Polymer Pendant Crown Thioethers for Removal of Mercury from Acidic Waste Streams-Characterization and Extraction Performance

摘要

The removal and immobilization of mercury(II) ions from industrial waste streams is a difficult and expensive problem requiring a robust extractant that is resistant to corrosive conditions. We have now developed an acid-resistant thiacrown polymer that has potential utility as a selective and cost-effective Hg~(2+) extractant. A new crown thioether, 2-hydroxymethyl-1,4,8,11,14-pentathiacycloheptadecane ([17]aneS_5-OH), was synthesized through reaction of 2,3-dimercapto-1-propanol with 4,7,10-trithiatridecane-l,13-di-p-toluenesulfonate; then treated with thionyl chloride to form 2-chloromethyl-1,4,8,11,14-pentathiacycloheptadecane ([17]aneS_5-Cl); followed by conversion to 2-(N-methyl)aminomethyl-1,4,8,11,14-pentathiacycloheptadecane ([17]aneS_5-NHMe), through reaction with methylamine. The synthesis of the 4-vinylbenzyl-substituted thiacrown was readily accomplished by treating with 4-vinylbenzyl chloride. Co-polymerization of the 4-vinylbenzyl-substituted thiacrown with DVB (80% divinylbenzene) using AIBN as the radical initiator generated the highly cross-linked crown thioether polymer. The polymer based material was tested for Hg(II) extraction activity from acidic solutions. The material was found to extract 95+% of the Hg in a pH range of around 1.5 to over 6.0, with contact times of less than 30 min and in the presence of high concentration of competing ions such as Pb, Cd, Al, and Fe. The spent polymer could also be stripped of the Hg~(2+) and reused without sufficient loss of loading capacity. Characterization of the binding sites by XPS and XAS show only some of the S atoms in the thiacrown participate in the binding of Hg. Our results indicate this polymer has the potential to treat highly acidic wastes efficiently. This thiacrown polymer is far more effective in extracting Hg~(2+) from aqueous solution than previously reported Hg~(2+) extrac-tants, not only being very fast and efficient and selective, but also independent of pH.