An Experiment Illustrating How Iron Metal is Used to Remediate Contaminated Groundwater

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An Experiment Illustrating How Iron Metal is Used
to Remediate Contaminated Groundwater

• Barbara Balko, Department of Chemistry
• Lewis Clark College
• Portland, OR

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Discovery
Contaminant hydrologists investigated the effect
that materials used in sampling groundwater had
on the concentration of halogenated solvents.
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Chemistry
Oxidation-Reduction Reaction Fe0 ? Fe2 2e-
Eo 0.44
V CCl4 2e- H ? CHCl3 Cl-
Eo 0.67 V ______________________________________
_______ CCl4 H Fe0 ? CHCl3 Cl- Fe2
Eo 1.11 V
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Kinetics
Rate -dRX/dt kFe active sitesRX -dRX/d
t kobsRX where kobs kFe active
sites expect kobs to be proportional to the
mass of iron used as well as the iron surface
area
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Application
Iron Wall
Pump-and-Treat
versus
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Uses
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Adapting the Technology to the Lab

• Dyes are used to simulate groundwater
  contaminants
• Degradation is followed using a visible light
  source and detector
• Dye-Iron interaction occurs in a sealed cuvet
• kobs is obtained by plotting ln(A/Ao) versus time
• Vary experimental parameters to learn details
  about the reaction mechanism

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Experiment
t 0
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Equipment/Chemicals
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Logistics

• Suitable for freshman undergraduates can also be
  used as a demonstration
• Requires two (or more) 3 hour lab periods
• Students are divided into groups of 2 4
• 1st week measure kobs under standard conditions
  plan experiment confirm that Beers law is
  satisfied
• 2nd week self-designed experiment
• Provide time for inter-group discussion and
  presentation of results
• Poster presentation

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Typical Results
Results obtained using Fluka iron, indigo carmine
(20 ppm), and a rotation rate of 18 rotations/min
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(No Transcript)
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Examples of Student Projects
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Effect of Temperature
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Students designed and constructed set-up to
control temperature
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Results Eact 64.1 kJ/mole
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Unintended result Rotator position matters
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Are Other Metals as Effective?
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Search for Metals with Similar Particle Sizes
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Correlation between Eo and Metal Reactivity?
Al3/Al Eo -1.66 V Zn2/Zn Eo -0.763
V Fe2/Fe Eo -0.440 V Sn2/Sn Eo -0.136 V
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Does Oxide Coating Slow Reaction?
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How to Control for Particle Scattering?
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Rusted Iron is Less Reactive
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Can Iron be Used to Remove Dye Stains in Cloth?
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How to Quantify Stain Removal?
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Other Project Ideas

• Effect of Mass of Iron Used
• Effect of Iron Surface Area
• Effect of Dye Concentration
• Source of Iron
• Rotation Rate
• Dye
• pH/buffering

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Trouble-Shooting

• Air Bubbles in Cuvets
• Oxygen Leakage into Cuvets
• Light Scattering
• Biased Sampling of Iron
• Adsorption of Dyes to Cuvets, Iron

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J. Chem. Ed. (78 (12), 1661, 2001)
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Resources MERL CD-ROM
Available here or send a request to
merl_at_ese.ogi.edu
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Chem. Educator (6, 172-179, 2001)
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Acknowledgements

• Paul Tratnyek, Dept. of Environmental Science and
  Engineering, Oregon Health and Sciences
  University
• Lewis Clark College Chemistry Department
• Accelerated General Chemistry, Spring 2002

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Is kobs linearly proportional to the mass of iron
used?
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Linear Correlation between kobs and the Mass of
Fe Used
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The Real World is More Complex.
The actual oxidant may be Fe2 or H2 due to the
reduction of dissolved oxygen and/or water by Fe0
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How does oxidation of the iron surface affect the
reaction long term?
Fresh reagent-grade Iron
Iron after 12 hrs exposure to aqueous CCl4
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Results Suggest Iron Cannot Remove Dye Stains
from Cloth and that Controls are Important!
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Implementation
Installation of an iron wall at a site formerly
occupied by a semiconductor manufacturing factory
(Sunnyvale, CA)
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Performance
The first field test of an iron wall (Canadian
Forces Base, Borden, Ontario) showed that
halogenated solvents would be degraded. The
performance of the wall did not deteriorate in
subsequent years.
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Locations
The map shows the iron walls installed (or under
construction) as of August 1999. There are also
iron walls in Europe, Australia, and Canada.
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Possible Topics for Class Discussion

• Oxidation-Reduction Reactions
• Pseudo First-Order Kinetics
• Environmental Chemistry
• Heterogeneous Reactions
• Corrosion
• Passive Film Growth
• Mass Transport