1,720,961 research outputs found
Stabilization of highly concentrated suspensions of iron nanoparticles using shear-thinning gels of xanthan gum
No full textNanoscale zerovalent iron (NZVI) particles have recently become subject of great interest in the field of groundwater remediation for their ability to treat a wide variety of organic and inorganic contaminants. However, the field application of this technology is strongly hindered by the lack of stability of NZVI water suspensions. This study demonstrates that highly concentrated NZVI slurries (15 g/L) can be stabilized for more than 10 days adding 6 g/L of xanthan gum biopolymer. Stability against aggregation and sedimentation was achieved in the range of ionic strength 6 × 10-3-12 mM and is mainly due to the formation of a viscous gel characterized by shear-thinning behaviour
Confronto dei trattamenti su scala reale con ferro zerovalente nanoscopico
No full textL'utilizzo del ferro nanoscopisco zerovalente (NZI) per la bonifica di acquiferi contaminati è stato proposto più di 10 anni fa, ma le applicazioni sono ancora poco numerose nonostante si sia raggiunta una buona conoscenza teorica ed esista una notevole richiesta di mercato. Dato che una delle ragioni principali del limitato sviluppo è la difficoltà dell'applicazione, in questo studio si analizzano le poche sperimentazioni su scala reale ad oggi documentate allo scopo di sistematizzare le informazioni scaturite da tali esperienze. Lo studio comprende anche dei casi di utilizzo di ferro di dimensioni maggiori come quello millimetrico. Dal confronto risulta che la nuova tecnologia non va a sostituire quella più tradizionale del ferro granulare, ma le si affianca in quanto quest'ultima rimane competitiva in determinati casi. Uno di questi è il trattamento di sorgenti localizzate con precisione: in questi casi la minor reattività dovuta alla minore superficie specifica del ferro granulare è compensata dal miglior contatto tra ferro e inquinante ottenuto dalla diversa modalità di introduzione del ferro nel mezzo poroso. Il NZVI ha tuttavia delle caratteristiche peculiari che lo distinguono nettamente dai materiali di dimensioni maggiori e che, in determinati casi, lo rendono superiore. La principale peculiarità è l'elevata reattività che riduce i tempi di bonifica, ma che comporta il rischio di una passivazione ad opera di elementi diversi dal DNAPL. La seconda peculiarità è la mobilità in falda. Questa caratteristica non ancora ben conosciuta, può essere sfruttata, ad esempio, per raggiungere porzioni di DNAPL non ben individuate, ma può anche dar luogo a migrazioni indesiderate del ferro iniettat
Ferro nanoscopico per la bonifica di acquiferi contaminati
No full textNell'ambito della bonifica di matrici ambientali inquinate, ed in particolare dei sistemi acquiferi, l'utilizzo di ferro zerovalente di dimensione nanometrica risulta essere una delle tecniche più interessanti e promettenti. Il ferro nanoscopico (nanoscale zerovalent iron - NZVI), caratterizzato da particelle di diametro estremamente piccolo e compreso tra 1 e 100 nm, da elevatissime superfici specifiche e da reattività superiori rispetto a quelle del ferro millimetrico, può essere iniettato direttamente in falda, sotto forma di dispersione colloidale, per trattare un'ampia gamma di contaminanti organici ed inorganici e per consentire il superamento dei limiti geometrici imposti dalla realizzazione di barriere reattive permeabili.
