Addition Of Calcite Research Articles

Experimental investigation of CO2-brine-calcite interactions under reservoir conditions

Deep geological formations such as saline aquifers and depleted oil and gas fields are potential sites for CO2 geological storage. The local host rock in these formations can have significant quantities of calcite present, such as in limestone or where carbonate formations have overlying chalk intervals. Therefore, the objective of this work is to understand how CO2-saturated brine interacts with calcite under reservoir conditions. Hydrothermal experiments were carried out over a 6month period to assess the potential for calcite to buffer brine and promote mineral carbonation over time. In addition, as the system had yet to reach equilibrium at 6months, geochemical modelling using PHREEQC was performed to calculate the equilibrium state. The dissolution and precipitation of minerals were investigated to determine the effect that these processes have on the properties of the rock, such as porosity. The addition of calcite to the brine resulted in a significant increase in brine pH from 2.03 to 5.72. However, once CO2 had been injected there was only a slight initial increase in pH, and therefore, the buffering effect of calcite is not sufficient to promote mineral carbonation. The formation of anhydrite, celestite and hematite was observed after 3months, although dissolution and precipitation were still taking place after 6months. The PHREEQC modelling conducted estimated an overall decrease in mineral volume of 2.3%, leading to an increase in porosity that is dependent on the SO42− concentration in the original brine. Therefore, brine composition needs to be considered when injecting CO2 into reservoirs containing calcite bearing rock.

Mikronize Kalsit ve Uçucu Kül Katkısının Beton Özelliklerine Etkisinin Araştırılması

Mikronize Kalsit ve Uçucu Kül Katkısının Beton Özelliklerine Etkisinin Araştırılması

Size-dependent response of foraminiferal calcification to seawater carbonate chemistry

Abstract. The response of the marine carbon cycle to changes in atmospheric CO2 concentrations will be determined, in part, by the relative response of calcifying and non-calcifying organisms to global change. Planktonic foraminifera are responsible for a quarter or more of global carbonate production, therefore understanding the sensitivity of calcification in these organisms to environmental change is critical. Despite this, there remains little consensus as to whether, or to what extent, chemical and physical factors affect foraminiferal calcification. To address this, we directly test the effect of multiple controls on calcification in culture experiments and core-top measurements of Globigerinoides ruber. We find that two factors, body size and the carbonate system, strongly influence calcification intensity in life, but that exposure to corrosive bottom waters can overprint this signal post mortem. Using a simple model for the addition of calcite through ontogeny, we show that variable body size between and within datasets could complicate studies that examine environmental controls on foraminiferal shell weight. In addition, we suggest that size could ultimately play a role in determining whether calcification will increase or decrease with acidification. Our models highlight that knowledge of the specific morphological and physiological mechanisms driving ontogenetic change in calcification in different species will be critical in predicting the response of foraminiferal calcification to future change in atmospheric pCO2.

Water-based drilling fluids: the contribution of xanthan gum and carboxymethylcellulose on filtration control

This study aimed mainly to evaluate the influence of xanthan gum (XG) and carboxymethylcellulose (CMC) in the filtration process of water-based drilling fluids, considering the conformational changes suffered by the polyelectrolyte with the addition of salt (NaCl) in different concentrations (0.17, 0.34 and 0.51 M). It was also evaluated the behavior of the fluid by the addition of calcite (calcium carbonate, CaCO3). Sixteen drilling fluids were prepared with the same xanthan gum concentration (major application as thickener to transport the cuttings), but different salinities and having or not CMC and calcite at constant concentrations. This strategy was adopted to evaluate the real contribution of each additive in the control of filtration performance, frequently unclear in the papers. In general, the fluids prepared in all brines showed lower viscosities and higher filtrate loss compared to fluids of sweet water. This effect was more strong in fluids containing only XG. The addition of CMC enhanced the viscosity and reduced the filtrate loss. However, the best results were obtained when calcite was added. The results indicated that XG contribution as thickener is not enough to control efficiently the fluid filtration even in the presence of calcite. However, the addition of CMC and calcite to XG salt solution increased the viscosity and decreased significantly the filtrate loss. This result was attributed to synergistic interactions between XG, CMC and calcite.

