A solvent suitable for extracting cesium from acidic nitrate media, such as that stored at the U.S. Department of Energy's Idaho National Engineering and Environmental Laboratory (INEEL), has been developed. The solvent possesses good chemical stability, displays excellent cesium selectivity, and provides good extraction and stripping performance with satisfactory phase-coalescence behavior. The calix[4]arene-crown-6 ether used in this solvent (1,3-alt-bis-n-octyloxycalix[4]arene-benzo-crown-6) was selected from a series of mono-and bis-crown-6 derivatives of 1,3-alternate calix [4]arenes that were shown to possess good stability to a simulant of INEEL's Sodium Bearing Waste (SBW). Calixarene -benzo crown ethers possessing an alkyl substituent at the 4-position of the benzocrown, such as calix[4]arene-bis-tert-octylbenzo -crown-6, were shown to be much more susceptible to nitration by the SBW simulant or by 4 M nitric acid than calixarene-benzo crown ethers without the alkyl substituent. The cesium distribution behavior for a solvent comprised of l,3-alt-bis-n-octyloxy -calix[4]arene-benzo-crown-6 at 0.01 M in an aliphatic diluent modified with a fluorine-containing alcohol was shown to be stable over the course of a 60 day continuous contact with the SBW simulant at 25 °C.Toward process development, cesium distribution ratios on extraction (SBW simulant), scrubbing (50 mM nitric acid), and stripping (1 mM nitric acid) operations demonstrated a functional solvent cycle using a solvent of this composition augmented by 0.001 M trioctylamine (TOA). Without this lipophilic amine, stripping is inefficient. The presence of TOA in the solvent had no adverse effect on the Cs distribution behavior during extraction and scrubbing operations, nor did TOA negatively impact the Cs/Na and Cs/K selectivity ratios.