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CaCO3
Terms modified by CaCO3 Selected AbstractsSedimentological, modal analysis and geochemical studies of desert and coastal dunes, Altar Desert, NW MexicoEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2007J. J. Kasper-Zubillaga Abstract Sedimentological, compositional and geochemical determinations were carried out on 54 desert and coastal dune sand samples to study the provenance of desert and coastal dunes of the Altar Desert, Sonora, Mexico. Grain size distributions of the desert dune sands are influenced by the Colorado River Delta sediment supply and wind selectiveness. The desert dune sands are derived mainly from the quartz-rich Colorado River Delta sediments and sedimentary lithics. The dune height does not exert a control over the grain size distributions of the desert dune sands. The quartz enrichment of the desert dune sands may be due to wind sorting, which concentrates more quartz grains, and to the aeolian activity, which has depleted the feldspar grains through subaerial collisions. The desert dune sands suffer from little chemical weathering and they are chemically homogeneous, with chemical alteration indices similar to those found in other deserts of the world. The desert sands have been more influenced by sedimentary and granitic sources. This is supported by the fact that Ba and Sr concentration values of the desert sands are within the range of the Ba and Sr concentration values of the Colorado River quartz-rich sediments. The Sr values are also linked to the presence of Ca-bearing minerals. The Zr values are linked to the sedimentary sources and heavy mineral content in the desert dunes. The Golfo de Santa Clara and Puerto Peñasco coastal dune sands are influenced by long shore drift, tidal and aeolian processes. Coarse grains are found on the flanks whereas fine grains are on the crest of the dunes. High tidal regimens, long shore drift and supply from Colorado Delta River sediments produce quartz-rich sands on the beach that are subsequently transported into the coastal dunes. Outcrops of Quaternary sedimentary rocks and granitic sources increase the sedimentary and plutonic lithic content of the coastal dune sands. The chemical index of alteration (CIA) values for the desert and coastal dune sands indicate that both dune types are chemically homogeneous. The trace element values for the coastal dune sands are similar to those found for the desert dune sands. However, an increase in Sr content in the coastal dune sands may be due to more CaCO3 of biogenic origin as compared to the desert dune sands. Correlations between the studied parameters show that the dune sands are controlled by sedimentary sources (e.g. Colorado River Delta sediments), since heavy minerals are present in low percentages in the dune sands, probably due to little heavy mineral content from the source sediment; grain sizes in the dune sands are coarser than those in which heavy minerals are found and/or the wind speed might not exert a potential entrainment effect on the heavy mineral fractions to be transported into the dune. A cluster analysis shows that the El Pinacate group is significantly different from the rest of the dune sands in terms of the grain-size parameters due to longer transport of the sands and the long distance from the source sediment, whereas the Puerto Peñasco coastal dune sands are different from the rest of the groups in terms of their geochemistry, probably caused by their high CaCO3 content and slight decrease in the CIA value. Copyright © 2006 John Wiley & Sons, Ltd. [source] Origin and palaeo-environments of calcareous sediments in the Moshaweng dry valley, southeast BotswanaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 6 2002S. Ringrose Abstract Quaternary sedimentation in the Moshaweng dry valley of southeastern Botswana is evaluated on the basis of geomorphological evolution and sedimentological analyses. Stratigraphic evidence reveals an upper surface (1095 m) containing abundant sil-calcrete, an intermediate surface (1085 m) in which sil-calcrete underlies nodular calcrete and lower (1075 m) surface in which sil-calcrete and nodular calcrete are interbedded. This subdivision is reflected in the geochemical composition of the sediments which show an overall trend of decreasing SiO2 content (and increasing CaCO3 content) with depth from the highest to the lowest surface levels. The calcretes and sil-calcretes represent modifications of pre-existing detrital Kalahari Group sand and basal Kalahari pebbles which thinned over a Karoo bedrock high. Modification took place during wet periods when abundant Ca++ -rich groundwater flowed along the structurally aligned valley system. With the onset of drier conditions, water table fluctuations led to the precipitation of nodular calcretes in the phreatic layer to a depth of about 20 m. A major geochemical change resulted in the preferential silicification of the nodular calcrete deposits. Conditions for silica mobilization may be related to drying-induced salinity and in situ geochemical differentiation brought about by pebble dissociation towards the top of the sediment pile. As calcretization and valley formation progressed to lower levels, silica release took place on a diminishing scale. Thermoluminescence dating infers a mid-Pleistocene age for sil-calcrete formation suggesting that valley evolution and original calcrete precipitation are much older. Late stage dissolution of CaCO3 from pre-existing surface calcretes or sil-calcretes led to the formation of pedogenic case-hardened deposits during a time of reduced flow through the Moshaweng system possibly during the upper or late Pleistocene. Copyright © 2002 John Wiley & Sons, Ltd. [source] Optimization of culture conditions for glucose oxidase production by a Penicillium chrysogenum SRT 19 strainENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 1 2010Ragini G. Bodade Abstract The enzyme glucose oxidase (GOD) has been used for a variety of biotechnological applications in food and pharmaceutical industries. In this study, the optimization of extracellular GOD production was carried out in a Penicillium chrysogenum SRT 19 strain isolated from contaminated and decaying cheese samples. Maximum GOD production was attained at pH 6 and 20°C in fermentation broth after 72,h of incubation. The effects of metal ions and sugars were screened for the induction of higher GOD production. The results revealed that glucose and lactose give the highest production of enzyme (0.670 and 0.552,U/mL, respectively) as compared with other sugars (sucrose, cellulose, mannitol and fructose). Out of the seven metal ions studied, CaCO3 (1.123,U/mL) and FeSO4 (0.822,U/mL) act as modulators, while MgSO4 (0.535,U/mL), CuSO4 (0.498,U/mL), HgCl2 (0.476,U/mL), ZnSO4 (0.457,U/mL) and BaSO4 (0.422,U/mL) yield lower production. The study therefore suggests that a strain of P. chrysogenum SRT 19 can be used as a new strain for GOD production. [source] Flux and turnover of fixed carbon in soil microbial biomass of limed and unlimed plots of an upland grassland ecosystemENVIRONMENTAL MICROBIOLOGY, Issue 4 2005J. Ignacio Rangel-Castro Summary The influence of liming on rhizosphere microbial biomass C and incorporation of root exudates was studied in the field by in situ pulse labelling of temperate grassland vegetation with 13CO2 for a 3-day period. In plots that had been limed (CaCO3 amended) annually for 3 years, incorporation into shoots and roots was, respectively, greater and lower than in unlimed plots. Analysis of chloroform-labile C demonstrated lower levels of 13C incorporation into microbial biomass in limed soils compared to unlimed soils. The turnover of the recently assimilated 13C compounds was faster in microbial biomass from limed than that from unlimed soils, suggesting that liming increases incorporation by microbial communities of root exudates. An exponential decay model of 13C in total microbial biomass in limed soils indicated that the half-life of the tracer within this carbon pool was 4.7 days. Results are presented and discussed in relation to the absolute values of 13C fixed and allocated within the plant,soil system. [source] Cadmium tolerance in the Nile tilapia (Oreochromis niloticus) following acute exposure: Assessment of some ionoregulatory parametersENVIRONMENTAL TOXICOLOGY, Issue 1 2006Sofia Garcia-Santos Abstract The Nile tilapia (Oreochromis niloticus) can tolerate very high levels of waterborne cadmium. It has one of the highest 96 h LC50 recorded for a freshwater teleost fish (14.8 mg/L Cd; hardness 50 mg/L CaCO3). Cadmium is known to perturb ion balance in teleost fishes. However, in an acute time course experiment, plasma Na+ concentrations were unaffected, and plasma Ca2+ values only decreased after 96 h exposure in a dose-independent manner. Branchial Na+/K+ -ATPase activity and ,-subunit protein level expression in crude gill homogenates were not affected by Cd exposure during this period. Branchial chloride cell numbers, identified as Na+/K+ -ATPase immunoreactive cells using immunohistochemistry, decreased 24 h after exposure but recovered thereafter. Histopathological changes did not follow a consistent pattern of variation with exposure time, and the alterations noted in gill epithelium were basically nonspecific to cadmium. Because of its tolerance, it can be concluded that the tilapia O. niloticus would not be a suitable test organism to evaluate sublethal toxicity of cadmium and the realistic impact of this pollutant in the environment. However, it certainly could contribute significantly to our understanding of the toxic mechanism of cadmium exposure in aquatic organisms. This is the first work to investigate the effect of waterborne pollutants on Na+/K+ -ATPase ,-subunit protein expression in fish gills. © 2006 Wiley Periodicals, Inc. Environ Toxicol 21: 33,46, 2006. [source] Influence of water chemistry on the acute toxicity of copper and zinc to the cladoceran Ceriodaphnia cf dubiaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2005Ross V. Hyne Abstract This study determined the influence of key water chemistry parameters (pH, alkalinity, dissolved organic carbon [DOC], and hardness) on the aqueous speciation of copper and zinc and its relationship to the acute toxicity of these metals to the cladoceran Ceriodaphnia cf dubia. Immobilization tests were performed for 48-h in synthetic or natural waters buffered at various pH values from 5.5 to 8.4 (other chemical parameters held constant). The toxicity of copper to C. cf dubia decreased fivefold with increasing pH, whereas the toxicity of zinc increased fivefold with increasing pH. The effect of DOC on copper and zinc toxicity to C. cf dubia was determined using natural fulvic acid in the synthetic water. Increasing DOC was found to decrease linearly the toxicity of copper, with the mean effect concentration of copper that immobilized 50% of the cladocerans (EC50) value 45 times higher at 10 mg/L, relative to 0.1 mg/L DOC at pH 6.5. In contrast, the addition of 10 mg/L DOC only resulted in a very small (1.3-fold) reduction in the toxicity of zinc to C. cf dubia. Copper toxicity to C. cf dubia generally did not vary as a function of hardness, whereas zinc toxicity was reduced by a factor of only two, with an increase in water hardness from 44 to 374 mg CaCO3/L. Increasing bicarbonate alkalinity of synthetic waters (30,125 mg/L as CaCO3) decreased the toxicity of copper up to fivefold, which mainly could be attributed to the formation of copper-carbonate complexes, in addition to a pH effect. The toxicity of copper added to a range of natural waters with varying DOC content, pH, and hardness was consistent with the toxicity predicted