Partendo da una trattazione di tipo generale lo studio affronterà i temi della produzione, della caratterizzazione, della mobilità e del trasporto del ferro nanoscopico in mezzi porosi saturi, prendendo in considerazione sia i vantaggi legati all'uso di questi materiali, sia gli aspetti ancora controversi e da indagare ulteriormente
AQUAREHAB – Injection of nanoscale iron suspensions for aquifer remediation: from lab test to field applicatios
No full textColloidal suspensions of engineered nanoparticles have been studied in recent years for waste water and in-situ groundwater remediation. Injectable Fe-based materials (nano- and micro-sized zero-valent iron particles, NZVI and MZVI) are an improvement on commonly used granular iron: they can be suspended in a slurry and directly injected into the source of contamination, overcoming most of the limitations of zerovalent iron permeable reactive barriers (PRBs). Moreover, colloidal particles show increased reactivity, thanks to their high specific surface area. To improve colloidal stability and transportability of MZVI and NZVI, the use of highly viscous shear-thinning carrier fluids have been suggested, and proved to be effective. This study, cofunded by European Union project AQUAREHAB (FP7 - Grant Agreement Nr. 226565), presents experimental and modeling results for the transport of highly concentrated (up to 20 g/l) non- Newtonian (namely, shear-thinning) slurries of MZVI and NZVI in sand packed columns. Assessing the mobility of iron-based colloids is a key issue for field applications of these materials. A transport model can provide an estimation of the radius of influence for the injection points, for a correct dimensioning of full scale remediations and to predict short- and long-term mobility of the iron particles injected in the subsurface. If compared to transport models developed for natural colloids and synthetic model particles (namely latex spheres), the model here presented incorporates more complex phenomena. Rheological properties of the shear-thinning carrier fluid, hydrodynamic parameters of the porous medium (porosity, permeability), and colloid concentrations (both suspended and deposed) are strongly inter-dependent, thus resulting in a complex set of coupled partial differential equations and constitutive relationships. The model results highlight that deposition of relevant amounts of iron particles onto the soil grains significantly reduce porosity and permeability, thus resulting in clogging phenomena, especially for nanoscale particles. Moreover, mechanical filtration is shown to play a role under certain hydrochemical conditions, thus influencing the particle transport
A Comparison Between Field Applications of Nano-, Micro-, and Millimetric Zero-Valent Iron for the Remediation of Contaminated Aquifers
No full textIn the last 10 years, the number of field applications of zero-valent iron differing from permeable reactive barrier has grown rapidly and at present are 112. This study analyzes and compares such field applications. By using statistical analysis, especially ANO VA and principal component analysis, this study shows that chlorinated solvent contamination can be treated efficiently by using zero-valent iron material singly or associated with other technologies. In the analyzed sample of case studies, the association with microbial dechlorination increased significantly the performances of nanoscale iron. This is likely due to the synergistic effect between the two processes. Millimetric iron was always used in association with source zone containment; therefore, it is not possible to distinguish the contributions of the two techniques. The comparison also shows that catalyst addition seems to not dramatically improve treatment efficiency and that such improvement is not statistically significant. Finally, the injection technology is correlated to the type of iron and to the soil permeabilit
Rheological characterization of NZVI suspensions for injection in porous media
No full textNanoscale zerovalent iron (NZVI) represents one of the most interesting reagents for the remediation of contaminated aquifers, but its application is hindered by a lack of colloidal stability. Prior studies have shown that nanoscale iron slurries can be successfully stabilized against aggregation and sedimentation through dispersion in xanthan solutions; thus, further research was carried out by focusing on the flow behavior of xanthan-modified NVZI suspensions. This work aims at understanding the rheological properties of NZVI-xanthan suspensions, which have been extensively tested under two different flow conditions: simple shear flow and flow through a porous medium. According to both experimental approaches, the suspensions show a shear thinning behavior that is dependent on iron concentration. These rheological properties are explained by referring to the microstructure of the colloidal system. Flow equations have been formulated and solved in radial coordinates in order to demonstrate the feasibility of such suspensions in field scale application
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A comparison between field applications of NZVI
No full textDespite the use of Nanoscale Zerovalent Iron (NZVI) for the remediation of contaminated aquifers was proposed more than 10 years ago, there's a wide literature and a good market demand, its application is still limited. The aim of this study is to understand the reason why the number of full scale applications is so small and to systematizes the information arising these experiences. For sake of comparison, the study includes also some clean up treatments where micrometric and granular iron particles were used. The case studies are compared from several point of view such as the target of the treatment, the invasivity, the hydrodynamic properties of the equifer, etc. From the comparison we can deduce that this new technology doesn't substitute the traditional one, which is still competitive for example from the economic point of view. NZVI has however some peculiar features, which makes it very different and superior to coarser iron. The first feature is the reactivity which shortens the remediation time but also makes iron prone to passivation. The second feature is the mobility in the aquifer, which helps the delivery of iron particles towards source areas, but can also lead to undesired migrations of iron particle
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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