Fractionation of heavy metals in liquefied chromated copper arsenate (CCA)-treated wood sludge using a modified BCR-sequential extraction procedure

For many years, chromated copper arsenate (CCA) was the most commonly used waterborne wood preservative in the world. Despite the decision of the US and Canadian wood preservation industry to voluntarily withdraw the use of CCA-treated wood from residential and consumer uses as of December 31, 2003 (USEPA, 2003), the use of CCA-treated wood for industrial purposes (e.g., utility poles and marine pilings) continues (Song et al., 2006; Block et al., 2007). In addition, with an expected average service life between 20–40 years, the amount of spent CCA-treated wood in the US and Canada will greatly expand from the current 3–4 to around 12 Mm3 y1 within the next 15 years (Kazi and Cooper, 2006). Many efforts have been made to develop appropriate alternative technologies for disposal of spent CCA-treated wood other than traditional landfills and incineration, which have raised environmental and human health concerns. A method to remove Cr, Cu, and As from spent CCA-treated wood based on wood liquefaction has been developed by Lin and Hse (2005). They reported that CCA-treated wood can be liquefied under similar liquefaction conditions as non-treated wood and up to 99% of the heavy metals can be removed from CCA-treated wood by adding ferrous salts during the liquefaction stage. In addition, CCA-wood complexes are either released from the decomposed lignin and cellulose or still remain as the complexes or chelates with decomposed lignin and cellulose during the liquefaction reaction, which should provide better accessibility for the extractants in the heavy metal removal step.