Altered volcanic ash layers of the Late Cretaceous San Felipe Formation, Sierra Madre Oriental (Northeastern Mexico): U[sbnd]Pb geochronology, provenance and tectonic setting

A detailed petrographic, geochemical, and UPb geochronological study of altered volcanic ash layers, collected in eight outcrops of the Late Cretaceous San Felipe Formation (Sierra Madre Oriental, Northeastern Mexico), has been carried out. The main objectives have been: (1) to establish a deposit period, and (2) to propose a reliable provenance-transport-deposit-diagenetic model. These volcano-sedimentary strata represent the altered remains of vitreous-crystalline ash (main grains: quartz + K-feldspar (sanidine) + Na-plagioclase + zircon + biotite; groundmass: glass + calcite + clinochlore + illite) deposited and preserved in a shallow, relatively large in area, open platform environment. Major and trace element geochemistry indicate that parent volcanism was mainly rhyodacitic to rhyolitic in composition. Discrimination diagrams suggest a link to continental arc transitional to extension tectonic setting. UPb geochronology in zircon has revealed that the volcanic ash was released from their sources approximately during the range 84.6 ± 0.8 to 73.7 ± 0.3 Ma, being transported to the depocenters. Burial diagenesis process was marked by: (a) a limited recycling, (b) the partial loss of original components (mainly K-feldspar, plagioclase, biotite and glass), and (c) the addition of quartz, calcite, illite and clinochlore. The location of the source area remains uncertain, although the lack of enrichment in Zr/Sc ratio suggests that ashes were subjected to relatively fast and short-distance transport process. El Peñuelo intrusive complex, at 130–170 km west of the depocenters, is the nearest known zone of active magmatism during the Upper Cretaceous. This intermediate to felsic pluton, characterized by a geochemical affinity to post-orogenic tectonic setting, could be linked to the volcanic sources.

Kinetics of CaCO3 precipitation in an anaerobic digestion process integrated with silicate minerals

Integration of silicate minerals in the anaerobic digestion (AD) process has recently been proposed as a way to sequester CO2, neutralize the pH and produce biobased products such as biogas and biofertilizers. The objective of this study was to investigate the kinetics of CaCO3 precipitation in an anaerobic digestion process integrated with a silicate mineral (wollastonite).The first series of experiments studied the precipitation kinetics during the methanogenic phase by addition of calciumacetate to anaerobic batch reactors. CaCO3 precipitation initiated when the ion activity product of Ca2+ and CO32− exceeded calcium carbonate monohydrate solubility product (Ksp of 5.7×10−8 at 35°C). Addition of calcite seed crystal at the start of the experiment showed that the precipitation could be initiated earlier by reducing the induction period. In these experiments, precipitation of CO2 in the form of CaCO3 showed an 52% increase in CH4 content of the biogas (71±0.5% v/v CH4) compared to that of the control experiment fed with sodium acetate (53±0.5% v/v CH4).In the second set of experiments, single-stage anaerobic batch digestions with 25g/l wollastonite (63–125μm) at two different substrate concentrations (5.5g/l and 17.5g/l insoluble starch) were studied. In these experiments the main processes of wollastonite dissolution and calcite precipitation occurred, however the limited separation of fermentation and methanogenesis phases resulted in a limited increase in methane content of the biogas. Although the precipitation was observed at lower supersaturation, the crystal growth followed the same pattern as in previous experiments with calcium acetate. In both sets of experiments, a self-regulating pH could be achieved in the system as the result of the presence of wollastonite which caused the pH to remain in the range of 5.7–7.9. Obtaining an improved biogas and a self-regulated pH in a digester contribute to the advantages of CO2 sequestration by means of silicate minerals in anaerobic digestion systems.