using the data obtained from the synthetic waters. [source] Evaluation of acute copper toxicity to larval fathead minnows (Pimephales promelas) in soft surface watersENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2005Eric J. Van Genderen Abstract The hardness-based regulatory approach for Cu prescribes an extrapolation of the toxicity-versus-hardness relationship to low hardness (,50 mg/L as CaCO3). Hence, the objective of the present research was to evaluate the influences of water quality on acute Cu toxicity to larval fathead minnow (Pimephales promelas) in low-hardness surface waters. Seasonal water sampling was conducted at 24 sites throughout South Carolina, USA, to determine the site-specific influences of soft surface-water conditions on acute Cu toxicity. Concurrent toxicity tests in laboratory water, matched for hardness and alkalinity (modified method), also were conducted to allow calculation of water-effect ratios (WERs). In addition, tests were conducted at recommended hardness levels (recommended method) for comparison of WER methodology in soft water. Surface-water conditions (average ± standard deviation, n = 53) were hardness of 16 ± 8 mg/L as CaCO3, alkalinity of 18 ± 11 mg/L as CaCO3, and dissolved organic carbon of 6 ± 4 mg/L. Dissolved Cu 48-h median lethal concentration (LC50) values varied nearly 45-fold across the dataset and greater than four-fold at individual sites. Spatial (p < 0.0001) and seasonal (p = 0.026) differences among LC50 values were determined for eight sites that had multiple toxicity results for one year. All modified WERs were greater than 1.0, suggesting that the site waters were more protective of Cu toxicity than the matched laboratory water. Some WERs generated using recommended methods were less than 1.0, suggesting limited site-specific protection. Based on these observations, extrapolation of the hardness-based equation for Cu at 50 mg/L or less as CaCO3 would adequately protect fathead minnow populations in soft surface waters. The WER results presented here demonstrate the inconsistency between hardness-based criteria and the methodology for deriving site-specific water-quality criteria in low-hardness waters. [source] Influence of water quality and age on nickel toxicity to fathead minnows (Pimephales promelas)ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2004Tham Chung Hoang Abstract This research characterized the effects of water quality and organism age on the toxicity of nickel (Ni)to fathead minnows (Pimephales promelas) to facilitate the accurate development of site-specific water-quality criteria. Nickel sulfate hexa-hydrate (NiSO4·6H2O) was used as the Ni source for performing acute toxicity tests (median lethal concentration after 96-h exposure [96-h LC50]) with <1-d-old and 28-d-old P. promelas under varying regimes of hardness, pH, alkalinity, and natural organic matter (NOM). The toxicity of Ni was inversely related to water hardness between hardness values of 20 and 150 mg/L (as CaCO3). Below 30 mg/L alkalinity, Ni toxicity was related to alkalinity. The effect of pH was confounded by hardness and the presence of NOM. In the absence of NOM, the toxicity of Ni increased as pH increased at high hardness and alkalinity. In general, 28-d-old fish were less sensitive than <1-d-old fish to Ni. This lower sensitivity ranged from 12-fold at low hardness and alkalinity (20 and 4 mg/L, respectively) to 5-fold at high hardness and alkalinity (100 and 400 mg/L, respectively). The presence of NOM (10 mg/L as dissolved organic carbon [DOC]) reduced Ni toxicity by up to 50%, but this effect appeared to be saturated above DOC at 5 mg/L. Incubating Ni with the NOM solution from 1 to 17 days had no effect on Ni toxicity. When using multivariate analysis, the 96-h LC50 for Ni was a function offish age, alkalinity, hardness, and NOM (96-h LC50 = ,0.642 + 0.270(fish age) + 0.005(alkalinity) + 0.018(hardness) + 0.138(DOC)). When using this model, we found a strong relationship between measured and predicted 96-h LC50 values (r2 = 0.94) throughout the treatment water qualities. The biotic ligand model (BLM) did not accurately predict Ni toxicity at high or low levels of alkalinity. Results of our research suggest that the BLM could be improved by considering NiCO3 to be bioavailable. [source] Relative sensitivity of bull trout (Salvelinus confluentus) and rainbow trout (Oncorhynchus mykiss) to acute copper toxicityENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2002James A. Hansen Abstract Bull trout (Salvelinus confluentus) were recently listed as threatened in the United States under the federal Endangered Species Act. Past and present habitat for this species includes waterways contaminated with heavy metals released from mining activities. Because the sensitivity of this species to copper was previously unknown, we conducted acute copper toxicity tests with bull and rainbow trout (Oncorhynchus mykiss) in side-by-side comparison tests. Bioassays were conducted using water at two temperatures (8°C and 16°C) and two hardness levels (100 and 220 mg/L as CaCO3). At a water hardness of 100 mg/L, both species were less sensitive to copper when tested at 16°C compared to 8°C. The two species had similar sensitivity to copper in 100-mg/L hardness water, but bull trout were 2.5 to 4 times less sensitive than rainbow trout in 220-mg/L hardness water. However, when our results were viewed in the context of the broader literature on rainbow trout sensitivity to copper, the sensitivities of the two species appeared similar. This suggests that adoption of toxicity thresholds that are protective of rainbow trout would be protective of bull trout; however, an additional safety factor may be warranted because of the additional level of protection necessary for this federally threatened species. [source] Phase Relations Between ,-Tricalcium Phosphate