Removal of heavy metals from a Chinese traditional medicine by supercritical CO₂ chelating extraction

This paper investigates the effects of pressure, temperature and a modifier (ethanol) on CO₂ supercritical-chelating extraction of heavy metal ions from a Chinese traditional medicine. The results indicate that the optimal temperature for extraction efficiency differ for the same conditions and increase in the order of Pb, As, and Cu, while the extraction efficiency for Hg decreases as the temperature increases. Increasing the extraction pressure or the modifier concentration in the supercritical CO₂, the extraction efficiencies for As, Pb, and Hg do not increase noticeably, while the extraction efficiency for Cu increased markedly. The extraction efficiencies for As, Hg, Cu increase with the extraction time but not for Pb.