High‐resolution experiments on chemical oxidation of DNAPL in variable‐aperture fractures

Abstract

Chemical oxidation of dense nonaqueous-phase liquids (DNAPLs) by permanganate has emerged as an effective remediation strategy in fractured rock. We present high-resolution experimental investigations in transparent analog variable-aperture fractures to improve understanding of chemical oxidation of residual entrapped trichloroethylene (TCE) in fractures. Four experiments were performed with different permanganate concentrations, flow rates, and initial TCE phase geometry. The initial aperture field and evolving entrapped-phase geometry were quantified for each experiment. The integrated mass transfer rate from the TCE phase for all experiments exhibited three time regimes: an early-time regime with slower mass transfer rates limited by low specific interfacial area; an intermediate-time regime with higher mass transfer rates resulting from breakup of large TCE blobs, which greatly increases specific interfacial area; and a late-time regime with low mass transfer rates due to the deposition of MnO 2 precipitates. In two experiments, mass balance analyses suggested that TCE mass removal rates exceeded the maximum upper bound mass removal rates derived by assuming that oxidation and dissolution are the only mechanisms for TCE mass removal. We propose incomplete oxidation by permanganate and TCE solubility enhancement by intermediate reaction products as potential mechanisms to explain this behavior. We also speculate that some intermediate reaction products with surfactant-like properties may play a role in lowering the TCEwater interfacial tension, thus causing breakup of large TCE blobs. Our quantitative experimental measurements will be useful in the context of developing accurate computational models for chemical oxidation of TCE in fractures.

Transport With Bimolecular Reactions in a Fracture‐Matrix System: Analytical Solutions With Applications to In Situ Chemical Oxidation

“…In the context of ISCO by permanganate, we should clarify that our formulation above does not consider the influence of permeability alteration and associated flow field evolution due to precipitation of the reaction product MnO 2 . Significant MnO 2 deposition and clogging of fractures has been observed in previous experimental studies (Arshadi et al, ; Tunnicliffe & Thomson, ). However, experimental studies of diffusion and reaction between permanganate and TCE do not report significant clogging of the porous matrix by MnO 2 or alteration of matrix transport properties (Struse et al, ).…”

Visualizing and quantifying the crossover from capillary fingering to viscous fingering in a rough fracture

“…[] and Arshadi et al . [] was followed to measure the aperture field of the fracture, which involves two steps: measuring the mean aperture and normalizing the aperture field measurement. We first injected a high‐viscosity fluid (glycerol, 1000 cP) at 2 mL/min to fully occupy the fracture cell, and then the mean fracture aperture was obtained by = m g / ρ g A p , where ρ g is the density of glycerol, m g is the injected mass into the fracture, and A p is the area of the fracture plane.…”

Fracture sealing by mineral precipitation: The role of small‐scale mineral heterogeneity

“…We constructed a transparent variable aperture fracture (15 × 15 cm) by mating two borosilicate glass surfaces: one rough and one smooth (for assembly details, see Arshadi et al [2015]). To create mineral heterogeneity, we seeded the flat surface with isolated regions of CaCO 3 using a modified procedure developed by Nancollas and Reddy [1971].…”