/s99-063.
Testo completoAbstract (sommario):
The objective of this study was to characterize soil carbonates and estimate their accumulation by using a method based on δ13C values of soil carbonate in pedons and landscapes. Dark Brown Chernozem soils of the Amulet Association (with mixed C3 and C4 plants) and native Black Chernozem soils of the Oxbow Association (with a pure C3 plants) were included. Six soil samples representing the Cca and Ck horizons of the Oxbow and Amulet Associations were chosen for detailed pedogenic carbonate studies, which include particle size fractionation, mineralogical identification, surface morphology examination, and stable carbon isotopic compositions analysis on the particle size fractions.X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses of the fractionated particle sizes indicated that dolomite dominates the carbonate occurring in the Ck horizons, and is mainly in medium and coarse silt fractions. In the Cca horizons, carbonate in clay and fine silt fractions is mostly calcite, whereas dolomite dominates the carbonates in medium and coarse silt fractions. Calcitic coatings on the surfaces of both silt and sand particles were observed. Stable carbon isotope ratio (δ13Cvalue) of carbonate was −8‰ in the clay fraction of Cca horizons in which carbonate is dominated by calcite. Carbonate in the fine particle size fractions of the Cca horizons is dominated by calcite and has the most depleted δ13C values, indicating that pedogenic carbonate occurs as calcite and mainly in the fine particle size fractions. In contrast, carbonates from coarse silts of Ck horizons were composed solely of dolomite and had the most enriched δ13C values (−1.1 to −1.4‰), a character of lithogenic carbonate. On a landscape basis, carbonate occurs mainly in the Cca horizons in mid- and upper slope soils as a result of moisture movement and ground water fluxes. Soils in the depressions were more leached and contained small amounts of carbonate, mostly in the 60- to 90-cm depth. Calculations from the δ13C values of soil carbonates indicate that about 50–68% of the carbonate in the Cca horizons of middle slope soils is of pedogenic origin, which is equivalent to a CaCO3 storage of 136–188 kg m−2. In contrast, 5 to 39% (0–36 kg m−2 CaCO3) of carbonate stored in the lower slope soils is of pedogenic origin. Thirty-one to fifty percent of the carbonate (equivalent to 100–134 kg m CaCO3) in upper slope soils is of pedogenic origin. Key words: Carbonate, pedogenic, calcite, dolomite, δ13C value, XRD, SEM, landscape
25
Zhu, Qing Xia, Wei Hui Jiang, Chuan Shao e Yi Bao. "Thermophysical and Mechanical Properties of Carbonated Hydroxyapatite". Key Engineering Materials 512-515 (giugno 2012): 989–93. http://dx.doi.org/10.4028/www.scientific.net/kem.512-515.989.
Testo completoAbstract (sommario):
The carbonated hydroxyapatite (CHA) was synthesized by precipitation-calcination method. The influences of carbonate subsitution on high-temperature sintering, thermal expansion coefficient (CET) and flexural strength were investigated by the high-temperature dilatometer, scanning electron microscopy (SEM) and universal testing machine. The results showed that the sintering temperatures of CHA were related to the initial carbonate contents. The sintering temperature decreased with increasing initial carbonate contents. The CET of CHAs decreased with the increase of carbonate content, due to the stoma caused by the partially decompostion of CHAs. The CHA ceramics tested were as strong in flexure strength when compared to non-carbonated hydroxyapatite.
26
Geluk, M. C. "Late Permian (Zechstein) carbonate-facies maps, the Netherlands". Netherlands Journal of Geosciences - Geologie en Mijnbouw 79, n. 1 (marzo 2000): 17–27. http://dx.doi.org/10.1017/s0016774600021545.
Testo completoAbstract (sommario):
AbstractThe Late Permian Zechstein carbonates in the Southern Permian Basin were deposited under marine conditions. The carbonates form part of a largely progradational infill, with a gradual northward facies shift. The paleogeography of the Zechstein carbonate deposits has been reviewed recently on the base of well data, cores and publications. This has resulted in three updated maps of the carbonate units. These maps reflect the increase in knowledge of the palaeogeography of the Zechstein as a result of several decades of subsurface exploration. It is found that deposition of the carbonates was controlled by various factors, i.e., rifting during deposition of the basal Zechstein, sea-level fluctuations and basin subsidence. This resulted in an overall E-W orientated facies distribution in the Zechstein carbonates, and in the gradual northward shift of the various facies belts in time.Reefs in the Zl Carbonate Member and off-platform highs and turbidites in the Z2 Carbonate Member have been identified as potential future exploration targets.
27
Zhou, Jiancheng, Wu Dongfang, Birong Zhang e Yali Guo. "Synthesis of propylene carbonate from urea and 1,2-propylene glycol over metal carbonates". Chemical Industry and Chemical Engineering Quarterly 17, n. 3 (2011): 323–31. http://dx.doi.org/10.2298/ciceq101123018z.