and Hydroxyapatite with Manganese(II): Structural and Spectroscopic PropertiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2006Isaac Mayer Abstract The preparation of Mn-containing ,-tricalcium phosphate (,-TCP) samples was achieved in two ways: a) transformation of precipitated Mn-containing calcium hydroxyapatite (HA) to ,-TCP by heating at 1100 °C, and b) preparation by solid-state reaction of a mixture of CaCO3, (NH4)2HPO4, and Mn(NO3)2 at 1100 °C. Powder X-ray diffraction (XRD) analyses of the samples, obtained by both methods, show well-defined patterns with structural data of the rhombohedral R3c, ,-TCP phase. The calculated lattice constants are smaller than those known for ,-Ca3(PO4)2 because of substitution of Ca2+ by Mn2+. EPR spectroscopy indeed reveals that manganese is divalent in the samples. Apparently, the Ca(5) site in the ,-TCP structure is occupied by Mn2+. The distribution of Mn2+ between the ,-TCP and the HA phase in the case of preparation (b) was studied by EPR spectroscopy, and a pronounced preference for the former lattice was found. Micron- and submicron-sized crystals with visible faces were observed by TEM in the case of ,-TCP prepared by solid-state reaction, and large micron-sized, droplike-shaped crystals, sensitive to beam radiation, were found in the case of samples prepared by heating HA at elevated temperatures. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Nanometer-Scale Mapping of Elastic Modules in Biogenic Composites: The Nacre of Mollusk ShellsADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Haika Moshe-Drezner Abstract In this study, a newly developed nanoscale modulus mapping is applied in order to visualize the 2D-distribution of mechanical characteristics in the aragonitic nacre layer of Perna canaliculus (green mussel) shells. Modulus maps provide lateral resolution of about 10 nm. They allow the aragonitic mineral (CaCO3) tablets and the interfaces between them to be clearly resolved, which are filled by an organic substance (mainly beta-chitin). The experimental data are compared with finite element simulations that also take into account the tip radius of curvature and the thickness of organic layers, as measured by means of scanning electron microscopy with back-scattered electrons. Based on this comparison, the Young modulus of beta-chitin is extracted. The obtained number, E, = 40 GPa, is higher than previously evaluated. The collected maps reveal that the elastic modules in the nacre layer change gradually across the ceramic/organic interfaces within a spatial range four times wider than the thickness of the organic layers. This is possibly due to inhomogeneous distribution of organic macromolecules within ceramic tablets. According to the data, the concentration of macromolecules gradually increases when approaching the organic/ceramic interfaces. A behavior of this type is unique to biogenic materials and distinguishes them from synthetic composite materials. Finally, three possible mechanisms that attempt to explain why gradual changes of elastic modules significantly enhance the overall resistance to fracture of the nacre layer are briefly discussed. The experimental findings support the idea that individual ceramic tablets, comprising the nacre, are built of the compositionally and functionally graded ceramic material. This sheds additional light on the origin of the superior mechanical properties of biogenic composites. [source] Amorphous Calcium Carbonate is Stabilized in ConfinementADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Christopher J. Stephens Abstract Biominerals typically form within localized volumes, affording organisms great control over the mineralization process. The influence of such confinement on crystallization is studied here by precipitating CaCO3 within the confines of an annular wedge, formed around the contact point of two crossed half-cylinders. The cylinders are functionalized with self-assembled monolayers of mercaptohexadecanoic acid on gold. This configuration enables a systematic study of the effects of confinement since the surface separation increases continuously from zero at the contact point to macroscopic (mm) separations. While oriented rhombohedral calcite crystals form at large (>10,µm) separations, particles with irregular morphologies and partial crystallinity are observed as the surface separation approaches the dimensions of the unconfined crystals (5,10,µm). Further increase in the confinement has a significant effect on the crystallization process with flattened amorphous CaCO3 (ACC) particles being formed at micrometer separations. These ACC particles show remarkable stability when maintained within the wedge but rapidly crystallize on separation of the cylinders. A comparison of bulk and surface free-energy terms shows that ACC cannot be thermodynamically stable at these large separations, and the stability is attributed to kinetic factors. This study therefore shows that the environment in which minerals form can have a significant effect on their stability and demonstrates that ACC can be stabilized with respect to the crystalline polymorphs of CaCO3 by confinement alone. That ACC was stabilized at such large (micrometer) separations is striking, and demonstrates the versatility of this strategy, and its potential value in biological systems. [source] Seawater Mg/Ca controls polymorph mineralogy of microbial CaCO3: A potential proxy for calcite-aragonite seas in Precambrian timeGEOBIOLOGY, Issue 2 2008J. B. RIES ABSTRACT A previously published hydrothermal brine-river water mixing model driven by ocean crust production suggests that the molar Mg/Ca ratio of seawater (mMg/Casw) has varied significantly (~1.0,5.2) over Precambrian time, resulting in six intervals of aragonite-favouring seas (mMg/Casw > 2) and five intervals of calcite-favouring seas (mMg/Casw < 