CESIUM RECOVERY FROM TANK WASTE USING THE CsHg ALLOYING REACTION IN HYDROPHOBIC ROOM-TEMPERATURE IONIC LIQUIDS: A GREEN CHEMISTRY APPROACH

摘要

The effects of residual moisture and oxygen on the electrochemical processing step for the recovery of Cs(I) extracted into the hydrophobic ionic liquids, tri-1-butylmethylammonium bis((trifluoromethyl)sulfonyl)imide (Bu{sub}3MeN{sup}+Tf{sub}2N{sup}-) or N-methyl-N-propylpiperidinium bis((trifluoromethyl)sulfonyl)imide (MePrPip{sup}+Tf{sub}2N{sup}-) containing the 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(I) at Hg electrodes is surprisingly tolerant of small amounts of water, but greatly affected by oxygen. However, sparging with dry N{sub}2 lowers the residual water and oxygen content of the extraction solvent to the level where the reduction of Cs(I) at Hg is possible. Thus, the entire treatment cycle for tank waste can be carried out in an open cell, provided that the cell is sparged with dry N{sub}2. MePrPip{sup}+Tf{sub}2N{sup}- + BOBCalixC6 was a better extraction solvent than Bu{sub}3MeN{sup}+Tf{sub}2N{sup}- + BOBCalixC6, but the former solvent was unstable toward metallic Cs and Cs(Hg){sub}x alloy.