Testo completoAbstract (sommario):
A series of single-metal carbonates and Pb-Zn mixed-metal carbonates were prepared as catalysts for alcoholysis of urea with 1,2-propylene glycol (PG) for the synthesis of propylene carbonate (PC). The mixed carbonates all show much better catalytic activities than the single carbonates, arising from a strong synergistic effect between the two crystalline phases, hydrozincite and lead carbonate. The mixed carbonate with Pb/Zn=1:2 gives the highest yield of PC, followed by the mixed carbonate with Pb/Zn=1:3. Furthermore, Taguchi method was used to optimize the synthetic process for improving the yield of PC. It is shown that the reaction temperature is the most significant factor affecting the yield of PC, followed by the reaction time, and that the optimal reaction conditions are the reaction time at 5 hours, the reaction temperature at 180 oC and the catalyst amount at 1.8 wt%, resulting in the highest PC yield of 96.3%.
28
Wei, Jiangong, Tingting Wu, Wei Zhang, Yinan Deng, Rui Xie, Junxi Feng, Jinqiang Liang, Peixin Lai, Jianhou Zhou e Jun Cao. "Deeply Buried Authigenic Carbonates in the Qiongdongnan Basin, South China Sea: Implications for Ancient Cold Seep Activities". Minerals 10, n. 12 (17 dicembre 2020): 1135. http://dx.doi.org/10.3390/min10121135.
Testo completoAbstract (sommario):
Cold seep carbonates are important archives of pore water chemistry and ancient methane seepage activity. They also provide an important contribution to the global carbon sink. Seep carbonates at three sediment layers (3.0, 52.1, and 53.6 mbsf) were collected at site W08B in the Qiongdongnan Basin of the South China Sea. This study investigated the mineralogy, microstructure, stable carbon and oxygen isotopes, trace elements, and U-Th dates of these carbonates to identify the relationship between methane flux and authigenic carbonate precipitation. The results showed that the δ13C and δ18O values of all carbonates are similar, indicating that the carbon source for shallow carbonates and deep carbonates has remained constant over time and included biogenic and thermogenic methane. Although carbonates were found in three sediment layers, the two main stages of methane seepage events were discernible, which was likely caused by the dissociation of gas hydrates. The first methane seep took place at 131.1–136.3 ka BP. During a dramatic drop in the sea level, the seep carbonate at 52.1 mbsf formed at 136.3 ka BP through the anaerobic oxidation of methane (AOM). The carbonate at 53.6 mbsf resulted from the vertical downward movement of the sulfate-methane transition zone with decreasing methane flux at 131.1 ka BP. This is the reason for the age of carbonates at 52.1 mbsf being older than the age of carbonates at 53.6 mbsf. The second methane seep took place at 12.2 ka BP. Shallow carbonate formed at that time via AOM and is now located at 3 mbsf. Moreover, thin-section photomicrographs of deep carbonate mainly consisted of matrix micrite and biological debris and acicular aragonite occurred as vein cement filling the pore spaces between the matrix micrite. The acicular aragonite was mainly influenced by the timing of the carbonate precipitation of minerals. This research identified a long history of methane seep activity reflected by the vertical distribution of carbonates.
29
Glazov, I. E., V. K. Krut’ko, O. N. Musskaya e A. I. Kulak. "Stabilization of the amorphous state of calcium carbonate-phosphates with phosphate ions". Doklady of the National Academy of Sciences of Belarus 66, n. 5 (3 novembre 2022): 501–8. http://dx.doi.org/10.29235/1561-8323-2022-66-5-501-508.
Testo completoAbstract (sommario):
Amorphous calcium carbonate-phosphate with a Ca/P ratio of 1.83 was precipitated from Ca2+, Ca2+, PO3–4, CO2-3 − containing solutions at pH 10 and stabilized by ethanol dehydration and followed by heating at 400 °C. The presence of PO3–4 ions in the structure of amorphous calcium carbonate-phosphate provides its increased resistance to transformation into crystalline phases. Aging in a Ca2+, PO3–4 , CO2-3 − containing mother solution at pH 10 for 4 days promotes the transformation of amorphous calcium carbonate-phosphate into amorphous calcium carbonate-phosphate / carbonated hydroxyapatite / calcite. The combined effect of PO3–4 и CO2-3 − ions in the aquatic environment on the crystallization of amorphous calcium carbonate-phosphate into carbonated hydroxyapatite contributes to a maximum stabilization of the amorphous state that provides a high extent of bioactivity.
30
Bright, Jordon, Chris Ebert, Matthew A. Kosnik, John R. Southon, Katherine Whitacre, Paolo G. Albano, Carola Flores et al. "COMPARING DIRECT CARBONATE AND STANDARD GRAPHITE 14C DETERMINATIONS OF BIOGENIC CARBONATES". Radiocarbon 63, n. 2 (19 gennaio 2021): 387–403. http://dx.doi.org/10.1017/rdc.2020.131.
Testo completoAbstract (sommario):
ABSTRACTThe direct carbonate procedure for accelerator mass spectrometry radiocarbon (AMS 14C) dating of submilligram samples of biogenic carbonate without graphitization is becoming widely used in a variety of studies. We compare the results of 153 paired direct carbonate and standard graphite 14C determinations on single specimens of an assortment of biogenic carbonates. A reduced major axis regression shows a strong relationship between direct carbonate and graphite percent Modern Carbon (pMC) values (m = 0.996; 95% CI [0.991–1.001]). An analysis of differences and a 95% confidence interval on pMC values reveals that there is no significant difference between direct carbonate and graphite pMC values for 76% of analyzed specimens, although variation in direct carbonate pMC is underestimated. The difference between the two methods is typically within 2 pMC, with 61% of direct carbonate pMC measurements being higher than their paired graphite counterpart. Of the 36 specimens that did yield significant differences, all but three missed the 95% significance threshold by 1.2 pMC or less. These results show that direct carbonate 14C dating of biogenic carbonates is a cost-effective and efficient complement to standard graphite 14C dating.
