Transcript Final Presentation (Power Point)

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
Two upwelling rich in alkalinity and CO2
Proposed site for remediation
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+
What we know…
Fe+2
Abiotic
Biotic
Time
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
Our Hypothesis...
The dominant iron oxidation
process is abiotic
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
The field design…
Seep
Unfiltered
Microcosm
Filtered
Microcosm
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
Back in the lab…
Samples analyzed
Ferrous iron concentration
Total iron concentration
Back in the lab…
This involved…
126 ferrous iron titrations
23 hours hot acid digestions
57 atomic absorption spectrophotometer
analysis
Ferrous Iron v. Time - Seep A
Unfiltered
Filtered
Ferrous Iron (mg/L)
200
160
120
80
40
0
0
6
12
Elapsed Time (hrs)
18
24
Ferrous Iron v. Time - Seep B
Unfiltered
Filtered
Ferrous Iron (mg/L)
200
160
120
80
40
0
0
12
24
Elapsed Time (hrs)
36
48
Ferrous Iron v. Time - Site 2
Unfiltered
Filtered
Ferrous Iron (mg/L)
60
40
20
0
0
12
24
Elapsed Time (hrs)
36
48
Total Iron v. Time - Site 2
Unfiltered
Filtered
160
Total Iron (mg/L)
140
120
100
80
60
40
20
0
0
12
24
Elapsed Time (hrs)
36
48
Alkalinity v. Time - Site 2
Alkalinity (mg/L as CaCo3)
Unfiltered
Filtered
250
200
150
100
50
0
0
12
24
Elapsed Time (hrs)
36
48
Conclusions…
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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
If I knew then what I know
now...
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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
Acknowledgement…
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Dr. Nairn
Acknowledgement…
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Dr. Nairn
Dr. Strevett
Acknowledgement…
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Dr. Nairn
Dr. Strevett
NSF REU
Sharon & Janna
Robbins
Rebecca Jim
Carrie Evenson
Jane Sund
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Erin Breetzke
Lisa Hare
Todd Wolfard
Jake Manko
Danette Miller
Jessica Brumley
Acknowledgement…
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Dr. Nairn
Dr. Strevett
NSF REU
Sharon & Janna
Robbins
Rebecca Jim
Carrie Evenson
Jane Sund
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Erin Breetzke
Lisa Hare
Todd Wolfard
Jake Manko
Danette Miller
Jessica Brumley
Kim Wahnee
Acknowledgement…
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Dr. Nairn
Dr. Strevett
NSF REU
Sharon & Janna
Robbins
Rebecca Jim
Carrie Evenson
Jane Sund
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
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Erin Breetzke
Lisa Hare
Todd Wolfard
Jake Manko
Danette Miller
Jessica Brumley
Kim Wahnee
Emily Spargo
Any Questions?