Solubility of metal chelates and their extraction from an aqueous environment via supercritical CO2

Solubility of nickel(II), copper(II), and chromium(III) hexafluoroacetylacetone and chromium(III) acetylacetone chelates was measured in supercritical CO2 at two different pressures (200 and 400 atm) and 60 degrees C. Solubility of fluorinated acetylacetone chelates was at least an order of magnitude higher than the non-fluorinated complexes. These pre-formed metal chelates as well metal diethyldithiocarbamate (DDC) and metal bis(trifluoroethyl)dithiocarbamate (FDDC) have also been extracted from aqueous environment using pure supercritical CO2. It was demonstrated that metal HFA chelates while exhibiting higher solubility in supercritical CO2 compared with metal FDDC chelates, exhibited lower extraction efficiency using the same extraction conditions. This behavior of metal HFA chelates is related to their stability in an aqueous environment. Direct extraction of Ni+2 and Cu+2 from an aqueous matrix was also achieved via in-situ chelation using diethyldithiocarbamate and bis(trifluoroethyl)dithiocarbamate as the ligands. Bis(trifluoroethyl)dithiocarbamate proved to be a more effective ligand for direct extraction of metal ions from aqueous environment using supercritical CO2. (C) 1997 Elsevier Science B.V.