31
Azdarpour, Amin, Radzuan Junin, Mohammad Asadullah, Hossein Hamidi, Muhammad Manan e Ahmad Rafizan Mohamad Daud. "Calcium Carbonate Production through Direct Mineral Carbon Dioxide Sequestration". Applied Mechanics and Materials 699 (novembre 2014): 1020–25. http://dx.doi.org/10.4028/www.scientific.net/amm.699.1020.
Testo completoAbstract (sommario):
Mineral carbon dioxide sequestration provides a leakage free and permanent method of CO2 disposal to produce environmentally benign and stable solid carbonates. FGD gypsum as a source of calcium was proposed as the potential feedstock in this study. The purpose of this laboratory study was to investigate the effects of reaction parameters such as CO2 pressure, reaction temperature, particle size, and ammonia solution concentration on calcium carbonate purity through Merseburg process. Increasing the reaction temperature as well as the pressure was very effective in improving the calcium carbonate purity. High purity calcium carbonate was produced when reaction temperature and CO2 was increased to 400 °C and 70 bar, resulting in 93% and 94% purity, respectively. Experimental results showed that reducing particle size was also effective in enhancing the calcium carbonate purity in which the smallest particles produced higher purity calcium carbonates rather than larger particles. The role of ammonia solution on calcium carbonate purity was found to be beneficial in improving the calcium carbonate purity in which increasing the ammonia solution increased calcium carbonate purity significantly in all experiments.
32
Marinkovic, Goran, Petar Papic, Jana Stojkovic e Veselin Dragisic. "Factors contributing to the formation of carbonated mineral water systems in Serbia". Annales g?ologiques de la Peninsule balkanique, n. 73 (2012): 117–24. http://dx.doi.org/10.2298/gabp1273117m.
Testo completoAbstract (sommario):
There are more than 65 occurrences of carbonated mineral water (CMW) within the territory of Serbia. More than 93 % of these systems are found in the geotectonic unit referred to as the Vardar Zone and on the fringes of nearby units. To the east, west and north of the Vardar Zone, CMWs are either rare or nonexistent. The area featuring CMWs is characterized by Tertiary magmatism, a complex geology and deep neotectonic structures. Based on ?13C values of CO2 and HCO3 - in several CMWs in Serbia, and also in carbonates and CO2 from liquid inclusions in several hydrothermal deposits around the world, it was concluded that CO2 in the lithosphere of Serbia could originate from hydrothermal carbonates, and carbonates from sedimentary, metamorphic and magmatic rocks. The findings clearly showed that the main generators of CO2 are located in the Vardar Zone and that CO2 degasification is accomplished through temperature metamorphosis of carbonates (dolomite, calcite). Based on the carbonate transformation temperatures and the temperature conditions in the lithosphere of Serbia, the CO2 might be the result of temperature-induced carbonate transformation below a depth of 3 km. Therefore, the conclusion of the study of CMWs in Serbia is that the formation of CMW systems in the lithosphere depends on the geochemical, temperature, and the magmatic and structural-neotectonic conditions.
33
Sun, Yuedong, Jörn Peckmann, Yu Hu, Xudong Wang, Shanggui Gong, Yongbo Peng, Duofu Chen e Dong Feng. "Formation of Tubular Carbonates within the Seabed of the Northern South China Sea". Minerals 10, n. 9 (29 agosto 2020): 768. http://dx.doi.org/10.3390/min10090768.
Testo completoAbstract (sommario):
A remarkable exposure of tubular authigenic carbonates was found on the seafloor in the Dongsha area of the South China Sea (SCS). The tubular carbonates, around 2–3 cm in diameter and usually less than 10 cm in length, represent broken fragments of once-larger pipes that now protrude from muddy sediments. The morphology, carbon and oxygen stable isotope compositions, and trace and rare earth element contents of the carbonates were analyzed to decipher the mode of carbonate formation. The tubular carbonates exhibit a dark brown coating of iron and manganese hydrous oxides, indicating prolonged exposure to oxic bottom waters. The carbonate content of the micritic pipes falls between 12.5 and 67.3 wt.% with an average of 42.0 wt.%, suggesting formation within the sediment. This inference is supported by trace and rare earth element patterns including a moderate enrichment of middle rare earth elements. Low δ13C values (as low as −50.3‰, Vienna Pee Dee Belemnite (VPDB)) suggest that carbonate precipitation was induced by the anaerobic oxidation of methane. The unusually positive δ18O values of the carbonates (as high as +5.3‰, VPDB) are believed to reflect the destabilization of locally abundant gas hydrate. Taken together, it is suggested that pipe formation was initiated by sediment-dwelling organisms, such as crustaceans or bivalves. The burrows subsequently acted as conduits for upward fluid migration. The lithification of the sediment directly surrounding the conduits and the partial filling of the conduits with carbonate cement resulted in the formation of tubular carbonates. Turbidity currents, sediment slumps, or the vigorous emission of fluids probably induced the fragmentation of tubular carbonates within the sediment. The carbonate fragments had been further subjected to winnowing by bottom currents. This study provides insight into the interaction of megafauna burrowing with fluid migration and carbonate formation at hydrocarbon seeps, highlighting the role of bottom currents and mass wasting on the formation of fragmented tubular carbonates.