Neolithic pottery from the Trieste Karst (northeastern Italy): A multi-analytical study

A group of Neolithic potsherds from caves of the Trieste Karst (northeastern Italy) belonging to the Vlaška Group has been studied through a multi-analytical approach mainly based on non-destructive X-ray computed microtomography (μCT) and portable X-ray fluorescence (XRF), combined with X-ray diffraction (XRD) and optical microscopy (OM) to investigate both manufacture technology and provenance of the vases. Most samples, probably produced using a modelling technique, were made using clay-silt size paste containing quartz inclusions, tempered with the addition of abundant calcite and some limestone fragments. Calcite minerals, very common in the karstic environment, were probably obtained by grinding speleothems. This peculiar paste seems to be typical of the Karst area since prehistoric times. One single sample (5880), characterized by an unusual shape recalling those of the Fiorano culture (present in Emilia-Romagna and Veneto), shows a fine-grained fabric with numerous grog fragments, quartz, minor feldspar but without calcite. The 2D and 3D μCT-derived fabric parameters, reflecting the manufacture technology, are also quite different from those of the local vases. These features suggest that sample 5880 was manufactured elsewhere and later reached the Karst, directly or indirectly. The combined use of conventional techniques and non-destructive XRF and μCT, which allows the quantification of clay material, lithic inclusions and porosity, has proved to be an effective approach to investigate both technology and provenance of ceramic materials.

Effect of initial LSI on wastewater softening: simultaneous removal of polyacrylamide residues

Industrial effluent was tested for softening and polyacrylamide (PAC) residue removal and correlated with the Langelier saturation index (LSI). Contrary to previously reported methods, the initial LSI (LSIin) was calculated using the pre-reaction pH, the inherent alkalinities of the original wastewater and the alkalinities added during softening, under the assumption that no physical or chemical reaction had started. During the softening optimization tests, higher LSIin predicted efficient softening, which was further confirmed by lower final LSI (LSIfin). The NaOH dose adjustment was more effective with 100% softening than that achieved by adjusting initial pH. Calcite seeding was more effective at pH 7 with lower LSIin in the range −2 to 2 than that at pH 10 with LSIin in the range 1–4.7. During NaOH dose optimization, LSIin was higher and LSIfin was lower at a higher soda ash to hardness molar ratio of 1.3:1 than that at a lower ratio of 1:1. Compact accelerated precipitation softening process removed 60% of the calcium and 41% of the PAC residues because calcium carbonate precipitates worked as a coagulation aid. Direct correlations between LSIin and softening efficiency in all processes (R2 = 0.95–0.98) confirmed the importance of LSI and explained the effects of calcite addition.

Investigation of rye straw ash sintering characteristics and the effect of additives

The understanding of ash sintering during combustion of agricultural residues is far from complete, because of the high heterogeneity of the content and composition of ash forming matters and the complex transformation of them. In order to make agricultural residues competitive fuels on the energy market, further research efforts are needed to investigate agricultural residues’ ash sintering behavior and propose relevant anti-sintering measures. The aim of this work was to investigate the ash characteristics of rye straw and effects of additives. Three additives were studied regarding their abilities to prevent and abate rye straw ash sintering. Standard ash fusion characterization and laboratory-scale sintering tests were performed on ashes from mixtures of rye straw and additives produced at 550°C. Ash residues from sintering tests at higher temperatures were analyzed using a combination of X-ray diffraction (XRD) and scanning electron microscopy–energy dispersive X-ray spectrometry (SEM–EDX). High sintering and melting tendency of the rye straw ash at elevated temperatures was observed. Severe sintering of the rye straw ash was attributed to the formation and fusion of low temperature K–silicates and K–phosphates with high K/Ca ratios. Among the three additives, calcite served the best one to mitigate sintering of the rye straw ash. Ca from the calcite promoted formation of high temperature silicates and calcium rich K–phosphates. In addition, calcite may hinder aggregating of ash melts and further formation of large ash slag. Therefore, the chemical reactions and physical restraining effects arose by calcite addition contributed to reduction of ash melts and sintering degree. Upon addition of kaolin, compositions of rye straw ash shifted from low temperature melting K–silicates to high temperature melting K–Al–silicates. The changes of ash chemistry were favorable for reducing sintering of the rye straw ash. As the Ca-sludge was added, reduction of sintering of the rye straw ash was less pronounced. Only K4CaSi3O9 and a small amount of KCaPO4 were identified in the rye straw ash as Ca-sludge was added.

