iron oxidation kinetics

Iron Oxidation Kinetics

Denae AthayWorking 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 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+

What we know…

Time

Fe+2

Biotic

Abiotic

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

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…

Filter

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 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

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

0

40

80

120

160

200

0 6 12 18 24

Elapsed Time (hrs)

Fer

rou

s Ir

on

(m

g/L

)

Unfiltered Filtered

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

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

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

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

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

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

Acknowledgement… Dr. Nairn

Acknowledgement… Dr. Nairn Dr. Strevett

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

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

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

Any Questions?