The evaluation of the dithizone performance as a complexing reagent for supercritical CO2 extraction of heavy metals from aqueous solutions

Abstract

Heavy metal ions in liquid samples, apart from classical methods of extraction, can also be efficiently and environmentally friendly extracted by the use of supercritical CO2, containing a suitable complexing agent - ligand. This study represents the experimental data for the extraction of three heavy metals (Cu, Zn and Cd) from aqueous samples in the presence of dithizone as a ligand. The extractions by supercritical CO2 were accomplished at p=120 bars with t=50°C through the use of the dynamic technique. After the CO2 addition to the aqueous solution containing corresponding heavy metal ions, the pressure and temperature were set and extraction was performed in three different time periods: 30, 60 and 120 min (t=const., p=const. with a CO2 flow rate of 2 mL min-1). Once the extraction was stopped, the CO2 was released slowly through a restrictor. Methanol was used as a modifier (v/v) 10% and the pH value was set to 10. After the accomplishment of the extraction process, the leftover aqueous solution in the extractor was analyzed for its metal content by the use of the Atomic Absorption Spectrophotometer (AAS). The overall performance of the use of the dithizone as a ligand in all three cases of heavy metal ions enhanced greatly the extraction efficiency of these ligand/metal species.