Transport and retention of nanoscale C60 aggregates in water-saturated porous media

Experimental and mathematical modeling studies were performed to investigate the transport and retention of nanoscale fullerene aggregates (nC(60)) in water-saturated porous media. Aqueous suspensions of nC(60) aggregates (95 nm diameter, 1 to 3 mg/L) were introduced into columns packed with either glass beads or Ottawa sand at a Darcy velocity of 2.8 m/d. In the presence of 1.0 mM CaCl2, nC(60) effluent breakthrough curves (BTCs) gradually increased to a maximum value and then declined sharply upon reintroduction of nC(60)-free solution. Retention of nC(60) in glass bead columns ranged from 8 to 49% of the introduced mass, while up to 77% of the mass was retained in Ottawa sand columns. When nC60 suspensions were prepared in deionized water alone, effluent nC(60) BTCs coincided with those of a nonreactive tracer (Br-), with minimal nC(60) retention. Observed differences in nC(60) transport and retention behavior in glass beads and Ottawa sand were consistent with independent batch retention data and theoretical calculations of electrostatic interactions between nC(60) and the solid surfaces. Effluent concentration and retention profile data were accurately simulated using a numerical model that accounted for nC(60) attachment kinetics and a limiting retention capacity.