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Title: Micron-Size Zero-Valent Iron Emplacement in Porous Media Using Polymer Additives: Column and Flow Cell Ex-periments

Abstract

At the Hanford Site, an extensive In Situ Redox Manipulation (ISRM) permeable reactive barrier was installed to prevent chromate from reaching the Columbia River. However, chromium has been detected in several wells, indicating a premature loss of the reductive capacity in the aquifer. Laboratory experiments have been conducted to investigate whether barrier reductive capacity can be enhanced by adding micron-scale zero-valent iron to the high-permeability zones within the aquifer using shear-thinning fluids containing polymers. Porous media were packed in a wedge-shaped flow cell to create either a heterogeneous layered system with a high-permeability zone between two low-permeability zones or a high-permeability channel sur-rounded by low-permeability materials. The injection flow rate, polymer type, polymer concentration, and injected pore volumes were determined based on preliminary short- and long-column experiments. The flow cell experiments indicated that iron concentration enhancements of at least 0.6% (w/w) could be obtained using moderate flow rates and injection of 30 pore volumes. The 0.6% amended Fe0 concentration would provide approximately 20 times the average reductive capacity that is provided by the dithionite-reduced iron in the ISRM barrier. Calculations show that a 1-m-long Fe0 amended zone with an average concentration of 0.6% w/w iron subject to a groundwater velocitymore » of 1 m/day will have an estimated longevity of 7.2 years.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
881325
Report Number(s):
PNNL-SA-48855
14892; TRN: US200612%%807
DOE Contract Number:
AC05-76RL01830
Resource Type:
Conference
Resource Relation:
Conference: 26th Annual American Geophysical Union Hydrology Days Conference Proceedings, March 20-22, 2006, Colorado State University, 131-139
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; ADDITIVES; AQUIFERS; CAPACITY; CHROMATES; CHROMIUM; COLUMBIA RIVER; FLOW RATE; HYDROLOGY; IRON; POLYMERS; POSITIONING; VELOCITY; Environmental Molecular Sciences Laboratory

Citation Formats

Oostrom, Mart, Wietsma, Thomas W., Covert, Matthew A., and Vermeul, Vince R. Micron-Size Zero-Valent Iron Emplacement in Porous Media Using Polymer Additives: Column and Flow Cell Ex-periments. United States: N. p., 2006. Web.
Oostrom, Mart, Wietsma, Thomas W., Covert, Matthew A., & Vermeul, Vince R. Micron-Size Zero-Valent Iron Emplacement in Porous Media Using Polymer Additives: Column and Flow Cell Ex-periments. United States.
Oostrom, Mart, Wietsma, Thomas W., Covert, Matthew A., and Vermeul, Vince R. Mon . "Micron-Size Zero-Valent Iron Emplacement in Porous Media Using Polymer Additives: Column and Flow Cell Ex-periments". United States. doi:. https://www.osti.gov/servlets/purl/881325.
@article{osti_881325,
title = {Micron-Size Zero-Valent Iron Emplacement in Porous Media Using Polymer Additives: Column and Flow Cell Ex-periments},
author = {Oostrom, Mart and Wietsma, Thomas W. and Covert, Matthew A. and Vermeul, Vince R.},
abstractNote = {At the Hanford Site, an extensive In Situ Redox Manipulation (ISRM) permeable reactive barrier was installed to prevent chromate from reaching the Columbia River. However, chromium has been detected in several wells, indicating a premature loss of the reductive capacity in the aquifer. Laboratory experiments have been conducted to investigate whether barrier reductive capacity can be enhanced by adding micron-scale zero-valent iron to the high-permeability zones within the aquifer using shear-thinning fluids containing polymers. Porous media were packed in a wedge-shaped flow cell to create either a heterogeneous layered system with a high-permeability zone between two low-permeability zones or a high-permeability channel sur-rounded by low-permeability materials. The injection flow rate, polymer type, polymer concentration, and injected pore volumes were determined based on preliminary short- and long-column experiments. The flow cell experiments indicated that iron concentration enhancements of at least 0.6% (w/w) could be obtained using moderate flow rates and injection of 30 pore volumes. The 0.6% amended Fe0 concentration would provide approximately 20 times the average reductive capacity that is provided by the dithionite-reduced iron in the ISRM barrier. Calculations show that a 1-m-long Fe0 amended zone with an average concentration of 0.6% w/w iron subject to a groundwater velocity of 1 m/day will have an estimated longevity of 7.2 years.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Mar 20 00:00:00 EST 2006},
month = {Mon Mar 20 00:00:00 EST 2006}
}

