Abstract: The present invention relates to a process and an apparatus for continuously extracting ions from a clear liquid or a liquid containing materials in suspension, by means of a bed of grains of exchange substances.The process comprises maintaining the bed in a permanent condition of fluidization by an absolutely continuous feed of liquid, and subjecting the bed to cyclic pulsation phenomena in such a way as to ensure grading of the grains on the basis of density, in dependence on their ion charge. To carry out that process, an apparatus comprises a fluidization column which does not have any plate capable of interfering with the grading operation, a pulsation generator which operates by taking off liquid at the top of the column and re-injecting it in a surge manner at the base of the bed, and a system for centrifuging the liquid to be treated, for removing the sandy materials therefrom.