Analytical Sciences

Extraction of Chromium(III) and Chromium(VI) Species from Solid Matrices Using Green Solvent Supercritical Carbon Dioxide

Joanna Shaofen WANG* and Kong-Hwa CHIU**

*Department of Chemistry, University of Idaho, Moscow, ID 83844-2343, USA
**Department of Applied Science, National Hualien University of Education, Hualien, Taiwan 970, ROC

Supercritical fluid extraction (SFE) provides an environmentally green technique to decontaminate chromium species from solid matrices using supercritical fluid carbon dioxide (ScCO₂). Methanol and a small amount of water were found to significantly improve the extraction efficiency. The fluorinated chelating agent lithium bis(trifluoroethyl)-dithiocarbamate (LiFDDC) was effective in removing Cr ions in methanol-modified CO₂ via in situ chelation/SFE technique. This paper indicates that the extraction efficiencies of Cr(III) and Cr(VI) from solid matrices can be greatly increased to more than 92% in the presence of a small amount of water, using 5% methanol-modified CO₂ containing LiFDDC as an extractant. Chromium species in a wood waste sample in the form of chromated copper arsenate (CCA) can be extracted, but the extraction efficiency is not as good as expected, possibly due to the complications of the chemistry of Cr species in different oxidation states and to matrix effects.

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