1,721,001 research outputs found
Bimetallic nZVI-induced chemical denitrification modelling using the shrinking core model
No full textIn this work the shrinking core model was used for the mathematical modelling of Cu(II)/Fe(0)-induced chemical denitrification in aqueous system. The nano-zero valent iron particles have already been demonstrated their efficiency in the nitrate removal process, and various authors have investigated the influence of several parameters, such as pH and Fe(0)/NO3-molar ratio, on the process. In particular, the addition of a second metal, such as Cu, has proved to improve the kinetic of the overall process, allowing to reduce also the nano-particle surface passivation. The present study reports the classical formulation of the shrinking-core model, applying it to the Fe(0)-Cu(II)/NO3-aqueous system. The static-film simplified hypothesis was assumed and the electrolyte transport equations for dilute system were considered to take into account in the model the influence of other ion species in solution. The model was then employed to fit the experimental data reported in a previous work, in order to estimate the diffusional and kinetic parameter of the process
Mathematical modelling of simultaneous nitrate and dissolved oxygen reduction by Cu-nZVI using a bi-component shrinking core model
No full textThis article proposes the aqueous system Cu-Fe(0)/NO3 − mathematical modelling through a classical shrinking core model, taking into account the presence of dissolved oxygen in the reaction medium and considering it in the model equation. In this work the nitrate reduction to ammonia was assumed to occur onto the lab-made bimetallic nano zero-valent iron (nZVI) surface, simultaneously with the nZVI consumption due to the oxidation carried out by dissolved oxygen. Kinetic tests were performed on synthetic nitrate solutions (0.5, 1, 1.5 mM) at stoichiometric Cu-Fe(0) nanoparticles concentration and the obtained data were interpreted through a bi-component shrinking core model. The nanoparticles were characterized through X-Ray powder Diffraction method at the end of the process to analyse the oxidation of the particles whereas nitrate, oxygen and Fe(0) concentration were monitored at different time steps of the experiments. The nitrate removal efficiency was close to 80% after 90 min of treatment and the oxygen concentration decreased very rapidly from about 8 mg L−1 to the asymptotic value of (<1 mg L−1). A non-linear regression of the obtained kinetic data allowed to estimate the kinetic and diffusional model parameters that were in line with theoretical considerations and experimental evidences
Kinetic study of nitrate removal from aqueous solutions using copper-coated iron nanoparticles
No full textNitrates are considered hazard compounds for human health due to their tendency to be reduced to nitrites, in particular in reducing environment. Nano zero valent iron (nZVI) represents an efficient and low-cost adsorbent/reductive agent for nitrate removal from groundwater and wastewaters and a little addition of a second metal species (Cu, Pd, Ni, Ag) has proven to increase process effectiveness, by enhancing stability and oxidation resistance of nanoparticles. In this work Cu/Fe nanoparticles were loaded in a NO3 (-) solution (100 mg L(-1)) and the removal efficiency was tested by monitoring nitrate concentration at selected time intervals. Results showed that the nitrate removal process involves both reduction and adsorption processes: the removal mechanism has been investigated, and the pseudo-first-order and pseudo-second-order-adsorption kinetic models were successfully tested
Competitive reaction modelling in aqueous systems. The case of contemporary reduction of dichromates and nitrates by nZVI
Full text linkIn various Countries, Cr(VI) still represents one of the groundwater pollutant of major concern, mainly due to its high toxicity, furthermore enhanced by the synergic effect in presence of other contaminants. As widely reported in the recent literature, nanoscale zero valent iron particles (nZVI-p) have been proved to be particularly effective in the removal of a wide range of contaminants from polluted waters. In this work, experimental tests of hexavalent chromium reduction in polluted groundwater in the presence of nitrate by nZVI-p are presented and discussed. The effect of different nitrate amounts on Cr(VI) reduction mechanism was investigated and the obtained results were successfully interpreted by the proposed kinetic model. nZVI-p produced by the classical borohydride reduction method were added in to synthetic solutions with the initial concentration of Cr(VI) set at 93, 62 and 31 mg L-1 and different nitrate contents in the range 10-100 mg L-1. According to the experimental results, nitrate showed an adverse effect on Cr(VI) reduction, depending on the nZVI/Cr(VI) and Cr(VI)/NO3 - ratio. The proposed kinetic model soundly grasps the competitive nature of the Cr(VI) reduction process when other chemical species are present in the treated solution
Artificial aggregate from non metallic automotive shredder residue
Full text linkUntil 2005 in the European Union (EU) approximately 12 M vehicles were yearly shredded, and 8 or 9 M t/
year of waste was produced. About 14 million tons of End of Life Vehicles (ELVs) are foreseen by 2015. This
huge amount of waste must be treated and disposed of in a sustainable way. The most common treatment
technologies, involve ELVs shredding to recover iron and steel (70%) and non ferrous metals (5%) from
vehicles. The remaining fraction, called Automotive Shredder Residue (ASR), and representing about 25% wt.
