Extraction of Heavy Metals from Wood with Supercritical CO₂

Abstract

We have been developing a process that uses supercritical CO₂ to detoxify environmentally hazardous waste, namely chromated copper arsenic- (CCA-) treated wood. We measured the solubility of CuHAsO₄, which is believed to exist in wood, and found it to be of the order of 10^-9 to 10^-8. We were able to correlate the experimental data by using a solution model. We then undertook experiments designed to extract metals from CCA-treated wood by using supercritical CO₂ and a chelating agent. The addition of acetylacetone as a chelating agent markedly enhanced the extraction yield. We found that the continuous addition of acetylacetone raised the extraction ratio to about 90%.