Abstract: A process for the treatment of aqueous solutions containing cations and anions, including aluminum sulphate and fluoride ions, for the recovery of the fluorine contained in the aqueous solution by means of an ion exchange plant, in which the aqueous solution flows through at least a strong acid cation-exchanger filter step, then a first weak basic anion-exchanger filter step which produces an almost complete separation of the sulphate ions, and after that a second weak basic anion-exchanger filter step which separates out the fluorine ions, and the fluoride is recovered from an eluate obtained during regeneration of the second anion-exchanger filter step.