Effect of Addition and Substitution of Micro Calcite on Strength and Durability Characteristics of HPC

Effect of Addition and Substitution of Micro Calcite on Strength and Durability Characteristics of HPC

Sintering of Rye Straw Ash and Effect of Additives

The effects of kaolin and calcite additives on the rye straw ash sintering behaviors were investigated. The rye straw ash has a high sintering tendency, with observation of severe fusion during combustion. The formation and melting of potassium silicates play key roles in sintering of the rye straw ash at elevated temperatures. Fusion characteristics temperatures of the rye straw ash were significantly increased upon kaolin and calcite addition. Kaolin addition led to formation of high temperature melting potassium aluminum silicates, which were revealed by XRD analyses. Due to formation of high temperature melting species due to kaolin addition, the severe sintering of the rye straw ash was significantly reduced. Addition of calcite provided CaO to react with silica in the rye straw ash, causing generation of high temperature melting calcium rich silicates. In addition, the dilution effect from calcite is a main reason for improved rye straw sintering behaviors.

Radiocarbon Dating, Mineralogy, and Isotopic Composition of Hackberry Endocarps from the Neolithic Site of Aşikli Höyük, Central Turkey

Carbonate is abundant in many Neolithic tells and is a potentially useful archive for dating and climate reconstruction. In this paper, we focus on the mineralogy, radiocarbon dating, and stable isotope systematics of carbonate in hackberry endocarps. Hackberry fruits and seeds are edible in fresh and stored forms, and they were consumed in large quantities in many Neolithic sites in the Near East, including the site of our study, Aşıkli Höyük in central Anatolia, an Aceramic Neolithic tell occupied from about 9.4 to > 10.3 BP (7.4 to > 8.3 BCE). Detailed 14C age control provided by archaeological charcoal permits a test of the fidelity in 14C dating of hackberry endocarps. Modern endocarps and leaves yield fraction modern 14C values of 1.050–1.066, consistent with levels present in the atmosphere when sampled in 2009. On the other hand, archaeological endocarps yield consistently younger ages than associated charcoal by ca. 130 14C years (ca. 220 calendar years) for samples about 10,000 years old. We speculate this is caused by the slight addition of calcite or recrystallization to calcite in the endocarp, as detected by scanning electron microscopy. Subtle addition or replacement of calcite by primary aragonite is not widely recognized in the 14C community, even though similar effects are reported from other natural carbonates such as shell carbonate. This small (but consistent) level of contamination supports the usefulness of endocarps in dating where other materials like charcoal are lacking. Before dating, however, hackberries should be carefully screened for mineralogical preservation and context. We examined the carbon and oxygen isotopic systematics of the fossil endocarps to try to establish potential source areas for harvesting. Most of the hackberries are enriched in 18O compared to local water sources, indicating that they were drawing on highly evaporated soil water, rather than the local (perched and regional) water table sampled in our study. Isotopic evidence therefore suggests that most but not all of the hackberries were harvested from nearby mesas well above the local streams and seeps fed by the water table.

Radiocarbon Dating, Mineralogy, and Isotopic Composition of Hackberry Endocarps from the Neolithic Site of Aşikli Höyük, Central Turkey

Carbonate is abundant in many Neolithic tells and is a potentially useful archive for dating and climate reconstruction. In this paper, we focus on the mineralogy, radiocarbon dating, and stable isotope systematics of carbonate in hackberry endocarps. Hackberry fruits and seeds are edible in fresh and stored forms, and they were consumed in large quantities in many Neolithic sites in the Near East, including the site of our study, Aşıkli Höyük in central Anatolia, an Aceramic Neolithic tell occupied from about 9.4 to > 10.3 BP (7.4 to > 8.3 BCE). Detailed14C age control provided by archaeological charcoal permits a test of the fidelity in14C dating of hackberry endocarps. Modern endocarps and leaves yield fraction modern14C values of 1.050–1.066, consistent with levels present in the atmosphere when sampled in 2009. On the other hand, archaeological endocarps yield consistently younger ages than associated charcoal by ca. 13014C years (ca. 220 calendar years) for samples about 10,000 years old. We speculate this is caused by the slight addition of calcite or recrystallization to calcite in the endocarp, as detected by scanning electron microscopy. Subtle addition or replacement of calcite by primary aragonite is not widely recognized in the14C community, even though similar effects are reported from other natural carbonates such as shell carbonate. This small (but consistent) level of contamination supports the usefulness of endocarps in dating where other materials like charcoal are lacking. Before dating, however, hackberries should be carefully screened for mineralogical preservation and context. We examined the carbon and oxygen isotopic systematics of the fossil endocarps to try to establish potential source areas for harvesting. Most of the hackberries are enriched in18O compared to local water sources, indicating that they were drawing on highly evaporated soil water, rather than the local (perched and regional) water table sampled in our study. Isotopic evidence therefore suggests that most but not all of the hackberries were harvested from nearby mesas well above the local streams and seeps fed by the water table.

