title: Polymer-modified Fe0 nanoparticles target entrapped NAPL in two dimensional porous media: effect of particle concentration, NAPL saturation, and injection strategy.
abstract: Polymer-modified nanoscale zerovalent iron (NZVI) particles are delivered into porous media for in situ remediation of nonaqueous phase liquid (NAPL) source zones. A systematic and quantitative evaluation of NAPL targeting by polymer-modified NZVI in two-dimensional (2-D) porous media under field-relevant conditions has not been reported. This work evaluated the importance of NZVI particle concentration, NAPL saturation, and injection strategy on the ability of polymer-modified NZVI (MRNIP2) to target the NAPL/water interface in situ in a 2-D porous media model. Dodecane was used as a NAPL model compound for this first demonstration of source zone targeting in 2-D. A driving force for NAPL targeting, the surface activity of MRNIP2 at the NAPL/water interface was verified ex situ by its ability to emulsify NAPL in water. MRNIP2 at low particle concentration (0.5 g/L) did not accumulate in or near entrapped NAPL, however, MRNIP2 at moderate and high particle concentrations (3 and 15 g/L) did accumulate preferentially at entrapped NAPL, i.e., it was capable of in situ targeting. The amount of MRNIP2 that targets a NAPL source depends on NAPL saturation (S(n)), presumably because the saturation controls the available NAPL/water interfacial area and the flow field through the NAPL source. At effective S(n) close or equal to 100%, MRNIP2 bypassed NAPL and accumulated only at the periphery of the entrapped NAPL region. At lower S(n), flow also carries MRNIP2 to NAPL/water interfaces internal to the entrapped NAPL region. However, the mass of accumulated MRNIP2 per unit available NAPL/water interfacial area is relatively constant (∼0.8 g/m(2) for MRNIP2 = 3 g/L) from S(n) = 13 to ∼100%, suggesting that NAPL targeting is mostly controlled by MRNIP2 sorption onto the NAPL/water interface.
authors.affiliation: Center for Environmental Implications of Nanotechnology (CEINT) and Department of Civil & Environmental Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213-3890, USA.
authors.forename: Tanapon
authors.initials: T
authors.lastname: Phenrat
authors.forename: Fritjof
authors.initials: F
authors.lastname: Fagerlund
authors.forename: Tissa
authors.initials: T
authors.lastname: Illangasekare
authors.forename: Gregory V
authors.initials: GV
authors.lastname: Lowry
authors.forename: Robert D
authors.initials: RD
authors.lastname: Tilton
mesh_terms: D000473:Alkanes; D052918:Environmental Restoration and Remediation / Q000379:methods*; D006843:Hydrocarbons, Chlorinated / Q000032:analysis / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D016062:Porosity; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D000473:Alkanes; D006843:Hydrocarbons, Chlorinated; D011108:Polymers; D014874:Water Pollutants, Chemical; C007548:n-dodecane; D007501:Iron