1 / 34

Abandoned Coal Mines: In-Situ Treatment of AMD with CCPs

Abandoned Coal Mines: In-Situ Treatment of AMD with CCPs. Jess W. Everett, Ph.D., P.E. Associate Professor Civil Engineering Rowan University. Abandoned Coal Mines: In-Situ Treatment of AMD with CCPs. Acid Mine Drainage Mines fill with water, seeps are formed

jacqueline-simon
Download Presentation

Abandoned Coal Mines: In-Situ Treatment of AMD with CCPs

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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. Abandoned Coal Mines: In-Situ Treatment ofAMDwith CCPs • Acid Mine Drainage • Mines fill with water, seeps are formed • Bacteria oxidize Pyrite (FeS2), 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. 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. Abandoned Coal Mines: In-Situ Treatment of AMD withCCPs • 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 SO2 emissions, excess remains in ash

  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. Overview • Mine description • Injection description • Results • Interpretation • Conclusions

  7. Mine Plan View Not to scale

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

  9. Seep Flow and Rainfall

  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. Tracer Injection Points

  12. Tracer Study Results Test Breakthrough Recovery MC, Rh 11 hr <1 % (120 d) MC, Cl 9 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. 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. Treatment description • ~ 420 tons of ash injected... • through five 2” injection wells... • using Oil-field technology

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

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

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

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

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

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

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

  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 CO2 with alkalinity • Phase III: Alkalinity consumption and flush

  24. Seep pH and Alkalinity after Injection

  25. Iron, Manganese, and Aluminum Concentrations in Seep

  26. From the CCP Phase I - Quick Lime • CaO + H2O --> Ca2+ + 2OH- • Exothermic • Fast (over within hours of injection) • Immediate generation of alkalinity • High pH • Most metals precipitate as hydroxide

  27. Phase I

  28. Phase IIa - CO2(aq) Reactions • CO2(aq) + 2OH- --> CO3 -- • may cause precipitation of CaCO3 • Some metals may precipitate as CO3s • CO2(aq) + CO3-- + H2O --> 2HCO3-

  29. CaCO3 Precipitation

  30. Phase IIb - CO2(g) Mass Transfer • What happens once the initial CO2(aq) is consumed • Mass Transfer from the mine headspace • CO2(g) <--> CO2(aq)

  31. ? Phase II

  32. Phase III • Consumption of aqueous alkalinity in reaction with acid • Flush of aqueous alkalinity • Dissolution of solid alkaline compounds • CaCO3, MeOH, MeCO3

  33. ? Phase III

  34. Conclusions • The injection of CCP increased pH and alkalinity • The pH in the mine is influenced by CO2(g) in the mine headspace • The longevity of treatment depends on acidity generation and seep flow

More Related