Formation and decomposition of C4F7 type calcium ferrites in superfluxed magnetite based pellets during oxidation and reduction

In the current work the reactions of magnetite based pellets with large additions of calcite (3%CaO) during reduction have been investigated. This made it possible to use both X-ray diffraction (XRD) and scanning electron microscopy (SEM) to detect reaction phases that normally occur in very small amounts. The main binding phase in the pellets after oxidation was (CaO,MgO,FeO)4(Fe2O3)7, whereas the one commonly reported in the literature is (CaO)(Fe2O3)2. During reduction at 500–700°C severe cracking occurred in these pellets, especially in the calcium ferrite phase. However, the decomposition of this phase began at 600°C, and therefore it is believed that the reason for the cracks is low strength of the phase itself, rather than weakness induced by reduction of the phase. Upon reduction of magnetite into wüstite at 800°C, the calcium began dissolving in the wüstite, and at 900°C porous calciowüstite had formed in the entire sample, except for some remaining magnetite left in the pellet cores.

Sintering Behavior of Kaolin with Calcite

The study of sintering behavior of clay raw materials might be difficult because, as it is well known, these clays have a complex mineralogical composition, which causes a series of phase transformations occurring during sintering. Those processes relate to major and minor clay minerals (such as phyllosilicates, quartz, calcite, dolomite and hematite). Kaolinite is one of the main components of the clay. In this work, we consider sintering of kaolin, with different addition of pure calcite. The following techniques were used: differential thermal analysis (DTA), thermogravimetry (TG/DTG), dilatometry (DIL), heating microscope probe and X-ray diffraction (XRD), and scanning electron microscopy (SEM). In addition, comparisons between the microstructure of the sintered bodies and their physical- mechanical properties have been made.

Effects of Additives on Barley Straw and Husk Ashes Sintering Characteristics

A growing interest has been observed for producing sustainable heat and power by combustion of residues from local agricultural production. However, ash related problems are inclined to occur due to high contents of problematic ash forming matter in such residues. The aims of this work were to examine ash characteristics of barley straw and husk and to find mixtures of fuels and additives that can be used as basis for producing pellets giving minimal problems during combustion. Influence of kaolin and calcite additives on the two fuel ashes’ sintering behaviors were investigated by X-ray fluorescence (XRF), ash fusion analyzer and X-ray diffraction (XRD) analysis. The results showed that, compared to barley straw ash, the barley husk ash has a higher sintering tendency, with observation of severe melting during combustion. Kaolin and calcite addition increased the melting temperatures of ashes from both barley straw and husk. Reactions between kaolin and potassium containing species in the barley straw and husk ashes were revealed by XRD analyses. With formation of high temperature melting species due to kaolin addition, the severe sintering of barley straw and husk ashes were significantly reduced. The dilution effect from calcite is supposed to be a main reason for improved barley straw and husk ash sintering behaviors. In addition, calcite addition led to formation of more calcium rich phases, which have higher melting points and contribute to low ash sintering degrees. Therefore, by using the additives, agricultural residues can be competitive for energy production in the future.

