Recovery of Metals from Aqueous Media by Extraction with Supercritical Carbon Dioxide

TLDR: In this article, the nonpolar character of a series of tetraalkylammonium dialkyldithiocarbamate ion pairs was influenced by the chain length of the alkyl substituent on the carbamate nitrogen and to a lesser extent, by the ammonium counterion.

Abstract: Measurements of solubilities in supercritical CO 2 corroborated the hypothesis that the nonpolar character of a series of tetraalkylammonium dialkyldithiocarbamate ion pairs was influenced (i) primarly by the chain length of the alkyl substituent on the carbamate nitrogen and (ii) to a lesser extent, by the chain length of the alkyl substituent(s) on the ammonium counterion. Similarly, the solubility of Zn-dithiocarbamate complexes decreased in the order dibutyl (DBDTC)>diethyl >pyrrolidine. An extraction protocol in which SC-CO 2 was saturated with tetrabutylammonium DBDTC prior to dynamic complexation/mobilization of 12-20 μg/mL Zn, Cd, or Pb analyte from aqueous solution resulted in >73% and >94% analyte removal within 5 and 15 min extraction, respectively