Mercury is a toxic and bioaccumulative chemical of global concern which poses serious health risks to the environment and biota. During the Cold War, the Savannah River Site (SRS) generated HLW due to reprocessing of used nuclear fuel (UNF) for weapons production. Hg(II) was used as a process catalyst for the dissolution of aluminum cladding of UNF, and then NaOH was added to prevent corrosion, which resulted in the precipitation of insoluble metals salts in HLW tanks. As 60,000 kg of Hg is estimated to be present in HLW tanks, integrated processing of HLW in the Defense Waste Processing Facility (DWPF) has resulted in a marked increase of Hg, including highly toxic organomercury species in low-activity waste streams that are directed to saltstone. Therefore complexation and extraction of Hg(II) from alkaline HLW is a promising method of remediation which may reduce the risk to workers and the environment, in the Savannah River and other HLW processing sites.
Herein we report two highly-efficient lipophilic disulfonamide (DSA) chelators for Hg(II) extraction from an SRS HLW custom simulant (SRS Tank 45) into n-dodecane:1-octanol (80:20 v/v). Specifically, we saw 83.5% (±4.7%) and 80.2% (±4.2%) Hg(II) recovery for DSA7 and DSA8, respectively, in a single load/stripping cycle. Titrations of DSA7 and DSA8 with HgCl₂ in CH₃CN followed by non-linear regression analysis yielded binding constants and mainly 1:2 Hg(II):DSA stoichiometry. Efforts of further characterization of Hg(II) complexation and extraction by Job plots, slope analysis, and other methods will be presented.

Anmanuel Perez

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