KINETICS OF CHELATING EXTRACTION OF HEAVY METALS BY SUPERCRITICAL CO_2
The kinetics of supercritical chelating extraction of heavy metal from a Chinese traditional medicine material was investigated.The extraction efficiencies of the heavy metals increased rapidly within the first 15min extraction at 40?℃ and 20.0?MPa by CO 2 modified with 5% ethanol solution containing 1% diethylammonium diethyldithiocarbamate as chelating reagent.Then, the extraction efficiencies increased slowly with time while that of Pb leveled off.The results indicated that the contents of trace heavy metals in the sample had major effects on the extraction rates when the chelating reagent was excessive.The chelating reaction is the rate-controlling step.The extraction of trace heavy metals from the Chinese traditional medicine material is controlled by a pseudo-first-order chelating reaction.