Final Report: Improving the Performance of Permeable Reactive Barriers: Enhancing Reactivity and Longevity through Understanding of Surface Oxides

EPA Grant Number: R827117
Title: Improving the Performance of Permeable Reactive Barriers: Enhancing Reactivity and Longevity through Understanding of Surface Oxides
Investigators: Tratnyek, Paul G. , Westall, John C.
Institution: Oregon Graduate Institute of Science & Technology , Oregon State University
EPA Project Officer: Lasat, Mitch
Project Period: October 1, 1998 through September 30, 2001 (Extended to November 30, 2002)
Project Amount: $374,252
RFA: Exploratory Research - Environmental Engineering (1998) RFA Text |  Recipients Lists
Research Category: Sustainability , Land and Waste Management , Engineering and Environmental Chemistry

Objective:

Recent experience with the remediation of contaminants with permeable reactive barriers (PRBs) containing zero-valent iron (ZVI) has shown that remediation performance is strongly affected by the layers of precipitates that form on the iron surface over time. The objective of this research project was to explore the extent to which long-term performance of PRBs can be predicted and enhanced through a mechanistic understanding of the role of precipitates in the treatment zone. The approach included electrochemical experiments with electrodes composed of iron metal and iron oxides, column and batch experiments that combine solution phase chemistry with surface analysis, and modeling to integrate experimental results with theory.

Summary/Accomplishments (Outputs/Outcomes):

The major accomplishments of this research project were along five fronts: (1) at Oregon Health and Science University (OHSU), we studied the reduction of several contaminants on iron metal electrodes; (2) at Oregon State University (OSU), we studied the reduction of several contaminants on iron oxide electrodes; (3) at OHSU, batch experiments were performed that show the variation of reactivity with the composition of iron metal; (4) at OHSU, column studies were conducted using trinitrotoluene (TNT) to probe how spatial and temporal changes in the geochemistry of the column influence its ability to remove contaminants; and (5) collectively, we initiated the development of a theoretical model of oxide film growth and how it effects contaminant reduction.

The first area of accomplishment involved the development of an electrochemical method for the study of solute reduction reactions at electrodes made of iron metal. This model system was used to show that dechlorination kinetics are mainly determined by charge transfer at the metal surface, whereas nitro reduction kinetics also are influenced by mass transfer of the contaminant to the iron surface. This approach also provided the first rigorous data to help address whether dechlorination by iron is a direct electron transfer process or is mediated by hydrogen that is formed on the iron surface by corrosion. This work constituted the doctoral thesis of Michelle Scherer, portions of which have been published in several journals (see Scherer, et al., 2001; Tratnyek, et al., 2001; Scherer, 1998).

The second area of accomplishment extended the application of electrochemical model systems to include iron oxides, which presumably cover iron metal under environmental conditions. This work involved the development and application of an electrochemical cell to study the rates of reduction of carbon tetrachloride (CT) and nitrobenzene (NB) by Fe(II) sites in an Fe(III)-oxide film. Fe(III) oxide films were prepared on gold electrodes and the Fe(II) sites were introduced into the film by controlled electrochemical reduction of a small fraction of the Fe(III) in the film. The fundamental mechanism of reduction and the factors affecting the overall reduction rate were investigated by varying the Fe(II) content in the iron oxide, controlling the mass transport of chemicals to the oxide surface, and varying the thickness of the oxide coating. This work constituted the doctoral thesis of Brian Logue and was published in Environmental Science & Technology (see Logue, et al., 2003; Logue, 2000).

The third area of accomplishment arose from batch experiments that were performed with granular iron from a variety of sources and with model contaminants of various chemical types (including several colorimetric indicators as well as CT, NB, and trichloroethene). The granular iron was analyzed using a variety of surface analysis techniques (e.g., x-ray photoelectron spectroscopy). The results of these analyses have been subject to correlation analysis to obtain a better understanding of the factors that control the reactivity of aqueous contaminants with iron metal. One manuscript that provides the first perspective on relative reaction rates across families of contaminant types has been submitted for publication (see Miehr, et al., 2003), and a followup manuscript on differences in reactivity of different types of iron is in preparation.

The fourth area of accomplishment, involving columns studies, should help resolve differences between results obtained in batch (or electrochemical) model systems and results obtained in columns or from the field. Working with TNT as our model contaminant, we have found that the distribution of products formed from TNT varies systematically with experimental variables such as the iron:solution ratio and the amount of time the iron was immersed in the solution. Preliminary descriptions of these results have been published, and a journal article on the results is in preparation (see Tratnyek, et al., 2002; Miehr, et al., 2003; Bandstra, et al., 2003).

The fifth area of research activity involves model development, which has continued beyond the period of this grant. The objective of this work is to reconcile the results obtained with electrochemical model systems with and without oxides present, batch experiments that involve rehydration of the air-formed passive film, and column or field experiments where the air-formed passive film on the iron has had considerable time to equilibrate with the solution chemistry. Preliminary results from this work are published in Bandstra, et al., 2003.

Conclusions:

We have shown that the reduction of contaminants occurs in the presence of ZVI, with and without a surface layer of oxide (or carbonate) precipitates. This layer of precipitates apparently mediates contaminant reduction by the transfer of charge through the precipitate layer, but reaction probably also occurs at defects (pits and crevices), where the intervening oxide film is minimal or nonexistent. The amount and reactivity of the authigenic surface precipitate layer depends on many system variables such as the amount of oxidant in the solution (dissolved oxygen and contaminants); other reactive solutes such as carbonate, nitrate, and natural organic matter; and the kinetics of reconstruction of the surface film mineralogy in response to solution chemistry.


