Multicomponent Reactive Transport in an In Situ Zero-Valent Iron Cell

Abstract

Data collected from a field study of in situ zero-valent iron treatment for TCE were analyzed in the context of coupled transport and reaction processes. The focus of this analysis was to understand the behavior of chemical components, including contaminants, in groundwater transported through the iron cell of a pilot-scale funnel and gate treatment system. A multicomponent reactive transport simulator was used to simultaneously model mobile and nonmobile components undergoing equilibrium and kinetic reactions including TCE degradation, parallel iron dissolution reactions, precipitation of secondary minerals, and complexation reactions. The resulting mechanistic model of coupled processes reproduced solution chemistry behavior observed in the iron cell with a minimum of calibration. These observations included the destruction of TCE and cis-1,2-DCE; increases in pH and hydrocarbons; and decreases in EH, alkalinity, dissolved O2 and CO2, and major ions (i.e., Ca, Mg, Cl, sulfate, nitrate). Mineral precipitation in the iron zone was critical to correctly predicting these behaviors. The dominant precipitation products were ferrous hydroxide, siderite, aragonite, brucite, and iron sulfide. In the first few centimeters of the reactive iron cell, these precipitation products are predicted to account for a 3% increase in mineral volume per year, which could have implications for the longevity of favorable barrier hydraulics and reactivity. The inclusion of transport was key to understanding the interplay between rates of transport and rates of reaction in the field.

Soils contaminated with explosives: Environmental fate and evaluation of state-of-the-art remediation processes (IUPAC Technical Report)

“…While contact with the iron surface is desired for HE destruction, it is also true that interstitial pore water both inside and downgradient of PRB will be laden with Fe +2 , Fe +3 , and associated minerals [369,370]. Moreover, when the hydraulic conductivities of the PRB no longer match regional groundwater velocity, as can occur with iron aging, secondary mineral precipitation can occur near the upgradient edge of the PRBs [353,362,371,372].…”

Performance of a PRB for the Remediation of Acidic Groundwater in Acid Sulfate Soil Terrain

“…Several researchers (Karvonen 2004;Komnitsas et al 2007;Li and Benson 2005;Liang et al 2003;McMahon et al 1999;Puls et al 1999a;Sarr 2001;Vogan et al 1999;Yabusaki 2001) have reported that armouring on the surface of reactive materials and chemical clogging of pores, by precipitated compounds during chemical reactions inside the PRB, decrease the long-term performance parameters such as reactivity, porosity and permeability. Significant concerns relating to precipitation of iron and aluminium oxides and hydroxides also exist in alkaline PRBs with acidic groundwater in ASS terrain because their solubilities are pH-dependent.…”

Corrosion of Metal Inclusions In Bulk Vitrification Waste Packages

“…Fortunately, this water reduction reaction is slow and kinetically unfavorable in most environmental systems because of the presence of other oxidizing agents. Because Fe(0) has a high reductive capacity, researchers have begun using it to treat groundwater contaminated with redox-sensitive heavy metals, radionuclides, and organics, such as trichloroethene (TCE) (Yabusaki et al 2001), nitro aromatic compounds (Klausen et al 2003), Cr(VI) (Fruchter 2002), U(VI) (Gu et al 1998;Abdelouas et al 1999), and Tc(VII) (Cantrell et al 1995). These experiments provide some information on the chemical reactions that occur during the corrosion of Fe(0).…”