Supercritical fluid extraction of toxic metals from woods containing preservatives

Although woods containing preservatives have been widely used for many years, some of these preservatives contain heavy metal compounds, so when the woods are incinerated, heavy metals remain in the ashes, creating a disposal problem. Supercritical fluid extraction is a promising technology for turning these hazardous wastes into harmless substances that can be safely recovered. Carbon dioxide is a suitable solvent for such extraction due to its moderate critical constants (Tc=304.2 K and Pc=7.38 MPa), inertness, and ready availability in purified form. The authors tested the use of supercritical carbon dioxide and found that regardless of their amount, chromium, copper and arsenic ions could definitely be extracted. Using acetylacetone as a reagent significantly improved the extraction efficiency. Supercritical carbon dioxide is thus a strong candidate as a solvent for extracting metals from woods safely and economically.