Abstract
Reactive iron particles hold promise for use in the destruction of contaminants in the subsurface environment. Application of these nano- to submicron-scale particles, however, may be limited by poor subsurface transport and non-uniform distribution of the reactive material. Delivery issues are particularly important when evaluating the efficacy of iron-based technologies for treatment of dense non-aqueous phase liquid (DNAPL) source zones. Current approaches for the delivery of reactive iron particles within DNAPL source zones are hindered by particle agglomeration, flow bypassing, and presence of non-target reactions. Encapsulation of the reactive particles within an oil-in-water emulsion is a novel approach that may overcome these limitations. For successful application, emulsion droplets must be sufficiently small to prevent pore clogging, the emulsion must remain stable (i.e., both the encapsulated iron within oil droplets and the oil droplets within the continuous aqueous- phase) during introduction to the contaminated porous media, and the emulsion must be designed so as to limit any unintended DNAPL mobilization. Kinetically-stable iron-containing oil-in-water emulsions with droplet sizes less than two micrometers were developed and column experiments conducted to assess the transport of these emulsions through sandy media of differing mean pore diameters. Results from column experiments indicate little evidence of retention of emulsion droplets. Effluent recoveries suggest that both the oil and iron components of the oil-in-water emulsion can be transported through sandy porous media without long-term permeability reduction. Emulsion transport was modeled using a modified filtration model that includes a Langmuir adsorption term to simulate monolayer adsorption. The model simulations capture the rise, plateau and tailing of the emulsion breakthrough curves. Predicted mobility distances indicate encapsulation of particles within an oil- in-water emulsion can promote iron transport within porous media.