[Show abstract][Hide abstract] ABSTRACT: This work presents a study on the chemisorption of CO2 by a bed of Ca(OH)2 powder subjected to the flow of a dry CO2/N2 gas mixture (1 vol.% CO2) at ambient temperature and atmospheric pressure. The amount of CO2 and vapor water in the effluent gas from the fluidized bed is analyzed by means of FTIR spectrophotometry. The results obtained indicate that, even in an almost dry atmosphere (RH ⪕ 0.01%), CO2 capture in the fluidized bed occurs by chemisorption on Ca(OH)2, as inferred from the rise of vapor water at the end of the fast carbonation phase. The use of nanosilica as an additive increases the gas–solids contact efficiency and, therefore, enhances CO2 chemisorption on Ca(OH)2 particles. This process is initially activated by free molecular water physisorbed on the material and becomes autocatalyzed by water produced from Ca(OH)2 carbonation. Accordingly, the addition of hydrophilic nanosilica, capable of retaining higher amounts of free molecular water, yields a further enhancement of the CO2 fast sorption capacity.
Full-text · Article · Apr 2013 · The Chemical Engineering Journal
[Show abstract][Hide abstract] ABSTRACT: In this work, we analyze the CO2 adsorption performance in a fluidized bed of a modified adsorbent, which is obtained by dry mixing a Ca(OH)2 fine cohesive powder (Geldart C) with a fluidizable silica nanopowder. The silica nanoparticle agglomerates serve as carriers of the adsorbent Ca(OH)2 fine particles, which are thus provided with a vehicle for improved fluidization. Experimental measurements are presented on the capture capacity of the modified adsorbent as compared to the original adsorbent. As the gas flow rate is increased, gas channeling in the fluidized bed of the original adsorbent causes a rapid decrease of the time for CO2 breakthrough in the effluent gas (BT) and the capture capacity at CO2 breakthrough (XBT). In contrast, because of the improvement of gas–solid contact efficiency, BT and XBT are appreciably increased for the modified adsorbent. Thus, even though the silica nanoparticle agglomerates do not contribute directly to CO2 adsorption, fluidization enhancement allows for maintaining relatively higher capture capacities at large values of the gas flow rate.
[Show abstract][Hide abstract] ABSTRACT: A method is presented for reducing the aggregative behavior of a commercial Ca(OH)2 fine powder for CO2 capture. SEM images showed that silica NP aggregates, which are easily fluidized, became coated with the Ca(OH)2 fine particles. TGA tests performed carbonation-calcination cycles demonstrated that the CO2 adsorption rate was increased in the fast carbonation stage. Degeneration of the adsorbent after a large number of carbonation-calcination cycles was lessened, which gave rise to a higher residual adsorption capacity. By improving fluidization homogeneity, the effective gas-solids contact surface was increased in a fluidized bed, which increased appreciably the CO2 breakthrough time and the adsorption capacity. This is an abstract of a paper presented at the CHISA 2012 - 20th International Congress of Chemical and Process Engineering and PRES 2012 - 15th Conference PRES (Prague, Czech Republic 8/25-29/2012).
[Show abstract][Hide abstract] ABSTRACT: A modified CO(2) adsorbent is obtained by dry mixing of a Ca(OH)(2) fine powder as received with a commercial silica nanopowder. Silica nanoparticles form light agglomerates of size of the order of tens of microns, which are uniformly fluidizable. These agglomerates act as dispersants of the Ca(OH)(2) fine particles, which coat the nanoparticle agglomerates likely due to contact charging. Ca(OH)(2) particles (CO(2) adsorbent) are thus provided with a vehicle for uniform fluidization. In this way, the contact efficiency between the CO(2) adsorbent and CO(2) in the fluidized bed is greatly enhanced. Experimental results show that the improvement of Ca(OH)(2) fluidizability serves to enhance the carbonation reaction in the fluidized bed.
[Show abstract][Hide abstract] ABSTRACT: In this work, we present an experimental study of the reduction of NO and the creation of NO2 by positive corona discharge in N2/O2 mixture (95% N2, 5%O2), where 200ppm of NO are injected at atmospheric pressure. The corona discharge was generated using a wire- to- cylinder reactor. The applied voltage is 5kV and 7 kV and it was maintained for 50 minutes. Ultraviolet absorption spectroscopy operating in the wavelength range 190-330 nm was used to identify the species and quantify their concentration, According to Beer Lambert law who give concentration from absorbance. The temperature was maintained constant for 300K. The obtained resultant show nitrous oxide NO has been destroyed with the augmenta¬tion of corona current. We note different times to NO removal, 50 minutes at 5 kV and 20 minutes at 7 kV. And we observe the creation of NO2 and the apparition of ozone O3.
