1. 1 Abandoned Coal Mines: In-Situ Treatment of AMD with CCPs Jess W. Everett, Ph.D., P.E. Associate Professor Civil Engineering Rowan University

2. 2 Abandoned Coal Mines: In-Situ Treatment of AMD with CCPs Acid Mine Drainage –Mines fill with water, seeps are formed –Bacteria oxidize Pyrite (FeS 2 ), often found w/ coal End products create water with low pH, high metals, and high acidity –pH drops even more when water leaves mine Oxidation and Hydrolysis

3. 3 Problems Caused by AMD? Low pH in seep water damages receiving stream ecosystem Metals in seep water precipitate and cover stream bottom Metal toxicity

4. 4 Abandoned Coal Mines: In-Situ Treatment of AMD with CCPs Coal Combustion Products –High volume residues (ash) produced during coal powered energy production –Some CCPs are alkaline Oxides/hydroxides may be present in raw coal or form during combustion Alkaline materials are used to control SO 2 emissions, excess remains in ash

5. 5 How does the in-situ process work? Injection of Alkaline waste: –Neutralizes acidity in mine –Precipitates some metals in mine by pH adjustment –Imparts alkalinity to seep water

6. 6 Overview Mine description Injection description Results Interpretation Conclusions

7. 7 Mine Plan View Not to scale

8. 8 Mine Side View Pyrite Oxidation AMD Seep Water Infiltration Not to scale pH = 4.4 Zero Alkalinity

9. 9 Seep Flow and Rainfall

10. 10 Mine Hydrology - Tracer Studies Estimated Mine Retention time ~ 5 yr Three Tracer Injections –Main Corridor (MC) Rhodamine WT (Rh) - 1 gallon, 20% –Florescent dye, 1 ppt detection limit –adsorption/precipitation problems Chloride (Cl) - 175 pounds of NaCl –100 ppb detection limit –Side Corridor (SC) Chloride (300 pounds of NaCl)

11. 11 Tracer Injection Points

12. 12 Tracer Study Results Test Breakthrough Recovery MC, Rh11 hr<1 % (120 d) MC, Cl9 hr * 11 % (30 d) SC, Cl 16 hr<0.3% (8 d) * more frequent sampling than test 1 Fast Breakthrough indicates some corridor flow, Poor Recovery indicates mixing / diffusion

13. 13 Tracers In Wells Tracer concentrations throughout mine approached seep value –nearly identical after 100 days Injection point concentration stayed higher –“pool” of tracer? Mixing/diffusion -- important mine process

14. 14 Treatment description ~ 420 tons of ash injected... through five 2” injection wells... using Oil-field technology

15. 15 A flour truck (to right), used to bring FBA to the site. Pneumatic trailers are partially visible at the left.

16. 16 Grout truck and pneumatic trailers. The grout truck mixes FBA from the pneumatic trailers with water from a frac tank, then injects the slurry into the mine.

17. 17 A close-up of the grout truck, used to mix and inject the FBA slurry into the mine.

18. 18 Total view of the site during injection. From Right to left: flour trucks, pneumatic trailers, grout truck, frac tank.

19. 19 Three frac tanks located at the seep. Seep is pipe in front of rightmost tank.

20. 20 Fire hose used to convey FBA slurry from the fixed location of the grout truck to the five well locations.

21. 21 Injection well. FBA was injected through the fire hose.

22. 22 Monitoring well, with pressure gauge. Little pressure increase was measured during injection

23. 23 Results and Interpretation Alkalinity and pH after Injection Metal concentration in seep Interpretation of results –Phase I :Reaction of AMD with Ash –Phase II: Reaction & Mass Transfer of CO 2 with alkalinity –Phase III: Alkalinity consumption and flush

24. 24 Seep pH and Alkalinity after Injection

25. 25 Iron, Manganese, and Aluminum Concentrations in Seep

26. 26 Phase I - Quick Lime CaO + H 2 O --> Ca 2+ + 2OH - –Exothermic –Fast (over within hours of injection) –Immediate generation of alkalinity –High pH –Most metals precipitate as hydroxide From the CCP

27. 27 Phase I

28. 28 Phase IIa - CO 2 (aq) Reactions CO 2 (aq) + 2OH - --> CO 3 -- –may cause precipitation of CaCO 3 –Some metals may precipitate as CO 3 s CO 2 (aq) + CO 3 -- + H 2 O --> 2HCO 3 -

29. 29 CaCO 3 Precipitation

30. 30 Phase IIb - CO 2 (g) Mass Transfer What happens once the initial CO 2 (aq) is consumed –Mass Transfer from the mine headspace CO 2 (g) CO 2 (aq)

31. 31 Phase II ?

32. 32 Phase III Consumption of aqueous alkalinity in reaction with acid Flush of aqueous alkalinity Dissolution of solid alkaline compounds –CaCO 3, MeOH, MeCO 3

33. 33 Phase III ?

34. 34 Conclusions The injection of CCP increased pH and alkalinity The pH in the mine is influenced by CO 2(g) in the mine headspace The longevity of treatment depends on acidity generation and seep flow