Mercury L3 and sulfur K-edge studies of Hg-bound thiacrowns and back-extracting agents used in mercury remediation

Abstract

Effective methods for the removal of mercury from water are in demand due to the high levels of mercury released from industrial and natural processes. Polymer pendant thiacrown compounds used for the sequestration of Hg(II) from aqueous solutions passed through columns have shown great promise as effective tools for remediation. The mercury can potentially be removed from the columns by extraction with diethyldithiocarbamate (dtc) and diphenylthiocarbazone, aka dithizone (dtz). In this study, Hg L3 and sulfur K-edge X-ray absorption spectroscopy are used to contrast the structure of the mercury thiacrown complex Hg[17]aneS5 with the structure of mercury bound to two potential back-extracting agents, Hg(dtc) 2 and Hg(dtz) 2. In Hg(dtc) 2, it was found that Hg(II) was bound to four sulfur atoms, with two Hg–S bond lengths of 2.66 Å and two Hg–S at 2.49 Å. In Hg(dtz) 2, Hg(II) was bound to two sulfur atoms with Hg–S bond distances of 2.38 Å and two nitrogen atoms with Hg–N at 2.54 Å. This contrasts with Hg[17]aneS5 with three Hg–S bonds at 2.40 Å. Mercury L3 and S K-edge results show that electron density shifts from sulfur in dtc and dtz, to mercury in Hg(dtc) 2 and Hg(dtz) 2. The increase in the number of bonds, and the more stable geometry and electron distribution in the back-extraction complexes confirms that these compounds are more stable than the mercury thiacrown complex, and thus suitable for regeneration of the pendant-arm [17]aneS 5 for further remediation processes.