SELENIUM MOBILITY IN COAL AND OVERBURDEN IN CENTRAL APPALACHIA

1. SELENIUM MOBILITY IN COAL AND OVERBURDEN IN CENTRAL APPALACHIA R.R. Maggard

2. INTRODUCTION ___________________________________ • Passage of SMRCA prioritizes issues such as AMD (Acid Mine Drainage) • Methods to predict, prevent, and remediate typical AMD have since been developed However… • Methods to deal with issues concerning selenium have taken a different path www.streamrestorationinc.org

3. INTRODUCTION (cont’d) ________________________________________ • EXAMPLE: • The analysis of iron for the entire geologic column never led to the conclusion that the “special handling” of all iron-bearing strata would prevent the formation of AMD. • Further study determined that pyritic iron was most problematic — not all iron present in the strata • This is the approach needed for selenium http://www.agen.ufl.edu/~chyn/age4660/lect/lect_18/coalstruc.gif

4. OBJECTIVES ________________________________________ • Determine the actual mobility of selenium in the strata • Which stratagraphic units are more problematic? • Concentrate analytical work on using typical acid base analysis in conjunction with selenium analysis • Incorporate several leaching techniques of potentially problematic strata in regard to Se mobility

5. METHODOLOGY FOR SELENIUM ANALYSIS _____________________________________________ • Solid composite samples were collected using methods approved for coals and soils • Prepared for analysis using SW-846 Method 3050B • Acid digestion • Resulting extract then analyzed for Se using method SD 7740 • Graphite Furnace Atomic Absorption Spectroscopy • Minimum detection level: 0.5 mg/kg • Hydride AF method www.seleniumspeciation.com

6. METHODOLOGY FOR SELENIUM LEACHABILITY ________________________________________ Trends noted during previous studies: • Se solubility and occurrences in mine discharges appear to be related to neutral—higher pH’s with water of moderate to high alkalinity • Se has been known to be associated with sulfur in overburden and coal samples • Se occasionally detected in shale samplesthat exceed the 1 mg/kg established by WVDEP for special handling that contain undetectable/very low levels of pyritic sulfur

7. METHODOLOGY FOR SELENIUM LEACHABILITY (cont’d) _______________________________ • As a result of these trends: • Several methods were developed to determine circumstances that may facilitate maximum Se leachability under somewhat natural conditions • Methods were designed to be a reproducible and simpleexpedited procedure

8. PROCEDURES ______________________________ • Samples from a single core hole were selected: • Selections were based on varying combinations of conditions found to exist in different rock types • Five (5) varying samples were selected • Sample Nos. 5, 8, 14, 12C, 16C http://nc.water.usgs.gov/ccp/2005Cove/photos/core910.jpg

9. PROCEDURES _________________________________________________________ • Sample #5 was selected with barely detectable pyritic sulfur of 0.01 percent with a net neutralization potential of 4.24 and a paste pH of 7.6 and a selenium value of 2.19 mg/kg by the Hydride AF Procedure. • Sample #8 was selected with below detectable value of pyritic sulfur <0.01 percent with a net neutralization potential of 13.73 and a paste pH of 7.7 and a selenium value of 1.02 mg/kg by the Hydride AF Procedure right at the threshold of the WVDEP special handling criteria of 1 mg/kg. • Sample #14 was selected with a 0.07 value for pyritic sulfur with a net neutralization potential of 1.86 and a paste pH of 7.6 and a selenium value of 0.75 mg/kg which is below the WVDEP threshold and was analyzed by the Hydride AF Procedure,

10. PROCEDURES (cont’d) ________________________________________________ • Sample #12C was selected with a below detectable value of pyritic sulfur <0.01 percent with a net neutralization potential of 0.91 and a paste pH of 6.2 and a selenium value of 4.92 mg/kg. This sample was analyzed by the GFAA Procedure. • Sample #16C was selected with an easily detectable value of pyritic sulfur of 0.82 percent with a deficiency of neutralization of 36.74 and a paste pH of 3.4 and a selenium value of 9.46 mg/kg. This sample was analyzed by the GFAA Procedure.

11. LEACHING METHOD NO. 1 _______________________________________ • Exposed for one hour to leaching solution while shaken • Sample size: 2 grams with 50 ml of leaching solution • Leaching solution ranged from pH of 2.0 (H2SO4) to 10.0 (CaO) • pH measured after one hour • Analyzed for: Total Se, Al, Fe, Mn, Ca, and Mg periodictable.com/Samples/025.7/s9s.JPG

12. Sample No. 5

13. % FeS2: 0.01 NP: 4.24 pH: 7.6 Se (mg/kg): 2.19

14. Sample No. 8

15. % FeS2: <0.01 NP: 13.73 pH: 7.7 Se (mg/kg): 1.02

16. Sample No. 14

17. % FeS2: 0.07 NP: 1.86 pH: 7.6 Se (mg/kg): 0.75

18. Sample No. 12C

19. % FeS2: <0.01* NP: 0.91 pH: 6.2 Se (mg/kg): 4.92

20. Sample No. 16C

21. % FeS2: 0.82* NP: -36.74 pH: 3.4 Se (mg/kg): 9.46

22. Blank

23. LEACHING METHOD NO. 1 (cont’d) _________________________________________________ • Review of previous tables: • All samples extracted measurable Se from 4 ug/l to 82 ug/l • Sample No. 5 had same levels as Sample No. 16C (4x the Se in the solid sample) • Maximum solubility of shales occurred at a pH of 9 • Maximum solubility of coals occurred at a pH of 2 • Soluble iron appeared to be related to selenium solubility in shales

24. LEACHING METHOD NO. 2 ___________________________________________ • Method was developed to determine relationship between sample size and volume of extract • Sample No. 14 chosen because it had the lowest measurable Se in original sample (0.75 mg/kg) • Sample size ranged from 0.5 g to 50 ml of extract at pH 9 to 2 g to 50 ml • To prevent contamination of extract by solids each run was duplicated with a 0.45 um filter and 0.20 um filter http://www.chemistryexplained.com/elements/images/chel_0001_0003_0_img0389.jpg

25. LEACHING METHOD NO. 2 (cont’d) ___________________________________ • Values of resultant extract: • Ranged from ~ 2 ug/l to 8 ug/l • Last runs of 2.0 g to 50 ml repeat values from previous leaching, yielding 7 and 8 ug/l in the extraction • Sample size and extract values appear to be approximately linear

27. PREVENTION AND TREATMENT _______________________________________ • Does the iron in AMD sludge prevent or reduce the mobility of selenium? • Dried AMD sludge was added to various overburden and coal samples • Idea proposed by Dr. P. Ziemkiewicz • Same leaching procedure was used as previously described with a 10 % addition of dried AMD sludge (by weight) • Soluble Se levels reduced17 to 33 %

29. CONCLUSIONS _______________________________________ • Solubility and mobility of Se as a result of various coal mining methods can be highly variable • Dependent on geochemical characteristics of parent rock source • Pyritic sulfur content may inhibit the solubility/mobility of Se in the water column • Lovett and Ziemkiewicz previously noted this possibility • Additional leaching studies are being conducted • GOAL: to better understand the circumstances of Se solubility and mobility and its prevention in Southern Appalachia coalfields