Journal Articles on this Report : 11 Displayed | Download in RIS Format

Other project views: All 30 publications 13 publications in selected types All 11 journal articles
Type Citation Project Document Sources
Journal Article Agrawal A, Ferguson WJ, Gardner BO, Christ JA, Bandstra JZ, Tratnyek PG. Effects of carbonate species on the kinetics of dechlorination of 1,1,1-trichloroethane by zero-valent iron. Environmental Science & Technology 2002;36(20):4326-4333. R827117 (2000)
R827117 (Final)
  • Abstract from PubMed
  • Abstract: ES&T - Abstract
    Exit
  • Journal Article Balko BA, Tratnyek PG. A discovery-based experiment illustrating how iron metal is used to remediate contaminated groundwater. Journal of Chemical Education 2001;78(12):1661-1664. R827117 (Final)
  • Abstract: JCE - Abstract
    Exit
  • Journal Article Gaspar DJ, Lea AS, Engelhard MH, Baer DR, Miehr R, Tratnyek PG. Evidence for localization of reaction upon reduction of carbon tetrachloride by granular iron. Langmuir 2002;18(20):7688-7693. R827117 (Final)
  • Abstract: ACS - Abstract
    Exit
  • Journal Article Logue BA, Westall JC. Kinetics of reduction of nitrobenzene and carbon tetrachloride at an iron-oxide coated gold electrode. Environmental Science & Technology 2003;37(11):2356-2362. R827117 (2000)
    R827117 (Final)
  • Abstract from PubMed
  • Abstract: ES&T - Abstract
    Exit
  • Journal Article Miehr R, Tratnyek PG, Bandstra JZ, Scherer MM, Alowitz MJ, Bylaska EJ. Diversity of contaminant reduction reactions by zerovalent iron: role of the reductate. Environmental Science & Technology 2004;38(1):139-147. R827117 (2000)
    R827117 (Final)
  • Abstract from PubMed
  • Abstract: ES&T - Abstract
    Exit
  • Journal Article Nam S, Tratnyek PG. Reduction of azo dyes with zero-valent iron. Water Research 2000;34(6):1837-1845. R827117 (Final)
  • Full-text: ScienceDirect - Full Text HTML
    Exit
  • Abstract: ScienceDirect - Abstract
    Exit
  • Other: ScienceDIrect - Full Text PDF
    Exit
  • Journal Article Scherer MM, Johnson KM, Westall JC, Tratnyek PG. Mass transport effects on the kinetics of nitrobenzene reduction by iron metal. Environmental Science & Technology 2001;35(13):2804-2811. R827117 (2000)
    R827117 (Final)
  • Abstract from PubMed
  • Full-text: ResearchGate - Full Text PDF
    Exit
  • Abstract: ES&T - Abstract
    Exit
  • Journal Article Scherer MM, Westall JC, Tratnyek PG. Discussion on "Electrochemical and Raman spectroscopic studies of the influence of chlorinated solvents on the corrosion behaviour of iron in borate buffer and in simulated groundwater" [Corrosion Science 42 (2000) 1921–1939]. Corrosion Science 2002;44(5):1151-1157. R827117 (Final)
  • Full-text: ScienceDirect - Full Text HTML
    Exit
  • Abstract: ScienceDirect - Abstract
    Exit
  • Other: ScienceDirect - Full Text PDF
    Exit
  • Journal Article Tratnyek PG, Scherer MM, Deng BL, Hu S. Effects of natural organic matter, anthropogenic surfactants, and model quinones on the reduction of contaminants by zero-valent iron. Water Research 2001;35(18):4435-4443. R827117 (Final)
  • Abstract from PubMed
  • Full-text: ScienceDirect - Full Text HTML
    Exit
  • Abstract: ScienceDirect - Abstract
    Exit
  • Other: ScienceDirect - Full Text PDF
    Exit
  • Journal Article Tratnyek PG, Reilkoff TE, Lemon AW, Scherer MM, Balko BA, Feik LM, Henegar BD. Visualizing redox chemistry: probing environmental oxidation-reduction reactions with indicator dyes. The Chemical Educator 2001;6(3):172-179. R827117 (2000)
    R827117 (Final)
  • Full-text: Research Gate - Abstract & Full Text PDF
    Exit
  • Abstract: Springer - Abstract
    Exit
  • Journal Article Tratnyek PG, Weber EJ, Schwarzenbach RP. Quantitative structure-activity relationships for chemical reductions of organic contaminants. Environmental Toxicology and Chemistry 2003;22(8):1733-1742. R827117 (Final)
  • Abstract from PubMed
  • Abstract: Wiley - Abstract
    Exit
  • Supplemental Keywords:

    groundwater, treatment walls, passive technologies, iron metal, Scientific Discipline, Air, Waste, Remediation, Environmental Chemistry, Engineering, Groundwater remediation, Engineering, Chemistry, & Physics, electrochemical technology, adsorbents, surface oxidation, permeable reaction barriers, iron, kinetic models, groundwater contamination, surfactants

    Progress and Final Reports:

    Original Abstract
  • 1999 Progress Report
  • 2000 Progress Report
  • 2001
  • 2002