Recovery of cesium extracted from simulated tank waste with an ionic liquid: Water and oxygen effects

The effects of residual water and oxygen on the electrochemical processing step for the recovery of Cs+ extracted into the hydrophobic ionic liquids, tri-1-butylmethylammonium bis((trifluoromethyl)sulfonyl)imide (Bu3 MeN+ Tf2 N-) or N -methyl- N -propylpiperidinium bis((trifluoromethyl)sulfonyl)imide (MePrPip+ Tf2 N-) containing the lipophilic ionophore, calix[4]arene-bis (t -octylbenzo-crown-6) from simulated aqueous tank waste was investigated in the presence of residual water and oxygen. The electrochemical reduction of ionophore-bound Cs+ at Hg electrodes is surprisingly tolerant of small amounts of water, but greatly affected by oxygen. However, sparging with dry N2 lowers the residual water and oxygen content of the extraction solvent to the level where the reduction of Cs+ at Hg is possible. Thus, the entire treatment cycle for the removal of Cs+ from tank waste using a hydrophobic ionic liquid can be carried out in an open cell, provided that the cell is sparged with dry N2. MePrPip+ Tf2 N- +BOBCalixC6 was found to be a better extraction solvent for Cs+ than Bu3 MeN+ Tf2 N- +BOBCalixC6, but the former solvent was unstable toward metallic Cs and/or Cs(Hg) x.