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Selenium Removal from Mine Waters Raymond J. Lovett, Ph.D. Environmental Chemist ShipShaper, LLP

This article discusses the difficulties in removing selenium from mine waters and presents cost-effective treatment options such as adsorption by iron hydroxides, bacterial reduction, reverse osmosis, and reduction by iron metal. It also evaluates the estimated costs of each method and concludes that iron metal removal is a promising but time-consuming option.

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Selenium Removal from Mine Waters Raymond J. Lovett, Ph.D. Environmental Chemist ShipShaper, LLP

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  1. Selenium Removal from Mine Waters Raymond J. Lovett, Ph.D. Environmental Chemist ShipShaper, LLP Morgantown, WV

  2. National Mine Land Reclamation Center, West Virginia University United States Office of Surface Mining Magnum Coal Company Catenary Coal SUPPORT

  3. [Se] = 13 ug/L [Fe] = 0.15 mg/L [SO4-2]= 980 mg/L Alkalinity = 235 mg/L as CaCO3 pH = 7.1 Typical Southern West Virginia Mine Water

  4. Problems • Overriding Concern • Regulatory limit near 5 ug/L • Specific Problems for Treatment • Low level of Se • Differing chemistries • Selenate, SeO4-2, Se(VI) • Selenite, SeO3-2, Se(IV)

  5. Selenium Removal Difficulties • Different dissolved species • No direct precipitation chemistries • Reduction of selenate is difficult (slow) • Sulfate may interfere

  6. Treatment System Objectives • Effluent maximally 5 ug/L Se • Low installation cost • Low operating cost • Passive

  7. Demonstrated Chemistries • Adsorption or co-precipitation by Fe(III) hydroxides • Biological (bacterial reduction) • Reverse osmosis • Reduction by Fe(0)

  8. Reduction with Iron Metal • SeO4-2 +Fe(0) => Fe(II,III) +Se(0) • SeO3-2 +Fe(0) => Fe(II,III) +Se(0)

  9. Selenium Species on Iron

  10. Field TrialCatenary Coal Test in a real setting Real, variable input chemistry Continuous Se Input

  11. Field Trial System

  12. Field Trial System

  13. Catenary Post Trial 1

  14. Catenary Post Trial 2

  15. Catenary Post Trial 3

  16. Catenary Post Trial 4

  17. Catenary Post Trial 5

  18. Reduction with Iron Metal • Potential • Removal of selenate and selenite • Passive • Problems • Iron Oxides/ Dissolved Fe, Mn • Exhaustion • Passivation • Expense (surface area)

  19. BacterialEstimated Cost • Flow = 285 gpm • Capital Cost = $7.2 to $10 million • O&M = Unknown

  20. Reverse OsmosisEstimated Cost • Flow = 200 gpm • Capital Costs = $1.2 million • O&M = $5.85 million/year

  21. Iron HydroxideEstimated Cost • Flow = 200 gpm • Capital Cost = $0.69 to 1.03 million • O&M = $1.39 million/year

  22. Zerovalent IronEstimated Cost • Flow = 250 gpm* • Capital costs = $478,000 • O&M = $150,000 to $300,000 * Gravity flow, includes surge

  23. Conclusions • Iron metal removes selenate and selenite, but currently requires long contact times • Manganese and iron generated • Temperature sensitive (?) • Less expensive than other methods

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