[Show abstract][Hide abstract] ABSTRACT: Positive wire-to-cylinder corona discharge in pure CO2 has been simulated using a model that includes elementary plasma processes (ionization, electron attachment and detachment, ion recombination, etc.) and chemical reactions between neutral species. The plasma chemistry model is included in the continuity equations of species, which are coupled with Poissons equation for the electric field and the energy conservation equation for the gas temperature. The experimental values of voltage and current are used as input data into the numerical simulation, and the spatial distributions of electrons, ions, atoms and molecules are then predicted for different gas flow rates. The average concentrations of ozone and carbon monoxide inside the discharge reactor have been experimentally determined by means of ultraviolet and FTIR spectrometry, and their values are compared with the results of the numerical simulation.
[Show abstract][Hide abstract] ABSTRACT: The formation of ozone and nitrogen oxides in synthetic air by negative DC corona discharge has been experimentally investigated. The electrical discharge was generated using a coaxial wire-cylinder corona discharge reactor, and different gas flow rates were imposed through the discharge cell. Ultraviolet absorption spectroscopy was used to identify and quantify the generation of chemical species.
[Show abstract][Hide abstract] ABSTRACT: The formation of nitrogen oxides (NO, NO<sub>2</sub>, N<sub>2</sub>O and N<sub>2</sub>O<sub>5</sub>) and ozone (O<sub>3</sub>) by negative DC and pulsed corona discharge has been investigated. The corona discharge was generated using a wire-to-cylinder reactor, filled with different mixtures of nitrogen and oxygen at atmospheric pressure and ambient temperature. Ultraviolet absorption spectroscopy operating in the wavelength range of 190 to 330 nm was used to identify the species and quantify their concentrations.
[Show abstract][Hide abstract] ABSTRACT: The Odiel and Tinto rivers, southwest Spain, form a fully mixed estuary. An industrial area that includes a complex dedicated
to the production of phosphate fertilizers is located by the Odiel River. This complex released phosphogypsum wastes directly
to the Odiel River and also disposed them on open air piles located by the Tinto River. Due to new EU regulations, wastes
are not directly released to the Odiel from 1998 on, although they are still disposed on the open air piles. The behavior
of 226Ra in a system like this estuary is complex, since radionuclides are affected by tidal actions and interactions with sediments
through adsorption/desorption reactions and erosion/deposition processes. A numerical 2D depth-averaged model of the estuary
has been developed, including processes mentioned above. It has been applied to reproduce experimental data measured after
a release from the industrial complex in the Odiel River and after an accidental release in the Tinto River from the gypsum
piles. The model has also been applied to simulate the self-cleaning process observed in the estuary after the direct releases
from the fertilizer complex were stopped.
Full-text · Article · Nov 2007 · Journal of Radioanalytical and Nuclear Chemistry
[Show abstract][Hide abstract] ABSTRACT: An experimental procedure has been developed for a rapid determination of the activity concentration of 226Ra and 224Ra in sediments by liquid scintillation counting. The importance of the method lies in its application to the measurement of sediments where the Ra-isotopes activity concentration has been increased due to an anthropomorphic enhancement based on releases of naturally occurring radioactive material (NORM). A sample pre-treatment, including a digestion with aqua regia and a precipitation of hydroxides, was applied to samples before the radium extraction, which was made by co-precipitation with barium. Measurements were done in a low background scintillation spectrometer Quantulus 1220, which can separate and detect simultaneously α and β particles. Additionally, some improvements are suggested for a better α and β interference correction of the results. The obtaining of radiochemical yields is also improved using 133Ba as tracer, which decays by emission of conversion electrons and γ-rays; the wide range of radiochemical yields obtained confirms the need of this analyses. The procedure has been applied to the measurement of riverbed sediments from an estuary in the south-west of Spain, affected in the past by direct and indirect phosphogypsum discharges.
No preview · Article · Oct 2005 · Radiation Measurements
[Show abstract][Hide abstract] ABSTRACT: A numerical model of the Odiel-Tinto estuary (Spain) has been developed to study the self-cleaning process that was evidenced from 226Ra measurements in water and sediments collected in the period 1999-2002, after direct releases from a fertilizer complex ceased (in 1998). The hydrodynamic model is first calibrated, and standard tidal analysis is carried out to calculate tidal constants required by the dispersion code to determine instantaneous water currents and elevations over the estuary. In this way, long-term simulations may be carried out. The dispersion code includes advective/diffusive transport of radionuclides plus exchanges with bottom sediments described through a kinetic approach. The dispersion model is first tested by comparing computed and measured 226Ra concentrations over the estuary resulting after releases in the Odiel and Tinto rivers. Next, it is applied to simulate the self-cleaning process of the estuary. The time evolution of radium concentrations in bed sediments is in generally good agreement with observations. The computed sediment halving time of the estuary is 510 days, which also is in good agreement with that estimated from measurements.