2) since the Late Archaean. To evaluate the viability of microbial carbonates as mineralogical proxy for Precambrian calcite-aragonite seas, calcifying microbial marine biofilms were cultured in experimental seawaters formulated over the range of Mg/Ca ratios believed to have characterized Precambrian seawater. Biofilms cultured in experimental aragonite seawater (mMg/Casw = 5.2) precipitated primarily aragonite with lesser amounts of high-Mg calcite (mMg/Cacalcite = 0.16), while biofilms cultured in experimental calcite seawater (mMg/Casw = 1.5) precipitated exclusively lower magnesian calcite (mMg/Cacalcite = 0.06). Furthermore, Mg/Cacalcite varied proportionally with Mg/Casw. This nearly abiotic mineralogical response of the biofilm CaCO3 to altered Mg/Casw is consistent with the assertion that biofilm calcification proceeds more through the elevation of , via metabolic removal of CO2 and/or H+, than through the elevation of Ca2+, which would alter the Mg/Ca ratio of the biofilm's calcifying fluid causing its pattern of CaCO3 polymorph precipitation (aragonite vs. calcite; Mg-incorporation in calcite) to deviate from that of abiotic calcification. If previous assertions are correct that the physicochemical properties of Precambrian seawater were such that Mg/Casw was the primary variable influencing CaCO3 polymorph mineralogy, then the observed response of the biofilms' CaCO3 polymorph mineralogy to variations in Mg/Casw, combined with the ubiquity of such microbial carbonates in Precambrian strata, suggests that the original polymorph mineralogy and Mg/Cacalcite of well-preserved microbial carbonates may be an archive of calcite-aragonite seas throughout Precambrian time. These results invite a systematic evaluation of microbial carbonate primary mineralogy to empirically constrain Precambrian seawater Mg/Ca. [source] Kinetics of Calcium Carbonate (CaCO3) Precipitation from a Icel-Yavca Dolomite Leach Solution by a Gas (Carbon Dioxide)/Liquid ReactionHELVETICA CHIMICA ACTA, Issue 3 2009Mehmet Yildirim Abstract The effects of time, CO2 -gas-injection pressure, and bulk temperature on the precipitation of Ca2+ ions as a precipitated calcium carbonate (PCC) from a dolomite leach solution were investigated. Precipitation periods from 1 to 7,min were examined, and experiments were run at CO2 -injection pressures of 200,800,kPa. Effects of bulk temperature were studied in the range from 40 to 70°, and precipitation rates of PCC were determined by measuring the Ca2+ concentrations in the initial and effluent solutions. Influences of these parameters on the subsequent incorporation of Mg2+ ions with the precipitate are discussed in detail. Kinetic analysis of the precipitation was performed by considering the rates as a function of CO -ion concentrations. Results obtained by this process clearly show that Ca2+ ions in the solution can successfully be precipitated as a calcium carbonate product containing 54.70% of CaO and 0.77% MgO, at the rate of 2.01,mM h,1. [source] The influence of diurnal temperatures on the hydrochemistry of a tufa-depositing streamHYDROLOGICAL PROCESSES, Issue 17 2003R. Drysdale Abstract At-a-station diurnal variations in carbonate hydrochemistry were measured during four observation periods at Davys Creek, a tufa-depositing stream in central NSW, Australia. Major ion concentrations and continuously logged measurements of specific conductivity, pH and temperature showed that changes in the amount of CaCO3 deposited upstream of the study reach were directly related to changes in diurnal water temperatures, which control the rate of CO2 efflux to the atmosphere. The greatest upstream losses occurred during the mid-afternoon water temperature peak, whereas the lowest upstream losses occurred at sunrise, when water temperatures were at their lowest. Cloudy days at all times of the year produced small diurnal water temperatures ranges (c. 2,5°C) and, consequently, relatively small changes in upstream CaCO3 loss (23,50 mg L,1) through the day. Clear sunny days, especially during summer months, produced large diurnal water temperature changes (up to c. 11°C), which in turn triggered diurnal changes in upstream CaCO3 loss of up to 100 mg L,1. By implication, the active reach of tufa deposition must advance downstream and increase in length during the evening and vice versa during the day. Given that the temperature of Davys Creek waters are a function of insolation, changes in the reach of tufa deposition under baseflow conditions are a direct function of the prevailing weather. This has implications for the palaeoclimatic interpretation of fossil tufa deposits. Copyright © 2003 John Wiley & Sons, Ltd. [source] Factors controlling the chemical evolution of travertine-depositing rivers of the Barkly karst, northern AustraliaHYDROLOGICAL PROCESSES, Issue 15 2002Russell N. Drysdale Abstract Groundwaters feeding travertine-depositing rivers of the northeastern segment of the Barkly karst (NW Queensland, Australia) are of comparable chemical composition, allowing a detailed investigation of how the rate of downstream chemical evolution varies from river to river. The discharge, pH, temperature, conductivity and major-ion concentrations of five rivers were determined by standard field and laboratory techniques. The results show that each river experiences similar patterns of downstream chemical evolution, with CO2 outgassing driving the waters to high levels of calcite supersaturation, which in turn leads to widespread calcium carbonate deposition. However, the rate at which the waters evolve, measured as the loss of CaCO3 per kilometre, varies from river to river, and depends primarily upon discharge at the time of sampling and stream gradient. For example, Louie Creek (Q = 0·11 m3 s,1) and Carl Creek (Q = 0·50 m3 s,1) have identical stream gradients, but the loss of CaCO3 per kilometre for Louie