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Iron Oxidation Kinetics

Iron Oxidation Kinetics. Denae Athay Working with Jessica Brumley, Danette Miller, Emily Spargo, Kim Wahnee, Dr. Nairn and Dr. Strevett REU 2000. Introduction to the site…. Mayer Ranch Volunteer wetland Cattail marsh receiving metal rich mine discharge

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Iron Oxidation Kinetics

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  1. Iron Oxidation Kinetics Denae Athay Working with Jessica Brumley, Danette Miller, Emily Spargo, Kim Wahnee, Dr. Nairn and Dr. Strevett REU 2000

  2. Introduction to the site… • Mayer Ranch • Volunteer wetland • Cattail marsh receiving metal rich mine discharge • Two upwelling rich in alkalinity and CO2 • Proposed site for remediation

  3. Introduction to the Experiment… • Iron is discharged in reduced form • Immediately begins to oxidize • Abiotic: oxygen from the atmosphere • Biotic: iron oxidizing bacteria • Thiobacillus ferrooxidans, Metallogium, Leptothrix Fe+2 + ¼ O2 + H+ = Fe3+ + ½ H2O Fe3+ + 3H2O = Fe(OH)3(s) + 3H+

  4. What we know… Fe+2 Abiotic Biotic Time

  5. What we don’t know… • Which process is dominant • Biotic oxidation normally dominates in acid mine drainage • Conditions not ideal for bacteria • Mayer is net alkaline with neutral pH • Why we care • Remediation design to enhance natural oxidation process

  6. Our Hypothesis... The dominant iron oxidation process is abiotic

  7. How we wanted to test this… • Sample mine drainage as a function of time to measure decrease in ferrous iron • Bacteria removed from one microcosm via 0.2 m filter • Comparison of iron oxidation rates indication dominant reaction

  8. The field design… Seep Filter Unfiltered Microcosm Filtered Microcosm

  9. The field design… • Step 1: pump mine drainage into microcosms (1 filtered to remove bacteria) • Step 2: microcosms placed in marsh to keep temperature constant • Step 3: samples taken from each at regular intervals (acidified) • In-situ measurements to monitor reactions • T, Alkalinity, Conductivity, Turbidity, DO, Salinity • Performed at both seeps and middle of marsh

  10. Back in the lab… • Samples analyzed • Ferrous iron concentration • Total iron concentration

  11. Back in the lab… • This involved… • 126 ferrous iron titrations • 23 hours hot acid digestions • 57 atomic absorption spectrophotometer analysis

  12. Conclusions… • Our data supports our hypothesis • Abiotic oxidation is dominant • Biotic oxidation is minimal • Remediation of the site • Aeration can drive the reaction to precipitate out the iron

  13. If I knew then what I know now... • Contamination is important to prevent • Pumping aerates the sample • Filter the samples • Take an initial sample • Avoid long periods without sampling • Plan ahead on sleeping arrangements

  14. Dr. Nairn Acknowledgement…

  15. Dr. Nairn Dr. Strevett Acknowledgement…

  16. Dr. Nairn Dr. Strevett NSF REU Sharon & Janna Robbins Rebecca Jim Carrie Evenson Jane Sund Erin Breetzke Lisa Hare Todd Wolfard Jake Manko Danette Miller Jessica Brumley Acknowledgement…

  17. Dr. Nairn Dr. Strevett NSF REU Sharon & Janna Robbins Rebecca Jim Carrie Evenson Jane Sund Erin Breetzke Lisa Hare Todd Wolfard Jake Manko Danette Miller Jessica Brumley Kim Wahnee Acknowledgement…

  18. Dr. Nairn Dr. Strevett NSF REU Sharon & Janna Robbins Rebecca Jim Carrie Evenson Jane Sund Erin Breetzke Lisa Hare Todd Wolfard Jake Manko Danette Miller Jessica Brumley Kim Wahnee Emily Spargo Acknowledgement…

  19. Any Questions? Any Questions?

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