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Selective Sequential Extraction for Mercury Speciation in Soil Samples

Selective Sequential Extraction for Mercury Speciation in Soil Samples. Presented by Michelle Briscoe President/Technical Director michelle@brooksrand.com. Presented September 29, 2013 DOE ASP Annual Workshop, Asheville, NC. Mercury Speciation vs. Fractionation.

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Selective Sequential Extraction for Mercury Speciation in Soil Samples

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  1. Selective Sequential Extraction for Mercury Speciation in Soil Samples Presented by Michelle Briscoe President/Technical Director michelle@brooksrand.com Presented September 29, 2013 DOE ASP Annual Workshop, Asheville, NC

  2. Mercury Speciation vs. Fractionation Speciation Hg(II), MeHg, Hg(0), etc. Fractionation  Volatile Hg Water-soluble Hg Strongly-complexed Hg A “fraction” (F) isa group of compounds having similar characteristics, such as bioavailability or environmental mobility, rather than a specific compound

  3. Selective Sequential Extractions Successive extractions of an aliquot of sample with increasingly strong reagents

  4. 5-Step SSE Sample Preparation

  5. 5-Step SSE Procedure

  6. Sequential chemical extraction profiles for individual mercury compounds Bloom, N. S.; Preus, E.; Katon, J.; Hiltner, M. Anal. Chim. Acta2003, 479, 233-248.

  7. Reference Materials • 3 RMs produced by Studio Geochimica (2005): pure Hg compounds dispersed in kaolin clay • Hg(0) : elemental Hg • HgCl2 : mercuric chloride • HgS : mercury sulfide (cinnabar) • NIST 2710 : Montana Soil • Highly contaminated soil from mining area

  8. Reference Materials Fractionation

  9. Why is Fractionation Important? Fractionation can provide important information about key soil characteristics to classify the potential risk associated with the mercury in the sample: • Bioavailable • Semi-mobile/Strongly-complexed • Non-mobile/Mineral-bound

  10. Bioavailable Mercury

  11. Semi-Mobile/Strongly-Complexed

  12. Non-Mobile/Mineral-Bound

  13. Drawbacks to SSE • Semi-quantitative, at best • Re-absorption onto particles (particularly in F1 & F2) can cause bias, esp. at low Hg concentrations • RMs may not be stable long-term, dispersing to different fractions • Method improvements may lead to problems with comparability of old data to new data • Labor-intensive (6 days to prep, plus 1-2 days to analyze); therefore, expensive!

  14. 5-Step SSE Case Studies at DOE Sites

  15. Case Studies for Soil Treatment • Soils were collected from the Oak Ridge Reservation (Y-12); < 200 mg/kg total Hg • Spiked with 2,000 or 10,000 mg/kg Hg(0) • Various treatment technologies were employed by various contractors in an attempt to stabilize the mercury prior to disposal of the soils

  16. Case Study #1(All values in mg/kg, ppm) BL = baseline (untreated) T1 = treatment #1 T2 = treatment #2 All samples were spiked with 10,000 mg/kg of elemental mercury, Hg(0)

  17. Case Study #1(All values in mg/kg, ppm) BL = baseline (untreated) T1 = treatment #1 T2 = treatment #2 All samples were spiked with 10,000 mg/kg of elemental mercury, Hg(0)

  18. Case Study #1 All samples were spiked with 10,000 mg/kg of elemental mercury, Hg(0)

  19. Case Study #2(All values in mg/kg, ppm) T1A = treatment of samples spiked with 10,000 mg/kg Hg(0) T1B = same treatment as T1, but pre-processed with a ball mill T2 = treatment of samples spiked with 2,000 mg/kg Hg(0) T3 = treatment of samples spiked with 10,000 mg/kg Hg(0)

  20. Case Study #2(All values in mg/kg, ppm) T1A = treatment of samples spiked with 10,000 mg/kg Hg(0) T1B = same treatment as T1, but pre-processed with a ball mill T2 = treatment of samples spiked with 2,000 mg/kg Hg(0) T3 = treatment of samples spiked with 10,000 mg/kg Hg(0)

  21. Case Study #2 All samples were spiked with 10,000 mg/kg of Hg(0), except Treatment #2 (2,000 mg/kg)

  22. Optional Add-Ons F(0) Step • Volatile gaseous Hg screen - Hg(0) • Reagent water extraction • Headspace measurement • Non-sequential F(6) Step • Digestion of pellet from F5 with HNO3, HCl, and HF (bomb) • Value is matrix dependent • No RM data

  23. EPA Method 3200 • Not entirely sequential • Provides less information • Some inorganic Hg complexes may be present in both the inorganic and extractable organic phases

  24. In Conclusion • The use of a multi-step selective sequential extraction procedure is a good tool for qualitatively assessing the availability and mobility of mercury present in a soil sample • Data users must be educated as to what information the data is providing, and what the limitations of the data are

  25. Questions? Thank you for your attention!

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