34
Ren, Fu Zeng, e Yang Leng. "Carbonated Apatite, Type-A or Type-B?" Key Engineering Materials 493-494 (ottobre 2011): 293–97. http://dx.doi.org/10.4028/www.scientific.net/kem.493-494.293.
Testo completoAbstract (sommario):
Carbonated apatite, the basic mineral component in human hard tissues and an important bioceramic material, has been extensively studied. However, its atomic arrangements in apatite crystal structure and its experimental characterization are still not lack of debating. We analyzed infrared (IR) vibrational spectroscopy for carbonated apatite determinations, by comparatively studying the IR spectra of hydroxyapatite and of surface carbonate absorption, biological apatites (human enamel, human cortical bone, and two animal bones) and carbonated apatite. The carbonated apatite samples were sythesized by various methods, including precipitation method, hydrothermal reaction and solid-gas reaction at high temperature. The comparative study indicates that the bands at ~880 cm-1, ~1413 cm-1, and ~1450 cm-1 should not be used to identify carbonated apatite since they may result from carbonate absorption on surfaces of apatite crystals or separated carbonate phase present with apatite crystals. The IR characteristic bands of carbonate substitution in apatites should be: ν3 at ~1465 cm-1 for type-B (CO3 substituting for PO4) and ν3 band at ~1546 cm-1 for type A (CO3 substituting for OH). These signature IR bands are further confirmed by the ab initio simulations.
35
Bhatt, Mahesh Datt, Maenghyo Cho e Kyeongjae Cho. "Density functional theory calculations for the interaction of Li+ cations and PF6– anions with nonaqueous electrolytes". Canadian Journal of Chemistry 89, n. 12 (dicembre 2011): 1525–32. http://dx.doi.org/10.1139/v11-131.
Testo completoAbstract (sommario):
The interaction of lithium (Li+) cation and hexafluorophosphate (PF6–) anion with nonaqueous electrolytes is studied by using density functional theory at the B3LYP/6–311++G(d,p) level in the gas phase in terms of the coordination of Li+ and PF6– with these solvents. Ethylene carbonate (EC) coordinates with Li+ and PF6– most strongly and reaches the anode and cathode most easily because of its highest dielectric constant among all the solvent molecules, resulting in its preferential reduction on the anode and oxidation on the cathode. For cyclic carbonates EC and propylene carbonate (PC), the structure Li+(S)4 is found to be the most stable. However, for linear carbonates dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), the formation of PF6–(S)n=1–3 is not favorable. Such analysis may be useful in applications for lithium ion batteries.
36
Patel, Ashim Kumar, Biswajit Mishra, Dewashish Upadhyay e Kamal Lochan Pruseth. "Mineralogical and Geochemical Evidence of Dissolution-Reprecipitation Controlled Hydrothermal Rare Earth Element Mineralization in the Amba Dongar Carbonatite Complex, Gujarat, Western India". Economic Geology 117, n. 3 (1 maggio 2022): 683–702. http://dx.doi.org/10.5382/econgeo.4890.
Testo completoAbstract (sommario):
Abstract The Amba Dongar carbonatite complex in western India comprises an inner ring of carbonatite breccia surrounded by a sövite ring dike. The various carbonatite units in the body include calcite carbonatite, alvikite, dolomite carbonatite, and ankerite carbonatite. The carbonate phases (calcite and ankerite) occur as phenocrysts, groundmass phases, fresh primary grains, and partially altered grains and/or pseudomorphs when hydrothermally overprinted. Rare earth element (REE) enrichment in the groundmass/altered calcite grains compared to the magmatic ones is ascribed to the presence of micron-sized REE phases. Fluorapatite and pyrochlore constitute important accessory phases that are altered to variable extents. Higher concentrations of Sr, Si, and REEs in fluorapatite are suggestive of a magmatic origin. Fresh pyrochlore preserves its magmatic composition, characterized by low A-site vacancy and high F in the Y-site, which on alteration becomes poorer in Na, Ca, and F and displays an increase in vacancy. The C-O isotope compositions of the carbonates also corroborate the extensive low-temperature hydrothermal alteration of the carbonatites. The REE mineralization is the result of interaction of the carbonatite with a sulfur-bearing, F-rich hydrothermal fluid that exsolved from late-stage carbonatitic magmas. The hydrothermal fluids caused dissolution of the primary carbonates and simultaneous precipitation of REEs and other high field strength element (HFSE)-bearing minerals. Complex spatial associations of the magmatic minerals with the REE fluorocarbonates, [synchysite-(Ce), parisite-(Ce), bastnäsite-(Ce)] and florencite-(Ce) point to the formation of these REE phases as a consequence of postmagmatic hydrothermal dissolution of the REEs from fluorapatite, pyrochlore, and carbonates. Ubiquitous association of fluorite and barite with REE minerals indicates transport of REEs as sulfate complexes in F-rich fluids. Precipitation of REE fluorocarbonates/florencite resulted from fluid-carbonate interaction, concomitant increase in pH, and decrease in temperature. Additionally, REE precipitation was aided and abetted by the removal of sulfur from the fluid by the precipitation of barite, which destabilized the REE sulfate complexes.
