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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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Research project assessing the impact of chromium in the environment l.jpg
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 l.jpg
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-


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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)


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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


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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


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Research Objective

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


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0.0 mg Cr+6/l

0.3 mg Cr+6/l

0.6 mg Cr+6/l


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Alkaline Digestion

SW-846 Method 3060A


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IC System

Detector

Analytical

Column

Integrator

Guard

Column

LC Pump


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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)




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Experiment 2

How Much CrVI is in CCA-Treated Wood


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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


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Experiment 3

Under what leaching conditions would Cr+6 form?



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

MSW LandfillLeachate

AlkalineLeachate

TCLP &SPLP


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Experiment 4

Will Cr+6 be formed in simulated alkaline leachate? Scenario: saturated concrete



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Experiment 5

Is Cr+6 formed during combustion of CCA-treated wood?


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