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 (Bu3MeN+Tf2N-) or N-methyl-N-propylpiperidinium bis((trifluoromethyl)sulfonyl)imide (MePrPip(+)Tf(2)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 N-2 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 N-2. MePrPip(+)Tf(2)N(-) + BOBCalixC6 was found to be a better extraction solvent for Cs+ than Bu3MeN+Tf2N- + BOBCalixC6, but the former solvent was unstable toward metallic Cs and/or Cs(Hg)(x). (c) 2006 The Electrochemical Society.