AIR LIFTING MECHANISMS AIR LIFTING MECHANISMS FOR OXIDATION IN FOR OXIDATION IN

UNDERGROUND MINESUNDERGROUND 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

In Situ In Situ AerationAeration

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.

Air Lift OperationAir Lift Operation

Air Lift Test DesignAir Lift Test Design

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

Equipment ConfigurationEquipment Configuration

DiffusersDiffusers

2 inch dia. #10 well screen large bubble

Sintered glass diffuser medium bubble

Test Pipe with Auto BurperTest Pipe with Auto Burper

12 inch

6 inch

Anemometer and MagnehelicAnemometer and Magnehelic

1.5 hp Regenerative Blower1.5 hp Regenerative Blower

300 gallon bucket300 gallon bucket

Test ProcedureTest 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.

Water ProductionWater Production

Drain Closed

Drain Open

Water Production 8 inch pipeWater Production 8 inch pipe

Sulfur Run BoreholeSulfur 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

Air Lift with Sampling PipeAir Lift with Sampling Pipe

Oxygen ConcentrationOxygen Concentration

Squares are set about 4 feetDiamonds are set about 3 feet

Oxygen Mass Transfer 12 inchOxygen Mass Transfer 12 inch

Oxygen Mass Transfer 10 inchOxygen Mass Transfer 10 inch

Oxygen Mass Transfer 8 inchOxygen Mass Transfer 8 inch

Oxygen Mass Transfer 6 inchOxygen Mass Transfer 6 inch

Oxygen Mass Transfer Oxygen Mass Transfer Comparison at 14 cfmComparison 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

Air Lift OperationAir 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

ConclusionsConclusions

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.

Conclusions Conclusions continuedcontinued

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.

Conclusions Conclusions continuedcontinued

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 it’s operation is low.

Borehole maintenance will be required.

Questions?Questions?

Task Force Reception 5:30Task Force Reception 5:30

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2010 JOINT MINING RECLAMATION CONFERENCE27th 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