Supercritical fluid extraction of mercury(II) ion via in situ chelation and pre-formed mercury complexes from different matrices

Extraction of both spiked mercury complexes and mercury ion from a variety of matrices such as sludge, fly ash, soil, filter paper, and sand was achieved using both pure and methanol-modified supercritical CO2. The neutral mercury complexes contained either diethyldithiocarbamate (DDC) or trifluoroethyldithiocarbamate (FDDC) as ligands. It was demonstrated that both Hg(DDC)(2) and Hg(FDDC)(2) could be extracted with high efficiency from inert matrices (i.e. sand and filter paper) using 5% methanol modified CO2. The extraction efficiency of Hg (DDC)(2) from fly ash and sludge, however, was poor under these conditions. On the other hand, Hg(FDDC)(2) could be extracted with greater than 95% efficiency from all matrices with 5% methanol-modified CO2. Recovery of Hg(II) from soil, fly ash, and sludge using NaDDC as an in situ chelating agent was less than 40% with pure CO2 (400 atm) at 80 degrees C, while recovery of Hg(II) from the same matrices using LiFDDC was greater than 90% with these conditions. Also, extraction efficiency of Hg(CH3)(2) and CH3HgCl from different matrices was determined. Extraction efficiency of greater than 90% was found for Hg(CH3)(2) regardless of the matrix, while recovery of CH3HgCl was matrix dependent. (C) 1999 Elsevier Science B.V. All rights reserved.