Conference:
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  • At the Hanford Site, an extensive In Situ Redox Manipulation (ISRM) permeable reactive barrier was installed to prevent chromate from reaching the Columbia River. However, chromium has been detected in several wells, indicating a premature loss of the reductive capacity in the aquifer. One possible cause for premature chromate breakthrough is associated with the presence of high-permeability zones in the aquifer. In these zones, groundwater moves relatively fast and is able to oxidize iron more rapidly. There is also a possibility that the high-permeability flow paths are deficient in reducing equivalents (e.g. reactive iron), required for barrier performance. One waymore » enhancement of the current barrier reductive capacity can be achieved is by the addition of micron-scale zero-valent iron to the high-permeability zones within the aquifer. The potential emplacement of zero-valent iron (Fe0) into high-permeability Hanford sediments (Ringold Unit E gravels) using shear-thinning fluids containing polymers was investigated in three-dimensional wedge-shaped aquifer models. Polymers were used to create a suspension viscous enough to keep the Fe0 in solution for extended time periods to improve colloid movement into the porous media without causing a permanent detrimental decrease in hydraulic conductivity. Porous media were packed in the wedge-shaped flow cell to create either a heterogeneous layered system with a high-permeability zone in between two low-permeability zones or a high-permeability channel surrounded by low-permeability materials. The injection flow rate, polymer type, polymer concentration, and injected pore volumes were determined based on preliminary short- and long-column experiments.« less
  • At the Hanford Site in Washington, an extensive In Situ Redox Manipulation (ISRM) permeable reactive barrier was installed to prevent chromate from reaching the Columbia River. However, chromium has been detected in several wells, indicating a premature loss of the reductive capacity in the aquifer. One possible cause for premature chromate breakthrough is associated with the presence of high-permeability zones in the aquifer. The potential emplacement of zero-valent iron (Fe0) into high-permeability Hanford sediments to enhance the barrier’s reductive capacity using shear-thinning fluids containing polymers was investigated in three-dimensional wedge-shaped aquifer models. Porous media were packed in the wedge-shaped flowmore » cell to create either a heterogeneous layered system with a high-permeability zone between two low-permeability zones or a high-permeability channel surrounded by low-permeability materials. The injection flow rate, polymer type, polymer concentration, and injected pore volumes were determined based on preliminary short- and long-column experiments. The flow cell experiments indicated that iron concentration enhancements of at least 0.6% (w/w) could be obtained using moderate flow rates and injection of 30 pore volumes. The aqueous pressure increased by a maximum of 25 KPa during infiltration, but a decrease in permeability was not observed. Under optimal conditions, the 0.6% amended Fe0 concentration would provide approximately 20 times the average reductive capacity that is provided by the dithionite-reduced Fe (II) in the ISRM barrier.« less
  • Laboratory and field studies have shown that fillings of metal that are predominantly Fe{sup 0} can rapidly dehalogenate a variety of chlorinated solvents, and several technologies have recently been proposed to use this reaction in remediation of contaminated ground water. This report describes results from a laboratory column designed to model the spatial distribution of chemical conditions when iron is applied as part of an in-situ permeable reactive barrier. The column contains a zone of granular iron located between up-gradient and down-gradient zones of sand, and has received deionized water with varying concentrations of CCl{sub 4} for over 6 months.more » Aerobic corrosion results in complete consumption of dissolved oxygen and precipitation of ferric hydroxides at the interface where water enters the iron-bearing zone. Within the iron-bearing zone, corrosion continues due to oxidation of the iron by water and carbon tetrachloride, resulting in increased pH and concentration of dissolved iron in the pore water. At the down-gradient interface, pH decreased as the result of precipitation of iron-bearing minerals. Carbon tetrachloride (up to 1.6 mM) was fully dehalogenated by the first sample port within the iron-bearing zone. The chloroform produced was further dechlorinated to dichloromethane, but at a slower rate. First-order disappearance kinetics for chloroform applied across the zone of iron, and k{sub obs} has changed little over several months. No evidence has been found so far for unusual reactivity of the chlorinated solvents at either the up-gradient or down-gradient interfaces.« less
  • Foam is potentially a promising vehicle to deliver nanoparticles for vadose zone remediation as foam can overcome the intrinsic problems associated with solution-based delivery, such as preferential flow and contaminant mobilization. In this work, the feasibility of using foam to deliver nanoscale zero valent iron (nZVI) in unsaturated porous media was investigated. Foams generated using surfactant sodium lauryl ether sulfate (SLES) showed excellent ability to carry nZVI. SLES and nZVI concentrations in the foaming solutions did not affect the percentages of nZVI concentrations in foams relative to nZVI concentrations in the solutions. When foams carrying nZVI were injected through themore » unsaturated columns, the fractions of nZVI exiting the column were much higher than those when nZVI was injected in liquid. The enhanced nZVI transport implies that foam delivery could significantly increase the radius of influence of injected nZVI. The type and concentrations of surfactants and the influent nZVI concentrations did not noticeably affect nZVI transport during foam delivery. In contrast, nZVI retention increased considerably as the grain size of porous media decreased. Oxidation of foam-delivered nZVI due to oxygen diffusion into unsaturated porous media was visually examined using a flow cell. It was demonstrated that if foams are injected to cover a deep vadose zone layer, oxidation would only cause a small fraction of foam-delivered nZVI to be oxidized before it reacts with contaminants.« less
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