37
Pouhet, Raphaëlle, e Martin Cyr. "Studies of Natural and Accelerated Carbonation in Metakaolin-Based Geopolymer". Advances in Science and Technology 92 (ottobre 2014): 38–43. http://dx.doi.org/10.4028/www.scientific.net/ast.92.38.
Testo completoAbstract (sommario):
The carbonation of Portland-cement-based materials involves the reaction between atmospheric CO2 and calcium ions in the pore solution. The formation of calcium carbonate is responsible for a decrease in the pH of the pore solution from 12.5 to 9, thus leading to the depassivation of steel reinforcements and their possible corrosion, and can also lead to efflorescence (white crystals formed on the surface). In metakaolin-based geopolymer activated by sodium silicate, in which calcium is almost non-existent, the presence of CO2 will lead to the formation of sodium carbonates. Since geopolymer can be carbonated, the risk of corrosion or efflorescence needs to be assessed. A pH study of the geopolymer pore solution showed a very fast decrease compared to OPC, with almost total carbonation after only 14 days. In natural atmospheric CO2 conditions, it was found that the formation of sodium carbonate did not lead to a decrease of the pH to below a value around 9, thus limiting the risk of corrosion by depassivation of reinforcement, but the large amount of carbonate suggested a significant risk of efflorescence. A study of accelerated carbonation performed under an atmosphere of 50% CO2 highlighted the formation of sodium bicarbonate resulting in a lower pH of the pore solution and a much larger amount of product formed. Finally the study of efflorescence carried out by semi-immersion tests in natural or accelerated conditions confirmed the different nature of the crystals formed (sodium carbonate or bicarbonate) but showed no significant impact on the amount of carbonated products. This study thus demonstrates that the accelerated carbonation test had very limited usefulness, given the rapidity of the natural reaction. Furthermore, it was found that this test did not reproduce reality as it led to different reaction products.
38
Hurai, V., M. Huraiová, P. Konečný e R. Thomas. "Mineral-melt-fluid composition of carbonate-bearing cumulate xenoliths in Tertiary alkali basalts of southern Slovakia". Mineralogical Magazine 71, n. 1 (febbraio 2007): 63–79. http://dx.doi.org/10.1180/minmag.2007.071.1.63.
Testo completoAbstract (sommario):
AbstractTwo types of carbonatic cumulate xenoliths occur in alkali basalts of the northern part of the Carpatho-Pannonian region, Central Europe. One is dominated by Ca-Fe-Mg carbonates with randomly distributed bisulphide globules (Fe1+xS2, x = 0–0.1), Mg-Al spinel, augite, rhönite, Ni-Co-rich chalcopyrite, and a Fe(Ni,Fe)2S4 phase. The second, carbonatic pyroxenite xenolith type, is composed of diopside, subordinate fluorapatite, interstitial Fe-Mg carbonates, and accessory K-pargasite, F-Al-rich ferroan phlogopite, Mg-Al spinel, albite and K-feldspar. All accessory minerals occur in ultrapotassic dacite-trachydacite glass in primary silicate melt inclusions in diopside, together with calcio-carbonatite and CO2-N2-CO inclusions. Textural evidence is provided for multiphase fluid-melt immiscibility in both xenolith types. The carbonatic pyroxenite type is inferred to have accumulated from differentiated, volatile-rich, ultrapotassic magma derived by a very low-degree partial melting of strongly metasomatized mantle. Mineral indicators point to a genetic link between the carbonatite xenolith with olivine-fractionated, silica-undersaturated alkalic basalt ponded at the mantle-crust boundary.
39
Bailey, K., M. Garson, S. Kearns e A. P. Velasco. "Carbonate volcanism in Calatrava, central Spain: a report on the initial findings". Mineralogical Magazine 69, n. 6 (dicembre 2005): 907–15. http://dx.doi.org/10.1180/0026461056960298.
Testo completoAbstract (sommario):
AbstractLate Tertiary-Quaternary volcanism around Calatrava, within the Hercynian massif of central Spain, is alkaline mafic-ultramafic, with ∼250 centres, mainly monogenetic cones and vents, with melilitite the most abundant eruptive. Carbonatite may be expected in association with melilitite and a clear example of magmatic carbonate emerged from a brief field reconnaissance. It is a vent filled with a mixed eruption of glassy melilitite lapilli in a carbonate matrix. Levels and profiles of trace elements are inseparable from recognized carbonatite, and totally unlike those in local sedimentary limestone and caliche. C and O isotopes are the same as those reported for carbonatite ashes in other provinces. Carbonate is present as globules in the melilitite glass, and as inclusions within large clinopyroxene and olivine grains, which are largely xenocrystic. Euhedral spinels in melilitite and carbonate matrix are chromite mantled with titano-magnetite, reported previously only from high-temperature kimberlite. Wehrlite fragments indicate direct eruption from the mantle. Phlogopite and chromian spinel are found only as inclusions in the olivine, pointing to a phlogopite-carbonate mantle source region of the type favoured for carbonatite and melilitite melt generation. Calatrava represents the most southerly and westerly expression in mainland Europe of intra-continental carbonatite-melilitite volcanism. Follow-up field visits have shown that carbonate volcanism is extensive and voluminous throughout the province, requiring a long-term research programme.
