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

An Experiment Illustrating How Iron Metal is Used to Remediate Contaminated Groundwater. Barbara Balko, Department of Chemistry Lewis & Clark College Portland, OR. Discovery .

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

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  1. An Experiment Illustrating How Iron Metal is Used to Remediate Contaminated Groundwater Barbara Balko, Department of Chemistry Lewis & Clark College Portland, OR

  2. Discovery Contaminant hydrologists investigated the effect that materials used in sampling groundwater had on the concentration of halogenated solvents.

  3. 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

  4. Kinetics Rate = -d[RX]/dt = k[Fe active sites][RX] -d[RX]/dt = kobs[RX] where kobs = k[Fe active sites] *expect kobs to be proportional to the mass of iron used as well as the iron surface area

  5. Application Iron Wall versus Pump-and-Treat

  6. Uses

  7. 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

  8. Experiment t = 0

  9. Equipment/Chemicals

  10. 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 Beer’s law is satisfied • 2nd week: self-designed experiment • Provide time for inter-group discussion and presentation of results • Poster presentation

  11. Typical Results Results obtained using Fluka iron, indigo carmine (20 ppm), and a rotation rate of 18 rotations/min

  12. Examples of Student Projects

  13. Effect of Temperature

  14. Students designed and constructed set-up to control temperature

  15. Results: Eact = 64.1 kJ/mole

  16. Unintended result: Rotator position matters

  17. Are Other Metals as Effective?

  18. Search for Metals with Similar Particle Sizes

  19. 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

  20. Does Oxide Coating Slow Reaction?

  21. How to Control for Particle Scattering?

  22. Rusted Iron is Less Reactive

  23. Can Iron be Used to Remove Dye Stains in Cloth?

  24. How to Quantify Stain Removal?

  25. 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

  26. Trouble-Shooting • Air Bubbles in Cuvets • Oxygen Leakage into Cuvets • Light Scattering • Biased Sampling of Iron • Adsorption of Dyes to Cuvets, Iron…

  27. J. Chem. Ed. (78 (12), 1661, 2001)

  28. Resources: MERL CD-ROM Available here or send a request to merl@ese.ogi.edu

  29. Chem. Educator (6, 172-179, 2001)

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

  31. Is kobs linearly proportional to the mass of iron used?

  32. Linear Correlation between kobs and the Mass of Fe Used

  33. 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

  34. How does oxidation of the iron surface affect the reaction long term? Fresh reagent-grade Iron Iron after 12 hrs exposure to aqueous CCl4

  35. Results Suggest Iron Cannot Remove Dye Stains from Cloth and that Controls are Important!

  36. Implementation Installation of an iron wall at a site formerly occupied by a semiconductor manufacturing factory (Sunnyvale, CA)

  37. 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.

  38. 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.

  39. Possible Topics for Class Discussion • Oxidation-Reduction Reactions • Pseudo First-Order Kinetics • Environmental Chemistry • Heterogeneous Reactions • Corrosion • Passive Film Growth • Mass Transport

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