of each vehicle, is generally landfilled. For more than two thirds, this last residue deals with combustible
materials (fibers, polyethylene etc..), suitable to be reused as a fuel, but a substantial amount of soil particles,
metals, glasses and plastics residues are also present. Consequently, a new sustainable way to reuse ASR is
to separate the organic from the inorganic fraction, and use them in combustion plants, gasification and in the
cement industry, respectively. Regarding this second way of recovery, several studies have been already
successfully performed with the aim of transforming ASR into aggregates for asphalt or cement mixes, by
thermal treatment followed by chemical treatment, or by physical processes, such as granulation. In this work,
a selected fraction of non metallic automobile shredder residue was immobilized in granules produced at room
temperature in a pilot scale granulator. Granules were obtained by mixing selected amount of ASR with a
binder (cement or lime) in the presence of additions (fly ash) and admixtures. The final aim of this work was to
investigate the mechanical properties of concrete samples produced using the artificial aggregate obtained
through different combinations of ASR, fly ash and binder. Additional freeze and thaw tests were finally
performed to assess concrete durability along time
Simultaneous aggregation and oxidation of nZVI in Rushton equipped agitated vessel. Experimental and modelling
No full textThe aim of this work was to investigate the aggregation of metallic iron nanoparticles in a Rushton equipped agitated vessel open at the atmosphere. The particles were synthetized using oxygen-free reagent solutions and subsequently were suspended in water in an open lab-scale agitated vessel. The particle size distribution, zeta-potential, pH and Fe(0) content were monitored over the time, up to the complete oxidation of the particles. During the oxidation process, the particle size distribution varied from a unimodal to a bi-modal and tri-modal distribution, clearly showing the generation of aggregates, characterized by irreversible bonds among the particles. The aggregation phenomenon was described by a simplified model, whereas the oxidation process was modelled according to the classical shrinking core model. The regressed dissolved oxygen diffusion coefficient, D p = 6.79 × 10 −13 m 2 s −1 was in line with the theoretical expectations, as well as the intrinsic kinetic constant rate, k c = 2.83 × 10 −7 m s −1 . As expected, the oxidation process was found to be a diffusion-controlled reaction, according to the low value of the second Damkohler number (equal to 7.5 × 10 −3 )
APPARECCHIATURA INTEGRATA PER LA PRODUZIONE E L'INGLOBAMENTO IN MATRICE DI SOLIDO CRISTALLIZZATO DI PARTICELLE SUBMICRONICHE E NANOPARTICELLE
No full textLa presente invenzione si riferisce ad un’apparecchiatura unica integrata innovativa per la produzione e l'inglobamento in una matrice di solido cristallizzato di particelle submicroniche e nanoparticelle di materiali inorganici e/o organici, a un processo che avviene in detta apparecchiatura e agli usi delle particelle submicroniche e nanoparticelle inglobate ottenute con tale apparecchiatura. In particolare l’invenzione si riferisce all’integrazione in un’unica apparecchiatura intensificata di un reattore a disco rotante e un cristallizzatore. L’apparecchiatura permette di ottenere direttamente il prodotto inglobato limitando la possibilità di deteriorare le particelle prodotte
Synthesis and CO2 adsorption capacity of biomass waste functionalized by nanoparticles
Full text linkTwo composite materials were synthesized based on sodium alginate and biochar derived from licorice processing waste functionalized with silicon dioxide nanoparticles (SiO2) and iron oxide (Fe2O3), respectively, enabling the valorization of industrial waste. The adsorptive capacities of the two materials (Alg-SiO2 and BCLFe2O3) toward CO2 in the gaseous stream with nitrogen were evaluated by acid titration of carbonates present in a trap for CO2 consisting of a KOH solution placed downstream of the adsorption column. The aim of the present work is to evaluate the CO2 adsorption capacity of material functionalized by nanoparticles. Adams–Bohart, Thomas models, and % removal efficiency curves for the adsorption were examined to investigate the dynamic behavior of the column. From the tests performed in CO2 and N2 flow, the BCL-Fe2O3 material was demonstrated to have an adsorbent higher capacity than Alg-SiO2, respectively CO2 adsorbed 25 and 6 mg/g
Production of nano zero valent iron particles by means of a spinning disk reactor
Full text linkNitrates are considered hazard compounds for human health due to their tendency to be reduced to nitrites, in particular in reducing environment. Nano zero valent iron (nZVI) represents an efficient and low-cost adsorbent/reductive agent for nitrate removal from groundwater. In this work, nZVI particles were produced by means of two different equipment types based on the same chemical synthesis method: a batch stirred tank reactor (BSTR) and a spinning disk reactor (SDR). This latter apparatus is capable to strongly promote micromixing at a steady-state, continuous condition, and such as qualifies to subsist in the framework of process intensification. Particle size distribution (PSD) of the obtained nZVI particles were measured by a DLS technique. The removal efficiency of the produced nVI particles were checked by using two NO3-solutions (1.6 and 6.4 mM) and by monitoring nitrate concentration reduction rates at selected time intervals. Results showed that the nZVI particles produced by SDR have a narrow PSD with a mean diameter of 65nm; on the contrary, particles produced by BSTR shows bimodal PSD with modal sizes of 105 nm and 400 nm, respectively. Experimental tests of nitrates reduction in water have been performed, using both the particles produced by the above mentioned techniques. Results of batch tests showed that the highest removal efficiency of nitrates was observed by using the nZVI particles produced by means of SDR, as a consequence of the higher average specific surface. Since nitrate removal process involves both reduction and adsorption processes, the removal mechanism has been investigated, and the pseudo-first-order reduction kinetic model was successfully tested and reported in both cases
- …