40
Popa, Monica, Mihai Anastasescu, Ioana Catalina Gifu e Jose M. Calderon Moreno. "Hydrophobic Carbonate Coatings on Pure Biodegradable Mg by Immersion in Carbonated Water: Formation Mechanism". Applied Sciences 12, n. 22 (17 novembre 2022): 11674. http://dx.doi.org/10.3390/app122211674.
Testo completoAbstract (sommario):
Mg is one of the few materials of choice for biodegradable implants, despite its rapid degradation when used without surface protection treatment. This study presents the effect of carbonation time on the formation of hydrophobic carbonate coatings grown on pure magnesium using a simple, green chemical conversion method in carbonated water. The evolution of the coating with immersion time in carbonating solution was studied in order to ascertain the mechanistic of coating formation by Raman and EDS spectroscopy, XRD, SEM and AFM microscopy. Wettability was investigated by contact angle measurements. The formation mechanism of the hydrophobic coating involves the surface nucleation of carbonates mediated by the dissolution of the native corrosion product, brucite Mg(OH)2, surface conversion into hydroxycarbonates, surface calcite nucleation and growth by attachment of nanoparticles, leading to the lateral growth of a continuous carbonate coating layer of intertwined calcite microcrystals.
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Rodina, Oksana A., Oleg S. Vereshchagin, Dmitry Yu Vlasov, Marina S. Zelenskaya, Dmitrii V. Pankin, Nikita V. Mitrofanov, Michael Yu Nikitin, Kseniia Yu Vasileva e Olga V. Frank-Kamenetskaya. "Cyanobacterial Communities of Carbonate Sediments and Biomineralization in Peterhof Fountains’ Water Supply System, Russia". Minerals 11, n. 11 (28 ottobre 2021): 1199. http://dx.doi.org/10.3390/min11111199.
Testo completoAbstract (sommario):
The role of cyanobacterial communities in the formation of carbonate sediments (ancient and modern) is not completely clear. We studied the cyanobacterial communities connected with carbonate sediments of the freshwater bodies feeding the historical Peterhof fountains (Saint-Petersburg, Russia). Cyanobacterial communities were studied by metagenome analysis and optical microscopy. Carbonates associated with cyanobacterial communities (both in situ and in vitro) were studied by powder X-ray diffraction analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Raman spectroscopy. The interconnection between the mineral composition of carbonate sediments and inhabiting microorganism species was established. The leading role of cyanobacteria in carbonate biomineralization in fresh water of Peterhof fountains water supply system was shown. Cyanobacteria of 24 genera were revealed in sediments composed of calcite and aragonite. The crystallization of carbonates on the surface of 13 species of cyanobacteria was found. Using model experiments, a significant contribution of cyanobacterial species of the Oscillatoriaceae family (Phormidium spp., Lyngbya sp., Oscillatoria formosa) to carbonate biomineralization is demonstrated.
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Kaniewski, Maciej, Marta Huculak-Mączka, Jakub Zieliński, Marcin Biegun, Krystyna Hoffmann e Józef Hoffmann. "Crystalline Phase Transitions and Reactivity of Ammonium Nitrate in Systems Containing Selected Carbonate Salts". Crystals 11, n. 10 (15 ottobre 2021): 1250. http://dx.doi.org/10.3390/cryst11101250.
Testo completoAbstract (sommario):
Samples of pure ammonium nitrate (AN) and its mixtures with calcium carbonate, potassium hydrogen carbonate and potassium carbonate were investigated with the use of differential thermal analysis with mass spectrometry, powder X-ray diffraction and scanning electron microscopy. The main objective of the study was to determine the influence of selected carbonate materials on phase transitions of ammonium nitrate and to consider a possibility to use such potassium salts as fillers in fertilizer production. It was proven that all carbonate salts caused the absence of a phase transition that normally would occur at around 84–86 °C. Potassium carbonates were too reactive in systems containing AN. Based on the performed study, it was concluded that even though potassium carbonates are not fit to replace mineral fillers in the production process of fertilizers containing ammonium nitrate, they could be used in lesser amounts to remove the presence of low-temperature phase transitions of AN.
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Kogarko, L. N. "Role of CO2 on differentiation of ultramafic alkaline series: liquid immiscibility in carbonate-bearing phonolitic dykes (Polar Siberia)". Mineralogical Magazine 61, n. 407 (agosto 1997): 549–56. http://dx.doi.org/10.1180/minmag.1997.061.407.07.
Testo completoAbstract (sommario):
AbstractThe Maimecha-Kotui province in the North of Siberian platform is the largest province of ultramafic alkaline rocks in the world. The province comprises thirty-seven central-type complexes together with numerous dykes. The majority of dykes are radially disposed around the ultramafic alkaline massifs. Data are presented for dykes of the Dolbykha carbonatite complex, which comprises olivine and melilite nephelinites; nosean, calcite and cancrinite phonolites; calcite trachytes and calcite carbonatites.Some peralkaline phonolitic dykes contain carbonate-bearing globules with sizes of 1−2 mm to 17−20 mm. Globules consist of polycrystalline calcitic aggregates together with albite, phlogopite, apatite, Sr-lueshite, zircon, ancylite, ilmenite and strontianite. The phonolites have phenocrysts of albite, phlogopite and ilmenite. Albite, phlogopite, calcite and nepheline are also present in the groundmass. Analysis of these materials in the light of experimental data on the liquid immiscibility in carbonate-silicate systems suggests that separation of carbonatite from phonolitic melts took place due to immiscibility in the liquid state. I propose that carbonate melts contained originally significantly higher alkali contents which were subsequently lost into the fluid phase due to the incongruent dissolution of calcium-sodium carbonates in aqueous fluid at low temperatures. The discovery of nyerereite in the carbonatite of Polar Siberia confirms this conclusion. I infer that one of the mechanisms for the genesis of carbonatite melt in Polar Siberia was liquid immiscibility in strongly differentiated phonolitic magmas.The generation of the carbonatites was probably controlled by the depth (and PCO2) of the crustal magma chamber where differentiation took place and probably also by the alkalinity of melts, and the rapidity of magma ascent to the surface.
