Selective extraction of mercury with ionizable crown ethers in supercritical carbon dioxide

The solubility of a tert-butyl-substituted dibenzobistriazolo-crown ether in methanol (5 mol %) modified CO[sub 2] has been determined to be in the order of 1 x 10[sup [minus]3] M at 60[degree]C and 200 atm. Using this proton-ionizable crown ether as an extractant in methanol (5%) modified CO[sub 2], quantitative extraction of Hg[sup 2[minus]] from sand and cellulose-based filter papers can be achieved at 60[degree]C and 200 atm if a small amount of water is present in the solid matrix. Other divalent metal ions including Cd[sup 2[minus]], Co[sup 2], Mn[sup 2+], Ni[sup 2+], Pb[sup 2[minus]], and Zn[sup 2+] are virtually not extractable under these conditions. Gold (Au[sup 3[minus]]) can be extracted by the macrocyclic ligand with a lower efficiency than Hg[sup 2[minus]]. Extraction of Hg[sup 2[minus]] from aqueous samples can also be achieved using methanol-modified CO[sub 2] containing the macrocyclic ligand. Formation of extractable metal chelates with the ligand at the pH defined by the CO[sub 2]-H[sub 2]O system appears to be an important factor determining the extraction efficiencies of the metal ions by this in situ chelation-supercritical fluid extraction technique. 15 refs., 2 figs., 3 tabs.