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Iron Oxidation Kinetics
Denae AthayWorking with Jessica Brumley, Danette Miller, Emily
Spargo, Kim Wahnee, Dr. Nairn and Dr. Strevett
REU 2000
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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
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Introduction to the Experiment…
Iron is discharged in reduced formImmediately begins to oxidize
Abiotic: oxygen from the atmosphereBiotic: iron oxidizing bacteria Thiobacillus ferrooxidans, Metallogium,
Leptothrix
Fe+2 + ¼ O2 + H+ = Fe3+ + ½ H2O
Fe3+ + 3H2O = Fe(OH)3(s) + 3H+
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What we know…
Time
Fe+2
Biotic
Abiotic
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What we don’t know…Which process is dominant
Biotic oxidation normally dominates in acid mine drainageConditions not ideal for bacteria
Mayer is net alkaline with neutral pH
Why we careRemediation design to enhance natural oxidation process
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Our Hypothesis...
The dominant iron oxidation process is abiotic
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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
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The field design…
Filter
Seep
Unfiltered Microcosm
Filtered Microcosm
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The field design…Step 1: pump mine drainage into microcosms (1 filtered to remove bacteria)Step 2: microcosms placed in marsh to keep temperature constantStep 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
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Back in the lab…Samples analyzed
Ferrous iron concentration
Total iron concentration
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Back in the lab…This involved…
126 ferrous iron titrations
23 hours hot acid digestions
57 atomic absorption spectrophotometer analysis
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Ferrous Iron v. Time - Seep A
0
40
80
120
160
200
0 6 12 18 24
Elapsed Time (hrs)
Fer
rou
s Ir
on
(m
g/L
)
Unfiltered Filtered
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Ferrous Iron v. Time - Seep B
0
40
80
120
160
200
0 12 24 36 48
Elapsed Time (hrs)
Fer
rou
s Ir
on (
mg
/L)
Unfiltered Filtered
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Ferrous Iron v. Time - Site 2
0
20
40
60
0 12 24 36 48
Elapsed Time (hrs)
Fer
rou
s Ir
on (
mg
/L)
Unfiltered Filtered
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Total Iron v. Time - Site 2
0
20
40
60
80
100
120
140
160
0 12 24 36 48
Elapsed Time (hrs)
To
tal
Iro
n (
mg
/L)
Unfiltered Filtered
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Alkalinity v. Time - Site 2
0
50
100
150
200
250
0 12 24 36 48
Elapsed Time (hrs)
Alk
alin
ity
(mg
/L a
s C
aCo
3)
Unfiltered Filtered
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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
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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
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Acknowledgement… Dr. Nairn
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Acknowledgement… Dr. Nairn Dr. Strevett
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Acknowledgement… 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
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Acknowledgement… 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
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Acknowledgement… 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
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Any Questions?