Size- and concentration-dependent deposition of fluorescent silica colloids in saturated sand columns: transport experiments and modeling

Abstract

This study investigates the size and concentration effects on the transport of silica colloids in columns of sandy aquifer material. Colloid transport experiments were performed with specifically developed fluorescent labeled silica colloids in columns of a repacked natural porous medium under hydro-geochemical conditions representative of sandy aquifers. Breakthrough curves and vertical deposition profiles of colloids were measured for various colloid concentrations and sizes. The results showed that for a given colloid concentration injected, deposition increased when increasing the size of the colloids. For a given colloid size, retention was also shown to be highly concentration-dependent with a non-monotonous pattern presenting low and high concentration specificities. Deposition increases when increasing both size and injected concentration, until a threshold concentration is reached, above which retention decreases, thus increasing colloid mobility. Results observed above the threshold concentration agree with a classical blocking mechanism typical of a high concentration regime. Results observed at lower colloid concentrations were not modeled with a classical blocking model and a depth- and time-dependent model with a second order kinetic law was necessary to correctly fit the experimental data in the entire range of colloid concentrations with a single set of parameters for each colloidal size. The colloid deposition mechanisms occuring at low concentrations were investigated through a pore structure analysis carried out with Mercury Intrusion Porosimetry and image analysis. The determined pore size distribution permitted estimation of the maximal retention capacity of the natural sand as well as some low flow zones. Altogether, these results stress the key role of the pore space geometry of the sand in controlling silica colloids deposition under hydro-geochemical conditions typical of sandy aquifers. Our results also showed originally that colloid mobility in porous media is not only favored at high colloid concentrations, but also at very low concentrations, which are more likely to be observed in groundwater.

Low mobility of CuO and TiO2 nanoparticles in agricultural soils of contrasting texture and organic matter content

“…) in agreement withVitorge et al (2013). No clear influence of the soil OM content on TiO2-NPs mobility could be evidenced in the six soils, because of their very low mobility.…”

“…This is possibly related to an increased soil structuration induced by the higher OM content in soil compared to the low OM soils (Jastrow 1996;Álvaro-Fuentes et al 2009). Such soil structuration improvement is indeed known to increase soil permeability through the formation of slightly bigger pores, which can facilitate the transfer of colloids or bacteria (Martins et al 2013;Vitorge et al 2013;Bagheri et al 2019). Under our conditions, the different apparent size and zeta potential values of CuO-NPs measured in the different soil solutions do not seem to significantly affect NPs mobility whatever the soil.…”

“…The analytic solution of the Convection Dispersion Equation (CDE) with a first-order loss term, µ, presented in Eq.1 was fitted to the bromide and NPs breakthrough curves using the Levenberg Maquardt algorithm (e.g. Martins and Mermoud 1999 ;Martins et al 2013;Vitorge et al 2013;Lakshmanan et al 2015).…”

Effect of Ionic Strength on the Transport and Retention of Polyacrylamide Microspheres in Reservoir Water Shutoff Treatment

“…As indicated by the M A values in Table , for all IS values (0.001, 0.01, 0.04, 0.10, and 0.20 M), the retention by attachment ranged between 0.37% and 4.65% of the total amount of injected polyacrylamide microspheres. These phenomena can possibly be attributed to the roughness of the sand grains, the particle size of the polyacrylamide microspheres, and the flow velocity of the fluid in the porous medium. ,− In general, at low flow velocities (which are usually associated with low hydrodynamic drag forces), favorable microsites on the sand grain surfaces would push the polyacrylamide microspheres with small particle sizes through energy barriers and into primary energy minima. The elimination of the energy barrier under high-IS conditions can enhance this process.…”

Combining microscopy with spectroscopic and chemical methods for tracing the origin of atmospheric fallouts from mining sites

“…Following the procedure described in Simonin et al, [33] and Vitorge et al, [34][35][36] a minimum of 100 particles and a maximum of 300 particles (about 10 representative particles were specifically analyzed for speciation) were analyzed for each sample of dust and fallout, in order to establish a particle morphology fingerprint for all of the studied site locations.…”