Full-text · Article · Apr 2005 · Science of The Total Environment
[Show abstract][Hide abstract] ABSTRACT: The estuary of the Odiel River has been affected by both direct discharges of phosphogypsum (radium enriched industrial waste) and dissolution and weathering of the exposed piles where this radium enriched waste was stored. In 1998 the waste management policy for industries changed. The direct discharges stopped and the new phosphogypsum piles were well protected against dissolution processes, avoiding any transference of radium into the environment. This work presents a study of the evolution with time (1999-2002) of the levels of 226Ra in river water and sediment samples with the new waste management policy. A liquid scintillation technique was used to measure the 226Ra activity concentration in sediment samples. A gas-proportional counter was also used to measure the 226Ra activity concentration in river water samples. The main conclusion is that a systematic and continuous decrease of the activity concentration of 226Ra with time in the Odiel River estuary is occurring. Thus, a possible self-cleaning in the estuary, once the direct waste discharges were avoided, can be inferred.
Full-text · Article · Sep 2004 · Science of The Total Environment
[Show abstract][Hide abstract] ABSTRACT: Experiment procedures have been developed for the determination of 226Ra and 224Ra activity concentration in solid and liquid samples collected around a non-nuclear industrial area, by liquid scintillation counting. The different radiochemical procedures developed in this work, have been adaptations of a radiochemical procedure previously used, for 226Ra and 224Ra determinations by LSC in drinking water, which was improved, refined up and adapted to the type of sample to be applied. These improved radiochemical methods have been applied to waste samples (phosphogypsum) produced by two factories which are engaged in phosphoric acid production, and to waters collected from the Odiel river, where during the sampling period a fraction of these wastes were released. 226Ra activity concentrations in the phosphogypsum ranged from 673 to 1178 Bq/kg dry weight, indicating that the wastes are particularly enriched in this radionuclide. Consequently, high 226Ra levels were easily found in the river waters analysed, especially in the neighbouring zones of the waste discharges.
Full-text · Article · Aug 2000 · Journal of Radioanalytical and Nuclear Chemistry
[Show abstract][Hide abstract] ABSTRACT: 226Ra activity concentration in river water was determined using a low background liquid scintillation counter. Radium was extracted
from the samples as Ra-BaSO4 precipitate which, afterwards, was dissolved with EDTA in ammonia medium. Solution was transferred into a low potassium glass
vial and then mixed with a scintillation cocktail. Two different scintillation cocktails were selected for comparison. Efficiency,
recovery yield and α/β separation were studied with both liquid scintillation cocktails. One single measurement, made one
month after radium separation, allows to calculate the226Ra concentration as well as to assess the presence of alpha contamination of the sample. In the case of negligible interferences,224Ra concentrations can be subsequently evaluated in the same sample by the measurement made just after chemical separation
of radium. This method has been applied for the determination of226Ra and224Ra activity concentrations in river water collected from different locations along the Odiel river estuary area (South-west
of Spain). The presence of chemical industry, the wastes of which are released into the river, could be connected with radium
activity concentration enhancements in the water.
Full-text · Article · Dec 1998 · Czechoslovak Journal of Physics
[Show abstract][Hide abstract] ABSTRACT: A method for the determination of Ra-isotopes in water samples has been developed. Ra is coprecipitated with Ba as sulphate. The precipitate is then dissolved with EDTA and counted with a liquid scintillation system after mixing with a scintillation cocktail. The study of the temporal evolution of the separated activity gives the isotopic composition of the sample, i.e. the Ra-224 and Ra-226 contribution to the total activity. The method has been applied to some Spanish drinking waters. (C) 1997 Elsevier Science Ltd.
Full-text · Article · May 1997 · Applied Radiation and Isotopes
[Show abstract][Hide abstract] ABSTRACT: The decomposition of CO 2 by the effect of negative corona discharge has been experimentally and numerically investigated for different admixtures of N 2 . The chemical kinetics model used in the simulation includes a wide variety of reactions between electrons, ions, atoms and molecules, such as ionization and recombination, electron-impact dissociation, dissociative recombination, dissociative attachment, thermal reactions between neutral chemical species, etc. Using the current-voltage characteristic as input data, the radial distributions of charged and neutral species has been predicted for different applied voltages and gas compositions. The generation of ozone, carbon monoxide and nitrogen oxides during the application of the corona discharge has been measured using ultraviolet and FTIR spectrophotometry.