Speciation of Chromium

Research Project: Assessing the Impact of Chromium in the Environment Funding provided by Florida Department of Environmental Protection

Chromium Exists as Several Chemical Species Most common oxidation states: 0, +3, +6 0: Elemental Chromium (Cr) +3: Trivalent Chromium Species: Cr +3, Cr 2 O 3 +6: Hexavalent Chromium Species: CrO 4 2-, Cr 2 O 7 -

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)

Difference between Cr(VI) and Cr(III) Factored into Regulations RCRA Regulations 40 CFR 261.4(b)(6)(i) A solid waste that is a characteristic or listed hazardous waste solely because of chromium is not hazardous if…..

(A) The chromium in the waste is exclusively (or nearly exclusively) trivalent chromium; and (B) The waste is generated from an industrial process which uses trivalent chromium exclusively (or nearly exclusively) and the process does not generate hexavalent chromium; and (C) The waste is typically and frequently man-aged in non-oxidizing environments.

Ingestion: –Cr(III): 78,000 mg/kg –Cr(VI): 390 mg/kg

Cr(III) versus Cr(VI) Hexavalent chromium exists in alkaline, strongly oxidizing environments Trivalent chromium exists in moderately oxidizing and reduced environments

pH Eh (V) Cr 2 O 3 CrO 4 2- Cr 2 O 7 - Cr 3+

pH Eh (V) Cr 2 O 3 CrO 4 2- Cr 2 O 7 - Cr 3+

Chromium in Wood Preservation The chromium in CCA preservative solution is hexavalent chromium. Upon fixation in the wood, Cr(VI) becomes converted to Cr(III)

When Might Cr(VI) Be Encountered? If wood is improperly fixed (as a result, for example, of inadequate fixation time at low temperatures) When in contact with oxidizing chemicals such as deck brighteners

Oxidation of Chromium in the Environment In the natural environment, chromium tends to exist as Cr(III) Oxidation of Cr(III) to Cr(VI) as a result of manganese (hydr)oxides

Methods of Cr(VI) Analysis Typical chromium measurements are total chromium (Cr(III) + Cr(VI) + other) Methods have been developed for Cr(VI) analysis Sample holding time is minimal

Methods of Cr(VI) Analysis Solvent extraction followed by total chromium analysis Colorimetric and Ion Chromatography Methods being Used

Tasks 1. Literature Review 2. Assessment of pH and ORP as indicators or Cr speciation 3. Evaluate kinetics of conversion of Cr(VI) to Cr(III) in natural soils 4. Develop guidance document

Kinetic Study Three different soil types have been selected They have beeb spiked with CCA solution to add a known amount of Cr(VI) The Cr(VI)/Cr(total) will be measured over time Leachable Cr(VI) and Cr(III) will be measured over time

Soil Types

Experimental Set Up 50 g of soil 10 ml of 2700 mg/L Hex. Cr

Alkaline Digestion SW-846 Method 3060A

The Method of Analysis SW-846 Method 7199 (Determination of Hexavalent Chromium in Drinking Water, Groundwater and Industrial Wastewater Effluents by Ion Chromatography)

Analytical System Detector Integrator Analytical Column Guard Column LC Pump

Calibration 0.05 ppm CrVI Area: ppm CrVI Area: ppm CrVI Area: ppm CrVI Area:

Calibration Curve

Reduction in CrVI with Time

Reduction in Leachable CrVI with Time

Future Schedule Begin Kinetic Study – Conduct for 6 months Measure Cr(VI) in various environmental matrices as function of ORP and pH –C&D Debris Leachate –SPLP Leachate –Contaminated Soil –Wood Ash Prepare Guidance Document