Research on the Speciation of Chromium as Relates to CCA

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

Master of Engineering Thesis Topic: Chromium Speciation in Environmental Media Impacted by the Wood Preservative Chromated Copper Arsenate Mr. Jin-Kun Song

Background

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 Cr 2 O 3 CrO 4 2- Cr 2 O 7 - Cr 3+ Eh (volts) Chromium Eh-pH Diagram

What is Fate of Chromium in CCA Treatment Process

The Treatment Process CCA Arsenic Acid (liquid) Chromic Acid (liquid) Copper Oxide (solid)

The Treatment Process CCA Untreated Wood Product Treatment Cylinder Drying and Fixation To Market

Fate of Chromium in CCA- Treatment Process –CrAsO 4 –Cu(OH)CrAsO 4 –CuCrO 4 –Cr(OH) 3 –Cr 6+ /wood complexes –Cr 3+ /wood complexes –Cu 2+ /wood complexes CrO 3 CuO As 2 O 5 Treating SolutionTreated Wood Cr +6 Cr +3

Fixation of CCA Cooper and Ung, 1992

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

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

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

0.0 mg Cr +6 /l0.3 mg Cr +6 /l0.6 mg Cr +6 /l

Alkaline Digestion SW-846 Method 3060A

IC System Detector Integrator Analytical Column Guard Column LC Pump

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)

Soil Types

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

Reduction in Total Cr+6 with Time

Reduction in Leachable Cr+6 with Time

Experiment 2 How Much CrVI is in CCA-Treated Wood

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

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

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

TCLP & SPLP MSW Landfill Leachate Alkaline Leachate

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

Chromium Leaching in Concrete Leachate

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

Remaining Tasks Data interpretation Final report