Abstract
Engineered aluminum oxide (Al2O3), titanium dioxide (TiO2), and silicon dioxide (SiO2) nanoparticles (NPs) are utilized in a broad range of applications; causing noticeable quantities of these materials to be released into the environment. Issues of how and where these particles are distributed into the subsurface aquatic environment remain as major challenges for those in environmental engineering. In this study, transport and retention of Al2O3, TiO2, and SiO2 NPs through various saturated porous media were investigated. Vertical columns were packed with quartz-sand, limestone, and dolomite grains. The NPs were introduced as a pulse suspended in aqueous solutions and breakthrough curves in the column outlet were generated using an ultraviolet-visible spectrophotometer. It was found that Al2O3 and TiO2 NPs are easily transported through limestone and dolomite porous media whereas NPs recoveries were achieved two times higher than those found in the quartz-sand. The highest and lowest SiO2-NPs recoveries were also achieved from the quartz-sand and limestone columns, respectively. The experimental results closely replicated the general trends predicted by the filtration and DLVO calculations. Overall, NPs mobility through a porous medium was found to be strongly dependent on NP surface charge, NP suspension stability against deposition, and porous medium surface charge and roughness.
Highlights
Metal oxide NPs (i.e. Al2O3, TiO2, and SiO2) have been recently introduced as agents for enhanced oil recovery (EOR) from hydrocarbon reservoirs[11,12,13]
The X-ray diffraction (XRD) analysis from aluminum oxide sample demonstrated that NP has alpha (α ) crystalline structure and its composition is pure Al2O3 (Fig. 1a)
There is a 35% to 40% difference in the size of the NPs depending on whether it was measured by XRD and TEM or reported by the manufacturer
Summary
According to DLVO theory, there is a relatively strong electrostatic barrier energy between SiO2-NPs and quartz-sand grains which indicates a strong repulsion (EDL) force between them. (a) FESEM-EDX analyses from quartz sand grains after the transport experiments, (a) Al2O3-NPs, (b) TiO2-NPs. The values of attachment efficiency, maximum transport distance, and deposition coefficient rate, for Al2O3-NP transport through dolomite porous medium, were calculated to be 0.134, 44.5 cm and 4.14 (h−1) respectively (Table 1). Results of the FESEM and EDX analyses show that the deposited TiO2-NPs were observed on the grains surfaces located in the middle of column (Fig. 6a). The trapped clusters may make networks up to micron size especially when the NPs and porous media
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