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Pasteris, J. D., C. H. Yoder, M. P. Sternlieb e S. Liu. "Effect of carbonate incorporation on the hydroxyl content of hydroxylapatite". Mineralogical Magazine 76, n. 7 (dicembre 2012): 2741–59. http://dx.doi.org/10.1180/minmag.2012.076.7.08.
Testo completoAbstract (sommario):
AbstractMechanisms for the incorporation of carbonate into minerals of the apatite group have been explored in both the geological and medical literature. An important problem with respect to biological apatite, which requires further clarification, is the hydroxyl content of the carbonated apatite of bone. Recent studies reveal bone apatite to contain only ∼20 mol.% of the hydroxyl content of stoichiometric hydroxylapatite, with negligible chloride or fluoride. We investigated the hypothesis that the development of vacancies in the hydroxyl channel sites is a charge-balancing mechanism for the substitution of carbonate ions into hydroxylapatite. Raman spectroscopic analyses of synthetic carbonated apatites (containing 1 to >15 wt.% carbonate) show that their hydroxyl ion concentration correlates inversely with carbonate concentration. The specific relationship between carbonate and hydroxyl concentration in these samples closely follows the theoretical relationship defined by type-B substitution of carbonate for phosphate in the apatite structure. However, the 6–8 wt.% carbonate concentration in bone apatite falls far short of accounting for all of the hydroxyl depletion that occurs in bone apatite. Some of the additional hydroxyl depletion in bone apatite might result from substitution of Na+ for Ca2+, but further mechanism(s), perhaps (HPO4)2– substitution, must also play a significant role.
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Kim, Yumi, e Yul Roh. "Microbially Induced Carbonate Precipitation Using Microorganisms Enriched from Calcareous Materials in Marine Environments and Their Metabolites". Minerals 9, n. 12 (21 novembre 2019): 722. http://dx.doi.org/10.3390/min9120722.
Testo completoAbstract (sommario):
Microbially induced Ca-carbonate precipitation (MICP) in general, refers to a process in which the urease secreted by microbes hydrolyzes urea to ammonium and carbon dioxide. The main objectives of this study were to identify the environmental factors (e.g., microbial growth, cell/metabolite presences, and calcium sources) that control Ca-carbonate formation and to investigate the mineralogical characteristics of the Ca-carbonate precipitated using ureolytic microorganisms cultured in marine environments. The two types of carbonate-forming microorganisms (CFMs), mixed cultures hydrolyzing urea, were enriched from calcareous materials in marine environments. The experiments using a CFM, Sporosarcina pasteurii, was also used for comparison. All the microbes were cultured aerobically in D-1 growth media that included urea. To investigate the effect of microbial growth states on Ca-carbonate precipitation, Ca-acetate was injected into the media before (i.e., lag phase) and after (i.e., stationary phase) microbial growth, and into the soluble microbial products (SMP) solution, respectively. XRD, FT-IR, and SEM-EDS analyses were used for mineralogical characterization of the precipitated Ca-carbonates. Results indicated that the Ca-carbonates, vaterite and/or calcite, precipitated under all the experimental conditions. The fastest precipitation of Ca-carbonates occurred in the SMP solution and formed calcite (size = 5–15 μm). When the concentrations of added Ca-acetate were varied from 0 to 0.5 M, the highest amounts of calcite, 22.8 g/L, were produced when 0.3 M Ca-acetate was injected. Therefore, the environmental factors (e.g., microbial growth, cell/metabolite presences, and calcium sources) could have an effect the rate of formation of Ca-carbonate and the types of carbonate minerals formed. Moreover, the use of cell-free SMP solution is expected to be applicable to Ca-carbonate precipitation in an environment where microbial growth is unfavorable.
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Wang, Fuyong, Peiqing Lian, Liang Jiao, Zhichao Liu, Jiuyu Zhao e Jian Gao. "Fractal Analysis of Microscale and Nanoscale Pore Structures in Carbonates Using High-Pressure Mercury Intrusion". Geofluids 2018 (7 giugno 2018): 1–15. http://dx.doi.org/10.1155/2018/4023150.
