695 research outputs found
Carbonation of alkaline paper mill waste to reduce CO2 greenhouse gas emissions into the atmosphere
International audienceThe global warming of Earth's near-surface, air and oceans in recent decades is a direct consequence of anthropogenic emission of greenhouse gases into the atmosphere such as CO2, CH4, N2O and CFCs. The CO2 emissions contribute approximately 60% to this climate change. This study investigates experimentally the aqueous carbonation mechanisms of an alkaline paper mill waste containing about 55 wt% portlandite (Ca(OH)2) as a possible mineralogical CO2 sequestration process. The overall carbonation reaction includes the following steps: (1) Ca release from portlandite dissolution, (2) CO2 dissolution in water and (3) CaCO3 precipitation. This CO2 sequestration mechanism was supported by geochemical modelling of final solutions using PHREEQC software, and observations by scanning electron microscope and X-ray diffraction of final reaction products. According to the experimental protocol, the system proposed would favour the total capture of approx. 218 kg of CO2 into stable calcite/ton of paper waste, independently of initial CO2 pressure. The final product from the carbonation process is a calcite (ca. 100 wt%)-water dispersion. Indeed, the total captured CO2 mineralized as calcite could be stored in degraded soils or even used for diverse industrial applications. This result demonstrates the possibility of using the alkaline liquidâsolid waste for CO2 mitigation and reduction of greenhouse effect gases into the atmosphere
Mineral sequestration of CO2 by aqueous carbonation of coal combustion fly-ash
International audienceThe increasing CO2 concentration in the Earth's atmosphere, mainly caused by fossil fuel combustion, has led to concerns about global warming. A technology that could possibly contribute to reducing carbon dioxide emissions is the in-situ mineral sequestration (long term geological storage) or the ex-situ mineral sequestration (controlled industrial reactors) of CO2. In the present study, we propose to use coal combustion fly-ash, an industrial waste that contains about 4.1 wt.% of lime (CaO), to sequester carbon dioxide by aqueous carbonation. The carbonation reaction was carried out in two successive chemical reactions, first, the irreversible hydration of lime. CaO + H2O â Ca(OH)2 second, the spontaneous carbonation of calcium hydroxide suspension. Ca(OH)2 + CO2 â CaCO3 + H2O A significant CaOâCaCO3 chemical transformation (approximately 82% of carbonation efficiency) was estimated by pressure-mass balance after 2 h of reaction at 30 °C. In addition, the qualitative comparison of X-ray diffraction spectra for reactants and products revealed a complete CaOâCaCO3 conversion. The carbonation efficiency of CaO was independent on the initial pressure of CO2 (10, 20, 30 and 40 bar) and it was not significantly affected by reaction temperature (room temperature â20â25â, 30 and 60 °C) and by fly-ash dose (50, 100, 150 g). The kinetic data demonstrated that the initial rate of CO2 transfer was enhanced by carbonation process for our experiments. The precipitate calcium carbonate was characterized by isolated micrometric particles and micrometric agglomerates of calcite (SEM observations). Finally, the geochemical modelling using PHREEQC software indicated that the final solutions (i.e. after reaction) are supersaturated with respect to calcium carbonate (0.7 †saturation index †1.1). This experimental study demonstrates that 1 ton of fly-ash could sequester up to 26 kg of CO2, i.e. 38.18 ton of fly-ash per ton of CO2 sequestered. This confirms the possibility to use this alkaline residue for CO2 mitigation
Arsenite sorption and co-precipitation with calcite
Sorption of As(III) by calcite was investigated as a function of As(III)
concentration, time and pH. The sorption isotherm, i.e. the log As(III) vs. log
[As(OH)3 degrees / Assat] plot is S-shaped and has been modelled on an extended
version of the surface precipitation model. At low concentrations, As(OH)3
degrees is adsorbed by complexation to surface Ca surface sites, as previously
described by the X-ray standing wave technique. The inflexion point of the
isotherm, where As(OH)3 degrees is limited by the amount of surface sites (ST),
yields 6 sites nm-2 in good agreement with crystallographic data. Beyond this
value, the amount of sorbed arsenic increases linearly with solution
concentration, up to the saturation of arsenic with respect to the
precipitation of CaHAsO3(s). The solid solutions formed in this concentration
range were examined by X-ray and neutron diffraction. The doped calcite lattice
parameters increase with arsenic content while c/a ratio remains constant. Our
results made on bulk calcite on the atomic displacement of As atoms along
[0001] direction extend those published by Cheng et al., (1999) on calcite
surface. This study provides a molecular-level explanation for why As(III) is
trapped by calcite in industrial treatments.Comment: 9 page
Synthesis of a Se0/Calcite Composite Using Hydrothermal Carbonation of Ca(OH)2 Coupled to a Complex Selenocystine Fragmentation
International audienceElemental selenium (Se0)/calcite composites were synthesized in a batch system by hydrothermal carbonation of calcium hydroxide under high CO2âAr pressure (90 bar) and high temperature (90 °C) coupled to a complex selenocystine fragmentation. Under O2-poor conditions, the composite consisted predominantly of spherical, amorphous nanoparticles of elemental red selenium (<500 nm) deposited on the calcite matrix. Conversely, under O2-rich conditions, the composite consisted rod-shaped, well-crystallized microparticles of elemental gray selenium (<25 ”m) dispersed in the calcite matrix. The carbonate matrix was constituted by nano- to microrhombohedral crystals (<2 ”m) and micrometric agglomerates and/or aggregates (<5 ”m). Our results present a new synthesis path to Se0/calcite composites, with spherical or rod-shaped Se0 morphology with high potential for medical (e.g., dietary supplement) or industrial (e.g., pigments) applications. Furthermore, this study may have implications in the field of biomineralization
Bose-Einstein source of intermittency in hadronic interactions
The multi-particle Bose-Einstein correlations are the source of
