Abstract: A compound of a chemical element to be isotopically enriched is placed in a working zone with an auxiliary material and temperature and pressure conditions are controlled to cause a liquid solution to occur. The liquid solution is injected through a nozzle into a separating chamber, for example, at substantially constant pressure and with slight elevation of temperature, to cause a phase change, the liquid solution yielding a solid phase which is enriched in respect of an isotope of the chemical element and a gaseous phase which is depleted. The series of such stages are arranged in cascade with the enriched solid phase being passed forward to the following stage for further enrichment and the depleted gaseous phase being passed back to the previous stage for further depletion. The arrangement is especially applicable to uranium enrichment, wherein the compound is uranium hexafluoride and the auxiliary material is tungsten hexafluoride.