Testo completoAbstract (sommario):
This paper investigated fractal characteristics of microscale and nanoscale pore structures in carbonates using High-Pressure Mercury Intrusion (HPMI). Firstly, four different fractal models, i.e., 2D capillary tube model, 3D capillary tube model, geometry model, and thermodynamic model, were used to calculate fractal dimensions of carbonate core samples from HPMI curves. Afterwards, the relationships between the calculated fractal dimensions and carbonate petrophysical properties were analysed. Finally, fractal permeability model was used to predict carbonate permeability and then compared with Winland permeability model. The research results demonstrate that the calculated fractal dimensions strongly depend on the fractal models used. Compared with the other three fractal models, 3D capillary tube model can effectively reflect the fractal characteristics of carbonate microscale and nanoscale pores. Fractal dimensions of microscale pores positively correlate with fractal dimensions of the entire carbonate pores, yet negatively correlate with fractal dimensions of nanoscale pores. Although nanoscale pores widely develop in carbonates, microscale pores have greater impact on the fractal characteristics of the entire pores. Fractal permeability model is applicable in predicting carbonate permeability, and compared with the Winland permeability model, its calculation errors are acceptable.
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Rumyantsev, Misha, Ilia A. Korablev e Sergey Rumyantsev. "The reaction of potassium xanthates with five-membered cyclic carbonates: selectivity of the underlying cascade reactions and mechanistic insights". RSC Advances 10, n. 60 (2020): 36303–16. http://dx.doi.org/10.1039/d0ra07428d.
Testo completoAbstract (sommario):
In this paper we describe the reaction between potassium xanthates and common five-membered cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC) with special focus on mechanisms of the underlied cascad transformations.
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Xu, Hengchao, Xiaotong Peng, Shun Chen, Jiwei Li, Shamik Dasgupta, Kaiwen Ta e Mengran Du. "Macrofaunal burrowing enhances deep-sea carbonate lithification on the Southwest Indian Ridge". Biogeosciences 15, n. 21 (30 ottobre 2018): 6387–97. http://dx.doi.org/10.5194/bg-15-6387-2018.
Testo completoAbstract (sommario):
Abstract. Deep-sea carbonates represent an important type of sedimentary rock due to their effect on the composition of the upper oceanic crust and their contribution to deep-sea geochemical cycles. However, the role of deep-sea macrofauna in carbonate lithification remains poorly understood. A large lithified carbonate area, characterized by thriving benthic faunas and a tremendous amount of burrows, was discovered in 2008, blanketing the seafloor of the ultraslowly spreading Southwest Indian Ridge (SWIR). Benthic inhabitants – including echinoids, polychaetes, gastropods and crustaceans – are abundant in this carbonate lithified area. The burrowing features within these carbonate rocks, as well as the factors that may influence deep-sea carbonate lithification, were examined. We suggest that burrowing in these carbonate rocks enhances deep-sea carbonate lithification. We propose that active bioturbation may trigger the dissolution of the original calcite and thus accelerate deep-sea carbonate lithification on mid-ocean ridges. Macrofaunal burrowing provides a novel driving force for deep-sea carbonate lithification at the seafloor, illuminating the geological and biological importance of bioturbation in global deep-sea carbonate rocks.
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Yamasaki, Nakamichi, Tang Weiping e Kazumichi Yanagisawa. "Solidification of CaCO3 containing SrCO3 by hydrothermal hot-pressing". Journal of Materials Research 8, n. 8 (agosto 1993): 1972–76. http://dx.doi.org/10.1557/jmr.1993.1972.
Testo completoAbstract (sommario):
Powders of calcium carbonate with strontium carbonate were solidified by mechanical compression under hydrothermal conditions. The effects of hydrothermal conditions such as temperature, pressure, and ratio of Ca/Sr on the reaction process and microstructure of the solidified bodies were examined. Solidification of every powder easily proceeded with shrinkage above 200 °C to 300 °C. The compacts of strontium carbonate were more easily solidified, and compressive strength was 190 MPa and its density was 93.5%. The solidification with shrinkage of compacts consisting of mixed powders of calcium and strontium carbonates was accelerated with an increase in strontium carbonate content. It was revealed that the small amount of strontium carbonate powder acts as a bonding material among large calcium carbonate particles.
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Shaheen, Robina, Paul B. Niles, Kenneth Chong, Catherine M. Corrigan e Mark H. Thiemens. "Carbonate formation events in ALH 84001 trace the evolution of the Martian atmosphere". Proceedings of the National Academy of Sciences 112, n. 2 (22 dicembre 2014): 336–41. http://dx.doi.org/10.1073/pnas.1315615112.
Testo completoAbstract (sommario):
Carbonate minerals provide critical information for defining atmosphere–hydrosphere interactions. Carbonate minerals in the Martian meteorite ALH 84001 have been dated to ∼3.9 Ga, and both C and O-triple isotopes can be used to decipher the planet’s climate history. Here we report Δ17O, δ18O, and δ13C data of ALH 84001 of at least two varieties of carbonates, using a stepped acid dissolution technique paired with ion microprobe analyses to specifically target carbonates from distinct formation events and constrain the Martian atmosphere–hydrosphere–geosphere interactions and surficial aqueous alterations. These results indicate the presence of a Ca-rich carbonate phase enriched in 18O that formed sometime after the primary aqueous event at 3.9 Ga. The phases showed excess 17O (0.7‰) that captured the atmosphere–regolith chemical reservoir transfer, as well as CO2, O3, and H2O isotopic interactions at the time of formation of each specific carbonate. The carbon isotopes preserved in the Ca-rich carbonate phase indicate that the Noachian atmosphere of Mars was substantially depleted in 13C compared with the modern atmosphere.