Granular soil structure indicates reclamation of degraded to productive soils: A case study in southeast Spain

Arocena, J. M., van Mourik, J. M. and Faz Cano, A. 2012. Granular soil structure indicates reclamation of degraded to productive soils: A case study in southeast Spain. Can. J. Soil Sci. 92: 243–251. Accelerated conversion of degraded landscapes in mining areas to productive ecosystems requires stimulation of soil formation. The evolution in microstructure and changes to chemical properties in metal mine wastes 5 yr after amendments with pig manure, sewage sludge and marble waste is reported. Mine wastes had <1% organic carbon, <0.05% total nitrogen, pH∼2.0, electrical conductivity up to 20 dS m−1and high concentrations of metals such as 22000 mg zinc kg−1and 7000 mg lead kg−1. After 5 yr, one time amendment increased total carbon (g kg−1) from 1.4 (control) to 5.6 (marble waste +sewage sludge) to 8.3 (marble waste+pig manure). Soil pH in amended plots was 6.0 compared with 2.8 in controls. Micromorphological characteristics clearly showed that primary and secondary calcite serve as active sorption sites for organic matter. These calcitic zones were areas conducive to root growth. Soil microstructure in amended mine wastes was dominantly granular, resulting from activities of soil organisms such as fungi and enchytraeds. Results suggest organic matter can be effectively enriched in mine waste deposits through simultaneous additions of pig manure, sewage sludge and calcite. Soil amendments promoting formation of granular structure can accelerate establishment of productive landscapes in degraded mine sites.

Influencia de la finura de molido del carbonato de calcio en las propiedades físico mecánicas y de durabilidad de los ladrillos de cerámica roja

The paper exposes the results of a study, at macro structural level, on the influence of the calcite grinding process fineness on the red ceramic bricks following properties: Compressive strength, Density, Absorption and Durability, though the performance of physical – mechanical and accelerated aging tests, when this is added in an amount inferior to the 10% in relation with the clay weight. It is proved that when this admixture is ground until fineness between 72 m and 150 m, the above mentioned properties are not affected, however it doesn’t occur this way when it is ground until a particle size of 297 m. The carried out study, demonstrates that with this specific surface, the calcite addition affects the red ceramic bricks physical-mechanical properties as well as their durability

Impact of Phosphate on Fluoride Removal by Calcite

Abstract Fluoride can be removed from wastewater by addition of calcite. However, fluoride is often found in complex mixtures where other contaminants can affect the removal process. Batch experiments were used to determine the impact of phosphate (PO43−) on the removal of fluoride from solution by calcite. In the experiments, up to 2,000 mg/L F− and 500 mg/L PO43− were used with 150 μm and 1.18 mm calcite fractions at solid-to-solution ratios of 1.00 and 33.33 g/L. Experimental results were analyzed with the geochemical model PHREEQ, which assumes fluoride and PO43− removal by precipitation as fluorite, fluorapatite, and hydroxyapatite. The model predicted that PO43− had no influence on fluoride removal below pH 11.6. This was inconsistent with the experimental data showing that the presence of a relatively small amount (17 mg/L) of PO43− resulted in a 20% reduction in F− removal, whereas 500 mg/L PO43− resulted in complete (100%) inhibition of fluoride removal. Results indicated that the removal of fluo...

Trace metals in recharge and discharge ground waters at two sites at the Baltic coast of Sweden

The distribution and controls of trace elements (Cd, Cr, Cu, Ni, Pb, Zn and U) in shallow groundwater in discharge and recharge zones were analysed at two sites on the Baltic coast of Sweden; one granite-dominated and one with a significant addition of calcite. Although the study sites differ in overburden geochemistry and groundwater trace metal concentrations, which were well reflected in the general groundwater composition, the relative hydrochemical differences between recharge and discharge ground waters were similar at both sites, and temporally stable. The concentrations of Cd, Cu, Ni and U were higher in soil tubes in recharge areas, but Cr was higher in discharge zones. Also concentrations of HS, Fe, Mn and NH4 were higher in discharge samples, which in combination with increased 34S values provide strong evidence of a transition from oxidizing to more reducing conditions along the groundwater flow gradient. In terms of trace metals, this might mean either mobilisation due to dissolution of trace-metal carrying Fe(III) and Mn(IV) phases, or immobilisation caused by precipitation of discrete trace-metal sulfides or co-precipitation with Fe sulfides. The results from this study show that the latter is dominant in both the carbonate and granite environments for the metals Cd, Cu and Ni. Chromium concentrations were likely coupled to organic complexation and were higher in discharge groundwater, where DOC was also more abundant. As the concentration of several potentially toxic trace metals were found to differ between recharge and discharge areas, a climate driven change in hydrology might have a substantial impact on the distribution of these metals.