Creek is twice that of Carl Creek. The Gregory River (Q = 3·07 m3 s,1), O'Shanassy River (Q = 0·57 m3 s,1) and Lawn Hill Creek (Q = 0·72 m3 s,1) have very similar gradients, but the rate of hydrochemical evolution of the Gregory River is significantly less than either of the other two systems. The results have major implications for travertine deposition: the stream reach required for waters to evolve to critical levels of calcite supersaturation will, all others things being equal, increase with increasing discharge, and the length of reach over which travertine is deposited will also increase with increasing discharge. This implies that fossil travertine deposits preserved well downstream of modern deposition limits are likely to have been formed under higher discharge regimes. Copyright © 2002 John Wiley & Sons, Ltd. [source] Submicrometer-Sized Vaterite Tubes Formed Through Nanobubble-Templated Crystal Growth,ADVANCED MATERIALS, Issue 19 2005W. Fan Electrolytic deposition is used to prepare submicrometer-sized vaterite (CaCO3) tubes (see Figure) in the absence of organic molecules, the presence of which was previously thought to be necessary for the growth of calcium carbonate crystals in complex morphologies. The mechanism of formation is shown experimentally to be hydrogen-nanobubble-templated crystal growth. [source] Stable Amorphous CaCO3 Microparticles with Hollow Spherical Superstructures Stabilized by Phytic Acid,ADVANCED MATERIALS, Issue 18 2005A.-W. Xu Amorphous CaCO3 (ACC) is stabilized by the presence of phytic acid, a natural inositol hexakisphosphate (IP6). Micrometer-sized hollow spheres of ACC have been obtained (see Figure). The spheres are stable for at least three months in solution, which is equivalent to that described for more complex special biopolymers in biomineralization processes, and by far exceeds the previously known stability of ACC prepared in the presence of synthetic molecules. [source] Electrical and thermal properties of nylon 6/calcium carbonate compositesADVANCES IN POLYMER TECHNOLOGY, Issue 4 2009M. A. Moussa Abstract Several polymer composites formed from nylon 6/CaCO3 with different ratios and particle sizes were prepared using modified and unmodified CaCO3 as inorganic filler. The modification of CaCO3 surfaces was carried out by adsorption of oleic acid from toluene. TGA and DSC measurements show that the glass transition temperatures reduced by the presence of inorganic filler, whereas the melting temperature did not influenced. In all prepared polymer composites, the presence of filler accelerates the degradation process of the polymer. Dielectric properties of the investigated samples were studied in the frequency range from 45 Hz to 1 MHz and at temperatures ranging between 50 and 200°C. The presence of CaCO3 led to a remarkable decrease in the conductivity of nylon 6. © 2010 Wiley Periodicals, Inc. Adv Polym Techn 28:257,266, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20165 [source] Recycling of the solid residue obtained from the pyrolysis of fiberglass polyester sheet molding compoundADVANCES IN POLYMER TECHNOLOGY, Issue 2 2009A. Torres Abstract This paper is part of a project devoted to study the pyrolysis process as an alternative for recycling sheet molding compound (SMC), a thermoset composite of polyester and fiberglass. A standard SMC was pyrolyzed under nitrogen, at 300, 400, 500, 600, and 700°C, for 30 min in a 3.5-dm3 autoclave. This paper focuses on the possibilities of reusing the fibers and fillers contained in the solid residue obtained from SMC pyrolysis. The solid pyrolysis residue was recycled in another thermoset composite, bulk molding compound (BMC), of polyester and fiberglass. The mechanical properties of BMCs prepared with different proportions of the solid residue (fiber + CaCO3 filler) from SMC pyrolysis were compared with those of BMCs prepared with the same proportions of virgin fiber and CaCO3. In summary, pyrolysis can be an appropriate technique for recycling SMC, with 500°C, the most suitable temperature for the process. Solid residues of 75 wt%, composed of 65 wt% of powdery material (mainly CaCO3) and 35 wt% of fiberglass, were obtained. Such solids can be recycled in a proportion of 6 wt% in BMC to replace virgin filler and fiberglass, with no detrimental effect on the BMC mechanical properties. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 28:141,149, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20150 [source] Identification and production of a bacteriocin from Enterococcus mundtii QU 2 isolated from soybeanJOURNAL OF APPLIED MICROBIOLOGY, Issue 5 2005T. Zendo Abstract Aims:, Identification of the bacteriocin produced by Enterococcus mundtii QU 2 newly isolated from soybean and fermentative production of the bacteriocin. Methods and Results:, The bacteriocin produced by Ent. mundtii QU 2 inhibited the growth of various indicator strains, including Enterococcus, Lactobacillus, Leuconostoc, Pediococcus and Listeria. The bacteriocin activity was stable at wide pH range and against heat treatment, but completely abolished by proteolytic enzymes. The bacteriocin was purified from the culture supernatant by the three-step chromatographic procedure. Mass spectrometry, amino acid sequencing and DNA sequencing revealed that the bacteriocin was similar to class IIa bacteriocins produced by other Ent. mundtii strains. The bacteriocin production decreased in the absence of glucose, nitrogen sources, or Tween 80 in MRS medium. Additionally, it was strongly suppressed by addition of Ca2+ (CaCO3 or CaCl2). In pH-controlled fermentations, the highest bacteriocin production was achieved at pH 6·0, whereas the highest cell growth was obtained at pH 7·0. Conclusions:,Ent. mundtii QU 2 produced a class IIa bacteriocin. Some growth factors (e.g. Ca2+ and pH) influenced the bacteriocin production. Significance and