Study of Extraction of Metals from CCA-Treated Wood with Supercritical CO2Containing Acetylacetone: Extraction of Cu by Continuous Addition of Acetylacetone

Abstract

Although waste CCA-treated wood containing toxic heavy metals (Cu, Cr, and As) can contaminate soil and be hazardous to human health, there is currently no reliable detoxification technique. To solve this problem requires a method for extracting the toxic metals from such wood. We have previously shown that supercritical CO2 with initially added acetylacetone (AA) as a chelating agent achieved a Cu extraction ratio of up to 71.0%. The purpose of this study was to explore conditions for improving the extraction efficiency of Cu: that is, to extract Cu by using supercritical CO2 with continuously added AA and to investigate the effect of the flow rate and AA/CO2 mixing ratio on the extraction behavior. The highest ratio we obtained for Cu was 89.4% at 14.7 MPa and 423.2 K with a flow rate of 0.40 mol/min and a mixing ratio of 4.8 mL of AA/mol of CO2. We found that the extraction process consisted of static and dynamic extraction stages and that a high flow rate produced a high extraction rate. After the extraction had proceeded for a while, the extraction rate decreased because of the decrease in the residual metal in the wood.