Some nuclear effluents contain traces of radioactive elements in sodium sal
t media, from which radioactive cesium must be separated. Various processes
(among them liquid/liquid extraction and ion exchange) can perform such se
paration, but they produce additional wastes. Therefore, nanofiltration has
been selected as a new separation process that may allow a large volume re
duction without generating additional wastes. Nanofiltration is a pressure-
driven membrane process, between ultrafiltration and reverse osmosis, that
can separate species at the ionic scale.
To perform the separation of cesium from highly salted aqueous medium, a na
nofiltration process was combined with a cesium-selective complexation step
. Ligands that were known to be highly cesium-selective in organic solvents
were synthesized and modified in order to make them hydrosoluble. Ligands
such as resorcinarenes or calixarenes were then tested through a nanofiltra
tion system. One of them allowed cesium removal of 90% in an aqueous medium
containing 250 g/L of sodium nitrate. By combining two such nanofiltration
-complexation stages, it is now possible to remove 99% of trace-level radio
active cesium.