air lifting mechanisms for oxidation in underground mines

1. 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

2. 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.

3. Air Lift Operation

4. 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

5. Equipment Configuration

6. Diffusers Sintered glass diffuser medium bubble 2 inch dia. #10 well screen large bubble

7. Test Pipe with Auto Burper 6 inch 12 inch

8. Anemometer and Magnehelic

9. 1.5 hp Regenerative Blower

10. 300 gallon bucket

11. 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.

12. Water Production Drain Closed Drain Open

13. Water Production 8 inch pipe

14. Sulfur Run Borehole Closing the Ball Valve

15. Air Lift with Sampling Pipe

16. Oxygen Concentration Squares are set about 4 feet Diamonds are set about 3 feet

17. Oxygen Mass Transfer 12 inch

18. Oxygen Mass Transfer 10 inch

19. Oxygen Mass Transfer 8 inch

20. Oxygen Mass Transfer 6 inch

21. Oxygen Mass Transfer Comparison at 14 cfm

22. 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

23. 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.

24. 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.

25. 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 it’s operation is low. Borehole maintenance will be required.

26. Questions?

27. Task Force Reception 5:30

28. Task Force Reception 5:30

29. Task Force Reception 5:30

30. 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