Impact of the Study:, A new soybean isolate, Ent. mundtii QU 2 was found to be a class IIa bacteriocin producer. Factors influencing the bacteriocin production described herein are valuable for applications of the bacteriocins from Ent. mundtii strains. [source] Fabrication of aragonite rosette superstructure through the weak interaction between nonionic polymers and Ca2+JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Shuxian Shi Abstract The controlled formation of aragonite by simple method under ambient condition is a big challenge for biomaterial scientists. In this article, we took poly (N -vinyl pyrrolidone) (PVP) as an example to investigate the influence of water-soluble nonionic polymers on the polymorphs of CaCO3 via CO2 diffusion method under ambient pressure and temperature, and found that the existence of PVP molecules favors the formation of aragonite with rosette superstructure. A possible mechanism is proposed that nonionic polymers can be doped into amorphous calcium carbonate (ACC) particles and further participate in the transformation process from ACC to aragonite and then promotes the formation of rosette superstructure through parallel aggregation by crosslinking the aragonite nuclei. The experiments of CaCO3 crystallization in presence of poly(ethylene oxide) (PEO) and poly(vinyl alcohol) (PVA) confirmed the mechanism. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] The partial replacement of silica or calcium carbonate by halloysite nanotubes as fillers in ethylene propylene diene monomer compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2009Pooria Pasbakhsh Abstract The effect of partial replacement of silica or calcium carbonate (CaCO3) by halloysite nanotubes (HNTs) on the curing behavior, tensile properties, dynamic mechanical properties, and morphological characteristics of ethylene propylene diene monomer (EPDM) composites was studied. Five different compositions of EPDM/Silica/HNT and EPDM/CaCO3/HNT compounds (i.e. 100/30/0, 100/25/5, 100/15/15, 100/5/25, and 100/0/30 parts per hundred rubber (phr)) were prepared on a two-roll mill. The results indicated that the replacement of CaCO3 by HNTs increased the tensile strength, elongation at break (Eb), and tensile modulus of composites from 0 to 30 phr of HNTs whereas for silica, the maximum tensile strength and Eb occurred at 5 phr loading of HNTs with an enhanced stress at 300% elongation (M300). The curing results show that, with replacement of silica or CaCO3 by HNTs, the cure time (t90) and cure rate (CRI) were decreased and increased, respectively. Scanning electron microscopy investigation confirmed that co-incorporation of 5 phr of HNTs with silica would improve the dispersion of silica and enhanced the interactions between fillers and EPDM matrix. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Comparison of mechanical properties of PP/SEBS blends at intermediate and high strain rates with SiO2 nanoparticles vs.JOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008CaCO3 fillers Abstract The present article focuses on the effect of two types of inorganic fillers (SiO2 and CaCO3) on the mechanical properties of PP/SEBS blend. The nominal particle diameters of SiO2 and CaCO3 are 7 nm and 1 ,m, respectively. The studied blend ratios were PP/SEBS/SiO2 (CaCO3) = 75/22/3 and 73/21/6 vol %. The morphology of polymer blends was observed and the distributions of the SEBS, SiO2, and CaCO3 particles were analyzed by transmission electron microscopy (TEM). Tensile tests were conducted at nominal strain rates from 3 × 10,1 to 102 s,1. The apparent elastic modulus has the local strain-rate dependency caused by SiO2 nanoparticles around SEBS particles in the blend of PP/SEBS/SiO2. The yield stress has weak dependency of morphology. The absorbed strain energy has strong dependency of the location of SiO2 nanoparticle or CaCO3 fillers and SEBS particle in the morphology. It is considered that such morphology, in which inorganic nanoparticles are located around SEBS particles, can prevent the brittle fracture while the increased local strain rate can enhance the apparent elastic modulus of the blend at the high strain rate. On the basis of the results of this study, the location and size of inorganic nanoparticles are the most important parameters to increase the elastic modulus without decreasing the material ductility of the blend at both low and high strain rates. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Effects of bivalve shell particles of hyriopsis cumingii on the performances of epoxy resin studied by positron annihilationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Xudong Sun Abstract Mussel shell particles sized in micrometer level have been prepared with a ball mill. The X-ray powder diffractrometer (XRD) and Fourier transform infrared (FTIR) results proved that the shell particles contained mainly CaCO3 in the form of aragonite, together with small amount of organic phase. EP modified with shell particles showed a much rougher fracture surface than unfilled EP. The mechanical properties have been improved obviously by adding the shell particles in EP from 1% to 5%. The particle would occupy a number of free volume holes of the EP matrix. This would lead to a decrease in the total free volume concentration of the composites. The particles acted as a bridge to make more molecules interconnected for the good interfacial adhesion, resulting in a reduction of the free volume hole size in the interfacial layers. I2 reached its highest value when 3% shell particles were added and then decreased as the shellparticles content increased. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Isothermal crystallization of high density polyethylene and nanoscale calcium carbonate compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Jiann-Wen HuangArticle first published online: 26 NOV 200 Abstract High density polyethylene (HDPE) and calcium carbonate (CaCO3) nanocomposites with maleic anhydride grafted HDPE (manPE) as a compatibilizer were prepared via compounding in a twin-screw extruder. The CaCO3 are well dispersed in the HDPE matrix from the observation of transmission electron microscope. The isothermal crystallization kinetics was studied by differential scanning calorimetry and simulated by Avrami and Tobin models. The nucleation constants and fold surface free energy were estimated from Lauritzen,Hoffman relation. The results indicate that both manPE and well-dispersed CaCO3 particles would act as nuclei to induce heterogeneous nucleation and enhance crystallization rate. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Dynamic mechanical properties and morphology of high-density polyethylene/CaCO3 blends with and without an impact modifierJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007Yu-Lin Yang Abstract Dynamic mechanical analysis and differential scanning calorimetry were used to investigate the relaxations and crystallization of high-density polyethylene (HDPE) reinforced with calcium carbonate (CaCO3) particles and an elastomer. Five series of blends were designed and manufactured, including one series of binary blends composed of HDPE and amino acid treated CaCO3 and four series of ternary blends composed of HDPE, treated or untreated CaCO3, and a polyolefin elastomer [poly(ethylene- co -octene) (POE)] grafted with maleic anhydride. The analysis of the tan , diagrams indicated that the ternary blends exhibited phase separation. The modulus increased significantly with the CaCO3 content, and the glass-transition temperature of POE was the leading parameter that controlled the mechanical properties of the ternary blends. The dynamic mechanical properties and crystallization of the blends were controlled by the synergistic effect of CaCO3 and maleic anhydride grafted POE, which was favored by the core,shell structure of the inclusions. The treatment of the CaCO3 filler had little influence on the mechanical properties and morphology. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3907,3914, 2007 [source] Effects on the removal of Pb2+ from aqueous solution by crab shellJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 11 2001Dong Seog Kim Abstract The effects of temperature, pH, chitin and chitosan on Pb2+ removal by crab shell were investigated. Pb2+ removal by crab shell was greater than that of chitin and chitosan, indicating that chitin did not contribute to Pb2+ removal by crab shell. The quantity and rate of Pb2+ removal increased as the pH value increased. The rate of Pb2+ removal increased with increased temperature, but the maximum amount of Pb2+ removal was constant irrespective of temperature. Metal ions (K+, Na+, Mg2+, Ca2+) were released from crab shell concomitant with Pb2+ removal by ion exchange. The amount of Ca2+ released was greater than any for other metal ions in both Pb2+ and Pb2+ -free solutions. The amount of Ca2+ released in Pb2+ solution was greater than that in Pb2+ -free solution, whereas CO32, release in Pb2+ solution was less than in Pb2+ -free solution. Pb2+ removal was mainly a consequence of dissolution of CaCO3(s) with consequence precipitation of Pb3(CO3)2(OH)2(s) and PbCO3(s). Pb2+ accelerated the dissolution of CaCO3(s) by ion exchange and the precipitation occurred both at the surface and in the inner part of the crab shell. © 2001 Society of Chemical Industry [source] In vitro analysis of intestinal absorption of cadmium and calcium in rainbow trout fed with calcium- and cadmium-supplemented dietsJOURNAL OF FISH BIOLOGY, Issue 3 2006B. Baldisserotto The protective effects of dietary Ca2+ supplementation against Cd accumulation in rainbow trout Oncorhynchus mykiss fed with Cd-contaminated food were evaluated in relation to chronic changes in intestinal absorption rates. The changes were measured ,in vitro'. The control diet contained c. 20 mg Ca2+ g,1 food and 0·25 ,g Cd g,1 food; the experimental diets were supplemented with CaCO3 and Cd(NO3)2·4H2O to levels of 50 mg Ca2+ g,1 food and 300 ,g Cd g,1 food, alone and in combination. The Ca2+ and Cd absorption rates were measured using radiotracers (45Ca, 109Cd) at total Ca2+ and Cd concentrations of 3·0 and 0·12 mmol l,1, respectively in the intestinal saline. Chronically elevated dietary Cd caused a significant increase in Cd absorption rate by up to 10-fold at 30 days in the mid-intestine. The high Ca2+ diet prevented this up-regulation of Cd transport rate. Conversely, intestinal Ca2+ absorption was significantly increased by two- to five-fold by the Ca2+ -supplemented diet at 30 days in both the mid- and posterior intestine, and this effect was eliminated when Cd was simultaneously elevated in the diet. Ca2+ and Cd probably interact at common pathways and transport mechanisms in the intestine, though independent pathways may also exist. [source] PRODUCTION OF LIQUID AND WHITE SOLID PEKMEZ IN TURKEYJOURNAL OF FOOD QUALITY, Issue 5-6 2005ALI BATU ABSTRACT The research was carried out to evaluate gelling and bleaching agents for white solid pekmez production. Grape juice with 26% total soluble solids as °Brix was used for the production of pekmez. Acidity was reduced with the application of sterile white soil containing 70.4% CaCO3, followed by tannin,gelatin clarification and filtration. The grape juice was concentrated to 76% total soluble solids by vacuum. Gelling treatments were designed to produce a solid pekmez by adding high or low methoxyl pectins or carboxymethylcellulose (CMC). It was found that sufficient gelling could be achieved using less than 0.5% CMC and 1% for either pectin. Also, a desirable white color was obtained with 1.5% soapwort juice and 3% egg white with the combination of 1% pectins. [source] | ||||||||||||||||||||||||||||||||||||||||