1,721,120 research outputs found
Enhanced Transport of Zerovalent Iron Nanoparticles in Saturated Porous Media by Guar Gum
No full textIn order to ensure adequate mobility of zerovalent iron nanoparticles in natural aquifers, the use of a stabilizing agent is necessary. Polymers adsorbed on the nanoparticle surface will give rise to electrosteric stabilization and will decrease attachment to the surface soil grains. Water saturated sand-packed columns were used in this study to investigate the transport of iron nanoparticle suspensions, bare or modified with the green polymer guar gum. The suspensions were prepared at 154 mg/L particle concentration and 0.5 g/L polymer concentration. Transport experiments were conducted by varying the ionic strength, ionic composition, and approach velocity of the fluid. Nanoparticle deposition rates, attachment efficiencies, and travel distances were subsequently calculated based on the classical particle filtration theory. It was found that bare iron nanoparticles are basically immobile in sandy porous media. In contrast, guar gum is able to ensure significant nanoparticle transport at the tested conditions, regardless of the chemistry of the solution. Attachment efficiency values for guar gum-coated nanoparticles under the various conditions tested were smaller than 0.066. Although the calculated travel distances may not prove satisfactory for field application, the investigation attested the promising role of guar gum to ensure mobility of iron nanoparticles in the subsurface environment
Probing effects of polymer adsorption in colloidal particle suspensions by light scattering as relevant for the aquatic environment: An overview
No full textModification of particle surfaces by adsorption of polymers is a process that governs particle behavior in aqueous environmental systems. The present article briefly reviews the current understanding of the adsorption mechanisms and the properties of the resulting layers, and it discusses two environmentally relevant cases of particle modification by polymers. In particular, the discussion focuses on the usefulness of methods based on light scattering to probe such adsorbed layers together with the resulting properties of the particle suspensions, and it highlights advantages and disadvantages of these techniques. Measurement of the electrophoretic mobility allows to follow the development of the adsorption layer and to characterize the charge of the modified particles. At saturation, the surface charge is governed by the charge of the adsorbed film. Dynamic light scattering provides information on the film thickness and on the behavior of the modified suspensions. The charge and the structure of the adsorbed layer influence the stability of the particles, as well as the applicability of the classical theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO). This fundamental knowledge is presented in the light of environmental systems and its significance for applied systems is underlined. In particular, the article discusses two examples of environmental processes involving adsorption of polymers, namely, the modification of particles by natural adsorption of humic substances and the tailoring of surface properties of iron-based particles used to remediate contaminated aquifer
Desalination of brackish groundwater and reuse of wastewater by forward osmosis coupled with nanofiltration for draw solution recovery
Full text linkEffects of Brownian force and pore structure on the removal of nanoparticles by porous membranes
Full text linkThis study investigated the effects of Brownian force on the transport and retention of nanoparticles within the pores of water filtration membranes using COMSOL Multiphysics®. Simulation results suggest that, at Péclet numbers below 10, the Brownian force may increase the frequency of nanoparticle collisions with pore walls to substantially increase log reduction rates (LRVs). Indeed, the LRVs increased linearly with attachment coefficient values; even at a low attachment coefficient of 0.001, high LRVs over 1.5 were observed under some geometries owing to the high frequency of nanoparticle-wall collisions. The calculated LRVs were inversely correlated with the Péclet numbers, whereas the slope of the inverse correlation was dependent on the membrane pore size. Complex structures, such as pore constriction, tortuosity, and non-uniform pore size, increased the LRV, whereas the overall porosity was not a determinant removal factor within the pores. In the configuration with parallel large and small pores, the Brownian force increased the number of nanoparticles entering the membrane through small pores relative to the numbers estimated based on water flow rates. These results indicate that the Brownian force may be an important particle removal factor within membrane pores under certain conditions; this should be considered when designing and operating membrane filters
Nanoscale iron characterization and mobility enhancements by means of biodegradable hydrocolloids
No full textIn the field of pollution remediation, and in particular of aquifer systems decontamination, the use of nanoscale zerovalent iron (NZVI) particles is one of the most interesting and promising technology. These particles can be suspended into a slurry, injected into the subsurface where they exploit the groundwater flow to embrace the source of contamination, thus treating a wide variety of contaminants and bypassing most of the limitation related to PRBs. However, very limited or no mobility of the nanoparticles has been shown in porous media. In order to enhance the mobility of iron nanoparticles in the subsurface, it is important to (i) prevent the formation of large aggregates that tend to be easily filtered and (ii) reduce the attachment of nanoparticles to the soil grains. Surface modifiers can increase the surface charge of the nanoparticles thereby providing electrostatic stabilization, and also create a surface brush layer which engenders long-range strong steric repulsion forces between particles and between particles and collectors. In the present study, after a description of the characterization of two commercial NZVI particles, the stabilizing effects and mobility enhancements deriving from dosing of biodegradable hydrocolloids on nanoscale iron suspensions were evaluated. Two commercial NZVI colloidal dispersions were employed: bare RNIP-DS particles and RNIP-10 AP SDS particles, modified by the supplier with addition of a biopolymer. Based on T.E.M. micrographs, the mean diameter of both suspensions is nanoscale (50÷80 nm), but particle size distributions exhibit a strong positive skewness. Bare RNIP-DS particles are generally larger than RNIP-10 AP SDS ones, due to the presence of larger magnetite particles. For both suspensions, theoretical values of specific surface area are smaller than experimental BET areas, especially for RNIP-10 AP SDS: it is likely that the particles have a surface roughness, which improves their surface area. Four biopolymers were added to RNIP-DS to study their effect on suspension stability. Guar gum was chosen as the best biopolymer between the four tested. Sedimentation profiles showed the ability of guar gum to effectively keep the iron nanoparticles suspended. Column experiments, run at conditions similar to those of natural groundwaters, confirmed the effectiveness of guar gum to enhance the mobility of NZVI particles in saturated porous medi
Characterization and mobility enhanchement of iron nanopowders suspensions for groundwater remediation
No full textIn the context of groundwater remediation, the use of zero-valent metals has been shown promising for the degradation of a wide range of contaminants. In particular, granular iron filings in permeable reactive barriers (PRBs) are a consolidated technology applied on a number of sites. Nanoscale zerovalent iron is characterized by tiny particles (1-100 nm) and by a specific surface area that is up to a hundred times higher than millimetric iron, thus also its reactivity is much higher. These particles can be suspended into a slurry and injected directly into the source of contamination in order to treat a wide variety of contaminants and bypassing most of the limitation related to PRBs. However, very limited or no mobility of the nanoparticles has been shown in both laboratory studies and field-scale tests. In the present study, after a description of the characterization of a commercial NZVI, the stabilizing effects and mobility enhancements deriving from dosing of biodegradable hydrocolloids on nanoscale iron suspensions will be investigate
Adsorption of polyelectrolytes to like-charged substrates induced by multivalent counterions as exemplified by poly(styrene sulfonate) and silica
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