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Review of Chromium Speciation Research

Review of Chromium Speciation Research. Research Project: Assessing the Impact of Chromium in the Environment. Assessing the Impact of Chromium in the Environment Funding provided by the Florida Department of Environmental Protection RCRA Program. Chromium Exists as Several Chemical Species.

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Review of Chromium Speciation Research

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  1. Review of Chromium Speciation Research

  2. Research Project:Assessing the Impact of Chromium in the Environment • Assessing the Impact of Chromium in the Environment • Funding provided by the Florida Department of Environmental Protection RCRA Program

  3. Chromium Exists as Several Chemical Species Most common oxidation states: 0, +3, +6 0: Elemental Chromium (Cr) +3: Trivalent Chromium Species: Cr+3, Cr2O3 +6: Hexavalent Chromium Species: CrO42-, Cr2O7-

  4. Chromium Speciation Important! • The characteristics and properties of trivalent chromium and hexavalent chromium are greatly different. • Cr(VI) is much more toxic and mobile than Cr(III)

  5. Chromium Eh-pH Diagram 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 Cr2O7 - CrO4 2- Cr 3+ Eh (volts) Cr2O3 0 2 4 6 8 10 12 14 pH

  6. Fate of Chromium in CCA-Treatment Process Treating Solution • CrAsO4 • Cu(OH)CrAsO4 • CuCrO4 • Cr(OH)3 • Cr6+/wood complexes • Cr3+/wood complexes • Cu2+/wood complexes Treated Wood • CrO3 • CuO • As2O5 Cr+6 Cr+3

  7. Research Objective • Examine the fate and behavior of hexavalent chromium in various environmental media impacted by CCA

  8. 0.0 mg Cr+6/l 0.3 mg Cr+6/l 0.6 mg Cr+6/l

  9. Alkaline Digestion SW-846 Method 3060A

  10. IC System Detector Analytical Column Integrator Guard Column LC Pump

  11. Experiment 1 • Examination of the fate of hexavalent chromium in soils spiked with CCA solution • Cr(VI)/Cr(total) concentrations were measured over time • Leachable Cr(VI) and Cr(III) concentrations measured over time (SPLP)

  12. Soil Types

  13. Reduction in Total Cr+6 with Time

  14. Experiment 2 How Much CrVI is in CCA-Treated Wood

  15. Results • Alkaline digestions on CCA-treated wood samples show Cr+6 concentrations in the range 7 to 250 mg/kg (less 3% of all Chromium) • SPLP leachates have no detectable Cr+6 concentrations

  16. Experiment 3 Under what leaching conditions would Cr+6 form?

  17. Chromium Leachability as a Function of Time(weathered wood sample)

  18. Chromium Leachability as a Function of Time(weathered wood sample) MSW LandfillLeachate AlkalineLeachate TCLP &SPLP

  19. Experiment 4 Will Cr+6 be formed in simulated alkaline leachate? Scenario: saturated concrete

  20. Chromium Leaching in Concrete Leachate

  21. Experiment 5 Is Cr+6 formed during combustion of CCA-treated wood?

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