Abstract: The invention relates to new calixarenes of formula: ##STR1## in which R.sup.1 represents a crown ether chain that includes at least two aryl or cycloalkyl rings,R.sup.2 is a hydroxyl or alkoxy group, or the two R.sup.2 groups together form a crown ether chain such as R.sup.1, and R.sup.3 represents a hydrogen atom or an alkyl group. The calixarenes are used to selectively extract caesium from aqueous solutions that notably have high concentrations of sodium.

Abstract: The invention relates to crown calix.vertline.4.vertline.arenes, their preparation process and their use for the selective extraction of cesium and actinides. These crown calixl4larenes comply with the formula: ##STR1## in which R.sub.1 represents a group of formula X(C.sub.2 H.sub.4 X).sub.m and X(C.sub.2 H.sub.4 X).sub.n YX(C.sub.2 H.sub.4 X).sub.n with X=O or N(R.sub.4), m=3, 4, 5 or 6, Y=cycloalkylene or arylene and n=1, 2 or 3. These crown.vertline.4.vertline.arenes, whose benzene nuclei are optionally substituted by alkyl groups, can be used as extractants, e.g. in liquid membrane form, for separating cesium from acid solutions containing sodium in a large quantity compared with the cesium quantity, e.g. irradiated fuel reprocessing plant effluents.

Abstract: The invention relates to novel calixarenes of formula: ##STR1## in which m is equal to 0 or 1, n is an integer from 2 to 8, with 4.ltoreq.n(m+1).ltoreq.8,R.sup.1 and R.sup.2, which can be the same or different, are alkyl or O-nitrophenoxyalkyl groups andR.sup.3 and R.sup.4, which can be the same or different, are alkyl or aryl groups.The calixarenes can be used for extracting actinides and lanthanides from aqueous solutions from spent fuel reprocessing.

Abstract: The invention relates to bis-crown calix[4]arenes, their preparation process and their use for the selective extraction of cesium and actinides. Bis-crown calix[4]arenes are in accordance with the formula: ##STR1## in which R.sup.1 and R.sup.2 respectively represent X(C.sub.2 H.sub.4 X).sub.m and X(C.sub.2 H.sub.4 X).sub.n with X.dbd.O, NH and/or N(CH.sub.3), m and n=3, 4, 5 or 6, or X (C.sub.2 H.sub.4 X).sub.p/2 XY(C.sub.2 H.sub.4 X).sub.p/2 with p=2 or 4 and Y=cycloalkylene or arylene. These bis-crown calix[4]arenes, whose benzene nuclei are optionally substituted by alkyl groups, can be used as an extracant, e.g. in the form of a liquid membrane, for separating cesium from acid solutions containing sodium in a large quantity compared with the cesium quantity, e.g. effluents of irradiated fuel reprocessing plants.