Study of C₆₀ transport in porous media and the effect of sorbed C₆₀ on naphthalene transport

In this study, the transport of water-stable “nano-C₆₀ particles” (a term used to refer to underivatized C₆₀ crystalline nanoparticles, stable in water for months) through a soil column (packed with Lula soil, 0.27% organic carbon) was investigated for the first time. Nano-C₆₀ particle breakthrough experiments were conducted at different flow rates, while other column operating parameters remained fixed through all the experiments. Nano-C₆₀ particles were observed to be more mobile at higher flow velocity: at the flow velocity of 0.38 m/d, the maximum percent of nano-C₆₀ breakthrough (C/C₀) was 47%; at the flow velocity of 3.8 m/d, the plateau value of nano-C₆₀ breakthrough was 60%; and at the flow velocity of 11.4 m/d, the plateau value of nano-C₆₀ breakthrough was almost 80%. At the low flow velocity (0.38 m/d), which is typical of groundwater flow, nano-C₆₀ particles showed very limited mobility: after about 57 pore volumes, they deposited to the soil column so rapidly that virtually no nano-C₆₀ was detected in the effluent. This observed “favorable deposition” (attachment efficiency α = 1) was probably due to “filter ripening.” Also the release of nano-C₆₀ particles after flow interruption was observed. The transport of naphthalene through the same soil column containing 0.18% nano-C₆₀ particles deposited was measured. A retardation factor of about 13 was observed, possibly suggesting that sorbed nano-C₆₀ particles in the soil column sorbed naphthalene similar to soil organic carbon. An asymmetric naphthalene breakthrough curve was observed, which is possibly due to “sorption nonequilibrium.”