air lifting mechanisms for oxidation in underground mines

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air lifting mechanisms for oxidation in
underground mines
Bruce Leavitt PE PG, Consulting Hydrogeologist
Washington, Pennsylvania
Prepared in conjunction with West Virginia
University under a grant from the Office of
Surface Mining Applied Science Research Program
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• In Situ Aeration
• Net alkaline mine drainage.
• Oxidize ferrous iron in mine drainage.
• Fe2 2.5 H2O 0.25 O2 Fe(OH)3 2 H
• Reaction rate proportional to pH.
• Lower reagent cost than hydrogen peroxide.
• Design parameters unknown.
• Potential for carbon dioxide removal.

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Air Lift Operation
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Air Lift Test Design

• Flow Testing
• 4 pipe diameters (12, 10, 8, and 6)
• 2 diffusers
• Multiple air flow rates
• Oxygen Transfer Testing
• High volume low DO source
• Same pipe diameters and diffusers

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Equipment Configuration
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Diffusers
Sintered glass diffuser medium bubble
2 inch dia. 10 well screen large bubble
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Test Pipe with Auto Burper
6 inch
12 inch
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Anemometer and Magnehelic
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1.5 hp Regenerative Blower
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300 gallon bucket
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Test Procedure

• Adjust dock height to less than ¼ inch from
  overflow
• Measure depth to diffuser.
• Warm up blower.
• Measure and adjust air flow. (before and after
  test)
• Read Magnehelic.
• Open 4 inch ball valve in dam.
• Close bypass valve time tank filling.
• Pump produced water back into lake.

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Water Production
Drain Closed
Drain Open
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Water Production 8 inch pipe
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Sulfur Run Borehole
Date pH DO ORP
9-30-2009 3.35 0.05 322
10-3-2009 3.40 0.09 313
10-5-2009 3.41 0.07 NA
Closing the Ball Valve
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Air Lift with Sampling Pipe
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Oxygen Concentration
Squares are set about 4 feet Diamonds are set
about 3 feet
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Oxygen Mass Transfer 12 inch
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Oxygen Mass Transfer 10 inch
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Oxygen Mass Transfer 8 inch
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Oxygen Mass Transfer 6 inch
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Oxygen Mass Transfer Comparison at 14 cfm
Pipe Diameter Aeration stone Well Screen Improvement
inch grams / minute grams / minute percent
12 4.14 3.55 16.6
10 5.03 3.38 48.8
8 4.87 3.05 59.6
6 3.41 2.01 69.6
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Air Lift Operation

• All air flows used in this testing can be
  achieved with a ¾ hp high-pressure regenerative
  blower. (smaller units are possible)
• At 0.10 / kW hr the daily cost of operation
  would be 1.34 or 490.00 per year.
• A ¾ hp high-pressure regenerative blower can be
  purchased for 700.00

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Conclusions

• The use of low pressure air to create flow in a
  zero static head setting has been demonstrated.
• The volume of water moved with such a small
  volume of air surpassed expectations.
• Five cubic feet of air per minute is able to
  generate 200 gallons per minute of water flow.
• Oxygen transfer to the produced water only
  achieved 25 percent to 30 percent saturation
  under the best conditions.

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Conclusions continued

• In most tests, there is not a significant
  difference between the DO produced by the well
  screen and the stone diffuser at the same depth.
• There is a tendency for the shallower depth
  setting to produce a higher DO than the deeper
  setting.
• Based on the calculated oxygen delivery to the
  mine, between 23.8 and 35.1 grams of iron per
  minute can be oxidized. This rate of iron
  oxidation is equal to 75.6 to 111.4 pounds iron
  per day.

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Conclusions continued

• Based on these tests the 8 inch riser with stone
  diffusers is the most economical configuration.
• Construction of a large diameter borehole may be
  expensive, but the cost of equipment and its
  operation is low.
• Borehole maintenance will be required.

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Questions?
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Task Force Reception 530
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Task Force Reception 530
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Task Force Reception 530
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2010 JOINT MINING RECLAMATION CONFERENCE 27th
Annual Meeting of the American Society of Mining
and Reclamation12 Annual PA Abandoned Mine
Reclamation Conference 4th Annual Appalachian
Regional Reforestation Initiative Mine Land
Reclamation Conference