Mobilization and transport of different types of carbon-based engineered and natural  nanoparticles through saturated porous media

Abstract: Carbon –based engineered nanoparticles have been widely used due to their small size and uniquephysical and chemical properties. They can dissolve in water, transport through soil and reach drinkingwater resources. The toxic effect of engineered nanoparticles on human and fish cells has beenobserved; therefore, their release and distribution into the environment is a subject of concern. In thisstudy, two types of engineered nanoparticles, multi-walled carbon nano-tubes (MWCNT) and C60 withcylindrical and spherical shapes, respectively, were used. The aim of this study was to investigatetransport and retention of carbon-based engineered and natural nanoparticles through saturated porousmedia. Several laboratory experiments were conducted to observe transport behavior of thenanoparticles through a column packed with sand as a representative porous media. The columnexperiments were intended to monitor the effect of ionic strength, input concentration and the effect ofparticle shape on transport. The results were then interpreted using Derjaguin-Landau-Verwey-Overbeak (DLVO) theory based on the sum of attractive and repulsive forces which exist betweennanoparticles and the porous medium. It was observed that as the ionic strength increased from 1.34mM to 60 mM, the mobility of the nanoparticles was reduced. However, at ionic strength lower than10.89 mM, mobility of C60 was slightly higher than that of MWCNTs. At ionic strength of 60 mMMWCNT particles were significantly more mobile. It is rather difficult to relate this difference to theshape of particle and further studies are required.The effect of input concentration on transport of MWCNTs and C60 was observed in bothmobility of the particle and shape of breakthrough curves while input concentration was elevated from7 mg/l to 100 mg/l. A site-blocking mechanism was suggested to be responsible for the steep andasymmetric shape of the breakthrough curves at the high input concentration.Furthermore inverse modeling was used to calculate parameters such as attachment efficiency,the longitudinal dispersivity, and capacity of the solid phase for the removal of particles. The inversionprocess was performed in a way that the misfit between the observed and simulated breakthroughcurves was minimized. The simulated results were in good agreement with the observed data.