''intermittency'' in high energy hadronic collisions. The power-law like
increase of factorial moments with decreasing bin size was obtained by complete
event weighing technique with gaussian approximation of space-time particle
emitting source shape. The value of source size parameter was found to be
higher than the common one fitted with the help of the standard Handbury
Brown-Twiss procedure.Comment: 12
Neurohypophysial Receptor Gene Expression by Thymic T Cell Subsets and Thymic T Cell Lymphoma Cell Lines
Abstract
Neurohypophysial oxytocin (OT) and vasopressin (VP) genes are
transcribed in thymic epithelium, while immature T lymphocytes express
functional neurohypophysial receptors. Neurohypophysial receptors belong
to the G protein-linked seven-transmembrane receptor superfamily and are encoded
by four distinct genes, OTR, V1R, V2R
and V3R. The objective of this study was to
identify the nature of neurohypophysial receptor in thymic T cell subsets purified by
immunomagnetic selection, as well as in murine thymic lymphoma cell lines RL12-NP
and BW5147. OTR is transcribed in all thymic T cell subsets and T cell lines, while
V3R transcription is restricted to CD4+ CD8+ and CD8+ thymic cells. Neither V1R nor
V2R transcripts are detected in any kind of T cells. The OTR protein was identified by
immunocytochemistry on thymocytes freshly isolated from C57BL/6 mice. In murine fetal
thymic organ cultures, a specific OTR antagonist does not modify the percentage of T
cell subsets, but increases late T cell apoptosis further evidencing the involvement of
OT/OTR signaling in the control of T cell proliferation and survival. According to these
data, OTR and V3R are differentially expressed during T cell ontogeny. Moreover, the
restriction of OTR transcription to T cell lines derived from thymic lymphomas may be
important in the context of T cell leukemia pathogenesis and treatment
Generic and Layered Framework Components for the Control of a Large Scale Data Acquisition System
The complexity of today's experiments in High Energy Physics results in a large amount of readout channels which can count up to a million and above. The experiments in general consist of various subsystems which themselves comprise a large amount of detectors requiring sophisticated DAQ and readout electronics. We report here on the structured software layers to control such a data acquisition system for the case of LHCb which is one of the four experiments for LHC. Additional focus is given on the protocols in use as well as the required hardware. An abstraction layer was implemented to allow access on the different and distinct hardware types in a coherent and generic manner. The hierarchical structure which allows propagating commands down to the subsystems is explained. Via finite state machines an expert system with auto-recovery abilities can be modeled
Integral correlation measures for multiparticle physics
We report on a considerable improvement in the technique of measuring
multiparticle correlations via integrals over correlation functions. A
modification of measures used in the characterization of chaotic dynamical
sytems permits fast and flexible calculation of factorial moments and cumulants
as well as their differential versions. Higher order correlation integral
measurements even of large multiplicity events such as encountered in heavy ion
collisons are now feasible. The change from ``ordinary'' to ``factorial''
powers may have important consequences in other fields such as the study of
galaxy correlations and Bose-Einstein interferometry.Comment: 23 pages, 6 tar-compressed uuencoded PostScript figures appended,
preprint TPR-92-4
PRACTICAL IMPLEMENTATION OF PHOTOGRAMMETRY FOR THE MODELLING OF A CYLINDRICAL HISTORICAL BUILDING
This work deals with the image capture for close-range photogrammetry in the context of the modelling of a round tower with repetitive texture (made of bricks), both inside and outside. For that purpose we test different acquisition strategies that differ in terms of camera path (straight or circular) and number of images acquired at each camera position, that is with or without oblique images. Besides, the formula to compute the curvilinear base according to a given overlap rate between successive frontal photos are written for each strategy. The comparisons rely on the observation of the aspect of the different dense point clouds (noise, holes), the deformation seen in the orthomosaics and values extracted from the photogrammetric projects such as metric accuracies with GCP. Our results confirm some art rules
Textural properties of synthetic nano-calcite produced by hydrothermal carbonation of calcium hydroxide
The hydrothermal carbonation of calcium hydroxide (Ca(OH)2) at high pressure
of CO2 (initial PCO2 1/4 55 bar) and moderate to high temperature (30 and 90
1C) was used to synthesize fine particles of calcite. This method allows a high
carbonation efficiency (about 95% of Ca(OH)2-CaCO3 conversion), a significant
production rate (48 kg/m3 h) and high purity of product (about 96%). However,
the various initial physicochemical conditions have a strong influence on the
crystal size and surface area of the synthesized calcite crystals. The present
study is focused on the estimation of the textural properties of synthesized
calcite (morphology, specific surface area, average particle size, particle
size distribution and particle size evolution with reaction time), using
Rietveld refinements of X-ray diffraction (XRD) spectra, Brunauer-Emmett-Teller
(BET) measurements, and scanning electron microscope (SEM) and transmission
electron microscope (TEM) observations. This study demonstrate that the
pressure, the temperature and the dissolved quantity of CO2 have a significant
effect on the average particle size, specific surface area, initial rate of
precipitation, and on the morphology of calcium carbonate crystals. In
contrast, these PTx conditions used herein have an insignificant effect on the
carbonation efficiency of Ca(OH)2. Finally, the results presented here
demonstrate that nano-calcite crystals with high specific surface area (SBET
1/4 6-10m2/g) can be produced, with a high potential for industrial
applications such as adsorbents and/or filler in papermaking industry
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