Abstract: A process for separating large amounts of uranium from small amounts of radioactive fission products, which are present in basic, aqueous carbonate containing solutions, by means of a basic, organic anion exchanger. Uranium values present as uranykl-carbonato complex in a basic, aqueous, carbonate containing solution can be separated from fission products of the group ruthenium, zirconium, niobium and lanthanide, and with a relatively high degree of decontamination as well. The aqueous solution is adjusted to a ratio of uranyl ion concentration to carbonate ion- or CO.sub.3.sup.-- /HCO.sub.3.sup.- concentration of 1(UO.sub.2.sup.++) to 4.5(CO.sub.3.sup.--, or CO.sub.3.sup.-- /HCO.sub.3.sup.-), or more, at a maximum U concentration of not more than 60 g/l. The adjusted solution is led over a basic anion exchanger made from a polyalkene matrix provided with a preponderant part tertiary and a minor part quaternary amino groups to adsorb fission products ions or fission products containing ions.